CHAPTER II

THE SPECIAL FACTS OF CONSCIOUSNESS

_A._ _THE ELEMENTS OF MENTAL LIFE_

§ 4. SENSATION

1. _The Newly Discovered Kinds of Sensations_

We shall discuss first the simplest facts of mental life, later their complications. It has often been objected that such a treatment is not in harmony with the fact that we are more familiar with the complications than with the simpler facts. But we are also more familiar with our body than we are with muscle cells, nerve cells, and blood corpuscles, and yet we do not object to beginning the study of biology by a study of the structural elements and their chief properties. No one understands this to mean that the cells of various kinds existed first separately and were then combined into the body which consists of them. No one should believe that the simple mental states existed separately and were then combined into those complications with which we have become familiar in everyday life. Simple mental states are abstractions. But we cannot hope to understand the complexity of mental life without using abstractions.

Through the sense organs our mind receives information about the external world. The traditional classification of the sensations divided them into five groups. But the distinction of five senses has been found to be insufficient. At least twice as many must be distinguished.

When psychologists tried to explain all human knowledge in terms of experience, they met with some difficulty in the description of our experience of solid bodies. Tactual sensation was found to be insufficient for this explanation, since it informs us only of the side-by-side position of things, that is, of only two dimensions. It was soon recognized that the movements of our limbs were important factors in this experience, and the question was asked: How do we perceive the spatial relations of our limbs and the resistances offered to changes in these spatial relations, that is, to movements? The first answer to this question was, that the muscles, being obviously a kind of sense organ which gives us the familiar sensations of fatigue and muscular pain, are also capable of sending in definite groups of afferent nervous processes according to their conditions of contraction and tension. This answer was quite true, as far as it went; and about 1870 the sensory neurons of muscles were actually discovered. The tendons connecting the muscles with the bones were also found to contain sensory neurons.

But this cannot be all, for we are able to judge the position of our limbs even when the muscles are completely relaxed and a limb is moved by another person. It is further a fact that a weight and the distance through which it is moved can be estimated with fair accuracy, whether the arm is sharply bent or straightened out, although the contraction and tension of the muscles is very different in these two cases. It is now known with some certainty how these estimations are made possible. The surfaces of the joints are furnished with nerves. Make a slow movement of the hand or a finger and attend to the sensation resulting from it. There is little doubt that the sensation is localized in the joint. This view is supported by the fact that electrical stimulation of a joint considerably decreases the accuracy of the estimation of weight and movement.

The three classes of sensations--muscular, tendinous, and articular--are customarily grouped together under one heading as _kinesthetic_ sensations, meaning literally sensations of movement. But, as we have noted, these sensations occur as the result not only of movements of our limbs, but also of pressure or pull when the limb is at rest. They always occur together with tactual sensations, but must nevertheless be strictly distinguished from them.

Soon after this distinction had been recognized, the tactual, or rather cutaneous, sense was found to consist of several senses. The impressions of touch, that is, of pressure on the skin, of temperature, and of pain had always been distinguished; but it had not been known that the areas of greatest sensitivity for touch are not identical with those for temperature, and that the sensitivity for pain may be greatly diminished without a corresponding change in the sensitivity for touch. It was only about 1880 that these observations were explained, when an anatomical separation of the neurons serving these different sensations was demonstrated. If we test the sensitivity of the skin by carefully stimulating single points, it is found that not every point of the skin is sensitive, but that the sensitive points are isolated by larger or smaller insensitive areas. It is further found that the points sensitive to warmth are different from those sensitive to cold or to pressure or to pain. This can easily be demonstrated for the cold points by touching the skin in a number of successive points with a steel pen or a lead pencil. Generally only the touch is perceived, but now and then an intense sensation of cold is felt on definite points, always recurring when these points are touched. It is somewhat more difficult to demonstrate the points sensitive to warmth. The sensation is in this case much less noticeable. The points sensitive to touch are on hairy parts of the skin always close to a hair; on other parts, for instance the palm of the hand and particularly the finger tips, they are located so close together that their separateness can be proved only by the use of very delicate instruments. The same is to be said of the pain points of the skin. We cannot, therefore, regard the skin as one organ of sense, but must regard it as containing four classes of organs serving the senses of warmth, cold, pressure, and pain.

We must be sure, of course, to distinguish between pain, as a sensation, and the feeling of unpleasantness which almost without exception accompanies pain. We must further distinguish the sensation of pain from intense cold, intense heat, strong pressure, dazzling light, all of which may produce pain as a secondary effect. But the sensation of pain is quite dissimilar from the sensations of cold, heat, pressure, and light, to which it is added in consequence of physiological conditions. The independence of the sensation of pain can easily be demonstrated by touching the cornea of the eye with a hair. Pain is then perceived without any touch or temperature sensation. The pricking sensation in our nose resulting from the breathing of chlorine or ammonia may also be mentioned as an illustration of the same point. Let us further understand that pain is not only a cutaneous sensation, but also a sensation localized in internal organs; for instance, headache, toothache, colic.

The most interesting discovery of a new sense organ concerns the labyrinth of the ear. It was made quite unexpectedly. The labyrinth consists of the inner ear proper, or the cochlea, the system of three semicircular canals, and between these two organs a pair of small sacs, each containing a little stone or otolith, built of microscopic lime crystals. All these organs, being all of the nature of cavities filled with fluid and communicating, were originally regarded as serving the sense of hearing, although no one was able to say how. It was observed, however, that stimulation or lesion of the semicircular canals and of the sacs did not affect hearing, but resulted in disturbances of the coördination of the muscular activities in locomotion and normal position. For more than fifty years these observations remained unexplained; and even then their explanation was but slowly accepted.

It is now recognized that the semicircular canals and the sacs are not organs of hearing, but organs informing the organism about the movements or position of the head, and indirectly of the body as a whole. The sensations coming from these organs are usually so closely bound up with kinesthetic and tactual sensations that we have not learned to become conscious of them as a separate kind. Nevertheless we may perceive them separately under favorable circumstances. If we close our eyes, turn quickly a few times on our heel, and suddenly stop, we are vividly conscious of being turned in the opposite direction. This is a perception mediated by the semicircular canals. The fluid ring in the horizontal canal gradually assumes the motion of the body, in consequence of its friction against the walls; and when the body suddenly stops moving, the fluid ring continues to move and to stimulate the sensory neurons for some time. If the body moves in a larger circle, for example on a merry-go-round or on a street car passing around a curve, the mind perceives an inclination of the body towards the convex side of the curve. If we go up in an elevator, we have the impression, just after the elevator has stopped, of moving a short distance down. These are sensations of the otolith organs.

The otoliths are slightly movable, one in the horizontal, the other in the vertical direction. If the body moves through a curve, the otolith which by centrifugal force is driven outwards stimulates the sensory neurons in the same manner in which it stimulates them when the body is inclined. The perception of the body’s position is therefore the same. If the body is quickly moved up or down, the vertical otolith at first lags behind, and at the stop, through its inertia, continues to move a little in the same direction. The result is a brief perception of the body moving in the opposite direction.

Artificial stimulation or lesion of the semicircular canals or otolith organs in animals tends to produce certain unexpected reflex movements of the body which the animal tries to counteract voluntarily, so that all kinds of unusual movements are observed. If these organs are destroyed, one source of information about the position and the movements of the body is lost. This loss is not very serious in man, in whom it occurs as a result of diseases of the ear; man can obtain his orientation from visual, kinesthetic, and pressure sensations in spite of this loss. It is far more serious in aquatic and flying animals. Pressure differences are of no account when the body has nothing but water or air on all sides. In a greater depth of water vision is practically impossible. Under these circumstances the semicircular canals and the otolith organs are highly important for an animal’s life. Unfortunately no definite names have thus far been adopted for these senses. They are frequently called the static sense or the sense of equilibrium. But these names are of doubtful value, since other senses too may inform us about our equilibrium.

The enumeration of our senses is not yet completed. What is hunger? What is thirst? What is nausea? These mental states are certainly similar, in some respects, to tones and odors. They are sensations. There is the difference, however, that we do not project them into external space, but think of them as characteristics of our own body’s condition. How is consciousness of these sensations brought about? No doubt, in a manner similar to that of the mediation of such sensations as odors and tones: through the stimulation of sensory neurons and the propagation of nervous processes toward the motor points of the body. The place of stimulation must be somewhere in our organs of nutrition, and thus these organs must be regarded also as a kind of sense organ. That the sensory function can be attributed to an organ in addition to another function has been proved by the example of the skin, muscles, and joints. The same may be said of other organs, for instance the lungs giving us the sensation of suffocation.

We possess, therefore, a large number of organs whose primary function is of an active kind, but which also give information as to the condition of those active functions. The sensations resulting from them are as independent of each other as tones are of color or taste. But they do not permit of as many subdivisions as the sensations of the so-called higher senses. For the emotional part of our mental life they are of the greatest significance. Since we do not project them into the external world, but think of them as significant of the functions of our internal organs, they are rightly called by the common name of _organic sensations_.

2. _The Other Sensations_

Besides the cutaneous sensations four classes were known to the older psychology: sensations of color, sound, odor, and taste. The relation of these sensations to the corresponding stimuli comprises a vast number of problems and theories, but we shall here state merely that which is of more general interest.

The taste--in the ordinary sense--of a substance is by no means made up exclusively of taste sensations in the special sense of this term. It is usually a complex of different sensations which almost invariably occur together. Only gradually do we learn to analyze this complex into its elements. Touch sensations of the tongue and palate often enter into the combination, for instance in a burning or astringent taste. Sensations of smell are of particular importance in this connection. The different kinds of meat, of wine, of bread, and of many other foods and beverages are distinguished almost exclusively by the smell. Aside from these accompanying sensations, there are only four tastes proper: sweet, sour, salt, bitter, in all their possible mixtures and relative degrees of intensity. In a manner comparable to the distribution of cutaneous sensations, the taste sensations have their end organs at definite points in the papillæ of the tongue and soft palate. The so-called taste buds contained in the walls of the papillæ seem to be sensitive according to the principle of the division of labor, some serving chiefly this, others chiefly that taste. It is possible that all the taste buds of the same papilla mediate the same taste sensation, so that each papilla might be said to be in the service of a particular taste.

The number of distinguishable odors is very large. Gaseous, fluid, and solid substances, minerals, plants, and animals have usually their characteristic, although often very faint, odors. As new substances are discovered or new mixtures of substances invented, the number of odors is increased. Unfortunately it has thus far been impossible to arrange this multitude of odors in a system according to a simple plan. Various groups of related odors have been formed by investigators (for example, the odor of flowers, fruit, musk, onion, decaying matter). But it is difficult to include all possible odors in such groups; and the relation between these groups is still unknown. One reason for this difficulty in understanding theoretically the sense of smell is the obvious fact that this sense has degenerated in man. The organ of smell, a spot in the upper part of each nasal cavity, is of small extent in man compared with that of animals. Even more superior are the animals to man with respect to the development of the olfactory nerve center. The degeneration is the result of a lack of use. Man, walking upright, has but rarely an opportunity of approaching objects with his nostrils closely enough to be able to smell them. The animal, searching for food on the ground, smells unceasingly.

The opposite is true for color sensations. They, too, are numerous, perhaps a million. But it is easy to group them into a system which permits us to understand their interrelations. The relations between the various colors are so simple that they can be symbolically represented by a geometrical figure, a double pyramid with a four-cornered base, like the one in figure 14. The vertical axis represents the visual sensations which are colorless, arrayed so that the brightest white is at one end, the darkest black at the other, the various grays between. The base of the pyramids, which is not perpendicular to the axis, but slanting, represents the series of colors of

the spectrum plus the non-spectral purples, between red and violet, all arranged in an orderly manner around the axis. The nearer we approach the axis, the less saturated, that is, the more whitish, or grayish, or blackish are the colors represented. The most saturated colors are therefore represented by the peripheral line of the base. The base is slanted because the most saturated colors are not all of the same brightness (meaning by this term exclusively lightness as opposed to darkness). The saturated yellow is much brighter than the saturated blue and must therefore be located here, symbolically, nearer the point of white than of black, while blue must be located nearer the point of black than of white. The figure shows clearly that it is impossible to deviate from the peculiar brightness of each saturated color without diminishing the saturation, for we cannot move up or down from any point of the peripheral line of the base and yet remain within the double pyramid, without approaching the axis. But if our starting point is a color of less than the maximum of saturation, we may change the brightness within certain limits without changing the saturation, for we may then, to a certain extent, move up and down parallel to the axis.

Some have represented the color system by a double cone, using as common base a circle. But a four-cornered base represents an additional fact of experience which is lost sight of in the circular plane. The four colors red, green, blue, and yellow possess this property: that any one of them is entirely dissimilar in color tone to any of the other three, while any given color other than these must resemble just two of these. No other four or any other number of colors can be found which fulfill exactly these conditions. In order to represent this fact symbolically, we ought to give the colors red, green, blue, and yellow distinguished places in the periphery of the basal plane, and this can be done most easily by choosing as a base a four-cornered plane.

By the aid of this color system it is easy to understand an abnormality of our color sense which occurs rather frequently, so-called color blindness. It is found almost exclusively among men, three per cent of them being affected, whereas it is very rare among women, although it is inherited through woman. Instead of three dimensions, two are sufficient for the representation of the color sensations of such individuals: a plane which is placed through the points white, black, blue, and yellow. The color sensations represented by those points of the pyramid which lie outside the plane just mentioned appear to the color-blind person yellowish if they are located on either side of the yellow triangle, so to speak; they appear bluish if they are located on either side of the blue triangle, and colorless if located exactly on either side of the axis. There are, however, a large number of minor differences not included or even expressed incorrectly in the above brief statement; the color-blind person, for instance, is more likely to see things yellowish than bluish. Since color-blind people may sometimes confuse such conspicuously different colors as red and green, they are often called red-green-blind. That they also confuse greenish blue with violet seems less remarkable to the normal person than the former fact. In testing a color-blind person one must not expect to find that he will confuse any red with any green. Brightness and saturation play here very important parts, and all kinds of individual differences have been observed. Nevertheless color-blind people fail to distinguish red and green much more frequently than people having a normal color sense, and should therefore be strictly excluded from any service in which the distinction of red and green is of importance, as in railway and marine signaling. For the normal person red and green are the ideal colors of signals, because yellow is not always sufficiently different from white, and a saturated blue is too dark.

It is interesting to observe that colors are never simple or complex in the sense in which a musical tone is simple and a chord is a multitude of tones, or lemonade is a mixture of sour and sweet. Any color sensation which is uniform over its area is as simple as any other. The colors which, in our color pyramid, are located between two of the four fundamental colors red, green, blue, and yellow are “mixtures” only in the sense that the mixed color _resembles_ two of those four, not that we are conscious of two separate sensations in one act of perception.

Nevertheless we often have to speak of mixed colors and of principal colors entering into mixtures. These phrases have many different meanings. Most colors which we see in actual life are mixtures in a physical sense, mixtures of ether waves, although our sense organ does not inform us as to whether they are mixtures or homogeneous light. White or gray or purple can never be anything but mixtures in this physical sense. In actual life the only color which is often simple, homogeneous light, is dark red, for physical causes which do not concern us here. But this physical complexity is irrelevant for the psychological question as to the simplicity or complexity of color sensation.

Even more confusion has been carried into the psychology of color by the fact that in dyeing and painting chemical substances are sometimes applied as they occur in nature or come from the factory, sometimes they are first mixed together and then applied. The painter cannot afford to have an infinite number of color pigments on the palette. He selects therefore a small number, at least white, red, yellow, and blue. This is for many ends sufficient, and he may therefore call these pigments his principal colors, and wonder why one should call green a “fundamental” color, since he can produce it by mixing blue and yellow. It is indeed no difficult task to find people who, like Goethe, are convinced that they are able to perceive in the green the yellow and the blue which the painter used in order to give us the impression of green.

Still another difference occurs in the use of the terms simple and mixed colors in physiology, with reference to the processes going on in the eye and the part of the nervous system connected with the eye. It is plain, therefore, that whenever we speak of colors we must state in what sense we do this.

Auditory sensations are usually divided into two classes: tones and noises. They do not often appear separately. A violin tone, for example, is accompanied by some noise, and in the howling of the wind tones may be discerned. Both may be perceived in many different intensities, and both may be said to be low or high. Many thousands of tones may be distinguished from the lowest to the highest audible. Within one octave, in the middle region, more than a thousand can be distinguished. The fact that in music we use only twelve tones within each octave arises from special reasons: first, the difficulty of handling an instrument of too many tones; and especially the fact that with a particular tone only a limited number of others can be melodically or harmonically combined with a pleasing result.

Just as the colors, so the tones are a continuum, that is, one can pass from the lowest to the highest tones without at any moment making a noticeable change. We refer to this continuum by the word pitch. But tones also possess what is called quality; that is, they are either mellow or shrill. This mellowness is to some extent dependent on the pitch of each tone, for low tones are never very shrill and high tones never very mellow. But to some extent a tone may be made more or less shrill and yet retain exactly the same musical value, the same pitch. This is brought about by the overtones, of which a larger or smaller number is nearly always added to musical tones. Without being perceived as separate pitches the overtones influence our consciousness of the mellowness of a tone--the fewer overtones, the mellower; the more overtones, the shriller the tone. Each musical instrument has its characteristic quality of tone, and in some instruments, especially in organ pipes, the quality is skillfully controlled by the builder, who “voices” each pipe so that it produces the required number of overtones of the right intensities.

It was said above that the overtones, as a rule, are not perceived as separate pitches added to the pitch of the fundamental tone. It is not impossible, however, to perceive them thus. Those who experience difficulty in perceiving the overtones as separate pitches may use at first special instruments, resonators, which are held against the ear and greatly increase each the intensity of a special overtone. After some practice one becomes aware of the pitch of an overtone without the aid of a resonator.

Noises may be classified into momentary and lasting noises. Examples of the former are a click and the report of a gun; examples of the latter, the roaring of the sea or the hissing of a cat. Many noises, as thunder, rattle, clatter, and the noises of frying and boiling, are mixtures of momentary and lasting noises.

From all we have said it follows that the function of hearing is an analyzing function, enabling the mind to separate that which has lost its separate existence when it acts upon the tympanum. Two or three tones sounding together are usually perceived as two or three tones. In hearing music we can simultaneously listen to several voices. When two people talk together we may to some extent follow them separately. This is obviously an ability of great importance in animal life, since different objects, characterized by different tones or noises, rarely separate themselves spatially as the colors of different objects do, but act upon the sense organ as a single compound.

There are, however, certain exceptions to the analyzing power of the ear. If two tones differ but little in pitch, they are not perceived as two, but a mean tone is heard beating as frequently in a second as the difference of the vibration rates indicates. The ear thus creates something new, but of course something definitely depending on the external processes. If two tones not quite so close in pitch are sounded, one or even several new tones are created, combination tones or difference tones, the pitch of the new tone being determined by the difference of the rates of vibration. These difference tones do not seem to serve any purpose in animal life. They are merely secondary phenomena, of little practical consequence, but of much interest to the student of the function of the organ of hearing.

We have seen that the number of classes of sensations is fairly large; but to state this number exactly is impossible. According as we count the muscles, the joints, the lungs, the digestive organs as several sense organs or as a single group, the number of classes of sensations is larger or smaller. However, it matters little whether we count them or not. We know that provision is made for everything needed. Information about the most distant things is obtained through the eye; information about the things in contact with the body or the body itself comes through the cutaneous and organic sense organs. Most varied is the information about things at a moderate distance, obtained through eyes, ears, and nose combined.

Many of the higher animals surpass man in one or the other respect through their sensory equipment. Many of the birds (for example, the carrier pigeons) have a sharper eye; dogs and other animals, a keener sense of smell. The sense of hearing in man seems to be equal to that of the higher animals, and the cutaneous sense perhaps superior. In one respect man is better equipped than his mode of living justifies, that is, in possessing the semicircular canals and the otolith organs, for which he has scarcely any use. In another respect he, as well as the animals, is very poorly equipped, that is, for the direct perception of the electromagnetic-optic phenomena of physics, only a small range of which can be perceived as a particular kind of sensations, namely, as colors.

3. _Temporal and Spatial Attributes_

The study of the simple in mental life, as previously mentioned, is always a study of abstractions. The actual experience even of the briefest moment never consists of a single sensation. And actual sensations are always characterized by more than the properties which we have thus far discussed. Colors always occupy space of a certain size and shape; tones come from a certain direction; both colors and tones are either continuous or intermittent, they are perceived simultaneously or in succession. We naturally inquire into the laws of these spatial and temporal relations. Unfortunately psychologists have not yet agreed on a definite answer to the question concerning space and time. The question is beset with difficulties, partly real, partly imaginary.

Is it possible to perceive temporal relations as sensory qualities as we perceive colors, tones, tastes, and smells as sensory qualities? We certainly lack a sense organ of time. But aside from this, it seems impossible to perceive duration at its beginning, when the end is not yet known; impossible to perceive it at the end, when its beginning no longer exists and can only be recalled in memory. It seems equally impossible to get direct knowledge of a spatial relation. Imagine one particular point _a_ of the skin or the retina of the eye. If this is stimulated, our mind receives a definite impression of touch or color, but no indication of or reference to any other point, since no other point is stimulated. Let the same be true for the point _b_. How, then, if _a_ and _b_ are stimulated simultaneously, can the mind receive an impression of distance between the two points, since there is no such consciousness in the perception of either of them? If the mere fact of an objective distance between the stimulated neurons were a sufficient explanation, then tones too should be localized differently.

Those who took these objections seriously tried to think of some means by which the objective, but not directly impressive, spatial relations could become known to the mind. It was suggested that the almost unceasing movements of the eyes and fingers, the chief organs of space perception, might have significance in this connection; that perhaps the kinesthetic sensations of eye and finger movement, being added to the visual or tactual impressions, made up the consciousness of spatial relationship.

All attempts, however, to prove the correctness of this and similar theories by applying them to the details of special experience, have failed. While there is no doubt that movements of our eyes and fingers are of great importance for the development and extension of the spatial consciousness in the individual as well as in the race, they are not the source from which springs the individual’s ability to perceive spatial relationship. The fundamental part of our ability of _spatial_ perception is inborn, just as our ability to perceive light or blueness or cold is inborn. From this inborn capacity for spatial perception the individual’s delicate and elaborate sense of space is derived.

The most convincing proof that there is an innate capacity for spatial perception, is the spatial consciousness of persons born blind, to whom an operation has given eyesight. The crystalline lenses of these persons have been as little transparent as ground glass, so that they have been unable to recognize any outlines of things. Nevertheless, they make spatial distinctions immediately after the operation for removal of the lens. Of course they cannot, without further experience, tell that a round thing is the ball with which they have been familiar through the sense of touch, or a long and narrow thing a walking stick. But they immediately perceive the round thing as something different from the long and narrow thing, without any tendency to confuse them. Spatial extent is therefore an attribute of visual and tactual sensation as brightness or darkness is an attribute of visual sensation, and mellowness or shrillness an attribute of tone; with this difference only, that spatial extent is not restricted to one sense, but is common to visual and cutaneous sensations. That this is founded on some kind of similarity of these senses cannot be doubted. But this similarity is to be looked for in structural peculiarities of the nerve centers, not in accessory mental states serving as special agents of spatial consciousness.

Very much the same is the case with time. Let us admit that the temporal consciousness of our ordinary life is largely mediated by accessory sensations and images. Minutes, hours, days, weeks, are not experienced directly as properties of sense perception, but are extensions of simpler experiences. But such extensions would be impossible if duration and succession were not, somewhere in our mental life, direct experiences. They are direct experiences in some very brief temporal perceptions occupying, say, only a fraction of a second. The flash of a lighthouse signal, the quick succession of sounds when a person knocks at a door, are perceived as having temporal attributes without any mediation by conscious states acting as agents. The _temporal_ attributes are elements of perception no less direct than the intensity of the light or of the sound. The same holds for all other sensations. Time is an attribute common to all. But here, as in space, we cannot tell exactly in what respect all senses are similar so far as the nervous processes are concerned. It seems that these processes or their after effects continue a certain time after the stimulation has ceased.

Another attribute common to all sense impressions is the belonging-together of sensations, the _unity in variety_, so to speak. The most striking example is the relationship of tones in harmony and melody. Tones of certain comparatively simple ratios of vibration belong together in a higher degree than others. We cannot explain this by reference to conscious agents mediating the effect. It is a fundamental attribute of each tonal combination, the conscious effect of our inherited nature. It is a property of sense, not of thought.

In other cases our consciousness of relationship is indirect, mediated by other conscious agents; for instance, when I group together voluntarily four or five adjoining holes of a sieve and perceive them as a unit. This grouping together would be impossible if the mind did not possess the native ability to perceive a number of sensational elements as a unit without altogether losing the consciousness of variety. It is a mere consequence of our inborn nature when we perceive as such units, for example, an animal romping among unchanging surroundings, a picket fence divided into groups by the fence posts, a familiar compound perfume, a dish made up of several familiar food substances. The same holds for successive elements. We could never perceive tones or noises in various rhythm forms if our mind did not possess the native ability to perceive a number of successive elements of sensation under certain conditions as a sensory unit.

Our numerical concepts are obviously only abstract symbols for units containing each a certain variety of elements.

4. _Sensation and Stimulus_

It is most interesting to observe the astonishing _absolute sensitiveness_ of some of our senses, that is, their ability to respond to exceedingly small stimuli. It has been a difficult task to design physical instruments as sensitive to sound as the ear. It has not been possible, thus far, to surpass the ear. The sensitiveness of the eye to the faintest light is estimated to be a hundred times that of the most sensitive photographic plates. Remember what a long exposure is necessary to photograph things in a rather dark room; but the eye takes a snap shot, so to speak, of a star of the fifth magnitude, or of a landscape in diffused moonlight. Man’s organ of smell is far inferior to that of many animals. Nevertheless a trace of tobacco smoke or musk in the air whose presence no chemist could detect is easily perceived through the nose. A gram is about one twenty-eighth of an ounce; a milligram is one thousandth of a gram. One millionth of a milligram of an odorous substance is sufficient to affect the organ of smell. Taste also is sensitive, particularly when supported, as in tasting wine or tea, by smell. The cutaneous and kinesthetic senses, on the other hand, are not very sensitive. A weak pressure, a small weight, a slight tremor of our limbs, a spatial extent, can be detected much more readily by delicate instruments than by our fingers or our kinesthetic organs.

Very important is the range of perceptibility. Our measuring laboratory instruments are, as a rule, adapted only to a small range. To weigh a heavy thing, like a stack of hay, we have to use a balance differing from that used by the prescription druggist. The watchmaker’s tools are much like those of the machinist, but neither could use the other’s tools. Nature cannot well provide separate sets of tools for delicate and gross work. With our hand we estimate the weight of ounces, pounds, and hundredweights. The same ear which perceives a falling leaf can be exposed to the thunder of cannon without ceasing to respond in its normal way. The eye which perceives a small fraction of the light of a firefly, can look at the sun somewhat covered by mist, radiating light many million times as intense. No laboratory instrument has an equal range of applicability.

This wide range of usefulness is made possible partly by purely mechanical provisions, partly by a special law of nervous activity usually called Weber’s law. The iris of the eye with pupil in the center is a readily changeable diaphragm. The stronger the external light, the smaller the pupil, and the reverse; so that the eye is capable of functioning at a stronger and also at a fainter illumination than it could function if the width of the pupil were of a medium, unchangeable diameter. The nose can smell faint odors better if larger quantities of the odorous substances are by sniffing brought into contact with the organ. Too strong odors are kept away by blowing out the air.

More important, however, than such mechanical devices is the effect of Weber’s law. If a stimulus is increased, the nervous excitation is also increased,--not absolutely, but only relatively to the stimulus before the increase. Suppose an oil lamp of ten candle power needs an addition of a two candle power light to make me observe that the illumination has changed. Nevertheless I shall not be able to observe a change of illumination if to an incandescent gas light of sixty candles two candles are added. The addition must be in proportion to the stimulus. Since sixty is six times ten and twelve is six times two, twelve candles must be added to make me observe the difference in illumination. To an arc light of two thousand candles four hundred have to be added to obtain the same result. If a postal clerk is able to recognize that a letter which he weighs on his hand and which is one twentieth heavier than an ounce, requires more than the one postage stamp attached to it, he will probably be found capable of observing in the same manner that a package of newspapers prepaid for one pound does not have the correct number of stamps if it is actually one twentieth heavier than a pound.

Another way of speaking of the law is this: If we imagine a definite stimulus successively increased by such amounts that the change of the sensation is each time just as noticeable as it was the last time, the added amounts of the stimulus are a _geometrical progression_. Let us express the fact that the change of the sensation can always be noticed _with the same ease_, by saying that the additions to the sensation are an arithmetical progression. We can then state Weber’s law in these simple words: If the sensation is to increase in arithmetical progression, the stimulus must increase in geometrical progression. This statement is mathematically identical with the most widely adopted statement of the law, namely, that _the sensation is proportional to the logarithm of the stimulus_.

The practical result of the law in our mental life is this: The mind is informed of a further increase in the intensity of the stimulus (however great this intensity may have become before this last increase) without having to respond to the absolute intensity of the stimulus with a correspondingly enormous activity of the animal organism. Thus the mind is enabled, figuratively speaking, to weigh a stack of hay or a druggist’s herb on the same balance, to apply the same tool to a watch or to a railroad locomotive, or at least to perform its work with a much smaller number of tools than would otherwise be required. In the eye, for instance, we have, as we see below, only two different kinds of receiving instruments for faint and for strong light.

It must be mentioned, however, that Weber’s law does not hold good over an unlimited range of intensities of stimulation. If the sun were twice as bright, it would not appear brighter to the eye. For such extreme intensities the law is no longer valid. Neither is it valid for exceedingly low intensities; it makes no difference to the eye whether the wall of a dark room is illuminated from a distance of three or four yards by the glow of one cigarette or a dozen. The logarithmic equation applies only to a certain--quite large--range of medium intensities. For this range our sensitiveness to change is not only constant, but also greatest. Changes in illumination within this range can be perceived as soon as the stimulus increases or decreases by about one hundred and fiftieth.

Weber’s law has still another practical significance. A thing which we recognize by the aid of the differences in illumination of its parts (as, for example, a stone relief) or by its differences in loudness (as a rhythm beaten on a drum) always retains, not the same absolute differences, but the same quotients or proportions of the different light or tone values, however our distance from the thing varies. Weber’s law, then, enables us to perceive the identity of the thing although the absolute light or tone values have undergone change. If our nervous activities were not regulated in accordance with Weber’s law, the relief and the rhythm might become unrecognizable at a greater distance, and the relief also at dusk.

A further important relation between our mental life and the external world consists in our much greater sensitiveness to the moving and changing than to the stable and permanent. A pencil point moved over the skin under slight pressure gives us a perception of the length and direction of the line traversed more accurate than the impression received from the edge of a screwdriver pressed on the skin. On the peripheral parts of the retina the sizes and distances of things are not easily perceived; but no difficulty is experienced in noticing a waving handkerchief or a starting animal. Only the small central part of the retina is adapted to the perception of the motionless.

The same statement holds for qualitative changes. The eye is not only more sensitive to that which qualitatively changes than to that which remains unchanged; it even loses its ability to perceive things if for a considerable time no qualitative changes occur. We have seen that our eye can take snap shots under conditions which would make this impossible for the photographic camera. But for time exposures, like those used in photographing faint stars, continued for hours, our eye is not suited. The eye, in such a case, would soon cease to distinguish anything. The eye completely fixed upon one set of objects soon sees their lighter parts darker, their darker parts lighter, their colored parts less colored--more grayish--that is, it sees everything gray on gray. This is technically called adaptation of the eye. Moving the eye suddenly, we become aware of this adaptation in peculiar after-images.

Similar adaptations occur in other sense organs. Constant pressure on the skin, unchanging temperature of not extreme degree, permanent odors, cease to be perceived. But what is new, what differs from the condition which was in existence just before, is perceived at once; and because of the sense organ’s adaptation for something else, as a rule it is seen with particular intensity. This is obviously the most favorable equipment for a struggle for life. Nothing is more dangerous in battle than surprise.

Our present knowledge of the mechanical, chemical, and physiological laws governing the peculiar dependence of the different kinds of sensations on special properties of the sense organs--that which is customarily called a theory of vision, a theory of audition, and so on, is rather unsatisfactory. Some thirty years ago much seemed to be perfectly explained which has since become mysterious again. This much has been learned, that the laws in question are far more complex than they were believed to be.

Only one statement about eyesight can here be made without fear of contradiction, that is, that the eye is a double instrument, one part of the organ serving in daylight, the other at dusk and in twilight. But this explains only a part of the total function of the eye. The retina of the eye consists of a great number of elements called rods and cones, forming a kind of mosaic. Twilight vision is served by the rods, which contain a sensitive substance called the visual purple. Most of the rods are in the peripheral parts of the retina, becoming less numerous toward the center. In the central area there are no rods at all. The only service of the rods is the mediation of a weak bluish-white sensation of various intensities, as in a moonlit landscape. Ordinary day vision is served by the cones, which are the only elements present in the center and become rare towards the periphery. All the variety of our color perception depends on the cones. In very faint illumination the colors of things cannot be perceived, although the things may still be distinguished from other objects. The rods alone are functioning then; the cones have “struck work.” Neither can the shape of things be perceived in dim light with normal definiteness, because the area of most distinct vision, the central area, contains only cones; reading, for instance, is impossible at twilight. The astronomer, in order to observe a very faint star, must intentionally look at a point beside the star, because of the lack of rods in the central area.

While the human eye normally possesses both rods and cones, certain species of animals have only one or the other kind of visual elements. Chickens and snakes possess only cones. This is the reason why chickens go to roost so promptly when the sun sets. Night animals, on the other hand, have mostly rods and few cones. This explains why bats come out only after sunset. In very rare cases human beings seem to possess only the rods, in cases of total color-blindness. The whole world appears colorless to them, only in shades of gray. They dislike greatly to be in brilliantly lighted places. They lack the keenness of normal eyesight because of the deficient function of the central area of the retina, which is normally best equipped.

A mechanical theory of hearing was worked out by Helmholtz nearly fifty years ago. This theory was at first generally accepted, but has in recent years lost much of its plausibility. The inner ear is a tube coiled up in the shape of a snailshell in order to find a better place in the lower part of the skull. Its coiling, of course, has little if any mechanical significance. The tube is divided into two parallel tubes by a kind of ribbon, the organ of Corti, containing the endings of the auditory neurons and also a comparatively tough membrane. Helmholtz made the hypothesis that the cross fibers of this membrane were under constant tension like the strings of a piano. The comparison with a piano was also suggested by the fact that the membrane in question tapers like the sounding board of a grand piano. As the piano resounds any tone or vowel, so this system of strings would resound any complex sound; that is, each of the tones contained in the complex would be responded to by those fibers whose tension, length, and weight determine a corresponding frequency of vibration. The analyzing power of the ear is well explained by this hypothesis, but there are considerable difficulties left. For instance, the fibers of the membrane, even the longest, are rather short for the low tones to which they are assumed to be tuned. And for the assumption of a constant tension of these fibers there is no analogon in the whole realm of biology, since living tissues always, sooner or later, adapt themselves and thus lose their tension.

Another theory avoids these difficulties by merely assuming that the ribbon-like partition of the tube, when pushed by the fluid, moves out of its normal position only to a slight extent and then resists, and that therefore the displacement of the partition must proceed along the tube. If successive waves of greater and lesser amplitude, as we find them in every compound sound, act upon the tympanum and indirectly upon the fluid in the tube, the displacement of the partition must proceed along the tube now farther, now less far, now again to another distance, and so on. Accordingly, one section of the partition is displaced more frequently, another section less frequently, others with still different frequencies in the same unit of time. This theory then makes the hypothesis that the frequency with which each section of the partition is jerked back and forth determines the pitch of a tone heard, and explains thus the analyzing power of the ear. What is chiefly needed in order to decide in favor of either of these or any other theory is a large increase in our knowledge through anatomical, physiological, and psychological investigation.

QUESTIONS

46. What are the newly discovered kinds of sensations?

47. How were they discovered?

48. What are the cutaneous senses?

49. What is the objection to speaking of the cutaneous sense as one?

50. What is pain?

51. Of what importance are the labyrinth senses (other than hearing) to man and various animals?

52. What is meant by organic sensations?

53. What are the four tastes?

54. How does the sense of smell in man compare with that of animals?

55. Why is the color pyramid superior to the color cone?

56. What are the chief symptoms of defective color vision?

57. What is not meant, and what is meant, by color mixtures?

58. Why does music use only twelve tones?

59. What is meant by the qualities of the tones of various instruments?

60. Are there any limits to the analyzing power of the ear?

61. What is the exact number of classes of sensations?

62. How does the sensory equipment of man compare with that of the animals?

63. What do we learn from experiments on blind-born persons who have been operated on?

64. In what experiences is time an attribute of sense perception?

65. Is tone relationship a property of sense or of thought?

66. Can you illustrate the absolute sensitivity of our sense organs?

67. How does the range of applicability of our sense organs compare with that of tools and instruments?

68. Can you illustrate Weber’s law?

69. What are the practical advantages obtained through Weber’s law?

70. Illustrate sensitiveness to change and movement.

71. How is the chief difference in the behavior of chickens and bats to be explained?

§ 5. IMAGINATION

Mind is influenced not only by that which is present, but also by the past and--one may say--the future, and by that which exists at another place. Consciousness of this kind is called imagery. I imagine a lion and recognize that he looks different from a horse. I recall the room in a hotel where I have recently spent a night and see that it differs from my study.

Imagery does not differ in content from percepts. There are as many kinds of images as there are sensations, and their attributes are the same. Imagination differs from perception only through its independence of external conditions in the formation of new combinations out of the sensory elements which have previously been experienced. Although the kinds of content of imagery do not differ from those of perception, imagery differs from perception, as a rule, in such a characteristic manner that in ordinary life we are not likely to mistake an image for a percept or a percept for an image. The imagined sun lacks brilliancy. Its imagined heat does not burn. A glowing match, perceived, surpasses those images. Only in childhood, in dreams, and in particular individuals (artists, for example), and under particular circumstances (like the imaginative supplementing of that of which only parts have stimulated the sense organ) can imagery come near being compared and confused with percepts. Generally the difference in _vividness_ remains great. A second difference is the lack of _details_ of images. As a rule only a few parts of a rich complex of sensations reappear when an image takes the place of the original percept. And the selection of these details is usually most grotesque. A third characteristic of images is their _instability_, fleetingness. Compared with the persistence of a percept, an image can scarcely be said to have any definite make-up since its composition changes from moment to moment. Images come and go in spite of our desire to keep them. They change like kaleidoscopic figures.

All this has its disadvantages; but also its great advantages. Being at once pictures and mere abbreviations or symbols of things, images aid effectively in our handling of things. If they were exactly like percepts, they would deceive us, as hallucinations do. Their very lack of details and their fleetingness enable our mind to grasp a greater multitude of things, to adjust itself more quickly and more comprehensively to its surroundings.

Independence of external causes and frequent recurrence from internal causes give to our imagery the character of a permanent possession of the mind. Not every part of this imagery is actually made use of, since these parts are too numerous, but every part is always available for use. This leads to the question as to the nature of the images while mind is not conscious of them, particularly the nature of their nervous correlate. Ever since the discovery of ganglion cells and nerve fibers the naïve conception has readily offered itself that every idea has its residence in a little group of cells, the idea of a dog in one, the idea of a tree in another, and so on. Some have calculated the number of cortical cells which would be necessary in order to provide a sufficient number of residences for all the ideas acquired by a human being during a long life. They have found that the cortical cells are numerous enough.

But the matter is not quite so simple. Our ideas, being made up of many mental elements, overlap. If the idea of a dog has its residence here, the idea of a lion its residence there, where, then, do we find the idea of a carnivore, the idea of another kind of dog, the ideas of the individual dogs known by me, the ideas of other carnivora, the idea of a mammal, of a vertebrate, of an animal in general? These ideas are interwoven in such manifold ways that it is difficult to assume that each should have its separate residence in the brain. It is still more difficult to apply this theory to the idea of barking, which can be imitated by man, being natural to a dog; or to the idea of white, which belongs to some dogs, but also to the clouds, the snow, the lily.

There are also anatomical difficulties. I look first at a dog, then at a goat. The elements of the retina which are stimulated are largely the same in both cases. This makes it difficult to understand why the nervous processes in the former case should all concentrate in one point of the cortex and in the latter case in an entirely different point. Or I hear the word _boxwood_ and later the word _woodbox_. The anatomical difficulty is the same.

The nervous correlates of ideas are obviously much more complicated than the theory of location in cell groups assumes. There can be no doubt that the nervous correlate of an idea, even of an elementary image, is a process going on in a large number of connecting neurons in the higher nerve centers, often widely distributed, like the meshes of a net. The individual neurons in question do not belong exclusively to this one idea, but, entering into numerous other combinations with other neurons, belong to numerous ideas. The nervous correlate of a latent idea, which is not conscious but ready to enter consciousness at any time, is not a material substance stored away somewhere, but a disposition on the part of neurons which have previously functioned together, to function again in the same order and connection.

QUESTIONS

72. In what respects do images not differ from percepts?

73. In what three respects are images as a rule distinguishable from percepts?

74. What are the advantages of the characteristics of images?

75. What is the nervous correlate of imagery?

76. What is the nervous correlate of a latent idea?

§ 6. FEELING

Sensations and their images are closely related mental states. They are of the same kind. As a third class of elementary mental states the feelings of pleasantness and unpleasantness are customarily added. But it would probably be more correct to say that these feelings are mental states of an altogether different kind, in comparison with which the distinction between sensations and images disappears. Pleasantness and unpleasantness never occur apart from sensation or imagery, whereas the latter states of consciousness may be free from any pleasantness or unpleasantness. The pleasantness which I experience is always the pleasantness of something--of the taste of a peach, or of my good health, or of a message received. However, we must not conceive this dependence of pleasantness and unpleasantness as similar to the dependence of color or pitch or spatial extent or duration on the thing to which these belong as its qualities. Color, pitch, and these other qualities are essentially determined by objective conditions, the physical properties of the thing in question. But pleasantness or unpleasantness is only to a slight extent, if at all, determined by objective conditions. Honey tastes very much the same whenever we eat it. A tune sounds very much the same whenever we hear it. But these sensory experiences are, in consequence of subjective conditions, now highly pleasant, now almost indifferent, now decidedly unpleasant.

The same colors and straight lines may be combined into a beautiful design or into an ugly one, the same descriptions of scenery and events into an attractive or a tedious book. A feeling which is already in existence may prevent the growth of an opposite feeling. On a rainy day we are likely to feel as if everything in the world were gray; on a sunny spring day as if everything were rosy. The grief-stricken or desperate person experiences a given situation with other feelings than the person full of joy or hope. A particularly strong factor in our life of feeling is the frequency of recurrence of a situation. The most beautiful music suffers from being played at every concert and on every street, the most delicious dish from being put on the table every day. On the other hand, a bitter medicine gradually loses its unpleasantness, an unpleasant situation becomes indifferent to a person whose profession compels him to face it frequently. As the unchanging is at a disadvantage in our life of perception, so is the recurrent in our life of feeling.

The subjective factor which determines what feelings accompany our perceptions may be defined as the relation of the situation perceived to the weal and woe of the organism. Pleasantness indicates that the impressions made upon the organism are adapted to the needs or capacities of the organism or at least to that part of the organism which is directly affected; unpleasantness indicates that the impressions are ill adapted or harmful. Exceptions to this rule may be explained through the great complexity of the situations by which the organism is often confronted, and through the complications resulting from the fact that the organism must adjust its activity not only to the present but also to the future, and not only in harmony with the present but also with past experience. Feeling is a reliable symptom and witness only for the present and local utility or inadequacy of the relation between the organism and the world. It is not a prophet of the future. Disease may result from eating sweets, whereas medicine is often bitter.

The addition of feeling to our perceptions and images, because of the peculiarities just mentioned, brings about great complications in the make-up of our mental states and increases enormously the task of classifying and comprehending our states of consciousness. The feelings accompanying images are originally the same as those which accompanied the perceptions in question. The memory image of the pain of flogging is unpleasant because the original pain was unpleasant. But the manifold connections of the images often result in unexpected feelings. The memory of an unpleasant experience may become a source of pleasure through the additional thought that the experience was the result of some folly of which one is no longer capable. The feeling accompanying a perception can change in a similar manner. A saturated green, as the color of a pasture or of an ornament, is pleasant; as the color of a girl’s cheek it would be highly unpleasant.

Not only are perceptions and images themselves sources of pleasantness and unpleasantness, but also their relations, spatial, temporal, and conceptual. The pleasure which we derive from looking at a picture or a landscape illustrates the dependence on spatial relations. The pleasure of a symphony or dramatic performance depends largely on temporal relations. Jokes and puzzles please us chiefly because of their conceptual, logical relations. It is plain, then, that every complex of sensations, supplemented by a large number of images, must become a stage, so to speak, on which countless scores of feelings play their parts. In so far as their perceptual and ideational bases may be kept apart, we may count as many of these feelings as we distinguish percepts or ideas. In so far as all these feelings are either pleasantness or unpleasantness, we may speak of the feelings as being only two in number. This may explain to us why such mental states as love, pride, sentimentality, the joy of the audience in a theater, the interest of the reader of a biography, appear at once simple enough, unitary enough, and yet inexhaustibly replete with contents and difficult of comprehension. This also explains the opposite views of so many writers, of whom some assert that the number of feelings is infinitely large, others that there are only two, pleasantness and unpleasantness, which may accompany an infinite number of sensation complexes. The difference between these writers is much less than appears from their words.

QUESTIONS

77. How are pleasantness and unpleasantness related to sensational states of consciousness?

78. How are pleasantness and unpleasantness related to objective conditions?

79. How does the repetition of an experience influence its pleasantness or unpleasantness?

80. What is the general subjective condition of pleasantness and unpleasantness?

81. Is feeling a prophet of the future?

82. What difficulties does the existence of feeling cause the psychologist?

83. Are there more than two feelings?

§ 7. WILLING

Willing is usually mentioned as being a distinct class of mental states. However, willing is not a special class in the sense in which perceptions, images, and feelings are called classes. To understand willing, let us consider certain typical actions of an infant which are based on inborn nervous connections. What do we mean by the feeding instinct? We mean unpleasant sensations of hunger and thirst followed by various movements of arms and legs, of crying, of sucking, until the unpleasantness of the situation ceases. The movements themselves are nothing mental. But while they are occurring they become known as kinesthetic sensations, partly also as visual or auditory sensations. Two classes of sensations may therefore be distinguished in any instinctive activity: those which correspond to the sensory phase of the reflexes in question, and those which result from the reflex movements. After frequent occurrence of these reflex movements, images of various parts of the whole satisfying process remain, and these, or some of them, become conscious even before any of the movements occur. For example, as soon as hunger is experienced the infant has also an image of the bottle, of the mother bringing it, of his own movements of grasping, sucking, and so on. The instinctive act has then been replaced by an act of will. _Willing, therefore, may be defined as instinct which foresees its end._

No new kind of mental state can be discovered in willing. There is nothing but sensations, feelings of pleasantness-unpleasantness, and images. If we give to such a combination of these three kinds of mental states the name of willing, we justify this new name by the fact that such combinations are the most original, the earliest conscious states which have occurred in our mental life. The first consciousness accompanies instinctive activity, and immediately a simple form of willing is made possible. From the genetic point of view, that is, if we are interested in the growth of our consciousness, willing is the most elementary form of consciousness. Perceptions, images, and feelings did not exist separately for some months or years to become afterwards united into willing. Willing was there when consciousness first awoke. On the other hand, if we are interested in describing the make-up of our present mental life,--that is, from the point of view of the psychologist searching for concepts of mental states,--sensations, images, and feelings are the most elementary forms of consciousness.

There is no will in the sense of a simple faculty, always remaining identical with itself, merely changing its direction and now applying itself to this thing, now to that thing. Will is an abstract word, referring to that which is common to all states of willing; but, like all abstractions, it does not possess any real existence apart from the realities from which it has been abstracted, that is, from the particular cases of willing occurring in each person’s life. Of course, there is no objection to using the abstract word _will_ without explaining each time that it is an abstraction. We need not hesitate to refer to typical differences between the cases of willing most frequently observed in one person and those observed in another by saying that one has a strong will, the other a weak, a vacillating will.

QUESTIONS

84. How may willing be defined?

85. Is willing an elementary kind of consciousness?

86. Why is it wrong to answer the preceding question simply by yes or no?

87. What is the will?

_B. THE FUNDAMENTAL LAWS OF MENTAL LIFE_

§ 8. ATTENTION

A ship, under the influence of several forces--the screw, the wind, the current--follows all of them simultaneously, and the place which it reaches after a certain time is the same as that which it would have reached if these forces had acted, each for the same length of time, but one after the other. External things, whenever they are under the influence of several forces, are governed by the law of the resultant. The mind’s mode of response is entirely different. When there are many things to see, as a crowd of actors on the stage, many things to hear, as a chorus and orchestra, and in addition some whispered words of our neighbor, the result is by no means the same as if all these impressions acted upon our mind successively. If time enough is given, our mind will successively respond to each of these impressions of sight and hearing. But if the response must occur quickly and be done with, it is restricted to a part of the impressions made by the external objects. A few of these impressions, specially favored by circumstances, affect our consciousness at the expense of the others. The latter are not entirely lost for our mind; but they fail to call forth separate responses, they fuse into a mere background upon which the favored impressions make their appearance. They are often spoken of as the fringe of the clearly conscious mental states.

One might call this selective effect the narrowness or focalness of consciousness; in ordinary life it is called attention. We say that attention is given to certain contents, and that the others are not attended to, that they are under the influence of inattention. There is no similar phenomenon in the whole inorganic world. In our mental life nothing is more ordinary. I look up and notice many things. But many more are projected upon my retina without succeeding in becoming noticed. When reading a book I cannot accomplish everything that I wish I could. Giving attention to the meaning, I fail to become conscious of the beauty of style. Looking for typographical errors, I fail to understand the logical connection of the sentences. For each purpose a new reading is necessary. Mental work requires the exclusion of piano music and crying babies. Thinking is not so easy while we are performing a gymnastic feat or walking at a rapid gait. When we are listening to difficult music, we shut our eyes. When a momentous question, a dangerous task, presents itself, we are in danger of losing our head; that is, being occupied by ideas of the magnitude of the event, we fail to become conscious of thoughts and memories of the simplest and most ordinary kind.

The popular view of attention is that it is an independent being, separate from the contents of the mind. Attention stands at the helm, and as the mind desires these or those contents, attention changes the ship’s course. This, of course, is pure mythology. The enhancement and impairment of impressions to which we refer in speaking of attention and inattention are not a peculiar activity of mind; they are simply the effects of peculiar relations existing between the impressions themselves. A few of these relations may be briefly discussed.

Whatever situation is capable of being a source of pleasantness or unpleasantness, is also likely to become enhanced in vividness, so that one may say that the value of an impression for our life of feeling is one of the factors determining attention. Any remark of a person near by, although merely whispered and hardly perceived by others, quickly rises to a high degree of consciousness in my mind if it concerns my reputation. That which we have experienced frequently, no longer causes much pleasantness or unpleasantness; and in accordance with this, it is not likely to be attended to.

This parallelism between feeling and attention is expressed in the word _interest_. We are interested in those things which conform to our habits of thinking. Because of this conformity they are useful to us at the present moment of our life, and therefore pleasant. Because of this conformity with our habits they become vividly conscious--they are attended to. What is unrelated to our habits of thinking is not useful to us at the moment and is therefore indifferent; and being unrelated, it attracts no attention. Everybody knows how readily the average member of a political party assents to the assertions made by the party leader, how readily the adherent of a religious faith accepts instances proving its correctness, how he unintentionally ignores anything which he cannot accept without opposition or discomfort.

Another factor determining attention is the relation of a new impression to the thoughts occupying the mind at the moment when the impression was made. That which is conscious prepares the path over which everything related may enter. Ordinarily the ticking of a clock remains unnoticed. But let the person think of the clock, or of time, and the next tick is clearly perceived. In order to notice a weak tone in a complicated chord, or a melody in polyphonic music, it is well to hear the tone or the melody first in isolation and try to keep it in mind until the chord or the music is played. A slight difference in the color of two leaves remains unnoticed; but if we are thinking of a color difference just before the leaves are shown to us, it becomes at once vivid in our consciousness. The puzzle pictures common in certain popular magazines would never convey the intended meaning to us, if we were not invited by the text to think of various things which they might represent. If we know beforehand in what order a lecturer will present his arguments to us, we can pay attention to the lecture much more easily and understand it better.

Attention is usually accompanied by numerous instinctive muscular activities, which contribute toward the continuation and toward a greater distinctness or intensity of the impression. When our visual organs are stimulated, the head and the eyes turn so that the impression may be received at the point of keenest vision. If the ear is stimulated, the head turns so that both ears assume the most favorable position with respect to the source of sound. When images occupy the mind, the eyes are directed at an indifferent, uninteresting object, or they are closed, the lips are pressed together, the limbs assume a position of rest. All this tends to keep away avoidable stimulation of the sense organs of the body. These instinctive movements are, of course, perceived as kinesthetic sensations, as varied forms of strain, of activity. Thus they give rise to the erroneous view that attention is a peculiar activity of the mind’s own content. This view is most emphatically expressed in the phrase “voluntary attention.” It often happens that we become conscious of the muscular adaptation characteristic of attention before the mental state to which attention is given has appeared. For example, we see lightning and at once imagine the thunder and the muscular adaptions of the ear and other parts of the body which generally occur when it thunders. Or we hear our teacher’s voice telling us that he will give an explanation, and we imagine the strain, the activity of our muscles, which begins as soon as he starts giving the explanation. This foreseeing of our activities we have above called willing. _The foreseeing of our attention is the will to give attention, is voluntary attention._

It is a peculiar fact that vividness of a certain thought or even a class of thoughts is never much prolonged. Other impressions or ideas take the place of those which are now focal. Under the most favorable conditions, the same ideas reappear again and again. This limited duration of attention is most conspicuous in children and is one of the greatest obstacles which the teacher has to overcome. Repeated orders to be attentive are of small value. They tend to call up a general notion of the matter which is being taught, and thus make it easier for the ideas presented by the teacher to enter consciousness. But the effect is not lasting because the very thought of being attentive cannot itself have a long duration. It is therefore preferable to take into account the nature of attending, and in accordance with it, to provide a certain change in the ideas presented--to present the matter in an interesting way.

QUESTIONS

88. What essential difference between mental function and mechanical function is referred to by the word _attention_?

89. Can you illustrate the chief facts of attention and inattention?

90. Can you illustrate the parallelism between the laws of feeling and of attention?

91. How is attention mentally prepared for?

92. How is attention assisted by special muscular activity?

93. What causes the illusion that attention is a voluntary activity of the mind upon its contents?

94. What practical problems are connected with the law of the duration of attention?

§ 9. MEMORY

While attention means limitation, memory means expansion. From the enormous number of impressions calling simultaneously for response, the mind selects a small group of those related to its present needs. But the mind may go beyond the limits of that which is presented and respond to impressions of a former time. We then speak of memory. When I hear the first verse of a poem which I have previously heard or read more than once, I continue to hear, in imagination, the following verses although the reader has stopped. When I see a black cloud drawing over the sky and the trees bowing under the pressure of the wind, I know that a thunderstorm is approaching. When I smell carbolic acid or iodoform, I look for a person wearing a bandage. In every case the mind tends toward expansion beyond the limits of the data presented at the moment. The mind thus restores the connections in which the accidentally isolated object of present interest has been experienced with other objects in the past.

We refer to this ability of expansion by the term _memory_, to the actual process of expansion by _reproduction_ or _association_. The immense importance of memory for life is easily understood. Nature repeats itself--not without some variations of the accompanying phenomena; but no group of phenomena, aside from such variations, fails to recur at frequent intervals. In reproducing what previously existed under similar conditions, our mind possesses, as a rule, a real knowledge of what now exists but happens to remain hidden, and of what is about to occur. Thus our mind adapts itself to those parts of the world which are for spatial or temporal reasons beyond the reach of our sense organs.

A special case of reproduction deserves to be mentioned because of its frequency of application. Two things may possess one common part while completely differing in other parts: for example, two words that rhyme, or a photograph and an oil portrait, or either of these and the face of the original. Let us call the parts of one thing _abcd_, those of another _cdef_. It easily happens that by mediation of the common parts, _cd_, the train of thought is carried from _ab_ to _ef_. Thus we may say that our train of thought is determined, not only by simultaneity of previous experience, which is often quite fortuitous, but also by similarity, by essential connection, by relationship.

The possibilities of reproduction are, of course, very numerous in each case of experience. At present I see before me some books of reference, on the hill at a distance a house partly hidden by trees, and many other things. All these have previously been in my mind, each in various temporal or essential connections with other things. An immense number of images might therefore be reproduced now in my mind. That as a matter of fact I do not become conscious of all of them needs no further explanation. It has been spoken of before when we discussed the limitation, the focalness of consciousness, that is, attention. We have also stated some of the rules determining the selection among these many possibilities. Let us here state these rules more definitely.

Whatever tends to bring about strong feeling, also tends to be reproduced. A brilliant success, but also a humiliating defeat, are not easily forgotten. They are always lying in ambush, so to speak, ready for the least opportunity. As in attention, so here even more, pleasant thoughts show this tendency more strongly than unpleasant ones. What is unpleasant is soon repressed. This is illustrated by such facts as the healing power of time, the painting of the future in glowing colors, the unfailing belief that advancing age has in the good old time.

A second law governing reproduction may be called the set of the mind. When a railway train enters a large station, there are many paths over which it might pass; but its actual path depends on the position which was given to the switches immediately before the train’s arrival. In a similar manner the path taken by the mind depends on the set established just a few seconds or minutes before by the contents of the mind. If during a conversation in English a French word is unexpectedly pronounced by some one, the other people, though perfectly familiar with the French language, may fail to understand it. The French sounds are unexpected--the track is there, but the switch is not properly set--and consequently the sounds remain ineffective. A certain book seen on my desk calls up associated ideas very different from those which are produced when I see it in the bookstore. The same thought leads to one conclusion in the dark or in a dream, to another conclusion in daylight or in the waking state. Every student is familiar with the difficulty of becoming conscious of the right kind of ideas after having just gone from one recitation room to another. After a few minutes the new set of the mind is established, and the difficulty has disappeared.

Many other factors are to be mentioned as influencing the train of thought. During the last decades many experimental investigations have been devoted, with much success, to their exact determination. Numerous methods have been used, some being only slight modifications of the conditions under which ideas are reproduced in ordinary life, others being more artificial in order to yield answers to special questions to which the other methods are not applicable. The common involuntary reproduction of ideas by words or pictures shown has been used in order to determine how this reproduction varies with different individuals under different circumstances, how much time it requires, and so on. Voluntary reproduction of impressions that have just been made (as used in school in dictation) has been used by presenting, optically or through speech, words, syllables, numbers, or pictures and telling the subject to write down everything remembered. The quantity of the matter retained, and the number and kind of errors, then permit many important conclusions. Also whole poems or pieces of prose have been memorized, and answers have been found to questions as to the length of time necessary for such memorizing under different conditions, and the number of additional repetitions needed to make the material learned available again after a greater number of days or weeks. The acquisition of the vocabulary of a foreign language or of a set of historical dates has been developed into a special method of hitting or missing. The material to be learned has been presented in pairs, and the number of pairs has been counted of which one element causes the mental reproduction of the other. By all these methods psychologists have definitely secured many rules which had been derived from earlier, less reliable experiences. Many new facts have also been discovered. Let us give a brief account of the results of this work.

That which has been in consciousness most recently is, other conditions being equal, reproduced most readily. For some time the memorized material is reproduced so easily that it seems to have found a permanent place in our mind. Soon, however, it begins to be forgotten. At first this forgetting goes on with great rapidity; but it becomes slower and slower, so that a person retains very little less after thirteen months than after twelve. Even after twenty years definite traces of a single former memorizing have been proved to exist. Nothing, therefore, is likely to be completely lost, although voluntary reproduction has long since become impossible.

The most important factor contributing toward certainty of reproduction is frequent repetition, of course with attention, for without attention no memorizing is possible. The experimental investigation of the influence of repetition has yielded, among minor ones, two particularly interesting results. One of them justifies an educational practice which had already been adopted by teachers because it seemed to be advisable. In order to memorize any material we should not try to force the desired end by accumulated repetition without pause. It is much more economical to devote a short time to learning, long enough for a few repetitions, to do this again after a pause of some hours or days and again after the same interval, until the desired effect is obtained. The total time required for obtaining this effect would be much greater if the total process of memorizing were to occur at one time without intermission.

Another result of experimental investigation is contrary to the tradition of educational practice. It has been proved that, in order to learn a long poem, monologue, or piece of prose, this should not be divided into smaller parts. It is uneconomical to learn each stanza or sentence separately. The whole should always be read from the beginning to the end, without introducing points of division which are not desired at the time of reproduction.

The method of involuntary reproduction has recently been applied to a problem of much practical significance. The attempt has been made to reveal thus associations of ideas which have been firmly established, but which the subject has strong reasons for keeping secret, for instance, the ideas forming the memory of a crime which he has committed. He is asked to tell or write as quickly as possible a word suggested by each of a great number of words presented to him in succession. Among these latter words are given some which have a special relation to the knowledge which the subject is suspected of possessing. If the suspicion is correct, it is likely to be shown in either of two ways in the answers to these test words. Either the expected (for instance incriminating) answers are actually given and reveal thus the subject’s knowledge; or if these answers are inhibited and voluntarily replaced by others of a more innocent appearance, the time of answering, the reaction time, is considerably increased. It may also happen that the subject, under these conditions, becomes confused and gives absolutely meaningless answers.

That the individual differences in the ability to memorize are very great, has always been observed. Modern psychology, however, has added to this knowledge an insight into the various kinds of differences and their proper causes. Let us notice the perception and imagery types. There are people who perceive and imagine very readily visual sensation groups. They give attention to the shape and color of the things rather than to any other sensible qualities, and they imagine visual shape or color very vividly so that the right and left, the above and below, of their imagery is clearly in their minds. In others auditory perception and auditory imagery are very vivid; in a third class of persons the same is to be said of kinesthetic mental states. We therefore distinguish visual, auditory, and kinesthetic types of consciousness. There may be also gustatory, olfactory, and other types, but they are of little practical importance. Extreme cases, where one of these classes of mental states is extraordinarily developed at the expense of all others, are rare. Eminent ability in art or music probably depends on such development. Generally, one kind of imagery is but slightly superior to the rest.

There seem to be further individual differences with respect to a predominance of either word images or images of the things of nature. All these differences bring about numerous variations of memory. The visual type is able to play chess blindfolded, to repeat a memorized series of numbers somewhat slowly also backwards. To the auditory type these performances seem miraculous. But the former in recalling easily confuses similar looking elements of such a memorized series, which the latter would certainly distinguish because of their difference in sound. The auditory type, however, confuses elements that are similar in sound or accent. The auditory and kinesthetic types depend largely on reading aloud for memorizing, while the visual type is scarcely aided by it. These differences are of much importance for all the various kinds of professional activity.

QUESTIONS

95. In what respect is memory the opposite of attention?

96. In what respect is reproduction by similarity superior to reproduction by simultaneity of previous experience?

97. Can you illustrate the relations between feeling and memory?

98. What is meant by the set of the mind?

99. Illustrate the dependence of memory on recency.

100. Illustrate the two laws of repetition.

101. What method has been devised for the diagnosis of memory which is not voluntarily revealed?

102. What is meant by perception or imagery types?

103. Can you illustrate the practical importance of the types of consciousness?

§ 10. PRACTICE

The word _practice_ refers to a number of different phenomena having this in common, that they occur when the same mental function is frequently repeated, either in immediate succession or with moderately long intermissions. To a large extent practice is identical with the selective and supplementing functions of the mind which are discussed above. But certain effects included in the term _practice_ cannot be understood thus and must be regarded as the signs of a more fundamental law of the mind. Setting aside, however, the distinction between fundamental and secondary regularities of mental function, two facts should be mentioned here.

The more frequently the same task is imposed upon our mind, the more perfectly--this is the first fact--is it carried out. But perfection has various aspects. So far as sense perception is concerned, perfection means a lowering of the so-called threshold of perception and of discrimination, especially the latter. Weaker sounds, lights, tastes are perceived; smaller differences of color, tone, weight, movement, size are correctly named. Perfection means also greater quickness of response. The same number of elements is perceived in less time, is memorized or reproduced more quickly. The rapidity of reading, thinking, writing, and other skillful movements is increased. Perfection means, further, an enlargement of the scope of the situation responded to. We are conscious of a greater number of its parts after having perceived a certain thing repeatedly. Of different things a greater number are simultaneously perceived. After repeated performance of a certain act, we take into account a greater number of circumstances and adapt it to them. That a certain activity which has been engaged in repeatedly can be continued longer at one time, may also be mentioned in this connection. So far as definite purposes are concerned, these are accomplished more and more economically and accurately, that is, with less expenditure of energy, with stricter avoidance of unnecessary movements, with a decreasing number of errors.

A second phenomenon of practice is the simplification of the conscious processes preceding purposive action. Unless there are particular causes, as anticipatory ideas or an extraordinary special interest, that which has often occurred tends to remain unconscious, so that the response may be called automatic. The ticking of a clock, the noise of a street, the laughing of a mountain stream, soon cease to be attended to, although attention to them is always possible. Reading, writing, arithmetical work, when being learned, include a vast number of states of consciousness which no longer occur when these activities are performed by a grown person. After thousand-fold repetition great rapidity of execution results from the omission of a multitude of mental states without which the performance could not originally have been brought about. But the original effects of those lost mental states are not at all lost. The same movements are carried out with the same accuracy as if they were governed by those mental states. Each single letter, even each word, is not found in the consciousness of a person who reads rapidly, and yet he pronounces the word correctly. Each single note or printed chord is not in the consciousness of the pianist, and yet he plays the chord correctly. The same holds for all complex movements that are slowly learned and often repeated, as knitting, sewing, swimming, horseback riding, dancing, skating. They finally require a minimum of mental energy. They become comparable in this respect to the native, instinctive movements; but in order to distinguish them from the native movements independent of consciousness, we call them automatic movements.

Practice, therefore, is a general term referring to the wonderful adaptation of mind to the external world for the purpose of self-preservation. By association and reproduction mind adapts itself to frequently recurring events and anticipates them. By practice it adapts itself to those events which recur with particular frequency and which are of particular importance. These events are through practice comprehended more delicately, more quickly, and more inclusively. They are responded to in a manner tested as the most fitting and most prompt, and yet requiring only a minimum of mental energy, of which more than a limited amount is at no time available. Without having to neglect the ordinary and as such important, mind has energy left to devote to that which is new, unusual, surprising.

QUESTIONS

104. What are the effects of practice on sense perception?

105. Illustrate how practice simplifies thought.

§ 11. FATIGUE

The conditions of fatigue are similar to those of practice. Fatigue occurs when mental functions are repeated too many times in immediate succession. But the result is not perfection, but deterioration of the performance. The sensitivity for weak stimuli or small differences of stimuli disappears. Attention is decreased, that is, fewer mental states are vivid, and they are also less vivid. New ideas do not easily enter consciousness. Reproduction, as in the processes of reading and arithmetic, is slow and inaccurate. Action becomes slow and awkward, and may cease altogether.

Fatigue is obviously a protective measure. When the continued performance of a task threatens to exhaust the organs, their resistance to the call for action increases, and finally they completely refuse to respond. Because of the continuity of all organic processes, this refusal in extreme cases is impossible without a lesser degree of refusal before the extreme is reached. The first indications of fatigue thus appear soon after a prolonged mental activity has begun, as a diminution of the effects of practice. This leads often to the astonishing consequence that a certain performance is executed better at the beginning of a practice period than at the end of the preceding period. The acquired practice is then still effective, while the effect of fatigue is absent. This experience does not justify the conclusion that skill has increased during the time of intermission.

Because of the great importance of fatigue for mental and bodily health, numerous investigators have in recent years undertaken to study it more closely by experimental methods. Especially fatigue caused by school work has been much under discussion in scientific and popular periodicals and even in the daily press. Little progress, however, has been made in our knowledge of fatigue. It has proved difficult to find reliable methods of measuring it, and the great complexity of the conditions has interfered with the interpretation of the experimental results. The attempt has been made to measure mental fatigue indirectly by measuring the muscular fatigue caused by repeatedly lifting a weight; or by measuring the minimum distance of two touches on the skin recognizable as two. Although there are probably relations of cutaneous sensitivity and of muscular fatigue to mental fatigue, they are not definitely known, and by some their very existence is doubted. Other tests used for the measurement of fatigue are adding numbers of several digits, adding a long series of digits, and taking dictation. In these tests the mental work is very one-sided and too simple to permit conclusions with regard to fatigue under ordinary conditions of mental activity. A disturbing element in these tests is the rapid perfection of the work under the influence of practice. If we choose more complicated tasks such as translation into another language, mathematical problems, or filling in words which have been omitted from a certain text, we cannot easily make two tasks sufficiently alike to be able to compare the results obtained from them.

But none of these methods solve the chief problem, namely, the determination of the point at which fatigue begins to be permanently harmful. There is no doubt that in moderate degrees fatigue is a perfectly normal phenomenon, involving no detriment to our future efficiency. Otherwise most people would be wrecked before they are fully grown. The experience of athletes and soldiers shows that even rather high degrees of fatigue are compatible with the normal growth of bodily strength. The same may be true for mental life. The assertions of great damage done to children by school work are--so far as normal children are concerned--certainly greatly exaggerated.

QUESTIONS

106. What are the effects of fatigue?

107. Into what complication does fatigue enter with practice?

108. What attempts have been made at measuring fatigue?

109. What is the chief problem in connection with fatigue?

110. Is the fatigue of school work harmful?

_C. THE EXPRESSIONS OF MENTAL LIFE_

§ 12. PERCEPTION AND MOVEMENT

The impression upon the mind is not the ultimate end of the nervous processes originating in the sense organs. The end is rather activity of the motor organs of the body, which we may here, accepting the naïve conception of matter and mind, regard as effects or expressions of mind. The complications of the mental life of a grown person tend to make this connection between mind and motor activity often obscure and doubtful. It seems that often we receive impressions quite passively. Nevertheless the connection exists. Every impression made upon the mind by the external world is in some way responded to by movement. The movement may occur in the stimulated sense organ itself, in the arms, the hands, the fingers, the legs, the feet, the head, the vocal organs, also in the internal organs, the heart, the blood vessels, the alimentary canal, the lungs. The significance of many of these movements is but insufficiently understood, for example, laughing, weeping, blushing, trembling. But those movements which directly affect the organism’s surroundings are easily understood. They may be classed under two headings, self-preservation and play. Another way of classifying them is to distinguish movement toward the object perceived and movement away from the object, without taking these terms in too literal a sense.

Innumerable illustrations for these classes of movements suggest themselves. A piece of bread put on the back of the tongue is moved down the esophagus by the proper muscular contractions. A particle moving into the wrong passage is thrown out again by coughing. If the palm of an infant is gently stroked, the hand closes and takes hold of the stroking finger. If the palm is scratched, the hand quickly recedes. A mild and steady light attracts the child’s eye, which follows the movements of the light. From an intense and flickering light the eye turns away. A piece of sugar is kept in the child’s mouth and moved about by the tongue until it is dissolved. A bitter root causes the lips to recede and the tongue to make a pushing movement. If the child is hungry, he cries, kicks, and strikes out with his arms until he is fed. After being fed he lies still so that digestion is not interfered with by the blood being drawn into the peripheral parts of the body.

Movements which do not serve self-preservation so directly are called play. When a cat perceives a mouse, she jumps at it and catches it. But before eating it, she usually lets it loose and catches it again, and so on several times. When she finds a ball of yarn, she treats it similarly, although she must know that it is not edible. A dog gnaws a bone because this contributes to his nutrition. But he also gnaws table legs and rugs, although these have no nutritive value. He chases rabbits and other small animals which he can eat. But he chases no less eagerly other dogs, wagons, cyclists, horses, none of which serve as articles of food for him. The same is true for man. The infant’s kicking, the small child’s breaking of his toys, do not have any immediate value. Men and animals respond to things not only by fighting, but also by play. The significance of playful movements is to be found in the exercise, the development, and the conservation of the abilities given to them by nature. As in the movements of self-preservation, so in play pleasantness and unpleasantness make their appearance. Extensive exercise of natural abilities is highly pleasant, enforced inactivity equally unpleasant.

But play is more than a general exercise of the bodily organs. It is a preparation for the specialized activities of the serious part of life. The animal meets in play things which behave very much like those things which it has to obtain for food. So it learns to obtain food at a time when food is not yet needed. It learns to defend itself when no one yet attacks it. The biological significance of the play movements obviously consists in this preparation for the special activities of life. Those animals which do not possess a strong tendency to play are thus at a disadvantage in the struggle for life, because they miss the opportunity for preparation. Serious activity and play accompany man and animal all through life; but the proportion changes. The young are taken care of by their parents, and play may therefore prevail. With maturity this changes, and less time is left for play.

All these movements of self-preservation and of play are natural inherited responses of the organism to its environment. Many of them do not appear at the very entrance into life, but at different stages of age and growth. They are the raw material from which all conduct is derived and built up. Their nervous conditions are the nervous processes in the reflex arches of the subcortical nerve centers. From the points of sensory stimulation, the nervous processes are carried into definite muscle groups so that definite movements occur. These movements are called _reflexes_ or _instincts_ according as they are rather simple or more complex. Both reflexes and instincts are inherited movements following in direct response upon sensory stimulation.

QUESTIONS

111. What is the ultimate end of every nervous process?

112. What are typical movements of self-preservation?

113. What are typical movements of play?

114. Is play more than a general exercise of the body?

115. Are all inherited movements possible immediately after birth?

116. What is the difference between reflexes and instincts?

§ 13. THOUGHT AND MOVEMENT

Consciousness is not a factor in reflex or instinctive movements. But these movements soon enter into a twofold connection with consciousness. (1) When such movements occur, they often result in consciousness. They are either seen, or perceived through the sense of touch or through the kinesthetic sense. These images of the movement become associated with the images originating from the sensory stimulations which give rise to the movement. (2) In consequence of this association the visual, touch, and kinesthetic images of the movement, particularly the most common, the kinesthetic, may themselves produce this movement to which they owe their existence. The mere thought of how one feels when performing a movement brings about, if it is vivid enough, the movement itself. The hearing of dance music awakens the kinesthetic ideas of dancing, and these become real movements, although perhaps only swaying movements of the body or the head. Vivid thinking similarly brings about whispering of words. Even vivid imagination of the movement of a foreign body has such powers. A passionate and excited billiard player thinks of the hoped-for movement of the running ball. This leads to imagery of a similar movement of his own body, and the result is the actual movement, rather ridiculous to the onlooker because it is entirely purposeless.

Through this connection with consciousness instinctive movements become voluntary movements. The term _voluntary_ means just this connection with consciousness; it has no other meaning.

Suppose a child sees something white and glittering and puts it instinctively into his mouth. It happens to be a lump of sugar. Its taste is pleasant. It is retained, dissolved, and swallowed. All the impressions, occurring at about the same time, become associated: the sight of the thing, the movements of the arm and hand, the taste, the movements of the tongue and the lips. The more frequently this thing happens, the more firmly established are the associations. Later the sight of sugar reproduces at once its taste, the visual and kinesthetic images of the movements, and the movements themselves--the arm is stretched out, the tongue and lips making sucking movements--although the sugar may be lying so far away that it cannot be touched. The child’s consciousness then contains what we have previously called will, and what may also be called desire: a vivid impression accompanied by pleasantness, sensations of restlessness, and an image of a pleasant conclusion of the whole experience. We say then that the child wills, desires, to have the sugar.

We can will to do only that which in its elements we have previously done by instinct. If we do not know how a movement feels when we perform it, of course we cannot bring it about by way of our consciousness, that is, by our will. Children have as much command of speech as they have acquired by instinctively producing speech sounds in response to accidental stimulations. This instinctive production occurs usually rather late in the case of certain sounds, as _k_, _r_, _sh_; and accordingly, in spite of all special efforts on the part of the parents, children learn to produce those sounds only at that late time. We presuppose, of course, that they are not deaf. For in deaf children the speech sounds instinctively produced do not enter into an association with the kinesthetic sensations and therefore cannot be voluntarily reproduced; that is, the children remain dumb. Many a grown person remembers that all his attempts at learning the pronunciation of a certain sound in foreign speech (take for example the gutteral German _r_, or the German _ch_, or the French nasal sounds) were in vain until by a mere accident, instinctively, he pronounced that very sound. After that he had command of it.

This interweaving of the instinctive reactions of the body with conscious life is of the greatest practical significance. However well adapted the inherited reflexes may be to the purpose of keeping the young animal alive, they are very insufficient in meeting the ever growing complications of life. And they are not perfect even in the beginning. A reflex is the response to a present and direct impression upon the organism; but very similar impressions may come from things of different properties. Poisonous substances often look and taste like articles of food. The enemy assumes the attitude of a friend welcoming you. Reflex action is powerless to give the organism the protection needed in such cases. Instinct is easily deceived. But as soon as the harmful consequences impress themselves upon the organism, the instinct is modified, and in the future these consequences will be avoided. The instincts are ready-made institutions intended to be applied to average conditions. Their readiness and completeness is in so far of inestimable advantage to the organism. If it had to learn everything necessary for life, it could not survive. But for the manifold deviations of the external world from the average no provision can be made in this manner.

The variation of the organism’s response is made possible by the existence of higher nerve centers, that is, of connecting neurons of a higher order, more remote from the sensory and motor points of the body. Let us imagine the proverbial reaction of a child to the sight of a flame, and discuss the successive stages of development by the help of figure 15. (1) The visual stimulation starts a nervous process from _s_{1}_, which passes through the bulb and spinal cord into the muscles of the arm at _m_{1}_. A small part of the current may branch off at _a_ and, instead of passing down towards _b_, take the direction of _v_. But the resistance in this direction is for the present so high that only an insignificant part of the process can take this way, and so no corresponding motor response is noticeable.

(2) While all this is still going on and the child’s arm is still moving forward, the heat of the flame acts as a pain stimulus at _s_{2}_. The nervous process produced passes over _c_ and _d_ to the muscles at _m_{2}_, whose contraction results in the arm’s being pulled back. This results in a third stimulation at _s_{3}_, which we need not trace farther here. But not the whole of the nervous process passes from _c_ down to _d_. A part of it, of considerable absolute magnitude because of the intensity of stimulation, passes from _c_ up to _p_ and thence over _k_ down to _d_ and finally also into _m_{2}_. This process going from _p_ to _k_, according to a general law of nervous activity, tends to attract other, weaker nervous processes, if the neuron connections make this possible. Consequently the nervous process from _s_{1}_ to _a_ is now turned mostly into the path _a-v-p_ and only an insignificant part of it continues to go from _a_ towards _b_. The consequence is that the resistance of the path _a-v-p-k-d_ is soon reduced to less than the resistance of the path _a-b_. The great significance of this fact becomes clear in the third stage of development.

(3) At some later time the flame again acts as a visual stimulus. But now, because of the change of resistance just explained, the nervous process takes for the most part the path over _a-v-p-k-d_, and the reaction follows at _m_{2}_ instead of at _m_{1}_. The child has learned to avoid the flame. The child, when seeing the flame, is conscious of the pain, as imagery, without having to receive the actual stimulation at _s_{2}_.

Thus the inflexible regularity of reaction gives place to another type of reaction, an adaptation, not only to those conditions which at the time make their impression upon the organism, but also to those conditions which are mere future possibilities. The experience of the past guides the organism into the future.

QUESTIONS

117. What is the twofold connection into which instinctive movement enters with consciousness?

118. Why is the movement of a billiard ball often accompanied by movements of the players or spectators?

119. What is a voluntary movement?

120. In what manner is will dependent on instinct?

121. Why do deaf children not acquire speech? Can they be taught to speak?

122. Why is the acquisition of foreign speech sounds by grown people often so slow?

123. What is the advantage to the organism of voluntary over instinctive action?

124. Can you describe the three stages of nervous development illustrating the proverb “A burnt child fears the fire”?