Harvard Psychological Studies, Volume 2
cm. The charts for individual choice were plotted for a comparison of
speeds rather than for accuracy.
It was noted for the hands:
(1) that every subject reacts more rapidly with the left hand;
(2) the eyes had little effect as to changing the speed-rate;
(3) single and double hand-movements were equally rapid.
Some subjects, as A., react more rapidly for the shorter lines, though no clearly marked evidence of this speed-increase is to be noted.
For the head, the results for both eyes opened and closed show the impossibility of separating the optimal or preferred rate of speed on the score of visual assistance or because of direction of head-movement.
There is a close agreement of the subject as to his best speed, and this is independent of special conditions; for example,
A. selects 50-57 beats per minute for 1 cm. and 48-68 for 10 cm.; G. has a preference for 61-66 and 56-71; Hu. rises to 103-125 for 10 cm. and selects 68-82 for 1 cm.; Le. 52-55 for 1 cm. and 45-52 for 10 cm., and so on.
We may say, then, that free rate-choice for head-movements results in a selection of some rate of speed that is not affected by the visual sense or direction of movement, and is strictly individualistic, covering a range of 50-130 beats per minute, and not increasing as the amplitude of movement is reduced.
Turning to individual choice of speed-rate, for the feet it will be seen that
(1) the non-visual records closely correspond as to chosen speed, and there is a less close correspondence of visual speeds;
(2) the visual records are ruled at a lower rate in some cases, but A., G., and Mo. show little difference;
(3) there is a tendency to speed up as the series progresses;
(4) the shorter lines are ruled with greater speed as a rule, though G. and Le. fail to show this phenomenon;
(5) The left-foot records show a higher speed-rate for all cases.
Among many interesting points that cannot be examined in this connection, such as relation of voluntary choice of rate to the main line of metronome records as regards accuracy, the fact of the higher rate of ruling for the left hand and foot stands most prominent.
Whether a record of head-movements to right or left, or other devices to compare the sides of the body or to contrast arm and leg speeds, will bear out this testimony is as yet unknown, so that the writer prefers to announce the result and not now fit theory to data. It may be said that the records were taken in reverse order and rearranged, as regards right and left foot or hand, and, in addition, the initial foot-movement varied with the subject, some being right and some left.
We ask finally: Is the time in which the greatest exactitude is produced, the same for every group of muscles; that is, has every motor apparatus the same natural rhythm? and: Is this natural rhythm a constant rapidity for all motor nerve-centres or does it depend upon the complexity and character of the movement?
The comparison will fall first on the averages and finally on the individual records.
The hand-movements show the following results:
Constant errors for 14 cm.:
For simple and weight accelerating and retarding motions, there is a close agreement about 120 beats for the minimum error for visual and right-hand non-visual records; left-hand non-visual records are spread more, but will also average the same.
For 10 cm. simple and compound movements the visual minimum errors are at 180-200 beats, while with the eyes closed the results are grouped about 60 beats; one record, that for l.h.e.c., has two minimum points at 60 and 180 beats, the latter being clearly a crossing of the 0 error-line, because of physiological limitations.
For 1 cm. simple and weighted minimum errors are grouped between 20 and 60 beats, while the simple and compound group show less regularity and a tendency to group minimum errors at 100 beats.
The head-movements show for both 1 and 10 cm. lines a minimum error at 180-200 beats, there being, however, one exception at 100 beats for 10 cm. head-backward movements.
The foot-movements show minimum errors at 80 beats for the right foot, and 180 and 100 beats for the left foot, visual and non-visual respectively.
Bearing in mind for a moment the individual choice records, there seems here a suggestion that the left foot is capable not merely of higher speeds, but of minimum errors at the higher rates as compared with the right foot.
No such differentiation of the hands can be discovered, however.
Mean errors:
For the hands:
For 14 cm. for simple and weighted results we find that the right-hand and left-hand eyes-open minimum errors are at 180 beats, but the non-visual left-hand minimums are at 30 beats.
For 10 cm. simple and compound records we find all minimum errors are between 160 and 200 beats.
For 1 cm. simple and weighted results there is a scattering of minimum errors from 20 to 200 beats, with a heavy preponderance at 200, and the same is true for the simple-compound series.
The head-movements minimum errors are at 40 beats without exception.
The foot minimum errors are distributed from 20-30 beats for the left foot to 160-180 for the right.
It is thus evident that each group of muscles and each motor centre has its own optimum, and that the conditions of complexity, resistance, etc., influence greatly the accuracy of the periodic movement impulse.
FOOTNOTE:
[Footnote 138: Woodworth: The Accuracy of Voluntary Movements, Psychological Review Monographs, no. 13, 1899.]
THE MOTOR POWER OF COMPLEXITY
BY C. L. VAUGHAN
A. COUNTING OF SIMPLE AND COMPLEX VISUAL OBJECTS
If every sensory stimulus has a motor reaction, then a simple figure perceived in any way ought to produce a somewhat different response from a more complex figure similarly perceived. Of course if only one figure of each kind is given it is difficult to measure in any way this difference, since it is so small. But we might make it measurable by multiplying the process. Therefore I have cut out a row of similar figures in a strip of cardboard and on another strip another series of a different pattern. Now if these rows are counted figure by figure each figure has a certain motor effect which influences the speed of counting, so that the time of counting (measured by the chronoscope) should give some indication of the comparative motor power of the figures in question.
In the accompanying illustration nine cards of various patterns are shown. Cards 1, 2, and 3 are comparatively simple patterns while 4, 5, and 6 are comparatively complex, Card 6 having the added complication of different kinds of figures on the same card. Cards 7, 8, and 9 form another group, Card 7 having the same letter throughout, Card 8 having letters composing a sentence and Card 9 a series of the letters, mostly consonants, mixed promiscuously. In order to prevent the subject from knowing the exact number, and thus, perhaps, bring in another influence at the end of the row, most of the different cards have different numbers of figures, but this difference is not great and some cards have the same number. The subject usually forgets, from one experiment to the next, the number on each card.
At first the experiment was performed with the figures in a straight row, instead of in the broken line which is seen in the illustration. In counting the straight rows, the observers found it hard to keep the place in the line. A subject would become confused and count some spot twice or else he would omit it altogether. Furthermore this disturbance was found to be much greater with some figures than with others, with Card 1, for example, more than with Card 2. Therefore the device was adopted of diversifying the line, both by placing some of the figures above and some below the line and by making the distances from one figure to the next, different in the different cases. And in order to prevent the subject from associating any peculiar turn in the line with a certain number counted, it was decided to have the arrangement on the different cards different. But it was still necessary to have the intervals between figures about the same in all the cards, and therefore the row was divided into sections of six figures each and these sections were used as units, variously arranged, in constructing the other rows. For example the first unit of Card 3 is the same as the second of Card 4. Sometimes this six-figure unit is turned end for end or upside down, and thus, though the same spaces are used, the cards appear dissimilar.
The subject would be seated at the table with one hand resting lightly on the key which sets the chronoscope in motion, his eyes raised so that the table in front of him is not seen. One of the cards would then be put in the proper position in front of him (always the same), and he is told that all is ready. He looks down at the card and as soon as he begins to count the first figures in the line he presses the chronoscope key, and when he has reached the end of the line he releases the key. The time for the operation is then noted. The whole series of cards is thus gone through. An extra card of which no record is taken is used for the first few tests so that the subject may be in the proper state when the first test to be noted down is taken. Also the order of the series is changed from one experiment to the next, each card taking its turn at being first and last. It was hoped in this way to distribute among the different cards the effects of practice and fatigue, and also to guard against any expectations on the part of the subject as to the character of the next card.
The subject is told to count as fast as he can, with a reasonable feeling of certainty as to his correctness, the main object being to have a uniform principle, in counting the different series. Wrong counts were excluded, but later on the same cards given again so as to keep the tables even. Subjects were not allowed to count the figures by groups, but one by one. At first a certain amount of difficulty was found in the fact that subjects in counting would repeat the numbers to themselves, and as they seemed to be retarded by this, especially in those numbers whose corresponding names have 2 or 3 syllables, the result was that we were getting the speed with which subjects could count the numbers from 1 up to 38 or 39 and this would be practically the same whatever the figure. But all the subjects were finally trained merely to think the number, or at least to have as little vocal adjustment as possible. When this was done the subject no longer felt that it was the speed with which he could count that was being measured but the rate at which he could take in the different figures on the card, one at a time.
Between three and four hundred tests were made of the counting of the figures on the nine cards, the work being divided among seven subjects, though not in exactly equal amounts. Since the number of figures on the different cards are different, I have found the time it takes to count one figure by dividing the total time by the number of figures on a card. The following table shows the average time taken by each subject for one figure on each card, time given in thousandths of seconds. _A.M.V._ stands for average mean variation.
_A._ _A.M.V._ _B._ _A.M.V._ _C._ _A.M.V._ _D._ _A.M.V._ _E._ 1 279.69 11.47 186.87 13.22 247.62 14.89 193.08 12.38 262.77 2 270.60 12.47 180.55 11.88 249.21 18.00 190.51 11.82 257.56 3 274.43 9.87 180.89 11.57 247.59 15.51 192.07 7.87 259.96 4 286.82 12.47 190.39 12.56 255.20 16.78 200.53 10.72 267.11 5 290.29 11.89 195.41 12.36 262.27 19.73 199.89 9.27 271.06 6 293.06 12.21 185.33 11.51 275.40 18.13 199.20 7.92 264.59 7 273.32 15.54 192.23 13.73 229.26 19.30 185.60 9.83 265.56 8 279.77 13.86 185.23 12.69 246.66 18.86 193.39 9.81 277.52 9 285.09 11.97 197 04 12.28 269.96 19.95 186.30 9.05 259.72
_A.M.V._ _F._ _A.M.V._ _G._ _A.M.V._ 20.20 217.00 12.32 442.63 36.51 16.03 195.00 9.50 431.00 24.39 17.41 191.50 11.03 434.83 24.28 20.31 226.40 29.11 445.71 14.58 20.86 233.50 20.46 459.17 18.92 15.00 220.80 14.92 432.17 26.87 19.20 189.20 30.31 402.13 21.34 14.93 220.70 21.79 388.77 27.48 14.27 210.34 11.71 419.57 18.22
A, B, C, D, E, F, G are the different subjects, and 1, 2, 3, 4, etc., refer to the cards with the different patterns. It is seen at a glance that great differences exist between the rates with which the different subjects count. Subject G had much fewer tests than the others, and thus, not having as much training, his average is higher in comparison than it would be had he had the same training.
Now if we compare the counting of the first three or relatively simple patterns with that of the next three or comparatively complex ones, we notice at once that the simple figures are almost invariably counted in less time than the complex, there being only two exceptions. B counts 6 a little faster than 1, and G counts 6 faster than 1 and 3. Even these apparent exceptions are easily explained. As noted already, subjects are much more apt to lose their place in counting certain cards than others. This is especially true of Card 1 even after the line is broken. Now Card 6 is arranged on a different plan from the others, for it has many kinds of figures on it. This is a great help in keeping one's proper place in the counting of the series, and since wavering between two figures is avoided, the series is counted more rapidly. But B is the most rapid in counting, of all the subjects, and it is natural that any differences in the ease of keeping place should show themselves here, since the more rapid the counting the easier it is to lose the proper position. This cannot be said of G, who is a slow counter, but on the other hand it may be noted that he had only a few cases, and at first the ability to keep one's position is much less than after considerable experience. So in Cards 6 and 1 there are two conflicting principles, degree of complexity and tendency toward confusion of position. Of course both these principles are present in all the other cards, but they reach a maximum in 1 and 6, in 1 extreme simplicity with difficulty in keeping place, in 6 extreme complexity with ease in keeping place. Card 1, it will be seen, is with nearly all subjects a little slower than 2 and 3, while 6 is generally faster than 4 and 5.
Therefore it would seem that the apparently small exceptions are not real exceptions, but variations due to the presence of other factors than mere differences in complexity of the figures used. In observing the averages for 7, 8, and 9 we see that as a rule 7 is fastest, 8 next, and 9 the slowest. The tables are not quite so regular as for the cards just given. B and G count 8 faster than 7, and E counts 9 faster than 7. The most of these cards have on them 36, 37, 38, or 39 figures. Card 8 has 43 letters. The subjects report that the last three on this card are counted much faster. They know, as soon as they reach 40, just how many there are, and it is hard to keep from counting the rest in a group. Otherwise they do not feel any difference in counting Cards 8 and 9. Arranging the letters in words does not affect the speed of counting, so far as they can see, for in counting they do not notice the words at all.
When we average the records of all the subjects giving equal weight to each subject, though the number of tests may be different with the different men, we get the following table. Time given in thousandths of seconds.
(1) 261.38 (2) 253.49 (3) 254.54 (4) 267.46 (5) 273.08 (6) 267.22 (7) 248.19 (8) 256.01 (9) 261.15
It is seen, from looking at this table, that all divergences from the general rule have stopped. Cards 1, 2, and 3 each take less time than any of the 4, 5, 6 group, and 7 is faster than 8 and 9. So the evidence seems very strong that it takes longer to count complex than simple figures. Should one object that the difference is extremely small, a few thousandths of a second, and that thus a slight error in one test might invalidate the result, we reply that the time which is given is the time in which we count just one figure of the given pattern, and that thus of course the difference between counting two different figures must be very small. Moreover there has been a remarkable agreement of the tests taken at different times. It is not a case of finding 1, 2, and 3 counted faster one day and 4, 5, and 6 counted faster the next, but 1, 2, and 3 are counted faster nearly every time. Occasionally 1 will take longer than one of the 4, 5, 6 group. And extremely seldom is there a case where the average of 1, 2, and 3 is not less than that of 4, 5, and 6.
The experiment seems to have proven that it takes a longer time to count a row of complex figures than a similar row of simple figures. _The complex figure exercises a retarding effect upon the eye as it sweeps along._ There is a greater amount of sensory stimulation, consequently a greater amount of motor excitement. This motor excitement does not act in harmony with the motor activity which impels the eyes along, but has a somewhat antagonistic effect. The eye is held more by the complex figure; it is a greater effort to withdraw the gaze to look at the next figure. A certain interest, as we say, on the psychological side tends to hold one to the figure looked at. This interest is greater (other things being equal) the greater the complexity of the figure. The nervous processes involved in counting, though admittedly in very small degree, are thus inhibited by the complexity of the figure and act more slowly.
B. REACTIONS TO SIMPLE AND COMPLEX OPTICAL IMPRESSIONS
Since the preceding experiments seem to show that reactions on optical impressions are different according as the figures are more or less complex, it would seem that we ought to be able to measure by graphic methods the reactions to visual fields of varying grades of complexity and in this way to demonstrate their different motor powers.
A Porter kymograph was used on which to register the reactions. Resting on the top of the drum, and revolving with it, was a circular band of white paper, upon which were pasted the different figures to be observed. A screen was placed in front of the kymograph, thus concealing the figures; but at their level was a little square window in the screen, which, when the eye was placed in the proper position, allowed the subject to see one of the figures but nothing more. A few inches in front of this window was an eye-rest which kept the eye properly placed. A tambour received the movement from the subject and communicated it to a straw which made a scratch on the smoked paper which covered the drum.
The figures used in this experiment form two series, one, composed of geometrical figures, varying in complexity from a circle to a very complex figure consisting of many overlapping squares, triangles, etc., and the other composed of colored figures varying in complexity from a simple square of one color to a very complex mixture of various colors. The area of the visual field is about the same in all cases,--an inch square. The geometrical figures were formed of black lines on a white background. The figures used are shown in the accompanying illustrations.
The subject would be seated in front of the screen, his eye at the eye-rest a few inches in front of the window in the screen, and the forefinger of the right hand on the tambour, which is to the right of and behind the screen, and thus not seen while the eye is at the rest. Then as the drum revolves and brings a figure in front of the window, the subject observes this figure carefully, and when it is all in the field of vision he presses down with his forefinger, thus producing a curve on the drum surface. _He tries to make the same finger-movement every time_, whatever the figure at the window may be. But his attention is not to be too much taken up with the making of the movement, for he must be closely observing the figure. If he looks at the figure until he observes its characteristics clearly and then turns his attention from this to the finger-movement, it is evident that the optical sensation would not have much effect upon the movement. The movement must be performed while his interest in the figure is highest. Now, after a little practice, any one can accustom himself to make a certain definite movement in about the same way every time, and he can then agree that he shall make this movement as a reaction to a given stimulation. Then when the stimulus comes he makes the movement without any longer thinking of the character of the movement. It has become, to a certain extent, automatic and can look out for itself.
This is the state into which I have tried to get my subjects. Their whole attention is to be taken up with the seeing of the figures in the window, and to these figures they are to react as automatically as possible. Thus, though finger-movements are usually voluntary, all the capricious character of voluntary action will be removed here, and if the stimulus is the same in all cases, the reaction tends to assume the form of a uniform movement. There is, then, a chance to see the influence of different optical stimuli upon this action.
Six different geometrical figures were seen at each revolution of the drum and six reactions given by the subject. Between figures a white surface would occupy the field of vision. The simple and complex figures were distributed so that the subject never knew what kind of a figure would come next. The purpose of the experiment was kept as much as possible from the knowledge of the subjects; but some, knowing my general problem, surmised quite correctly my main object here.
Ten revolutions were made at each sitting, thus causing the subject to react ten times to each figure. Then a new drum paper was taken and the case with the colored figures placed upon it. This had five colored figures, and ten revolutions were made also in this case. Thus, in all, in any one day, the subject would make one hundred and ten of these finger-movements.
Since we have in all these experiments tried to find out in the different figures merely differences in the _amount_ of the reaction, and not differences in the character of the reaction, we shall keep up this method here. Now a stronger reaction makes a higher curve, and since the drum is all the while revolving, and since the higher the curve, other things being equal, the longer it takes, the stronger reaction will also make a wider curve. So it would seem that if we wish to observe the differences in the amounts of reaction the most natural course to pursue would be to measure the heights and widths of the curves we have registered. This accordingly has been done.
In our discussion of these measurements let us, then, first, take up the curve heights, and of these, those of the geometrical figures which we call _U_, _V_, _W_, _X_, _Y_, _Z_. The height is measured from a base-line [drawn by revolving the drum after the subject has taken his finger from the tambour] to the highest point reached. These measurements are taken from two hundred reactions to each figure, divided among seven different subjects.
_Heights of Curves_ _U_ _V_ _W_ _X_ _Y_ _Z_ _Subject_ A 6.83 6.68 6.59 6.55 6.63 6.79 B 8.64 7.26 6.41 7.79 6.39 9.75 C 6.67 6.55 6.73 6.85 5.87 8.53 D 21.35 21.26 21.46 21.90 21.33 21.31 E 16.13 15.77 15.17 15.85 15.29 16.08 F 16.90 16.97 16.14 16.52 15.81 17.91 G 11.42 11.32 11.39 11.48 11.06 11.10
87.94 85.51 83.89 86.94 82.38 91.48
_Average_ 12.56 12.26 11.98 12.42 11.77 13.07
_Arranged in order of height of curve_ _Z_ _U_ _X_ _V_ _W_ _Y_ 13.07 12.56 12.42 12.26 11.98 11.77
If we put the figures in the order of strongest reaction for the different subjects we get the following table:
_Subject_ A _U_ _Z_ _V_ _Y_ _W_ _X_ B _Z_ _U_ _X_ _V_ _W_ _Y_ C _Z_ _X_ _W_ _U_ _V_ _Y_ D _X_ _W_ _U_ _Y_ _Z_ _V_ E _U_ _Z_ _X_ _V_ _Y_ _W_ F _Z_ _V_ _U_ _X_ _W_ _Y_ G _X_ _U_ _W_ _V_ _Z_ _Y_
It is seen from these results that, although the subjects differ, the height of the curve varies directly with the complexity of the figure. The order of the figures, which we get by measuring the height of the curves and then putting that figure with the highest curve first, with the next highest second, and so on, is exactly the same order in which we should put them if we were asked to put the most complex first, the next second, and so on. Though the individual subjects may vary somewhat from this rule, when they are all grouped together there are no exceptions.
The variations of the reactions with the different subjects may be shown very clearly in the following way, where the different figures are in the left-hand side arranged in order of descending complexity. "1st place," etc., refer to the order of arrangement of the figures by the different subjects as shown in preceding tables. Thus, _Z_, 3 times, 1st place, means that three subjects have in the average a higher curve for _Z_ than for any other figure.
1_st place_ 2_d place_ 3_d place_ 4_th place_ 5_th place_ 6_th place_
_Z_ 3 times 2 times 0 times 0 times 2 times 0 times _U_ 2 times 2 times 2 times 1 time 0 times 0 times _X_ 2 times 1 time 2 times 1 time 0 times 1 time _V_ 0 times 1 time 1 time 3 times 1 time 1 time _W_ 0 times 1 time 2 times 0 times 3 times 1 time _Y_ 0 times 0 times 0 times 2 times 1 time 4 times
One can see at a glance from this, how, as the figures decrease in complexity, they take their position further on in the series. If a diagonal is drawn from the upper left-hand corner to the lower right, it will pass through or near the larger numbers in the table, thus showing that the figures belong in the ordered series in the places already shown.
Next in order let us take up the measurements of the widths of curves for the same geometrical figures which we have been considering.
_Widths of Curves in mm._
_U_ _V_ _W_ _X_ _Y_ _Z_ _Subject_ A 20.83 20.59 20.93 21.22 20.21 21.89 B 11.18 10.77 10.46 10.31 9.92 10.79 C 4.28 4.43 4.10 3.78 4.95 4.70 D 21.08 19.36 18.33 18.75 18.17 21.09 E 14.22 13.85 13.40 13.56 11.96 14.13 F 17.00 15.26 15.92 16.52 14.52 16.47 G 5.25 5.19 5.30 5.08 5.11 5.37
93.84 89.45 88.44 89.22 84.84 94.44
_Average_ 13.40 12.78 12.63 12.75 12.12 13.49
_Order_ _Z_ _U_ _V_ _X_ _W_ _Y_ 13.49 13.40 12.78 12.75 12.63 12.12
If as before we take the orders for the different subjects, we get the following table:
_Subject_ A _Z_ _X_ _W_ _U_ _V_ _Y_ B _U_ _Z_ _V_ _W_ _X_ _Y_ C _Y_ _Z_ _V_ _U_ _W_ _X_ D _Z_ _U_ _V_ _X_ _W_ _Y_ E _U_ _Z_ _V_ _X_ _W_ _Y_ F _U_ _X_ _Z_ _W_ _V_ _Y_ G _Z_ _W_ _U_ _V_ _Y_ _X_
Here, as before, in the case of the heights, it is seen that though the order is different with the different subjects, yet the general tendency is to place the most complex figures first and the simplest last. The most simple figure _Y_ never comes in front of the fifth place except with subject C, who places it first. This exception may be ascribed to the fact that this subject, on account of his going away, did not have so many tests. In fact only one day's work of 10 reactions for each figure is recorded, and it is but natural that some variations from the standard should occur in his case.
If now, as before, we investigate where each figure occurs in the series for the different subjects we get the following table:
_Times in_ 1_st place_ 2_d place_ 3_d place_ 4_th place_ 5_th place_ 6_th place_ Z 3 3 1 0 0 0 U 3 1 1 2 0 0 V 0 0 4 1 2 0 X 0 2 0 2 1 2 W 0 1 1 2 3 0 Y 1 0 0 0 1 5
Here we again see the large numbers on a line from the upper left-hand to the lower right-hand corner.
Thus we get the following order from the geometrical figures as measured by the height and width of the curves:
_Height_ _Z_ _U_ _X_ _V_ _W_ _Y_ _Width_ _Z_ _U_ _V_ _X_ _W_ _Y_
The only difference, it is seen, is that the positions of _V_ and _X_ are reversed in the two series. Such a change would on our principle be fairly likely to occur, since _V_ and _X_ are figures near to each other in complexity and the motor effects are very similar.
In the same manner, the following tables show the reactions to the colored figures of different grades of complexity. And first, as before, is the table of the heights of the curves for the different subjects, given in millimetres. The numbers given represent the averages of all reactions made. We will call the figures, for the sake of reference, _L_, _M_, _N_, _O_, _P_.
_L_ _M_ _N_ _O_ _P_ _Subject_ A 5.75 6.01 5.90 5.82 5.74 B 6.72 5.56 6.35 7.53 4.94 C 10.92 10.90 10.76 10.52 10.99 D 25.49 25.42 26.23 25.89 25.52 E 20.63 20.82 20.37 20.55 20.30 F 15.67 15.23 15.15 15.98 14.51
85.18 83.94 85.26 86.29 82.00
_Average_ 14.20 13.99 14.21 14.38 13.67
Order arranged as before in a descending series according to height of curve:
_O_ _N_ _L_ _M_ _P_ 14.38 14.21 14.20 13.99 13.67
This is exactly, as I should judge, the order of the complexity of the figures reacted to.
The arrangement by the individual subjects is as follows:
_Subject_ A _M_ _N_ _O_ _L_ _P_ B _O_ _N_ _L_ _M_ _P_ C _P_ _L_ _M_ _N_ _O_ D _N_ _O_ _P_ _L_ _M_ E _M_ _L_ _M_ _N_ _P_ F _O_ _L_ _M_ _N_ _P_
We see that individual differences are stronger here than in the geometrical figures, but that the same tendency to react more strongly to the complex is present in nearly every case. This can be brought to the eye more clearly if we observe the table in which is shown the position of the different figures in the series of the different subjects.
_Times in_ 1_st place_ 2_d place_ 3_d place_ 4_th place_ 5_th place_ O 2 1 2 0 1 N 1 2 0 3 0 L 0 3 1 2 0 M 2 0 2 1 1 P 1 0 1 0 4
_M_ here presents the principal exception, coming too often in the first place.
Finally we give the tables for the widths of the curves for the colored figures; and first the table of the averages of all the subjects for all the figures:
_L_ _M_ _N_ _O_ _P_ _Subject_ A 25.76 24.27 25.06 24.77 23.14 B 9.42 9.49 9.06 9.84 8.11 C 5.85 5.35 5.62 5.80 5.24 D 13.68 13.53 13.18 13.26 13.38 E 22.06 21.37 22.50 22.17 20.44 F 16.30 15.08 16.65 16.76 15.13
93.07 89.09 92.07 92.60 85.44
_Average_ 15.51 14.85 15.35 15.43 14.24
Order, arranged in a descending series according to width of curve:
_L_ _O_ _N_ _M_ _P_ 15.51 15.43 15.35 14.85 14.24
Here the order is not just the same as we got from a measurement of the heights. The three complex figures have changed places somewhat, but there is no exchange of a simple and a complex.
The arrangements by the individual subjects are as follows:
_Subject_ A _L_ _N_ _O_ _M_ _P_ B _O_ _M_ _L_ _N_ _P_ C _L_ _O_ _N_ _M_ _P_ D _L_ _M_ _P_ _O_ _N_ E _N_ _O_ _L_ _M_ _P_ F _O_ _N_ _L_ _P_ _M_
The three complex figures have different places with different subjects, but very seldom is a simple figure found among the complex, or _vice versa_.
This can be seen easily from the following table:
_Times in_ 1_st place_ 2_d place_ 3_d place_ 4_th place_ 5_th place_ _L_ 3 0 3 0 0 _O_ 2 2 1 1 0 _N_ 1 2 1 1 1 _M_ 0 2 0 3 1 _P_ 0 0 1 1 4
A theoretical word may close our report.
The growth of biology and physiology has tended to show that there is no break in the nervous mechanism. The stimulus goes to the brain and out through motor channels to muscles, glands, etc. The nervous current does not wait in the brain for the permission of the mind to leave on its journey to a muscle nor does it need mental reënforcement. The nervous current as a whole is a unity. The nervous system is a physiological instrument for producing the appropriate reaction to a certain stimulus. In the unicellular organism there is no nervous system, but the protoplasm receives the stimulus and produces the reaction. As we go up in the animal series a differentiation is seen to be present in the organism. Some parts are more concerned with the receiving of stimuli and others with the approach toward or withdrawal from the stimulating object. There is a division of labor. The nervous system is developed as a means of rapid communication between the different parts, but this communication is a physiological one. The stimulus sets up a chemical action in the sensory organ which is transmitted along the nervous path to the motor organ which is caused to react. As we ascend the animal series the differentiation becomes greater and greater, and consequently the means of communication must become more and more complex. So trunk lines are formed which lead to a centre, and from this centre again go out main lines which divide and subdivide until the muscles are reached. The centre acts as a kind of automatic switch-board.
Accepting such a view of the nervous system it must be granted that different stimulations would produce different reactions. It was my aim in the experimental work which has been described to show that this is true. And while much work has already been done in showing that different kinds, or different amounts of stimulation produce differences in reactions, it seemed important to demonstrate also that mere differences in the complexity of the stimulus bring about differences in the reaction. So the experiment of counting figures of different complexity was entered upon, and we found that it took longer to count figures the more complex they were in spite of the fact that the act of counting seems always the same. The question is how must the fact that counting becomes slower and slower, as the figures become more complex, be interpreted?
When we count a row of figures, the eyes do not move along at a regular uniform rate, but make a quick jump from one figure to the next, halt a moment, make another jump, and so on. Now, I think the principal difference comes in with the figures of different complexity in the time the eye halts at each figure. The halt is longer the more complex the figure is. It is well known that any visual object which stimulates the retina is brought by a reflex movement of the eye to the place of clearest vision. Of two objects stimulating the eye at the same time, the more pronounced one will produce the reflex and will hold the eye longer than a weaker stimulus. Similarly here, the more complex figure produces a stronger reflex and holds the eye longer than the simple figure. This is repeated at every figure in the series.
The complex figures have more features about them, all of which by way of the retina and optic nerve are represented in the cortex and thus more cortical cells are involved, which in turn produce a stronger stimulation of the muscles which move the eye in the proper way to see the figure, and thus the eye is held more strongly by the complex than by the simple figure.
Again in the second experiment, the subject reacts more strongly to the complex as shown already in explaining the first experiment and for the same reasons. It might be said that in looking at the colored figures, _e. g._, that since the same amount of retina is stimulated, the reaction ought to be the same. But we may presume that the complex figure, on account of the different shapes and contrasts on its surface, will more variously affect the same amount of retina and that the nervous currents sent to the cortex will, many of them, be stronger than those from the simple figure and will thus cause the cortical cells to be more strongly excited, or by a process of irradiation the stimulation will spread to adjoining cells and thus finally more cells be stimulated. However this may be, the amount of discharge into motor cells is certainly greater and the muscular reaction, therefore, also greater.
The interesting side of our results is thus given in the fact that we have here two activities--counting with highest speed and making hand-movements of certain length--which are performed every time with exactly the same intention and with the subjective impression of equal result, and which yet show marked differences according to the complexity of the psycho-physical stimuli. It is a new contribution to our knowledge of the independent motor power of ideas.
ANIMAL PSYCHOLOGY
THE MUTUAL RELATIONS OF STIMULI IN THE FROG RANA CLAMATA DAUDIN[139]
BY ROBERT M. YERKES
I. ANIMAL BEHAVIOR AND THE SENSES
Since the behavior of an animal is conditioned by its senses, it is extremely important that the comparative psychologist should have accurate and detailed knowledge of the sense-impressions received by his subjects. Knowledge of the so-called "special senses" does not suffice for the satisfactory description of behavior, for there are several other kinds of sense-data of equal or even greater importance than those of the five special senses. As investigation of the subject progresses the banefulness of the notion that all sense-experience is summed up in "the five special senses" becomes more and more evident. For the comparative psychologist the senses are not five, six, eight, or ten, but as numerous as are the kinds of sense-data which condition animal activities. There can be no doubt that many of the lower animals are largely dependent upon senses which are not included in the conventional special sense list. The contention that certain organs which are commonly recognized as sensory in function, the cristæ acusticæ of the ear, for instance, are merely reflex control organs, has little weight in this connection, for every sense-organ is part of a motor control mechanism, and so far as we are able to judge from available evidence each has as an accompaniment of its functioning a mode of sensation. If there are two kinds of peripheral organs in connection with the afferent nerves, namely, those whose functioning has sensation for an accompaniment and those in which motor control is the sole phenomenon, it is high time that the fact were definitely known.
Even a thoroughly accurate knowledge of the general condition of the senses in a particular phylum, genus, or species may be of trifling value in the study of the behavior of a given individual, for within these groups the state of development and relative importance of a sense may differ strikingly. Herrick,[140] in his admirable investigation of the sense of taste in fishes, has rendered comparative psychology an important service by showing that even a highly developed sense may be of markedly different value in the associative life of different species. The cat-fish, according to Professor Herrick's observations, obtains its food primarily by the aid of taste-impressions, the hake by the aid of touch, and the sea-robin chiefly by means of vision. All three of the senses mentioned are possessed by each of the fishes, yet their values differ so widely that an understanding of the habits and associative processes of any one of the species would be impossible except in the light of just such facts as Herrick has discovered. Clearly, then, we must know the relative importance of the various sense-impressions received by an animal before we can discuss its behavior or psychic characteristics intelligently.
Furthermore, if behavior is to be serviceably described in terms of stimuli and physiological conditions it is necessary first of all to recognize that an animal responds to a situation, not to any one independent and isolated stimulus. Every situation, to be sure, may be analyzed into its component simple stimuli, but the influence of each and all of these stimuli is conditioned by the situation. Too often in our accounts of an animal's behavior we name some one stimulus as the condition of the reaction and entirely neglect the situation, without which the stimulus would have been of quite different value to the animal. For any given stimulus other external and internal stimuli constitute an environment. The complete description of a reaction demands knowledge of all the stimuli which enter into the situation and of their mutual relations of interference or supplementation. A frog which in its native habitat and undisturbed by an unusual situation would react violently to the light touch of a stick may give no sign of reaction to the same stimulus when a human being stands nearby. The influence of the tactual stimulus has been changed entirely by the simultaneous appearance of visual, olfactory, and possibly still other sense-data (man). The animal reacts not to the touch alone, but to this stimulus as part of a certain situation. The general effect of a situation we often speak of as excitement, timidity, etc. These are words for which must be substituted in our accounts of animal behavior accurate descriptions of the situations. Experimental studies prove that an animal must become thoroughly accustomed to the general situation in which it is to be observed before the influence of any particular condition can be studied to advantage.
Only a few of the important reactions of an animal to either external or internal stimuli are visible to the casual observer, and many of them can be detected only by the employment of indirect methods. Frequently the lack of a visible motor response to a new situation is good evidence of a fundamentally important reaction. The death-feigning opossum, crustacean, or insect, truly reacts by becoming motionless. As Whitman[141] has shown in the case of the leech it is as hazardous to judge of the degree of sensitiveness of another animal solely on the basis of our own as it is to maintain that lower animals possess only the senses which are ours. Varied, indirect and delicate methods are necessary in the investigation of the senses, as the results of the experiments to be described below help to prove.
It is my purpose in this paper to call attention to and emphasize the importance of studying stimuli in their mutual relations of interference and supplementation. This I shall do by presenting the results of an investigation of the behavior of the green frog. I shall discuss briefly, first, the sense-data received by the animal, their relative importance, significance, and mutual relations, and, next, the phenomena of reënforcement and inhibition.
II. THE SENSORY REACTIONS OF THE GREEN FROG
The following sensory reactions have been observed in the frog, but most of them have not been studied with care: olfactory, temperature, visual, tactual, equilibrational, and auditory. It is my purpose to investigate each of these senses in such fashion that we shall know the receptive capacity of the animal. Thus far I have completed only the work on auditory reactions, but the chemical and temperature senses and vision will be discussed in similar fashion later.
At present there is little known concerning the chemical senses. Unpublished observations made by Mr. Sherwin in this laboratory indicate the existence of olfactory sensitiveness to camphor, iodine, and several other strong stimuli. The reactions to the stimuli were slow, however, and there is no reason to believe that the sense of smell is of great importance to the animal. Of taste barely more is known than that it is present.
There is marked sensitiveness to variations in temperature, as I have demonstrated by preliminary test experiments, but the limits, distribution, and significance of this sensitiveness remain to be investigated. I am not aware that the existence of temperature spots has been determined. In connection with a study of the reactions of frogs to light Torelle[142] discovered that the animals suddenly become inactive and usually attempt to bury themselves when brought into a temperature of 8° to 10° C. This reaction is prompt and definite; its value to an animal which hibernates is evident, yet one would scarcely anticipate the suddenness and regularity with which it occurs.
My studies of habit-formation and reaction-time[143] have revealed the importance of vision in the life of the frog. Perception of movement appears to be of far greater value to the animal than perception of form or color. The spectral colors are discriminated in all probability, for the animals react very differently to those of the blue end than to those of the red. According to Torelle blue is preferred to red. There is evidence that red has a higher stimulating value than blue, and the apparent avoidance of red in Torelle's experiments may be due to this fact. None of the work with which I am familiar demonstrates that the suspected color-reactions are due to stimulation of the eye. They may be due to stimulation of the skin, for Parker[144] has shown that the reactions of _Rana pipiens_ to light are due to stimulation of the sink as well as of the eyes, or they may even be due to intensity instead of color.
The tactual-auditory sense series is better known and also, it would appear, better developed than the chemical series. A large portion of the body surface of the green frog is keenly sensitive to mechanical stimulation, and Steinach[145] by measurement of electrical changes in the nerves of the skin has discovered the existence of "touch spots." His method, which is ingenious, promises to be of considerable value in the objective investigation of the senses, but it involves operations on the subject which inevitably destroy the normal condition of the sense.
According to Steinach we have in the negative variation in the electrical condition of nerves during stimulation a phenomenon which may be used in the determination of the threshold of stimulation as well as in the investigation of irritability. In a previous paper[146] I have discussed the associational rôle of tactual impressions as well as the tactual reaction-time. All my observations lead me to believe that touch is a highly developed and important sense in the green frog.
Of the senses intermediate between touch and hearing that of equilibration has been most discussed. Certainly there is good reason to suppose that the sense-organs of the semicircular canals of the ear furnish the animal with impressions of position, movement, and possibly also of direction. Further study of the tactual-auditory senses of frogs may indicate the existence of conditions similar to those discovered by Parker in certain fishes, in which, as he remarks, "the skin, lateral line organs and ears represent, figuratively speaking, three generations of sense-organs. The oldest is the skin stimulated by varying pressures, such as are produced by irregular currents, and capable of initiating equilibrational responses. From the skin have been derived the lateral line organs stimulated by water vibrations of low rate, and also significant for equilibration. Finally, from the lateral line organs have come the ears stimulated by water vibrations of a high rate and important for equilibration. The ear, unlike the skin and lateral line organs, is differentiated for its two functions, the sacculus for hearing, the utriculus for equilibration."[147]
The sense of hearing remains to be considered. My attention was first drawn to this subject by failure to obtain motor reactions to sounds in the investigation of the time-relations of the neural processes of the green frog. Although a large number of sounds of different qualities, pitches, and intensities were employed, no visible motor reactions were observed. This led me to seek the significance of what appeared to be either a surprising lack of sensitiveness to changes in the environment which would naturally be expected to stimulate the animal, or an interesting and important case of the inhibition of reaction to auditory stimuli. This suggested the question, Are frogs deaf, or do they under certain conditions completely inhibit their usual reactions to sound?
In the literature on the senses and reactions of frogs I have found nothing which contributes importantly to our knowledge of the sense of hearing. Most of the investigations which deal with the ear are concerned with the equilibrational and orientational functions of the labyrinth organs, and have nothing whatever to say about hearing. In the natural histories the existence of a well-developed sense of hearing is usually assumed, and numerous instances of what are supposed to be reactions to sound are cited. It is to be noted, however, that none of the observations in these popular works furnishes satisfactory proof of the exclusion of the influence of visual stimuli. Among the few references to frog audition of which I have knowledge, the only one which seems worthy of special notice is that of Gaupp in his Anatomie des Frosches. Since his few paragraphs sum up the state of our knowledge on the subject, while at the same time furnishing an illustration of the assumption of hearing on the basis of analogy, I present the substance of them in free and slightly abbreviated translation.
"The labyrinth organ has an acoustic and non-acoustic (static) function. For these two functions, according to the leading if not generally accepted view, entirely different portions of the organ are in question, and since the non-acoustic is attributed to the three _Cristae acusticae ampullarum_ and the three _Maculae_ (_M. recessus utriculi_, _M. sacculi_, _M. lagenae_), there remain for the acoustic function only the _Papilla basilaris_ and the _Macula neglecta_. It is not certain, however, that the non-acoustic organs do not participate in the acoustic function.
"With regard to the acoustic sense of the frog nothing exact is known. That it exists, and that in good development, is certain. The existence of the drum and columella, and the fact that frogs have a voice are unmistakeable proofs of hearing. The participation of the _Papilla basilaris_ in acoustic functions is rendered certain by comparative anatomical studies: the _Papilla basilaris_ is the nerve end-organ from which, in the mammalia, the undoubtedly acoustic organ of Corti arises. From analogy of structure we may also infer an acoustic function in the _Macula neglecta:_ on this, as on the _Papilla basilaris_, there is a simple tectorial membrane, and further the _Pars neglecta_, like the _Pars basilaris_, has a strong thick wall which only in a limited region, namely, where it approaches a part of the perilymphatic space, is markedly thinner." (For fish Breuer (1891) has already stated that if they really hear--which is proved--the _Macula neglecta_ alone can come into consideration in connection with the function, for there is no _Papilla basilaris_ in fishes, and the six other nerve end-organs apparently serve the non-acoustic function.)[148]
As the green frog does not respond visibly to sounds under experimental conditions, I found it necessary to employ indirect methods in the study of audition. By observing the influence of sounds on respiration and on the reactions to certain electrical, tactual, and visual stimuli, I obtained results which, since they have already been described in detail elsewhere,[149] may be summarized here as follows:
1. Observation of frogs in their natural habitat shows that they are stimulated by sounds, but the sense of hearing apparently serves rather as a warning sense which modifies reactions to other simultaneous or succeeding stimuli than as a control for definite auditory motor reactions.
2. Experimental tests prove that sounds modify the frog's reactions to visual and tactual stimuli. When the sound accompanies the visual or tactual stimulus it serves to reënforce the reaction to the other stimulus, but when given alone it never causes a motor reaction.
3. The green frog responds to sounds made in the air, whether the tympana be in the air or in water. There is some evidence that the influence of auditory stimuli is most marked when the drum is half-submerged in water. The influence of sounds upon tactual reactions is evident when the frog is submerged in water to a depth of 4 cm.
4. Sounds varying in pitch from those of 50 to 10,000 vibrations per second affect the frog. The most striking results were obtained by the use of an electric bell with a metal gong. With this sound in connection with a weak tactual stimulus a maximum reaction may often be obtained even when either stimulus alone causes no perceivable reaction.
5. Sounds modify the reactions of the frog after tympana and columellæ are removed. Cutting of the eighth cranial nerves causes disappearance of the influence of sound. It is clear, then, that the reactions to sounds are really auditory reactions and that the sense of hearing in the frog is fairly well developed, although there is little evidence of such a sense in the motor reactions of the animal.
6. Experiments during the spring months show marked influence of sounds for both males and females, whereas experiments made during the winter indicate a much diminished sensitiveness to auditory stimuli in both sexes, but especially in the male.
III. THE MUTUAL RELATIONS OF STIMULI
In studying the various influences of complication of stimuli in the frog, I have used two methods: the measurement of reaction-time and of the amount of reaction. The reaction-time results will be presented first.
Reaction-time to electric stimulation of the skin was studied with special attention to the influence of other stimuli which were given in definite temporal relation to the electric stimulus. A Hipp chronoscope, controlled by a Cattell's falling screen, served as a time-measuring apparatus. The other essentials of the apparatus were a reaction-box, and devices for giving the stimuli and indicating the reaction. On the bottom of the reaction-box a series of wires were so placed that an electric stimulus could be given to the frog resting upon them by the closing of a key in the hands of the experimenter. In preparation for each experiment the frog was placed upon these open circuit wires in such a position that the weight of its body pressed upon a delicate spring in the floor of the box, thus causing the chronoscope circuit to be completed. The forward jump of the frog in response to stimulation caused the breaking of this circuit by the release of the spring upon which the animal rested. When all was in readiness for an experiment the chronoscope was started, and a key closed which simultaneously gave an electric stimulus to the frog and completed a circuit which caused the chronoscope record to begin. The stimulus consisted of a current from one or more "Mesco" dry cells. The motor reaction of the frog broke the chronoscope circuit, thus causing the chronoscope record to stop. It was then possible for the experimenter to read from the dials of the chronoscope the time, in thousandths of seconds, intervening between stimulus and reaction (reaction-time). In case of additional stimuli in connection with the electric, various simple devices were introduced to meet the demands of the experiments. These will be described in connection with the statement of results in each case.
_Electric and photic stimuli._ A photic stimulus was given from one to two seconds before the electric stimulus by the turning on of a sixteen-candle-power incandescent light, which was placed thirty cm. in front of the frog in the case of one series of experiments and fifteen cm. above it in another. The light uniformly inhibited reaction to the electric stimulus, as is shown by the results of Table 1.
TABLE 1
Title of investigation,--Electric-Visual (Red Light). Experimented on,--Green Frog No. 4. Harvard Psychological Laboratory,--9.40 A.M., Feb. 28, 1902. Chronoscope control average, 189σ,--Electric stimulus, 1 Cell.
NO LIGHT.
_Number of_ _Experiment._ _Reaction-time._ 1 152σ 2 145 3 221 4 327 5 263 6 271 7 329 8 215 9 225 10 216
LIGHT BEFORE ELECTRIC STIM.
11 No reaction. 12 No reaction. 13 No reaction. 14 No reaction. 15 No reaction.
NO LIGHT.
16 216
The inhibitory influence of light depends upon the intensity of the electric stimulus. Even a very strong light will not cause much retardation of reaction to a three or four cell current. As the strength of the electric stimulus decreases the delay of reaction increases, until finally there is complete inhibition. At this point, an electric stimulus, to which the frog would react almost invariably when there is no disturbing condition, will fail to cause reaction in the presence of a sudden increase in light intensity.
Merzbacher[150] states that the leg reflex of a frog, so placed that its legs hang free in the air, is greater in response to a given cutaneous stimulus in darkness than in daylight.[151]
_Electric and visual stimuli_ (moving object). For the purpose of determining the effect upon reaction-time to an electric stimulus of stimulation of the eye by a rapidly moving object, experiments were made in which, as in the case of electric and photic stimuli, reactions to electric stimulus alone and to the visual and electric were observed alternately. Thus in the case of each pair of reactions it was possible to note whether the visual stimulus shortened or lengthened the reaction-time. The visual stimulus was given by quickly moving a finger before a window in the reaction-box.
Two series of twenty pairs of reactions each were taken with each of two frogs. In the first series the finger was suddenly moved across the window and the electric stimulus was given either simultaneously or a small fraction of a second later. It was impossible to arrange for accurate measurement of the temporal relations of the two stimuli in the case of these tests. In the second series the finger was moved back and forth before the opening in the reaction-box for an interval of at least a second before the electric stimulus was given.
These experiments, which were in the nature of preliminary tests, yielded the following results. When the stimuli were given almost simultaneously the visual reënforced the electric as was indicated by a shortening of the reaction-time. As appears in the upper part of Table 2, the average time of forty reactions, twenty for each frog, to the electric stimulus was 148^{σ},[152] and to the same stimulus when it followed the visual 128^{σ}. Furthermore, examination of the several pairs of reactions shows, as is indicated in the table, that there were twenty-seven cases in which the visual stimulus caused shortening of the reaction-time (reënforcement of the electric stimulus) to thirteen in which it caused lengthening (inhibition). When the visual stimulus preceded the electric by at least a second, the reaction-time to the electric stimulus was greatly lengthened. The averages are 150^{σ} for the electric stimulus alone, 178^{σ} when it was preceded by the visual. In this series there are twenty-five cases of inhibition to fourteen of reënforcement.
_Electric and visual stimuli_ (moving red disc). The indications of the importance of the temporal relations of stimuli, so far as reaction-time results are concerned, furnished by these crude preliminary observations led to a more accurate study of the subject. A revolving disc, which moved at the rate of one revolution per minute, was so arranged that at a certain point it closed an electric circuit in which a magnet had been placed. This magnet attracted a steel arm at the end of which a disc of red cardboard 12 mm. in diameter was suspended. With the making of the circuit the steel arm was drawn downward suddenly and the red disc, by reason of the vibrations of the arm moved rapidly back and forth in front of a window in the reaction-box. In this way the moving object was exposed to view about ten cm. to the right and three cm. in front of the right eye of the frog. The revolving disc, a fraction of a second later, completed the electric stimulus circuit. Thus both stimuli were given automatically, at such an interval apart as the experimenter desired. In the two series of results now to be described the intervals were 0.1 and 0.5 second respectively.
TABLE 2
Reaction-time to Electric Stimulation Alone, and to the Same when preceded for 0.1, 0.5, or 1.0 Second by Visual Stimulus.
Key: 1 = Frog. 2 = Electric Alone. 3 = Visual 0.1" before elect. 4 = Number Inhibited. 5 = Number Reënforced. 6 = Number Equal. 7 = Visual 1.0" before elect.
1 2 3 4 5 6 2 7 4 5 6
Preliminary Series. Visual Stimulus Moving Finger. Averages for 20 reactions. No. 5. 179ˢ 158ˢ 6 14 0 163ˢ 206ˢ 14 6 0 No. 6. 116 98 7 13 0 136 150 11 8 1 Gen. Aver. 148 128 13 27 0 150 178 25 14 1
Visual Stimulus Moving Red Disc. Visual 0.1" before electric. Visual 0.5" before electric.
Series I. Averages for 25 reactions.
No. 5. 177 163 10 15 0 170 255 15 9 1 No. 6. 148 112 6 19 0 115 178 18 7 0
Series II. Averages for 25 reactions.
No. 5. 135 120 7 18 0 155 259 24 1 0 No. 6. 128 111 6 19 0 132 227 17 7 1 Gen. Aver. 147 126 29 71 0 143 230 74 24 2
These series consisted of twenty-five pairs of reactions each, with two animals. The results of the series are presented separately, in the lower half of Table 2, because the experiments which constitute them were separated by a period of three weeks. It is to be noted that these results agree fully with those of the preliminary series. The visual stimulus of a moving red disc, given 0.1 second before a 2 cell electric stimulus, reënforces the electric reaction, _i. e._, it shortens the time of reaction. The same visual stimulus given 0.5 second before tends to inhibit the electric reaction, _i. e._, it lengthens the time of reaction.
_Tactual and auditory stimuli._ Since in the frog auditory stimuli under experimental conditions seldom if ever cause visible motor reactions, the study of the influence of this mode of stimulation upon the reactions to other simultaneous or succeeding stimuli is of special interest. In the investigation of the relations of auditory stimulation to other forms of reaction _amount_ of reaction instead of _reaction-time_ was taken as a measure of the influence of the stimulus. By a method the details of which may be most easily understood by reference to the plan of the apparatus in Figure 1, the influence of auditory stimuli on the leg-movement induced by tactual stimulation was observed.
In these experiments the frog sat astride a wooden support, held in position by linen bands over the back and a wire screen cap over the head. The hind legs hung free, and any movement of one of them in response to a stimulus could be read in millimetres by reference to a scale on the wooden support. This method of measuring the value of a stimulus in terms of leg-reflex has been used by several investigators--most recently by Merzbacher.[153] I have found it desirable, as did Merzbacher, to observe the movements of a shadow of the leg on the scale and thus read the amount of movement, rather than to watch the leg itself and attempt to project it upon the scale.
As is indicated in Fig. 1, the auditory and tactual stimuli were given automatically by means of a swinging pendulum, _P_, which was held in position by the magnet _a_ until released by the experimenter. Early in its swing the pendulum turned the key, _m_, thus completing a circuit which caused the auditory stimulus to be given; later in the swing the key, _n_, was turned, and the tactual stimulus thus given through the magnetic release of the lever, _l_. The interval between the auditory and the tactual stimuli could be varied from 0 to 2" by changing the position of the key, _n_. For intervals over 1" it was necessary to arrange this key so that the tactual stimulus was given at some time during the return swing of the pendulum.
The auditory stimulus used was either the sound of a quick hammer blow (momentary stimulus of Series I), or the ringing of an electric bell for a certain length of time (prolonged stimulus of Series II). In Fig. 1 the bell is shown. It was placed eighty cm. from the frog, and in order that the influence of vibration of the experiment table might be avoided it was suspended from the pendulum frame. When the hammer was used it was placed sixty cm. from the frog, on the pendulum table. The holder for the frog and the tactual apparatus occupied a separate table which was not disturbed by the jars of the pendulum table.
The tactual stimulus was given by a rubber cone, _T_, two mm. in diameter at its apex. This rubber point, after the electric release of the lever to which it was attached, struck the frog at the middle point of a line drawn between the posterior margins of the tympana. The intensity of the stimulus could be varied by weighting the lever, _l_, at _w_.
All experiments were made with the green frog, _Rana clamata_ Daudin. The reactions were taken regularly at half-minute intervals in pairs: first, a tactual stimulus reaction, then an auditory-tactual reaction. Ten, fifty, or one hundred pairs constituted a series. So far as the condition of the frog is concerned there seems to be nothing undesirable in long series, for fatigue does not appear, and so long as the animal is kept moist and in an unconstrained position, it continues to react normally, and without frequent struggles to escape. The advantage for the purposes of this investigation of taking the reactions in pairs, rather than taking separate series of reactions for each stimulus or combination of stimuli, is obvious. It enables us to compare directly the reactions of each pair, in other words those reactions which took place under most nearly identical conditions, and to note at once whether the auditory stimulus reënforced or inhibited the tactual reaction.
During a series the intensity of the tactual stimulus was changed as conditions demanded, but for any one pair of reactions it was always the same. It not infrequently happened that an intensity which at first caused merely a slight movement of the leg, later in the series uniformly brought about a maximal contraction, or the reverse might be true, and inasmuch as a maximal reaction to the tactual stimulus alone left no opportunity for judging of the influence of the auditory stimulus, when it was given in addition to the tactual, it was always necessary in such cases so to alter the intensity of the tactual stimulus that a medium reaction resulted.
The frogs, after being placed in the saddle-like holder and held firmly for a few seconds, seldom struggled very much, but if bound tightly they became irresponsive to the stimuli.[154] It was, therefore, necessary after they had quieted down to loosen the bands which held them in position. For the purpose of excluding the influence of visual stimuli a wire screen cap covered with black cloth was put over the head; this served to keep the animal in position as well as to exclude visual stimulation.
_a. Momentary auditory stimulation._ Four frogs were used for a study of the influence of the momentary sound produced by a hammer blow, and for each of these animals fifty pairs of reactions were recorded in series each day. The temporal relation of the stimuli was changed daily during a week of experimentation: the results therefore consist of fifty pairs of reactions with each frog for each of the following seven intervals: (1) Auditory and tactual stimuli simultaneous, (2) auditory .25" before tactual, (3) auditory .45" before, (4) auditory .15" before, (5) auditory .65" before, (6) auditory .35" before, (7) auditory .90" before. The intervals were used in the experiments in the above order to avoid the formation of the definite habits of reaction which regular increase in the interval would have favored.
Typical of the results with all the animals are the following (Table 3) which were obtained with No. 1, a male. The figures in each case indicate the average of fifty reactions. Reënforcement and inhibition are expressed in terms of the tactual reaction, _i. e._, the auditory-tactual reaction is so many per cent greater (reënforcement) or less (inhibition) than the tactual. In the tables reënforcement is indicated by the + sign; inhibition by the - sign. In the last column of the table is given the number of reactions that were reënforced or inhibited. This was determined by comparing directly the reactions of each pair. Cases in which the two reactions were the same were distributed equally between the two classes: tactual reactions reënforced by auditory stimulus, and tactual reactions inhibited by auditory stimulus. Assuming that the auditory stimulus was without effect upon the tactual reaction, the number of reactions in these two classes would be approximately the same, hence all auditory-tactual reactions over half in a series, _i. e._, over twenty-five, which are greater than the corresponding tactual reactions, are reënforced reactions, and can be taken as a measure of the reënforcing influence of the auditory stimulus. In the same manner all reactions over half which show inhibition can be taken as a measure of the inhibitory value of the auditory stimulus.
As preliminary tests described in an earlier paper[155] furnished evidence of sex-differences, it is worth while to compare the results given by the males and females in these experiments with momentary auditory stimulation. For purposes of comparison I have presented in Table 4 the reënforcement-inhibition values given by the males and females for each interval. Column one contains the value of the auditory-tactual reaction in terms of the tactual reaction; column two, the number of reactions in excess of half which were reënforced or inhibited.
TABLE 3. FROG NO. 1. MOMENTARY AUDITORY STIMULUS, HAMMER BLOW. WEIGHT USUALLY 5 OR 10 GRAMS
Reaction Reaction Amount of Number of to to Auditory Reënforc'm't reactions Tactual and Tactual or Reënforced Interval. Stim. Stim. Inhibition. or Inhibited.
0" 6.84mm. 11.08mm. +62.0% +17.0 .15 22.22 28.96 +30.3 +17.0 .25 16.30 21.72 +33.3 +13.0 .35 24.90 25.32 + 1.7 + 0.5 .45 17.56 13.64 -22.3 -10.0 .65 17.46 15.72 -10.0 - 6.0 .90 31.26 31.48 + 0.7 + 0.5
TABLE 4. MOMENTARY AUDITORY STIMULUS, HAMMER BLOW
_Males_ _Females_ Nos. 1 and 3. Nos. 2 and 4. Per centum No. of Per centum No. of Interval Diff. Reacts. Diff. Reacts. 0" +82.5% (Reënf't) +17.5 +58.0% +12.7 .15 +58.1 +17.0 +25.4 + 8.5 .25 +32.3 +12.7 +39.8 +12.7 .35 + 4.0 + 1.2 - 9.7 - 3.2 .45 -13.5 (Inhibition) - 7.2 -13.9 - 7.2 .65 -12.5 - 6.2 -11.8 - 7.2 .90 - 0.7 - 1.5 - 2.6 - 0.5
In these results two striking differences between the males and females appear: first, the reënforcement is not so great for the females as for the males; second, inhibition appears earlier and continues longer with the females than with the males. The average reënforcement with simultaneous stimuli is 82.5% for the males against 58.0% for the females. Inhibition begins to appear in case of the females when the interval between the stimuli is .25" to .35"; in case of the males it appears between .35" and .45". Finally at .90" interval inhibition is slightly greater for the females.
Although the exact significance of these facts is unknown, it is not improbable that they are indicative of fundamentally important sex-differences in reaction to sound. The males among frogs are usually the vocalists, although in some species the females also croak. Moreover, in case of the green frog the tympanum of the male is much larger than that of the female. The results presented would seem to indicate that certain sounds stimulate the males to activity, whereas they inhibit activity in the females.
Graphically represented, the results of the momentary auditory stimulus experiments with frogs Nos. 1, 2, 3, and 4 are as follows:
The curves are all plotted by the method which will now be described in connection with Fig. 2. This figure presents the reënforcement-inhibition curves for the males No. 1 (solid line in the figure) and No. 3 (broken line). If in this figure we let the zero-point on the ordinates represent the value of the reaction to the tactual stimulus when given alone, then the value of the reaction to the auditory-tactual stimuli would be represented at some point above the zero-point if this reaction was greater than the tactual reaction (reënforcement), and below the zero-point if the reaction was less than the tactual (inhibition). Since one of our chosen measures of reënforcement and inhibition is the amount, in per cent of tactual reaction, by which the auditory-tactual reaction exceeds or falls short of the tactual reaction, such a curve of reënforcement-inhibition as that of Fig. 2 (solid line) can be constructed at once from the data given in column four of Table 3. Here the auditory stimulus, when simultaneous with the tactual, caused 62% reënforcement, as is indicated in the figure. The figures in the left-hand margin of the curves indicate amount of reënforcement or inhibition in per cent of tactual reaction; those at the bottom of the curves mark the intervals. On the curves dots indicate the intervals used in the experiments. Each of the curves is plotted on the basis of 700 reactions.
In every way comparable with the curves for the males No. 1 and No. 3 in Fig. 2 are those for the females No. 2 and No. 4 of Fig. 3. The similarity of the two curves in each figure is noteworthy. Inasmuch as the conditions of experimentation were the same for all the animals this would seem to indicate sex-differences which are worthy of further investigation. The curves show clearly the greater reënforcement in the males, and the greater inhibition in the females.
Figures 4 and 5 are the reënforcement-inhibition curves for the same series of experiments plotted on the basis of the _number_ of reactions in excess of half that were reënforced or inhibited. As there were fifty pairs of reactions with each frog for each interval, uniform reënforcement would be represented by twenty-five reactions above the base-line; uniform inhibition by twenty-five reactions below the base-line. The number of reactions is indicated by the figures in the left margin; the intervals, by those below the base-line. As an illustration of the application of the method of plotting, the curve for male No. 1 (solid line) of Fig. 4 is constructed from the data of column five of Table 3. With simultaneous stimuli 17 reactions in excess of half, _i. e._, 17 + 25, or 42, were reënforced; at .35" interval .5 of a reaction was the average amount of reënforcement; at .45" interval 10 reactions in excess of half, _i. e._, 35, were inhibited, therefore the curve falls to 10 below the base-line.
Just as Figures 2 and 3 permit of direct comparison of the results of the measurement of the _amount_ of reënforcement and inhibition for males and females, so Figures 4 and 5 make possible comparison in similar fashion of the _number_ of reënforced and inhibited reactions for the sexes. It is to be noted that the two sets of curves, plotted on the bases of _amount_ and _number_ of reaction, agree in all important respects.
Figure 6 is the composite curve of amount of reënforcement-inhibition for the four animals; Figure 7 is the composite curve of the number of reactions reënforced and inhibited.
Summarily stated, the results of the experiments thus far described are: (1) The auditory stimulus of a quick hammer blow produces the maximum amount of reënforcement of tactual reaction when it is given simultaneously with the tactual stimulus; (2) as the interval between the auditory and the tactual stimulus approaches .35″ the amount of reënforcement gradually decreases; (3) when given .35″ before the tactual stimulus the auditory is practically without effect upon the tactual reaction; (4) as the interval increases above .35″ inhibition begins to appear; (5) the inhibitory influence of the auditory stimulus is greatest when the interval is about .45″; (6) when the interval is as long as .90″ the auditory stimulus is again ineffective. It thus appears that the reënforcement-inhibition curve of this particular stimulus under the conditions described is representative of a neural process which completes itself, in passing through two phases, a positive phase (reënforcement) and a negative phase (inhibition), in about one second.
_b. Prolonged auditory stimulation._ The experiments previously described have proved that a momentary auditory stimulus, which when given alone never produces a visible motor reaction, either reënforces or inhibits the reaction to a tactual stimulus which it accompanies or precedes. The experiments now to be described were made for the purpose of ascertaining whether reënforcement and inhibition occur in the same way if the auditory stimulus is prolonged, instead of momentary.
In a trial series of experiments with frog No. 1, one hundred pairs of reactions were recorded for each of six intervals of auditory stimulation. The auditory stimulus was given by the ringing of an electric bell. For all intervals the ringing of the bell continued until the tactual stimulus was given. When the two stimuli were given simultaneously the auditory stimulus was necessarily momentary, as in the foregoing experiments, but for all other relationships of the stimuli the bell rang for a certain length of time before the tactual stimulus was given. The six relations of the stimuli were: (1) simultaneous, (2) bell .2″ before and until tactual, (3) bell .6″ before, (4) bell 1.05″ before, (5) bell 1.5″ before, and (6) bell 2.0″ before. The other conditions of these experiments were the same as those previously described, except that the auditory stimulus was here given by the opening of the key which released the pendulum, instead of being given by the turning of a key in the course of the pendulum swing. This method of giving the auditory stimulus as the pendulum was released was found unsatisfactory because of the irregularity of the magnetic release; at one time the pendulum would start immediately, at another time there would be a delay of as much as .1″.
The reënforcement-inhibition curve plotted on the basis of the 1200 reactions in this series is presented in Fig. 8. Before stopping to consider the important features of this curve we should note the results of certain more accurate experiments with prolonged auditory stimulation.
With two animals, No. 2, a female, and No. 3, a male, fifty pairs of reactions were taken for nine different intervals (see Table 5) of auditory stimulation. Each of the curves of Figures 9 and 10 is therefore based upon 900 reactions. The conditions for these experiments were the same as those for the momentary stimulation series, save that the electric bell took the place of the electrically actuated hammer, as the mechanism for auditory stimulation.
The important facts exhibited by the results of these prolonged auditory stimulation experiments in contrast with those with momentary auditory stimulation are: (1) That whereas for the momentary auditory stimulus of a hammer blow the reënforcement is greatest for simultaneous stimuli, in case of the prolonged stimulation with the electric bell, reënforcement increases during an interval of .25″ of auditory stimulation. Hence, the two conditions of stimulation give us different types of reënforcement-inhibition curve. For the momentary stimulus the maximum reënforcement appears at simultaneity, and for the prolonged stimulus at .25″; (2) that the transition from reënforcement to inhibition occurs at 1.2″ in the prolonged stimulation curves, while in the momentary stimulation curves it occurs at .35″; (3) that the maximum inhibition which appears in the curves under discussion at about 1.5″ is less in comparison with the amount of reënforcement than that of the momentary stimulation curves; (4) that the auditory stimulus becomes ineffective when the interval during which it continues before tactual stimulation is 2.0″. The curves of Figures 8, 9, and 10 are then representations of a neural process which passes through a positive and a negative phase in about 2″. The effect of prolongation of the auditory stimulation interval is to lengthen the period of reënforcement; the period of inhibition shows little modification.
For the purpose of showing in greater detail the nature of the results of this work the data from which the curves of Figures 9 and 10 were constructed are presented in the accompanying Table 5.
Having now presented the results of my own investigation I wish to call attention to certain of their relationships to the work of other investigators, and to discuss briefly their significance.
TABLE 5. PROLONGED AUDITORY STIMULATION (ELECTRIC BELL)
_Frog No. 2._ _Female._ _Weight usually 25 grams._
Auditory Number of and Amount of Reactions, Tactual Tactual Reënforcement Reënforced Interval. Stimulation. Stimulation. or Inhibition. or Inhibited.
0″ 9.20 mm. 12.12 mm. + 31.7% +10.0 .25 4.56 11.88 +160.5 +22.5 .45 8.94 16.94 + 89.5 +18.5 .65 17.18 22.50 + 31.0 +15.5 .90 9.42 13.32 + 41.4 +14.5 1.20 10.54 9.64 - 8.5 - 2.5 1.40 24.00 20.64 - 14.0 - 6.0 1.58 19.16 17.80 - 7.1 - 7.0 1.95 14.50 15.40 + 6.2 + 5.5
_Frog No. 3._ _Male._ _Weight usually 5 or 10 grams._
0″ 14.92 mm. 25.20 mm. + 68.9% +11.0 .25 15.88 38.54 +142.7 +24.0 .45 13.48 26.02 + 92.9 +13.5 .65 18.30 27.94 + 52.6 +13.0 .90 20.94 29.06 + 38.8 + 9.5 1.20 21.90 30.58 + 39.6 + 1.0 1.40 19.18 18.34 - 4.4 - 5.5 1.58 32.24 26.30 - 18.1 - 3.0 1.95 13.86 14.14 + 2.0 + 2.0
VI. DISCUSSION OF LITERATURE AND RESULTS
The literature on reënforcement and inhibition is large, and even that portion of it which deals especially with the importance of the temporal relations of stimuli in connection with reënforcement and inhibition is so extensive that it does not seem worth while to attempt to give a systematic résumé of it for the purposes of this paper. I shall therefore call attention merely to those investigations which have contributed directly to the solution of the problems with which we are now concerned.
Bowditch and Warren[156] discovered that knee-jerk in the human subject is reënforced when an auditory, a visual, or a tactual stimulus precedes the tendon blow by .1″ to .5″, whereas the same stimuli have an inhibitory influence when they are given from .5″ to 1.0″ before the tendon blow.
At the suggestion of Bowditch, Cleghorn[157] undertook to investigate the influence of complication of stimuli upon voluntary movements. In this research graphic records taken in connection with an ergograph indicated (1) that "a sensory stimulus" applied just as the muscle was beginning to contract (voluntarily) caused an increase in the height of the contraction, and (2) that the relaxation following a contraction with intercalated sensory stimulus is quicker and more complete than when no stimulus is given (p. 344). Cleghorn did not give special attention to the significance of the temporal relations of the stimuli which he employed, and his work was limited to the phenomenon of reënforcement of voluntary action by reason of the appearance, during the progress of his research, of an excellent paper on the interference of stimuli by Hofbauer.[158]
Hofbauer covered thoroughly the ground which Cleghorn had planned to work over. The ergographic method was employed also by Hofbauer in his very careful study of the interference of impulses in the central nervous system of man. It was noticed that while the subject was rhythmically contracting a certain group of muscles in response to some prearranged signal (_e.g._, the sound of a metronome) the report of a pistol caused the contraction which immediately followed it to be much greater than the average of the rhythmic series, while the next contraction was correspondingly less than the average. It thus appeared that the sudden sound caused, first, reënforcement of the voluntary movement, then, inhibition. The reënforcement is greatest, according to Hofbauer, when the voluntary movement occurs immediately after the pistol report. When the report precedes the metronome signal by .2″ reënforcement is still marked, but thereafter it decreases rapidly in amount, until finally at .5″ inhibition appears. When the interval between the two stimuli is 1.0″ the first stimulus has practically no effect upon the voluntary movement in response to the second. (Hofbauer, p. 558.)
What Bowditch and Warren, not to mention other students of the subject, have described for reflex action in man, Hofbauer, Cleghorn, and others have shown to hold true also of voluntary movements. Unfortunately my own investigation was completed up to the point of the writing of this paper before I read Hofbauer's work, so I have not followed methods of dealing with my data which would make our results directly and easily comparable. But, whatever may be the relations of our results in detail, there can be no doubt that what he has demonstrated for man is true in its important aspect of the reënforcement-inhibition phenomena for the frog.
Important in their bearings upon the phenomena of reënforcement and inhibition which we are now considering, are the various studies of refractory period and rhythm of nerve cell and fibre. The existence of a refractory period in neural substance, similar to that demonstrated for certain kinds of muscle by Marey,[159] Englemann,[160] Kaiser,[161] Cushny and Matthews,[162] Woodworth,[163] and many others, has been proved by Broca and Richet.[164]
Broca and Richet found that in the normal dog the refractory period of the nerve substance is too short to be easily detectable, they therefore experimented with animals which were lightly chloralized and kept at a temperature of 30 to 34° (the mean normal temperature of the dog is about 39.5°). Under these conditions a dog, when two identical stimuli (quality and intensity the same) were applied to the cerebral cortex successively, exhibited the following reactions: (1) When the stimuli were separated by .01″ they reënforced one another (addition); (2) when the interval was .1″ they inhibited the reaction partially (subtraction).
Concerning this phenomenon Richet writes in his dictionary of physiology (p.5): "Marey showed, in 1890, that the heart of the frog, at certain moments of systole, was inexcitable. Now our experiments prove that the cerebral apparatus, a certain time after the excitation, also ceases to be excitable: it then has a refractory phase, and this refractory phase is much more prolonged than that of the cardiac muscle." In a later publication Richet[165] makes the somewhat startling statement that a refractory period is not exhibited by the nerves of cold-blooded animals. In the tortoise, according to his results, reënforcement occurs so long as the interval between the two stimuli is not greater than 2″, while for longer intervals each stimulus to all appearances works independently. Richet seems to have generalized from a study of the tortoise. That his generalization is unwarranted seems to me highly probable in the light of the results of this paper, for there are many reasons for supposing that the reënforcement-inhibition phenomena with which we have been dealing in case of the frog are manifestations of the existence of the same process in the nervous system which under somewhat different conditions of experimentation exhibits itself in the so-called refractory period.
The researches of Richet and his students indicate that the time of the process which conditions the phenomena of reënforcement-inhibition is about .1″. Stimuli given at .1″ intervals do not interfere with one another. That the process underlying the refractory period and the reënforcement-inhibition phenomena of our experiments is a rhythmic double-phase process is made still more probable by the following results. Horsley and Schäfer[166] found that the rate of response of the monkey to cortical stimulation was 12 per second, and Schäfer[167] discovered that the maximum rate of volitional impulses in man is 10 to 12 per second.
It was shown by Exner that certain movements of the foot of a rabbit could be produced by stimulating either the cortex or the skin of the foot. Simultaneous stimulation of both regions gives reënforcement. Stimulation of the cortex, if given not more than 3″ before subliminal stimulation of the skin, renders the latter effective. When both stimuli are subliminal each makes the subsequent one effective if the interval between them is not over 1/8″ (Schäfer[168]). Similarly for the dog Exner[169] proved that cortical and cutaneous stimuli reënforced one another, when both were subliminal, if the interval between them was not greater than .6″. Cortical and auditory stimuli, and auditory and cutaneous (of the skin of foot) gave similar results.
Physiologists have long been familiar with several aspects of the phenomena of reënforcement and inhibition in the frog, but I know of no detailed study of the significance of the temporal relations of stimuli in this connection. Goltz[170] called attention to the inhibition of the croaking reflex by peripheral stimulation, as well as to several similar phenomena. Nothnagel,[171] Lewisson,[172] and Wydensky[173] further contributed to our knowledge of the interference effects of stimuli in the frog. Wydensky proved that the application of an induced current to a nerve-muscle preparation may result in either contraction or relaxation of the muscle, according to the frequency of stimulation.
More recently Merzbacher[174] has dealt with the influences of complication of stimuli in the frog with the purpose of ascertaining the relations of the sense-organs to the reflex movements of the animal. His first paper is concerned especially with the functional importance of the eye in connection with reflexes. Unfortunately for the demands of this research, he did not attend particularly to the temporal relations of his stimuli. That a visual and a cutaneous stimulus were given either "at the same time or within a short interval of one another" (p. 250) is not the sort of information our problems demand.
According to Merzbacher's very interesting results a visual stimulus reënforces the reaction to a cutaneous stimulus. As the results of this paper show, this is only half a truth, for the two stimuli may either reënforce or inhibit one another's reactions. As Merzbacher observed no evidences of reaction to auditory stimulation he presumably did not attempt to study the influences of the ear in connection with reflexes.
There can be no doubt that the words reënforcement and inhibition as at present used in connection with the functions of the nervous system cover a multitude of widely differing phenomena. We can at once distinguish at least two important kinds of reënforcement or inhibition: first, that which is due to the functioning of special augmentary or inhibitory portions of the nervous system; second, that which is the result of the complication of stimuli. Any and every process in the nervous system may have either a reënforcing or an inhibiting influence upon simultaneous or succeeding processes; doubtless most processes or impulses at various times have both effects. The nervous system is constantly being modified by impulses from many sources, which suppress or strengthen one another according to their relative intensity, their temporal relations, and the motor relations of the portions of the organism which they affect.
The existence of the so-called refractory period in brain cortex and nerve indicates that every stimulus causes certain fundamentally important changes in the condition of the neural substance. These changes we may for convenience of illustration describe as modification of excitability, or of the functional capacity of central or peripheral tissues. Every stimulus causes a portion of the neural substance to pass from its normal state through a condition of increased excitability, which we may designate the positive phase, to a condition of diminished excitability, the negative phase. There is first an increase in the functional capacity of the tissues, then a decrease. If during the course of the change produced by a given stimulus a second stimulus becomes effective its result in reaction is determined by the particular phase of the tissues upon which it intrudes. If the nervous system is in the condition of increased excitability, and the two stimuli act upon sensory regions whose motor connections are not antagonistic, the reaction will be reënforced, as we say, by the previous stimulus; if, however, the second stimulus falls upon the negative phase of the nerve substance, the reaction will be partially or totally inhibited.
The facts which are most prominent as the result of this investigation are, first, that the temporal relation of stimuli is an important condition of certain forms of reënforcement and inhibition; second, that the interference effects of two stimuli cannot be studied to advantage without attention to the relations of the forms of reaction which are appropriate to each stimulus.
V. SUMMARY
1. Motor reactions of the green frog to electric stimuli are inhibited either partially or wholly by photic stimuli. The visual stimulus of a moving object has a like effect. It has been found, furthermore, that the same visual stimulus may either inhibit or reënforce the motor reaction in response to electric stimulation. When the two stimuli are given simultaneously reënforcement occurs, when the visual stimulus precedes the electric by half a second or more inhibition appears.
2. An auditory stimulus, which does not produce any visible reaction when given alone, modifies respiration and the reactions to other stimuli when given in connection with them.
3. The momentary auditory stimulus of a quick hammer blow when simultaneous with tactual stimulation reënforces the reaction to the latter stimulus. This reënforcement, or increase in the amount of reaction, ranges from 50 to 100% of the average reaction to the tactual stimulus alone. When the auditory stimulus is given before the tactual reënforcement occurs in gradually decreasing amount until the interval between the two stimuli reaches .35″; at this point the auditory stimulus has no apparent effect upon the tactual reaction. As the interval is still further increased inhibition appears and continues for intervals between .35″ and .9″. Reënforcement is greatest when the two stimuli are simultaneous; inhibition is greatest when the momentary auditory stimulus precedes the tactual by .4″ to .6″. When the interval reaches .9″ the first stimulus does not affect the reaction to the second.
4. Reënforcement is greater for the males than for the females; inhibition appears sooner and lasts longer in case of the females. This apparently indicates that the males are stimulated to activity by certain auditory stimuli, whereas the females are rendered passive by similar sounds.
5. Prolonged auditory stimulation by means of an electric bell causes reënforcement and inhibition, according to the temporal relations of the stimuli, as does momentary auditory stimulation, with the following differences: The maximum reënforcement occurs when the tactual stimulus is given about .25″ after auditory stimulation has begun; reënforcement continues for a period of 1.2″, _i. e._, when the electric bell continues to ring until the tactual stimulus is given, it reënforces the tactual reaction from simultaneity to 1.2″. Inhibition then appears, and continues until 1.8″. Both momentary and prolonged auditory stimulation cause first reënforcement, then inhibition of the appropriate reaction to a tactual stimulus.
6. The reënforcement-inhibition curves for the frog are very similar to those for man.
7. In case of the several pairs of stimuli whose interference effects have been studied reënforcement-inhibition appears. The first stimulus reënforces reaction to the second so long as the interval between them is not more than about .4″, while it inhibits the reaction when the interval is longer. Whether this reënforcement-inhibition curve as given in the experiments described may similarly be obtained for any and every pair of stimuli, no matter what their relation to reactions, remains to be determined.
8. In connection with the study of the mutual relations of stimuli of which this paper gives an account certain facts concerning the sense of hearing have been discovered. A summary statement of the results on hearing may be found on page 551.
FOOTNOTES:
[Footnote 139: The results brought together in this paper have been published in part in connection with other work in the following papers: Inhibition and Reënforcement of Reaction in the Frog, Jour. of Comp. Neurol. and Psychol., vol. 14, p. 124, 1904. Bahnung und Hemmung der Reactionen auf tactile Reize durch akustische Reize beim Frosche, Arch. f. d. ges. Physiol., vol. 107, p. 207, 1905. The Sense of Hearing in Frogs, Jour. of Comp. Neurol. and Psychol., vol. 15, p. 279, 1905.]
[Footnote 140: The Organ and the Sense of Taste in Fishes, Bulletin U.S. Fish Commission for 1902, pp. 237-272.]
[Footnote 141: Animal Behavior, Woods Hole Lecture Series, p. 300, 1899.]
[Footnote 142: The Response of the Frog to Light, American Journal of Physiology, vol. 9, p. 476, 1903.]
[Footnote 143: The Instincts, Habits and Reactions of the Frog, Harvard Psychological Studies, vol. 1, p. 590, 1903.]
[Footnote 144: The Skin and the Eyes as Receptive Organs in the Reactions of Frogs to Light, American Journal of Physiology, vol. 10, p. 31, 1903.]
[Footnote 145: Ueber die electromotorischen Erscheinungen an Hautsinnesnerven bei adaequater Reizung, Archiv für d. ges. Physiologie, vol. 63, p. 503, 1896.]
[Footnote 146: Harvard Psychological Studies, vol. 1, p. 592, 1903.]
[Footnote 147: Abstract of paper read before Section F of American Association for the Advancement of Science in Philadelphia, 1904. Science, vol. 21, p. 265, 1905. See also Bulletin of the U. S. Fish Commission for 1902, pp. 45-64, and the same for 1904, pp. 183-207.]
[Footnote 148: Anatomie des Frosches, VI, Lehre von Integument und von den Sinnesorganen, pp. 751, 752, 1904.]
[Footnote 149: Journal of Comparative Neurology and Psychology, vol. 15, pp. 279-304, 1905.]
[Footnote 150: Ueber die Beziehungen der Sinnesorgane zur den Reflexbewegungen des Frosches, Arch. f. d. ges. Physiol., vol. 81, pp. 222-262, 1900.]
[Footnote 151: "Blendung oder blosse Lichtentziehung erhoht die Erregbarkeit für mechanische Reize" (p. 253).]
[Footnote 152: Thousandths of a second.]
[Footnote 153: Arch. f. d. ges. Physiol., vol. 81, p. 227, 1900.]
[Footnote 154: A case of inhibition.]
[Footnote 155: Arch. f. d. ges. Physiol., vol. 107, p. 213, 1905.]
[Footnote 156: Journal of Physiology, vol. 9, pp. 60, 61, 1890.]
[Footnote 157: American Journal of Physiology, vol. 1, p. 336, 1898.]
[Footnote 158: Arch. f. d. ges. Physiol., vol. 68, p. 546, 1897.]
[Footnote 159: Travaux du Laboratoire de Marey, 1876.]
[Footnote 160: Arch. f. d. ges. Physiol., vol 59, p. 309, 1894.]
[Footnote 161: Zeitschr. f. Biol., vol. 32, p. 1, 1895.]
[Footnote 162: Journal of Physiology, vol. 21, p. 213, 1897.]
[Footnote 163: American Journal of Physiology, vol. 8, p. 213, 1902.]
[Footnote 164: Comptes rendus, vol. 124, p. 573, 1897.]
[Footnote 165: Nature, vol. 60, p. 629, 1899.]
[Footnote 166: Journal of Physiology, vol. 7, p. 101, 1886.]
[Footnote 167: Journal of Physiology, vol. 7, p. 111, 1886.]
[Footnote 168: Text-book of Physiology, p. 841, London, 1900.]
[Footnote 169: Arch. f. d. ges. Physiol., vol. 28, p. 495, 1882.]
[Footnote 170: Beiträge zur Lehre von den Functionen der Nervencentren des Frosches, p. 41, Berlin, 1869.]
[Footnote 171: Centralb. f. d. med. Wissensch., vol. 7, p. 211, 1869.]
[Footnote 172: Arch. f. Anat., u. Physiol., p. 259, 1869.]
[Footnote 173: Arch. d. Physiol. norm. et pathol., vol. 4, p. 690, 1892.]
[Footnote 174: Arch. f. d. ges. Physiol., vol. 81, p. 222, 1900.]
THE TEMPORAL RELATIONS OF NEURAL PROCESSES
BY ROBERT M. YERKES
Muscle contraction-time, according to the determinations of several investigators, varies about .0035".[175] Sanderson states that the time for direct stimulation of the muscle is approximately .0035" and for indirect stimulation, by means of the nerve, .007". The rate of nerve-transmission in the frog ranges from 25 to 35 metres per second.
Reflex reaction-time, as might be expected, varies widely with the nature of the reaction elicited by a stimulus, the condition of the animal, and the quality and strength of the stimulus. For many of the simple motor reactions of the frog it ranges between 20 and 60^{σ}.[176] Whether reflex reaction-time is to be sharply contrasted with instinctive and voluntary reaction-times, or whether they indistinguishably merge into one another is a question of considerable interest and importance for the student of the evolution of activity.
Voluntary reaction-time may be as short as 150^{σ} or as long as life, in an animal capable of profiting by experience as does the frog. It is preëminently the delayed type of reaction-time.
So much concerning the temporal relations of neural processes in the frog being well established, the purpose of the present paper is to call attention to some experimental results which indicate the existence of clearly defined types of reaction, and suggest possible values of reaction-time as a sign of mind.
The specific problems to be considered are: (1) Do reaction-times, in any given animal, range with equal frequency of occurrence from short to long, or are there certain modes (most frequented classes) which indicate definite types of reaction, such, for example, as the reflex, instinctive, etc.? (2) If there is distribution of the reaction-times about one or more modes, what are the types of reaction indicated thereby? (3) Finally, is reaction-time of service as a sign or measure of consciousness?
I wish especially to call attention to the fact that this paper deals with the reactions of the frog, not with animal reactions in general.
REACTIONS TO ELECTRICAL STIMULATION AND TYPES OF REACTION
Two years ago in connection with a discussion of the reaction-time of the green frog to electrical and tactual stimuli,[177] I presented a curve showing the distribution of 277 reaction-times to an electrical stimulus. The curve exhibited two clearly defined modes: one at between 60 and 70^{σ} and the other at about 160^{σ}. There was further a group of delayed reactions ranging about 500^{σ}. This form of distribution was interpreted, at the time, as indicative of three types of reaction, called, respectively, the reflex, the instinctive, and the delayed.
I have since obtained and examined with reference to form of distribution the further data which are presented in this paper. The reactions are all those of the green frog to electrical stimulation. The stimulus was applied by means of wires on the reaction-board on which the frog rested during the experiments. When reaction occurred in response to the electrical stimulus a circuit through the time-measuring apparatus was broken by the release of a delicate spring which had been held in place up to the instant of reaction by the weight of the frog. A Hipp chronoscope, controlled by a Cattell falling screen, served as a time-measuring mechanism. Three intensities of stimulus were used: (1) A current from one Mesco dry cell, (2) from two cells, and (3) from four cells.
Of the reactions whose time was measured there are three series. Series I is constituted by the recorded reaction-times in response to a one-cell stimulus, Series II, those in response to a two-cell stimulus, and Series III, those in response to a four-cell stimulus. The number of reactions, range and mode of each series are as follows:
Number of reactions Range Mode Series I 193 161-798^{σ} 235^{σ} Series II 288 41-647 235 Series III 256 61-178 105
The distribution of the 481 reaction-times of Series I and II is shown by Figure 1; that of the 256 reaction-times of Series III, by Figure 2. For both of these distribution polygons the reaction-times were arranged in ten^{σ} classes, beginning with the class 41-50^{σ}[178] in the case of the combined Series I and II and with the class 61-70^{σ} in the case of Series III.
Series I exhibits a primary mode at 235^{σ}. There are no reflex reactions in this series, unless it be maintained that the reflex reactions of the frog may have a reaction-time of over 160^{σ}, but there are a number of delayed reactions, some of which have reaction-times as long as 798^{σ}. This intensity of stimulation (one cell) may be said to call forth prompt reactions, which we may provisionally call instinctive, and delayed reactions, which have all the appearances of voluntary acts. There are no reactions which come within the range commonly considered as the reflex range of the frog (20-60^{σ}), and there are relatively few delayed reactions: almost all centre about the mode 235^{σ}.
Series II, in contrast with Series I, exhibits a secondary mode at 65^{σ} in addition to the primary mode at 235^{σ}. The stimulus-intensity of this series (roughly twice as great as that for Series I) induces a variety of short reaction, which did not appear in the case of the one-cell stimulus, and at the same time fewer delayed reactions. The range of the reaction-times for the two series is about the same, but the lower limits are markedly different.
Observation of the subjects during the experiments revealed two methods of reaction to the two-cell stimulus: a locomotor reaction (jump) which at once removed the animal from the source of stimulation, and a twitch of the hind legs which was instantly followed by the above-mentioned locomotor reaction. The leg reactions constitute the reflex group of Fig. 1, the usual prompt locomotor reactions, the instinctive group, and the slow locomotor reactions, the delayed or voluntary group.
It is to be noted that the instinctive reaction-time mode is the same for the two intensities of stimulation. This apparently indicates that change in intensity of stimulation causes a change in the type of reaction, not merely a gradual change in the position of the mode. For example, the modal reaction-time of 235^{σ} given by a one-cell stimulus did not shift to 200^{σ} or lower, as might have been expected, but instead there appeared a new type of reaction. The average reaction-times for the two series indicate a decrease in time with increase in intensity of stimulation, but they give no indication of the really important difference in the two series of reactions. The great importance of the distribution of the data, in addition to the common statistical quantities, is manifest.
Series III, whose reactions occurred in response to a very strong stimulus, differs in several important respects from the other series. Its range is much narrower, only 117^{σ}. Delayed reactions are lacking, and so also, curiously enough, are the reflex reactions of Series II. Instead of either or both of the modes of Series II, there appears in Series III an intermediate mode at 105^{σ}.
Our interpretation of these facts is facilitated by results of observation of the reacting subject. The leg reflex which frequently occurred in response to the two-cell stimulus never appeared in response to the four-cell stimulus. This in part explains the lack of the short reaction-time mode of Series II; it does not, however, account for the lack of delayed reactions. The latter fact may be referred to the intensity of the stimulus. Another difficulty in interpretation appears in connection with the intermediate mode, 105^{σ}. Is this to be considered an instinctive mode, as were those at 235^{σ}, or a reflex mode? Where is the line between reflex and instinctive action to be drawn? These results very clearly indicate that no line can be drawn, except quite arbitrarily. Reflex reaction-time, in the case of the frog, is continuous with instinctive, yet for any given situation the reflex, instinctive, and delayed (voluntary?) modes are likely to appear, as, for example, in the case of the data of this paper. Our conclusion must be, therefore, that although types of reaction are indicated by reaction-time results, the mode for a given type varies too much in position with different conditions to make it possible to say that a particular reaction-time is that of a certain type.
We may safely say, then, that for any given subject, the muscle contraction-time, nerve transmission-time, and simple sensory reaction-time to the constant stimulus in question being known, we should be able safely to interpret reaction-time records in terms of reaction types. For reflex, instinctive, and voluntary are terms which designate modes of reaction, albeit not isolated classes, for they intergrade.
Whether there are more types of reaction than are indicated by the data of this report does not concern us at present, for the practical as well as the theoretical bearings of our conclusions depend upon the existence of types, and not upon their number.
REACTION-TIME AS AN INDICATION OF CONSCIOUSNESS
Hesitation in reaction is commonly accepted as an important sign of volitional consciousness in man; consequently delayed reactions in lower animals are supposed to be indicative of psychic processes. Granting this much, reaction-time may be used as a sign of consciousness. It cannot be denied that the longer the reaction-time of a given animal the greater the probability that the reaction is conditioned by mental processes. Such a statement, it is true, has a basis neither better nor worse than that of most of our inferences concerning the nature of the actions of our fellow beings. As I have already attempted to show in a discussion of criteria of consciousness in animal psychology,[179] there is no one criterion of consciousness which can be used alone satisfactorily, but instead there are numerous signs of mind each of which has value according to the number and variety of our observations concerning its occurrence in connection with states of consciousness. The more of such signs we discover and learn to evaluate properly in relation to consciousness in its different grades and to one another, the safer will be our inferences concerning the existence of mental processes in animals.
Reaction-time is presented in this paper as an additional sign of mind. Like all other signs it is of value only if used as one of a series of indications of mental life. For if we attempt to judge of consciousness by reference to reaction-time alone, we may be seriously misled, whereas if we use it in connection with docility, variability, neural specialization, and other recognizedly valuable signs, we may be greatly aided in our inference. As in juristic procedure judgment is not based upon one bit of evidence nor even upon the evidence of a single witness, but upon evidence accumulated from all available sources, so in our attempts to judge of the existence of consciousness, it matters not whether the being be human or infra-human, we should make use of all phenomena which are recognized as signs of mind. The chief task of comparative psychology at present is the discovery and evaluation of signs of mind.
Reaction-time data, however, furnish another sign, or, as I prefer to call it in this case, measure of the intensity of consciousness; for variability of the time of reaction as well as its duration is significant. Reflex reaction-time is relatively constant, instinctive varies considerably, and the variability of voluntary reaction-time is extremely large. Degree of variability of reaction-time may be used as an indication of consciousness in the same way that variability in the form of reaction is used. The higher the power of consciousness the greater the variety in form of reaction and the variability of the reaction-time.
Reaction-time studies, as well as introspection and the investigation of animal behavior, indicate the importance of three activity concepts: automatism, instinct, and will. The automatic act is quick and relatively constant in form as well as reaction-time, while all signs lead us to infer that consciousness, when it accompanies the act, is a sequent phenomenon and not a condition of the act. The instinctive act is both slower and more variable in form and time than the automatic: consciousness is indicated as an accompaniment, and apparently it is at times a condition of the act. The will-act is extremely variable, unique in form, and almost without limits of reaction-time, for the conscious organism may react to the present situation in a fifth of a second, a day, or a year. Will is experience in action: it is our name for individually acquired control, and voluntary action is above all consciously conditioned activity.
Reaction-time, with respect to its two aspects of duration and variability, may be used as a sign or criterion of consciousness, for in accordance with the nature of these two sets of facts we classify acts as reflex, instinctive, or voluntary.
FOOTNOTES:
[Footnote 175: Sanderson: Journal of Physiology, vol. 18, p. 147. Tigerstedt: Archiv f. Physiologie, p. 111, 1895. Boruttau: Archiv f. Physiologie, p. 454, 1892.]
[Footnote 176: ς = thousandths of a second.]
[Footnote 177: Yerkes: Harvard Psychological Studies, vol. I, p. 609, 1903.]
[Footnote 178: The last four classes of Fig. 1 are 100^{ς} classes, 401-500, 501-600, 601-700, 701-800.]
[Footnote 179: Yerkes: Journal of Philosophy, Psychology, and Scientific Method, vol. 2, p. 143.]
THE MENTAL LIFE OF THE DOMESTIC PIGEON
AN EXPERIMENTAL STUDY OF CERTAIN EMOTIONAL AND ASSOCIATIVE PROCESSES
BY JOHN E. ROUSE
I. INTRODUCTION
Naturalists have observed the habits of pigeons, and physiologists since Flourens have subjected them to numerous experiments, but so far they seem to have received little psychological study. As a contribution to this interesting field the present paper reports an investigation of certain emotional and associative processes of the domestic pigeon. Since the literature of the subject is meagre, I shall state at the beginning a few related facts which I have gathered from various sources; then I shall discuss in detail the problems, methods, and results of my several experiments.
The brain of the pigeon is well developed, although the hemispheres are unconvoluted. When they are removed, the animal retains unaltered its reflex and vital activities, but ceases for a time at least to show evidence of mental life, for example, memory and will.[180] In the normal animal sight and hearing are acute, and touch seems keen, although the claws are not used for grasping and eating, as in the case of more intelligent birds, especially, parrots. There is considerable sensitiveness to temperature changes. Taste, and probably smell, appear to be deficient.[181] The "sense of support" is marked, even in the young.[182]
Since the pigeon seems to dream and also to miss its absent mate, some observers believe that imagery is present. There is certainly local memory, and also capacity to observe. Various intelligent acts have been reported.[183] The remarkable homing habits of the carrier pigeon have received no satisfactory explanation. While Cyon[184] suggests the stimulation of the nasal organs by air currents, Thauzièr[185] holds to the electrical theory; they agree, however, that certain higher psychical processes are probably involved.
Graber's[186] tests indicate that pigeons have no color-preference. Beebe's[187] statement concerning birds in general is peculiarly true of pigeons: "There are few species which do not show the emotions of love and sympathy, and ... one will sometimes pine and die of grief at the loss of its mate." After referring to their patient care of the young, he adds: "Indeed, sympathy is the keynote in the development of the higher mental faculties." These birds communicate, but their language consists of comparatively few sounds. As in many other birds, the play-instinct is highly developed.
II. PROBLEMS AND METHODS
My study of the pigeon's _emotional life_ had for its object certain respiratory "expressions." These were investigated by means of a pneumographic tracing, secured while the animal was comfortably fastened in a shallow nest, partially open below. A small box was placed over the bird, and apparatus was so arranged that the time of giving various stimuli was recorded automatically on the smoked paper of the kymograph drum, below the breathing-curve. A third line indicated rate of drum movement. Although some interesting results were obtained, the chief significance of the research consists in its demonstration of the fact that this method of studying animal mind is valuable.
In the study of _association_ I sought to determine the sense-data which the process involves, its method of formation (with due regard to social conditions), its rapidity, permanence, and modifiability, and also its probable degree of complexity. Material contributing to the subject was secured by observing the behavior of the animal when seeking to obtain food by overcoming such obstacles as labyrinths with wire passages, and latches, when the food was left in view, or by finding it when out of sight. In the latter case it was placed in a box occupying a customary place in a group of exactly similar boxes, or else in a box of color or form unlike the other members of the group and variously arranged, from time to time, with respect to them. When the animals were learning the labyrinth habits, various stimulations were given them; later the character of some of these was altered, and the resulting changes in behavior were noted. After the habits had been thoroughly learned, the birds were given a rest for some weeks, and then tested again under the old conditions. A few trials were arranged with special reference to the study of imitation; the animals here were tested as to their ability to execute simple but unfamiliar acts, after having only seen them performed by an animal previously trained. Throughout the associational tests the animals very seldom received food in their cages; but as they were tested daily and allowed to satisfy their hunger completely at the last test, they were never in a state of "utter hunger"--a condition which most experimenters think best to avoid. A series of tests, given at the conclusion of the investigation, indicated that the odor of the food had not assisted the animals in reaching it.
In the two series of experiments (emotion and association) thirty-five animals in all were used. They were confined in large cages in a fairly well lighted and ventilated room, and were fed wheat, cracked corn, and occasionally fruit, and kept well supplied with fresh water and sand. They generally remained in a healthy condition throughout the tests, especially during the winter. To exclude, as far as possible, the disturbing influence of fear, they were usually handled only after the room had been darkened. As the noise made by the curtains was objectionable, the birds were tested with the room illuminated by incandescent lamps; the light was turned off before the birds were placed in position for the trials, and again before they were removed from the apparatus to the cages. It is generally agreed that an experimenter should be out of sight when giving a test. I am convinced that it is important to avoid being seen by the animals at any time. This involves great inconvenience, especially when one employs the pneumographic method, but better results are thus obtained.
For practical suggestions as to apparatus and methods I am greatly indebted to Dr. Robert MacDougall, at the beginning of my investigation, and to Dr. Robert M. Yerkes, throughout. I also owe much to the researches of Zoneff and Meumann,[188] Thorndike,[189] Mills,[190] Small,[191] and Kinnaman.[192] Porter's[193] interesting study of sparrows was made almost simultaneously with the investigation here reported. Fewer animals were used by him, but in some instances more tests were given.
III. INVESTIGATION OF EMOTION[194]
1. _Respiration in general._ The normal breathing-curve in pigeons is quite similar in contour to that of the human subject, although the rhythm is more rapid and the pauses are less pronounced. When acoustical, visual, olfactory, or tactual stimuli are given, various modifications appear, for example, quickening, deepening, and minor irregularities. It was noticed that meaningless stimuli (pistol-shots) quickly lose their disturbing influence, whereas the breathing remains sensitive to those of a significant character, such as the noises made by other birds. It was also found that a stimulus which no longer affects the breathing will sometimes occasion disturbance if accompanied by a second stimulus of another order, although of a weak intensity (summation).
2. _Respiratory reactions to light._ As the easy control of conditions makes vision an excellent field in which to work, light reactions were investigated in detail. Two distinct series of tests were given. One sought to determine the relation between quality of light and reaction; the other, between intensity of light and reaction. Four colors of one intensity and three intensities of one color, respectively, were used. In the first series four stimuli, one for each of the colors, red, yellow, green, and blue, were given daily; in the second series five daily stimuli were given, of the same intensity for any one day, and one minute apart; this made it possible to observe also the effect of repetition. Each stimulus was given at the beginning of a respiration and continued two seconds. When the tracings were studied, various modifications were noted, but special attention was paid to alterations in rate of breathing. In the case of both sets of trials an immediate quickening usually occurred after stimulation, and occasionally shallowing[195] and minor irregularities of contour.
In the first set of tests ten animals were used for twenty-five days. Average results indicated that red and yellow are less stimulating than green and blue. To secure data that would assist in the interpretation of these results, an investigation was made of the animals' color-preference. This was done by recording, at thirty-minute intervals, the position of the birds when confined, singly, in a box one half of which was illuminated (from the side) by light of one color, and one half by light of different color but of the same intensity. A water screen excluded the heat rays. After nine records had been taken the colored glasses were interchanged, and the animal's position relatively to the two colors was observed as before. This was repeated with the other colors until each of the four had been used with each of the other three. There were far more choices of green and blue than of red and yellow, though none of the colors was avoided. It seemed a question of _degree of liking_, rather than of liking or disliking. As stated, Graber's experiments indicated that pigeons have no color-preference, but his results are probably untrustworthy, since he tested several animals at once and apparently was not careful to change the colored glasses regularly. Putting together our two sets of data (the latter stated first) we have the following comparison:
R Y G B Color choices of } 5 animals } 72 129 167 172
Breathing-rise of} 10 animals } 9.94% 10.39% 10.41% 12.11%
Although the proportions do not hold, there is a direct correspondence between the two series of responses; hence it would seem that _increased respiratory activity is an expression of agreeable feeling_ in pigeons, and this especially since the breathing, when varying at all in amplitude, usually became shallower, and also showed certain minor irregularities of contour, as often occurs in human respiration during moderate stimulation of a pleasant character.[196]
In the second series of respiratory tests four animals were used for fifteen days. Average results showed nothing as to the relation between intensity of stimulus and amount of quickening, since the three intensities used, 1, 2, and 4, produced reactions, respectively, as follows: 6.6%, 4.3%, and 6.4%. This may have been because the three intensities were employed each on different days. When the reactions are averaged according to daily succession, without regard to the intensities of the stimuli, we get the following results: first reaction, 8.0% rise in rate; second, 3.7%; third, 4.1%; fourth, 5.7%; and fifth, 6.9%. We should have expected the second daily response to be less vigorous than the first, since the animals were perhaps better prepared for the second stimulation. That the reactions increased thereafter was probably due, partially to summation, and partially to the fact that the short illuminations occasioned mental action (_perception_ of interior of box, increased _desire_ to escape, etc.) which involved heightened, rather than depressed, breathing activity, and thus worked directly against the dulling tendency of repetition.[197]
IV. INVESTIGATION OF ASSOCIATION
1. _Labyrinth experiments._ Four labyrinths in all were used (L, M, H, O). Each was constructed by attaching moveable wire partitions in a wooden box, covered with chicken wire. The pigeon was admitted through a small entrance compartment which was fastened at one end of the box, and which communicated with it by means of a lifting door, operated by pulling a cord from behind the observation curtain. Food was placed within the maze, and usually at the opposite end. Before beginning the tests the bird was allowed to become thoroughly familiar with the box without the partitions. After a few trials it learned to go to the food immediately upon entering the box. The partitions were then put into position, and the bird was tested as to the time required (except in the case of labyrinth O) and as to the method employed in reaching the food. The time was measured by means of a stop-watch, and the bird's horizontal movements were recorded on a small plot of the labyrinth; other general observations were added.
A. _Habits in Labyrinth L_
In this labyrinth (Fig. 1) six animals were tested once daily for thirty days, and five of these again after two and six weeks, respectively. On entering the labyrinth with the partitions in place the first time, a bird started on its usual direct course toward the food-box; running against the first partition it made vigorous efforts to push through, flying at the wire and often clinging to it for a short time; some of these random movements eventually brought it to the left of the compartment, and thence, through the opening, into the second compartment, and so on through the others, until finally it reached the food by a series of fortunate accidents.[198] The same general reaction was shown in case of the next few tests, except that fewer and fewer useless movements were made, and that the right ones were carried out with greater and greater precision. Later the animal had no difficulty in reaching the food; it did not run against the partitions, enter the blind alley, nor display such general signs of uncertainty as pausing and looking about. The process of learning in this case was obviously one of "trial and error," or the selection of useful movements. From the mass of random movements constituting the reaction to the unfamiliar environment, only those which enabled the bird to reach the food were retained and improved; the others gradually disappeared until finally the path taken became the shortest one possible, and was entered upon and pursued without hesitation by each animal as soon as it was allowed to enter the labyrinth. The time required for the tests is given in Table I.
It will be seen at a glance that the absolute time required for reaching the food varied for the individuals (see especially the results given by different birds in the case of test 1), but that the several periods for any one bird were relatively similar to those for another; and also that the time was long at first, but rapidly shortened from test to test, thus showing a steady advance in the learning process. Various lapses occurred (for example, A, 8; C, 13; E, 10) after the habit had been fairly well fixed.
In tests 18-22 the time-shortening was due principally to quickening of movements which had already become well defined. The great importance of visual data is brought out by the abrupt lengthening of the periods in the case of tests 23-25, and 26-30, where the light intensities were decreased. The lengthening was roughly proportional to the change of illumination. In the relative darkness the birds had to re-acquire the habits. The same mistakes were made as at first (running against partitions, and into the blind alley), yet here, as before, there was a ready adjustment. That the food was out of sight, or at least very much less visible, probably made no difference, since it was found that the birds would readily go to the old place after both food and food-box had been removed. In order to exclude the light entirely without making their movements invisible to me, I blindfolded the birds by means of a thin black hood, comfortably adjusted over their eyes and top of head; as a result, none was able to make the course in twenty minutes. The first turn, however, was usually made naturally, perhaps because associated with certain non-visual sense-data (sound of the lifting door, and perhaps tactual impressions of the close entrance compartment, etc.). Rats[199] seem far less dependent upon visual data than do pigeons. The great permanence of the pigeons' habits is shown by comparing the periods for tests 31-3, given after two and six weeks of rest, respectively, with those for tests 18-22.
TABLE I. TIME REQUIRED TO REACH FOOD IN LABYRINTH L
_Animals_
_Trials_, A B C D E F _Average_ 1 daily. ' " ' " ' " ' " ' " ' " ' " { 1) 28:50 :59 42:20 49:04 22:13 4:04 24:35 { 2) 7:22 :22 25:47 10:17 :48 2:02 7:46 { 3) 1:18 :12 8:29 12:35 :12 1:41 4:05 { 4) :32 :21 10:51 1:26 :19 :52 2:24 { 5) :24 :28 2:36 2:18 :12 1:33 1:15 { 6) :25 :26 1:10 :55 :12 1:50 :50 { 7) :15 :24 :28 :32 :15 2:09 :41 { 8) 1:05 :23 :33 1:19 :17 1:46 :54 1 { 9) :16 :24 :57 :58 :10 :26 :32 {10) :24 :32 1:15 :51 2:12 :31 :58 {11) :12 :21 1:40 :30 :17 :54 :39 {12) :16 :32 :49 1:34 :22 1:18 :49 {13) :13 :18 2:30 :18 :10 :42 :42 {14) :29 :32 :27 :31 :25 :36 :30 {15) 1:00 :24 :30 :31 :12 :35 :32 {16) :19 :52 1:10 :22 :17 :24 :34 {17) :14 :14 :31 :39 :13 :57 :28
{18) :13 :09 :29 :13 :16 :29 :18 {19) :10 :10 :36 :26 :07 :14 :17 2 { 20) :11 :15 :34 :17 :07 :10 :16 {21) :13 :14 :34 :16 :09 :21 :18 {22) :09 :16 :26 :14 :08 :11 :14
{23) :12 :42 1:29 :39 5:53 :13 1:31 {24) :20 :17 1:31 :33 :15 :13 :31 3 { 25) :15 :24 :40 :28 :19 :20 :24
{26) 1:21 16:29 1:22 13:54 3:51 1:36 6:26 {27) 3:36 4:45 :44 1:03 1:09 2:59 2:23 4 { 28) :51 1:24 :46 1:04 :56 1:09 1:02 {29) :51 :41 1:10 :40 2:17 :11 :58 {30) 2:04 :18 :41 :14 :07 :19 :37
5 { 31) :08 :33 :25 :07 :07 :16 6 { 32) :09 :15 :20 :08 :31 :17
1: With 18-candle-power illumination of the room.
2: Same illumination; tests given after the animals had heard four other pigeons pecking in the labyrinth.
3: With 2-candle-power illumination, other conditions the same.
4: With a slight illumination through single curtain, other conditions the same.
5: After two weeks' rest, conditions as in 2.
6: After six weeks' rest, conditions as before.
Let us now notice the gradual progress of learning in three important parts of the maze, as shown in Fig. 2. It will be seen that in the beginning the animals started upon their usual course and pressed against the first partition (stage 1), but that later they touched it less and less (stages 2 and 3), and that finally they avoided it entirely (stage 4). The adjustment here was fairly simple: the sound made by the opening of the entrance door, and the glimpse thus given of the labyrinth, gradually came to be conditions of the movements of turning to the left, on emerging from the entrance, and passing along the compartment toward the opening, where impressions, mostly visual, in the same manner determined the movements of turning to the right and entering compartment 2.
The blind alley was naturally a decided obstacle. The pigeons learned to avoid this compartment by going around it only after many unsuccessful attempts to go through it. During the first test the animals entered it many times (stage 1); on emerging they returned to the second or the first compartment, only to encounter the pen again when they re-advanced toward the food; finally, on reëmerging from the annoying enclosure, perhaps for the eighth or tenth time, they might happen to turn to the right instead of going forward as usual toward the entrance of the box, and thus make their way along the new passage and reach the food. For the next few tests they usually entered the blind alley, but less frequently, and they remained for shorter periods (stages 2-4). Later they merely entered (stage 5); and still later they passed very near the opening without entering, or only paused a moment before it (stage 6); and finally they passed it without the slightest hesitation, walking briskly, but with well-directed movements, midway between the partitions (stages 7-8). The act of turning seemed to be an especially important factor in this habit. We notice that it was a turn to the right (most probably accidental) which first enabled the animals to get beyond the opening of the blind alley; that this same act was repeated in each successive trial until, by the gradual shortening of the loop forming the path taken by the animals in passing into, and from, the labyrinth it was finally reduced to a mere pause (stage 6); and that this later disappeared entirely, leaving only the left turn, which instead was now conditioned by the visual data at that part of the labyrinth and carried the animal past the entrance of the blind alley.
The animals did not come in contact with the second partition until they had almost learned to pass the opening of the blind alley (see stage 6). This was probably because the turn to the left which was made on approaching _x_ was associated with visual data derived from points farther along the course (_y_), and when the animals reached _z_, compartment 2, these same data were received and were sufficient to occasion the turn to the left there also, thus bringing the birds against the partition. The adjustment was made principally on the basis of new sense-data arising from running against the wire, looking at it more closely, etc. For a few trials the birds made the turn at _x_ too quickly, and thus failed to reach the third compartment. One of my most intelligent subjects made this mistake in the third test, and again in the sixth and seventh, and retained the act almost unchanged through the tenth, eleventh, twelfth, thirteenth, fourteenth, sixteenth, seventeenth, twentieth, and twenty-first tests, so strong was the tendency to continue a movement once begun, though it was really disadvantageous.[200]
After reaching the food and satisfying their hunger, the animals often returned to the maze passages, seeking an exit; but they never "explored" passages or showed other evidence of "free curiosity" and "desire to know all their new surroundings," as Small reports concerning rats.[201]
B. _Habits in Labyrinth M_
Five of the animals previously used were next tested twice daily, forenoon and afternoon, for five days, in a larger, more complicated maze. It had two blind alleys, and the food-box was near the centre (see Fig. 3). The animals' general behavior was similar to that before observed. The periods are given in Table II.
TABLE II. TIME REQUIRED TO REACH FOOD IN LABYRINTH M
_Animals_ _Trials_, A B C E F _Average_ 2 daily. ' " ' " ' " ' " ' " ' " (1) 16:25 2:55 6:33 3:26 4:11 6:42 (2) :55 4:10 2:24 3:36 :23 2:18 (3) 1:12 :55 8:27 9:06 2:07 4:21 (4) :48 :44 2:31 :34 1:04 1:08 (5) :27 :16 :14 :16 :14 :17 (6) :18 :32 :25 :15 :27 :23 (7) :14 :11 :31 :44 :30 :26 (8) :12 :16 :57 :16 :48 :30 (9) :12 :18 :23 :16 :16 :17 (10) :10 :19 :16 :15 :28 :18
Although this maze was much more difficult, it will be seen that the animals learned the route to the food far more readily than before. The first period in this series was only about one fourth as long as the first period in the other, and the course was mastered sooner (by the fifth trial instead of by the ninth). There was less pressing against the wire than before, and unsuccessful movements were sooner discontinued. This improvement was probably due entirely to experience gained in dealing with the first maze. Thorndike speaks of the gradually increasing ability of animals to deal with successive contrivances.[202] The average results given in Tables I and II are plotted in Fig. 4, next page.
C. _Habits in Labyrinth H_
Since hearing is an important sense in pigeons, we should expect them to be capable of useful acoustical associations. Several things occurred in the course of the two preceding experiments which seemed to indicate that this is true; for example, although I could move about, rather noisily, in the darkened room, without apparently disturbing any of the birds, some few showed signs of fright (moving about restlessly) on hearing the low, grating noises made by lifting the hanging door of the cage, sounds which had always preceded the handling of the subjects before experimentation, and which had probably become signs to them of being taken.
To investigate this kind of association I constructed a labyrinth (see Fig. 5) in connection with which sounds could be utilized as one form of sense-data. The passages were so arranged that along the route leading to the food there were three blind alleys, which the animals would surely enter before mastering the course. In another part of the room were placed, very close to each other, two electric gongs of the same size, but of different material. One was of metal and gave a clear ringing sound; the other was of wood and gave a low rattling noise.
When an animal was learning the route (as in the other two mazes) I sounded the gongs, the metallic, as the bird approached and entered the blind alleys, by openings _M_, _O_, and _R_, and the wooden, as it emerged from them and proceeded along the proper course, and occasionally after it had reached the food. The ringing sound was also given after the animal passed _P_ and was approaching _Q_. When the new route was fairly well learned, I changed the order of the sound stimuli, ringing one gong at the places where the other had previously been sounded, and compared the records thus obtained with those obtained when the sounds were given in the original order. As an animal is liable to become confused by the sounds, or else quickly accustomed to them, I thought it best to give only a few trials, one trial with the usual order of sound stimulations, the next immediately following with the reversed order, and so on till four pairs of records had been secured, the series of trials being completed in a single day. Four animals were thus tested. The periods of the various trials are shown in Table III.
TABLE III. SOUND ASSOCIATION, LABYRINTH H
_Time required to reach food under different sound conditions_
I _Order of gongs the same as when_ _course was being learned._
_Animals_ _Trials_ A B E G " " " " (1) 13 19 24 17 (2) 16 12 13 16 (3) 10 16 20 14 (4) 12 19 10 12
Total, 51 66 67 59 " 243
II _Order of gongs reversed._
_Animals_ _Trials_ A B E G " " " " (1) 14 16 18 27 (2) 37 17 16 27 (3) 14 19 26 11 (4) 27 22 21 14
Total, 92 74 81 79 " 326
In the case of thirteen of the sixteen tests given with reversed acoustical conditions (see column II) the periods were longer than the corresponding ones given alternately with them for comparison, and there was an average time-lengthening of 5.2 seconds per trial, or 34.2%. The following is a short description of the animals' reactions to the changed conditions. It corresponds to the time-values expressed in column II of the table.
Bird A: test 1, animal undisturbed; test 2, drew back from _S_, turned to the left and went toward _R_, but later returned and passed _S_ without pausing; test 3, paused at _O_ for a short interval, but did not enter the blind alley; test 4, paused at _O_ again, later drew back from _S_, turned to the left and entered blind alley 3; it soon escaped, and this time passed _S_ without being disturbed, although it paused at _T_ and _U_.
Bird B: tests 1 and 2, animal apparently undisturbed; test 3, a few slight pauses at openings; test 4, drew back from _S_, entered blind alley 3, but soon escaped and passed _S_ without hesitation.
Bird E: test 1, undisturbed; tests 2 and 4, paused at openings; test 3, turned back from _S_, entered blind alley 3, and paused at several places later when passing toward F.
Bird G: test 1, many pauses; test 2, turned from _S_ and entered blind alley 3; test 3, undisturbed; test 4, drew back from _S_, went toward _R_, but did not enter the blind alley.
As the animals gave little attention to the wooden gong, but were always sensitive to the metallic one, their observed movements probably must be accounted for chiefly on the basis of certain visual and organic sense-data _now with_, and _now without_, the ringing sound. The data governing the start (as already noticed) were probably sufficient for the avoidance of the first blind alley when the gongs were reversed. In case of the other two, however, the birds had come to depend upon acoustical data, and when these were lacking as they approached the openings _O_ and _Q_, the left turn could not readily be initiated, hence certain hesitations and misdirections of movement frequently occurred. Experience with the blind alley in the first experiment assisted the animals in dealing with the second blind alley here, but mistakes were made. Visual data usually were sufficient to produce the proper turn at _Q_, but when the ringing sound was given just afterwards, it sometimes occasioned the left turn, thus bringing the animals toward the opening of the blind alley. While the tests given were not such as would indicate how far pigeons can discriminate sounds, they certainly show that these birds are capable of useful sound associations, although visual ones are evidently of greater importance to them.
D. _Habits in Labyrinth O_
I next made tests in which tactual and electrical sense-data could also be utilized. In one of the passages of a simple labyrinth was placed a board 8 in. square and 3/4 in. thick, over which were stretched copper wires which formed a series of interrupted electrical circuits. By closing a key a bird could be stimulated whenever it stepped upon the wire surface. A second key was connected with a metallic gong. When an animal on its way through the maze first stepped upon the wire surface, electrical and acoustical stimuli were given; later it was allowed to walk across the board without being thus stimulated; afterward acoustical stimuli were given it at various parts of the maze.
Eight animals were used. All were found quite sensitive to the electrical shocks, and when next tested they avoided the board, especially if the gong sounded as they approached. Some would show signs of uneasiness anywhere in the maze on hearing the gong. When the board was so placed that they had to pass over it in reaching the food, _when once on it_ they moved very leisurely, often lingering; and if they stepped upon the wire surface in the darkened maze, they showed no evidence of being frightened. Evidently no association had been formed between the peculiar tactual stimulus of touching the wires and the electrical shocks which had at first been given. But the tactual stimulus may have been below the threshold. Yerkes[203] saw evidence of association of this kind in the frog; this animal, however, is probably much more sensitive to tactual stimulation received from surfaces over which it passes than is the pigeon.
The results of these four experiments indicate that the pigeon easily acquires complicated labyrinth habits; that these remain fixed for some weeks at least; that acoustical, visual, and certain organic data are the most important sensory factors; and that the process of learning is one of "trial and error," in which the animal comes to form such a close connection between the sense-data of the interior of the box and those other sense-data arising from movements involved in reaching the food, that when the box impressions are again encountered the other sense-data are revived and readily condition the proper movements. How much memory of eating was involved in these tests cannot be told; but it was certainly not an essential part of the mental act.[204] Proper guidance throughout the course was the main thing, and this was determined by definite sense-data. That recognition, discrimination, and perhaps choice were to some extent present seems likely from the animal's hesitating movements at certain critical points. Thus it is highly probable that when the bird approached a blind alley which it had always entered before (see Fig. 2, stage 6), two alternatives were recognized, to enter, as before, or not to do so, as was usual thereafter, and that the pause had for its mental correlate a state closely bordering upon what in us would be deliberation.
2. _Release experiments._ Under this heading are included certain cage experiments in which some act, such as touching a lever, pecking, or stepping upon a platform, resulted in the opening of the door, and thus enabled the animal to escape and secure the food lying in view without. The animal was admitted to the cage through an entrance compartment as in the case of the maze trials. Before being tested it was allowed to become familiar with the cage and to reach the food directly by passing out through the open door. When first in the cage the animals did not seem to notice the release apparatus, and hence they probably did not begin learning the method of escape until later when they entered the cage and found the door closed, and the ordinary exit thus obstructed.
A. _Latch Tests_
The cage here employed was an 18-inch cubical box. The top was of chicken wire and the bottom and three sides of heavy boards; the fourth side was formed by narrow vertical bars and a wire door which opened inwardly and was held by a latch working on the outer surface of the bars. At first a long wooden latch was used, which the animals raised when reaching out for food. As this seemed an unnatural act, downward pressure was substituted by attaching to the latch, now made smaller and of brass, a string which ran over a pulley above the door and down into the cage. As nooses did not seem adapted to the birds, the end of the string was attached to a wooden lever which worked on the inner surface of the bars, about three inches from the floor. Eight animals were tested four times daily (twice in the forenoon and twice in the afternoon) for ten days. The time required to escape and the animals' behavior were recorded as in the case of the labyrinth tests.
When they first entered the box (singly as in the other experiments) and found the usual exit closed they made various attempts to push through between the bars, springing and often flying about with great force and persistency. In course of their random movements they touched the bar and opened the door and thus escaped. Later the unnecessary movements were mostly dropped and the necessary ones became highly specialized. The first association was established between the box impressions received on entering and the movements involved in approaching the front of the box and depressing the lever; later a connection was formed between the sensations of touching the lever, of hearing the sound of the opening door, of feeling the jar, etc., and the movements of turning away from the lever and passing out. The sight of the opening door seemed to be of less service to the birds than the sound and jar. Each animal soon came to touch the bar at the point of least resistance, and usually with considerable precision. The time required by the several birds is shown in Table IV, next page. The daily average results are plotted in Fig. 6, above.
TABLE IV. TIME REQUIRED TO ESCAPE FROM CAGE BY USING LATCH
_Animals_ _Trials,_ _Daily_ _4 daily._ A B C E F G H I _Av._ _Average_ ' " ' " ' " ' " ' " ' " ' " ' " ' " ' " (1) :03 :06 3:20 :08 :03 1:10 4:30 :23 1:13 (2) :05 1:10 :59 1:50 2:00 :10 2:46 1:00 1:00 (3) 5:28 :29 1:04 :21 :29 :52 2:33 4:05 1:55 (4) :31 1:45 3:52 :14 :06 :23 2:40 2:30 1:30 (1:25) (5) :15 :10 2:25 :03 :10 :07 :31 :50 :34 (6) :17 2:00 5:03 :03 :05 :15 :39 :10 1:04 (7) :08 :20 :36 :31 :03 :11 :30 :46 :23 (8) :03 :54 :47 :28 :03 :55 :06 :47 :30 (:38) (9) 1:12 :34 :39 :17 :03 :04 :21 :20 :26 (10) :02 :19 :28 :07 :01 :03 :20 :47 :16 (11) :02 :51 :09 :14 :03 :02 1:46 :47 :29 (12) :02 :15 :24 :12 :02 :02 1:17 :27 :20 (:23) (13) :03 :19 :22 :07 :06 :04 :48 :11 :15 (14) :02 :15 :22 :09 :02 :02 :20 :19 :11 (15) :08 :06 :12 :05 :02 :02 :03 :06 :06 (16) :03 :18 :44 :10 :02 :03 :02 :21 :13 (:11) (17) :02 :17 :41 :03 :07 :07 :11 :06 :12 (18) :02 :42 :26 :05 :01 :03 :31 :15 :16 (19) :04 :13 :48 :04 :01 :02 :15 :14 :13 (20) :04 :32 :35 :04 :01 :02 :08 :22 :15 (:14) (21) :03 :13 :10 :13 :09 :01 1:10 :16 :17 (22) :03 :05 :10 :11 :03 :02 :39 :26 :12 (23) :02 :07 :17 :05 :03 :15 :20 :26 :12 (24) :02 :14 :04 :02 :01 :02 :09 1:03 :12 (:12) (25) :01 :03 :05 :04 :01 :02 :31 :24 :09 (26) :02 :04 :08 :01 :01 :05 1:34 :33 :19 (27) :02 :03 :03 :03 :10 :05 :15 :39 :10 (28) :02 :04 :03 :01 :06 :05 :23 :51 :12 (:12) (29) :02 :04 :10 :03 :02 :06 :23 :21 :09 (30) :01 :03 :03 :02 :11 :02 :09 1:08 :12 (31) :21 :03 :11 :03 :01 :03 :28 :11 :10 (32) :03 :02 :04 :02 :01 :03 :11 :42 :09 (:10) (33) :02 :02 :03 :10 :01 :03 :18 :17 :07 (34) :02 :02 :03 :02 :01 :03 :11 :11 :04 (35) :01 :02 :03 :02 :01 :02 :18 :09 :05 (36) :01 :03 :03 :03 :03 :02 :04 :10 :04 (:05) (37) :01 :02 :07 :02 :04 :01 :11 :09 :05 (38) :01 :02 :02 :02 :02 :01 :08 :03 :03 (39) :02 :04 :11 :01 :02 :02 :14 :08 :06 (40) :01 :02 :03 :01 :01 :03 :10 :03 :03 (:04)
The periods here were similar to those given in the maze tests--the time was long at first, then it shortened very rapidly for a few trials, then more slowly but still constantly, until the act became thoroughly familiar. The process was one of "trial and error" throughout. As before, various lapses occurred, even although the animals were as persistent as usual in their efforts to escape. When the lever was moved to the side or back of the box, none of the animals could escape. In general, pigeons show less ingenuity in dealing with latches than do sparrows, according to Porter's[205] observations, although in some other tests they are equally apt.
B. _Pecking Tests_
The preceding series of trials proved the animals' ability to utilize certain touching or clawing movements, at first accidental, in making an escape, and showed that these could become highly specialized. Desiring to carry out similar tests in the case of pecking movements, which are quite as natural to pigeons, I arranged a contrivance by means of which the act of pecking at corn-grains fastened to a small piece of cardboard (placed just outside the cage, but within easy reach through an opening in the wire) would open the cage-door by making a delicate electrical contact. Four animals were tested.
On entering the cage they endeavored to escape as before; failing in this they began pecking about until they found the corn-grains and made the contact which opened the door and allowed them to escape to the food without. Three of the animals made their escape in this way several times; but the habit seemed to be one that could not be readily learned, as the successive periods showed little shortening.
Thinking that the pecking of things at a definite place perhaps complicated the matter, I removed the electrical apparatus and arranged to open the door myself by pulling a string whenever the pigeon pecked anywhere upon entering the box. Preliminary experiments with Bird J indicated some ability to profit by this kind of experience. As the act of pecking could be used to advantage in a series of imitation trials, this animal only was allowed to learn to escape by actually pecking; the others were reserved for the imitation tests next to be reported.
C. _Imitation Tests_
In the experiments already reported the animals were used individually and usually out of sight of the others, although in the same room and within hearing of them. When efforts were made in some of the experiments to test the animals in a separate room, signs of fear and discontent were often noticed, and it was necessary to return to the first room to continue the tests. Some instances were noticed in which a pigeon would do what it saw another doing. For example, one of my subjects would not eat one day, being ill apparently; but when I put two others into the compartment with it, and they began eating the food lying about, it also began pecking. Its act could not have been due to its only then happening to see the corn, for it had before looked toward the food when this was thrown to it.
Desiring to test, under definite conditions, the imitative ability of these animals, I arranged trials in which birds were allowed to see a useful, but simple act performed by another bird, and then were given an opportunity to execute the act themselves. Using the animal which I had trained for the purpose, I allowed its series of acts (entrance to box, pecking, release, and food-eating without) to be observed by another animal, confined in a small wire compartment (similar to the entrance compartment before used) attached to the side of the large cage. Care was taken to see that the confined bird was observing, or at least was looking toward the acting one; in case of doubt, the trial was repeated. Later the trained animal was replaced by the observing one, and the latter's reaction was noted. Five animals, in all, were tested, and each was given two opportunities to escape after having seen the trained animal perform the act ten successive times. None of them, however, showed any signs of trying to escape by repeating the movements so often performed by the bird familiar with the act, but each rushed against the sides of the cage and tried to push through at various places, just as the trained bird had done when first learning the habit.
As the act, or series of acts, was rather too complex to be easily observed and utilized by the other pigeons, I arranged two much simpler tests. In one case the leading bird was taught to open the cage-door by stepping upon a platform (the lowering of which made an electrical contact); in the other, to avoid a blind alley, enter a short passage, and ascend a wooden plane (inclined at an angle of thirty degrees) which led into another box containing food. In these tests it was more difficult for the series of acts to be viewed, but the animals, singly as before, were placed at a point of vantage and apparently saw the movements of the other animals.
Of the five birds tested in the platform experiment, four utterly failed to escape in the two trials given. The fifth, in its second test, went to the platform promptly and thus made its escape, but the success may have been accidental, or due to the animal's experience of seeing and approaching the platform in its first test. In the labyrinth experiment only one bird (second test) avoided the blind alley and went directly up the inclined plane to the food; this success was probably due to experience in the first test. There was certainly no evidence that the animals had grasped the nature of the problem; nothing to indicate that the performance of the trained animal had supplied data for the guidance of future conduct, that is, for the conditioning of the necessary movements, in this case those of pecking, stepping upon a platform, or avoiding a blind alley and ascending an inclined plane.[206]
These results are similar to those which other experimenters have secured in the case of chicks, cats, dogs, monkeys,[207] and also rats.[208] Although the method I employed is doubtless open to the criticism of being artificial,[209] some value at least should be attached to the results; if so it would seem probable that imitation in pigeons is not above the "instinctive" stage, and that learning depends entirely upon first hand experience, upon really doing the thing, and not upon merely seeing it done.
3. _Position, Color and Form Tests._ The apparatus used in these experiments consisted of small boxes, six inches in height, and open at the top. Sometimes they were exactly similar, and sometimes they differed in color or in form. They were moveably attached, six inches apart, to a board which was placed in a large wire-covered box, having an entrance compartment as in the case of the mazes and cages. Food was placed in one of the small boxes, and the pigeons were allowed to find it twice; later each bird was tested as to its ability to return to the food by depending upon the position of the box in the group, or upon its color or its form. Tests were given in series of six, and the box which was first approached was recorded as the animal's choice for that test. If it made a wrong selection, it was allowed to look about until it found the box containing the food, but in no case was it permitted to satisfy its hunger until the last test of the series. The animal apparently did not see the food until it approached the box, and subsequent tests demonstrated that it was not guided by odor.
A. _Position Tests_
In this series of trials I used at first six, later nine food-boxes, four inches square and covered with dark gray paper. The board to which the several receptacles were fastened was shifted at irregular intervals to various oblique angles; this was done to prevent the animal from being assisted by the position of the food-box in the larger box rather than in the group of similar boxes. After a bird had been tested sufficiently for one position it was then used, for a week or so, in some other experiment, and thus given an opportunity to forget, to some extent at least, the old experience before being taught to find the food in a box placed elsewhere in the group. For the positions 2, 3, and 4, in the group of six similar boxes, eight animals were each given thirty tests in series of six, as stated above. For the positions 5, 6, and 7, in the group of nine similar boxes, the experiments were shortened. Six animals were given twenty-four trials each, two animals for each of the three positions.
The animals quickly learned the position of the food-box and passed to it promptly when released from the entrance compartment. Changing the position of the board to which the food-boxes were attached did not affect the animals' ability to reach the food readily. They usually selected the proper box as before, although frequently they went around the end of the board and approached the food from the opposite side. The general distribution of choices in the case of positions 2, 3, and 4 is given in Table V; the rate of learning, in Table VI.
With a single exception (Bird B, box 3) the box containing the food was far more often chosen than any one of the empty boxes, and usually more often than all of them combined, the average right choices being: position 2, 62%; position 3, 57.7%; position 4, 53.3%. It will be seen that the animals were more successful in finding the food in the second position than in either the third or the fourth, that is, positions nearer the end were more easily located. But what is of greater interest to us is the rate of learning to go to the right box. This is indicated by the increasing number of right choices from series to series. (Table VI.) That the increase was small was due to the fact that the animals learned so quickly in the first series of six tests that little improvement could be made thereafter; what they could learn they acquired early in the experiment. There is some evidence of improvement after the first series in the case of box 4, a more difficult position, and the average for all three boxes shows a slight improvement from series 1 to series 5, although a falling-off is seen in the last series: 26, 27, 27, 31, 28. The same general features appear in the case of the incomplete tests (positions 5, 6, and 7). For each box there were, on the average, 26 right choices in the possible 48. There were more right choices in the case of box 7 than in the case of either box 6 or box 5, box 7 being nearer one end (box 9). There was little evidence of learning after the first series of trials.
TABLE V. ASSOCIATION OF POSITION: GENERAL DISTRIBUTION OF CHOICES
_Choices of boxes 1 to 6 when food was placed in boxes 2, 3, and 4_
_Food in box 2_ _Food in box 3_ _Food in box 4_ _Boxes_ _Boxes_ _Boxes_ _Animals_ 1, 2, 3, 4, 5, 6. 1, 2, 3, 4, 5, 6. 1, 2, 3, 4, 5, 6. (B) 1 18 4 6 1 0 1 1 8 7 8 5 0 0 2 21 4 3 (C) 2 20 6 1 1 0 0 9 19 2 0 0 0 7 2 15 6 0 (E) 4 18 2 3 2 1 0 6 18 3 3 0 2 6 2 15 3 2 (F) 5 20 1 2 2 0 1 6 18 3 2 0 0 2 5 14 8 1 (G) 0 18 5 2 2 0 0 3 13 5 7 2 0 0 3 17 9 1 (H) 0 22 4 3 1 0 1 0 18 4 6 1 0 4 8 15 3 0 (I) 4 18 3 1 3 1 0 1 23 6 0 0 0 6 7 15 2 0 (J) 1 17 7 5 0 0 3 0 21 3 2 1 1 4 3 16 6 0
Total, 17 151 32 26 12 2 6 26 138 33 28 9 3 29 32 128 41 7
TABLE VI. ASSOCIATION OF POSITION: DISTRIBUTION OF RIGHT CHOICES
_Choices from series 1 to series 5 in the case of boxes 2, 3, and 4_
_Box 2_ _Box 3_ _Box 4_ _Series_ _Series_ _Series_ _Animals_ 1, 2, 3, 4, 5. 1, 2, 3, 4, 5. 1, 2, 3, 4, 5. (B) 4 4 5 2 3 2 2 1 1 2 4 4 4 5 4 (C) 5 4 2 5 4 4 4 4 4 3 3 3 2 2 5 (E) 3 4 4 3 4 4 4 2 5 3 3 2 2 4 4 (F) 5 4 3 5 3 5 3 3 4 3 0 2 4 4 4 (G) 3 4 4 3 4 2 2 4 2 3 3 3 2 4 5 (H) 4 4 4 5 4 4 3 4 5 2 3 3 4 3 2 (I) 1 4 3 5 5 4 4 5 6 4 2 1 3 4 5 (J) 4 5 4 3 1 3 4 6 4 4 3 3 3 4 3
Total, 29 33 29 31 29 28 26 29 31 24 21 21 24 30 32 Average for the three boxes, 26, 27, 27, 31, 28.
The method of learning in these position tests was the same as that noticed in previous experiments, namely, building upon chance successes. When first admitted to the large box containing the row of small ones at the farther end, the animal accidentally found the receptacle containing the food, and later associated the movements involved in reaching that position with various sense-impressions of the box, especially those experienced upon entering--certain tactual impressions of the small entrance compartment, sound of the lifting door and sight given of the interior of the large box.
While the results clearly indicate that pigeons readily learn the position of objects, nothing is proved as to "counting." Some experimenters speak of similar trials as "number-tests," just as they do of "form-tests," but this is probably going too far. To investigate counting in animals, experiments should be arranged which minimize spatial responses. These tests certainly show that pigeons can discriminate positions readily, especially toward the ends of the group, but little more is certainly indicated. Porter[210] says: "If we do not find in birds the power to count, we have in their nice sense for the location of a member of a series ... something of that preliminary number-sense which Ribot describes as belonging to children and savages."
B. _Color Tests_
To investigate the animals' ability to utilize colors[211] in finding their food, I employed the same apparatus as before, except that six boxes were used throughout and each was covered with paper of a different color: red, yellow, green, blue (Bradley's standards, except red, _RO_ being substituted), gray, and black. The boxes covered with black and gray paper were employed merely to complete the group of six. The same method as before was employed, except that the board to which the boxes were attached was left stationary at the end of the large box, and also that the position of all six boxes was changed irregularly for each test.
The general behavior of the animals at the beginning of these tests was quite similar to that shown in the preceding experiment; but it was soon evident that colors occasioned them far more difficulty than positions. The general distribution of choices is given in Table VII. It will be seen that the proper box was usually chosen more often than any one of the empty ones, but never oftener than the other five combined, as occurred in the position tests; also that in the case of each color there were instances in which another color was as often, or more often selected. Yet it is clear that colors may serve as valuable sense-data for these animals. In the first series of six tests (see Table VIII) there were few right choices or none, but in each succeeding series the number increased. The learning process was evidently of the same type as before observed (selection, in this case gradual, of chance but useful movements), and involved visual data largely.
TABLE VII. COLOR ASSOCIATION. GENERAL DISTRIBUTION OF CHOICES
_Choices of all 6 boxes when food was placed in red, yellow, green, or blue boxes_
_Food in Red Box_ _Food in Yellow Box_ _Animals_ R, Y, G, B, B'k. G'y. R, Y, G, B, B'k, G'y. (B) 12 6 7 3 2 0 2 12 6 7 0 3 (C) 15 8 1 4 2 0 3 12 1 6 3 5 (E) 11 8 5 3 3 0 3 10 5 3 5 4 (F) 7 5 9 6 2 1 6 6 5 6 3 4 (G) 9 1 7 5 3 5 5 11 6 3 2 3 (H) 13 3 5 3 3 3 5 9 6 3 3 4 (I) 11 5 2 4 6 2 4 10 5 4 3 4 (J) 10 0 6 8 4 2 5 10 3 3 5 4
Total, 88 36 42 36 25 13 33 80 37 35 24 31
_Food in Green Box_ _Food in Blue Box_ _Animals_ R, Y, G, B, B'k, G'y. R, Y, G, B, B'k, G'y. (B) 4 5 12 4 5 0 1 3 5 10 6 5 (C) 3 4 14 5 1 3 3 1 2 13 2 9 (E) 1 9 7 11 0 2 3 5 5 10 3 4 (F) 0 8 9 6 0 7 0 3 6 11 5 5 (G) 2 5 16 2 4 1 5 5 4 5 4 7 (H) 1 3 15 5 6 0 7 5 5 6 4 3 (I) 0 4 15 6 2 3 5 5 3 9 5 3 (J) 4 1 12 9 1 3 6 4 4 7 5 4
Total, 15 39 100 48 19 19 30 31 34 71 34 40
TABLE VIII. COLOR ASSOCIATION. DISTRIBUTION OF RIGHT CHOICES
_Choices from series 1 to series 5 in the case of red, yellow, green, and blue boxes_
_Red Box_ _Yellow Box_ _Green Box_ _Animals_ 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, (B) 0 1 2 4 5 1 2 3 2 4 1 2 2 4 3 (C) 2 2 4 3 4 1 2 3 3 3 3 2 3 4 2 (E) 2 1 2 3 3 1 0 3 2 4 0 1 1 1 4 (F) 0 1 1 2 3 0 2 2 1 1 0 1 2 3 3 (G) 0 2 3 2 2 2 2 1 3 3 2 4 3 3 4 (H) 1 1 3 4 4 0 2 2 2 3 2 3 4 3 3 (I) 1 2 3 3 2 1 2 2 3 2 1 3 3 3 5 (J) 1 2 2 2 3 1 2 1 2 4 1 1 3 3 4
Total, 7 12 20 23 26 7 14 17 18 24 10 17 21 24 28
_Blue Box_ 1, 2, 3, 4, 5, 1 3 1 2 3 3 2 2 3 3 0 1 3 2 4 1 1 2 4 3 1 1 0 0 3 0 1 2 2 1 0 2 2 3 2 1 2 1 1 2
7 13 13 17 21
There is no evidence that the color-preference of the animals assisted them in choosing correctly, in fact, they were rather less successful in dealing with those colors for which they had previously shown decided preference,[212] since the whole number of right choices was less in the case of the green and blue boxes (85) than in the case of the red and yellow ones (92), and since there was a relative diminution in the rate of learning toward the last in case of the former boxes.[213]
To test the animals' ability to discriminate shades of colors in finding their food, two birds were used, with four boxes, each covered with a different shade of red paper, and two with the boxes covered with green paper. The brightness of the different shades was not measured, but to the eye it seemed to be equal in each of the cases. The food was placed in the box having the most nearly saturated color, and twenty-four trials in series of six, as before, were given each bird. The results were quite similar to those secured with different colors. With the red shades there were twenty-two choices of the best saturated shade to eight, ten, and eight, respectively, of the other three; and with green, twenty-one to nine, ten, and eight. The 43 correct choices were distributed from series 1 to series 4 as follows: 7, 11, 12, and 13, which shows learning as before. The relatively large number of right choices was probably due, partially to the fact that fewer alternative choices were possible since only four boxes were used, instead of six, and partially to the fact that the box containing the food may have been slightly brighter than the others.
Throughout these trials the position-element was a decidedly disturbing factor. When the animals were first learning to choose a box of a definite color, some would show a marked tendency to approach a receptacle occupying a certain position, and would persist in this from series to series. Others at first showed no special preference for certain positions, but, after happening to make a correct choice, they would return to that same place the next time, and thus miss the right box which had been changed for the new test.
C. _Form Tests._
In this experiment the six food-boxes were each of different form: triangular, square, oblong, hexagonal, circular, and elliptical. They were of the same capacity, and were covered with light-brown paper. As in the preceding experiment, the birds were tested for only four of the boxes, and were given thirty trials each. Six animals were used, and as they were not the same as those previously employed, the square box (which had always been used before) had no advantage over the others in attracting the birds at the beginning of the trials. The tests were given as in the preceding experiment, except that it did not seem necessary to change the position of each of the six forms before giving each test; it was thought sufficient to move the food-box, and, if a wrong choice had been made in the preceding test, also the box wrongly chosen. The results are shown in Tables IX and X.
TABLE IX. FORM ASSOCIATION. GENERAL DISTRIBUTION OF CHOICES
_Choices of all 6 boxes when food was placed in Tri., Sq., Hex., or Cyl. boxes_
_Food in Tri._ _Food in Sq._ _Animals_ Tri. Sq. Ob. Hx. Cyl. El. Tri. Sq. Ob. Hx. Cyl. El. (U) 8 6 5 5 2 4 5 9 6 1 6 3 (V) 9 2 3 6 7 3 5 8 5 2 5 5 (W) 8 7 3 4 5 3 5 8 5 3 3 6 (X) 11 5 2 5 3 4 5 8 3 6 3 5 (Y) 11 4 5 4 2 4 4 9 5 6 3 3 (Z) 8 3 7 4 4 4 6 11 7 3 1 2
Total, 55 27 25 28 23 22 30 53 31 21 21 24
_Food in Hex._ _Food in Cyl._ _Animals_ Tri. Sq. Ob. Hx. Cyl. El. Tri. Sq. Ob. Hx. Cyl. El. (U) 5 5 3 11 3 3 6 5 3 5 8 3 (V) 4 4 5 8 5 4 6 6 3 4 7 4 (W) 3 5 3 10 7 2 4 3 4 3 10 6 (X) 4 5 4 7 6 4 2 5 4 4 9 6 (Y) 3 4 2 8 6 7 3 2 5 6 9 5 (Z) 5 4 2 11 3 5 3 5 4 4 9 5
Total, 24 27 19 55 30 25 24 26 23 26 52 29
TABLE X. FORM ASSOCIATION. DISTRIBUTION OF RIGHT CHOICES
_Choices from series 1 to 5 in the case of Tri., Sq., Hex., and Cyl. boxes_
_Food in Tri._ _Food in Sq._ _Food in Hex._ _Food in Cyl._ _Animals_ 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, (U) 2 0 2 1 3 1 2 2 2 2 2 1 2 3 3 1 1 2 1 3 (V) 1 1 2 3 2 2 1 1 2 2 0 1 2 3 2 1 2 2 1 1 (W) 1 2 1 2 2 2 1 2 1 2 1 2 2 2 3 1 2 2 3 2 (X) 1 2 3 3 2 0 2 2 3 1 1 2 2 1 1 1 1 2 3 2 (Y) 1 2 3 2 3 2 2 2 3 2 1 1 2 1 3 0 2 2 2 3 (Z) 1 2 2 2 1 0 2 3 3 2 1 2 2 4 2 1 2 3 1 2
Total, 7 9 13 13 13 7 10 12 13 11 6 9 12 14 14 5 10 13 11 13
It will be seen that each animal chose the right box oftener than any other one box, but not oftener than all of them; also that there was a small increase in the number of right choices from series to series. No one of the four forms seemed better discriminated than the others if we may judge from the practical equality of right choices made in each case (55, 53, 55, 52) or from the similar increase in number of right choices from series to series; the hexagonal and cylindrical boxes received fewer choices in the first series than did the triangular and square, but this was exactly counterbalanced in the last series. The triangular box was more often confused with hexagonal and square, and the square with triangular and oblong, than with the others. For the hexagonal box the cylindrical was more frequently mistaken than were the other forms, especially the oblong; and with the cylindrical the elliptical was more frequently confused than were the others, especially the oblong. In this series of tests nothing new as regards general behavior or method of learning was observed.
TABLE XI. POSITION, COLOR AND FORM ASSOCIATION
_Total Right Choices_[214] _Right choices from series 1 to series 5_[215] 1 2 3 4 5 _Position_ 57.9% 54.2% 55.6% 56.9% 63.2% 59.0% _Color_ 35.3% 16.2% 29.7% 37.0% 42.7% 51.6% _Form_ 29.8% 17.4% 26.4% 34.7% 35.3% 35.3%
If we compare the results obtained in these three experiments (see Table XI and Fig. 7), we shall see that the pigeons were governed much more by the position of the food-box than by either its color or its form, and that color was better associated than form. Position was a most important factor throughout, as was observed also by Porter[216] in the case of the English sparrow. Porter[217] also found that his sparrows could associate color better than form. In the position-tests the pigeons showed very little improvement from series to series (see table); almost all that the animals could learn was acquired at the beginning. The more difficult color- and form-trials, however, showed almost constant improvement, although we should have expected this to be greater in the latter case than it was. When judged entirely by the actual number of right choices in a given kind of tests, some of the birds made a very poor showing; but from the standpoint of increasing number of right choices they appeared in a wholly different light.
Thus, for example, bird F (Table VII) made only 33 right choices in a possible 120, yet their arrangement is significant, being, from series 1 to series 5, respectively, 1, 5, 7, 10, 10. It is probable that there would have been still greater improvement had the tests been continued; perhaps the animal would have become as proficient in finding its food by depending upon the color of the receptacle usually containing it, as by relying upon the position of the box in the group.
V. SUMMARY
1. Respiration in pigeons is sensitive to various stimuli, and since its alterations of rate, amplitude, etc., can be easily recorded pneumo-graphically without frightening the animals, it may well serve as a process through which to study their mental life.
2. By repetition meaningless stimuli, for example, pistol-shots, quickly lose their disturbing influence; whereas the breathing remains sensitive to those of a significant character, such as the noises made by other birds.
3. Reaction to light of moderate intensity consists principally in an immediate quickening, the amount varying with the color; since a direct correspondence was found between color-preference and breathing-rate, it would seem that here agreeable feeling involves increased breathing activity.
4. Visual, acoustical, probably tactual, and certainly organic data, are the principal sensory factors of the associations of pigeons.
5. The animals readily form useful associations by a method of "trial and error," or the selection of successful movements which were at first accidental.
6. Apparently a pigeon does not learn by merely seeing a new act performed by another pigeon; yet there are instances of simple ("instinctive") imitation, and "trial and error" learning is not wholly independent of social conditions, since it proceeds much more satisfactorily if the animal is trained at least within hearing distance of other pigeons.
7. When a habit is being formed, the "period" required for the first test is usually very long, but learning proceeds quite rapidly during the next few trials; later it is more gradual, but it continues till the act becomes thoroughly familiar.
8. Associations are fairly permanent, and some remain practically unaltered for at least six weeks. Modification is easily accomplished, however, on the basis of new experience.
9. Pigeons differ widely both as to the ease with which they acquire associations and also as to their permanence. Difference in activity seems the chief reason for this.
10. While these birds seem mentally inferior to English sparrows and to various mammals which have been tested in a similar manner, they are capable of numerous ready adjustments. They discover circuitous labyrinth passages, they learn to manipulate latch apparatus when adapted to their natural habits and conveniently placed, and they easily reach their food by depending upon the position, color, or form of the box containing it. But the process is apparently simple association throughout. There is no evidence of higher mental activity--no looking the situation over and acting accordingly, no "reasoning" in the proper sense of the word, but only blind movements, some of which are retained and become highly specialized, merely because successful.
FOOTNOTES:
[Footnote 180: D. Ferrier: The Functions of the Brain, p. 111, London, 1886.]
[Footnote 181: A. Hill: Can Birds Smell? Nature, vol. 71, pp. 318, 319, 1905.]
[Footnote 182: W. Mills: The Nature and Development of Animal Intelligence, pp. 248, 250, New York, 1898.]
[Footnote 183: Hachet-Souplet: Examen Psychologique des Animaux, pp. 33-38, Paris, 1900. See also Riverside Natural History, vol. 4, pp. 240, 241, Cambridge, 1888.]
[Footnote 184: Orientation chez le pigeon-voyageur, Revue Scientifique, vol. 13, pp. 352-359, 1900.]
[Footnote 185: Orientation du pigeon-voyageur, Revue Scientifique, vol. 2, pp. 417-420, 453-457. 1904.]
[Footnote 186: Grundlinien zur Erforschung des Helligkeits- und Farbensinnes der Tiere, p. 102, Prague, 1888.]
[Footnote 187: Some Notes on the Psychology of Birds, Seventh Annual Report of the New York Zoölogical Society, p. 154, 1902.]
[Footnote 188: Ueber die Begleiterscheinungen psychischer Vorgänge in Athem und Puls, Philosophische Studien, vol. 18, pp. 7-14, 1901.]
[Footnote 189: Animal Intelligence, pp. 8-12, 31-36, 51-55, New York, 1898.]
[Footnote 190: Nature of Animal Intelligence and Methods of Investigating It, Psychological Review, vol. 10, pp. 262-274, 1897.]
[Footnote 191: An Experimental Study of the Mental Processes of the Rat, American Journal of Psychology, vol. 11, pp. 135-164; vol. 12, pp. 206-210, 1900-1901.]
[Footnote 192: Mental Life of Rhesus Monkeys in Captivity, American Journal of Psychology, vol. 13, pp. 97-148, 180-210, 1902.]
[Footnote 193: A Preliminary Study of the Psychology of the English Sparrow, American Journal of Psychology, vol. 15, pp. 313-346, 1904.]
[Footnote 194: For a more complete report of this special part III, see the writer's paper, Respiration and Emotion in Pigeons, Journal of Comparative Neurology and Psychology, vol. 15, pp. 494-513, 1905.]
[Footnote 195: If shallowing accompanies quickening, the respiratory activity may be no greater than before; but since depth alterations were seldom observed in these trials after the first day of experimentation, the rise in rate may be taken as a fair measure of the influence of the stimulus.]
[Footnote 196: P. Zoneff und E. Meumann: _op. cit._, pp. 57, 58.]
[Footnote 197: R. MacDougall: The Physical Characteristics of Attention, Psychological Review, vol. 3, pp. 162, 176, 177, 1896.]
[Footnote 198: Thorndike: _op. cit._, pp. 13-15.]
[Footnote 199: Small: _op. cit._, vol. 12, pp. 236, 237.]
[Footnote 200: Small (_op. cit._, vol. 11, p. 146) states that in his rats "the persistence of useless motor habits is striking" and "explainable by the supposition that the movements are touched off automatically."]
[Footnote 201: _Op. cit._, vol. 12, p. 214.]
[Footnote 202: _Op. cit._, p. 28.]
[Footnote 203: The Instincts, Habits and Reactions of the Frog, Harvard Psychological Studies, vol. 1, pp. 591-593, 1903.]
[Footnote 204: Small: _op. cit._, vol. 12, pp. 230, 231.]
[Footnote 205: _Op. cit._, pp. 318, 319.]
[Footnote 206: C. L. Morgan: Animal Behaviour, pp. 179-193, London, 1900; Animal Life, and Intelligence, p. 453, Boston, 1891.]
[Footnote 207: Thorndike: _op. cit._, pp. 54, 56, 57, 60, 61; The Mental Life of the Monkeys, Psychological Review, Monograph Supplement, vol. 3, pp. 318, 319, 1901. Kinnaman: _op. cit._, pp. 198-200.]
[Footnote 208: Small: _op. cit._, vol. II, p. 160.]
[Footnote 209: W. Mills: Nature of Animal Intelligence and Methods of Investigating It, Psychological Review, vol. 10, pp. 262-274, 1897.]
[Footnote 210: _Op. cit._, p. 335. See also C. L. Morgan: Introduction to Comparative Psychology, p. 232, London, 1900.]
[Footnote 211: Cornish states (Animals at Work and Play, p. 30) that hunters near the Caspian are able to decoy partridges by use of brilliant colors.]
[Footnote 212: See the writer's paper, Respiration and Emotion in Pigeons, _op. cit._, p. 502.]
[Footnote 213: One of Porter's sparrows was less successful with yellow and red than with blue and green. He says: "This may be partly explained from the fact that she was more afraid of these." _Op. cit._, pp. 338, 339. See also E. L. Thorndike: Instinctive Reactions of Young Chicks, Psychological Review, vol. 6, pp. 283-284, 1899.]
[Footnote 214: Tables V, VII, and IX.]
[Footnote 215: Tables VI, VIII, and X.]
[Footnote 216: _Op. cit._, p. 338.]
[Footnote 217: From the tables (_op. cit._, pp. 330-339) it seems that the right choices for position, color, and form, were respectively, 40%, 58% and 20%. The comparatively small number of correct position choices was probably due to his using ten boxes instead of six, as in the other two series. My results given in Table XI were secured under almost exactly comparable conditions. Compare results of Kinnaman in case of the Rhesus monkey, _op. cit._, pp. 130, 131, 134, 141, and 177.]
REACTIONS OF THE CRAYFISH
BY J. CARLETON BELL
The crayfish has long been the typical Crustacean for anatomical and physiological investigations, but it is only recently that its reactions to sensory stimuli have been made the object of experimental study. The purpose of this paper is to describe the reactions of the animal to certain sensory stimuli under experimental conditions, and to estimate the relative importance of these stimuli in the life of the organism.
I. REACTIONS TO VISUAL STIMULI
Huxley[218] states that crayfish avoid direct sunlight, hiding under stones during the day, and becoming active in the evening. On the other hand, they are attracted like moths to fires lighted on the bank at night, and may be scooped out by hand. Abbott,[219] giving an account of the burrowing crayfish, _Cambarus diogenes_, states that it is very difficult to observe the animals at work, since all their digging is done at night. It would seem from the account of Miss Hoppin, quoted by Garman,[220] that the blind crayfish, _Cambarus pellucidus_, is not altogether insensitive to light, for, reporting on the fauna of the caves of Missouri, she says that the crayfish are all found near the entrance to the cave, where there is considerable light. In the dark recesses there are only little white fishes. Blind fish and crayfish are also taken from the wells in the neighborhood, where the crayfish are found only in wells that are rather shallow and light; the fish, on the other hand, are only obtained from deep, dark wells.
According to the above accounts it would appear that the crayfish is negatively phototactic to direct sunlight or diffuse daylight, but positively phototactic to a light at night, and moreover, that light may influence the behavior of the animal even when the eyes have ceased to function.
The directive influence of light upon the movements of the crayfish has never been experimentally studied to my knowledge. Dearborn[221] thinks that light has no effect upon the animals. Yerkes[222] and Towle[223] have shown that Daphnia move toward the light. Bethe[224] finds that Carcinus is negatively phototactic, and also shows a tendency to hunt out corners. When the eyes are varnished with lampblack, the phototaxis disappears, but the tendency to seek out corners still remains. Bethe says that he has observed the same phenomenon in the crayfish. Keeble and Gamble[225] discovered that _Hippolyte varians_ responds positively to light under all conditions, and Palæmon is just as markedly negative. _Macromysis_, however, reacted now positively now negatively, depending on the background. A black (absorbing) background called forth a positive response, while a white (scattering) background produced a negative reaction. Spaulding,[226] in studying the habits of the Hermit Crab (_Eupagurus_), found that it is strikingly positively phototactic. When animals are placed in an aquarium, one half of which is shaded, none of them are ever noticed inside of the dark line. Herrick[227] notes that lobsters are nocturnal, and avoid the light when placed in a tank, and Bateson[228] says that prawns and shrimps lie hidden during the day, and are active only at night. Parker,[229] in a study of Copepods, finds that the females have a strong positive phototaxis for light of a low intensity, while males show a weak negative phototaxis. To light of over 100-candle power at a distance of 10 cm. or to direct sunlight the female Copepods are negative, while the reaction of the males does not seem to be altered.
In his work on _Carcinus_, Bethe obtained retraction of the eye-stalks by suddenly throwing a strong light on the eye by means of a mirror. "Usually the eyes were quickly drawn in and protruded again, sometimes several times in rapid succession, like a man blinking under a sudden, strong light." When a dark object, the size of the hand, was moved just over the water, the eyes were seldom retracted, but the antennules were usually drawn in. Lemoine[230] observed that in Astacus retraction was due to touch alone, and that no light, however strong, was able to bring about such a reaction. Gulland[231] takes just the opposite view with reference to Astacus, stating that there are no setæ of any sort on the eye-stalk, and therefore it is insensitive to touch, but is withdrawn only because the animal sees the object by which the stimulus is given. If a curved needle is used, and the stimulus is applied from behind, no retraction follows. Dearborn,[232] however, working with Cambarus, agrees with Lemoine in saying, "Withdrawal of the ophthalmites into their sockets occurs only on contact with some hard object,--not from any light-stimulus of an ordinary sort." I may say in passing that in none of the following experiments on Cambarus was there ever a sign of retraction due to stimulation by light, the retraction always taking place in response to a touch-stimulus.
Lyon,[233] in his study of compensatory movements of the eye-stalks, found that when the eyes were painted with lampblack, the crayfish showed a reduction of about 10% in the compensatory movements when rotated in vertical planes, but the compensation remained the same for rotation about the dorsi-ventral axis. On rotation in the dark the compensatory movement of the eyes was found to be from 5° to 8° less than in the light.
EXPERIMENTAL
In the investigations to be described, 58 crayfish of the species _Cambarus affinis_ were made use of, and for identification the animals were marked on the back with white enamel paint, the males receiving the even numbers from 2 to 64, the females the odd numbers from 1 to 51.
1. _Reactions to White Light_
The questions proposed for investigation were, (_a_) How does the crayfish react to diffuse daylight; (_b_) to reflected sunlight; (_c_) to direct sunlight; (_d_) to artificial light of different intensities? (_e_) What is the influence of previous conditions of exposure to light upon the reactions of the animal? (_f_) Do changes of temperature affect the reactions?
A wooden box, 80 cm. long, 25 cm. wide, and 20 cm. high, painted black on the inside, and constructed so as to hold water, was covered with a heavy black cloth to exclude the light from above. The front end of the box was of glass, thus admitting the light from the end. In all the experiments except those with direct sunlight, this glass end was covered with black cardboard in which a hole 10 cm. long and 5 cm. high had been so cut that the light was admitted at the middle of the bottom of the glass. The direct sunlight was admitted through the whole of the glass end. At the rear of the box a piece of black cardboard was so arranged that an aperture was afforded for observing the animals without admitting any appreciable amount of light, and this aperture could be readily closed by a slide when not in use.
The method of experimentation was to place the animal in the box about 20 cm. from the glass end, and observe whether it went toward or away from the source of light. The animals were experimented on in two groups of five each, and one hundred observations were made on the individuals of each group with each intensity of light, that is, twenty observations on each animal. In order to check the influence of the orientation of the animal at the time of exposure to the stimulus, the following four positions for placing the animal were chosen: (1) Head toward the light; (2) Head away from the light; (3) At right angles to the light with right side toward it; (4) At right angles with the left side toward the light. Thus five observations were made on each animal of each group in each position, exposed to each of the different intensities of light.
Seven different intensities of light were employed, and the results have been arranged in eight sets, as follows: I. Diffuse daylight in dry box, _i. e._, the animals were taken out of their ordinary medium, water, and were exposed to the stimulus of diffuse daylight in the air. The reactions under these conditions, however, were so slow and so unsatisfactory that the test was abandoned after the first group, and thus the second group has nothing to show for itself under this head. The remaining seven sets of observations were made on animals placed in 10 cm. of water at 15° C. II. Diffuse daylight. III. Reflected sunlight. The box was placed near a window on a clear day, and the sunlight was thrown in horizontally by means of a mirror. IV. Direct sunlight. On a clear day the box was placed in such a position that the sun shone in directly and illuminated the front half of it. V. 9-candle-power incandescent electric light. This lamp was marked 16 c., but it had been used a great deal, and on being tested with a Lummer-Brodhun photometer showed only 9 c. VI. An incandescent electric light of about 50 c. This lamp was marked 100 c., but had been used considerably and was slightly smoked. Unfortunately it was broken before there was any opportunity to test it. Judging from the fact that another 100 c. lamp of the same manufacture, in slightly better condition, measured 64 c., the estimate of 50 c. seemed a safe one. VII. The incandescent electric light alluded to above, which measured 64 c. VIII. An arc light which varied in intensity from 150 c. to 250 c.
In intensities V and VI the lamp was placed 5 cm. from the glass end of the box to allow the interposition of a heat-screen consisting of an alum solution in a flat glass jar 5 cm. thick. Reckoned in candle-metres, therefore, the intensity of the illumination at the surface of the animal in V was 144 c. m., and that in VI was about 800 c. m. In VII two heat-screens were used, and between these was placed a lens of considerable but not accurately determined curvature, so that it is impossible to express the intensity in candle-metres. In VIII the light was so variable that such an expression would mean nothing.
Unfortunately it was impossible to keep the two groups constant throughout the whole series, owing to the death of two individuals in each group during the experimentation. Group 1 was composed of nos. 1, 3, 4, 8, and 9, of which 1 and 8 were replaced by nos. 13 and 42 respectively. Group 2 was begun with nos. 23, 27, 32, 34, and 38, and the vacancies caused by the death of 23 and 32 were filled by nos. 21 and 36. The following table exhibits the reactions to the different intensities of light, + indicating an orientation toward the source of light, - an orientation away from the light, and ± an indifferent orientation, which usually means no movement at all.
TABLE I. SUMMARY OF REACTIONS TO WHITE LIGHT
Group 1 Group 2 Totals + - ± + - ± + - ± I. 23 48 29 23 48 29 II. 49 47 4 19 81 68 128 4 III. 40 60 30 70 70 130 IV. 47 52 1 36 64 83 116 1 V. 51 49 30 70 81 119 VI. 39 61 39 61 78 122 VII. 28 72 28 71 1 56 143 1 VIII. 35 63 2 37 60 3 72 123 5
312 452 36 219 477 4 = 531 929 40 = 1500
The following table gives the average time required for orientation for each group. The time of each animal in seconds was noted with a stop-watch from the instant the animal was placed in the box until a definite orientation was assumed with reference to the light. If no orientation followed within three minutes, the result was called indifferent.
TABLE II. AVERAGE TIME OF ORIENTATION
Intensities I II III IV V VI VII VIII Ave. Group 1 (144) 52 11 4-1/2 9 8-1/2 11 19 16-1/2 Group 2 9 3 4 4 5 4 5 5
Inspection of these tables shows that when the animals were taken from the water and placed in diffuse daylight in the air (I), their movements were so sluggish that in twenty-nine cases out of one hundred there was no orientation within the three-minute limit. Moreover, in the seventy-one cases where there was definite orientation the average time was over two minutes (144 seconds). While, therefore, the conditions were quite different from the normal environment of the animal, it is interesting to note that of the cases where orientation did take place the negative reactions were more than twice as many as the positive. In II, where the animals were under the same conditions of diffuse daylight but in the water, a wide variation in the reactions of the two groups is noted. In group 1 they are about equally divided between positive and negative, while in group 2 there is the largest proportion of negative reactions in the whole series. It will be observed that the time for group 1 is extremely long compared with the other averages, and this doubtless indicates a general sluggishness and lack of sensitiveness to stimuli in the animals, which might to some extent account for the difference in reaction. If we consider the totals of both groups for each intensity, we are led to conclude that there is no appreciable difference in the reactions of crayfish to diffuse daylight, to sunlight, or to artificial light within the limits here employed. A slight exception to this is found in VII, where the 64 c. lamp with the lens caused a somewhat more uniform negative reaction. The action of direct sunlight in IV is rather remarkable in that with the lowest proportion of negative reactions in the whole series we also observe the shortest time-average, indicating that the animals are the liveliest and most sensitive. This would seem to indicate that while the animals are in general somewhat negatively phototactic to all light-stimuli of moderate intensity the action of direct sunlight tends to reduce the negative phototaxis to a minimum. If we consider the totals of the two groups separately we observe that group 1 has only 57% of negative reactions while group 2 shows 68%. This is rather in accordance with what we would expect from the general time-average, which is over three times as much for group 1 as for group 2. But although we may in a general way connect rapidity of orientation with a large percentage of negative reactions, it will not do to carry it to individual cases, for it was observed that no. 27 showed 83% of its reactions negative, yet its total time-average was 10 sec., the highest in its group.
In general, then, we conclude that the crayfish is negatively phototactic in the proportion of about two to one. This apparently contradicts the statement made by Huxley that crayfish "are attracted like moths to fires lighted on the bank at night." For surely if this were the case some such tendency would have been observed in these experiments. On the other hand, there is no such marked and definite response to light as in the case of Daphnia or Hippolyte or Palæmon or the Hermit Crab. The action of the stimulus is by no means mechanical and constant, but there is wide variation in individuals.
As was mentioned in the description of the method of experimentation, four different positions for placing the animal were chosen with the idea that the initial position of the animal with respect to the light might have some influence on the direction of its movement. To determine what this influence might be, a careful record was kept of the orientation with reference to each one of these positions, and the following table gives a summary of these observations. In the table position I is where the animal is placed with its head toward the light; position II, with head away from the light; position III, at right angles to the light with the right side toward it; position IV, at right angles with left side to light.
TABLE III. INFLUENCE OF POSITION ON LIGHT REACTIONS
Position I Position II Position III Position IV Totals + - ± + - ± + - ± + - ± + - ±
Group 1 85 108 7 61 135 4 74 114 12 92 95 13 312 452 36 Group 2 39 133 3 48 126 1 57 118 75 100 219 477 4
124 241 10 109 261 5 131 232 12 167 195 13 531 929 40
Since the animals have been shown to be somewhat negatively phototactic, we should expect that position II, with the head away from the light, would show the largest number of negative reactions, and this is what we find if we take the sum of both groups. But by the same course of reasoning we should expect position I, with head toward the light, to yield the smallest number of negative reactions, a condition which prevails neither in the sum nor in either of the groups. On the whole we can only say that difference of position seems to have remarkably little influence on the orientation of the animals.
In his work on the eye of the crayfish, Parker[234] called attention to the migration of the pigment in the retinular cells under the influence of light. The question now arose, what influence, if any, does this pigment migration exert upon the reactions of the crayfish to light? The time required for pigment migration in the eye of the crayfish has never been determined to my knowledge, but from the work of Parker[235] on Palæmonetes it was thought that confinement in the dark for about an hour would be sufficient to bring about a retraction of the pigment. Accordingly, group 1 was kept in the dark for one hour, group 2 for one hour and a half, before experimentation. A further test was made to observe the effects of pigment expansion, both groups having been exposed for one hour and a half to the rays of a 32 c. incandescent electric light at a distance of 40 cm. The apparatus used in the reaction-tests was the box described above, with the 64 c. light as a stimulus. As to the method of observation, each group was placed in the centre of the box at right angles to the horizontal rays of light, and the position of each animal was accurately noted at intervals of one minute for one hour. In reporting the results, all the observations of animals in the half of the box nearest the light are denominated positive, those in the half farthest from the light negative. The results are given in Table IV, where line I indicates the reactions after confinement in the dark, line II those after exposure to the light.
TABLE IV. INFLUENCE OF PREVIOUS CONDITIONS UPON REACTIONS TO LIGHT
Group 1 Nos. 13 3 4 9 42 Totals + - + - + - + - + - + - I 54 6 60 5 55 48 12 60 167 133 II 59 1 60 60 9 51 55 5 183 117
Group 2 Nos. 21 27 31 36 38 Totals + - + - + - + - + - + - I 5 55 5 55 7 53 10 50 4 56 31 269 II 38 22 60 13 47 45 15 16 44 116 184
Let it be said at once that these results do not offer an altogether satisfactory basis for an answer to the question proposed above. Some of the animals would take up a position during the first ten minutes and remain in it for the rest of the hour. Whether the position taken was due solely to the light, or was owing to thigmotactic influences, or whether it depended on the way in which the animal was released, are questions which cannot be answered, and for this reason the conclusions to be drawn from the table are tentative. If we examine the table we find that the totals of both groups agree in manifesting a decrease in negative results for line II, after exposure to the light, as compared with line I, after confinement in the dark. This is what we would expect from negatively phototactic animals. When taken from the dark the pigment is retracted, and the sensitive retinal substance is exposed to the direct action of a rather strong light. The negative tendency of the animal we should expect to find accentuated. The decrease in negative reactions is especially marked with group 2, which was shown above to be much the livelier of the two, and all the individuals except no. 27 share in the change. In group 1 the decrease is not so striking, and is observed to be due to two individuals solely. Inexplicable is the preponderance of positive over negative reactions in the results for group 1.
All of the experiments thus far described were carried out in water at approximately 15° C. The question naturally arises, what will be the result of raising or lowering the temperature upon the reactions of the animals to light? Unfortunately the experiments anent this question are fragmentary and incomplete, but the results will be given for what they are worth. The same apparatus and the same intensity of light (64 c.) were used as in the preceding paragraph. The results, presented in Table V, are arranged in three sets, as follows: The line marked I represents the results obtained from group 1 at a temperature of 5° C. The animals were placed in the box one at a time, as in Table I, and their orientation noted. They were set at right angles to the rays of light, five times with the right and five with the left side toward the source of the stimulus. No observations were made upon group 2 at 5° C., and those on group 1 are so few as to have a questionable value. Line II gives the reactions of both groups of animals in water at 25° C., and in this set the animals were placed in all four of the positions indicated for Table III. Line III presents the reactions of the animals in water at 25° C. by the method outlined for Table IV, _i. e._, each group of animals was placed in the centre of the box, and observed at intervals of one minute. To obviate the objection of the animals remaining in one spot, they were reset every ten minutes in the middle of the box, at right angles to the entering rays.
TABLE V. REACTIONS TO LIGHT AT DIFFERENT TEMPERATURES
Group 1 Nos. 13 33 4 42 9 Totals + - + - + - + - + - + - I 7 3 4 6 2 8 2 8 8 2 23 27 II 16 4 14 6 11 9 9 11 13 4(±3) 63 34(±3) III 19 41 13 47 39 21 17 43 27 33 115 185
Group 2 Nos. 21 27 31 36 38 Totals + - + - + - + - + - + - II 12 8 5 15 12 8 15 5 13 7 57 43 III 12 48 12 48 31 29 42 18 44 16 141 159
Judging from lines II and III we may say that there is a tendency toward a decrease of the negative phototaxis with an increase in temperature. It is true that group 1 in line III maintains the average, 62% negative reactions, but the others are much lower than this, line II even going over to positive phototaxis in both groups. In line III the animals of both groups were extremely active during the first ten minutes, rushing about from one end of the box to the other, pushing each other back and forth, and in general exhibiting great restlessness. Some of the animals when first put into the water reacted with a sort of cramp reflex, which was followed in a few seconds by intense activity. After the first ten minutes the animals began to grow more quiet, and in twenty or thirty minutes they had become quite sluggish, scarcely moving out of the position in which they were reset. During the period of restlessness the males showed marked sexual activity, rushing up to the females, pushing them about, seizing them, and trying to turn them over in spite of their vigorous resistance. One of the males, no. 36, did succeed in turning a female on her back twice, although she struggled violently to escape,--a thing which the female never does in the ordinary sexual act. The rise in temperature, therefore, seemed to stimulate the males to sexual activity, but not the females.
2. _Reactions to Colored Light_
No observations have ever been made, so far as I know, on the reactions of the crayfish to colored light. Lyon, in his work on compensatory eye-movements, found that rotation in blue light gave a compensatory movement only slightly less than that in white light, while in red light the compensation was only a little larger than in darkness. In some animals the interposition of an opaque object between the eye and the source of light caused an elevation of the eye 1° or 2° toward the vertical. Red glass acted like an opaque object, blue glass produced no effect, _i. e._, blue light had the same effect as white light. To observe whether the same thing applied to movement reactions was the object of the following experiments.
_a. Reactions to Horizontal Colored Light._ The same apparatus was used as in the previous experiments, viz., the dark box with light from the 64 c. lamp entering horizontally at the end. Across half of this end were placed pieces of colored glass of a saturated blue, green, yellow, and red. The colored light obtained by this means was not spectrally pure, but it was the nearest to it that could be obtained. A more serious objection is that the intensities were not the same, the red and the yellow being very appreciably brighter than the blue and the green. In addition to observations with these colors, a piece of black cardboard was introduced in the same position as the glass, thus cutting off the light from that half of the box. This, to preserve the uniformity of the series, is denominated black. The animals were placed in the centre of the box, on the line separating the white from the colored light, and were observed at intervals of one minute for forty minutes, the position of each animal being accurately noted. At the end of every ten minutes the animals were reset at the centre of the box. The following table gives a summary of the results for each individual. Here again it was impossible to keep the groups constant owing to the death of individuals during the progress of the experiment.
TABLE VI. REACTIONS TO HORIZONTAL COLORED LIGHT
Group 1 Group 2 Animals 13 37 41 42 44 33 4 9 43 46 Sum 21 27 31 36 38 52 Sum Sum Total Blue 12 9 21 30 18 90 23 2 24 13 37 99 189 White 28 31 19 10 22 110 17 38 16 27 3 101 211
Green 15 9 23 36 17 100 12 19 3 28 40 102 202 White 25 31 17 4 23 100 28 21 37 12 98 198
Yellow 20 10 31 28 19 108 17 11 28 37 35 128 236 White 20 30 9 12 21 92 23 29 12 3 5 72 164
Red 26 9 32 20 17 104 2 30 16 29 36 113 217 White 14 31 8 20 23 96 38 10 24 11 4 87 183
Black 24 27 12 27 26 116 15 18 26 25 5 89 205 White 16 13 28 13 14 84 25 22 14 15 35 111 195
In this table the colored lights are arranged in the order of the spectrum from blue to red. On the hypothesis that blue light has practically the same effect upon animal reactions as white light, while red is about the same as darkness, we might expect that the reactions would be about equally divided between the blue and the white, and that there would be a gradually increasing difference in number as we go down the table, reaching the maximum with the last pair, black-white. This, we see, however, is not quite the case. In both groups the white has a slightly larger number of reactions than the blue, while the pair green-white shows numbers more nearly equal. In the sum totals the yellow shows a greater preponderance over the white than any other color, and the black and white are very nearly equal. Group 1, it is true, shows a fairly regular ascending scale in reactions to the colored lights with the exception of the red, and the same might be said of group 2 if it were not for the very low number of reactions to the black and the exceptionally high showing of the yellow. On the whole, however, the differences are so small and the individual variations are so large that we can only conclude that for these conditions colored light has little or no effect on the reactions of the animals.
In the foregoing experiment the light came from a broad spiral coil inside the bulb of the lamp, and the distance from it to the edge of the glass was so small compared with the length of the box that there was no sharp dividing-line between the colored light and the white, but rather a wedge-shaped block of lessening saturation of the color, and this wedge, having the point toward the light, took up the whole of the box at the extreme farther end. Thus the imaginary central line dividing the white light from the colored departed farther and farther from the reality as the rear of the box was approached. To obviate this difficulty and to get a check on the previous work, the following series of experiments was undertaken.
_b. Reactions to Vertical Colored Light._ The same box was used as in the previous experiments, but the end was closed with a black cloth, and an electric light marked 32 c. but measuring only 22 c. was hung exactly over the middle of the box, 40 cm. from the bottom. By means of wires it was arranged that a plate of colored glass could be swung in such a manner that all of one half the box (the whole of one end) was illuminated with the desired color, while the other half was either left white or illuminated with another color. In this way there was a fairly sharp dividing-line between the two colors. The animals were observed at intervals of one minute for 40 minutes, and reset at the middle on the dividing-line every ten minutes as before. Table VII gives the results of the observations.
In this set of experiments it was possible to keep the groups intact except that in group 1 no. 13 had to be replaced by no. 46. If now we conceive the colors arranged in the order of the spectrum with black at one end and white at the other, and consider the black a lower stimulus than the white, we have the ascending series black, red, yellow, green, blue, white. Now since the animals have already been shown to be somewhat negatively phototactic, we should expect them to prefer a color of lower stimulus to one of higher. Turning to the sum totals in the table we find that the first color of each pair (which is always the lower stimulus) has the larger number of reactions in every case but one, the first pair of red-blue. As was stated above, it was impossible to secure colored light of the same intensity by means of the glass at our disposal, and in the present case the red was considerably brighter than the blue. Owing to the fact already mentioned that different intensities of white light seem to have no effect on the reactions it was thought that these differences in the intensities of the colored lights might be overlooked. Since the only thing that could be thought of to account for the anomalous behavior to the red-blue was this difference in intensity, another experiment was undertaken with the same animals under slightly different conditions. A glass aquarium about 40 cm. long by 20 cm. wide was covered with black cardboard and black cloth in such a manner that light could enter only through a space 5 cm. wide at the bottom of each end. Each of these ends was covered, the one with blue, the other with red glass, and 15 cm. from each end was placed an electric light marked 32 c. Later, however, it was found that one of these lamps measured 30 c. and the other 22 c. The red light was found to be much more intense to the eye than the blue, so the former was damped down with tissue paper until the two appeared to have the same intensity. The second pair of red-blue in Table VII gives the results of the observations under these conditions, and these are found to be in harmony with the rest of the table, _i. e._,[236] the color giving the lower stimulus has the higher number of reactions.
TABLE VII. REACTIONS TO VERTICAL COLORED LIGHT
Group 1 Group 2 Group 3 Sum Animal no. 13 37 41 43 44 Sum 21 27 36 38 52 Sum 54 56 58 60 62 Sum Total
Blue 17 22 14 25 29 107 11 21 26 27 26 111 26 32 26 28 10 122 340 White 23 18 26 15 11 93 29 19 14 13 14 89 14 8 14 12 30 78 260
Green 17 26 11 21 29 104 21 27 30 7 26 111 29 31 26 10 9 105 320 White 23 14 29 19 11 96 19 13 10 33 14 89 11 9 14 30 31 95 280
Yellow 25 21 12 20 35 103 12 20 34 25 29 120 19 20 9 28 22 98 321 White 15 19 28 20 15 97 28 20 6 15 11 80 21 20 31 12 18 102 279
Red 37 33 23 22 28 143 21 30 30 33 22 136 32 37 26 33 28 156 435 White 3 7 17 18 12 57 19 10 10 7 18 64 8 3 14 7 12 44 165
Black 23 20 1 28 34 106 9 12 25 40 32 112 25 32 18 34 16 125 343 White 17 20 39 12 6 94 31 28 15 14 88 15 8 22 6 24 75 257
Black 20 15 13 27 37 112 16 11 16 27 24 94 36 40 18 29 29 152 358 Red 20 25 27 13 3 88 24 29 24 13 16 106 4 22 11 11 48 242
Black 20 25 26 20 32 123 22 15 39 40 32 148 33 22 34 34 11 134 405 [236] Blue 20 15 14 20 8 77 18 25 1 8 52 7 18 6 6 29 66 195
Red 25 17 28 18 8 96 3 15 21 28 20 87 21 13 15 14 28 91 274 Blue 15 23 12 22 32 104 37 25 19 12 20 113 19 27 25 26 12 109 316
Red 21 27 22 10 36 116 13 40 24 21 28 126 22 25 18 21 16 102 344 [237] Blue 19 13 18 30 4 84 27 16 19 12 74 18 15 22 19 24 98 256
The most striking feature of the table is the marked predominance of the red over the white. Here the red reaches 73% of the total number of reactions, and inspection shows that this predominance is uniform not only through the groups but even for the individuals. The constancy of this reaction and the fact that it is so much more frequent than the one to the black as compared with the white, would lead one to expect that the red would have the higher percentage in the combination black-red. Such, however, is not found to be the case, although it does happen with one group. If the arrangement of our color-scale in accordance with increasing intensity of stimulus were correct, we should expect a gradually increasing predominance in reactions to colored light over those to white in the first five pairs. Instead of this we find that green and yellow stand nearest to the white, blue and black come next and are almost equal, while red is very much higher than any. In the pairs black-red and black-blue the red holds its predominance over the blue at about the same rate as in the second pair of the direct comparison, red-blue. The wide individual variations, however, in all these reactions to colored light, except perhaps in the case of red-white, indicate that there is nothing very regular, stereotyped, or mechanical about them. The most that can be said is that in a general way the red end of the spectrum furnishes a less intense stimulus to negative reaction than the blue.
A tendency to habit formation was noticed during the course of these experiments, and it is possible that this may have influenced the results somewhat. Many individuals apparently formed a habit of going to a certain corner as soon as they were reset at the centre. The positions in which they were set were varied and they were headed in different directions, but within a minute after they were released in the middle of the box they would be found in their favorite corner. This was especially the case with no. 38 in Table VI, and I think accounts in some measure for the persistent avoidance of the white. In no case did this continue throughout the whole series, but would sometimes be noted for two or three days at a time in the case of an individual. What were the controlling factors in this habit formation, the means by which orientation and recognition were effected, I was unable to determine.
3. _Reactions to Objects_
In no case did an animal give any sign of perceiving stationary objects in its path or of avoiding them in any way that could be referred to a visual stimulus. When the animal approached an obstruction there was no hesitation in the movement until the object was touched. Usually even when the antenna had touched the object the animal did not stop, but continued until the contact of the chelæ or even of the rostrum made further movement in that direction impossible.
With moving objects the case was quite different. Here the condition and disposition of the individual animal seemed to be the deciding factors. Often when the animals were trying to climb out of a shallow pan in which they were kept in the experimenting-room, raising a finger or holding out a pencil would be sufficient to make them stop or even start back into the pan. Nor was this response occasioned by any change in the intensity of light, such as that caused by a shadow falling on the animal, for they would react to a movement made on the opposite side of them from the window. In fact, no. 56, the most active in response to moving objects, seemed to react more vigorously to a motion made on the opposite side than when it was made between him and the light. Whenever a person came near the aquarium he and one or two others would take an attitude of defence, and would "face about" to correspond to any movement the person made toward one side or the other. When in the pan mentioned above, any movement of a person within two or three yards of him usually called forth a reaction on his part, and if the pan were placed on the table and the person moved slowly round it, the animal turned with the person, making a complete circuit of the pan.
Reaction to a smaller moving object, however, was not so marked. A black object, 20×8×8 cm., was suspended above the middle of the pan so that if set swinging it would just pass over the top. When it was pulled to one side the animal responded slightly, but after the first swing he seemed to pay no more attention to it. When the operator stepped out from behind the screen, the animal was as keen in its response as before. The experiment was now tried of allowing the object to approach from one direction while the operator moved to a position at right angles to its line of movement. Without hesitation the animal moved so as to keep fronting the operator, without paying any attention to the movement of the smaller object, although this was much nearer.
These observations on the reactions of the crayfish to stationary and moving objects are in line with the conclusions of Plateau[238] and Exner[239] drawn from observations on other Arthropods. It is Exner's belief that the compound eye is a visual apparatus which is almost worthless for detecting the _forms_ of objects, especially if these objects are stationary, but that it may furnish a very keen perception of _moving_ objects.
II. EXPERIMENTS WITH SOUNDS
Hensen[240] stated that Palæmon and Mysis reacted to sounds made by striking a thin, resonant board floating on the surface of the water, or by tapping the walls of the aquarium or of the room. Beer[241] repeated Hensen's experiments, but denied that the Crustacea reacted to sounds, and claimed that their movements were due to visual and tactual stimuli. Prentiss[242] confirmed Beer's results on Palæmonetes, and noted that the reactions were only slightly diminished by the removal of the otocysts, but that removal of the antennæ and antennules caused their almost complete cessation. More extended experiments were made on the fiddler crab, _Gelasimus pugilator_, which is on land a good deal of the time, and Prentiss's conclusions are: "(1) The reactions formerly attributed to sound-stimuli are nothing more than tactile reflexes. (2) The otocyst has little or no part in calling forth these reactions. (3) There is no direct evidence to prove that decapod Crustacea hear, and until such evidence has been obtained, we are not warranted in ascribing to the otocyst a true auditory function."
The experiments performed on the crayfish in this connection all resulted negatively and go to confirm Beer's and Prentiss's conclusions. Rapping upon a board floating in the water, and tapping the sides of the aquarium did not cause the slightest apparent reaction in the animals under observation, even though the vibration of the water could be plainly perceived by the sense of touch in the hand. When a rather large electric bell was sounded just over the surface of the water some reactions were observed which were evidently due to the movements of the hammer, but there was nothing which could be referred to the sound-stimuli. If the bell was held against the sides of the aquarium, or in the water near the animals, the vibration could be plainly felt by the fingers, yet no reactions on the part of the crayfish were observed. A metal snapper making a crack like a small pistol-shot was tried both in and out of the water but with no success in producing a reaction. A large hand tuning-fork, when held with its base pressed firmly against the glass walls of the aquarium, gave a deep rich tone of great volume, or when lightly touched to the glass produced a shrill, piercing, penetrating sound which was extremely sharp and disagreeable. Here again the vibrations of the water were quite perceptible to the hand at a distance of 10 cm., yet in neither case was there a sign of a reaction. Finally two electric tuning-forks, one of 256, the other of 512 vibrations per second, were tried on the animals taken one by one, and especial attention was given to the regular movement of the little thread-like appendages which keep up the current of water to the gills, with the idea that perhaps their rate of movement might be affected. In no case was there the slightest movement that could be referred to vibration, although here again the tactile stimulus was very perceptible to the finger. None of these experiments, then, give any indication that the crayfish reacts to vibratory stimuli which to the human ear produce sound.
III. ROTATION EXPERIMENTS
It has been found that the higher vertebrates, on being rotated on a turn-table, exhibit all the symptoms which accompany the sensation of dizziness in man. The question arises, to what degree and in what manner do invertebrates respond to rotation? Schaefer,[243] the first to take up this question, denied on rather meagre observations that Crustacea respond in any way to rotation on the turn-table. Kreidl[244] showed that this statement was altogether too sweeping, that Palæmon reacts very definitely to rotation by running in the opposite direction. Bunting[245] tried the crayfish, but all the rotation experiments resulted negatively, so she was led to confirm Schaefer's statement so far as the crayfish is concerned. Bethe[246] found that Carcinus behaved in a very definite manner on being rotated, that during the rotation the animals ran in the opposite direction to that in which they were turned, and as soon as the motion ceased they began running in the other direction. Finally Lyon,[247] while agreeing with Bunting that adult crayfish do not react to rotation, discovered that young animals two or three centimetres long react very prettily to the movement, going in a direction opposite to the turn. To confirm and if possible extend these observations on the crayfish was the purpose of the following experiments.
It was soon found that a great deal depended on the method of experimentation. None of the experimenters mentioned above gives any detailed description of the manner in which the experiments were carried out. One is left uncertain whether the animals were placed on the periphery of the turn-table or over the centre, whether in the former case they were set with their heads toward the centre or away from it, or placed at right angles to a radius, or whether they were merely set down in any chance fashion and whirled about. The same indefiniteness exists in most of the accounts as to how fast they were turned, and whether the experiments were performed in the air or in the water. Finally it is not stated whether the rotation was always in the same direction, or whether its direction was alternated.
The turn-table used in the following experiments was one that had to be turned by hand, so that it was impossible to regulate the speed accurately. The crank, however, was not attached directly to the rotating board, but was connected with it by means of a gearing so that one turn of the crank produced about ten turns of the table. This gearing gave a steadying effect to the motion so that the speed could be kept tolerably constant. A circular pan, about 15 cm. in diameter at the bottom with the sides slightly sloping outward, was set so that its centre coincided with the axis of the rotating table. It was in this pan that all the experiments were tried. Through various preliminary experiments to determine the most favorable speed, it was found that a rotation rate of over one turn of the table per second produced such a strong centrifugal force that unless the animals were set exactly over the centre they were swept off against the side of the pan in such a manner that it was difficult to decide whether the rotation as such had any effect upon their movements. It was finally decided that the best results were obtained from a rate of approximately one rotation in two seconds.
It soon became evident that when the larger and more sluggish crayfish were merely dropped in the pan and rotated there was no particular reaction. This was true whether the animals rotated were in the air or in the water. The smaller and more active crayfish, however, showed a decided tendency to run either with or against the direction of the rotation, especially when the experiments were carried on in the water. In no case was there any tendency to go in the opposite direction when the rotation ceased, except in so far as the animals were carried along by the water. To get a quantitative expression for these tendencies a more delicate method of experimentation was resorted to. If there was a tendency on the part of the active animal to move either with or against the rotation, such a tendency might also be supposed to exist in the sluggish animal, only in the latter the inertia was sufficiently strong to prevent its appearance. If, however, the animals should be set radially to the periphery of the pan, the tendency to go with or against the rotation would be exhibited in the direction in which they turned out of the radial position. For it was found that no animal would remain in that position for any great length of time. Two groups of animals were used for these experiments, five animals in each group, and the first group was selected from the smallest and most active animals, the second from the largest and most sluggish. Each animal was set in two positions, position I, with the head toward the centre, position II, with the head away from the centre. Each animal was given ten trials in each position, and the number of times it turned in a direction _with_ the rotation is set down in the + column, the number of times it turned _against_ the rotation is indicated in the - column. In general from 5 to 15 turns were necessary for the orientation of the animal, though sometimes the number ran up to 30 or 40. Each trial was made in the opposite direction to the preceding one, in order to avoid the formation of any habit in turning. All these experiments were carried out in water, the depth of which in the pan was about 4 cm. In order that there should be no difference between the velocity of the water and that of the pan, the table was rotated a few times before the animal was put in. As a check a series of experiments of 5 in each position was performed in the air on the more active group.
The following table shows the results of these experiments in rotation:
TABLE VIII. REACTIONS TO ROTATION
In Water In Air Sum I II Sum I II Sum Total Group 1 + - + - + - + - + - + - + - 44 5 5 10 5 15 1 4 5 1 9 6 24 49 2 8 4 6 6 14 5 1 4 1 9 7 23 56 3 7 8 2 11 9 5 3 2 8 2 19 11 62 4 6 10 14 6 2 3 2 3 4 6 18 12 64 2 8 9 1 11 9 1 4 1 4 2 8 13 17 Sum 16 34 31 19 47 53 9 16 7 18 16 34 63 87 Group 2 21 5 5 3 7 8 12 27 2 8 5 5 7 13 36 7 3 8 2 15 5 37 2 8 3 7 5 15 54 5 5 6 4 11 9 Sum 21 29 25 25 46 54 46 54 Sum Total 37 63 56 44 93 107 9 16 7 18 16 34 109 141
Examination of the table reveals great individual variation. Some animals, as nos. 44, 49, and 37, turn rather constantly against the direction of the rotation, while others, as nos. 56 and 36, are almost as constant in their movement with the rotation. On the whole we observe that for each group, and for Group 1 in both water and air, there is a slightly greater tendency to go against the rotation than with it. This tendency, strange to say, comes out much more clearly in the air than in the water. It is evident, however, from the variation exhibited that there is nothing very stereotyped or mechanical about the reaction. Mention should be made of the fact that usually (though not always) the animals not only oriented themselves with reference to the rotation, but moved forward in that direction as long as the rotation continued.
IV. GEOTAXIS, BAROTAXIS, AND TURNING
(1) _Geotaxis._ So far as my knowledge extends, no experimental work has been done to determine the geotaxis of decapod Crustacea. Most of the vertebrates are positively geotactic, while a great many of the invertebrates, particularly unicellular organisms, larvæ of moths and butterflies, slugs, etc., are negatively geotactic. Parker[248] found that in the case of the Copepod, _Labidocera æstiva_, the females exhibited strong, the males weak, negative geotaxis. In the investigation of the geotaxis of the crayfish, two sets of experiments were undertaken. In the first the method of procedure was as follows:
On a level table before a window a board was so arranged that it could be set at an inclination of 5°, 10°, 15°, 20°, and 25° either toward or away from the window. Starting, let us say, with the inclination toward the window, each one of a group of five animals was placed on the board with the right side to the window five times. The board was then inclined the same amount away from the window and the process was repeated. The same procedure was carried out with the animals set with the left side to the window. The following table gives the results of this set of experiments.
TABLE IX. GEOTAXIS IN FRONT OF WINDOW
10 12 14 16 18 Totals + - ± + - ± + - ± + - ± + - ± + - ± 5° 14 5 1 11 7 2 11 9 13 7 8 10 2 57 38 5 10° 13 7 12 7 1 13 6 1 16 4 14 6 68 30 2 15° 17 3 14 6 16 3 1 17 3 9 11 73 26 1 20° 12 8 17 3 18 1 1 19 1 14 6 80 19 1 25° 18 2 19 1 19 1 17 3 16 4 89 11
From this table it appears that the crayfish is positively geotactic, and that the positive geotaxis increases regularly with the increase in inclination. As a check on these results another set of experiments was undertaken with different animals under different conditions. The board was placed on a level table in the centre of a darkened room, and the operator stood behind a screen so as to be quite hidden from the animals. In order to observe the orientation a 2 c. incandescent electric light was suspended directly above the spot where the animals were set, at a distance of 60 cm. above the board. Each animal of a group of five was set five times in each of four positions, viz., head down the incline, head up the incline, and at right angles to it with first the right and then the left side down the slope. The results were as follows:
TABLE X. GEOTAXIS IN DARKENED ROOM
41 46 48 51 64 Totals + - ± + - ± + - ± + - ± + - ± + - ± 5° 12 4 4 13 4 3 8 10 2 14 5 1 11 7 2 58 30 12 10° 14 5 1 13 6 1 11 8 1 13 6 1 14 3 3 65 28 7 15° 16 4 15 5 13 7 11 6 3 14 2 4 69 24 7 20° 16 4 19 1 16 4 20 17 2 1 88 11 1
It will be observed that Tables IX and X agree quite well in the main, and we may conclude that the crayfish is positively geotactic and that the positive reactions vary from 58% at 5° to 89% at 25°.
(2) _Barotaxis._ Verworn[249] uses the term barotaxis in an inclusive sense to cover all pressure phenomena that can be classed under the sub-heads of thigmotaxis, rheotaxis, and geotaxis. It seems preferable to me to employ the term in a more restricted sense of reaction to pressure other than the pull of gravity, the flow of a current, or the contact with bodies. The following experiment with the crayfish furnishes us, I think, with a case in point.
A glass aquarium, 54 cm. long and 28 cm. wide, was so inclined that the water was 20 cm. deep in one end and 8 cm. deep in the other. A board was so anchored that one end rested on the bottom at the shallow end of the aquarium while the other end projected slightly out of and above the deepest water. The board was about 45 cm. long, so that its slope was very gradual. Nine animals were placed in this aquarium and observed for three successive days. If we denote the bottom of the deep end of the aquarium by A, the shallow end under the board by B, the shallow end on top of the board by C, and the end of the board at the surface of the water by D, the results of the observations were as follows: On the first day 1 animal was found at D, 6 at C, and 2 at B. On the second day 5 were at C, 3 at B, and 1 at A. On the third day 1 was at D, 4 at C, and 4 at B. Totals, 2 at D, 15 at C, 9 at B, and 1 at A.
While these observations were too few to base very positive statements on, the striking fact that only one animal was found at A, the deep end of the aquarium, whereas 15 were noted on top of the board at C, indicates strongly that the animals avoid the deeper water. That the animals were found _on top_ of the board, not under it, indicates that the observation is not to be referred to thigmotaxis, although the latter is doubtless very strong, as we shall see later. It should be observed that the negative barotaxis works against and overcomes the marked positive geotaxis which, as we have just seen, the animals exhibit in the air. Under the influence of the positive geotaxis, we should expect to find the greater number of the animals at A,--a condition which is speedily realized if we let the water run out of the aquarium. We conclude, therefore, that at certain pressures (specifically at the pressure exerted by water at a depth of 20 cm.) the crayfish is negatively barotactic.
(3) _Turning._ In the experiments with light it was observed that very seldom do the animals, when placed upon a surface, move off at once in a straight line, but usually they first turn through an angle of 90° or more and then start off straight. This came out strongly in the work on geotaxis, where oftentimes, when the animal was set with the head up the incline, the reactions would be preponderantly positive, whereas when set with the head down the incline the reactions were on the whole negative. In other words, when headed up the incline the animal would go down, and when headed down he would more often go up. Some experiments were tried under various conditions to determine how general this tendency is. The table presents the results in condensed form.
TABLE XI. EXPERIMENTS IN TURNING
Nos. 10 12 14 16 18 Sum 7 9 15 17 25 Sum I III 90°- 8 5 6 8 10 37 2 4 7 5 5 23 90° 4 6 7 2 2 21 3 1 4 90°+ 8 9 7 10 8 42 5 5 3 5 5 23 II IV 90°- 2 1 2 2 7 9 3 1 2 15 90° 1 1 2 4 3 5 3 3 1 16 90°+ 7 9 7 10 6 39 12 1 9 11 11 44
Nos. 41 43 46 48 64 Sum Sum V Totals 90°- 9 11 12 14 2 48 130 90° 2 1 2 1 3 9 54 90°+ 9 8 6 5 15 43 191
In this table the first line indicates the number of times each animal turned less than 90° when starting off from the position in which it was set, the second line the number of times the amount of turn was practically 90°, and the third more than 90°. The five parts of the table mark the different conditions; in Part I twenty observations were made on each animal placed on a level board before the window, and set now with the right now with the left side toward the window. In Parts II and III the animals were set with the head turned now toward now away from the window. In Parts IV and V the animals were placed on a level board in the middle of a darkened room with a 2 c. light about three feet above them. This was to exclude any possible directive influence of light. In all cases the operator was concealed by a screen. In Parts I and V twenty observations were made on each animal, in II and III ten, and in IV fifteen.
Rarely the animal would turn completely round and start off in the direction originally set, but usually the turn was between 90° and 180°. When once the animal began to move off, it would ordinarily keep to an approximately straight line. How seldom this was observed when the animals were first set down may be judged from the fact that out of a total of 375 observations in only 18 did the animals move straight ahead from their original position. From the table we observe that in over 65% of the cases (a proportion of almost two to one) the animals turned through 90° or more before starting off. At present the writer has no explanation to offer for this phenomenon.
V. THIGMOTAXIS AND TOUCH REACTIONS
(1) _Thigmotaxis._ Experiment has shown that there are some animals which tend to avoid contact with objects as much as possible, and on the other hand there are animals that seek to get as much of the surface of their bodies as possible in contact with objects. The former are spoken of as negatively, the latter as positively thigmotactic. Does the crayfish show any tendency in the one way or the other, and if so is it positively or negatively thigmotactic? In a large glass aquarium, 80 cm. long and 40 cm. wide, was a thin wooden box, 22 cm. long and 16 cm. wide, set in one corner 4 cm. from the glass walls. At the bottom of the box was an opening where the crayfish could enter. The following table shows the disposition of the animals for 27 different days, on which one examination was made each day. Line I indicates the number of times each animal was found against the walls of the aquarium, line II in the 4 cm. space between the box and the walls of the aquarium, line III inside the box against its sides, and line IV resting freely in the middle of the aquarium or in the middle of the box.
TABLE XII. THIGMOTAXIS REACTIONS
Animal 4 5 9 13 21 27 29 31 33 35 36 37 38 39 41 42 43 44 45 46 47 48
I 4 9 2 10 4 17 16 6 6 10 3 2 11 9 3 2 1 9 1 15 II 5 2 13 18 9 5 2 4 5 22 1 14 11 3 6 11 1 9 4 7 III 2 1 2 5 1 9 3 2 3 11 2 24 7 1 4 14 9 1 5 IV 1 11 2 1 2 4 4 1 2
Animal 49 51 52 54 56 58 60 62 64 Sum Totals I 6 11 3 1 2 4 7 10 12 195 II 8 3 7 5 8 1 3 2 1 190 III 1 16 9 5 10 3 2 2 154 IV 1 1 2 1 33 572
In order to appreciate the significance of the figures in this table it is necessary to consider the amount of lateral surface with which it was possible to come in contact in each case. In IV of course it was zero, in III it was 76 cm. with four corners in close proximity, in II it was only 38 cm. and one corner, but the space was so narrow that there was practically a contact-surface on both sides, and in I there was 212 cm. of lateral surface with three corners. I mention corners in this connection because they were almost invariably occupied. If we examine the table with these facts in mind, we find, (1) that the number of animals resting freely without contact with any lateral surface is very small, only about 6% of the whole; (2) that the number of animals found in the narrow space between the box and the walls of the aquarium is very large in proportion to the length of the space: indeed the animals were frequently found wedged into this space three or four deep; (3) that the number of animals found in the box was probably due largely to the fact that they found in it a greater lateral contact-surface, particularly in the corners, than was possible outside.
Two or three minor considerations are of interest. The animals were frequently observed "on edge" about half out of the water, that is, with the ventral surface of the body pressed against the vertical surface against which they were resting. This was also observed where the water was so deep that none of the members could touch the bottom. It was perhaps on account of the quality of the surface affording a rougher contact that so large a number of the animals were found in contact with the wooden box rather than the smooth, slippery surface of the glass. In the centre of the aquarium a wooden stopper 2 cm. in diameter projected about 15 cm. above the surface of the water. Very often a crayfish would be found almost at the top of this stopper, completely out of the water. This tendency to climb was frequently observed in the light-reaction experiments, where the animals would climb up on any piece of wood that chanced to be left in the box. It reminds one of the tree-climbing crabs of the West and East Indies. Along the creeks of Ohio I have frequently seen crayfish that had climbed up on logs or sticks that projected some feet out of the water.
In the table we see decided evidences of "habit" in the sense of an animal returning to the same place which it had occupied. No. 5 has almost half the observations in the open, nos. 21, 37, and 39 showed a decided preference for the space between the box and the aquarium wall, while nos. 38, 44, and 52 were more frequently found on the inside of the box. This recurrence to a particular position also came out in the light-reaction work, where an individual would return to the same spot in the box for days at a time as soon as released.
From the above considerations we conclude that the crayfish is strongly positively thigmotactic and that this thigmotaxis probably plays a most important part in the life of the animal.
(2) _Touch Reactions._ Lemoine[250] investigated the reactions of crayfish to touch-stimuli and found that the plates of the telson, the sternal portions of the thorax, the abdominal pleopods, the chelæ, and particularly the antennæ toward their points are especially sensitive, but that nowhere, even on the back of the carapace, is a touch-stimulus altogether devoid of reaction. Gulland[251] found that a needle could be inserted between the tufts of setæ on the chelæ without causing any reaction, but as soon as one of the hairs was touched, the chelæ closed with a snap. Considering the setæ as the organs of touch, he claimed to have found that the eyes, eye-stalks, and carapace (which he says have no setæ) are impervious to tactile impressions. This claim of Gulland's is strangely at variance with the facts. In no case have I been able to bring about retraction of the eye-stalk by visual stimulation, but a very light touch-stimulus on the eye itself or on the eye-stalk or a stronger stimulus on some portion of the head will cause the eye to be drawn in. It is true that after repeated stimulation the eye is retracted no longer, and with a heavy bristle one can make a perceptible indentation in the corneal surface without the eye being withdrawn.
The antennæ, from their anatomical structure, their position, and the manner in which they are carried, are generally considered the special organs of touch. Nevertheless, as far as the reactions of the animal are concerned, a stimulation of the antennæ by touch produces a less decided response than almost any other portion of the body. If the stimulus is very light no reaction at all is observed in most cases, and if stronger the antennæ are moved away, but that is all. A stimulation of the edge of the telson produces a more decided reaction. Either the animal folds it under the abdomen at once or faces about like a flash in an attitude of defence; frequently both reactions occur. While the response to stimulation of the chelæ was decided, that to touch on the first chelipedes was quicker and more accurate. The mouth-parts are also very sensitive to touch. I cannot agree with Gulland's assertions as to the insensitiveness of the carapace, for I have been able to find no place upon it where a light-stimulation would not produce a reaction. In this connection a curious phenomenon is characteristic of the animal. If the carapace or the front portion of the abdomen be lightly stroked with a solid object such as a pencil, the animal will slowly turn toward the stimulus on its antero-posterior axis. If, now, a like stimulus be applied on the other side, the animal will roll back through the normal position to a like inclination toward the stimulus on the other side. If the alternation be kept up and the change made quickly, a continuous and curious rolling movement is maintained, the animal growing more and more excited until it scampers off with a kind of cramp-like motion. With some animals this rolling reflex is more marked than with others, but in no case is it altogether lacking. Some animals have been known to roll so far over that they topple over on their backs. Dr. Yerkes informs me that he has observed the same phenomenon in a less degree with turtles when the edge of their shell is stimulated by scratching. The movement seems to be caused by the reflex stimulation of the extensor muscles on the opposite side of the body from the part stimulated. The thrust of the legs thereby brought about raises that side of the body and thus causes a rotation to some extent about the antero-posterior axis. But how was this connection between the stimulation of one side of the body and the contraction of the extensor muscles of the other side established? I have no doubt that it is intimately connected with the positive thigmotaxis described above. These animals live under loose stones for the most part, and thus the carapace gets a great deal of stimulation. If the animal is stimulated on one side, a contraction of the extensor muscles of the opposite side tends to roll the animal toward the source of the stimulus, and hence to increase the contact. In the race-history of the animal this has doubtless been advantageous in enabling it to escape the dangers of its habitat.
* * * * *
In a succeeding paper the writer hopes to discuss the reactions of the crayfish to chemical stimuli. In conclusion he desires to make acknowledgment to Dr. Robert M. Yerkes of the Harvard Psychological Laboratory for kindly suggestions and helpful criticism throughout the course of the investigation.
SUMMARY
(1) Crayfish are somewhat negatively phototactic, going away from rather than toward the source of light in the ratio of 62% to 38%. The different intensities employed in this investigation produced very little difference in the reactions. The average reaction-time was much less for the group of animals which showed the highest percentage of negative reactions, indicating a greater general sensitiveness. Variations of the position in which the animals were set affected the results very slightly.
(2) Previous confinement in the dark tended to increase slightly the number of negative reactions, and previous exposure to strong light tended to decrease the number, but the results were not constant. An increase in temperature tended to decrease the number of negative reactions to light, but here again the results were somewhat conflicting.
(3) Reactions to horizontal colored light showed a tendency to go to the colored light rather than to the white in the following order: Blue 47%, green 50.5%, black (or the absence of light) 51%, red 54%, yellow 59%. In the case of vertical colored light the comparison with the white resulted somewhat differently, as follows: Green 53%, yellow 53.5%, blue 57%, black 57%, red 72.5%. In the latter experiments the animals showed a marked and constant preference for the red.
(4) The animals showed no signs of reaction to static objects from visual stimulation, i. e., there is no evidence of visual perception of form in the case of stationary objects. Moving objects, especially large ones, are plainly perceived and definitely reacted to.
(5) There were no reactions whatever caused by those vibrations which to the human ear produce sound. So far as these experiments go, the animals cannot be said to hear.
(6) In rotation experiments individual animals were rather constant in moving either with or against the direction of the rotation, but no definite tendency for all animals was observed.
(7) The pull of gravity was followed with constantly increasing frequency from 58% at 5° to 89% at 25°. Therefore we conclude that the animals are positively geotactic. They are negatively barotactic, avoiding the pressure of water at the depth of 20 cm., and this is sufficient to overcome their positive geotaxis. When placed upon a level surface the animals show a peculiar tendency to turn through a greater or less angle before starting out in a straight line. In only 18 out of 375 observations, or 5%, did the animals start straight, in 30% they turned through an angle of less than 90°, and in 65% they turned through an angle of 90° or more.
(8) The crayfish is positively thigmotactic in a marked degree, as is indicated by the fact that in only 33 out of 572 observations, or less than 6%, were the animals found resting in the open, while in 190, or 33%, they were found in a narrow opening between two vertical surfaces.
(9) The animal is sensitive to touch over the whole surface of the body, but especially on the chelæ and chelipedes, the mouth-parts, the ventral surface of the abdomen, and the edge of the telson. If one side of the carapace or of the dorsal surface of the abdomen be stimulated, the extensors of the legs on the opposite side are contracted, and the animal turns on its antero-posterior axis toward the source of the stimulus. If opposite sides be stimulated alternately, a peculiar rolling motion is set up.
FOOTNOTES:
[Footnote 218: An Introduction to the Study of Zoölogy, illustrated by the Crayfish, Internat. Sci. Ser., 1880.]
[Footnote 219: How the Burrowing Crayfish works, Inland Monthly, Columbus, Ohio, vol. 1, pp. 31, 32, 1885.]
[Footnote 220: Cave Animals from Southwestern Missouri, Bull. Mus. Comp. Zoöl. Harv. Univ., vol. 17, pp. 225-239, 1889.]
[Footnote 221: Notes on the Individual Psychophysiology of the Crayfish, Amer. Jour. of Physiol., vol. 3, pp. 404-433, 1900.]
[Footnote 222: Reactions of Entomostraca to Stimulation by Light, II, Reactions of Daphnia and Cypris, Amer. Jour. of Physiol. vol. 4, pp. 405-422, 1900; Reactions of Daphnia pulex to Light and Heat, Mark Anniversary Volume, pp. 359-377, 1903.]
[Footnote 223: Heliotropism of Cypridopsis, Amer. Jour. of Physiol., vol. 3, pp. 345-365, 1900.]
[Footnote 224: Das Nervensystem von Carcinus mænas, I, Arch. f. mikros. Anat., vol. 50, pp. 460-547, 589-640, 1897.]
[Footnote 225: The Color Physiology of Higher Crustacea, Phil. Trans., London, Series B, vol. 196, pp. 295-388, 1904.]
[Footnote 226: An Establishment of Association in Hermit Crabs (_Eupagurus longicarpus_), Jour. Comp. Neur. and Psych., vol. 14, pp. 49-61, 1904.]
[Footnote 227: The American Lobster; A Study of its Habits and Development, Bull. U. S. Fish Comm., vol. 15, pp. 1-252, 1895.]
[Footnote 228: Notes on the Senses and Habits of some Crustacea, Jour. Marine Biol. Assoc'n., Plymouth, N. S., vol. 1, pp. 211-214, 1889.]
[Footnote 229: The Reactions of Copepods to Various Stimuli, Bull. U. S. Fish Comm., vol. 21, pp. 103-123, 1902.]
[Footnote 230: Recherches pour servir à l'histoire des systèmes nerveux, musculaire, et glandulaire de l'écrevisse, Ann. des Sci. Nat., Series 5, vol. 9, pp. 99-280; vol. 10, pp. 5-54, 1868.]
[Footnote 231: The Sense of Touch in Astacus, Proc. Roy. Physiol. Soc., Edinburgh, vol. 9, pp. 151-179, 1886.]
[Footnote 232: _Loc. cit._]
[Footnote 233: Contribution to the Comparative Physiology of Compensatory Movements, Amer. Jour. of Physiol., vol. 3, pp. 86-114, 1899.]
[Footnote 234: The Retina and Optic Ganglia in Decapods, especially in Astacus fluviatilis Mitth. Zool. Stat. Neapel., vol. 12, pp. 1-73, 1895.]
[Footnote 235: Photomechanical Changes in the Retinal Pigment Cells of Palæmonetes, etc., Bull. Mus. Comp. Zoöl. Harv. Univ., vol. 30, pp. 273-300, 1897.]
[Footnote 236: No. 46 substituted.]
[Footnote 237: The second pair of red-blue gives the results of an experiment under somewhat different conditions as described above.]
[Footnote 238: Recherches expérimentales sur la vision chez les Arthropodes, Mém. Corronnés de l'Acad. Roy. des Sci. etc. de Belgique, vol. 43, pp. 1-91, 1889.]
[Footnote 239: Die Physiologie der facettirten Augen von Krebsen und Insekten, 1891.]
[Footnote 240: Studien über das Gehörorgan der Dekapoden, Zeitsch. f. wiss. Zool., vol. 13, pp. 319-412, 1863.]
[Footnote 241: Vergleichend-physiologische Studien zur Statocysten-function, I. Ueber den angeblichen Gehörsinn und das angebliche Gehörorgan der Crustaceen, Arch. f. d. ges. Physiol., vol. 73, pp. 1-49, 1898; Idem. II. Versuche an Crustaceen, Arch. f. d. ges. Physiol., vol. 74, pp. 364-382, 1899.]
[Footnote 242: The Otocyst of Decapod Crustacea, Bull. Mus. Comp. Zoöl. Harv. Univ., vol. 36, pp. 165-251, 1901. (Contributions, no. 123.)]
[Footnote 243: Das Verhalten wirbelloser Thiere auf der Drehscheibe, Zeitsch. f. Psych. und Physiol. d. Sinnesorgane, vol. 3, pp. 185-192, 1892.]
[Footnote 244: Weitere Beiträge zur Physiologie des Ohrenlabyrinthes, II. Mittheilung, Versuche an Krebsen, Sitzungsb. Kais. Akad. Wiss., Wien., vol. 102 (Part. 3), pp. 149-174, 1893.]
[Footnote 245: Ueber die Bedeutung der Otolithenorgane für die geotropischen Functionen von Astacus fluviatilis, Arch. f. d. ges. Physiol., vol. 54, pp. 531-537, 1893.]
[Footnote 246: Das Nervensystem von Carcinus mænas, I. Arch. f. mikros. Anat., vol. 50, pp. 460-547, 589-640, 1897.]
[Footnote 247: Contribution to the Comparative Physiology of Compensatory Movements, Amer. Jour. of Physiol., vol. 3, pp. 86-114, 1899.]
[Footnote 248: The Reactions of Copepods to Various Stimuli, Bull. U. S. Fish Comm., vol. 21, pp. 103-123, 1902.]
[Footnote 249: General Physiology, English translation by Frederic S. Lee, 1899.]
[Footnote 250: Recherches pour servir à l'histoire des systèmes nerveux, musculaire, et glandulaire de l'écrevisse, Ann. des Sci. Nat., series 5, vol. 9, pp. 99-280; vol. 10, pp. 5-54, 1868.]
[Footnote 251: The Sense of Touch in Astacus, Proc. Roy. Physiol. Soc. Edinburgh, vol. 9, pp. 151-179, 1886.]
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* * * * * +----------------------------------------------------------------+ | | | Transcriber notes: | | | | Please note, _underscore_ indicates italics, equals sign around| | the word indicates bold. | | Fixed various punctuation. | | P.47. 'to +5.93' may be 'to +:+5.93', however leaving it. | | P.142. The Standard for F calculation should be 110.40 total, | | not 122.40, with the average 3.94, not 4.35. Corrected table. | | P.47. 'for eyes at 0' added a degree like the others. | | P.272. 'abcab, cabe', changed 'cabe' to 'cabc 'as there is no | | 'e' and it looks to be 'c'. | | P.143. The Standards for Active M. Total calculation should | | be 65.40, not 59.40, with the average 4.67, not 4.24. | | The average for Total Passive M. should be 71.00 not 72.00. | | Corrected table. | | P.144. The Standards for F. Total calculation should be 120.11,| | not 117.04, with the average 4.45, not 4.33. The average for | | M. should be 4.19 not 4.20. Corrected table. | | P.145. Correct the net results on table IV. | | First table: | | Raised or lowered #25 2.1 to 2.7. #27 8.9 to 8.7. #28 3.5 to 4.| | Totals: 131 total is 132. 48.1 total is 47.9. 270 to 271.1. | | Net lowered 221.9 change to 223.2. | | Average lowering of each color judgment, 221.9/756 = .293 | | change to: 223.2/756 = .295 | | % of judgments of color not affected, 131/756 = 17+ is | | 132/756 = 17+. | | | | Second table: | | Raised or lowered, #8 36.3 is 36.4. #14 3.72 is 37.2. | | Total Raised 829.7 is 749.8, Net lowered 820.9 is 741. | | Average lowering of each tone judgment, 1.08+ is .98+ | | | | P.146. Table V. 2nd.--Lowered #18 8.2 is 8.6, change the | | total to 20.4. | | Net lowered change from 581.3 to 560.9 | | | | P.147. | |1st table: The Net + raised should be 640.5, not 649.5; with | | the 'Average raising of each tone judgment,' being 1.69, not | | 1.71. Changed in table. | |2nd table: -3.3 Net result lowered in #11 moved to | | #12 and is now +3.3. No figures affected. | | | | P.149. Table VII. 1st table. | | #15 Net result + 1 should be - 1. Moved. This does not affect | | negative figures. | | However, the + figure total is 197.5, not 186.5. | | Making the net raised 182.3. | | Averaging raising of each tone judgment, .45 is .48+ | | | | P.150. Table VIII. | | 1st table. #16. 1 Raised is 1 Lowered. Moved. #21 Raised 2.2 | | is 3.2, changed. | | Total Net Result needs to be changed from 11. to 12. | | Total Raised net result needs to be changed from 211.7 | | to 221.9, making Net raised = 209.9. | | Average raising of each tone judgment, .52 is .55+ | | | | P.151. Table IX. | | 2nd table. #13. raised 41.6 is 41.8. Changed. | | Total for Net Result Raised 130.0 is 150.2. . | | Net raised Grand total is 88.8. | | Average raising of each active touch judgment, .17+ is .22+ | | | | P.152. Table X. | | 1st table. #4 Net result raised, 4.3 is 4.6 = Total 57. | | Net lowered is 54.4. | | | | P.153. Table XI. First table. No. of colour 10-17 illegible. | | corrected. | | Points raised total & net raised 282.2 is 292.2. | | Average raising of each color judgment, .72- is .75-. | | | | 2nd. table. #2. Net Result - 13 changed to 11. | | Total Net Result - 56 is 54. | | Net raised, 104 is 106. | | Avererage .26+ is .27+. | | | | P.154. Table XII. | | First table. Total of column Raised, 226 change to 22 | | Total of column Lowered, 100 change to 101 | | | | P.313. 'obseved' changed to observed. | | Table I. Obs B row, 13.9 sec., taken out sec. | | | | P.400. (b) 'irrevelant' changed to 'irrelevant'. | | Footnote 128: 'Wahrscheinlichkeitseechnung' changed to | | 'Wahrscheinlichkeitsrechnung' | | P.463. moved 0 & 0 up one column in L. row of table from the | | percentage line | | P.499. Table. 23 Huggins. c. N. 98 first column '+55' changed | | to +'5.5'. | | P.550. Added closing quotation at: is markedly thinner." | | P.551. 'under expermental' changed to 'under experimental'. | | Footnote 141. 'Woods Holl' changed to 'Woods Hole'. | | P.583. 'thoughout' changed to 'throughout'. | | P.594. Fig. 4. 'The rise curve' changed to 'The rise on curve'.| | P.606. 'mimimize' changed to 'minimize'. | | P.638. Table XI. No. II, first row, 90deg: the minus was added.| | Note: Carat followed by { } indicates superscription. | | | +----------------------------------------------------------------+