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diff --git a/78983-0.txt b/78983-0.txt new file mode 100644 index 0000000..a88b07f --- /dev/null +++ b/78983-0.txt @@ -0,0 +1,794 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 78983 *** + + + + + LITTLE BLUE BOOK NO. 1476 + Edited by E. Haldeman-Julius + + What You Should Know + About Your Sensations + + Grace Adams + + HALDEMAN-JULIUS PUBLICATIONS + GIRARD, KANSAS + + + + + Copyright, 1929, + Haldeman-Julius Company + + + PRINTED IN THE UNITED STATES OF AMERICA + + + + +CONTENTS + + + Page + + The Importance of Sensations 5 + + The Nature of Sensations 7 + + How Sensations Occur 8 + + How We Feel 10 + + Visual Sensations 13 + + Common Abnormalities of Vision 16 + + How We See in the Light and in the Dark 19 + + The Importance of the Sense of Smell 22 + + The True Sense of Taste 24 + + The Complexity of Our Perceptions 26 + + Localization on the Skin 28 + + + + +WHAT YOU SHOULD KNOW ABOUT YOUR SENSATIONS + + + + +THE IMPORTANCE OF SENSATIONS + + +Since man first became interested in the processes taking place in his +own mind, his dreams and emotions and thoughts, he has wondered if +he could understand these relatively elusive processes as thoroughly +as he could the more stable facts of the material universe. And ever +since Epictetus and Aristotle began to collect the facts of mental life +and formulate them into the laws which were later to become the basis +of the study of psychology, philosophers and theologians and natural +scientists have debated whether or not this study of the human mind +constituted a real science. The champions of both sides of the question +are worthy of attention. + +Epictetus and Aristotle considered their psychological investigations +strictly scientific. Yet as fascinating and as authoritative as their +studies appeared to their contemporaries, their opinions lose value +today, because none of the discipline with which they were familiar are +accounted scientific by exact modern standards. + +From the scientific movement to which Descartes gave such impetus in +the seventeenth century until the time of Herbert Spencer, psychology +was not considered a science but a mystical preoccupation not unlike +theology. In Diderot’s Encyclopedia of 1752 we find psychology defined +as that branch of philosophy which “defines the human soul and gives +an account of its activities.” Bacon also classified psychology as one +of the philosophies of the soul. With it he included soothsaying and +witchcraft which in his day were supposed to be the two most practical +applications of psychology. + +Comte was the first authority to place psychology among the natural +sciences instead of the philosophies. But curiously enough the one +branch of psychology which he considered exact enough to be classified +along with biology was the one branch of psychology which today is +thought to be completely and absolutely unscientific--phrenology. + +Since the time of Spencer, who accepted psychology as an independent +science following biology and preparatory to sociology, its scientific +status has been fairly generally accepted. Still there have been some +violent dissenters. Kant, in particular, prophesied that there could +never be a science of psychology because mental phenomena could never +be treated mathematically. And the old debate is still raging. John B. +Watson when he adopted his behavioristic platform threw aside all of +the laboriously got results of the introspectionists and functionalists +because he considered them inexact, and irremediably so, when compared +with the results of the biologists and chemists. Many of these same +introspectionists and functionalists feel that the revolutionary and +far-reaching theories of Freud and Jung and Adler are too hypothetical +and too general ever to form the basis of an exact science. + +Yet in one field all but the most radically behavioristic admit that +traditional psychology has justified its scientific claims. This field +comprises the human sensations. + + + + +THE NATURE OF SENSATIONS + + +Sensations are the mental ultimates of the psychological universe just +as the chemical elements are the ultimates of the chemical universe. +Sensations are the colors that we see--the reds and greens and purples +and blacks and whites and greys; the tactual experiences that we +feel--the warmths and colds and tickles and pains and aches; the tones +and noises that we hear; all the vast number of odors that we smell +and our few simple tastes of salt, sweet, sour and bitter. Of course +these simple experiences very seldom appear isolated. They come to +us as integral parts of much more complex experiences, as the taste +of lemonade, the smell of a flower or the colors of a landscape. In +this they parallel the elements of the other sciences which must be +separated out, artificially if necessary, before they can be adequately +studied. + +It is a little ironical that at the very time Kant was denying +that any mental phenomena could ever be treated mathematically the +psychologists, themselves, were bringing the facts of sensation +under mathematical laws and the natural scientists were accepting +these laws as scientific, for it is to be assumed that biologists +and physicists might be more jealous of the limits of an exact +science than philosophers. The natural scientists, however, did +more than complacently accept the psychologists’ own investigations +of sensations; they verified and extended them and pointed out new +fields for the psychologists to explore. This was, of course, no mere +altruistic gesture. Natural scientists, themselves, have a real and +pertinent interest in all sensory problems and it is in their solution +that we come to understand the relations between the three sciences of +physics, biology and psychology, the differences among them and their +interdependence on one another. + + + + +HOW SENSATIONS OCCUR + + +One particular physiological organ or group of organs is responsible +for each of our five senses: the internal ear for sound, the retina of +the eye for color, the papillae of the tongue for taste, and so on. +Each of these special organs responds to a definite type of physical +stimulation: the retina to vibrations of the ether, the internal +ear to sound waves, the tongue to chemical solutions. Every simple +psychological sensation has, then, a rather complicated causal history +and it depends not only on the form of the physical stimulus but also +on the peculiar make-up of its special organ. + +Every physiological organ of the human body is, of course, subject to +a wide range of individual differences. Some hearts are weaker than +others, some livers more sluggish, and some lungs less efficient in +their functions. It is only natural that the sense organs should differ +also. And they do. Yet on the whole they are surprisingly uniform. All +eyes react so typically to certain physical stimuli, and all noses to +others, that physicists themselves call these stimuli by the names +of the psychological sensations that they normally evoke. A light +wave of 687 millimicrons, for example, is known as a red wave because +when it impinges upon the normal retina it produces a red sensation, +and a vibration of 527 is called a green wave for the same reason. A +temperature of 12 degrees centigrade is marked as cold because when it +stimulates the human skin it produces a cold sensation, and 45 degrees +C. is hot because it produces the psychological experience of heat. +Chemists are so familiar with the typical odors of certain substances +that they accept these odors as invariable attributes of the substance. +At times, however, our usually well behaved sense organs respond to +the wrong type of stimuli and paradoxical sensations result. Neither +ether vibrations nor sound waves are necessarily involved when we +receive a severe blow on the head, yet such an accident can cause our +ears to “ring” and our eyes to “see stars.” And a perfectly normal +human being can feel a cold indistinguishable from normal cold when his +skin is stimulated by a temperature of 45 degrees C. (or 113° F.). To +understand this paradox it is necessary to familiarize ourselves with +the anatomy and physiology of the skin. + + + + +HOW WE FEEL + + +The whole surface of the human skin is not equally sensitive to +stimulation. In fact, a very large proportion of it is completely +insensitive. But dotted throughout this insensitive area are hundreds +of thousands of tiny sense organs. They are clustered together much +thicker in some regions of the body than in others, and wherever +they are more numerous the skin is, of course, more sensitive; yet +everywhere there is a sufficient number of them to make us unaware, +unless we investigate carefully, that there are any portions which are +insensate. These organs are of three different kinds and each kind +is responsible for a special type of sensation. The most numerous, +the corpuscles of Meissner, give us our experiences of pressure, the +bulbs of Kraus provide our sensations of cold and the corpuscles of +Ruffini those of warmth. In a square centimeter of the skin there are +approximately twenty pressure spots, thirteen cold spots and two warm +spots. + +When a pressure spot is touched very lightly by a small narrow object +it reacts with a sensation which may be described as a tickle. The same +sensation can be got by gently moving a hair on the forearm or the +back of the hand for the corpuscles of Meissner are situated directly +beneath and to the windward of the hair bulbs and a movement of the +hairs stimulates them adequately. If the pressure is made a little +stronger, the tickle becomes a sensation of contact. Both the tickle +and the contact are definitely experiences of pressure. If the same +pressure spot is stimulated very carefully by either a cold or a warm +object, the experience will still be one of pressure. The pressure will +be neither warm nor cold for the pressure spots can respond only with +tactual sensations. They are as insensitive to thermal stimulations as +are the many other portions of the skin where there are no temperature +spots. The warm and cold spots, alone, give us all our experience of +temperature. + +When a cold spot is stimulated by an object whose temperature is +between 12 and 15 degrees C., a cold sensation is felt. When a stimulus +whose temperature is between 37 and 40 degrees C. is brought in contact +with a warm spot, the typical sensation of warmth results. If, however, +the cold stimulus is applied to the warm spot, nothing at all is felt. +The warm spots do not respond at all until the temperature reaches 37 +degrees. Similarly the cold spots do not react to warm stimuli, warmth +can be realized only from a warm spot. Yet when the temperature reaches +45 degrees C. (113° F.) the cold spots do respond, but with neither +warmth nor heat. They are cold spots, not warm spots, therefore they +can react in only one way--with a cold sensation. So we find that +due to the physiological functioning of an anatomical sense organ, a +physically hot stimulus really feels cold. + +These three groups of sense organs, the pressure, cold and warm spots, +are the only sense organs on the whole surface of the body. Even +the pain which we feel when our skin is pricked or lacerated is not +represented by a special organ. Pain is experienced whenever a nerve +is stimulated directly and cutting the skin immediately exposes a +nerve and pain results. The only other organs from which we receive +any tactual sensations are the muscle spindles which produce aches and +soreness, the spindles of the tendons from which come our sensations +of strain, and the corpuscles of the joints which give us subcutaneous +pressure. Yet think of the wealth of tactual experiences which we have +every day, in fact, every few minutes. Not only such gross experiences +as hunger and thirst and fatigue and dizziness, but simple perceptions +of wetness and oiliness and smoothness and roughness and heaviness +and lightness. There are no specific sense organs for any of these +experiences. They are brought about by the six sense organs already +mentioned and the free nerve endings of pain functioning singly or in +combination, in greater or less degree. + +There are not even any special sense organs of heat. Yet heat appears +as a unique sensation. It is different from warmth because warmth is +essentially comfortable while heat has a distinct and disagreeable +sting. The characteristic sting of heat is recognized whenever we +refer to pepper and other spices as hot. Psychologically, of course, +the sensation of heat is unique and simple, but on its biological +side it is slightly complicated. It is occasioned by the simultaneous +response of a warm spot and a cold spot, or several warm and cold +spots, to a stimulus of more than 45 degrees C. And it can be produced +in no other way. The warm spots, of course respond normally, the cold +spots paradoxically. The normal response is more vigorous than the +paradoxical, consequently we do not often realize the sensory quality +of the cold, while the warmth comes into consciousness. Ordinarily, +then, heat is warm. With particular stimuli and in certain regions of +the body where cold spots are particularly numerous, however, trained +psychologists are able to detect a heat which is cold. Also it is not +an especially rare occurrence to feel cold when we plunge our hands +unknowingly into very hot water. + +Wetness, which seems almost as simple as heat, is produced by the +simultaneous stimulation of a cold spot and a pressure spot. It is +really nothing more than a cold pressure. It is true that we speak of +being wet when we are in a warm bath, but it is only when the water +begins to cool that we get the typical wet perception. This explains +why cold objects so often feel damp when there is actually no moisture +on them and why it is very difficult to determine whether cloth is +dry or not when it is held close to a hot fire, also why we are so +generally unconscious of the continual moisture of our own bodies. + + + + +VISUAL SENSATIONS + + +The number of perceptions produced by the relatively few sense +organs of the skin seems quite insignificant when compared to the +many different colors occasioned by the activity of the retina of +the eye, for the microscopic organs in the retina bring about all +of our sensations of color and of light and shade. All of the rest +of the rather elaborate apparatus of the eye has to do with spacial +perceptions; with form and distance and movement and size. + +The normal human retina is sensitive to only some four hundred wave +lengths of light. The others, like the ultra violet rays, lie outside +the visible spectrum. Yet so efficient is that one small layer of +the eye that it can convert these four hundred ether vibrations into +approximately twelve million hues and tints and chromas. This number +seems astounding because it would probably be impossible for anyone to +name as many as twelve hundred separate colors. In fact, although the +persons responsible for the new shades in women’s stockings seem to +have an unlimited color-vocabulary, most of us get along satisfactorily +with an extremely limited one. Yet the fact that only a very few of +these twelve million hues and shades have common names does not mean +that they cannot all be detected under suitable conditions. Take the +one color, black, for instance. How many vastly different shades do you +group under that one word? + +You can probably name immediately some ten, or maybe twenty objects +which you would without hesitation describe as black. Black velvet, +black satin, black cotton, black wood, coal, soot, ink, and so on. It +is possible that it may never have occurred to you that these blacks +are not identical. Yet a little critical attention to them will show +you how very different they really are. The black paper looks decidedly +grayish when placed beside the velvet. The velvet, itself, begins to +pale when it is compared to the darkness of the inside of a black tube. +The same variety holds for whiteness. White paper is different from +white enamel and white paint. Indeed, it is somewhat difficult to find +two kinds of paper whose whiteness is identical. And the white that is +got from clear sky reflected in a mirror makes the white of any object +look positively dirty. + +Without examining any true colors at all we have already collected a +variety of shades. And this variety grows when we remember all of the +various grays which are darker than the whites but lighter than the +blacks. Von Kries, the German physiologist, found that there were two +hundred and four different shades of gray between the blackest of black +paper and the whitest of white paper. And Kulper, the psychologist, +estimated that the best visible black is a thousand times darker than +the best visible white. + +As soon as the true colors are added to the blacks and whites and +grays, the possible visual sensations begin to multiply almost +limitlessly. There are literally thousands of reds: dull reds, bright +reds, yellowish reds, bluish reds. And there are bluish greens, +greenish blues, yellowish greens and greenish yellows. But there is a +limit to these color combinations. There are no reddish greens, no +greenish reds, no yellowish blues and no bluish yellows. + + + + +COMMON ABNORMALITIES OF VISION + + +The astonishingly wide variation of hues and tints and chromas is +visible to the majority of human beings. There is a large class, +however, whose visual range is much narrower. About three percent of +the male population is known to be partially color blind, that is +insensitive to certain visual stimuli. To such individuals blue and +yellow appear as they do to persons with normal color vision; but they +see both red and green as grey, greenish yellow and orange as greyish +yellow, and bluish green and purple as greyish blue. Partial color +blindness is hereditary and although it usually occurs only in males, +it is transmitted by females. Thus a partially color blind man may have +both sons and daughters who are color normal. All of the children of +his sons may also have normal color vision, but the male offspring of +his daughters will be partially color blind. + +There are also a number of individuals who are totally color blind, +who see no colors at all. Total color blindness is also hereditary and +is also more prevalent among males than among females, but it is much +rarer than partial color blindness and should be confused neither with +that nor with true blindness. Blind persons see neither colors nor +blacks nor whites nor greys. As Helmholtz put it they “see things in +the same way in which we ourselves see what is behind our backs; that +is to say, they do not see at all.” But totally color blind persons +can see; in a dim light they can see exceptionally well. They can +distinguish objects visually as well as persons with normal eyes, but +for them these objects never possess any color. They always appear grey. + +The two forms of color blindness seem more creditable when we realize +that everyone is often either partially or totally color blind. All +of us are partially color blind to objects which we see in indirect +vision, or “out of the corner of the eye.” Many of us, of course, never +realize this deficiency, because we usually pay very little attention +to our indirect vision. If an object interests us we immediately turn +our eyes toward it and focus them upon it and its colors become clear. +But if you will hold an orange or a greenish blue pencil parallel to +and about a foot away from your right ear while your eyes are steadily +focused directly in front of you, and move the pencil gradually until +it is directly in front of your nose, you will find that at the side +of your eye the orange pencil looks only yellow and the greenish blue +pencil only blue. The red and green do not appear until the pencil is +almost within the focus of your eyes. It is only at the very center +then that the eye is color normal. It is partially color blind at the +sides. And it is always totally color blind, of course, in the dark. + +If we wake up suddenly on a black night or go quickly from a brightly +lighted room into one that is much darker, we at first seem to be +quite blind--to be incapable of distinguishing anything. Gradually, +however, our eyes become accustomed to the darkness--the psychologists +say that they become dark adapted, and we can make out the outlines of +familiar objects, can see that parts of the room are lighter and parts +darker than others. But we cannot distinguish any colors. We do not +even see any clear blacks or whites. Everything appears grey. And that +is the way the whole world in daylight as well as in darkness looks to +the totally color blind--as a series of darker or lighter greys. + +The inability to distinguish the hues of colors is not the only thing +which differentiates the way we see in the dark from the way we see in +daylight. We have already noted the fact that under good illumination +the center of the eye is the area of clearest vision. Those objects +upon which our eyes are focused are the ones which appear clearest to +us. Offhand we would suspect that the same principle held in the dark. +Yet it is very easy to demonstrate that it does not. Some night when +you are out of doors look up at the sky and select one small isolated +star and remember carefully just where it is. Then try to focus your +eye upon it. You will find that this is impossible. As soon as you +stare directly at it it disappears, but reappears as soon as you search +for it. This process can be continued indefinitely--a disappearing and +reappearing which is so rapid that the star actually seems to twinkle. +Whenever you look directly at it it is gone, but as soon as you +shift your eyes ever so slightly it is back again. Carefully verified +experiments which elaborate this simple experience have convinced +psychologists of the fact that at night all eyes are completely blind +at the center where in daylight they have the clearest vision. And +totally color blind eyes show this same deficiency in daylight as well +as in the dark. They twitch continually when their possessors attempt +to read. + +So much for the psychological side of visual sensations. If we wish an +explanation of them, of their variety and of their peculiarities, we +must turn once more to anatomy and physiology. + + + + +HOW WE SEE IN THE LIGHT AND IN THE DARK + + +The retina of the eye contains a quantity of microscopic structures, +some of which may be roughly described as rods, others as cones. The +cones are scattered over the entire retina but are thickest at the very +center. The rods have about the same distribution except that they +are entirely lacking at the center. From pathological cases and from +histology the function of these tiny structures has been determined. + +A human eye which contains no rods has never been discovered but the +eyes of fowls and pigeons show this defect, and these animals are +apparently quite blind at night. All of their activities are carried +on in the daylight. Hens do not even lay eggs in total darkness. +Conversely the retinas of nocturnal animals, such as bats and owls and +moles, are almost entirely lacking in cones but are richly supplied +with rods. These and similar findings, together with the psychological +differences of night and day vision, have led psychologists and +biologists alike to conclude that the rods and cones, although they +are very similar in structure, serve two very different functions. The +cones provide us with daylight vision, apparently, while the rods, +alone, are responsible for the manner in which we see in the dark. The +rods are completely inactive in daylight but begin to respond to weak +stimuli as soon as twilight (real or artificial) sets in. And the cones +which are reacting continuously during every second that it is light, +become functionally useless in the dark. + +The cones alone are responsible for true colors. Many theories have +been advanced to explain their functioning, but they are too long and +too complicated to be reviewed here. This much can be stated, however; +only three photo-chemical substances reacting to light produce all +of our many different hues. The same substance reacting in different +ways gives us both red and green, another both blue and yellow, and a +third both black and white. When more than one substance responds to +stimulation we get the intermediate colors which resemble one or more +of these primary colors, for instance, purple which resembles both blue +and red, and orange which is like both red and yellow. In normal eyes +all three substances are found only at the center and consequently it +is only at the center that all colors are visible. In partially color +blind eyes the red-green substance is absent from the center as well as +the periphery and the partially color blind, therefore, can see only +the colors which contain either yellow or blue. In the absence of blue +or yellow stimuli they see only grey. The totally color blind eye is +completely deficient in cones. The totally color blind use their rods +for daylight as well as dark vision. + + + + +THE IMPORTANCE OF THE SENSE OF SMELL + + +We have spent so much time on visual and tactual sensations because +they represent the two senses which have been investigated most +thoroughly on the physical and biological side. We know not only just +what these groups of sensations are psychologically but how they are +physically and biologically produced. Vision has another claim to +careful study. It, along with audition, is known as a higher sense +and is used more by civilized man than the lower senses of touch, +taste and smell. We depend upon our eyes and ears as guides throughout +all of our practical life and they are the two senses which have the +highest biological development. Aside from their original function of +orientation, civilization has forced them to serve two still higher +purposes. Our eyes and ears are responsible both for the language which +we use in conversation and for our two special forms of culture--art +and music. We have no highly developed gustatory or olfactory art and +although both of these senses are very important in our daily lives, +we never use them as conscious means of communication. Yet viewed in +relation to the evolution of the race, smell is the most important of +all our senses. In the extension of the olfactory organs of the reptile +we find the first hint of the development of a brain. And in all +animals which live on the land the sense of smell is highly specialized. + +Fish have no real olfactory sensations. The piscatorial organ which +corresponds to the mammalian nose is really an organ of taste. +Even animals which spend the greatest part of their lives in the +water--whales, dolphins and seals--have very rudimentary olfactory +organs and probably no real sensations of smell. Birds, also, contrary +to common opinion, have a very poor sense of smell and exceedingly +efficient eyes. The power which is usually attributed to their +olfactory sensitivity is actually due to their extraordinarily keen +sight. It has been proven by experiments that if a decaying animal +carcass is carefully concealed carrion birds will pass directly by it +without pausing to investigate. In all animals, however, who habitually +live upon the ground, olfactory experiences are remarkably numerous and +varied. It is easy to verify this fact by observing the behavior of +insects and any four-footed mammals, especially dogs. But it is hard to +believe that human beings are equally sensitive to odors. Yet they can +be. + +The human olfactory sense has been extensively investigated but at the +present time no one has been able to state the exact number of smells +which the human nostrils are capable of detecting. The chief difficulty +lies in the fact that while the tactual and visual senses, for example, +are physically limited, new odorous stimuli are being discovered every +day. Each slightly different chemical compound produces a new odor and +each new species of plant life carries its own typical smell. Already +there is reasonable experimental ground for assuming that there are +sensations from all of the other sense departments put together. + +There are two principal reasons why we are generally unaware of this +wealth of olfactory experiences. The first is that man habitually walks +on two feet so that his nose, compared to that of other mammals, is +very far from the ground and smells have a tendency to cling to the +ground. Consequently, those smell stimuli which do reach his nostrils +are very weak by the time they arrive there and are, therefore, +generally ignored in favor of the more insistent visual and auditory +tactual stimuli. In the second place, the most frequent and the +strongest odors we experience we customarily ascribe to our sense of +taste. We speak of the taste of our food when we are actually referring +to its smell. + +It is very easy to prove by experiment how limited is our sense of +taste but we even have a very strong hint of the fact during our +everyday life, or rather during that part of our everyday life when +we are afflicted by a severe cold in the head. At such times we think +that even the most savory meal has very little taste. Yet common sense +should tell us that our tongues, which in adult life contain almost +all of the sense organs of taste, are not seriously impaired by a bad +cold. We should know that it is our noses, in which the olfactory organ +is situated, which are really affected. It is the sense of smell which +we habitually confuse with that of taste which is weakened. It is not +entirely out of commission, however. There is a small passage at the +back of the mouth, leading to the nose, of which we are disagreeably +conscious when we choke. In swallowing, air laden with odorous +particles is pushed up through this passage, the posterior nares of +the nostrils are immediately stimulated and smell is experienced. This +arrangement is quite evident to us when we take medicine which has a +particularly disagreeable odor. Holding the nose helps a great deal +until the dose is actually swallowed. If you should continue to hold +your nose and, instead of swallowing, rinse your mouth thoroughly, +you would be surprised to find how very little unpleasant “taste” the +medicine contained. A rather agreeable sweetness might be all that +remained. + + + + +THE TRUE SENSE OF TASTE + + +When all odor is completely eliminated by stopping the nostrils +with cotton and the surface of the tongue is stimulated directly, +it has been discovered that there are only four fundamental tastes, +sour, salt, sweet and bitter. A particular region of the tongue is +responsible for each of these four tastes. It is very easy to find +these specialized parts for, while the functional organ of the nose +is so securely hidden that it is almost impossible to stimulate it +directly, the gustatory organs are visible to the naked eye. They are +contained in the tiny bright red spots, or papillae, that dot the +duller surface of the tongue everywhere except in the center. Although +any single papilla is apt to contain several kinds of taste buds and +may, therefore, be sensitive to more than one taste, and although the +buds which respond to salt are fairly equally distributed over the +sensitive area of the tongue, those which react to sweet, sour and +bitter are grouped on different regions. Language recognizes this +distribution. + +We describe as a sweet expression one in which the lips are drawn +toward the tip of the tongue and the tip, itself, is flattened out. +The taste buds which respond to sweet stimuli are found clustered at +the tip of the tongue. In a sour expression the lips are drawn back +from the tip of the tongue and down toward the sides. And the sour +taste buds are thickest on the sides of the tongue. When a face wears +a bitter expression the tongue itself is pulled back until it is in +contact with the roof of the mouth. And the bitter taste buds are found +almost exclusively at the rear of the tongue. + +Testing these three facial expressions before the mirror will afford +you a little innocent amusement, but remembering what they represent +will help you to get the full effect of desirable tastes and to avoid +the disagreeable qualities of others. A bitter tablet, for example, +should not be placed at the rear of the tongue where you would get +the full benefit of its bitterness, but rather in the center which is +relatively insensitive to any taste. + +The manner in which children lick a stick of candy shows that they +realize unconsciously how they can make the most of its sweetness. The +taste buds also explain another habit of children which is usually +frowned upon by their elders--that of taking large mouthfuls. Children +have many more taste buds than adults. They are distributed not only +over the whole surface of the tongue but on the insides of the cheeks +as well. Consequently when children stuff their mouths until their jaws +bulge, they actually get a great many more gustatory sensations than +when they have only a dainty morsel on their tongues. If the taste buds +in the cheeks did not atrophy early in life, there would probably be +nothing ill mannered about large mouthfuls. As it is, large mouthfuls +are quite useless to adults. The food has to be directly on their +tongues before they can taste it. So, forgetting the days when bulging +cheeks were so delightful, adults become intolerant of a habit which +was once both pleasant and useful. + + + + +THE COMPLEXITY OF OUR PERCEPTIONS + + +Because it is possible to isolate particular sensations and study them +in detail, as we have attempted to do here, it must not be assumed +that we customarily experience them in so simple a manner. Even at +birth the human nervous system is a tremendously complicated affair. +There are cross connections among the senses. From the very first most +of our sensations seem to us completely bound up with other processes. +A pure sensation is a very rare occurrence. A color is nearly always +the color of something--of cloth or leather or paper or liquid. All of +the objects which have colors have textures also. They look rough or +smooth or glossy or dull. And the color and texture seem inalterably +mixed together. It is only when we look at a rainbow or the rays of +a spectroscope that we see a color which does not appear to be an +integral part of some object. + +Tones seem to belong less to the objects which produce them--to exist +by themselves to a greater degree. Yet it is much more difficult to +produce a simple tone than a pure color. In this case the trouble +lies not so much with the nervous system as in the physical stimulus +itself. There are not as many audible tones as there are discernible +colors and odors, but there are some eleven thousand of them. The tone +got from a musical instrument is not, however, a simple tone or a pure +sensation. It is a combination of many tones, some of which are more +intense than others. These extra tones or partials are produced by +the musical instrument itself and they cannot be eliminated because a +musical instrument is essentially a complicated vibrating body. With +each vibration it produces over-tones as well as a principal tone. It +is the different intensities of the partial tones which give timbre to +instruments. It is by their characteristic timbres that we are able to +distinguish a G struck on a piano from the G of an organ or a violin or +a saxophone. + +Because it is so difficult to produce simple tones, psychologists have +been unable to discover a great deal about our sense of audition. The +physical side of sound has been adequately investigated, but we have to +resort to musical terminology when we try to describe the sensations +which are produced. + +We have already discovered, then, in the case of the three lower +senses, our perceptions appear so unified that we seldom realize that +they are complex. Wetness seems to be a unique experience until we +recognize that it is composed of cold and pressure. So completely +blended are our tastes and smells that a severe cold in the head is +required for their conscious separation. And psychologists had to wait +for years, until a soldier had a strange cortical injury, before they +learned how complicated a process is tactual localization. + + + + +LOCALIZATION ON THE SKIN + + +Localizing a spot on the surface of the skin seems to be the very +simplest of matters. An itch occurs on the hand and automatically we +scratch it. Sometimes, it is true, the itch comes in the small of the +back and we cannot quite reach it. But we can at least point out its +approximate position to some other person. Both the scratching and +the pointing seem to be as simple as reflex actions. This apparent +simplicity led the psychologist Loetze to believe that every single +spot on the body had a special attribute which he called a “local +sign.” According to his doctrine we know exactly where we have been +touched the instant that we are aware of the touch itself. Henri, +another psychologist, discovered, however, that if he was stimulated on +the skin when his eyes were closed and tried to locate the exact spot +before he opened his eyes again, he made large errors of localization +and the errors were as great on the finger as on the forearm. This +discovery cast grave doubt on the doctrine of the local sign. + +During the late war two psychologists, Gelb and Goldstein, were +attached to a German army hospital. One day a patient was brought in, +who had had both of his occipital lobes destroyed, but the rest of his +nervous system was still intact. This meant that he had absolutely no +visual cognitions but the rest of his mental functions were unimpaired. +Gelb and Goldstein immediately began to experiment with him and they +got some rather startling results. + +If the patient was lying quietly with his eyes shut and was touched +on some part of his body, perhaps his left foot, he knew that he had +been touched but he had no idea of the place. He did not know whether +it was on the leg or the forehead or the chest or the hand. It made no +difference how intense the stimulus was or how long it was continued. +As long as he remained motionless he could not tell where it was. +If, however, he was allowed to move his body as much as he wished, he +could localize the place touched almost exactly but he did it in a very +strange way. He at first wriggled about so that he set his entire body +in motion. Then gradually he would move less and less. If the stimulus +was applied to his right index finger, he would, after a few squirms +of his whole body, move only his trunk, then only his right arm, then +just his forearm, his right hand, his fingers, and finally only the +stimulated finger. Then he could say just where the pressure was felt. + +If he was touched in two places at once, as long as he was quiet, he +would feel only one. If the two stimuli happened to be very close +together, for instance both on the same finger, even by wriggling he +could not discover that they were two. But if they were rather widely +separated he could by the proper movements locate first one and then +the other. + +When he was allowed to touch the place stimulated, his method was the +same as when he wriggled his body. At first he would run his finger +aimlessly over his skin, gradually bringing it closer and closer to the +stimulated area until the exact spot was hit upon. + +These results led Gelb and Goldstein to the conclusion, which was +foreshadowed by Henri, that immediate localization is always a function +of vision. And they agreed with the findings of some rather different +experiments which had been carried on at Cornell University several +years before. The subjects of these experiments had to be real +scientific martyrs. They were required to swallow a rubber tube in +which there was an electric coil. The tube reached from the mouth to +the bottom of the stomach and at intervals there were openings in it +through which the experimenter could send an electric shock. All of +the subjects had the greatest difficulty in locating the shocks; they +could feel them clearly enough but they could not discover in which +part of their digestive tracts they were. A stimulation might be at the +extreme end of the tube and the subject would report that it was in his +thorax. A shock at the esophagus would be referred to the bottom of the +stomach, and so on. + +If localization is primarily a matter of vision, these errors are +easily accounted for. No one has a very complete mental picture of the +inside of his own digestive tract. When we localize sensations there we +must do so by reference to the more familiar external body. But since +the sensations are felt internally, not on the outside, it is only +natural that the reference should often be erroneous. Doctors recognize +this. They accept a patient’s statement that he has a pain but they +are not so quick to take his word for its exact location. Instead +they investigate. And when they thump about first at one place then +at another, they are using the same method of localization which Gelb +and Goldstein’s soldier employed when he ran his finger over his body. +Fortunately, this method, though much slower than visual localization, +is usually successful. + + + + +Transcriber’s Note: + +- Inconsistencies in hyphenation have been standardized. + +- Minor punctuation errors have been changed without notice. + +- Spelling was retained as in the original except for the following +changes: + + Page 21: “spent so much time is” to “spent so much time on” + Page 27: “most of our sensations some” to “most of our sensations + seem” + Page 27: “a pure sensation. It it” to “a pure sensation. It is” + + + +*** END OF THE PROJECT GUTENBERG EBOOK 78983 *** |