3. THE PERCEPTION OF SPACE
Many have been the philosophical controversies over the nature of space and our perception of it. The psychologists have even quarreled concerning whether we possess an innate sense of space, or whether it is a product of experience and training. Fortunately, for our present purpose we shall not need to concern ourselves with either of these controversies. For our discussion we may accept space for what common sense understands it to be. As to our sense of space, whatever of this we may possess at birth, it certainly has to be developed by use and experience to become of practical value. In the perception of space we must come to perceive distance, direction, size, and form. As a matter of fact, however, size is but so much distance, and form is but so much distance in this, that, or the other direction.
The Perceiving of Distance.—Unquestionably the eye comes to be our chief dependence in determining distance. Yet the muscle and joint senses give us our earliest knowledge of distance. The babe reaches for the moon simply because the eye does not tell it that the moon is out of reach. Only as the child reaches for its playthings, creeps or walks after them, and in a thousand ways uses its muscles and joints in measuring distance, does the perception of distance become dependable.
At the same time the eye is slowly developing its power of judging distance. But not for several years does visual perception of distance become in any degree accurate. The eye's perception of distance depends in part on the sensations arising from the muscles controlling the eye, probably in part from the adjustment of the lens, and in part from the retinal image. If one tries to look at the tip of his nose he easily feels the muscle strain caused by the required angle of adjustment. We come unconsciously to associate distance with the muscle sensations arising from the different angles of vision. The part played by the retinal image in judging distance is easily understood in looking at two trees, one thirty feet and the other three hundred feet distant. We note that the nearer tree shows the detail of the bark and leaves, while the more distant one lacks this detail. The nearer tree also reflects more light and color than the one farther away. These minute differences, registered as they are on the retinal image, come to stand for so much of distance.
The ear also learns to perceive distance through differences in the quality and the intensity of sound. Auditory perception of distance is, however, never very accurate.
The Perceiving of Direction.—The motor senses probably give us our first perception of direction, as they do of distance. The child has to reach this way or that way for his rattle; turn the eyes or head so far in order to see an interesting object; twist the body, crawl or walk to one side or the other to secure his bottle. In these experiences he is gaining his first knowledge of direction.
Along with these muscle-joint experiences, the eye is also being trained. The position of the image on the retina comes to stand for direction, and the eye finally develops so remarkable a power of perceiving direction that a picture hung a half inch out of plumb is a source of annoyance. The ear develops some skill in the perception of direction, but is less dependable than the eye.
4. THE PERCEPTION OF TIME
The philosophers and psychologists agree little better about our sense of time than they do about our sense of space. Of this much, however, we may be certain, our perception of time is subject to development and training.
Nature of the Time Sense.—How we perceive time is not so well understood as our perception of space. It is evident, however, that our idea of time is simpler than our idea of space—it has less of content, less that we can describe. Probably the most fundamental part of our idea of time is progression, or change, without which it is difficult to think of time at all. The question then becomes, how do we perceive change, or succession?
If one looks in upon his thought stream he finds that the movement of consciousness is not uniformly continuous, but that his thought moves in pulses, or short rushes, so to speak. When we are seeking for some fact or conclusion, there is a moment of expectancy, or poising, and then the leap forward to the desired point, or conclusion, from which an immediate start is taken for the next objective point of our thinking. It is probable that our sense of the few seconds of passing time that we call the immediate present consists of the recognition of the succession of these pulsations of consciousness, together with certain organic rhythms, such as heart beat and breathing.
No Perception of Empty time.—Our perception does not therefore act upon empty time. Time must be filled with a procession of events, whether these be within our own consciousness or in the objective world without. All longer periods of time, such as hours, days, or years, are measured by the events which they contain. Time filled with happenings that interest and attract us seems short while passing, but longer when looked back upon. On the other hand, time relatively empty of interesting experience hangs heavy on our hands in passing, but, viewed in retrospect, seems short. A fortnight of travel passes more quickly than a fortnight of illness, but yields many more events for the memory to review as the "filling" for time.
Probably no one has any very accurate feeling of the length, that is, the actual duration of a year—or even of a month! We therefore divide time into convenient units, as weeks, months, years and centuries. This allows us to think of time in mathematical terms where immediate perception fails in its grasp.
5. THE TRAINING OF PERCEPTION
In the physical world as in the spiritual there are many people who, "having eyes, see not and ears, hear not." For the ability to perceive accurately and richly in the world of physical objects depends not alone on good sense organs, but also on interest and the habit of observation. It is easy if we are indifferent or untrained to look at a beautiful landscape, a picture or a cathedral without seeing it; it is easy if we lack interest or skill to listen to an orchestra or the myriad sounds of nature without hearing them.
Perception Needs to Be Trained.—Training in perception does not depend entirely on the work of the school. For the world about us exerts a constant appeal to our senses. A thousand sights, sounds, contacts, tastes, smells or other sensations, hourly throng in upon us, and the appeal is irresistible. We must in some degree attend. We must observe.
Yet it cannot be denied that most of us are relatively unskilled in perception; we do not know how, or take the trouble to observe. For example, a stranger was brought into the classroom and introduced by the instructor to a class of fifty college students in psychology. The class thought the stranger was to address them, and looked at him with mild curiosity. But, after standing before them for a few moments, he suddenly withdrew, as had been arranged by the instructor. The class were then asked to write such a description of the stranger as would enable a person who had never seen him to identify him. But so poor had been the observation of the class that they ascribed to him clothes of four different colors, eyes and hair each of three different colors, a tie of many different hues, height ranging from five feet and four inches to over six feet, age from twenty-eight to forty-five years, and many other details as wide of the mark. Nor is it probable that this particular class was below the average in the power of perception.
School Training in Perception.—The school can do much in training the perception. But to accomplish this, the child must constantly be brought into immediate contact with the physical world about him and taught to observe. Books must not be substituted for things. Definitions must not take the place of experiment or discovery. Geography and nature study should be taught largely out of doors, and the lessons assigned should take the child into the open for observation and investigation. All things that live and grow, the sky and clouds, the sunset colors, the brown of upturned soil, the smell of the clover field, or the new mown hay, the sounds of a summer night, the distinguishing marks by which to identify each family of common birds or breed of cattle—these and a thousand other things that appeal to us from the simplest environment afford a rich opportunity for training the perception. And he who has learned to observe, and who is alert to the appeal of nature, has no small part of his education already assured.
6. PROBLEMS IN OBSERVATION AND INTROSPECTION
1. Test your power of observation by walking rapidly past a well-filled store window and then seeing how many of the objects you can name.
2. Suppose a tailor, a bootblack, a physician, and a detective are standing on the street corner as you pass by. What will each one be most likely to observe about you? Why?
3. Observe carefully green trees at a distance of a few rods; a quarter of a mile; a mile; several miles. Describe differences (1) in color, (2) in brightness, or light, and (3) in detail.
4. How many common birds can you identify? How many kinds of trees? Of wild flowers? Of weeds?
5. Observe the work of an elementary school for the purpose of determining:
a. Whether the instruction in geography, nature study, agriculture, etc., calls for the use of the eyes, ears and fingers.
b. Whether definitions are used in place of first-hand information in any subjects.
c. Whether the assignment of lessons to pupils includes work that would require the use of the senses, especially out of doors.
d. Whether the work offered in arithmetic demands the use of the senses as well as the reason.
e. Whether the language lessons make use of the power of observation.
CHAPTER VIII
MENTAL IMAGES AND IDEAS
As you sit thinking, a company of you together, your thoughts run in many diverse lines. Yet with all this diversity, your minds possess this common characteristic: Though your thinking all takes place in what we call the present moment, it goes on largely in terms of past experiences.
1. THE PART PLAYED BY PAST EXPERIENCE
Present Thinking Depends on Past Experience.—Images or ideas of things you have seen or heard or felt; of things you have thought of before and which now recur to you; of things you remember, such as names, dates, places, events; of things that you do not remember as a part of your past at all, but that belong to it nevertheless—these are the things which form a large part of your mental stream, and which give content to your thinking. You may think of a thing that is going on now, or of one that is to occur in the future; but, after all, you are dependent on your past experience for the material which you put into your thinking of the present moment.
Indeed, nothing can enter your present thinking which does not link itself to something in your past experience. The savage Indian in the primeval forest never thought about killing a deer with a rifle merely by pulling a trigger, or of turning a battery of machine guns on his enemies to annihilate them—none of these things were related to his past experience; hence he could not think in such terms.
The Present Interpreted by the Past.—Not only can we not think at all except in terms of our past experience, but even if we could, the present would be meaningless to us; for the present is interpreted in the light of the past. The sedate man of affairs who decries athletic sports, and has never taken part in them, cannot understand the wild enthusiasm which prevails between rival teams in a hotly contested event. The fine work of art is to the one who has never experienced the appeal which comes through beauty, only so much of canvas and variegated patches of color. Paul says that Jesus was "unto the Greeks, foolishness." He was foolishness to them because nothing in their experience with their own gods had been enough like the character of Jesus to enable them to interpret Him.
The Future Also Depends on the Past.—To the mind incapable of using past experience, the future also would be impossible; for we can look forward into the future only by placing in its experiences the elements of which we have already known. The savage who has never seen the shining yellow metal does not dream of a heaven whose streets are paved with gold, but rather of a "happy hunting ground." If you will analyze your own dreams of the future you will see in them familiar pictures perhaps grouped together in new forms, but coming, in their elements, from your past experience nevertheless. All that would remain to a mind devoid of a past would be the little bridge of time which we call the "present moment," a series of unconnected nows. Thought would be impossible, for the mind would have nothing to compare and relate. Personality would not exist; for personality requires continuity of experience, else we should be a new person each succeeding moment, without memory and without plans. Such a mind would be no mind at all.
Rank Determined by Ability to Utilize Past Experience.—So important is past experience in determining our present thinking and guiding our future actions, that the place of an individual in the scale of creation is determined largely by the ability to profit by past experience. The scientist tells us of many species of animals now extinct, which lost their lives and suffered their race to die out because when, long ago, the climate began to change and grow much colder, they were unable to use the experience of suffering in the last cold season as an incentive to provide shelter, or move to a warmer climate against the coming of the next and more rigorous one. Man was able to make the adjustment; and, providing himself with clothing and shelter and food, he survived, while myriads of the lower forms perished.
The singed moth again and again dares the flame which tortures it, and at last gives its life, a sacrifice to its folly; the burned child fears the fire, and does not the second time seek the experience. So also can the efficiency of an individual or a nation, as compared with other individuals or nations, be determined. The inefficient are those who repeat the same error or useless act over and over, or else fail to repeat a chance useful act whose repetition might lead to success. They are unable to learn their lesson and be guided by experience. Their past does not sufficiently minister to their present, and through it direct their future.
2. HOW PAST EXPERIENCE IS CONSERVED
Past Experience Conserved in Both Mental and Physical Terms.—If past experience plays so important a part in our welfare, how, then, is it to be conserved so that we may secure its benefits? Here, as elsewhere, we find the mind and body working in perfect unison and harmony, each doing its part to further the interests of both. The results of our past experience may be read in both our mental and our physical nature.
On the physical side past experience is recorded in modified structure through the law of habit working on the tissues of the body, and particularly on the delicate tissues of the brain and nervous system. This is easily seen in its outward aspects. The stooped shoulders and bent form of the workman tell a tale of physical toil and exposure; the bloodless lips and pale face of the victim of the city sweat shop tell of foul air, long hours, and insufficient food; the rosy cheek and bounding step of childhood speak of fresh air, good food and happy play.
On the mental side past experience is conserved chiefly by means of images, ideas, and concepts. The nature and function of concepts will be discussed in a later chapter. It will now be our purpose to examine the nature of images and ideas, and to note the part they play in the mind's activities.
The Image and the Idea.—To understand the nature of the image, and then of the idea, we may best go back to the percept. You look at a watch which I hold before your eyes and secure a percept of it. Briefly, this is what happens: The light reflected from the yellow object, on striking the retina, results in a nerve current which sets up a certain form of activity in the cells of the visual brain area, and lo! a percept of the watch flashes in your mind.
Now I put the watch in my pocket, so that the stimulus is no longer present to your eye. Then I ask you to think of my watch just as it appeared as you were looking at it; or you may yourself choose to think of it without my suggesting it to you. In either case the cellular activity in the visual area of the cortex is reproduced approximately as it occurred in connection with the percept, and lo! an image of the watch flashes in your mind. An image is thus an approximate copy of a former percept (or several percepts). It is aroused indirectly by means of a nerve current coming by way of some other brain center, instead of directly by the stimulation of a sense organ, as in the case of a percept.
If, instead of seeking a more or less exact mental picture of my watch, you only think of its general meaning and relations, the fact that it is of gold, that it is for the purpose of keeping time, that it was a present to me, that I wear it in my left pocket, you then have an idea of the watch. Our idea of an object is, therefore, the general meaning of relations we ascribe to it. It should be remembered, however, that the terms image and idea are employed rather loosely, and that there is not yet general uniformity among writers in their use.
All Our Past Experience Potentially at Our Command.—Images may in a certain sense take the place of percepts, and we can again experience sights, sounds, tastes, and smells which we have known before, without having the stimuli actually present to the senses. In this way all our past experience is potentially available to the present. All the objects we have seen, it is potentially possible again to see in the mind's eye without being obliged to have the objects before us; all the sounds we have heard, all the tastes and smells and temperatures we have experienced, we may again have presented to our minds in the form of mental images without the various stimuli being present to the end-organs of the senses.
Through images and ideas the total number of objects in our experience is infinitely multiplied; for many of the things we have seen, or heard, or smelled, or tasted, we cannot again have present to the senses, and without this power we would never get them again. And besides this fact, it would be inconvenient to have to go and secure afresh each sensation or percept every time we need to use it in our thought. While habit, then, conserves our past experience on the physical side, the image and the idea do the same thing on the mental side.
3. INDIVIDUAL DIFFERENCES IN IMAGERY
Images to Be Viewed by Introspection.—The remainder of the description of images will be easier to understand, for each of you can know just what is meant in every case by appealing to your own mind. I beg of you not to think that I am presenting something new and strange, a curiosity connected with our thinking which has been discovered by scholars who have delved more deeply into the matter than we can hope to do. Every day—no, more than that, every hour and every moment—these images are flitting through our minds, forming a large part of our stream of consciousness. Let us see whether we can turn our attention within and discover some of our images in their flight. Let us introspect.
I know of no better way to proceed than that adopted by Francis Galton years ago, when he asked the English men of letters and science to think of their breakfast tables, and then describe the images which appeared. I am about to ask each one of you to do the same thing, but I want to warn you beforehand that the images will not be so vivid as the sensory experiences themselves. They will be much fainter and more vague, and less clear and definite; they will be fleeting, and must be caught on the wing. Often the image may fade entirely out, and the idea only be left.
The Varied Imagery Suggested by One's Dining Table.—Let each one now recall the dining table as you last left it, and then answer questions concerning it like the following:
Can I see clearly in my "mind's eye" the whole table as it stood spread before me? Can I see all parts of it equally clearly? Do I get the snowy white and gloss of the linen? The delicate coloring of the china, so that I can see where the pink shades off into the white? The graceful lines and curves of the dishes? The sheen of the silver? The brown of the toast? The yellow of the cream? The rich red and dark green of the bouquet of roses? The sparkle of the glassware?
Can I again hear the rattle of the dishes? The clink of the spoon against the cup? The moving up of the chairs? The chatter of the voices, each with its own peculiar pitch and quality? The twitter of a bird outside the window? The tinkle of a distant bell? The chirp of a neighborly cricket?
Can I taste clearly the milk? The coffee? The eggs? The bacon? The rolls? The butter? The jelly? The fruit? Can I get the appetizing odor of the coffee? Of the meat? The oranges and bananas? The perfume of the lilac bush outside the door? The perfume from a handkerchief newly treated to a spray of heliotrope?
Can I recall the touch of my fingers on the velvety peach? On the smooth skin of an apple? On the fretted glassware? The feel of the fresh linen? The contact of leather-covered or cane-seated chair? Of the freshly donned garment? Can I get clearly the temperature of the hot coffee in the mouth? Of the hot dish on the hand? Of the ice water? Of the grateful coolness of the breeze wafted in through the open window?
Can I feel again the strain of muscle and joint in passing the heavy dish? Can I feel the movement of the jaws in chewing the beefsteak? Of the throat and lips in talking? Of the chest and diaphragm in laughing? Of the muscles in sitting and rising? In hand and arm in using knife and fork and spoon? Can I get again the sensation of pain which accompanied biting on a tender tooth? From the shooting of a drop of acid from the rind of the orange into the eye? The chance ache in the head? The pleasant feeling connected with the exhilaration of a beautiful morning? The feeling of perfect health? The pleasure connected with partaking of a favorite food?
Power of Imagery Varies in Different People.—It is more than probable that some of you cannot get perfectly clear images in all these lines, certainly not with equal facility; for the imagery from any one sense varies greatly from person to person. A celebrated painter was able, after placing his subject in a chair and looking at him attentively for a few minutes, to dismiss the subject and paint a perfect likeness of him from the visual image which recurred to the artist every time he turned his eyes to the chair where the sitter had been placed. On the other hand, a young lady, a student in my psychology class, tells me that she is never able to recall the looks of her mother when she is absent, even if the separation has been only for a few moments. She can get an image of the form, with the color and cut of the dress, but never the features. One person may be able to recall a large part of a concert through his auditory imagery, and another almost none.
In general it may be said that the power, or at least the use, of imagery decreases with age. The writer has made a somewhat extensive study of the imagery of certain high-school students, college students, and specialists in psychology averaging middle age. Almost without exception it was found that clear and vivid images played a smaller part in the thinking of the older group than of the younger. More or less abstract ideas and concepts seemed to have taken the place of the concrete imagery of earlier years.
Imagery Types.—Although there is some difference in our ability to use imagery of different sensory types, probably there is less variation here than has been supposed. Earlier pedagogical works spoke of the visual type of mind, or the audile type, or the motor type, as if the possession of one kind of imagery necessarily rendered a person short in other types. Later studies have shown this view incorrect, however. The person who has good images of one type is likely to excel in all types, while one who is lacking in any one of the more important types will probably be found short in all.4 Most of us probably make more use of visual and auditory than of other kinds of imagery, while olfactory and gustatory images seem to play a minor rôle.