Part 22

Of the many thousands of persons who handle our silver dollar, but few happen to observe the lion's head which lies concealed in the representation of the familiar head of Liberty; frequently even a careful examination fails to detect this hidden emblem of British rule; but, as before, when once found, it is quite obvious (Fig. 1).[10] For similar reasons it is a great aid in looking for an object to know what to look for; to be readily found, the object, though lost to sight, should be to memory clear. Searching is a mental process similar to the matching of a piece of fabric in texture or color, when one has forgotten the sample and must rely upon the remembrance of its appearance. If the recollection is clear and distinct, recognition takes place when the judgment decides that what the physical eye sees corresponds to the image in the mind's eye; with an indistinct mental image the recognition becomes doubtful or faulty. The novice in the use of the microscope experiences considerable difficulty in observing the appearance which his instructor sees and describes, and this because his conception of the object to be seen is lacking in precision. Hence his training in the use of the microscope is distinctly aided by consulting the illustrations in the textbook, for they enable his mental eye to realize the pictures which it should entertain. He may be altogether too much influenced by the pictures thus suggested to his mental vision, and draw what is really not under his microscope at all; much as the young arithmetician will manage to obtain the answer which the book requires even at the cost of a resort to very unmathematical processes. For training in correct and accurate vision it is necessary to acquire an alert mental eye, that observes all that is objectively visible, but does not permit the subjective to add to or modify what is really present.

II

The importance of the mind's eye in ordinary vision is also well illustrated in cases in which we see or seem to see what is not really present, but what for one cause or another it is natural to suppose is present. A very familiar instance of this process is the constant overlooking of misprints--false letters, transposed letters, and missing letters--unless these happen to be particularly striking. We see only the general physiognomy of the word, and the detailed features are supplied from within; in this case it is the expected that happens. In a series of experiments by Professor Münsterberg a word was briefly shown, while just before a certain idea or train of thought was suggested. Under these circumstances the word shown was often misread in accordance with the suggested idea; if the idea of future is suggested, part may be read as past; if vegetable is the suggested line of thought, fright may be read as fruit, and so on. Reading is thus done largely by the mental eye; and entire words, obviously suggested by the context, are sometimes read in, when they have been accidentally omitted. This is more apt to occur with the irregular characters used in manuscript than in the more distinct forms of the printed alphabet, and is particularly frequent in reading over what one has himself written. In reading proof, however, we are eager to detect misprints, and this change in attitude helps to make them visible. It is very difficult to illustrate this process intentionally, because the knowledge that one's powers of observation are about to be tested places one on one's guard, and thus suppresses the natural activity of the mind's eye and draws unusual attention to objective details. Let the reader at this point hold the page at some distance off--say, eight or twelve feet--and draw an exact reproduction of the letters shown in Fig. 2. He should not look at Fig. 2 at close range nor read further in the text until this has been done; and _perhaps_ he may find that he has introduced strokes which were not present in the original. If this is not the case, let him try the test upon those who are ignorant of its nature, and he will find that most persons will supply light lines to complete the contours of the letters, which in the original are suggested but not really present; the original outline, Fig. 2_a_, becomes something like Fig. 2_b_, and so on for the rest of the letters. The physical eye sees the former, but the mental eye sees the latter. I tried this experiment with a class of some thirty University students of Psychology, and, although they were disposed to be quite critical and suspected some kind of an illusion, only three or four drew the letters correctly; all the rest filled in the imaginary light contours; some even drew them as heavily as the real strokes. I followed this by an experiment of a similar character. I placed upon a table a figure (Fig. 3) made of light cardboard, fastened to blocks of wood at the base, so that the pieces would easily stand upright. The middle piece, which is rectangular and higher than the rest, was placed a little in front of the rest of the figure. The students were asked to describe precisely what they saw; and with one exception they all described, in different words, a semicircular piece of cardboard with a rectangular piece in front of it. In reality there was no half-circle of cardboard, but only portions of two quarter-circles with the portion back of the middle piece omitted. The students, of course, were well aware that their physical eyes could not see what was behind the middle cardboard, but they inferred, quite naturally, that the two side pieces were parts of one continuous semicircle. This they saw, so far as they saw it at all, with their mind's eye.

III

There is a further interesting class of illustrations in which a single outward impression changes its character according as it is viewed as representing one thing or another. In a general way we see the same thing all the time, and the image on the retina does not change. But as we shift the attention from one portion of the view to another, or as we view it with a different mental conception of what the figure represents, it assumes a different aspect, and to our mental eye becomes quite a different thing. A slight but interesting change takes place if we view Fig. 4 first with the conception that the black is the pattern to be seen and the white the background, and again try to see the white as the pattern against a black background. I give a further illustration of such a change in Fig. 5. In our first and natural view of this we focus the attention upon the black lines and observe the familiar illusion, that the four vertical black bands seem far from parallel. That they are parallel can be verified by measurement, or by covering up all of the diagram except the four main bands. But if the white part of the diagram be conceived as the design against a black background, then the design is no longer the same, and with this change the illusion disappears, and the four bands seem parallel, as they really are. It may require a little effort to bring about this change, but it is marked when once realized.

A curious optical effect, which in part illustrates the change in appearance under different aspects, is reproduced in Fig. 6. In this case the enchantment of distance is necessary to produce the transformation. Viewed at the usual reading distance, we see nothing but an irregular and meaningless assemblage of black and white blotches. At a distance of not less than fifteen to eighteen feet, however, a man's head appears quite clearly. Also observe that after the head has once been realized it becomes possible to obtain suggestions of it at nearer distances.

A much larger class of ambiguous diagrams consists of those which represent by simple outlines familiar geometrical forms or objects. We cultivate such a use of our eyes, as indeed of all our faculties, as will on the whole lead to the most profitable results. As a rule, the particular impression is not so important as what it represents. Sense-impressions are simply the symbols or signs of things or ideas, and the thing or the idea is more important than the sign. Accordingly, we are accustomed to interpret lines, whenever we can, as the representations of objects. We are well aware that the canvas or the etching or the photograph before us is a flat surface in two dimensions, but we see the picture as the representation of solid objects in three dimensions. This is the illusion of pictorial art. So strong is this tendency to view lines as the symbols of things, that if there is the slightest chance of so viewing them, we invariably do so; for we have a great deal of experience with things that present their contours as lines, and very little with mere lines or surfaces. If we view outlines only, without shading or perspective or anything to definitely suggest what is foreground and what background, it becomes possible for the mind to supply these details and see foreground as background, and _vice versa_.

A good example to begin with is Fig. 7. These outlines will probably suggest at first view a book, or better a book-cover, seen with its back toward you and its sides sloping away from you; but it may also be viewed as a book opened out towards you and presenting to you an inside view of its contents. Should the change not come readily, it may be facilitated by thinking persistently of the appearance of an open book in this position. The upper portion of Fig. 8 is practically the same as Fig. 7, and if the rest of the figure be covered up, it will change as did the book cover; when, however, the whole figure is viewed as an arrow, a new conception enters, and the apparently solid book cover becomes the _flat_ feathered part of the arrow. Look at the next figure (Fig. 9), which represents in outline a truncated pyramid with a square base. Is the smaller square nearer to you, and are the sides of the pyramid sloping away from you toward the larger square in the rear? Or are you looking into the hollow of a truncated pyramid with the smaller square in the background? Or is it now one and now the other, according as you decide to see it? Here (Fig. 12) is a skeleton box which you may conceive as made of wires outlining the sides. Now the front, or side nearest to me, seems directed downward and to the left; again, it has shifted its position and is no longer the front, and the side which appears to be the front seems directed upward and to the right. The presence of the diagonal line makes the change more striking: in one position it runs from the left-hand _rear_ upper corner to the right-hand _front_ lower corner; while in the other it connects the left-hand _front_ upper corner with the right-hand _rear_ lower corner.

Fig. 14 will probably seem at first glimpse to be the view of a flight of steps which one is about to ascend from right to left. Imagine it, however, to be a view of the under side of a series of steps; the view representing the structure of overhanging solid masonwork seen from underneath. At first it may be difficult to see it thus, because the view of steps which we are about to mount is a more natural and frequent experience than the other; but by staring at it with the intention of seeing it differently the transition will come, and often quite unexpectedly.

The blocks in Fig. 15 are subject to a marked fluctuation. Now the black surfaces represent the bottoms of the blocks, all pointing downward and to the left, and now the black surfaces have changed and have become the tops, pointing upward and to the right. For some the changes come at will; for others they seem to come unexpectedly, but all are aided by anticipating mentally the nature of the transformation. The effect here is quite striking, the blocks seeming almost animated and moving through space. In Fig. 16 a similar arrangement serves to create an illusion as to the real number of blocks present. If viewed in one way--the black surface forming the tops of the blocks--there seem to be six, arranged as in Fig. 17; but when the transformation has taken place and the black surfaces have become the overhanging bottoms of the boxes, there are seven, arranged as in Fig. 18. Somewhat different, but still belonging to the group of ambiguous figures, is the ingenious conceit of the duck-rabbit shown in Fig. 19. When it is a rabbit, the face looks to the right and a pair of ears are conspicuous behind; when it is a duck, the face looks to the left and the ears have been changed into the bill. Most observers find it difficult to hold either interpretation steadily, the fluctuations being frequent, and coming as a surprise.

IV

This collection of diagrams serves to illustrate the principle that when the objective features are ambiguous, we see one thing or another according to the impression that is in the mind's eye; what the objective factors lack in definiteness the subjective ones supply, while familiarity, prepossession, as well as other circumstances influence the result. These illustrations show conclusively that seeing is not wholly an objective matter depending upon what there is to be seen, but is very considerably a subjective matter, depending upon the eye that sees. To the same observer a given arrangement of lines now appears as the representation of one object and now of another; and from the same objective experience, especially in instances that demand a somewhat complicated exercise of the senses, different observers derive very different impressions.

Not only when the sense-impressions are ambiguous or defective, but when they are vague--when the light is dim or the forms obscure--does the mind's eye eke out the imperfections of physical vision. The vague conformations of drapery and make-up that are identified and recognized in spiritualistic _séances_ illustrate extreme instances of this process. The whitewashed tree or post that momentarily startles us in a dark country lane takes on the guise that expectancy gives it. The mental predisposition here becomes the dominant factor, and the timid see as ghosts what their more sturdy companions recognize as whitewashed posts. Such experiences we ascribe to the action of suggestion and imagination--the cloud "that's almost in shape like a camel," or "like a weasel," or "like a whale." But throughout our visual experiences there runs this double strain, now mainly outward and now mainly inward, from the simplest excitements of the retina up to the realms where fancy soars free from the confines of sense, and the objective finds its occupation gone.

FOOTNOTE:

[10] In order to obtain the effects described in the various illustrations it is necessary in several cases to regard the figures for a considerable time and with close attention. The reader is requested not to give up in case the first attempt to secure the effect is not successful, but to continue the effort for a reasonable period. Individuals differ considerably in the readiness with which they obtain such effects; in some cases, such devices as holding the diagrams inverted, or at an angle, or viewing them with the eyes half closed, are helpful.

MENTAL PREPOSSESSION AND INERTIA

I

Those who are actively engaged in educational pursuits are called upon from time to time to consider the nature of the difficulties in the imparting of knowledge, the psychological impediments that stand in the way of successful instruction. These are many and various; and pertain as well to the givers as to the receivers of learning. This large and well threshed field I have no intention of gleaning once more; I desire simply to draw attention to one form of difficulty on the part of the learner, which has been brought home to me so frequently and at times so forcibly, that I should be inclined to select it as the most salient stumbling-block in the successful acquisition of those branches of study which it falls to my lot to expound.

This characteristic, which may be called mental prepossession, is well illustrated in the following narrative, the truth of which, however, is not guaranteed. The story dates from the exciting days when the American public was completely fascinated by the mental gymnastics of the "spelling bee;" and relates that towards the close of a very fierce contest with the alphabet, when only a few stalwart champions remained to encounter the erratic eccentricities of English orthography, the conductor of the "bee" announced with an air of grave importance a word that he felt quite certain would retire not a few of the spelling virtuosi. He then asked their closest attention to his precise pronunciation, and solemnly gave utterance to what for all the world sounded like _cat_. Each hearer attempted to spell this extraordinarily difficult word with a suitably unusual rearrangement of the letters suggested by the sound, and when each effort had in turn been pronounced a failure, the information was given that the correct spelling was _c-a-t_. _Hæc fabula docet_ that when one expects a difficulty he is apt to find it or to make it. Believing the problem to be unusual, he applies unusual methods to its solution; believing it to be complex, he overlooks the simple means by which its mysteries may be unlocked. It matters little how this reputation has come about, whether as the result of personal prejudice or of inherited tradition, whether suggested by the technicality of the subject or the awkwardness of the treatment, whether by the use of a few unusual terms or operations, or by any one of the countless methods, conscious and unconscious, by which such impressions are formed,--the result will be much the same.