Fig. 14.—Color Pyramid.Fig. 14.—Color Pyramid.
the spectrum plus the non-spectral purples, between red and violet, all arranged in an orderly manner around the axis. The nearer we approach the axis, the less saturated, that is, the more whitish, or grayish, or blackish are the colors represented. The most saturated colors are therefore represented by the peripheral line of the base. The base is slanted because the most saturated colors are not all of the same brightness (meaning by this term exclusively lightness as opposed to darkness). The saturated yellow is much brighter than the saturated blue and must therefore be located here, symbolically, nearer the point of white than of black, while blue must be located nearer the point of black than of white. The figure shows clearly that it is impossible to deviate from the peculiar brightness of each saturated color without diminishing the saturation, for we cannot move up or down from any point of the peripheral line of the base and yet remain within the double pyramid, without approaching the axis. But if our starting point is a color of less than the maximum of saturation, we may change the brightness withincertain limits without changing the saturation, for we may then, to a certain extent, move up and down parallel to the axis.
Some have represented the color system by a double cone, using as common base a circle. But a four-cornered base represents an additional fact of experience which is lost sight of in the circular plane. The four colors red, green, blue, and yellow possess this property: that any one of them is entirely dissimilar in color tone to any of the other three, while any given color other than these must resemble just two of these. No other four or any other number of colors can be found which fulfill exactly these conditions. In order to represent this fact symbolically, we ought to give the colors red, green, blue, and yellow distinguished places in the periphery of the basal plane, and this can be done most easily by choosing as a base a four-cornered plane.
By the aid of this color system it is easy to understand an abnormality of our color sense which occurs rather frequently, so-called color blindness. It is found almost exclusively among men, three per cent of them being affected, whereas it is very rare among women, although it is inherited through woman. Instead of three dimensions, two are sufficient for the representation of the color sensations of such individuals: a plane which is placed through the points white, black, blue, and yellow. The color sensations represented by those points of the pyramid which lie outside the plane just mentioned appear to the color-blind person yellowish if they are located on either side of the yellow triangle, so to speak; they appear bluish if they are located on either side of the blue triangle, and colorless if located exactly on either side of the axis. There are, however, a large number of minordifferences not included or even expressed incorrectly in the above brief statement; the color-blind person, for instance, is more likely to see things yellowish than bluish. Since color-blind people may sometimes confuse such conspicuously different colors as red and green, they are often called red-green-blind. That they also confuse greenish blue with violet seems less remarkable to the normal person than the former fact. In testing a color-blind person one must not expect to find that he will confuse any red with any green. Brightness and saturation play here very important parts, and all kinds of individual differences have been observed. Nevertheless color-blind people fail to distinguish red and green much more frequently than people having a normal color sense, and should therefore be strictly excluded from any service in which the distinction of red and green is of importance, as in railway and marine signaling. For the normal person red and green are the ideal colors of signals, because yellow is not always sufficiently different from white, and a saturated blue is too dark.
It is interesting to observe that colors are never simple or complex in the sense in which a musical tone is simple and a chord is a multitude of tones, or lemonade is a mixture of sour and sweet. Any color sensation which is uniform over its area is as simple as any other. The colors which, in our color pyramid, are located between two of the four fundamental colors red, green, blue, and yellow are “mixtures” only in the sense that the mixed colorresemblestwo of those four, not that we are conscious of two separate sensations in one act of perception.Nevertheless we often have to speak of mixed colors and of principal colors entering into mixtures. These phrases have many different meanings. Most colors which we see in actual life are mixtures in a physical sense, mixtures of ether waves, although our sense organ does not inform us as to whether they are mixtures or homogeneous light. White or gray or purple can never be anything but mixtures in this physical sense. In actual life the only color which is often simple,homogeneous light, is dark red, for physical causes which do not concern us here. But this physical complexity is irrelevant for the psychological question as to the simplicity or complexity of color sensation.Even more confusion has been carried into the psychology of color by the fact that in dyeing and painting chemical substances are sometimes applied as they occur in nature or come from the factory, sometimes they are first mixed together and then applied. The painter cannot afford to have an infinite number of color pigments on the palette. He selects therefore a small number, at least white, red, yellow, and blue. This is for many ends sufficient, and he may therefore call these pigments his principal colors, and wonder why one should call green a “fundamental” color, since he can produce it by mixing blue and yellow. It is indeed no difficult task to find people who, like Goethe, are convinced that they are able to perceive in the green the yellow and the blue which the painter used in order to give us the impression of green.Still another difference occurs in the use of the terms simple and mixed colors in physiology, with reference to the processes going on in the eye and the part of the nervous system connected with the eye. It is plain, therefore, that whenever we speak of colors we must state in what sense we do this.
It is interesting to observe that colors are never simple or complex in the sense in which a musical tone is simple and a chord is a multitude of tones, or lemonade is a mixture of sour and sweet. Any color sensation which is uniform over its area is as simple as any other. The colors which, in our color pyramid, are located between two of the four fundamental colors red, green, blue, and yellow are “mixtures” only in the sense that the mixed colorresemblestwo of those four, not that we are conscious of two separate sensations in one act of perception.
Nevertheless we often have to speak of mixed colors and of principal colors entering into mixtures. These phrases have many different meanings. Most colors which we see in actual life are mixtures in a physical sense, mixtures of ether waves, although our sense organ does not inform us as to whether they are mixtures or homogeneous light. White or gray or purple can never be anything but mixtures in this physical sense. In actual life the only color which is often simple,homogeneous light, is dark red, for physical causes which do not concern us here. But this physical complexity is irrelevant for the psychological question as to the simplicity or complexity of color sensation.
Even more confusion has been carried into the psychology of color by the fact that in dyeing and painting chemical substances are sometimes applied as they occur in nature or come from the factory, sometimes they are first mixed together and then applied. The painter cannot afford to have an infinite number of color pigments on the palette. He selects therefore a small number, at least white, red, yellow, and blue. This is for many ends sufficient, and he may therefore call these pigments his principal colors, and wonder why one should call green a “fundamental” color, since he can produce it by mixing blue and yellow. It is indeed no difficult task to find people who, like Goethe, are convinced that they are able to perceive in the green the yellow and the blue which the painter used in order to give us the impression of green.
Still another difference occurs in the use of the terms simple and mixed colors in physiology, with reference to the processes going on in the eye and the part of the nervous system connected with the eye. It is plain, therefore, that whenever we speak of colors we must state in what sense we do this.
Auditory sensations are usually divided into two classes: tones and noises. They do not often appear separately. A violin tone, for example, is accompanied by some noise, and in the howling of the wind tones may be discerned. Both may be perceived in many different intensities, and both may be said to be low or high. Many thousands of tones may be distinguished from the lowest to the highest audible. Within one octave, in the middle region, more than a thousand can be distinguished. The fact that in music we use only twelve tones within each octave arises from special reasons: first, the difficulty of handling an instrument of too many tones; and especially the fact that with a particular tone only a limited number of others can be melodically or harmonically combined with a pleasing result.
Just as the colors, so the tones are a continuum, that is, one can pass from the lowest to the highest tones without at any moment making a noticeable change. We refer to this continuum by the word pitch. But tones also possess what is called quality; that is, they are either mellow or shrill. This mellowness is to some extent dependent on the pitch of each tone, for low tones are never very shrill and high tones never very mellow. But to some extent a tone may be made more or less shrill and yet retain exactly the same musical value, the same pitch. This is brought about by the overtones, of which a larger or smaller number is nearly always added to musical tones. Without being perceived as separate pitches the overtones influence our consciousness of the mellowness of a tone—the fewer overtones, the mellower; the more overtones, the shriller the tone. Each musical instrument has its characteristic quality of tone, and in some instruments, especially in organ pipes, the quality is skillfully controlled by the builder, who “voices” each pipe so that it produces the required number of overtones of the right intensities.
It was said above that the overtones, as a rule, are not perceived as separate pitches added to the pitch of the fundamental tone. It is not impossible, however, to perceive them thus. Those who experience difficulty in perceiving the overtones as separate pitches may use at first special instruments, resonators, which are held against the ear and greatly increase each the intensity of a special overtone. After some practice one becomes aware of the pitch of an overtone without the aid of a resonator.
Noises may be classified into momentary and lasting noises. Examples of the former are a click and the report of a gun; examples of the latter, the roaring of the sea or the hissing of a cat. Many noises, as thunder, rattle,clatter, and the noises of frying and boiling, are mixtures of momentary and lasting noises.
From all we have said it follows that the function of hearing is an analyzing function, enabling the mind to separate that which has lost its separate existence when it acts upon the tympanum. Two or three tones sounding together are usually perceived as two or three tones. In hearing music we can simultaneously listen to several voices. When two people talk together we may to some extent follow them separately. This is obviously an ability of great importance in animal life, since different objects, characterized by different tones or noises, rarely separate themselves spatially as the colors of different objects do, but act upon the sense organ as a single compound.
There are, however, certain exceptions to the analyzing power of the ear. If two tones differ but little in pitch, they are not perceived as two, but a mean tone is heard beating as frequently in a second as the difference of the vibration rates indicates. The ear thus creates something new, but of course something definitely depending on the external processes. If two tones not quite so close in pitch are sounded, one or even several new tones are created, combination tones or difference tones, the pitch of the new tone being determined by the difference of the rates of vibration. These difference tones do not seem to serve any purpose in animal life. They are merely secondary phenomena, of little practical consequence, but of much interest to the student of the function of the organ of hearing.
We have seen that the number of classes of sensations is fairly large; but to state this number exactly is impossible. According as we count the muscles, the joints,the lungs, the digestive organs as several sense organs or as a single group, the number of classes of sensations is larger or smaller. However, it matters little whether we count them or not. We know that provision is made for everything needed. Information about the most distant things is obtained through the eye; information about the things in contact with the body or the body itself comes through the cutaneous and organic sense organs. Most varied is the information about things at a moderate distance, obtained through eyes, ears, and nose combined.
Many of the higher animals surpass man in one or the other respect through their sensory equipment. Many of the birds (for example, the carrier pigeons) have a sharper eye; dogs and other animals, a keener sense of smell. The sense of hearing in man seems to be equal to that of the higher animals, and the cutaneous sense perhaps superior. In one respect man is better equipped than his mode of living justifies, that is, in possessing the semicircular canals and the otolith organs, for which he has scarcely any use. In another respect he, as well as the animals, is very poorly equipped, that is, for the direct perception of the electromagnetic-optic phenomena of physics, only a small range of which can be perceived as a particular kind of sensations, namely, as colors.
The study of the simple in mental life, as previously mentioned, is always a study of abstractions. The actual experience even of the briefest moment never consists of a single sensation. And actual sensations are always characterized by more than the properties which we have thus far discussed. Colors always occupy space of a certainsize and shape; tones come from a certain direction; both colors and tones are either continuous or intermittent, they are perceived simultaneously or in succession. We naturally inquire into the laws of these spatial and temporal relations. Unfortunately psychologists have not yet agreed on a definite answer to the question concerning space and time. The question is beset with difficulties, partly real, partly imaginary.
Is it possible to perceive temporal relations as sensory qualities as we perceive colors, tones, tastes, and smells as sensory qualities? We certainly lack a sense organ of time. But aside from this, it seems impossible to perceive duration at its beginning, when the end is not yet known; impossible to perceive it at the end, when its beginning no longer exists and can only be recalled in memory. It seems equally impossible to get direct knowledge of a spatial relation. Imagine one particular pointaof the skin or the retina of the eye. If this is stimulated, our mind receives a definite impression of touch or color, but no indication of or reference to any other point, since no other point is stimulated. Let the same be true for the pointb. How, then, ifaandbare stimulated simultaneously, can the mind receive an impression of distance between the two points, since there is no such consciousness in the perception of either of them? If the mere fact of an objective distance between the stimulated neurons were a sufficient explanation, then tones too should be localized differently.
Those who took these objections seriously tried to think of some means by which the objective, but not directly impressive, spatial relations could become known to the mind. It was suggested that the almost unceasing movements of the eyes and fingers, the chief organs of spaceperception, might have significance in this connection; that perhaps the kinesthetic sensations of eye and finger movement, being added to the visual or tactual impressions, made up the consciousness of spatial relationship.
All attempts, however, to prove the correctness of this and similar theories by applying them to the details of special experience, have failed. While there is no doubt that movements of our eyes and fingers are of great importance for the development and extension of the spatial consciousness in the individual as well as in the race, they are not the source from which springs the individual’s ability to perceive spatial relationship. The fundamental part of our ability ofspatialperception is inborn, just as our ability to perceive light or blueness or cold is inborn. From this inborn capacity for spatial perception the individual’s delicate and elaborate sense of space is derived.
The most convincing proof that there is an innate capacity for spatial perception, is the spatial consciousness of persons born blind, to whom an operation has given eyesight. The crystalline lenses of these persons have been as little transparent as ground glass, so that they have been unable to recognize any outlines of things. Nevertheless, they make spatial distinctions immediately after the operation for removal of the lens. Of course they cannot, without further experience, tell that a round thing is the ball with which they have been familiar through the sense of touch, or a long and narrow thing a walking stick. But they immediately perceive the round thing as something different from the long and narrow thing, without any tendency to confuse them. Spatial extent is therefore an attribute of visual and tactual sensation as brightness or darkness is an attribute of visual sensation, and mellowness or shrillness an attribute of tone; withthis difference only, that spatial extent is not restricted to one sense, but is common to visual and cutaneous sensations. That this is founded on some kind of similarity of these senses cannot be doubted. But this similarity is to be looked for in structural peculiarities of the nerve centers, not in accessory mental states serving as special agents of spatial consciousness.
Very much the same is the case with time. Let us admit that the temporal consciousness of our ordinary life is largely mediated by accessory sensations and images. Minutes, hours, days, weeks, are not experienced directly as properties of sense perception, but are extensions of simpler experiences. But such extensions would be impossible if duration and succession were not, somewhere in our mental life, direct experiences. They are direct experiences in some very brief temporal perceptions occupying, say, only a fraction of a second. The flash of a lighthouse signal, the quick succession of sounds when a person knocks at a door, are perceived as having temporal attributes without any mediation by conscious states acting as agents. Thetemporalattributes are elements of perception no less direct than the intensity of the light or of the sound. The same holds for all other sensations. Time is an attribute common to all. But here, as in space, we cannot tell exactly in what respect all senses are similar so far as the nervous processes are concerned. It seems that these processes or their after effects continue a certain time after the stimulation has ceased.
Another attribute common to all sense impressions is the belonging-together of sensations, theunity in variety, so to speak. The most striking example is the relationship of tones in harmony and melody. Tones of certain comparatively simple ratios of vibration belong together in a higherdegree than others. We cannot explain this by reference to conscious agents mediating the effect. It is a fundamental attribute of each tonal combination, the conscious effect of our inherited nature. It is a property of sense, not of thought.
In other cases our consciousness of relationship is indirect, mediated by other conscious agents; for instance, when I group together voluntarily four or five adjoining holes of a sieve and perceive them as a unit. This grouping together would be impossible if the mind did not possess the native ability to perceive a number of sensational elements as a unit without altogether losing the consciousness of variety. It is a mere consequence of our inborn nature when we perceive as such units, for example, an animal romping among unchanging surroundings, a picket fence divided into groups by the fence posts, a familiar compound perfume, a dish made up of several familiar food substances. The same holds for successive elements. We could never perceive tones or noises in various rhythm forms if our mind did not possess the native ability to perceive a number of successive elements of sensation under certain conditions as a sensory unit.
Our numerical concepts are obviously only abstract symbols for units containing each a certain variety of elements.
It is most interesting to observe the astonishingabsolute sensitivenessof some of our senses, that is, their ability to respond to exceedingly small stimuli. It has been a difficult task to design physical instruments as sensitive to sound as the ear. It has not been possible, thus far, to surpass the ear. The sensitiveness of the eye to the faintestlight is estimated to be a hundred times that of the most sensitive photographic plates. Remember what a long exposure is necessary to photograph things in a rather dark room; but the eye takes a snap shot, so to speak, of a star of the fifth magnitude, or of a landscape in diffused moonlight. Man’s organ of smell is far inferior to that of many animals. Nevertheless a trace of tobacco smoke or musk in the air whose presence no chemist could detect is easily perceived through the nose. A gram is about one twenty-eighth of an ounce; a milligram is one thousandth of a gram. One millionth of a milligram of an odorous substance is sufficient to affect the organ of smell. Taste also is sensitive, particularly when supported, as in tasting wine or tea, by smell. The cutaneous and kinesthetic senses, on the other hand, are not very sensitive. A weak pressure, a small weight, a slight tremor of our limbs, a spatial extent, can be detected much more readily by delicate instruments than by our fingers or our kinesthetic organs.
Very important is the range of perceptibility. Our measuring laboratory instruments are, as a rule, adapted only to a small range. To weigh a heavy thing, like a stack of hay, we have to use a balance differing from that used by the prescription druggist. The watchmaker’s tools are much like those of the machinist, but neither could use the other’s tools. Nature cannot well provide separate sets of tools for delicate and gross work. With our hand we estimate the weight of ounces, pounds, and hundredweights. The same ear which perceives a falling leaf can be exposed to the thunder of cannon without ceasing to respond in its normal way. The eye which perceives a small fraction of the light of a firefly, can look at the sun somewhat covered by mist, radiating light many milliontimes as intense. No laboratory instrument has an equal range of applicability.
This wide range of usefulness is made possible partly by purely mechanical provisions, partly by a special law of nervous activity usually called Weber’s law. The iris of the eye with pupil in the center is a readily changeable diaphragm. The stronger the external light, the smaller the pupil, and the reverse; so that the eye is capable of functioning at a stronger and also at a fainter illumination than it could function if the width of the pupil were of a medium, unchangeable diameter. The nose can smell faint odors better if larger quantities of the odorous substances are by sniffing brought into contact with the organ. Too strong odors are kept away by blowing out the air.
More important, however, than such mechanical devices is the effect of Weber’s law. If a stimulus is increased, the nervous excitation is also increased,—not absolutely, but only relatively to the stimulus before the increase. Suppose an oil lamp of ten candle power needs an addition of a two candle power light to make me observe that the illumination has changed. Nevertheless I shall not be able to observe a change of illumination if to an incandescent gas light of sixty candles two candles are added. The addition must be in proportion to the stimulus. Since sixty is six times ten and twelve is six times two, twelve candles must be added to make me observe the difference in illumination. To an arc light of two thousand candles four hundred have to be added to obtain the same result. If a postal clerk is able to recognize that a letter which he weighs on his hand and which is one twentieth heavier than an ounce, requires more than the one postage stamp attached to it, he will probably be found capable of observing in the samemanner that a package of newspapers prepaid for one pound does not have the correct number of stamps if it is actually one twentieth heavier than a pound.
Another way of speaking of the law is this: If we imagine a definite stimulus successively increased by such amounts that the change of the sensation is each time just as noticeable as it was the last time, the added amounts of the stimulus are ageometrical progression. Let us express the fact that the change of the sensation can always be noticedwith the same ease, by saying that the additions to the sensation are an arithmetical progression. We can then state Weber’s law in these simple words: If the sensation is to increase in arithmetical progression, the stimulus must increase in geometrical progression. This statement is mathematically identical with the most widely adopted statement of the law, namely, thatthe sensation is proportional to the logarithm of the stimulus.
The practical result of the law in our mental life is this: The mind is informed of a further increase in the intensity of the stimulus (however great this intensity may have become before this last increase) without having to respond to the absolute intensity of the stimulus with a correspondingly enormous activity of the animal organism. Thus the mind is enabled, figuratively speaking, to weigh a stack of hay or a druggist’s herb on the same balance, to apply the same tool to a watch or to a railroad locomotive, or at least to perform its work with a much smaller number of tools than would otherwise be required. In the eye, for instance, we have, as we see below, only two different kinds of receiving instruments for faint and for strong light.
It must be mentioned, however, that Weber’s law does not hold good over an unlimited range of intensities of stimulation. If the sunwere twice as bright, it would not appear brighter to the eye. For such extreme intensities the law is no longer valid. Neither is it valid for exceedingly low intensities; it makes no difference to the eye whether the wall of a dark room is illuminated from a distance of three or four yards by the glow of one cigarette or a dozen. The logarithmic equation applies only to a certain—quite large—range of medium intensities. For this range our sensitiveness to change is not only constant, but also greatest. Changes in illumination within this range can be perceived as soon as the stimulus increases or decreases by about one hundred and fiftieth.Weber’s law has still another practical significance. A thing which we recognize by the aid of the differences in illumination of its parts (as, for example, a stone relief) or by its differences in loudness (as a rhythm beaten on a drum) always retains, not the same absolute differences, but the same quotients or proportions of the different light or tone values, however our distance from the thing varies. Weber’s law, then, enables us to perceive the identity of the thing although the absolute light or tone values have undergone change. If our nervous activities were not regulated in accordance with Weber’s law, the relief and the rhythm might become unrecognizable at a greater distance, and the relief also at dusk.
It must be mentioned, however, that Weber’s law does not hold good over an unlimited range of intensities of stimulation. If the sunwere twice as bright, it would not appear brighter to the eye. For such extreme intensities the law is no longer valid. Neither is it valid for exceedingly low intensities; it makes no difference to the eye whether the wall of a dark room is illuminated from a distance of three or four yards by the glow of one cigarette or a dozen. The logarithmic equation applies only to a certain—quite large—range of medium intensities. For this range our sensitiveness to change is not only constant, but also greatest. Changes in illumination within this range can be perceived as soon as the stimulus increases or decreases by about one hundred and fiftieth.
Weber’s law has still another practical significance. A thing which we recognize by the aid of the differences in illumination of its parts (as, for example, a stone relief) or by its differences in loudness (as a rhythm beaten on a drum) always retains, not the same absolute differences, but the same quotients or proportions of the different light or tone values, however our distance from the thing varies. Weber’s law, then, enables us to perceive the identity of the thing although the absolute light or tone values have undergone change. If our nervous activities were not regulated in accordance with Weber’s law, the relief and the rhythm might become unrecognizable at a greater distance, and the relief also at dusk.
A further important relation between our mental life and the external world consists in our much greater sensitiveness to the moving and changing than to the stable and permanent. A pencil point moved over the skin under slight pressure gives us a perception of the length and direction of the line traversed more accurate than the impression received from the edge of a screwdriver pressed on the skin. On the peripheral parts of the retina the sizes and distances of things are not easily perceived; but no difficulty is experienced in noticing a waving handkerchief or a starting animal. Only the small central part of the retina is adapted to the perception of the motionless.
The same statement holds for qualitative changes. The eye is not only more sensitive to that which qualitatively changes than to that which remains unchanged; it evenloses its ability to perceive things if for a considerable time no qualitative changes occur. We have seen that our eye can take snap shots under conditions which would make this impossible for the photographic camera. But for time exposures, like those used in photographing faint stars, continued for hours, our eye is not suited. The eye, in such a case, would soon cease to distinguish anything. The eye completely fixed upon one set of objects soon sees their lighter parts darker, their darker parts lighter, their colored parts less colored—more grayish—that is, it sees everything gray on gray. This is technically called adaptation of the eye. Moving the eye suddenly, we become aware of this adaptation in peculiar after-images.
Similar adaptations occur in other sense organs. Constant pressure on the skin, unchanging temperature of not extreme degree, permanent odors, cease to be perceived. But what is new, what differs from the condition which was in existence just before, is perceived at once; and because of the sense organ’s adaptation for something else, as a rule it is seen with particular intensity. This is obviously the most favorable equipment for a struggle for life. Nothing is more dangerous in battle than surprise.
Our present knowledge of the mechanical, chemical, and physiological laws governing the peculiar dependence of the different kinds of sensations on special properties of the sense organs—that which is customarily called a theory of vision, a theory of audition, and so on, is rather unsatisfactory. Some thirty years ago much seemed to be perfectly explained which has since become mysterious again. This much has been learned, that the laws in question are far more complex than they were believed to be.
Only one statement about eyesight can here be madewithout fear of contradiction, that is, that the eye is a double instrument, one part of the organ serving in daylight, the other at dusk and in twilight. But this explains only a part of the total function of the eye. The retina of the eye consists of a great number of elements called rods and cones, forming a kind of mosaic. Twilight vision is served by the rods, which contain a sensitive substance called the visual purple. Most of the rods are in the peripheral parts of the retina, becoming less numerous toward the center. In the central area there are no rods at all. The only service of the rods is the mediation of a weak bluish-white sensation of various intensities, as in a moonlit landscape. Ordinary day vision is served by the cones, which are the only elements present in the center and become rare towards the periphery. All the variety of our color perception depends on the cones. In very faint illumination the colors of things cannot be perceived, although the things may still be distinguished from other objects. The rods alone are functioning then; the cones have “struck work.” Neither can the shape of things be perceived in dim light with normal definiteness, because the area of most distinct vision, the central area, contains only cones; reading, for instance, is impossible at twilight. The astronomer, in order to observe a very faint star, must intentionally look at a point beside the star, because of the lack of rods in the central area.
While the human eye normally possesses both rods and cones, certain species of animals have only one or the other kind of visual elements. Chickens and snakes possess only cones. This is the reason why chickens go to roost so promptly when the sun sets. Night animals, on the other hand, have mostly rods and few cones. This explains why bats come out only after sunset. In very rarecases human beings seem to possess only the rods, in cases of total color-blindness. The whole world appears colorless to them, only in shades of gray. They dislike greatly to be in brilliantly lighted places. They lack the keenness of normal eyesight because of the deficient function of the central area of the retina, which is normally best equipped.
A mechanical theory of hearing was worked out by Helmholtz nearly fifty years ago. This theory was at first generally accepted, but has in recent years lost much of its plausibility. The inner ear is a tube coiled up in the shape of a snailshell in order to find a better place in the lower part of the skull. Its coiling, of course, has little if any mechanical significance. The tube is divided into two parallel tubes by a kind of ribbon, the organ of Corti, containing the endings of the auditory neurons and also a comparatively tough membrane. Helmholtz made the hypothesis that the cross fibers of this membrane were under constant tension like the strings of a piano. The comparison with a piano was also suggested by the fact that the membrane in question tapers like the sounding board of a grand piano. As the piano resounds any tone or vowel, so this system of strings would resound any complex sound; that is, each of the tones contained in the complex would be responded to by those fibers whose tension, length, and weight determine a corresponding frequency of vibration. The analyzing power of the ear is well explained by this hypothesis, but there are considerable difficulties left. For instance, the fibers of the membrane, even the longest, are rather short for the low tones to which they are assumed to be tuned. And for the assumption of a constant tension of these fibers there is no analogon in the whole realm of biology, since livingtissues always, sooner or later, adapt themselves and thus lose their tension.
Another theory avoids these difficulties by merely assuming that the ribbon-like partition of the tube, when pushed by the fluid, moves out of its normal position only to a slight extent and then resists, and that therefore the displacement of the partition must proceed along the tube. If successive waves of greater and lesser amplitude, as we find them in every compound sound, act upon the tympanum and indirectly upon the fluid in the tube, the displacement of the partition must proceed along the tube now farther, now less far, now again to another distance, and so on. Accordingly, one section of the partition is displaced more frequently, another section less frequently, others with still different frequencies in the same unit of time. This theory then makes the hypothesis that the frequency with which each section of the partition is jerked back and forth determines the pitch of a tone heard, and explains thus the analyzing power of the ear. What is chiefly needed in order to decide in favor of either of these or any other theory is a large increase in our knowledge through anatomical, physiological, and psychological investigation.
QUESTIONS46. What are the newly discovered kinds of sensations?47. How were they discovered?48. What are the cutaneous senses?49. What is the objection to speaking of the cutaneous sense as one?50. What is pain?51. Of what importance are the labyrinth senses (other than hearing) to man and various animals?52. What is meant by organic sensations?53. What are the four tastes?54. How does the sense of smell in man compare with that of animals?55. Why is the color pyramid superior to the color cone?56. What are the chief symptoms of defective color vision?57. What is not meant, and what is meant, by color mixtures?58. Why does music use only twelve tones?59. What is meant by the qualities of the tones of various instruments?60. Are there any limits to the analyzing power of the ear?61. What is the exact number of classes of sensations?62. How does the sensory equipment of man compare with that of the animals?63. What do we learn from experiments on blind-born persons who have been operated on?64. In what experiences is time an attribute of sense perception?65. Is tone relationship a property of sense or of thought?66. Can you illustrate the absolute sensitivity of our sense organs?67. How does the range of applicability of our sense organs compare with that of tools and instruments?68. Can you illustrate Weber’s law?69. What are the practical advantages obtained through Weber’s law?70. Illustrate sensitiveness to change and movement.71. How is the chief difference in the behavior of chickens and bats to be explained?
QUESTIONS
46. What are the newly discovered kinds of sensations?
47. How were they discovered?
48. What are the cutaneous senses?
49. What is the objection to speaking of the cutaneous sense as one?
50. What is pain?
51. Of what importance are the labyrinth senses (other than hearing) to man and various animals?
52. What is meant by organic sensations?
53. What are the four tastes?
54. How does the sense of smell in man compare with that of animals?
55. Why is the color pyramid superior to the color cone?
56. What are the chief symptoms of defective color vision?
57. What is not meant, and what is meant, by color mixtures?
58. Why does music use only twelve tones?
59. What is meant by the qualities of the tones of various instruments?
60. Are there any limits to the analyzing power of the ear?
61. What is the exact number of classes of sensations?
62. How does the sensory equipment of man compare with that of the animals?
63. What do we learn from experiments on blind-born persons who have been operated on?
64. In what experiences is time an attribute of sense perception?
65. Is tone relationship a property of sense or of thought?
66. Can you illustrate the absolute sensitivity of our sense organs?
67. How does the range of applicability of our sense organs compare with that of tools and instruments?
68. Can you illustrate Weber’s law?
69. What are the practical advantages obtained through Weber’s law?
70. Illustrate sensitiveness to change and movement.
71. How is the chief difference in the behavior of chickens and bats to be explained?
Mind is influenced not only by that which is present, but also by the past and—one may say—the future, and by that which exists at another place. Consciousness of this kind is called imagery. I imagine a lion and recognize that he looks different from a horse. I recall the room in a hotel where I have recently spent a night and see that it differs from my study.
Imagery does not differ in content from percepts. There are as many kinds of images as there are sensations,and their attributes are the same. Imagination differs from perception only through its independence of external conditions in the formation of new combinations out of the sensory elements which have previously been experienced. Although the kinds of content of imagery do not differ from those of perception, imagery differs from perception, as a rule, in such a characteristic manner that in ordinary life we are not likely to mistake an image for a percept or a percept for an image. The imagined sun lacks brilliancy. Its imagined heat does not burn. A glowing match, perceived, surpasses those images. Only in childhood, in dreams, and in particular individuals (artists, for example), and under particular circumstances (like the imaginative supplementing of that of which only parts have stimulated the sense organ) can imagery come near being compared and confused with percepts. Generally the difference invividnessremains great. A second difference is the lack ofdetailsof images. As a rule only a few parts of a rich complex of sensations reappear when an image takes the place of the original percept. And the selection of these details is usually most grotesque. A third characteristic of images is theirinstability, fleetingness. Compared with the persistence of a percept, an image can scarcely be said to have any definite make-up since its composition changes from moment to moment. Images come and go in spite of our desire to keep them. They change like kaleidoscopic figures.
All this has its disadvantages; but also its great advantages. Being at once pictures and mere abbreviations or symbols of things, images aid effectively in our handling of things. If they were exactly like percepts, they would deceive us, as hallucinations do. Their very lack of details and their fleetingness enable our mind to grasp a greatermultitude of things, to adjust itself more quickly and more comprehensively to its surroundings.
Independence of external causes and frequent recurrence from internal causes give to our imagery the character of a permanent possession of the mind. Not every part of this imagery is actually made use of, since these parts are too numerous, but every part is always available for use. This leads to the question as to the nature of the images while mind is not conscious of them, particularly the nature of their nervous correlate. Ever since the discovery of ganglion cells and nerve fibers the naïve conception has readily offered itself that every idea has its residence in a little group of cells, the idea of a dog in one, the idea of a tree in another, and so on. Some have calculated the number of cortical cells which would be necessary in order to provide a sufficient number of residences for all the ideas acquired by a human being during a long life. They have found that the cortical cells are numerous enough.
But the matter is not quite so simple. Our ideas, being made up of many mental elements, overlap. If the idea of a dog has its residence here, the idea of a lion its residence there, where, then, do we find the idea of a carnivore, the idea of another kind of dog, the ideas of the individual dogs known by me, the ideas of other carnivora, the idea of a mammal, of a vertebrate, of an animal in general? These ideas are interwoven in such manifold ways that it is difficult to assume that each should have its separate residence in the brain. It is still more difficult to apply this theory to the idea of barking, which can be imitated by man, being natural to a dog; or to the idea of white, which belongs to some dogs, but also to the clouds, the snow, the lily.
There are also anatomical difficulties. I look first ata dog, then at a goat. The elements of the retina which are stimulated are largely the same in both cases. This makes it difficult to understand why the nervous processes in the former case should all concentrate in one point of the cortex and in the latter case in an entirely different point. Or I hear the wordboxwoodand later the wordwoodbox. The anatomical difficulty is the same.
The nervous correlates of ideas are obviously much more complicated than the theory of location in cell groups assumes. There can be no doubt that the nervous correlate of an idea, even of an elementary image, is a process going on in a large number of connecting neurons in the higher nerve centers, often widely distributed, like the meshes of a net. The individual neurons in question do not belong exclusively to this one idea, but, entering into numerous other combinations with other neurons, belong to numerous ideas. The nervous correlate of a latent idea, which is not conscious but ready to enter consciousness at any time, is not a material substance stored away somewhere, but a disposition on the part of neurons which have previously functioned together, to function again in the same order and connection.
QUESTIONS72. In what respects do images not differ from percepts?73. In what three respects are images as a rule distinguishable from percepts?74. What are the advantages of the characteristics of images?75. What is the nervous correlate of imagery?76. What is the nervous correlate of a latent idea?
QUESTIONS
72. In what respects do images not differ from percepts?
73. In what three respects are images as a rule distinguishable from percepts?
74. What are the advantages of the characteristics of images?
75. What is the nervous correlate of imagery?
76. What is the nervous correlate of a latent idea?
Sensations and their images are closely related mental states. They are of the same kind. As a third class ofelementary mental states the feelings of pleasantness and unpleasantness are customarily added. But it would probably be more correct to say that these feelings are mental states of an altogether different kind, in comparison with which the distinction between sensations and images disappears. Pleasantness and unpleasantness never occur apart from sensation or imagery, whereas the latter states of consciousness may be free from any pleasantness or unpleasantness. The pleasantness which I experience is always the pleasantness of something—of the taste of a peach, or of my good health, or of a message received. However, we must not conceive this dependence of pleasantness and unpleasantness as similar to the dependence of color or pitch or spatial extent or duration on the thing to which these belong as its qualities. Color, pitch, and these other qualities are essentially determined by objective conditions, the physical properties of the thing in question. But pleasantness or unpleasantness is only to a slight extent, if at all, determined by objective conditions. Honey tastes very much the same whenever we eat it. A tune sounds very much the same whenever we hear it. But these sensory experiences are, in consequence of subjective conditions, now highly pleasant, now almost indifferent, now decidedly unpleasant.
The same colors and straight lines may be combined into a beautiful design or into an ugly one, the same descriptions of scenery and events into an attractive or a tedious book. A feeling which is already in existence may prevent the growth of an opposite feeling. On a rainy day we are likely to feel as if everything in the world were gray; on a sunny spring day as if everything were rosy. The grief-stricken or desperate person experiences a given situation with other feelings than the personfull of joy or hope. A particularly strong factor in our life of feeling is the frequency of recurrence of a situation. The most beautiful music suffers from being played at every concert and on every street, the most delicious dish from being put on the table every day. On the other hand, a bitter medicine gradually loses its unpleasantness, an unpleasant situation becomes indifferent to a person whose profession compels him to face it frequently. As the unchanging is at a disadvantage in our life of perception, so is the recurrent in our life of feeling.
The subjective factor which determines what feelings accompany our perceptions may be defined as the relation of the situation perceived to the weal and woe of the organism. Pleasantness indicates that the impressions made upon the organism are adapted to the needs or capacities of the organism or at least to that part of the organism which is directly affected; unpleasantness indicates that the impressions are ill adapted or harmful. Exceptions to this rule may be explained through the great complexity of the situations by which the organism is often confronted, and through the complications resulting from the fact that the organism must adjust its activity not only to the present but also to the future, and not only in harmony with the present but also with past experience. Feeling is a reliable symptom and witness only for the present and local utility or inadequacy of the relation between the organism and the world. It is not a prophet of the future. Disease may result from eating sweets, whereas medicine is often bitter.
The addition of feeling to our perceptions and images, because of the peculiarities just mentioned, brings about great complications in the make-up of our mental states and increases enormously the task of classifying and comprehendingour states of consciousness. The feelings accompanying images are originally the same as those which accompanied the perceptions in question. The memory image of the pain of flogging is unpleasant because the original pain was unpleasant. But the manifold connections of the images often result in unexpected feelings. The memory of an unpleasant experience may become a source of pleasure through the additional thought that the experience was the result of some folly of which one is no longer capable. The feeling accompanying a perception can change in a similar manner. A saturated green, as the color of a pasture or of an ornament, is pleasant; as the color of a girl’s cheek it would be highly unpleasant.
Not only are perceptions and images themselves sources of pleasantness and unpleasantness, but also their relations, spatial, temporal, and conceptual. The pleasure which we derive from looking at a picture or a landscape illustrates the dependence on spatial relations. The pleasure of a symphony or dramatic performance depends largely on temporal relations. Jokes and puzzles please us chiefly because of their conceptual, logical relations. It is plain, then, that every complex of sensations, supplemented by a large number of images, must become a stage, so to speak, on which countless scores of feelings play their parts. In so far as their perceptual and ideational bases may be kept apart, we may count as many of these feelings as we distinguish percepts or ideas. In so far as all these feelings are either pleasantness or unpleasantness, we may speak of the feelings as being only two in number. This may explain to us why such mental states as love, pride, sentimentality, the joy of the audience in a theater, the interest of the reader of a biography,appear at once simple enough, unitary enough, and yet inexhaustibly replete with contents and difficult of comprehension. This also explains the opposite views of so many writers, of whom some assert that the number of feelings is infinitely large, others that there are only two, pleasantness and unpleasantness, which may accompany an infinite number of sensation complexes. The difference between these writers is much less than appears from their words.