Byextensityis meant the space-differences of sensations. The touch of the point of a toothpick on the skin has a different space quality from the touch of the flat end of a pencil. Low tones seem to have more volume than high tones. Some pains feel sharp andothers dull and diffuse. The warmth felt from spreading the palms of the hands out to the fire has a "bigness" not felt from heating one solitary finger. The extensity of a sensation depends on the number of nerve endings stimulated.
Thedurationof a sensation refers to the time it lasts. This must not be confused with the duration of the stimulus, which may be either longer or shorter than the duration of the sensation. Every sensation must exist for some space of time, long or short, or it would have no part in consciousness.
All are familiar with the "five senses" of our elementary physiologies, sight, hearing, taste, smell, and touch. A more complete study of sensation reveals nearly three times this number, however. This is to say that the body is equipped with more than a dozen different kinds of end-organs, each prepared to receive its own particular type of stimulus. It must also be understood that some of the end-organs yield more than one sense. The eye, for example, gives not only visual but muscular sensations; the ear not only auditory, but tactual; the tongue not only gustatory, but tactual and cold and warmth sensations.
Sight.—Vision is adistancesense; we can see afar off. The stimulus ischemicalin its action; this means that the ether waves, on striking the retina, cause a chemical change which sets up the nerve current responsible for the sensation.
The eye, whose general structure is sufficiently described in all standard physiologies, consists of a visual apparatus designed to bring the images of objects to aclear focus on the retina at thefovea, or area of clearest vision, near the point of entrance of the optic nerve.
The sensation of sight coming from this retinal image unaided by other sensations gives us but two qualities,light and color. The eye can distinguish many different grades of light from purest white on through the various grays to densest black. The range is greater still in color. We speak of the seven colors of the spectrum, violet, indigo, blue, green, yellow, orange, and red. But this is not a very serviceable classification, since the average eye can distinguish about 35,000 color effects. It is also somewhat bewildering to find that all these colors seem to be produced from the four fundamental hues, red, green, yellow, and blue, plus the various tints. These four, combined in varying proportions and with different degrees of light (i.e., different shades of gray), yield all the color effects known to the human eye. Herschel estimates that the workers on the mosaics at Rome must have distinguished 30,000 different color tones. Thehueof a color refers to its fundamental quality, as red or yellow; thechroma, to its saturation, or the strength of the color; and thetint,to the amount of brightness (i.e., white) it contains.
Hearing.—Hearing is also a distance sense. The action of its stimulus is mechanical, which is to say that the vibrations produced in the air by the sounding body are finally transmitted by the mechanism of the middle ear to the inner ear. Here the impulse is conveyed through the liquid of the internal ear to the nerve endings as so many tiny blows, which produce the nerve current carried to the brain by the auditory nerve.
The sensation of hearing, like that of sight, gives us two qualities: namely,toneswith their accompanying pitch and timbre, andnoises. Tones, or musical sounds,are produced by isochronous or equal-timed vibrations; thusCof the first octave is produced by 256 vibrations a second, and if this tone is prolonged the vibration rate will continue uniformly the same. Noises, on the other hand, are produced by vibrations which have no uniformity of vibration rate. The ear's sensibility to pitch extends over about seven octaves. The seven-octave piano goes down to 27-1/2 vibrations and reaches up to 3,500 vibrations. Notes of nearly 50,000 vibrations can be heard by an average ear, however, though these are too painfully shrill to be musical. Taking into account this upper limit, the range of the ear is about eleven octaves. The ear, having given usloudnessof tones, which depends on the amplitude of the vibrations,pitch, which depends on the rapidity of the vibrations, andtimbre, orquality, which depends on the complexity of the vibrations, has no further qualities of sound to reveal.
Taste.—The sense of taste is located chiefly in the tongue, over the surface of which are scattered many minutetaste-bulbs. These can be seen as small red specks, most plentifully distributed along the edges and at the tip of the tongue. The substance tasted must be insolution, and come in contact with the nerve endings. The action of the stimulus ischemical.
The sense of taste recognizes the four qualities ofsour,sweet,salt, andbitter. Many of the qualities which we improperly call tastes are in reality a complex of taste, smell, touch, and temperature. Smell contributes so largely to the sense of taste that many articles of food become "tasteless" when we have a catarrh, and many nauseating doses of medicine can be taken without discomfort if the nose is held. Probably none of us, if we are careful to exclude all odors by pluggingthe nostrils with cotton, can by taste distinguish between scraped apple, potato, turnip, or beet, or can tell hot milk from tea or coffee of the same temperature.
Smell.—In the upper part of the nasal cavity lies a small brownish patch of mucous membrane. It is here that the olfactory nerve endings are located. The substance smelled must be volatile, that is, must exist in gaseous form, and come in direct contact with the nerve endings. Chemical action results in a nerve current.
The sensations of smell have not been classified so well as those of taste, and we have no distinct names for them. Neither do we know how many olfactory qualities the sense of smell is capable of revealing. The only definite classification of smell qualities is that based on their pleasantness or the opposite. We also borrow a few terms and speak ofsweetorfragrantodors andfreshorclosesmells. There is some evidence when we observe animals, or even primitive men, that the human race has been evolving greater sensibility to certain odors, while at the same time there has been a loss of keenness of what we call scent.
Various Sensations from the Skin.—The skin, besides being a protective and excretory organ, affords a lodging-place for the end-organs giving us our sense of pressure, pain, cold, warmth, tickle, and itch.Pressureseems to have for its end-organ thehair-bulbsof the skin; on hairless regions small bulbs called thecorpuscles of Meissnerserve this purpose.Painis thought to be mediated by free nerve endings.Colddepends on end-organs called thebulbs of Krause; andwarmthon theRuffinian corpuscles.
Cutaneous or skin sensation may arise from eithermechanicalstimulation, such as pressure, a blow, or tickling, fromthermalstimulation from hot or cold objects,fromelectricalstimulation, or from the action of certainchemicals, such as acids and the like. Stimulated mechanically, the skin gives us but two sensation qualities,pressureandpain. Many of the qualities which we commonly ascribe to the skin sensations are really a complex of cutaneous and muscular sensations.Contactis light pressure.Hardnessandsoftnessdepend on the intensity of the pressure.Roughnessandsmoothnessarise from interrupted and continuous pressure, respectively, and require movement over the rough or smooth surface.Touchdepends on pressure accompanied by the muscular sensations involved in the movements connected with the act. Pain is clearly a different sensation from pressure; but any of the cutaneous or muscular sensations may, by excessive stimulation, be made to pass over into pain. All parts of the skin are sensitive to pressure and pain; but certain parts, like the finger tips, and the tip of the tongue, are more highly sensitive than others. The skin varies also in its sensitivity toheatandcold. If we take a hot or a very cold pencil point and pass it rather lightly and slowly over the skin, it is easy to discover certain spots from which a sensation of warmth or of cold flashes out. In this way it is possible to locate the end-organs of temperature very accurately.
Fig. 17.--Diagram showing distribution of hot and cold spots on the back of the hand. C, cold spots; H, hot spots.Fig.17.—Diagram showing distribution of hot and cold spots on the back of the hand. C, cold spots; H, hot spots.
The Kinæsthetic Senses.—The muscles, tendons, and joints also give rise to perfectly definite sensations, but they have not been named as have the sensations from most of the other end-organs.Weightis the most clearly marked of these sensations. It is through the sensations connected with movements of muscles, tendons, and joints that we come to judgeform,size, anddistance.
The Organic Senses.—Finally, to the sensations mentioned so far must be added those which come from the internal organs of the body. From the alimentary canal we get the sensations ofhunger,thirst, andnausea; from the heart, lungs, and organs of sex come numerous well-defined but unnamed sensations which play an important part in making up the feeling-tone of our daily lives.
Thus we see that the senses may be looked upon as the sentries of the body, standing at the outposts where nature and ourselves meet. They discover the qualities of the various objects with which we come in contact and hand them over to the mind in the form of sensations. And these sensations are the raw material out of which we begin to construct our material environment. Only as we are equipped with good organs of sense, especially good eyes and ears, therefore, are we able to enter fully into the wonderful world about us and receive the stimuli necessary to our thought and action.
1. Observe a schoolroom of children at work with the aim of discovering any that show defects of vision or hearing. What are the symptoms? What is the effect of inability to hear or see well upon interest and attention?
2. Talk with your teacher about testing the eyes and ears of the children of some school. The simpler tests for visionand hearing are easily applied, and the expense for material almost nothing. What tests should be used? Does your school have the test card for vision?
3. Use a rotator or color tops for mixing discs of white and black to produce different shades of gray. Fix in mind the gray made of half white and half black; three-fourths white and one-fourth black; one-fourth-white and three-fourths black.
4. In the same way mix the two complementaries yellow and blue to produce a gray; mix red and green in the same way. Try various combinations of the four fundamental colors, and discover how different colors are produced. Seek for these same colors in nature—sky, leaves, flowers, etc.
5. Take a large wire nail and push it through a cork so that it can be handled without touching the metal with the fingers. Now cool it in ice or very cold water, then dry it and move the point slowly across the back of the hand. Do you feel occasional thrills of cold as the point passes over a bulb of Krause? Heat the nail with a match flame or over a lamp, and perform the same experiment. Do you feel the thrills of heat from the corpuscles of Ruffini?
6. Try stopping the nostrils with cotton and having someone give you scraped apple, potato, onion, etc., and see whether, by taste alone, you can distinguish the difference. Why cannot sulphur be tasted?
No young child at first sees objects as we see them, or hears sounds as we hear them. This power, the power of perception, is a gradual development. It grows day by day out of the learner's experience in his world of sights and sounds, and whatever other fields his senses respond to.
Need of Knowing the Material World.—It is the business of perception to give us knowledge of our world of materialobjectsand their relations inspaceandtime. The material world which we enter through the gateways of the senses is more marvelous by far than any fairy world created by the fancy of story-tellers; for it contains the elements of all they have conceived and much more besides. It is more marvelous than any structure planned and executed by the mind of man; for all the wonders and beauties of the Coliseum or of St. Peter's existed in nature before they were discovered by the architect and thrown together in those magnificent structures. The material advancement of civilization has been but the discovery of the objects, forces, and laws of nature, and their use in inventions serviceable to men. And these forces and laws of nature were discovered only as they were made manifest through objects in the material world.
The problem lying before each individual who would enter fully into this rich world of environment, then, is to discover at first hand just as large a part of the material world about him as possible. In the most humble environment of the most uneventful life is to be found the material for discoveries and inventions yet undreamed of. Lying in the shade of an apple tree under the open sky, Newton read from a falling apple the fundamental principles of the law of gravitation which has revolutionized science; sitting at a humble tea table Watt watched the gurgling of the steam escaping from the kettle, and evolved the steam engine therefrom; with his simple kite, Franklin drew down the lightning from the clouds, and started the science of electricity; through studying a ball, the ancient scholars conceived the earth to be a sphere, and Columbus discovered America.
The Problem Which Confronts the Child.—Well it is that the child, starting his life's journey, cannot see the magnitude of the task before him. Cast amid a world of objects of whose very existence he is ignorant, and whose meaning and uses have to be learned by slow and often painful experience, he proceeds step by step through the senses in his discovery of the objects about him. Yet, considered again, we ourselves are after all but a step in advance of the child. Though we are somewhat more familiar with the use of our senses than he, and know a few more objects about us, yet the knowledge of the wisest of us is at best pitifully meager compared with the richness of nature. So impossible is it for us to know all our material environment, that men have taken to becoming specialists. One man will spend his life in the study of a certain variety of plants, while there are hundreds of thousands of varieties all about him; another will study a particular kind of animal life,perhaps too minute to be seen with the naked eye, while the world is teeming with animal forms which he has not time in his short day of life to stop to examine; another will study the land forms and read the earth's history from the rocks and geological strata, but here again nature's volume is so large that he has time to read but a small fraction of the whole. Another studies the human body and learns to read from its expressions the signs of health and sickness, and to prescribe remedies for its ills; but in this field also he has found it necessary to divide the work, and so we have specialists for almost every organ of the body.
How a Percept is Formed.—How, then, do we proceed to the discovery of this world of objects? Let us watch the child and learn the secret from him. Give the babe a ball, and he applies every sense to it to discover its qualities. He stares at it, he takes it in his hands and turns it over and around, he lifts it, he strokes it, he punches it and jabs it, he puts it to his mouth and bites it, he drops it, he throws it and creeps after it. He leaves no stone unturned to find out what that thing really is. By means of thequalitieswhich come to him through the avenues of sense, he constructs theobject. And not only does he come to know the ball as a material object, but he comes to know also its uses. He is forming his own best definition of a ball in terms of the sensations which he gets from it and the uses to which he puts it, and all this even before he can name it or is able to recognize its name when he hears it. How much better his method than the one he will have to follow a little later when he goes to school and learnsthat "A ball is a spherical body of any substance or size, used to play with, as by throwing, kicking, or knocking, etc.!"
The Percept Involves All Relations of the Object.—Nor is the case in the least different with ourselves. When we wish to learn about a new object or discover new facts about an old one, we do precisely as the child does if we are wise. We apply to it every sense to which it will afford a stimulus, and finally arrive at the object through its various qualities. And just in so far as we have failed to use in connection with it every sense to which it can minister, just in that degree will we have an incomplete perception of it. Indeed, just so far as we have failed finally to perceive it in terms of its functions or uses, in that far also have we failed to know it completely. Tomatoes were for many years grown as ornamental garden plants before it was discovered that the tomatoes could minister to the taste as well as to the sight. The clothing of civilized man gives the same sensation of texture and color to the savage that it does to its owner, but he is so far from perceiving it in the same way that he packs it away and continues to go naked. The Orientals, who disdain the use of chairs and prefer to sit cross-legged on the floor, can never perceive a chair just as we do who use chairs daily, and to whom chairs are so saturated with social suggestions and associations.
The Content of the Percept.—The percept, then, always contains a basis ofsensation. The eye, the ear, the skin or some other sense organ must turn in its supply of sensory material or there can be no percept. But the percept contains more than just sensations. Consider, for example, your percept of an automobile flashing past your windows. You reallyseebut very little of it, yetyouperceiveit as a very familiar vehicle. All that your sense organs furnish is a more or less blurred patch of black of certain size and contour, one or more objects of somewhat different color whom you know to be passengers, and various sounds of a whizzing, chugging or roaring nature. Your former experience with automobiles enables you to associate with these meager sensory details the upholstered seats, the whirling wheels, the swaying movement and whatever else belongs to the full meaning of a motor car.
The percept that contained only sensory material, and lacked all memory elements, ideas and meanings, would be no percept at all. And this is the reason why a young child cannot see or hear like ourselves. It lacks the associative material to give significance and meaning to the sensory elements supplied by the end-organs. The dependence of the percept on material from past experience is also illustrated in the common statement that what one gets from an art exhibit or a concert depends on what he brings to it. He who brings no knowledge, no memory, no images from other pictures or music will secure but relatively barren percepts, consisting of little besides the mere sensory elements. Truly, "to him that hath shall be given" in the realm of perception.
The Accuracy of Percepts Depends on Experience.—We must perceive objects through our motor response to them as well as in terms of sensations. The boy who has his knowledge of a tennis racket from looking at one in a store window, or indeed from handling one and looking it over in his room, can never know a tennis racket as does the boy who plays with it on the court. Objects get their significance not alone from their qualities, but even more from their use as related to our own activities.
Like the child, we must get our knowledge of objects, if we are to get it well, from the objects themselves at first hand, and not second hand through descriptions of them by others. The fact that there is so much of the material world about us that we can never hope to learn it all, has made it necessary to put down in books many of the things which have been discovered concerning nature. This necessity has, I fear, led many away from nature itself to books—away from the living reality of things to the dead embalming cases of words, in whose empty forms we see so little of the significance which resides in the things themselves. We are in danger of being satisfied with theformsof knowledge without itssubstance—with definitions contained in words instead of in qualities and uses.
Not Definitions, But First-hand Contact.—In like manner we come to know distance, form and size. If we have never become acquainted with a mile by actually walking a mile, running a mile, riding a bicycle a mile, driving a horse a mile, or traveling a mile on a train, we might listen for a long time to someone tell how far a mile is, or state the distance from Chicago to Denver, without knowing much about it in any way except word definitions. In order to understand a mile, we must come to know it in as many ways as possible through sense activities of our own. Although many children have learned that it is 25,000 miles around the earth, probably no one who has not encircled the globe has any reasonably accurate notion just how far this is. For words cannot take the place of perceptions in giving us knowledge. In the case of shorter distances, the same rule holds. The eye must be assisted by experience of the muscles and tendons and joints in actually covering distance, and learn to associate these sensations withthose of the eye before the eye alone can be able to say, "That tree is ten rods distant." Form and size are to be learned in the same way. The hands must actually touch and handle the object, experiencing its hardness or smoothness, the way this curve and that angle feels, the amount of muscular energy it takes to pass the hand over this surface and along that line, the eye taking note all the while, before the eye can tell at a glance that yonder object is a sphere and that this surface is two feet on the edge.
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 aninnatesense 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 perceivedistance,direction,size, andform. 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 itsplaythings, 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 thedetailof the bark and leaves, while the more distant one lacks this detail. The nearer tree also reflects morelightandcolorthan 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. Inthese 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.
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 isprogression, 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 thatwe call theimmediate presentconsists 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 actualdurationof 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.
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 oninterestand the habit ofobservation. It is easy if we are indifferent or untrained to look at a beautiful landscape, a picture or acathedral withoutseeingit; it is easy if we lack interest or skill to listen to an orchestra or the myriad sounds of nature withouthearingthem.
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.
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.
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.
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 atrigger, 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 unconnectednows. Thought would be impossible, for the mind would havenothing 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.
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 ofimages,ideas, andconcepts. 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 thecells of the visual brain area, and lo! aperceptof 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 casethe cellular activity in the visual area of the cortex is reproducedapproximately as it occurred in connection with the percept, and lo! animageof 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 mentalpictureof my watch, you only think of its generalmeaningand 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 anideaof 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 wehave 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. Whilehabit, then, conserves our past experience on the physical side, theimageand theideado the same thing on the mental side.
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 breakfasttables, 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 velvetypeach? 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 canget 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 thevisualtype of mind, or theaudiletype, or themotortype, 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.
Binet says that the man who has not every type of imagery almost equally well developed is only the fractionof a man. While this no doubt puts the matter too strongly, yet images do play an important part in our thinking.
Images Supply Material for Imagination and Memory.—Imagery supplies the pictures from which imagination builds its structures. Given a rich supply of images from the various senses, and imagination has the material necessary to construct times and events long since past, or to fill the future with plans or experiences not yet reached. Lacking images, however, imagination is handicapped, and its meager products reveal in their barrenness and their lack of warmth and reality the poverty of material.
Much of our memory also takes the form of images. The face of a friend, the sound of a voice, or the touch of a hand may be recalled, not as a mere fact, but with almost the freshness and fidelity of a percept. That much of our memory goes on in the form of ideas instead of images is true. But memory is often both aided in its accuracy and rendered more vital and significant through the presence of abundant imagery.
Imagery in the Thought Processes.—Since logical thinking deals more with relations and meanings than with particular objects, images naturally play a smaller part in reasoning than in memory and imagination. Yet they have their place here as well. Students of geometry or trigonometry often have difficulty in understanding a theorem until they succeed in visualizing the surface or solid involved. Thinking in the field of astronomy, mechanics, and many other sciences is assisted at certain points by the ability to form clear and accurate images.
The Use of Imagery in Literature.—Facility in the use of imagery undoubtedly adds much to our enjoymentand appreciation of certain forms of literature. The great writers commonly use all types of images in their description and narration. If we are not able to employ the images they used, many of their most beautiful pictures are likely to be to us but so many words suggesting prosaic ideas.
Shakespeare, describing certain beautiful music, appeals to the sense of smell to make himself understood:
... it came o'er my ear like the sweet soundThat breathes upon a bank of violets,Stealing and giving odor!
Lady Macbethcries:
Here's the smell of the blood still:All the perfumes of Arabia will not sweeten this little hand.
Milton hasEvesay of her dream of the fatal apple:
... The pleasant sav'ry smellSo quickened appetite, that I, methought,Could not but taste.
Likewise with the sense of touch:
... I take thy hand, this handAs soft as dove's down, and as white as it.
Imagine a person devoid of delicate tactile imagery, with senseless finger tips and leaden footsteps, undertaking to interpret these exquisite lines:
Thus I set my printless feetO'er the cowslip's velvet head,That bends not as I tread.
Shakespeare thus appeals to the muscular imagery:
At last, a little shaking of mine armAnd thrice his head thus waving up and down,He raised a sigh so piteous and profoundAs it did seem to shatter all his bulkAnd end his being.
Many passages like the following appeal to the temperature images:
Freeze, freeze, thou bitter sky,Thou dost not bite so nighAs benefits forgot!
To one whose auditory imagery is meager, the following lines will lose something of their beauty:
How sweet the moonlight sleeps upon this bank!Here we will sit and let the sounds of musicCreep in our ears; soft stillness and the nightBecome the touches of sweet harmony.
Note how much clear images will add to Browning's words: