OTES IN PSYCHOLOGY 
 
 on lectures supplementary to 
 
 JAMES' PSYCHOLOGY 
 
NOTES IN PSYCHOLOGY 
 
 on lectures supplementary to 
 
 JAMES' PSYCHOLOGY 
 
 by 
 
 JOSEPH JASTROW, Ph. D. 
 
 Professor of Psychology in the University of Wisconsin 
 
 Privately printed for the use of classes in the 
 Unive-sity of Wisconsin 
 
 MADISON, WISCONSIN 
 19 12 
 
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 Copyright 1912 
 By Joseph Jastrow 
 
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PREFATORY NOTE 
 
 The presentation to large classes in a limited period 
 of a survey of topics in Psychology most important 
 for introductory study requires all the pedagogical 
 aids that can be made available. The instructor must 
 select his material, bringing to the teaching an indi- 
 vidual emphasis, and inevitably supplementing the 
 text in the process. The generous use of demonstra- 
 tions and charts and diagrams within the lecture hour 
 makes large draughts upon the student's attention 
 and interferes with his notes. The present notes are 
 the result of these conditions. The problems of Sense- 
 Perception are considered the standard ones for the 
 beginning student; a comprehension of principles is 
 regarded as fundamental. It seems better to carry a 
 few problems to a fair degree of completeness than to 
 attempt too broad a survey. Moreover, as these notes 
 are supplementary to James' Psychology, they must 
 be considered along with the text, to restore the 
 proper perspective. Points satisfactorily covered by 
 the text receive no comment or restatement. It has 
 been found impracticable to include in lectures (twice 
 a week for one semester) much of the material of the 
 latter half of the text. The notes will be used by the 
 author in an introductory manual in preparation, the 
 copyright of which is held by Henry Holt & Co. 
 
CHAPTER I. 
 Introductory. 
 
 Topic I. The Nature of Psychology. Psychology, 
 as the science of mental functions, studies the pro- 
 cesses that bring the individual into relation with his 
 environment. Environment embraces the physical 
 world, which contains various forms of energy, and 
 the several biological factors which form the condi- 
 tions of life. 
 
 A special relation obtains between the mind and 
 the body. The nervous system represents the physio- 
 logical basis of mental functions. The principle that 
 physiological states condition mental states is illus- 
 trated by the effect of bodily injuries, and by the 
 action of drugs, both of which show very decided 
 changes of mental state, such as unconsciousness, lack 
 of motor control, emotional exhilaration or depression, 
 hallucinations, impairment of memory, etc. The same 
 principle of relation between mental states and fluc- 
 tuations in the condition of the nervous system is 
 shown in detail in the minuter changes of condition. 
 These are illustrated by the effects of fatigue, of 
 hunger, of difference between morning and evening, 
 of influences of the weather, of digestion, and of a 
 score of the more delicate variations which make it 
 safe to assume that to every mental state there corre- 
 sponds some kind of a physiological state of the ner- 
 vous system. 
 
CHAPTER II. 
 Sensb-Pkrception. 
 
 Topic II. General Characteristics of Sensation. 
 
 Sensation represents the simplest mental process that 
 participates in the mental life. Sensations are thus 
 the first things in consciousness. It is possible to dis- 
 tinguish the bare effect on the organism of being ex- 
 posed to a stimulus, and to call this the sense-impres- 
 sion. The stimulus is some form of energy in the 
 outer world ; and the sense-organ represents the adap- 
 tation of a cell to receive this form of energy. Accord- 
 ingly the sum total of our sensations is limited by 
 the variety of forms of energy which we have senses 
 to receive. All such adaptations are special, and 
 again are limited in range. Thus: the cells of ^.he 
 retina respond to light-vibrations, and the cells of 
 the end-organ in the ear respond to air-vibrations. 
 Having these specialized responsive organs, we see 
 colors and hear sounds. But the range of color which 
 Ave see is limited by the structure of these cells. AYe 
 know that there are vibrations below the red and be- 
 yond the violet which are just the same kind of vibra- 
 tions, but which we do not see. Similarly we can see, 
 but not hear as sound, the vibrations of a stick which 
 is not vibrating rapidly enough to produce an audible 
 tone ; and we can show that when vibrations get more 
 rapid than the upper limit of hearing, there is a rush 
 of air, but no musical tone. Once more, we know 
 that there are forms of physical energy, like magnet- 
 
 6 
 
ism, for which we have no sense-organs whatever ; we 
 cannot feel the presence of a magnetic field. It may 
 be assumed that the kind and range of our senses rep- 
 resents the maximum utility of sensory functions. 
 
 Topic III. Body-informing and World-informing 
 Use of the Senses. The sensations give information 
 regarding conditions of the body for use and protec- 
 tion, particularly as pain and pleasure ; and this fac- 
 tor remains even when it becomes secondary. The 
 chief development of the senses is towards giving in- 
 formation of the outside world; and this use may be 
 called intellectual. It results in the making of dis- 
 tinctions. The 1 accuracy of the sense, or its delicacy, 
 is measured by the smallness of the distinctions which 
 it makes. These distinctions are both in matters of 
 degree and of kind, or quality. What we really dis- 
 tinguish are qualities of objects, but the information 
 may be reduced by psychology to types of qualities, 
 such as color and form, and again size and distance 
 for vision; or loud and low, high and deep tones 
 for hearing; heavy and light, hot and cold, for 
 touch ; sour and sweet for taste ; and so on. In all 
 these distinctions the factor of use, or pain and 
 pleasure as protective, remains, but in many cases 
 is slight, giving way to distinction. 
 
 Topic IV. Sensation and Action. The use of dis- 
 tinctions is to regulate conduct. Situations must be 
 distinguished so that they may be appropriately re- 
 acted to. In considering distinctions, it is important 
 to think of the situations as simply as possible, and 
 as they commonly occur in nature. Distinctions are 
 directed to. objects. There is a strong tendency to 
 refer all sensations outward and in terms of mean- 
 ing, to perceive objects and disregard sense-impres- 
 
 7 
 
sions. As a consequence, for the higher senses we are 
 very little aware of sense-impressions, and at once 
 infer the presence and nature of the objects which 
 cause them. Hence, we often fail to realize the basis 
 in sensation of the result which we perceive or infer. 
 For example, we know that we distinguish the direc- 
 tion of sounds, but need experiment to prove that the 
 basis of this distinction is a difference in intensity 
 in the two ears. Again, we are very likely to infer 
 that a light that is growing brighter is nearer. We 
 are not usually aware that brightness is the basis of 
 our inference of nearness. "What we seem to perceive 
 are objects or situations in accordance with their most 
 familiar appearance ; the basis of such perception are 
 simple sensible qualities. Out of these sensations we 
 at once build up objects. We seem to perceive them 
 as a whole, and overlook the steps involved. 
 
 Topic V. Intensity. Among the qualities in com- 
 mon to all sensation is that of intensity, which is the 
 simple distinction of more or less. Intensity has the 
 advantage of being easily studied. Changes in de- 
 gree, such as that of a weight growing heavier, of a 
 light growing brighter, of a sound growing louder, 
 are relatively simple distinctions. It is true that the 
 sensation may change slightly in quality as the weight 
 grows heavier or the sound louder or the light 
 brighter; but we can distinguish the predominant 
 element of change of degree, and can usually distin- 
 guish this from a qualitative change, such as that the 
 tone becomes higher, or the light more bluish, or the 
 pressure duller or sharper. Changes in intensity have 
 been minutely studied. One of the important results 
 is that relative! differences are shown to be more im- 
 portant than absolute ones. This is again in accord 
 
 8 
 
with natural use, and indicates that there is a stand- 
 ard of utility in making distinctions. It may be illus- 
 trated in terms of weight by saying that one ounce 
 added to four or five ounces will be much more marked 
 than one ounce added to twenty or twenty-five ounces. 
 When this principle is made accurate, it would read 
 that a change of one ounce in a pound would be about 
 as perceptible as a change of two ounces in two 
 pounds. Just how far the law holds will be seen 
 later. The principle is clear that the perceptibility 
 of the difference stands in very definite relation to 
 the total impression. It is also true that sudden 
 changes are more perceptible than gradual ones. We 
 do not observe that a room is growing warmer as we 
 sit in it, but someone coming from outdoors notices 
 that it is too hot. Another general factor is contrast, 
 which means; that the present condition of the organ 
 affects the impression, and also that one impression 
 affects another. Such contrast is an illustration of 
 the fact that a sensation is relative, and its effect de- 
 pends upon the total impression. Thus, if one hand 
 be placed in hot water and the other in cold, and both 
 transferred to the same dish of lukewarm water, it 
 will seem cold to the hand that has been in hot water, 
 and warm to the one that has been in cold water. 
 Similarly, colors will have a very different effect when 
 placed upon background or another. There are, how- 
 ever, many varieties of contrast to be noticed later. 
 
 (It should be noted that the general subject of this 
 chapter is a survey of the qualities which many or all 
 sensations have in common, and of the general pro- 
 cesses involved in sensation.) 
 
CHAPTER III. 
 Vision. 
 
 Topic VI. The Organ of Vision. The study of 
 vision is best adapted to illustrate the principles of 
 sense-perceptions. It makes it possible to trace step 
 by step all the processes from the physical stimulus 
 to the most complex sense-perceptions. "We must 
 consider that the organ of vision, which is the eye, is 
 primarily an organ for color-perception, and again 
 an organ for the perception of form. These two or- 
 ders of perception are concentrated in the retina, 
 and specifically in a single layer of the retina known 
 as the rod-and-cane layers. These form the end- 
 organs of vision, and are probably at once the end- 
 organs for color and for form. It will be altogether 
 best to describe the structure and functions of the 
 eye in terms of form-perception. 
 
 Topic VII. The Formation of the Image: (a) 
 Structure of the Eye. All vision depends upon the 
 formation of an image on the retina. Our first inquiry 
 is as to the structure of the eye, particularly with ref- 
 erence to the parts that lead to the formation of the 
 image, and the method by which each part contributes 
 to the result. 
 
 The eye is a sphere a little deeper than broad, and 
 flattened in front, and is about seven-eighths of an 
 inch in diameter. It consists of three coats : the outer 
 or sclerotic, which in front becomes vaulted and trans- 
 parent, forming the cornea; the middle coat, called 
 
 10 
 
the choroid in back, which in front becomes flattened 
 as the iris, with the opening in it, the pupil. Inside 
 is the third coat, the retina alone, which stops at the 
 margin of the ring formed by the junction at once of 
 the retina, the choroid-and-iris, and the sclerotic-and- 
 cornea. In addition the solid or liquid contents of the 
 eye appear first in the vitreous humor, quite the' 
 largest in mass, filling all the space between the retina 
 and the iris, except that there is a depression in its 
 anterior surface in which rests the second important 
 solid body, the lens. The space, flat in back and 
 vaulted in front, between the iris and the choroid, is 
 filled with a watery substance and is called the 
 aqueous humor. In addition there are within the eye 
 various blood-vessels, particularly in the choroid, 
 bringing its rich blood-supply, the ligaments which 
 hold the lens in place and which are attached to the 
 two important ciliary muscles through the action of 
 which the lens contracts. The eyeball as a whole is 
 harnessed by a set of six muscles, four of which are 
 straight, one above, one below, one external, and one 
 internal, and two of which are oblique. 
 
 In terms of function the sclerotic coat serves as the 
 solid wall keeping the eye in shape, and also as the 
 points of attachment for the muscles. The cornea is 
 of a similar structure as the sclerotic, but transparent 
 to permit the passage of light. The lens has the im- 
 portant function of breaking or refracting the line of 
 light so that the imagine falls on the retina, and not in 
 front or in back of it, and that as well for! near, for 
 middle, or for far distances— this process being known 
 as accommodation. The iris contains the mechanism 
 of light adjustment, the pupil becoming very small 
 in strong light and expanding in weaker light. Con- 
 
 11 
 
sidered generally, the eye may be regarded as the 
 retina, which in turn is the expansion of the optic 
 nerve, and a set of accessory mechanisms for regu- 
 lating the light and forming the image, of which the 
 chief are the lens and the iris. 
 
 Topic VIII. The Formation of the Image, (b) 
 Processes and Conditions. While we see with nearly 
 the entire extent of the retina, a fundamentally 
 important condition of accurate vision is that the 
 image shall fall on the fovea. Human vision is pecu- 
 liarly foveal vision, which means that directly in the 
 center of the retina there is a depression, or fovea, in 
 which vision is concentrated. A ray of light entering 
 horizontally through the exact center of the pupil, 
 would reach the center of the fovea. The structure 
 of the retina shows that the visual elements, or rods 
 and cones, are most closely concentrated at this point, 
 in extent, a space of about one-eighth of an inch. 
 Furthermore, at this point there are cones alone, 
 and these closely crowded. Towards the margins of 
 the fovea there is about one cone to a circle of rods 
 surrounding it; and in the areas farther away from 
 the fovea in all directions the proportions of cones 
 to rods diminish, and both elements are more and more 
 separated by other tissue. This distribution proves 
 that the rod-and-cone layer is the layer of visual per- 
 ception, and that the cone is more intimately connected 
 with the visual process than the rod. (For structure 
 of retinal layers, see text.) A complementary proof 
 is furnished by the existence of the blind spot, which 
 is the entrance of the optic nerve. At this point, a 
 little to the inside of the fovea, the fibres of this 
 nerve pierce through all the coats of the eye. The 
 retina may be pictured as the spread-out ends of these 
 
 12 
 
fibres. Naturally, at this point there are no rods and 
 cones, and hence no vision. (For experiment proving 
 the blind spot, see text.) 
 
 Topic IX. General Conditions of Vision. The con- 
 ditions under which the eyes are used may be divided 
 into "vision with the eye at rest" and "vision with 
 the eye in motion ; ' ' again into ' • vision with one eye ' ' 
 (monocular) and "vision with two eyes" (binocular). 
 For purposes of exposition it is well to accept as the 
 standard "vision with one eye at rest." This affords 
 the simplest conditions. As a matter of experience, 
 the use of the two eyes jointly and in constant motion 
 is the dominant method. The largest share of infor- 
 mation, as well as the normal use of the eyes, involves 
 binocular vision and constantly moving vision. Con- 
 formably to the general discussion, we may call 
 "vision with the eyes at rest," passive and "with the 
 eyes in motion" active. It will be recalled that we 
 have but two types of sensation: (1) the stimulation 
 of a specialized sense-organ, or (2) the feeling accom- 
 panying the contraction of muscle. The sensibility of 
 the retina represents the former type ; the contraction 
 of the muscles in moving the eye, the latter. Active 
 vision combines the two, and refers to the total sum 
 of information which we get from the retinal images, 
 as well as from the feeling of ocular movement. 
 
 Remembering the practical and theoretical import- 
 ance of these four modes of using the eye or eyes, we 
 ask the typical question for each sense, namely, 
 "What are the kinds of information which the sense 
 affords, and how do we get them?" Such analysis 
 must be complete, must yield simple and distinctive 
 types of information. For vision the analysis yields 
 the following result : * 
 
 13 
 
A. The Light-and-Color Sense. B. Space-Percep- 
 tion. These two are doubtless related to quite differ- 
 ent phases of the visual process. The colors and the 
 shapes of objects are seen combined; but the color 
 factor and the space factor are readily separated 
 mentally. We distinguish Light and Color, and sub- 
 divide the qualities of space-perception as follows : 
 
 I. Direction. 
 
 II. Form. A. Light. 
 
 III. Size. also 
 
 IV. Distance. B. Color. 
 V. Solidity. 
 
 YI. Movement. 
 
 What this analysis means is that the visual differ- 
 ence between one object and another may be reduced 
 to differences, first, of color (as blue or red), and 
 brightness (as light or dark) ; and secondly, to differ- 
 ences in space relations, of directions (as right or left, 
 up or down), of form (as round, square, hexagonal, 
 or again leaf-shaped, heart-shaped, etc.), of size (as 
 large and small), of distance (as far and near), of 
 solidity (as flat or solid, or variations in depth in 
 the third dimension), and finally of motion (as moving 
 or at rest). This analysis might be carried farther, 
 resulting in fewer factors at the expense of conveni- 
 ence. This answers the question, "What kind of 
 information is thus given?" The answer to the 
 method by which we receive them involves the separate 
 treatment of each problem. 
 
 It is further true that we may obtain these space- 
 perceptions from the eye at rest or in motion, from 
 the single eye or the two eyes. It is further the case 
 that no neiv perception is added by the more elaborate 
 
 14 
 
visual processes; and it is likewise true that (with 
 the partial exception of solidity) there is no form of 
 information which is not obtainable through the single 
 eye at rest. The difference is largely one of conveni- 
 ence, extent, and variety of spacial experience; but 
 that means a great practical difference. It will be best 
 to consider each of these factors of space-perception 
 in terms of single vision with the eye at rest, and then 
 observe the variations in the process due to the pres- 
 ence of binocular vision, and again of the movements 
 of the eye. 
 
 Topic X. The Perception of Direction and Form. 
 These perceptions result directly from the method of 
 formation of the image. The perception of direction 
 in the single eye at rest is determined by the position 
 on the retina at which the image is formed. Owing 
 to the inversion of the rays by the lens, the upper 
 half of the retina corresponds to the lower field of 
 vision, and the lower half of the retina to the upper 
 field of vision ; similarly whatever I see on the extreme 
 right in space falls on the inner half of the right eye, 
 and what is to my left in space falls on the outer half 
 of the right eye ; and again conversely, if I use the left 
 eye alone. As all rays entering the eye cross at the 
 nodal point, which is a little back of the center of the 
 lens, it is easy to find the position on the retina of a 
 point in space by simply connecting that point with 
 the nodal point, and extending the line to the retina. 
 Owing to this fixed relation, I come to associate definite 
 regions in space with definite positions on the retina ; 
 and this association is never seriously interfered with 
 by the fact that I use two eyes, and that the eyes are in 
 constant motion. A convincing proof of this fixed 
 association is obtained by closing the eyes and pres- 
 
 15 
 
sing the little finger lightly against the eyeball on the 
 inner (left) side of the right eye. This mechanical 
 pressure will cause a dull illumination, which in turn 
 will be referred to a region in space on the extreme 
 right-hand side. It is thus easy to formulate the prin- 
 ciple of direction. Objects above, like those on the 
 ceiling, are associated with the lower part of the 
 retina, and objects on the floor with the upper part of 
 the retina, and so on. Direction is then due to the 
 fixed association between position on the retina and 
 position in space, the relation in turn determined by 
 the inversion of the image under constant conditions. 
 
 The perception of form, or shape, is likewise deter- 
 mined by the formation of the image. The retinal 
 image is a facsimile of the object seen. Its outline, 
 or contours, will accordingly reproduce the outline 
 or contours of the object, and this miniature will be 
 accurate 'in light and shade, color, and form. The 
 difference, then, between a square and a disk is in 
 the combination of stimulated points. This convenient 
 phrase summarizes the condition on which depends 
 the perception of form. The accuracy of form-percep- 
 tion depends upon the accuracy of the mechanism of 
 the eye in forming a sharp and distinct image. It has 
 its limits in the power of the lens to focus for near, or 
 in some eyes for distant objects; but given a clear 
 image, the form-perception results. Here again, con- 
 stant association through experience familiarizes and 
 facilitates the rapid perception of distinctions of form. 
 
 It is difficult to arrange a test of the sense of direc- 
 tion alone, and not much .easier that of form alone, 
 since both are so commonly involved with other per- 
 ceptions. For direction, one might arrange in a dark 
 room that a single pin-point of light shall appear for 
 
 16 
 
an instant, disappear, and then another reappear at 
 a different place, and the subject be required to indi- 
 cate the difference of direction between the first and 
 the second points. For form, again, one might take a 
 series of ellipses slightly changing the proportions of 
 the two axes, and determine which is the more ellipti- 
 cal; or again, one might arrange very slight differ- 
 ences in irregular shapes, like inkblots, and determine 
 how far changes could be detected. The test of the 
 ellipses at once suggests that size, in the difference 
 between the vertical and horizontal axes, would enter, 
 and again that the difference between one curve and 
 another is merely that of a difference in the arrange- 
 ment of change of direction. Thus a straight line is a 
 line that does not change its direction, and a circle 
 is one that constantly changes its direction. None the 
 less, direction and form, though commonly combined 
 with other space-perceptions, are sufficiently distinct 
 to be separately considered. Though expressible in 
 terms of direction, form is a simple perception. 
 
 A special problem arises from the inversion of the 
 image, and it might be supposed that to see an object 
 erect with an inverted image requires explanation. 
 Since, however, the whole process is a matter of asso- 
 ciation, it is just as easy to learn to associate the lower 
 part of the retina with the upper part of the field of 
 space as vice-versa. The demonstration given in the 
 class showed that by means of casting a shadow on the 
 retina, we can prove that an erect image (for the 
 retina does not recognize the impression to be a 
 shadow, and treats it like an image) would be pro- 
 jected and seen inverted. 
 
 Topic XI. The Perception of Size and Distance. 
 While the perceptions of form and direction depend 
 
 17 
 
wholly upon the position and distribution of the 
 retinal image, the perception of size depends upon it 
 primarily but under the assumption that other rela- 
 tions are constant. It may, then, be said that, other 
 things being equal, the size of the retinal image will be 
 a sufficient clue to the size of the object. Of two 
 objects at the same distance) from the eye, the larger 
 will throw an image upon the retina proportionately 
 larger than the smaller one. It is, however, obvious 
 that other things as a rule are not equal, and that pri- 
 marily the one factor making distance and size rela- 
 tive judgments — indeed relative to one another — is 
 the fact that size varies with distance and distance 
 with size. We are thus compelled to speak of the 
 apparent and the real size of an object. 
 
 The figures shown on the blackboard illustrate how 
 a set of objects may all be of the same size, but at dif- 
 ferent distances from the eye, and accordingly have 
 images of different sizes; or again that three objects 
 of different sizes may be so adjusted in their distances 
 from the eye that all three, the nearer, the middle, and 
 the farther object, may have a retinal image of pre- 
 cisely the same size. In practice, accordingly, we can 
 distinguish three types of problems: First, with 
 objects at the same distance, to judge of their relative 
 size. For this the size of the image is adequate. 
 Second, for objects at a different distance but known 
 or assumed to be of the same size, to judge of their 
 relative distance. Such judgment of distance would 
 in the one eye be accomplished by the" mechanism of 
 accommodation, as will be explained presently. Third, 
 and most usual, objects at different distances and of 
 different sizes, to be judged at once relatively as to 
 their size and distance. This complex problem, involv- 
 
 18 
 
ing many factors, is the one in which we gain great 
 proficiency. 
 
 Returning to the first problem, there is little to add, 
 since, the determination of the distance of an object 
 being somehow accomplished, the judgment of size 
 depends upon the size of the retinal image. However 
 this is often so complicated by movements of the eye, 
 by differences in shape and in direction, that it still 
 remains true that the perception of size is as a rule not 
 simple. The point will be considered again in connec- 
 tion with the movements of the eye. 
 
 The perception of distance independently of size 
 depends upon the feeling of the set, or amount of con- 
 traction, of the ciliary muscle, which in turn sets the 
 lens to give an accurate image upon the retina. We 
 may call this briefly the process and the feeling of 
 accommodation. It has its sensory counterpart in the 
 blurredness of the image, which we disperse by 
 changing the accommodation and thus sharpening the 
 image. In a familiar space and within short range, 
 say twenty feet, the shifting accommodations in order 
 to produce clear images would sufficiently determine 
 judgments of distance. Since both size and distance 
 are relative and can be expressed in terms of changes 
 of angle of vision, it follows that a much smaller 
 change of distance at a nearer range will induce as 
 much feeling of change as a considerably larger change 
 of distance at a larger range. To move the finger 
 away an inch or so at a distance of five or six inches 
 involves far larger changes of accommodation, as well 
 as of size of retinal image, than to move it an inch or 
 two at a distince of twelve inches. But for every suc- 
 cessive foot the difference in set (and in size of image) 
 rapidly diminishes. It has been calculated that the 
 
 19 
 
changes of accommodation substantially stop at twenty 
 feet, and further that within this distance the .reading 
 distance of ten or twelve inches covers the largest 
 changes of accommodation. 
 
 The combined problem of judging size and distance 
 jointly is one that requires large experience to solve, 
 and which under unfamiliar conditions we often fail 
 to solve accurately. Experiments in the dark room 
 show that the ordinary judgments of the distances of 
 objects are complex, the judgment depending on their 
 known size, on their relative position tot one another, 
 on the cutting off of images, on the way in which the 
 objects catch and reflect the light, and on other details. 
 It is only when these are eliminated that we get a 
 clear notion of the power to judge distance and size by 
 the combined processes of size of image and of accom- 
 modation. It may be added that the question as to 
 which factor leads in the joint process, or which step 
 is first taken, again depends upon circumstances, and 
 possibly individual habit. Do we first judge the dis- 
 tance and then determine the size, or get the size and 
 then determine the distance? The most generally 
 correct answer is that we shift from one to the other, 
 and by mutual adjustment clear up the size and 
 distance together. In this process the eyes may 
 readily be deceived, and illusions of judgment result. 
 This problem will be further considered under 
 ' ' Binocular Vision. ' ' 
 
 Topic XII. The Perception of Solidity. The na- 
 ture of this perception is easily defined, but the variety 
 of its appearance complicates the problem. It refers 
 to the third dimension of objects, as well as to the 
 relation of the parts of an object in depth, thus includ- 
 ing perspective. At the simplest, the distinction is 
 
 20 
 
between a flat and a solid, and as illustrated between 
 a disk and a hemisphere. Neglecting the matter of 
 light and shade, and still considering vision with one 
 eye at rest, the disk is distinguished from the hemi- 
 sphere because all parts of the disk require the same 
 accommodation, while to see the center of the hemi- 
 sphere clearly requires a nearer accommodation than 
 to see its edges clearly. If the hemisphere were a 
 hollow half-ball, then focusing for the edges would 
 require closer accommodation than for the center. 
 Similarly for the skeleton pyramid as held with the 
 larger square nearer, thus looking into the pyramid, 
 or with the smaller square nearer, and looking down 
 its sides, the retinal images of the single eye in the 
 two cases may be precisely alike, yet the two appear- 
 ances are instantly distinguished, and this again by 
 the difference in the shif tings of accommodation. Such 
 is the perception of solidity at its simplest. 
 
 Topic XIII. Vision with Two Eyes. The further 
 consideration of solidity involves binocular vision. 
 The first problem is the question of seeing singly with 
 the two eyes. Clearly the images on the two retinae 
 as formed by a single object are related ; and when the 
 eyes are directed towards an object, the image thereof 
 falls on the fovea of each eye at the same time. This 
 process is called fixation, and is popularly called 
 "looking" at an object. It is accomplished by a move- 
 ment of the internal (or external) muscles. 
 
 Topic XIV. Movements of the Eyes. Of the six 
 muscles attached to each eye, there are four straight 
 muscles, — upper and lower, internal and external — 
 and two oblique muscles, again upper and lower. The 
 oblique muscles cooperate with the others, and give 
 a torsional movement to the eyeball. The upper 
 
 21 
 
straight muscle raises the eyeball, as in looking at the 
 ceiling, and the lower straight muscle turns the eyeball 
 downward, as in looking at the floor. The upper and 
 lower muscles of the two eyes always work together, 
 there being no power to raise one eye and lower the 
 other, for the very good reason that this would not 
 lead to single vision. When the two eyes turn to the . 
 right, it is done by a pull on the external muscle of the 
 right eye and the internal muscle of the left eye ; and 
 when, conversely, the eyes turn to the left, it is done 
 by a pull of the external muscle of the left eye and 
 the internal muscle of the right eye. If the eyes move 
 from a point on the floor to the left, and then roll 
 obliquely to look at a point on the ceiling and to the 
 right, and theni again move back to the point on the 
 floor, all six muscles of both eyes have been brought 
 into play. Such general movements, by which objects 
 in space are examined are called movement of explora- 
 tion. In addition, the distinctive type of movement 
 which consists of a pull on the two internal muscles 
 when an object nearby is to be looked at is converg- 
 ence, and the converse pull on the two external muscles 
 when the fixation is transferred from a point nearby 
 to a point far off, is called divergence. Instead of 
 constantly referring to these movements as movements 
 of convergence and divergence, they are often referred 
 to as movements of convergence, or again, convergence 
 shif tings. It thus appears that the internal and exter- 
 nal muscles participate as well in movements of ex- 
 ploration, and that they alone have this additional 
 power of being moved in a converse combination for 
 convergence and divergence. 
 
 The conditions of single vision may be expressed 
 by saying thai} an object in space will under normal 
 
 22 
 
conditions be seen singly when the images thereof fall 
 on the two foveae, or on points of the retina equi- 
 distant from the foveae and in the same direction. The 
 word direction here needs no definition so far as up 
 and down is concerned, since the eyes inevitably move 
 up and down together; but as applied to horizontal 
 movements the words "same direction" now mean 
 that the points on the retinae must be in the same di- 
 rection—either in both eyes to the right of the fovea or 
 in both eyes to the left of the fovea. Observe that this 
 means that a point internal of the fovea in the one eye 
 corresponds to a point external of the fovea in the 
 other eye, and vice versa. Such points are called cor- 
 responding points. The eyes are have such large ex- 
 perience in moving together that they instantly and 
 quite unconsciously assume the correct position to 
 obtain single vision, the guiding clue being the clear- 
 ing up of blurred images. It must still be, said that 
 movements of accommodation in each eye always 
 accompany the convergence movements of the two 
 eyes, so that the combined movement at once brings 
 the image on the fovea of each eye and focuses that 
 image sharply at that point. 
 
 Topic XV. Double Images. It might almost be 
 said that under the conditions described, single vision 
 will take place, and that under all other conditions we 
 should see double. The fact that double images do 
 not bother us, and indeed that we ignore them, is due 
 to the constant movements of the eyes in convergence 
 and divergence, which destroy or disperse double 
 images as soon as formed. It takes some practice to 
 learn not to move the eyes, and thus to attend to and 
 see the double image. The simplest condition for ob- 
 serving them is at near range, holding the finger, F, 
 
 23 
 
as the point of fixation, and some other point, P, as a 
 pencil, as a point to be seen in indirect vision, both 
 points in the horizontal plane. If the finger be held at 
 about eight inches from the eye and the pencil at 
 about double the distance, and the finger-nail be 
 sharply fixated, two images of the pencil would 
 appear, one to either side of the finger-nail. Con- 
 versely, if the finger be held at the further distance 
 and the pencil at the nearer, again two images of the 
 pencil would appear. These form the two chief condi- 
 tions for the appearance of double images, which may 
 be expressed as one by saying that the point of fixa- 
 tion is at a different distance from the eyes than the 
 point of indirect vision. These two types of double 
 images' require opposite movements to destroy or dis- 
 sipate them. For the first experiment, a movement 
 of divergence, or spreading of the eyes apart, is 
 necessary to transfer the fixation from finger to pencil 
 —from P to P ; and for the second a movement of con- 
 vergence is necessary to transfer the fixation from 
 finger to pencil— from F to P. Prepare a diagram of 
 the experiment. In brief, then, we know that the 
 finger is nearer than the pencil, or the pencil nearer 
 than the finger, because of our feeling as to the kind 
 of movement necessary to get rid of these double 
 images. In practice they appear not so much as double 
 images, which are distinct only when the points are 
 nearby and separated, but as blurred images. Further- 
 more, observe that in the two experiments the double 
 images of the pencil are spread farther apart when 
 the pencil is near than when the pencil is far; and in 
 addition if, when the pencil is near, you close the right 
 eye, the opposite, or left, double image will disappear ; 
 or with the pencil farther away, the closing of the 
 
 24 
 
right eye will momentarily make disappear the right- 
 hand image. Prove this on the diagram. 
 
 Topic. XVI. Binocular Perception of Distance and 
 Solidity. It thus appears that we have two processes 
 for perceiving distance and solidity; accommodation 
 in the single eye and convergence in the joint working 
 of the two eyes. Experiments show that the converg- 
 ence gives the more accurate judgment for all but 
 very near distances, and the readiest judgment for 
 all. While accommodation is pretty well equalized 
 at twenty feet or so, convergent shiftings are still use- 
 ful at forty feet, and possibly anywhere from forty to 
 a hundred, or even two hundred feet. Obviously 
 both changes are relative, as explained under ac- 
 commodation. The point at which the two eyes are 
 approximately parallel represents the limit of con- 
 vergence. The perception of solidity in binocular 
 vision involves another, and in principle the most im- 
 portant factor, namely the fact that the two images on 
 the two eyes are slightly different. This factor is 
 called retinal dissimilarity; and the stereoscope 
 demonstrates the part that it plays in the perception 
 of solidity. 
 
 Topic XVII. Sterescopic Vision. The proof that 
 retinal dissimilarity and convergence shiftings to- 
 gether furnish the perception of the three-dimensional 
 w T orld is given by the stereoscope, one of the most 
 wonderful if simple instruments ever invented. The 
 stereoscope is a synthetic instrument, which puts to- 
 gether the factors which analysis has found, and actu- 
 ally reconstructs the third dimension of space out of 
 two-dimensional materials. The principle of the 
 stereoscope is that of giving to each eye its own image, 
 and furnishing a convenient method of combining the 
 
 25 
 
two images. In the form in which it is popularly 
 known, the stereoscopic photograph consists of two 
 views of an object, taken a little distance apart, the 
 distance corresponding nearly or accurately to the 
 separation of the two eyes in the head. Thus the two 
 pictures actually show how the two images on the two 
 eyes would differ; and it will be observed that these 
 differences may be extremely slight for all objects at a 
 great or considerable distance from the camera, but 
 that the differences increase decidedly for objects near 
 by. Examining a stereoscopic photograph of the 
 latter class, it is easy to make out that in the right and 
 left pictures the views of objects in the foreground 
 are more different than of objects in the background. 
 These differences illustrate what is meant by retinal 
 dissimilarity. 
 
 The simplest demonstration is afforded by diagrams, 
 and best by outline figures without background. The 
 truncated pyramid with the square base, which is the 
 shape of the models shown in class, may serve at once 
 to indicate the measure and distribution of retinal 
 dissimilarity, and to show how the images may be 
 combined in the stereoscope and actually produce the 
 effect of solid reality. Any instrument that gives each 
 eye its own image and combines them is a stereoscope ; 
 and several varieties of such instrument were demon- 
 strated. 
 
 As to the relative parts played by retinal dissimi- 
 larity and by convergence shiftings, observation 
 shows that the dissimilarity alone suggests solidity, 
 and produces it for simple figures, but is completed 
 and made far more realistic by the movements of con- 
 vergence. Thus a stereoscopic view grows in depth 
 as the eyes look at it, and often the moment of the ap- 
 
 26 
 
pearance of intense solidity can actually be detected. 
 This requires adjustment of the eyes and clearness of 
 view. Hence the need of more accurate devices for 
 persons whose eyes do not naturally work well to- 
 gether. Note clearly that the fully developed stereo- 
 scopic impression is not) an imitation or a suggestion 
 of reality, but an actual reproduction. What the eyes 
 see in looking at a stereoscopic picture is precisely 
 what they see in looking at reality. 
 
 Topic XVIII. Secondary Factors in Depth-Per- 
 ception. At this stage a distinction must be made 
 between the the primary factors of depth-perception 
 and the secondary ones. The term primary always 
 refers to information obtained through processes 
 going on in the organ of perception— in this case, in 
 the eye; and the term secondary refers to inferences 
 from the observed relations of objects as modified by 
 experience. For purposes of analysis the primary 
 factors always dominate, but in practice the secondary 
 factors may come to be the more important and reli- 
 able. The secondary factors of depth-perception relate 
 to qualities of the objects and their distribution in 
 space. They may be enumerated as (a) light and 
 shade; (b) interposition of objects; (c) perspective; 
 (d) familiarity. In addition there are others playing 
 occasional and accidental parts. Light and shade is a 
 very comprehensive clue of depth-perception, because 
 most objects are opaque and cast shadows, and the 
 differences of lighting indicate position in the third 
 dimension of space. All these secondary factors are 
 inferences, and suggest, rather than create the per- 
 ception of solidity. That light and shade is an in- 
 ference from the assumption that the direction of light 
 is from above, the photograph of the turret shows. 
 
 27 
 
Similarly, light and shade is so powerful that it always 
 suggests and carries the conviction of solid objects. 
 The interposition of objects refers to the principle 
 that the nearer objects more or less obstruct the view 
 of the more distant ones, or again that the forward 
 portion of an object interrupts its more remote parts. 
 This too was variously illustrated. Familiarity is a 
 complex factor, and refers to the known relations of 
 size and distance, as well as to position in space. The 
 only method to show clearly the importance of this 
 factor is by application to situations which are unfa- 
 miliar. 
 
 Topic XIX. Relative Place of Primary and Sec- 
 ondary Factors. A stereoscopic diagram of a simple 
 geometrical figure dispenses with all such aids as light 
 and shade, interposition of objects, perspective, and 
 familiarity, and proves that the primary factors alone 
 are sufficient to create the perception of solid objects. 
 This demonstrates the adequacy of the primary 
 factors, and that in principle they are sufficient to 
 induce the result. Conversely, if we take two photo- 
 graphs side by side and combine them in the stereo- 
 scope, but have these photographs absolutely alike, 
 then we shall have all of the secondary factors sug- 
 gestive of solidity, or reenforcing the perception of 
 solidity, but not the primary factors. At first sight 
 a good photograph sufficiently suggests solidity, and 
 the uninitiated might mistake such an effect as a true 
 stereoscopic impression ; but by comparing such a pair 
 of photographs with a pair which show the stereo- 
 scopic differences, the enormous increase in vividness 
 and realism of depth-perception by adding the pri- 
 mary to the secondary factors once more illustrates 
 that the real depth-perception is stereoscopic— that is, 
 
 2S 
 
involves primary factors with or without the realistic 
 aids of one or another of the secondary factors. It is 
 clear that all art that deals with representations on 
 surfaces, like photographs, engravings, paintings, and 
 so forth, utilize only the secondary effect, and suggest 
 solidity. The stereoscopic picture is accordingly in a 
 class by itself. The art of painting is in this sense an 
 illusion or suggestion. 
 
 As to the relative importance of the several factors, 
 a few examples indicate how under different circum- 
 stances familiarity and perspective may be supple- 
 mented by the true stereoscopic effect. Differences 
 of foreground and background may be suggested by 
 the photographic perspective, but are decidedly rein- 
 forced by the stereoscopic effect. Cases of unusual 
 positions of the eye, involving complex interpretations, 
 are also much better solved under true stereoscopic 
 vision, as the examples shown illustrate. 
 
 Topic XX. The Stereoscopic Range. Retinal dis- 
 similarity and convergence shiftings, as well as many 
 of the secondary factors, depend for their effect upon 
 the range at which the eyes are working. It is clear 
 that in general the primary factors will be most de- 
 cisive for near ranges; and that retinal dissimilarity, 
 as well as convergence shiftings, will rapidly diminish 
 with the increase in the distance of the object. Ac- 
 cordingly, it is the secondary factors that alone remain 
 strongly operative at long distances. Thus in looking 
 out of the window at a series of trees, which may be of 
 all sorts of shapes and sizes and positions, I get some 
 information of relative nearness and farness, par- 
 ticularly of the nearer group of trees, from retinal 
 dissimilarity and convergence shiftings. I get this 
 perception the more clearly when there is a striking 
 
 29 
 
object in the foreground. But beyond a moderate 
 range, my real information becomes of the secondary 
 order— light and shade, notably, the interposition of 
 objects, and perspective. That is why outdoor effects 
 in stereoscopic vision need hardly be very stereoscopic, 
 if they only give a clue by having an object in the 
 foreground. We thus conclude that practically the 
 secondary factors may in many views be more effective 
 than the primary ones, though in principle the reverse 
 relation holds. 
 
 A peculiar relation applies to the retinal dissimi- 
 larity of objects at close ranges and in the horizontal 
 plane. If at this range objects were presented as they 
 appear on the retina, the nearer object would look 
 to us altogether too large. In other words, for very 
 close objects we allow the known size to interfere with 
 the actual image; and when confronted with the 
 actual images of very close objects, they seem to us 
 wholly out of perspective. Note that these grotesque 
 out-of-perspective views actually correspond to the 
 retinal images. It is the virtue of stereoscopic photo- 
 graphs that they can combine anything that the eyes 
 can see, and these seemingly out-of-proportion views 
 when stereoscopically combined show the correct rela- 
 tion. 
 
 Topic XXI. The Perception of Color. The per- 
 ception of color offers an instructive contrast to space- 
 perception in that the sensory element is so entirely 
 dominant, and -the factor of inference or secondary 
 interpretation so entirely absent. While we do not 
 know the precise process that goes on when color is 
 perceived, and are quite ignorant of what process goes 
 on in the eye when we see red which is different from 
 some other process resulting in the perception of blue, 
 
we are none the less warranted in assuming some dis- 
 tinctive impression of the rod-and-cone layer in the 
 retina, and presumably some different stimulation of 
 the constituent elements of each cone. Our knowledge 
 of the physiology of color is thus most inadequate. Of 
 the physical cause of the stimulus to which our eyes 
 respond with the sensation of color, we know definitely 
 that it is the rate of vibration of the light-carrying 
 medium from 470 billion per second for the red to 722 
 billion for the violet. If a beam of light be broken up 
 by passing it through a prism, the different degrees of 
 refraction spread out the rays into its constiuent 
 wave-lengths, thus forming the spectrum. But the 
 spectrum really represents the limit of responsiveness 
 of the color-perceiving elements. There are of course 
 vibrations of similar kind beyond the red and the 
 violet, to which, however, our organs do not respond. 
 As a consequence, our description of color sensations is 
 largely psychological. 
 
 Topic XXII. Facts and Theories of Color-percep- 
 tion. A theory of color-perception must express 
 the observed facts in an intelligible form, throw some 
 light upon their relations, and if possible reduce the 
 complex phenomena to a unified and simple set of rela- 
 tions. The importance and description of the facts 
 may be modified in terms of the preferred theory. Of 
 greatest importance are the following : 1. Color 
 Range and Color Mixture. The normal range of color 
 seems definitely fixed by the spectrum. The question 
 as to how many color distinctions we can distinguish 
 involves the analysis of the kinds of change to which 
 our eyes are responsive. For this purpose it is best 
 to speak of the light-color sensations, since the inten- 
 sity of the light is itself a factor of the composite 
 
result. For the; purposes of color this change means 
 that with added white light the color grows brighter, 
 and with added black it grows darker. In addition 
 for colors of the spectrum there is the gradual change 
 as for example of a yellow that grows more towards 
 the orange, or a yellow that becomes greenish. We 
 must also think of the spectrum as converted into a 
 circular ring, joining the violet and the red ends, the 
 mixture of violet and red forming the purple. In 
 addition there is a third type of change which may 
 best be expressed by the . term of saturation, which 
 means that a red is as red as it can be, and that a 
 departure from this means a lack of saturation. Com- 
 bining these various changes it has been estimated 
 that the eye can distinguish a large number, certainly 
 two thousand or more, different color impressions, 
 though naturally the differences would not receive 
 ordinary names. In practical work in dye-houses, 
 color scales are in use involving a very large number 
 of distinctions. But this fact in turn means that 
 colors when mixed fuse into a merged effect; nor is 
 it the case that the resultant mixed impression can be 
 obtained only by using one and the same set of com- 
 ponents. The principle of color mixture that best 
 illustrates the processes is that of rapid revolution; 
 and the nature of the results will be gathered from 
 the demonstrations. The principle of the after-image, 
 or after-effect, thus involved is explained in the text. 
 2. Complementary Colors. The most striking fact 
 in color-perception is that a pair of colors such as red 
 and green, or blue and yellow, when combined, instead 
 of giving an intermediate color, as for example red 
 and yellow giving orange, or red and blue giving 
 purple, will neutralize and give no distinctive color 
 
 32 
 
at all, but a neutral gray. It is possible to find a 
 complementary color for any color tone. This, how- 
 ever, is but one definition of complementary color. 
 A second mode of reaching it is to subtract from the 
 spectrum one color, and the mixture of the remainder 
 forms the complementary. This likewise is shown in 
 the demonstration. A third mode of reaching it is 
 through fatigue. The eye when fatigued for red will 
 see neutral light as green, and vice versa. In this 
 connection may be mentioned also the fact of color 
 contrast. This is of two orders : first, simple, or back- 
 ground contrast, which expresses the different appear- 
 ance of a color according to the background against 
 which it is seen; and second, the distinctive comple- 
 mentary contrast, which once more shows comple- 
 mentary color as a contrasting color with the major 
 stimulation. This is in a sense subjective, and appears 
 instantly without fatigue, as the various disks with a 
 colored sector andi a black-and-white ring show. 
 
 In this connection attention is called to the distinc- 
 tion between the positive after-image and the negative 
 after-image. The positive after-image expresses the 
 rather long period which an impression remains on 
 the retina, and which makes possible its fusion with 
 succeeding impressions. It is difficult to catch the 
 positive after-image separately as such, but if one 
 allows the eye to wander rapidly across a checker- 
 board, there appears for an instant an after-image 
 of the board which is an exact reproduction of the 
 board itself. If the checkerboard be looked at a little 
 longer, then the negative after-image appears, lasts 
 much longer, is partly a fatigue effect, and is dis- 
 tinguished by the fact that all the white squares 
 appear in the after-image as black, and all the black 
 
 33 
 
ones as white; while in the positive after-image the 
 white squares appear as white and the black as black. 
 The main effect of the positive after-image is in the 
 fusion of successive impressions. It forms the prin- 
 ciple of color-mixture, and it is the breaking up and 
 avoidance of this fusion that is necessary to get the per- 
 ception of movement through interrupted glimpses. 
 The negative after-image of colors appears in their 
 complementary colors. While the negative after-image 
 need not be a fatigue phenomenon, the best illustra- 
 tion is the persistence as a deep purple ball of a 
 view of the golden setting sun. It is clear that com- 
 plementary color contrast shows the same kind of an 
 effect, but without reaching the state of fatigue. 
 
 3. Color-blindness. Our knowledge of color-per- 
 ception is markedly increased by its abnormal varie- 
 ties. It is not wholly clear how the color-blind eye 
 is defective; but the most marked type is that of a 
 confusion of red and green with one another and with 
 gray. Whether there are types within this group, of 
 red-blindness and green-blindness, is again doubtful; 
 but it is clear that the frequency of color-blindness 
 shows the absence of one of the constituent factors 
 of color-perception. Color-blindness should not be 
 confused with weakness or subnormal capacity to make 
 color distinctions. The latter is subject to education, 
 and does not follow the characteristic confusions of 
 the color-blind. The most common classification is that 
 of regarding the normal eye as perceiving both black- 
 and-white distinctions, red-and-green distinctions, 
 and blue-and-yellow distinctions; next the ordinary 
 form of color-blindness perceiving black-and-white 
 distinctions and blue-and-yellow distinctions, but not 
 the red-and-green; and third, the totally color-blind, 
 who perceive black and white alone. 
 
 34 
 
4. Color Theories. A theory of color must accord- 
 ingly be able to state these facts in terms of the theory, 
 and in a measure to account for them. The older 
 theory bears the name of Ytaung-Helmholtz. It 
 assumed the existence of three elements, a red-perceiv- 
 ing cone, a violet-perceiving, and a green-perceiving. 
 This was of course a pure hypothesis and increased 
 observation shows less and less in its favor. The rival 
 theory or theories all agree upon some form of simple 
 process, one aspect of which gives rise to the red sen- 
 sation and another to the green, and so on for blue and 
 yellow, and again for black and white. The various 
 objections and details of these theories are too com- 
 plex to be included. In conclusion it should be noted 
 that distinctions of luminosity are involved in the 
 black-and-white distinction, but may be separately 
 tested by the minimum changes of brightness which the 
 eye can distinguish — that is, independently of combi- 
 nation with color. Visual acuity, or accuracy of 
 form-perception for varying distances, which is the 
 common test of vision, again has no constant relation 
 to accuracy of color-perception. 
 
 Topic XXIII. Perception of Movement. A final 
 distinction which the eye makes is that between objects 
 in motion and objects at rest. This is an inference 
 from changes of position. Motion may be distin- 
 guished as progressive, such as that of a point passing 
 against a background, or the hand of a clock moving 
 across the marks on the dial, and phase movement, 
 which shows successive appearances, such as the rota- 
 tation of a ball, or a man running, or a bird flying. 
 Both may be combined, the distinction being that of a 
 man simply marking time and keeping step, or of ac- 
 tually stepping and advancing. The principle is sim- 
 
pie. It can be shown that the eyes do not see while 
 they move, and that, accordingly, we get a series of 
 glimpses. From the combination of successive glimpses 
 of changes of position, we form the inference of move- 
 ment. This is the principle of the kinetoscope, or 
 motion picture, and is exactly analogous to that of the 
 stereoscope in that the latter makes solidity out of its 
 elements, and the former makes motion out of an 
 interrupted view of a succession of successive glimp- 
 ses. It is essential that the glimpses be very short, and 
 again that the interrupted periods between the glimp- 
 ses shall be relatively long, so that the after-image 
 of the one glimpse may have disappeared before the 
 next comes; otherwise there would be mere fusion on 
 the principle of color-mixture. The kinetoscope as 
 demonstrated shows how the appearance of movement 
 may be accurately reproduced if these two conditions 
 be obeyed. In stantaneous photography has furnished 
 the means of very exact reproductions of phases of 
 movement, 
 
CHAPTER IV. 
 Hearing. 
 
 Topic XXIV. Hearing and the Perception of 
 Sound. The approach to the problem of the percep- 
 tion of sound puts the question, "What are the kinds 
 of information which we receive through the sense 
 of hearing, and how do we obtain them?" Hearing 
 offers a direct contrast to sight in that the part played 
 by inference is small and the direct effect of the im- 
 pression is large. This appears likewise in the fact 
 that the pleasure-and-pain value of sounds is de- 
 cided, and finds its analogy in color for vision. But 
 music as an art depends much more upon mere sen- 
 sory values than do the arts appealing to the eye. 
 
 Another general approach is by considering the 
 physical cause of the sensation, the physiological pro- 
 cess, and the psychological result. In the case of 
 tone, the physical cause is well known, consisting 
 merely in simple properties of air- vibrations ; varia- 
 tions in force, in rapidity, and in their mode of com- 
 bination. It is characteristic of the sense of hearing 
 that the ear can perceive cumulative impressions. 
 Sounds heap up, like the murmur of many voices in 
 a crowded room; and we have developed the power 
 of attention necessary to listen to selected portions of 
 what reaches the ear. 
 
 The simplest enumeration of the qualities of sounds 
 would first recognize the general distinction between 
 tones and noises, which will be discussed later. Of 
 
 37 
 
both it is true that they have (1) direction, referring 
 to their location in space; (2) intensity, which is the 
 common distinction of loudness, a distinction also 
 used in connection with the location and with other 
 tonal effects; (3) that most characteristic distinction 
 of pitch, which refers to a tone as high or low, and 
 which is as distinctive for hearing as color is for 
 vision; (4) that complex characteristic Called quality, 
 which determines a large range of distinctions such 
 as those between one human voice and another, be- 
 tween the same melody played on the piano or on the 
 violin, and so on; to which, may be added (5) dura- 
 tion, a very different type of quality and one which 
 in a sense applies to all sensations, but has a peculiar 
 part in the distinctions of tones. It refers to the 
 longer or shorter period of time during which the 
 stimulus acts. 
 
 Topic XXV. Structure and Function of the Ear. 
 It is necessary to understand how the physical stimu- 
 lus of the air- waves makes its way through the audi- 
 tory apparatus, and eventually reaching the parts of 
 the auditory nerve, sets up there that action of which 
 the perception of tone is the psychological' side. Re- 
 ferring for details to the text and demonstrations, it 
 may be noted in summary that the human ear con- 
 sists of three divisions: one the external ear, includ- 
 ing that part which is on the outside of the head and 
 is commonly called the ear, and the opening or audi- 
 tory passage at the end of which lies diagonally an 
 oval membrane, the tympanum or ear-drum. This is 
 the division between the external and the middle ear. 
 The middle ear, together with the internal ear, lies 
 in a hollowed-out, box-like portion of the temporal 
 bone. The middle ear is filled with, air, and must be 
 
 38 
 
filled with air to maintain the same pressure on the 
 inside of the tympanum as exists in the outer air. 
 This is done by means of the Eustachian tube, which 
 goes from the back of the mouth to this space in the 
 temporal bone. It is normally closed by a valve, but 
 during the act of swallowing, as again for a longer 
 period during yawning, the valve opens, permitting 
 an interchange of air, and thus constantly restoring 
 the air-pressure. Besides the air, the contents of the 
 middle ear consists of a chain of three bones: the 
 hammer, the lower tip of the handle of which is in- 
 serted in the center of the tympanum and the rounded 
 head of which plays into a hollowed portion of the 
 second bone, the anvil, which in turn has a long pro- 
 cess reaching downward, and at the tip of this process 
 there goes off at right angles the third bone, the stir- 
 rup. The bones take their names from the shape of 
 familiar objects. They are delicately articulated, and 
 act essentially as a whole. A vibration of the tym- 
 panum brings about a modified vibration of the plate 
 of the stirrup, which is set substantially parallel to 
 the tympanum. This plate of the stirrup rests against 
 a membrane which is the separation between the mid- 
 dle and the internal ear. The internal ear consists of 
 a membranous lining following the hollowed-out por- 
 tions of the temporal bone, and is filled with a liquid 
 both within the membrane and around it. The inter- 
 nal ear consists of the vestibule, or common meeting 
 point of two structures located at this point. Of these 
 two structures the one is the set of three semicircular 
 canals. These have nothing to do with the hearing, 
 but form the organ of equilibrium, and will be con- 
 sidered later. There remains the very minute snail- 
 shell, or cochlea, which contains the two organs of 
 
 39 
 
hearing, and also the very considerable auditory 
 nerve, or to speak more accurately the eighth cranial 
 nerve, the fibres of which are formed not alone by 
 the nerve of hearing but also by the nerve fibres sup- 
 plying the semicircular canals. 
 
 One may consider the cochlea as a tube which is 
 first somewhat complexly subdivided, and then coiled 
 two and a half times upon itself. A cross section of 
 one of these coils would show an undivided lower por- 
 tion and an upper portion in turn subdivided into 
 two by an oblique membrane, thus dividing off a tri- 
 angular space in which, naturally following the spiral 
 of the entire structure, lie the organs of hearing. It 
 is not possible to be perfectly sure what constitutes a 
 unit of this organ of hearing, and it may be safer to 
 regard it as made up of a pair of arches of Corti 
 with its strand of fibres of the auditory nerve, and 
 the fibre of the basilar membrane upon which it rests, 
 together with a group of inner and outer hair-cells to 
 either side of each arch. The careful protection of 
 this organ of hearing indicates the delicacy of the 
 minute impulses in the liquid which is the final form 
 assumed by the vibrations of the air. 
 
 Topic XXVI. The Processes of Hearing. The dis- 
 tinctions made by the sense of hearing are in the form 
 of the recognition of sounds. Such recognition pro- 
 ceeds in terms of distinctions which in turn must have 
 a physical! cause in the character of the outer vibra- 
 tions, a physiological process in the way in which the 
 hearing mechanism is acted upon, and a psychological 
 result in the distinctive sensations felt. We proceed, 
 as usual, from the last, and summarize the distinctions 
 leading to the recognition of sounds as (1) those of 
 direction, referring to the point in space from which 
 
 40 
 
the sound proceeds; (2) those of intensity of loud- 
 ness; (3) those of pitch, which is the specific charac- 
 teristic of sounds; (4) those of quality; (5) those of 
 duration. . . = ,%%\ 
 
 The perception of direction is a very poor one in 
 the human ear, and is one of the powers presumably 
 lost through the loss of the power of moving the ear, 
 which many of the lower animals retain. The shape 
 of the human ear is also but slightly helpful, while 
 the funnel-shaped ear of the horse or cat is evidently 
 a better collector of sounds. The mobility of the ear 
 in a horse, in each ear pointing separately and thus 
 exploring and testing the direction of sound, accounts 
 for the accuracy with which such an animal locates 
 direction. The difficulty of locating a sound, such as 
 that of a cricket in the room, and again the serious 
 difficulty of vessels at sea in a fog in locating the 
 approach and direction of movement of another ves- 
 sel—all this shows the relatively poor development of 
 the sense of direction in the human ear -as compared 
 with the animal proficiency. The main principle of 
 direction is that of the difference in intensity in the 
 two ears. Hence it is comparatively easy to locate 
 sounds definitely on the right or on the left, while 
 sounds in front or in back, and again below and above, 
 are readily confused. Tests are difficult for the reason 
 that sounds are 'modified by their echoes, and this 
 often enables one to distinguish between noises near 
 the floor or above one 's head. That the outer ear 
 still acts as a reflecting surface is shown by the un- 
 usual effect of one's voice as one speaks while holding 
 the hands in front of and close to the ears. 
 
 The perception of loudness has as its physical cause 
 the energy or height of the air-waves. It is relatively 
 
 41 
 
simple to test the capacity to make distinctions of in- 
 tensity, and we constantly use it in locating a sound 
 as growing or decreasing in loudness, We also use 
 it in regulating the loudness of the voice, and in rec- 
 ognizing distinctions of shading in a musical per- 
 formance. One may test this sense by observing how 
 slight a distance a watch may be removed or ap- 
 proached from a fixed point, and the direction of the 
 change of position be recognized. Another simple 
 test is to drop a small shot on a glass plate with the 
 ear five or ten feet away, and to note from what dis- 
 tance the shot must be dropped to produce an ob- 
 servably louder sound. A telephone instrument may 
 similarly be used to record the same distinction. This 
 power should not be confused with the acuity of 
 hearing, which would be measured by the smallest 
 sound that one can just hear. Persons differ in this 
 respect, and in old age a diminishing sensitiveness of 
 hearing results in the loss of slighter sounds. 
 
 The remaining auditory perceptions assume such 
 a large part in musical distinctions that they are best 
 discussed under that head. It should, however, be 
 observed that the training of the ear is primarily for 
 the distinction and recognition of sounds, and that 
 in principle there is no difference between such recog- 
 nition or appreciation of sounds that are not speci- 
 fically musical and of those that are. It is possible 
 to show that the physical cause of a musical tone is the 
 regularity or periodicity of the vibrations, while an 
 irregular and non-periodic tone produces a noise. All 
 noises contain a tone element, and almost all tones a 
 noise element. The distinction appears in language, 
 which also represents the type of sound distinctions. 
 The vowels are tones, and the consonants noises. The 
 
 42 
 
names of these, such as dentals, which are noises made 
 by the teeth, and Unguals, noises made by the tongue, 
 and labials, which are noises made by the lips, indi- 
 cate the character of the noise, which is then vocalized 
 by combination with vowels. The accurate recogni- 
 tion of speech shows the tremendous power of the ear 
 in recognizing slight differences of sound and of asso- 
 ciating meaning with these sounds. 
 
 Topic XXVII. Musical Perception. The percep- 
 tion of pitch refers to the distinction recognized as 
 that of high and low tones. All tones and noises have 
 a pitch more or less constant or variable, and the dis- 
 tinction between a man's voice and a woman's! voice, 
 between one voice and another, between types of 
 noises, all involve distinctions of pitch. It is, how- 
 ever, easier to study them at their * simplest. Such 
 simple tones as made by tuning-forks or whistles or 
 reeds bring out the special distinction of pitch. The 
 keyboard of a piano again represents pitch distinc- 
 tions, arranged, however, in a musical scale. The 
 physical cause of pitch is the frequency or length of 
 the waves. High tones represent very rapid air- 
 vibrations, and low tones slower vibrations, and thus 
 longer ones. The limits of pitch in a sense are similar 
 to the limits of color for the eye, and are readily de- 
 termined. It may be shown that air-vibrations can 
 be seen when vibrating from five to fifteen vibrations 
 per second, but do not form a recognizable tone until 
 about from twenty-four to twenty- eight per second. 
 These low, dull, vibrating tones are used only in con- 
 nection with higher tones. Thei upper limit of hear- 
 ing is tested by some form of whistle, which gives 
 rise to a very slight, piercing, shrill sound. The upper 
 limits vary, but a general average of from twenty to 
 
 43 
 
thirty thousand vibrations or more is the result of 
 the test. However, musical tones above four or six 
 thousand vibrations are sparingly used. 
 
 The power to make small and definite pitch-distinc- 
 tions probably varies more than any other sense capa- 
 city. While this should not be confused with musical 
 perception, it is the basis of it. A test of the power 
 of pitch-distinction, and also of the position of tones 
 in the scale, is readily made by some tone-testing 
 apparatus, or again by a series of tuning forks, each 
 one differing by a few vibrations from the next. The 
 most favorable interval for such tests are vibrations 
 of from three hundred to six hundred per second, 
 and within this limit a sensitive ear can perceive as 
 higher or lower two tones varying by a vibration or 
 two. The difference of such tones is often heard when 
 it is impossible to say confidently which is higher and 
 which lower. Ears less acute in this respect would 
 vary almost indefinitely, so that to some ears even 
 differences of fifteen or twenty vibrations per second 
 are not very distinct and recognizable. When we 
 leave the simple tests of the range of pitch and of 
 pitch-distinction, we enter the special kinds of dis- 
 tinction upon which music depends. Before taking 
 up this point it should be noted that another general 
 quality of tones is their very brief after-effect, thus 
 contrasting with the long after-effect of colors. Colors 
 fuse readily if impressions are exposed eight or more 
 per second. Tones remain distinct even though they 
 follow one another at the rate of several hundred per 
 second. All this is provided for by the mechanism of 
 the ear. The principle of the physiological process 
 for pitch-perception is one of selection; and we may 
 think of the spiral series of end-organs as acting 
 
 44 
 
selectively by the principle of sympathetic vibration ; 
 so that a tone of one pitch will set going only a definite 
 unit or units of the hearing apparatus. On this as- 
 sumption it is easy to construct the type of physio- 
 logical processes correlated with pitch-distinction. 
 
 Topic XXVIII. Special Aspects of Musical Per- 
 ception. The central distinction is that concerning 
 pitch ; but the power of pitch-distinction is essentially 
 altered by the peculiar type of recognition of pitch- 
 relations for which the term "sense of interval" may 
 be adopted. The fact thus expressed is a peculiar, in- 
 deed a unique one in the field of sensation, for it 
 expresses a sensitiveness to relations independently 
 of absolute pitch. It must not be supposed that the 
 fundamental elements of musical perception are pos- 
 sessed only by the few, or the musical in the technical 
 sense. Everyone who recognizes a familiar simple 
 tune whether played on one instrument or another, 
 whether played on the upper octaves of the piano or 
 on the lower, shows the essential recognition of the 
 sense of interval ; for the recognition that the succes- 
 sion of tones is the same expresses the essential fact. 
 Viewing this fact more closely, it appears at once that 
 the recognition of succession in terms of interval, 
 which is called melody, does not apply equally to any 
 and all intervals. It appears specifically that the 
 human ear is sensitive to the recognition of certain 
 intervals. It is the accounting for this fact that con- 
 stitutes the successful analysis of tones. 
 
 The first stage in this analysis is the demonstra- 
 tion that the differences that we call quality, and 
 which appear in tones of the same pitch but produced 
 by different musical instruments, are all due to com- 
 plication of the fundamental, which gives the domi- 
 
 45 
 
nant tone, with the presence of overtones. Simply 
 stated, all tones are complex, and the physical cause 
 of this complexity is again a physical tendency for a 
 string, a semi-enclosed body of air, or other musical 
 instrument to break up into parts, and to have these 
 parts vibrate along with the vibration of the string, 
 etc., as a whole. The quality, the richness, the total 
 effect of a tone is thus due to the kind andj strength 
 and distribution of overtones which accompany the 
 fundamental. Nor must it be supposed that this type 
 of distinction applies to music alone. It is just as 
 true of noises and of speech; for speech is the result 
 of using the vocal cords as an instrument, which is 
 further reenforced and directed by the organs con- 
 cerned in speech. Viewed as a single instrument, the 
 voice can give rise to tones of its own pitch ; and such 
 distinctions as the vowels o, a, the German ii, and so 
 on, must be due to difference of quality, the quality 
 resulting from the different positions of the cavity of 
 the mouth, which by reenforcing different types and 
 ranges of overtones produces the resulting sound. 
 This is not a matter of speculation, for it has been 
 demonstrated that a. series of tuning forks of varied 
 pitches, when sounded together, actually reproduce 
 the tones o, a, and so forth. 
 
 Returning to the sense of interval, we reach the 
 essential distinction between the musical and the non- 
 musical ear. The musical ear recognizes the correct- 
 ness of intervals, and, as indicated, of particular in- 
 tervals. The two most common intervals are the 
 octave and the fifth. The octave is represented by 
 the relation of one to two, and the fifth by the rela- 
 tion of two to three. The other intervals composing 
 the musical scale also represent, for the most part, 
 
 46 
 
c' 
 
 d' 
 
 e' 
 
 f 
 
 g' 
 
 a' 
 
 b' 
 
 256 
 
 288 
 
 320 
 
 341.3 
 
 382 
 
 426.6 
 
 480' 
 
 simple numerical relations. The conditions leading 
 to the adoption of the musical scale are too compli- 
 cated to be here considered, but the vibration-rates 
 for the middle octave are given below: 
 
 b' c" 
 512 
 
 The relation of c' to c" is that of one to two, and 
 forms an "octave" ; the relation of c' to g' (2 to 3) is 
 the "fifth"; the interval c' to F (3 to 4) forms a 
 "fourth"; c' to e' (4 to 5) forms a "major third"; 
 c' to a' (3 to 5) is a "major sixth." Omitting de- 
 tails, it may be said that these, together with one or 
 two other intervals, constitute the most pleasing and 
 the most commonly used intervals in simple melody, 
 while other intervals are used with less consonant 
 effect. 
 
 In view of all these considerations, the striking 
 fact remains that we are more sensitive to interval 
 than to pitch, more sensitive to relations of tone that 
 are slightly out of tune because the interval is flat or 
 sharp than to any absolute pitch distinction. The 
 explanation for the existence of this sense goes back 
 to the unconscious education which the ear is con- 
 stantly receiving in the relations of fundamentals to 
 overtones in any complex tone ; for these are the same 
 relations that are repeated in the interval. The fur- 
 ther complication of music is the obvious and essen- 
 tial one of the existence of harmony, namely that we 
 hear the resultant effect of many tones combined. 
 If there were only melody and no harmony, we 
 should be reduced to tunes that could be played with 
 one finger on the piano. It is obvious that the exist- 
 ence of harmony enormously increases the range and 
 
 47 
 
nature of musical effect ; but still more, harmony gives 
 the ear a correctness of appreciation of interval which 
 supplements and perfects that supplied by melody. 
 Thus a piano-tuner adjusts a given key not merely by 
 testing whether in connection with a lower and a 
 higher tone it forms a proper scale, that is, a proper 
 interval or succession; but he tests it still more by 
 placing the given tone in a group of three or more, 
 that is, a chord, observing whether the sound of the 
 combined chord is correct. 
 
 In conclusion let it be noted that musical percep- 
 tion supplies the simplest conditions for the analysis 
 of tones, and further shows how the distinctions which 
 the ear recognizes are appreciated. It must be ever 
 borne in mind that these principles are equally ap- 
 plicable to the distinctions of speech and to those of 
 noises, but that here they are complicated by all 
 manner of recognitions which cannot be expressed in 
 terms of pure pitch or quality. Consideration should 
 also be had of the factor of duration. This expresses 
 not merely the fact that the ear is sensitive to time 
 distinctions, but that these time-relations enter into 
 and combine with other factors of musical effect. As 
 a pure time-distinction one may refer to the tele- 
 graphic language, which is a code combining long and 
 short clicks into arrangements of letters. So also in 
 music, time is expressed by whole-tones and half-tones 
 and quarter-tones, and so on, and the duration during 
 which a tone is sustained contributes much to its 
 effect. But in addition there is the time-relation of 
 the tone itself. Thus when we distinguish between a 
 violin and a piano tone, it is true that thej main dis- 
 tinction is one of quality, which means that the piano 
 brings out certain overtones in a different intensity 
 
 48 
 
and distribution than does the violin. It means, how- 
 ever, equally that the mode of swelling, of increasing 
 of the piano tone and the rapidity with which it 
 reaches its highest effect, and then in turn with which 
 it dies out, give it an entirely different time-effect 
 from the long-drawn-out bowing of a violin tone. 
 Thus duration, along with intensity, pitch, quality, 
 and the developments of pitch and quality into the 
 sense # of interval, and the resultant apprecation of 
 melody and harmony, give the range of musical per- 
 ception. 
 
 49 
 
CHAPTER V. 
 
 Smell and Taste. 
 
 Topic XXIX. The Sensations of Smell and Taste. 
 
 This group of sensations is important as illustrat- 
 ing the range of application of what are commonly 
 known as the lower senses. This term refers pri- 
 marily to the fact that these senses are closely at- 
 tached to use or service in terms of protection, and 
 have slight intellectual development. Of the two, 
 smell is the more extensive sense ; and in terms of 
 evolution sight and smell occupy a peculiar position, 
 which is due to their leadership as distance senses. 
 It is clearly of importance to an animal to become 
 aware of objects of danger or of interest at long 
 range, and there is some reason for dividing organ- 
 isms into those that appreciate long range situations 
 by smell and those who appreciate them by sight. 
 The birds illustrate the latter, having long-range 
 vision and a poor sense of smell. This is proved by 
 Darwin's experiment of distributing paper bags con- 
 taining meat along the sea-beach and noting that the 
 condors swerving about would fly near to, but not 
 examine the paper bags, indicating that they could 
 not smell the contents; but that when one bird had 
 accidentally broken through the bag and the meat 
 was exposed, they instantly pounced upon all of them 
 and quickly devoured the meat. Similarly, birds of 
 prey discover the presence of carrion at long range, 
 and show their superiority of vision, which we have 
 
 50 
 
recognized in the phrase "the eye of the eagle." 
 Such animals as the dog show a corresponding supe- 
 riority of the sense of smell and a lesser development 
 of vision. In the human brain the shrunken appear- 
 ance of the olfactory lobes is very striking, indicating 
 that in man this sense is degenerate. 
 
 The sense of smell protects the respiratory passage, 
 so that only wholesome air may be breathed, and the 
 alimentary canal, so that only wholesome food may 
 be swallowed. The lower passage of the nose is the 
 respiratory passage, and the upper chamber, in which 
 the end-organs of smell are situated, is only distinctly 
 stimulated when we deliberately sniff the air to per- 
 ceive odor. Both the anatomy and the physiology con- 
 tribute little to our knowledge ; and it is equally true 
 that the physical cause of distinctive odors is not 
 definitely assigned. Odors are accordingly classified 
 empirically, using for the most part the names of 
 flowers and fruits and essences prepared by nature or 
 by manufacture. Thus we speak of a violet-like odor, 
 or a peach-like odor, or the odor of tar or wax, 
 and so forth. The general reaction to odors is one in 
 terms of their pleasant or unpleasant character, and 
 in a moderate way an esthetics of odor is used. 
 
 The sense of taste is much more limited, and refers 
 in the main to the simple distinction of sweet, sour, 
 bitter, and salt. Here again there is distinct use for 
 protection of the alimentary canal. We need salt, and 
 thus have a taste for it. .Similarly we need sweets, 
 though here the sense of luxury makes possible an 
 esthetic development of satisfaction. The combined 
 use of taste and smell in the recognitions of eating 
 forms an excellent example of a psychological com- 
 plex, that is, of a single recognition due to composite 
 
 51 
 
factors. Thus if, with the eyes closed, a morsel be 
 placed into the mouth, it might at once be recognized 
 as a bit of raspberry jelly. Such recognition is, as all 
 recognition, in terms of quality ; and we may enumer- 
 ate the qualities as the smoothness, the softness, the 
 sweetness, the acidity, the peculiar flavor, and equally 
 the temperature. Together these qualities constitute 
 the basis of recognition. Some of them are tactile, 
 like the smoothness, or motor, like the softness; the 
 acid and sweet are taste stimulation; and the flavor 
 belongs to smell. 
 
 It can readily be shown that the larger part of food 
 recognition is due to odor or flavor. When affected 
 with a cold, we taste food but little ; but the sense of 
 taste itself is not affected, only that of smell. So per- 
 sons who have no sense of smell distinguish salt, sweet, 
 bitter, as well as others, but they do not distinguish 
 the flavor on which the recognition of food depends, 
 and experiment confirms this conclusion. It can be 
 shown that with the nostrils held we should fail to 
 recognize such distinctions as veal and chicken, or 
 again, scraped apple or scraped potato, or again tea 
 and coffee, or in brief all flavors which are used in 
 cooking. These are appeals to the nose, though the 
 attention is so much more concentrated upon the 
 mouth that we wrongly refer the source of sensation 
 to taste. 
 
 While; thus these senses minister to protection and 
 useful recognition, they have a limited intellectual 
 development. It is clear that the dog in distinguish- 
 ing the footsteps of his master from hundreds of 
 others makes an intellectual distinction. It is a dis- 
 tinction quite parallel, though not as explicit and 
 conscious as that which a druggist might make in 
 
 52 
 
recognizing the contents of bottles from their odors. 
 We moderately use this sense of distinction for smell 
 and also for taste, but we are mostly sensitive to the 
 pleasant and unpleasant side thereof. But in chem- 
 istry, as well as in food preparation, delicate percep- 
 tions of flavor and taste enter and form the basis of 
 distinctions. Such a professional use of this sense as 
 that of tea-tasting, in which the values of teas are 
 assorted by the verdicts of the professional on the 
 basis of flavor and taste, indicates the possibility of 
 intellectual use of such senses. It may be added that 
 tests of power to distinguish slight differences in odor 
 or in taste, and again of the power to detect the pres- 
 ence of small amounts of familiar stimuli, yield re- 
 sults which show a great variety according to the 
 particular objects used. In some respects the sense 
 of smell is very delicate, the nose recognizing the 
 presence of so minute a fraction of a grain of musk 
 that it even defies chemical analysis. On the other 
 hand, for other types of substances the recognitions 
 are vaguer and the power of distinction is less marked. 
 It may further be noted that both taste and smell are 
 subject to contrast and to fatigue, so that we get 
 used to odors and also tire of them, and that over- 
 stimulation readily enters. 
 
 53 
 
CHAPTER VI. 
 Touch and Movement. 
 
 Topic XXX. The Tactile Sensations in General. 
 
 The word touch is popularly used to cover a variety 
 of sensations obtained through the skin. It is easy 
 to recognize that many different types of sensation 
 are here present. Temperature is most readily dis- 
 tinguished from the rest. The active use of the skin 
 in feeling as against touching indicates the composite 
 play of movement in connection with touch. We know 
 that therd are only two types of sensations, those re- 
 sulting from the stimulation of a special sensory sur- 
 face and those accompanying the contraction of 
 muscles. The latter are called kinesthetic, and they 
 are of special relation to touch not only because of 
 the constant use of motion with touch, but because 
 of the extensive nature of the tactile surfaces and the 
 large variety of muscle-sensations that merge with 
 tactile ones. 
 
 Classification of touch qualities is not easy, and the 
 best is open to considerations of convenience. We 
 may distinguish first the bare sense of contact, which 
 gives at the least the sense of awareness of a touch 
 feeling, like that of a fly alighting upon the skin or 
 of brushing against a spider web. The skin is at many 
 points aided by sensitive hairs which give increased 
 sensitiveness to such bare information of contact. 
 The thinness of the skin, as over joints, also illustrates 
 a delicate variety of this simplest type of tactile sen- 
 sitiveness. 
 
 54 
 
The sense of locality represents the fact that the 
 position of a touch upon the skin is localized approxi- 
 mately or accurately. This is a factor of the distri- 
 bution of the nerves of touch. There is no danger of 
 confusing a touch on the foot or on the shoulder- 
 blade with one on the hand. Similarly, a touch on 
 the hand is readily distinguished from one on the 
 elbow or upper arm, and again on the right hand from 
 one on the left hand. Bringing these distinctions 
 to their limit, different points on the finger-tip would 
 in turn give a difference in feeling; but eventually 
 this vanishes. The standard test to show this fact 
 and as well to illustrate the distinction of such 
 sensibility is the "compass-point" test. This shows 
 that the minimum separation of two points necessary 
 to have the points felt as two varies decidedly on dif- 
 ferent parts of the skin area. The distance is about 
 three or four millimeters for the palm of the hand, 
 nine or ten millimeters for the back, and one and one- 
 half or two millimeters for the tip of the forefinger, 
 while very coarse areas, as between the shoulder- 
 blades on the back, may require a separation of the 
 points to twenty or twenty-five millimeters— substan- 
 tially an inch. The natural way to account for this 
 difference of sensibility is by supposing that in the 
 coarsely perceiving areas relatively few fibres supply 
 relatively large surfaces, while on the finger-tips a 
 large number of nerve-fibres supply a very small area 
 of skin. This distribution would then account for the 
 ability to localize better on the finger-tip than on the 
 palm of the hand, and it would give a more distinctive 
 quality to the more finely perceiving areas. 
 
 From this same condition arises the most character- 
 istic form of tactile distinction, that relating to the 
 
 55 
 
space qualities, which may be enumerated as form, 
 together with size, which in turn includes length as 
 well as area. The principle is best illustrated in the 
 perception of form, and of this the simplest type 
 would be the distinction between a square hollow 
 tube and a round hollow tube of the same size. The 
 tests at once show that whether or not the distinction 
 is felt depends upon the size of the tube. Quite large 
 tubes, half an inch or more in diameter, will not be 
 distinguished as to form on the back of the hand or 
 even on the palm of the hand, but tubes of half the 
 size will be accurately distinguished on the finger- 
 tips. There is a yet finer tactile organ, namely, the 
 tip of the tongue; and here a pair of needles but a 
 quarter of a millimeter apart may still be distin- 
 guished as two. The tongue can also distinguish mi- 
 nute differences of form, such as that of a needle with 
 a round eye or a needle with an elongated eye, which 
 give no impression when pressed on the finger-tip. 
 It is this type of distinction that the blind practice in 
 reading raised letters, and it is easy to show how dif- 
 ficult such distinctions are, even in very large letters. 
 It must be added that the actual way in which the 
 perception of form by touch best proceeds is through 
 feeling. The finger rapidly moves over the surface 
 and thus decidedly increases the clearness of the form 
 distinction. 
 
 As each sense has its Specific quality, so that of 
 touch gives rise to texture, and the simplest example 
 of this is the distinction between rough and smooth. 
 [Regular surfaces may be arranged by weaves in 
 strands of different thicknesses; and thus the sense 
 of roughness and smoothness may be accurately tested. 
 Here again the active sense of feeling makes distinc- 
 
 56 
 
tions more readily than the mere sense of contact. 
 This touch quality is not limited to roughness and 
 smoothness, but extends to allied distinctions, as the 
 feel of the pile of velvet, the different types of com- 
 posite qualities as wetness, stickiness, oiliness, gritti- 
 ness, and so on. 
 
 The sense of pressure upon the skin represents a 
 different phase of contact, and one which in the 
 passive form is not of large practical use. It may, 
 however, be tested by the power to distinguish be- 
 tween differences of pressure or of weight resting 
 upon the finger. Such a sense is relatively coarse, 
 distinctions on the palm of the hand being about 1 / 5 
 or 1 / 7 ; which means that the weight must be increased 
 by this amount before it is clearly perceived as heavier. 
 When, however, the active sense of pressure is used, 
 as in lifting weights, distinctions as small as 1 / 15 can 
 under favorable circumstances be made; that is, a 
 "short" pound of fifteen ounces could be detected by 
 lifting as lighter than a true pound of sixteen ounces. 
 
 Topic XXXI. The Sense of Temperature. Quite 
 distinct from this group of sensations resident in the 
 skin is the sense of temperature, it being very obvious 
 that a feeling of warmth or of cold is of a wholly 
 different nature than that of weight or of form or of 
 texture. It is also true that in terms of origin and 
 of function temperature has a very different status. 
 It is now known that there are special temperature 
 organs, and further that the particular points of the 
 skin at which the sense of heat as best felt are differ- 
 ent from those at which the sense of cold best appears. 
 It may then be assumed that there are special nerves 
 to convey impressions of heat, and probably special 
 nerves to convey sensations of cold as distinct from 
 
 57 
 
heat. Temperature has a special body-regulating 
 value, owing to the fact that we are warm-blooded 
 animals and that the maintenance of a constant tem- 
 perature is essential to health and vitality. As a con- 
 sequence, marked deviations of temperature affect the 
 physiological mechanism, and all functions suffer in 
 intense cold or again in intense heat. But apart from 
 this general regulation, there is the fact that what we 
 feel as cold is the loss of heat from the body, and 
 what we feel as warmth is the adding to the heat of 
 the body. It thus results that the temperature-sense, 
 if compared with the thermometer, is constantly mis- 
 informing us. Thus a surface of flannel and a sur- 
 face of iron exposed in the same room are really of 
 like temperature; but the iron feels cold because it 
 takes heat away from the body, and the flannel feels 
 warm because it reflects heat back to the body. So 
 similarly the sense of temperature is subject to con- 
 trast; and if the one hand be placed in cold water 
 and the other in hot, and then both simultaneously 
 plunged into lukewarm water, the hand that has been 
 in the cold water will feel the lukewarm water as hot, 
 and the other will feel it as cold. These contradictory 
 sensations will gradually disappear as the new adjust- 
 ment takes place. Similarly in coming from outdoors 
 the room may seem warm, and in leaving a warm room 
 for the .cold outdoors the most marked sensation ap- 
 pears by contrast. Owing to this mode of reaction of 
 the temperature sense, one must determine its power 
 of making distinctions with reference to definite tem- 
 peratures ; and it may be said that for moderate tem- 
 peratures of from 80 to 100 degrees Fahrenheit -dis- 
 tinctions of one or two degrees, or even less, can be 
 made by the finger under favorable conditions. One 
 
 58 • 
 
may also learn to associate definite feelings with abso- 
 lute temperature, thus guaging the reading of the 
 thermometer by the feel of the air or water. 
 
 Topic XXXII. Kinesthetic Senses. The sensa- 
 tions accompanying movement may be considered with 
 reference to their extent and with reference to their 
 intetisity. In all movement we accomplish work, and 
 work is measured in foot-pounds, the foot represent- 
 ing the extension and the pound the intensity. Con- 
 sidering the latter element first, we know that in lift- 
 ing a weight there is a double process, that of the 
 feeling accompanying the outgoing effort, and sec- 
 ondly that of the feeling of the return sensation. It 
 is the adjustment of the one of these to the other that 
 makes it possible to exercise energy in accordance 
 with intention. Thus the experience of raising a 
 pitcher of water and finding it flying up in the hand 
 shows that the very act of lifting the pitcher involves 
 an anticipation of the presumable weight of it by 
 means of the presumable effort necessary to lift it, 
 while the return sensation in this case reports that 
 the pitcher (empty when it was supposed to be full) 
 is unexpectedly light. The effort being released, it 
 expends itself in raising the pitcher up in the air. 
 This double process of the outgoing effort and the 
 return report is also the basis of skill, whether exer- 
 cised by the sense of touch or by touch and sight. The 
 special mechanism of this regulation will be consid- 
 ered later. At present it is sufficient to recognize the 
 nature of the kinesthetic sensation and its connection 
 with the sense of touch. Thus active touch represents 
 more particularly the resulting increase of feeling 
 from moving the hand about, at the same time focusing 
 the attention upon the tactile sensation, while the 
 
 59 
 
kinesthetic sense implies the use of muscular contrac- 
 tion with the attention directed either to the degree or 
 the extent and distribution of the contraction. It is 
 clear that active touch not only gives a better sense of 
 weight by lifting, but it gives a better sense of form, 
 and again of length or of area, by the complicated 
 process of feeling. In lifting weights there is the 
 feeling of pressure of the weight against the skin, 
 but this is less accurate than the sense of effort due 
 to muscular contraction. 
 
 Attention should be directed to the joint sense, 
 the best example of which is its use in feeling the 
 thickness of a board or a book or a sheet of paper or 
 a cloth between the thumb and forefinger. This is 
 again kinesthetic in type, and represents a remark- 
 ably accurate distinction. It will be simply tested by 
 placing between the thumb and forefinger a random 
 number of pages in a book, and trying to select with 
 the other hand an equal number. Differences of two 
 or three pages in a hundred are readily told; and 
 experts can judge the weight of paper or the thick- 
 ness of cloth quite accurately by this means. 
 
 Topic XXXIII. Sensation in the Guidance of 
 Movement. There remain to be considered various 
 types of sensation which are specifically developed 
 with reference to the guidance of movement, includ- 
 ing the locomotion of the body as a whole from place 
 to place, as well as the specific movements by which 
 the mind expresses itself in conduct. These are by no 
 means of like type, but have in common the illustra- 
 tion of the sensory guidance of movement. 
 
 The Sense of Equilibrium. The first type relates 
 to the specific sensations by means of which the 
 equilibrium of the body is maintained in movement, 
 
 60 
 
and also the sense of direction is guided. In consid- 
 ering the ear, we found a set of organs, the semi- 
 circular canals, which have nothing to do with hear- 
 ing, but which have been shown to be the special 
 organs of this sense of equilibrium. The normal 
 function of these organs is to indicate the slightest 
 departure from the normal vertical position, and thus 
 to stimulate the righting or correcting movements nec- 
 essary to restore equilibrium. The three canals at 
 once suggest the action of spirit-levels, and are doubt- 
 less related to the three dimensions of space. Two 
 of the canals are vertical, the one running fore and 
 aft, and the other from side to side; while the third 
 canal lies below them in a horizontal position. It is 
 this horizontal canal that seems especially sensitive 
 to disturbance, being aroused by turning rapidly on 
 one's heel, thus inducing the familiar sense of dizzi- 
 ness. The mechanism of this action is the pressure 
 of the liquid within the canals against the nerve- 
 endings in the swollen ends of the canals. Similarly 
 sensations of disturbance in the vertical fore-and-aft 
 canal would be induced by swinging, while the irregu- 
 lar movements of a tossing ship would seriously affect 
 all the canals. While the action of the canals is best 
 observed in their disturbance in the sense of dizziness, 
 it is obvious that their normal function is through 
 such disturbance to induce the slight compensating 
 movements necessary to the restoration of equilibrium. 
 The susceptibility to dizziness, and to dizziness in the 
 various planes, varies in individuals. Its most famil- 
 iar symptom is a lack of coordination between the 
 specific sensations of the canals and vision. Thus 
 after spinning on one's heel the walls of the room 
 seem to go around, which is of course an illusion in- 
 
 61 
 
duced by this conflict between the "semicircular" sen- 
 sation and the attempt of the eyes to catch up to 
 them. It is interesting that the necessity of such a 
 guiding sense was hardly suspected until in recent 
 times, while the demonstrations of the semicircular 
 canals as the organs of the sense of equilibrium is 
 relatively recent. 
 
 Another example of sensations guiding the sense of 
 movement is that referring to passive locomotion, of 
 which in recent times we have large experience. It 
 has been shown) that we have no true sense of move- 
 ment, but infer it only from irregular jars and jolts, 
 or from the pressure of the wind against the face, 
 or again from the passing of objects along the road, 
 and finally from some slight disturbance in the semi- 
 circular sensations. This is another example of a 
 complex dependent largely upon inference. One illus- 
 tration of it is familiar. When sitting in a railway 
 car in the depot and the train adjoining moves out, 
 there is a strong feeling that one is moving back- 
 wards. This is illusory, and is the inference of back- 
 ward movement from the forward movement of the 
 next train,— just as in traveling we pass fences, trees, 
 houses, etc., and their moving backward becomes an 
 index of our moving forivard. The very fact that we 
 can thus induce a feeling of movement from a sensa- 
 tion shows how largely inferential it is. The sense 
 of movement is decidedly increased in riding in an 
 open trolley by the pressure of air against the exposed 
 parts of the body, and again by all the irregularities 
 of jolt and jar. Moving in an elevator gives a new - 
 direction of up-and-down sensation, and in the mo- 
 ment of starting and stopping, there is a decided and 
 often unpleasant feeling, which is of "semicircular" 
 
 62 
 
origin. In this direction, too, illusions of motion may 
 be produced. 
 
 The Sensory Guidance of Manual Skill. A very 
 special relation obtains between the eye and the hand, 
 and illustrates the complex guidance contributing to 
 manual skill. The hand carries out its movements 
 under the direction of the eye, but also under the 
 guidance of kinesthetic sensations. As a consequence, 
 the kinesthetic sensation alone will suffice, though with 
 diminished accuracy. Thus in learning to write with 
 my eyes open, I have incidentally learned to write 
 with my eyes closed. The kinesthetic sensations are 
 adequate to induce the proper forms of the letters. 
 Similarly in learning to use the typewriter one 
 depends largely upon vision, though the touch system 
 throws a fairly independent guidance upon kines- 
 thetic sensation ; and naturally the blind use the type- 
 writer freely on the basis of kinesthetic sensations 
 alone. 
 
 The principle is even better illustrated in the rela- 
 tion between speech and hearing. The child learns to 
 speak by the double regulation of feeling the proper 
 positions of its own vocal mechanism and of correcting 
 the spoken sounds by the criterion of the ear. Thus 
 while learning to speak by ear through hearing the 
 sounds of his own voice, the child incidentally, but 
 quite inevitably, learns to speak without hearing, and 
 through the kinesthetic sensations of the vocal cords 
 alone. Accordingly, if in youth or adult life one 
 becomes deaf, one does not lose the power of speech, 
 the kinesthetic guidance remaining adequate. Even 
 more than this is shown by the natural relation that 
 connects deafness with muteness. There is no physio- 
 logical, but only psychological reason why the child 
 
 63 
 
born deaf should become a mute. It lacks the incen- 
 tive to speak supplied by hearing its own voice. In 
 recent years, deaf children are taught to speak, though 
 naturally not as accurately as hearing children, by 
 the guidance of the kinesthetic sensations alone. 
 They are encouraged to make sounds and to note the 
 position of lips and throat of the speaking teacher. 
 The utterances are corrected again and again, until 
 they acquire the entire speaking process by kines- 
 thetic guidance. 
 
 Topic XXXIY. The Space and Time Relations of 
 Sensations. All senses have the quality of duration, 
 but our knowledge of the sense of time is not gained 
 equally from all of the senses. The auditory sense of 
 time is best developed. The ticking of a clock, as well 
 as the rhythmical movements, suggests how this form 
 of guidance is largely thrown upon the ear. In 
 rhythmical movement, as in dancing, and in keeping 
 step, the music gives the time guidance ; such rhythm 
 of expression requires the auditory accompaniment for 
 accuracy as well as for pleasure. The motor tendency 
 is shown in the impulse to beat time to marches or 
 similar melodies. It is also true that the ear will more 
 accurately judge slight differences in interval, and 
 guage intervals of time accurately, of which again the 
 telegraphic language is an admirable example. Time- 
 relations for vision are of a totally different order, and 
 fusion introduces complications. 
 
 In a very similar sense the eye is the great space- 
 sense, and judgment of positions in space are largely 
 visual. It is true that the ear has a spacial reference 
 in the location of sounds and in the estimate of their 
 distance, but it does not grasp space-relations directly 
 as does the eye. This contrast further shows the ear 
 
 64 
 
to be the great successive sense, giving relations of 
 succession, as melody, or again in speech and in the 
 development of the drama, while the eye gives the 
 sense of simultaneity, of contrast in composition, per- 
 mitting of a large field and quick change of attention. 
 The ear attends to but a single impression, but receives 
 many impressions in rapid succession. The eye is con- 
 fused by too rapid succession of impressions, and per- 
 ceives motion only, as we have seen, by inferences 
 from successive changes of position. 
 
 Of the remaining senses, touch and tliei kinesthetic 
 sense contribute considerably to the perception of 
 space; and the essential space-concepts may be ob- 
 tained, as in the case of the blind, from these alone. 
 Thus there have been blind mathematicians, and even 
 blind sculptors. The remaining senses hardly enter, 
 except to the slight extent to which successive effects, 
 notably those of contrast, affect taste and smell sensa- 
 tions. 
 
 05 
 
CHAPTER VII. 
 
 The Nervous System. 
 
 Topic XXXV. The Nervous System. General 
 Structure. The nervous system may be thought of 
 as composed of units of structure, which in turn are 
 combined into systems serving different types and 
 varieties of functions. The gross dissection of the 
 nervous system reveals in certain sections masses of 
 fibres, and in other sections groups of cells or cell- 
 bodies of various forms. These in turn are massed 
 and grouped in complicated relations. To bring some 
 order and system into their description, a general tpog- 
 raphy of relation of parts is necessary, and as well a 
 microscopic study of the structural units of which 
 these masses are composed. The models will serve best 
 for the first problem, and diagrams prepared on the 
 basis of microscopic sections will illustrate the second. 
 
 The ' ' central ' ' nervous system refers to the contents 
 of the brain and spinal column, while the "peri- 
 pheral ' ' nervous system refers to the whole set of con- 
 nections from sense-organs inward to the central nerv- 
 ous system, and to the connections outward from the 
 central nervous system to the muscles and glands of 
 the body. The word nerve, or nerve-trunk, as used 
 with reference to the optic nerve as a sensory nerve, 
 or again to any of the motor nerves serving such 
 muscles as the biceps or triceps muscle, refers to the 
 connection of nerve-fibres on their way from sense- 
 organ to center, or from center to muscle. There are 
 
 6G 
 
thus two ways of describing the make-up of the 
 nervous system ; and each is convenient. No confusion 
 will result from combining both methods. The first 
 would then describe the peripheral nervous system as 
 made up of nerves, in turn sensory or motor, and the 
 sense-nerve-endings, like the rods and cones in the eye 
 or the special end-organs of taste or smell, together 
 with the nerve-endings imbedded in the muscle fibres, 
 through which the impulses to contract reach the 
 muscles. Within the central nervous system one would 
 speak of nerve-fibres or connections and of nerve-cells. 
 Thus the outer layer, or cortex, of the brain, repre- 
 sents a great mass of these nerve cells, while the great 
 tracts of fibres from brain to spinal cord and running 
 down the spinal cord would be spoken of as fibres. In 
 reality, however, each unit of the nervous system is a 
 cell or cell-body with a double set of projections. Such 
 a unit is called a neurone. This method of describing 
 the nervous system is unquestionably the more accur- 
 ate, and should remain in the background when w T e 
 use the convenience of the other form of description. 
 The nervous system thus described becomes a compli- 
 cated chain, a cluster of neurones which serve a unified 
 function. 
 
 Topic XXXVI. The Parts of the Central Nervous 
 System. It is convenient to divide the central 
 nervous system into first, the spinal cord ; second, the 
 enlarged end of the spinal cord, called the medulla; 
 third, the brain-stem, which is the further continuation 
 of the mass of organs built up into the medulla as a 
 sort of stem for the great overhanging masses, of which 
 the two great parts are the cerebral hemispheres, or big 
 brain, and the cerebellum, or little brain. A further 
 convenient term is that of the basal ganglia as refer- 
 
 67 
 
Paths from 
 motor region of cerebral 
 cortex to lower centers^ 
 
 mnotor neurone of a 
 cranial nerve 
 
 Secondary efferent 
 neurone in sympathetic 
 system 
 
 Path from center in 
 medulla to lower centers 
 
 Path from cerebellum 
 ..to 5pmal cord 
 
 TTledulla 
 
 Spma) cord 
 
 otor neurone going 
 to voluntary muscle fibre. 
 
 Ttlotor Tracts. 
 
 'Plate I. 
 
ring more particularly to the mass or collection of 
 nerve cells grouped about the head of the brain-stem. 
 The spinal cord is to be conceived both as a con- 
 ductor of impressions, which is represented by the 
 fibre-columns or tracts — and in this sense it is a means 
 of communication between the higher portions of the 
 nervous system in the brain and the set of muscles and 
 sense-organs of the parts of the body below the head,— 
 and also as a center for reception and expression of 
 function. In a general way it is the cell-bodies or the 
 gray matter that represents the function of the spinal 
 cord as a center of impressions, and the white matter 
 of the fibre-columns that represent its function as a 
 conductor of impressions. As a center of impressions 
 the spinal cord must be thought of as a series of 
 centers, and naturally changes its function at differ- 
 ent levels. At the lower levels the nerves leaving the 
 spinal cord are going to the muscles innervating the 
 legs ; and similarly incoming nerve fibres at this level 
 are bringing in the tactile feelings from the lower part 
 of the body. In the middle areas the spinal cord is a 
 center functions for the chest ; and at the upper level, 
 between the shoulder blades, the great nerves go off to 
 innervate the muscles of the arm and hand; and 
 equally at this level are received incoming sensory 
 nerves carrying in the impressions from the skin of 
 hand and arm. While it is true that the functions 
 served by the spinal cord as a center are typically 
 ''lower" functions, of the type to be called reflex, it 
 must be remembered that this is but true in general, 
 and that functions of the same order also are served 
 by parts of the central nervous system within the 
 brain. This is partly the mere matter of position, 
 since clearly the sense-organs of the head would have 
 
 69 
 
their lower-type centers within the brain and not at 
 the lower level of the cord. Viewed anatomically, the 
 appearance of a cross-section of the spinal cord shows 
 in its imbedded central part, shaped like the letter H 
 or the wings of a butterfly, the collections of gray 
 matter ; and surrounding this the several fibre systems 
 which represent the basis of the spinal cord as a con- 
 ductor of impressions. The minute anatomy of the 
 cord may be gathered from the models and charts 
 shown. 
 
 Attention is directed to the manner of function at 
 each level of the spinal cord where sensory nerve- 
 fibres enter and the motor nerve-fibres issue. It will 
 be seen that along with each such part there is a 
 swelling or ganglion, into which the entering nerve- 
 fibres go, and from which they are redistributed to the 
 spinal cord, which they enter on the posterior side. 
 The motor nerves issue from the anterior side, pass 
 by this ganglion, and go out to the muscles. 
 
 Viewing these provisions from the neurone point 
 of view, we consider a motor cell as situated in the 
 anterior horn of the gray matter of the spinal column. 
 This is a complex, many-branched cell, with a promi- 
 nent nucleus, and from it there goes out one main 
 projection, which eventually ends in the muscle, more 
 or less distant from the cord. A type of such a unit 
 is shown in the diagram (Plate IV). Similarly, refer- 
 ring to the diagram labelled "Path of Conduction in 
 the Spinal Cord, ' ' it will be easy to trace the first, or 
 sensory neurone, which begins in the bit of the skin 
 in which its terminal organs are imbedded, passes 
 inward as a single nerve-fibre to the spinal ganglion, 
 which it enters and from which it emerges ready to 
 travel upward in the spinal cord in that portion de- 
 
 70 
 
voted to sensory functions. Here in turn it ends in a 
 many-branched ending near to the beginning of the 
 next neurone, the cell-body of which, again many- 
 branched, intertwines with, without actually touching, 
 the final endings of the first neurone. This in turn 
 goes upward to the higher connection. All sensory 
 neurones in this diagram are indicated by upward- 
 pointing arrows. Similarly parts of the motor neu- 
 rones are indicated by downward-pointing arrows, the 
 connection showing how they issue at different levels. 
 There are also shown the type of cross-connection by 
 which a sensory neurone reaches the opposite side of 
 the spinal column. 
 
 Referring to the text, as well as to the plates, for 
 detailed descriptions of the other portions of the 
 nervous system, we shall at once proceed to a descrip- 
 tion of the structure of the brain. 
 
 Topic XXXVII. The Structure of the Brain. The 
 brain may be considered as composed of the cortex, or 
 outer layer, usually about three-eights of an inch 
 thick, markedly convoluted, and the projecting con- 
 nections from it and into it from lower nerves. Here 
 it may be noted that the contrary arrangement ob- 
 tains from that in the spinal cord, where the fibres 
 are on the outside, while in the brain proper they are 
 imbedded within the gray mass. It is this inversion 
 that contributes much to the complication of following 
 the paths or tracts. Further, the brain consists of the 
 two hemispheres with a deep cleft or fissure dividing 
 them. These two hemispheres are joined by a great 
 mass of transverse fibres which form the corpus cal- 
 losum, or hard body, shaped somewhat like a sickle, 
 which serves to make the two hemispheres function as 
 one. A large part of the interconnecting fibres belongs 
 
 71 
 
Paths from medulla an 
 pons to basal ganglia' 
 
 Sensory neurone^ 
 of a cranial nerve/ 
 
 Paths from 
 
 garvgijA 
 
 to 
 cerebral 
 cortex 
 
 Paiks from 
 cerebellum to 
 ba.66.1 g&.r\gli& 
 
 Association neurones 
 in medulla"'^ 
 
 Cerebellar afferent 
 tract 
 
 Tlledulla 
 
 Paths from spinal 
 cord lo meduiU 
 
 mal cord 
 
 Association neurone In 
 center in spinal cord 
 
 Visceral sensory neurone. 
 
 ensory 
 
 Plate II 
 
 Tracts 
 
 Somatic berxsonj 
 neurone 
 
to the systems connecting coordinate portions of one 
 hemisphere with those of the other. Next there is im- 
 bedded towards the center of the combined brain mass 
 a set of further collections of gray matter set about 
 the head of the brain-stem which collectively we may 
 call the basal ganglia. These represent intermediary 
 stations for the reception of lower chains of neurones 
 and the beginnings of upper chains of neurones. 
 Since the fibre systems must in turn pierce these, and 
 in part go around them, the anatomy becomes very 
 complex. Finally, there emerges through this mass 
 the great stalk or main body of the stem, which con- 
 tains the paths of conduction from and to the spinal 
 cord and brain. Still another portion of the con- 
 ducting fibres are those joining the hemispheres with 
 the cerebellum. The cerebellum is composed of a cen- 
 tral lobe and two lateral lobes, and these in turn are 
 connected by a massive strand of fibres running 
 around the central brain-stem and called the pons, or 
 bridge. 
 
 The special function of the cortex requires some 
 further description of its divisions. These may be 
 readily understood by observing that each hemisphere 
 is divided into four lobes, the frontal lobe, the tem- 
 poral lobe, the occipital lobe and the parietal lobe. The 
 divisions between these areas may in turn be under- 
 stood by observing, first, that the chief fold or great 
 fissure of the brain is one that runs diagonally from 
 the junction of the frontal and temporal lobes, ob- 
 serving next and obliquely to this the great central 
 fissure, called the fissure of Rolando. In the diagram 
 labelled ' ' Sensory Tracts, ' ' as also in the one labelled 
 "Motor Tracts," the brain is shown in outline with 
 these two fissures alone. The frontal lobe is roughly 
 
 73 
 
speaking the part of the brain forward of this great 
 central fissure. The parietal lobe is that part of the 
 same back of this and as far back as the occipital lobe, 
 which is indicated by the projection of the great 
 crease or fissure of Sylvius. The temporal lobe is that 
 part below the fissure of Sylvius, and the occipital 
 lobe the rear portion overhanging the cerebellum. It 
 should further be noted that while these areas refer 
 mainly to the side or lateral view of the brain, parts of 
 the cortex appear also on the median and under, or 
 basal view. While these divisions of the brain and 
 nervous system are adequate for an understanding 
 of the function, it is desirable to study the many 
 minute divisons indicated in the text and by the 
 models and diagrams. 
 
 As to the minute structure of the cortex— and the 
 same applies in part to the basal ganglia— it is pos- 
 sible only to indicate a series of pictures to show the 
 variation in different parts of the central nervous 
 system and further to connect such variations in some 
 general way with differentiation of function. Differ- 
 ent methods of preparing and staining microscopic 
 sections of the cortex, as well as of the cerebellum and 
 basal ganglia, show different types and areas of cells. 
 In the accompanying diagrams, observe first a sec- 
 tion of the cortex taken from the motor area, and 
 another, from the visual area. It will be seen that 
 these are differently arranged in layers, with differ- 
 ent groupings and forms of cell-bodies. On the same 
 diagram is given also a different form of preparation 
 which shows as well the minute cross-connections of 
 fibres, which in this relation are also called axones, 
 and the different types of cells. Here the star-shaped, 
 or stellate cells characteristic of the visual area 
 
 74 
 
appear. In the plate labelled "The Cortex of the 
 Cerebrum" are shown in connection the four layers 
 from the cortex downward, indicating once more the 
 difference of appearance and distribution of the 
 neurones and their projections. While these details 
 are of great importance to the anatomist, they may be 
 looked upon here as illustrating the variety of struc- 
 ture which is probably connected with some as yet 
 obscure and minute difference of function. These 
 several pictures may be interpreted as different views 
 of terminal neurones, in turn forming parts of chains 
 of neurones to and from the cortex of the brain, to- 
 gether with neurones serving as associational connec- 
 tions from one part of the cortex to another. Further 
 details will be suggested in connection with the study 
 of brain functions. 
 
 Topic XXXVIII. Functions of the Nervous 
 System. Referring to James, pages 91 to 101, for 
 the description of functions in the brain of the frog 
 and of the pigeon, and of allied nervous structures 
 in the higher animals, the following principles are 
 emphasized : first, the purpose of the nervous system is 
 to act as a center of correlation and coordination. 
 The nervous system centralizes all the other systems 
 of the body. The circulatory system, the respiratory 
 system, the digestive system, the muscular system, 
 the sensory system, all are in a sense represented in 
 the nervous system. As a consequence the coordinate 
 action of all parts of the bodily economy is provided 
 for in their nervous connections. For example, in 
 running along a given path the eye must hold the 
 runner to a straight line; the legs must alternately 
 support and advance the body, moving in rapid suc- 
 cession; the sensations from each step must be prop- 
 
 75 
 
r- «* 
 
 
 'Vjt 
 
 
 
 
 cO 
 
 o 
 
 ■ o to 
 
erly received and coordinated with the next forward 
 movement; the, lungs must accelerate their breathing 
 to supply the necessary air ; and with it the circulation 
 and heart-beat must keep step. This centralizing 
 agency is the nervous system. FV)r the most part the 
 study of conduct relates to the voluntary coordination 
 for useful purposes of muscles, under the guidance of 
 sense-organs. This coordination further involves the 
 constant shifting of the combinations of muscles used 
 in different occupations. Running and jumping and 
 skating and walking and riding a bicycle all involve 
 leg muscles, but in varied combinations. The nervous 
 system thus represents in its complex connections pro- 
 visions for the most manifold variety of combinations 
 not alone in conduct, and specifically in those 
 acquired coordinations which we call skillful move- 
 ments, but as well in the accompanying adjustment of 
 the other systems of the body. Likewise on the sen- 
 sory side, digestion brings in sensory feelings of a 
 vague, emotional nature, more conspicuous in their 
 disturbance than in their normal function. Fatigue 
 and recuperation, sleepiness and wakeful alertness 
 similarly condition mental function. 
 
 A further principle of importance is that suggested 
 by the statement that the same muscles are repeatedly 
 represented at different heights. This involves on the 
 one hand that the higher center has no direct con- 
 nection with the muscle. The higher center can but 
 command or direct the lower center, which alone has 
 an outlet to the muscle. Accordingly one cannot 
 judge from the nature of a muscular reaction alone 
 whether it is a high-grade action or a low-grade action. 
 Winking may be purely reflex, and winking may be 
 voluntary. The final distinction between the low- 
 
grade and high-grade action is that the former is a 
 direct response to sensory stimuli alone, involving 
 slight or no consideration, while all types of higher 
 action are indirect, or distinctly modified by consid- 
 eration. Such consideration represents the- complex 
 field of memory, of forethought, of imagination, of 
 thinking. It does this at least for our own high-grade 
 actions. But even in the actions of lower animals, 
 where these processes go on in much simpler form, 
 something analogous enters to distinguish high-grade 
 from low-grade actions. The recognition of a situa- 
 tion is the most common test; and the fact that the 
 pigeon without its hemispheres will not recognize food 
 or the call to which iti responded when normal, indi- 
 cates the parallel function of the higher centers in 
 the pigeon and in man. The difference is the 
 enormous difference of the extent and variety of the 
 consideration that enters. 
 
 From the descriptions in the text it will be inferred 
 that a very much larger share of the general behavior 
 of the lower-type organisms is accomplished and pro- 
 vided for by their lower centers as compared with the 
 similar conduct involving the higher centers ; and that 
 in turn the converse relation obtains in the human 
 nervous system, where by far the larger share of 
 function is of the higher type, leaving relatively little 
 to the lower function except in cooperation with the 
 higher. This brings about the frequent relation that 
 actions which are ordinarily accompanied by slight 
 consciousness and little volition may at any moment 
 be drawn into the field of consciousness and directly 
 regulated and controlled. A further consequence of 
 this relation is that volitional acts as well as a goodly 
 part of the reflexes and similar automatic actions of 
 
 78 
 
man are acquired. They may be acquired, and very 
 many of them are acquired, in early stages of infancy. 
 Others are acquired, or at least perfected, at later 
 periods. One of the most significant examples is that 
 of walking, which is a coordination that requires in the 
 child months, even years of practice before it becomes 
 fully automatic and well performed, but eventually 
 reaches so extreme a stage of automatism as to be 
 carried on with the minimum attention and direction. 
 It is characteristic that at any moment the higher 
 centers may take the walking function under control. 
 Thus in walking across a slippery or a muddy place, 
 we instantly take charge of the walking process, 
 attend to it and closely regulate it. Similarly the 
 varied movements with knife, fork, and spoon in 
 eating are the results of much practice and some de- 
 liberate training. We cultivate acceptable manipula- 
 tions of this kind, and avoid those that are considered 
 bad form. Such acquired mechanisms easily fall en- 
 tirely into the field of habit, which as generally 
 understood, means the consciously acquired actions 
 which have become habitual. 
 
 Another principle of great importance is that of 
 inhibition. The relation of higher to lower centers 
 is not merely that of guiding, but also that of checking 
 action. Control involves both. If in walking I slip 
 and tend to fall, I automatically throw out my arm to 
 keep or restore my balance. If, however, I am carry- 
 ing in my arm a breakable and precious package, I 
 will check or inhibit this tendency and save the pack- 
 age, even at the cost of injury to myself. So equally 
 I may experience the reflex irritation which would be 
 relieved by a cough, but I can restrain to some extent 
 the actual coughing. Once more, in swallowing I de- 
 
 79 
 
liberately bring the food to the point where the reflex 
 swallowing mechanism will take care of it; but if in 
 time I feel something objectionable in the food, I can 
 still reverse and check the action. The inhibition or 
 control of function forms a very large part of volun- 
 tary action ; and restraint requires as much effort, and 
 at times more effort than does the release of muscular 
 contractions. This is due in part to the natural ten- 
 dency for all stimuli to pass over into action. Thus 
 when hearing lively marching music it' takes more 
 effort to restrain from beating time to it than to let 
 the motor impulse find its natural outlet. 
 
 Topic XXXIX. The Analysis of Types of Conduct, 
 While the distinction between lower and higher, or 
 between reflex and voluntary action, is useful and the 
 contrast definite, it is obvious that all manners and 
 degrees of complexity of action exist between the two, 
 with no sharp distinction at any stage of the series. 
 Reflex actions are themselves more or less reflex, and 
 involve different degrees and kinds of coordination. 
 It is customary to use the word ' ' automatic, ' ' and in 
 particular, * ' primary automatic actions ' ' to refer to a 
 series of actions of the general reflex order, but which 
 involves a larger degree of adjustment. Actions of a 
 frequently repeated type which supply their own 
 stimulus, such as breathing, form examples of primary 
 automatic actions. Swallowing is intermediate in stage, 
 the recurrent necessity of swallowing the saliva form- 
 ing the repeated stimulus. So equally winking goes on 
 in constant succession to clear the eye of any irrita- 
 tion ; and these recurrent actions are more likely to be 
 spoken of as automatic than as reflex, although the 
 distinction in grade of nervous function is slight. 
 Within the reflex field one may cite the pupillar reflex 
 
 81 
 
as the most automatic, since it is present at birth, and 
 needs no practice to make it perfect, is mechanical and 
 specialized, enters into very little relation with other 
 actions, has no feeling connected with it, and admits 
 of no control. Wje may contrast with this winking, 
 which is not innate but is a function that matures in 
 the child at about the end of the third month, has a 
 feeling connected with it, and may to some extent be 
 controlled. Feeling is essential to control. We can 
 only make voluntary such reflex actions as have con- 
 nected with them some degree of feeling. The con- 
 trol of natural functions is part of voluntary train- 
 ing. The point is sufficiently illustrated in the more 
 mature control of laughter or in checking the display 
 of our emotions by expression, when the occasion 
 makes it improper. The restraint of tears is another 
 example. All this illustrates the variety of status 
 which one or another action may have in the mental 
 economy while yet its type is reflex or automatic. 
 
 The large group of actions called "secondary auto- 
 matic actions" represent the field of acquired reflexes, 
 or the general field of habit. Walking forms a con- 
 spicuous example, and, at first voluntary, soon be- 
 comes quite automatic. Even so highly complex and 
 intellectual a process as talking may become so auto- 
 matic that it will actually take place in sleep. Writing 
 is a still more complicated and necessarily a voluntary 
 and closely coordinated action, but its mechanical 
 steps may become automatic. For example, in copy- 
 ing from a text the mind may wander while the pen 
 keeps on and the eyes take in the words and letters, 
 so that after a brief interval the writer is surprised to 
 find that he has copied correctly, but with much re- 
 duced attention. The large field for the illustration of 
 
 82 
 
habit is furnished by the acquired habits of manipu- 
 lation with the hands, as in the several processes of 
 dressing ; or again manipulations of knife and fork in 
 eating; in gesture and pose. These acquired habits 
 always represent an individual factor, so that they are 
 not quite the same in one person as in another. Many 
 of these habits are acquired by imitation with very 
 slight deliberate attention. Such action develops by 
 easy stages into voluntary actions which always 
 remain voluntary, though it incorporates automatic 
 factors. Thus in speaking in public to an audience, 
 the main attention goes to the thought of what is to be 
 said, while the automatic shaping of the words pro- 
 ceeds. 
 
 A further relation in this function of the nervous 
 system is the fact that actions best performed with 
 large automatic control are not as well performed 
 when deliberately and consciously carried out. Thus 
 the difficulty that is sometimes experienced in swal- 
 lowing a pill is due to the attention and effort directed 
 to it. Swallowing goes on perfectly well automati- 
 cally. So again in walking when w T e are made self- 
 conscious, as in coming late at a concert or in church, 
 the walking is unnatural, because not sufficiently 
 automatic. It will be seen that the large range of 
 function is voluntary and conscious, but is likely at 
 any moment to shift in the degree of control or con- 
 sciousness accompanying it, or again in the measure 
 to which automatic habitual reactions participate in 
 the result. 
 
 It is hardly possible to interpret all these relations 
 in terms of the nervous system, but it is useful to con- 
 ceive of the nervous system as providing in its com- 
 plexity of relations for these varieties of conduct regu- 
 
 83 
 
lation. Were conduct not of such several varieties 
 and degrees* of complexity, were the correlations not 
 so vast in number and so variable, the structure »of 
 the nervous system, though composed of similarly 
 constituted units of function, would be adequate on 
 a much simpler basis, — fewer specialized divisions, 
 lesser complexity of combination, more limited in- 
 terplay of parts. 
 
 Topic XL. The Higher and Highest Cerebral 
 Functions. The cortex of the brain represents the 
 highest type of centers, and their action represents 
 the most developed and complex function of the 
 nervous system. The cortex participates in a great 
 range of conduct, often supplying merely the directive 
 or coordinating factor and more typically raising the 
 action through the associations which are aroused into 
 a complicated mental act. The nature of these mental 
 accompaniments, which for the present may be indi- 
 cated by such a term as consideration or association, 
 or again memory as reflecting past experience, and 
 prudence as anticipating future results, will be duly 
 considered in later topics. The present purpose is to 
 gain a picture of the processes that accompany rela- 
 tively simple actions of the voluntary and considerate 
 type. At the simplest the movement of an infant's 
 hand towards a bright light is illustrative. The sen- 
 sory stimulus from the eye must excite the terminal 
 organs, which now we may picture as the expansions 
 of a sensory neurone, must travel along to a point in 
 the brain-stem which represents the end of this first 
 neurone. (So much of the path is formed by a group 
 of fibres in the optic nerve.) From here the impulse 
 passes to a second link in the neurone-chain and 
 travels upwards and backwards until it reaches the 
 
 84 
 
visual center in the occipital region of the cortex. 
 From here in turn the impulse radiates through con- 
 nections already established between these centers of 
 visual reception and the centers of motor control ; and 
 in this group of cells lie those particular motor cells 
 which represent the movements of the hand; the out- 
 going impulse travels downward until it reaches the 
 end of this central motor neurone, which in turn 
 passes over the impulse to the terminal motor neurone, 
 which has its origin in the large cells of the anterior 
 horn of the spinal cord at the level between the 
 shoulder-blades, and from here travels along what we 
 should now call a motor nerve, and releases by a special 
 type of contraction the combination of muscles which 
 we call the movement of approaching or grasping. 
 When, however, the result of placing the hand near 
 the flame is pain, instantly another process similar 
 to the former is set up, must again travel to the brain 
 and back to the spinal cord, and reverse the move- 
 ment, which is represented by the withdrawal of the 
 hand. It is thus clear that even the simplest action 
 involves a large nervous connection, and its detailed 
 description would be almost endless. The physi- 
 ologist's problem is to trace the assignment of paths 
 in the nervous system to these several varieties of 
 action and connections. If we contrast with grasping 
 the indefinitely more complex act of reading, it will 
 be seen that the general description is the same, but 
 that the chief difference is in the endless complications 
 within the cortex, the associations in terms of memory 
 and meaning which the visual symbol that we call a 
 word arouses. 
 
 In such illustrations the essential point is to select 
 the relations which are typical and characteristic. 
 
 85 
 
These may be regarded as lying primarily within the 
 associations of the cortical centers. Such associations 
 must be formed by experience, and their establishment 
 represents the education of the nervous system. The 
 difference between one act and another lies primarily 
 in the scheme of associations which it involves. Such 
 a scheme always involves preventative elements, which 
 are in terms of actual sensation, and representative 
 elements, in terms of meaning associated with them. 
 Thus the act of reading involves the seeing of the 
 page of letters, which is the presentative element, but 
 distinctively the recollection of the meaning associated 
 with the form. One sees a page of Chinese as clearly 
 as a page of English; but the Chinese is purely pre- 
 sentative and represents so much visual form, while 
 in the page of English the form is but slightly attended 
 to, the attention going at once to the meaning. While 
 we cannot point out in detail what may correspond 
 to this important difference in the nervous system, 
 we feel warranted in regarding it as the highest form 
 of cortical function on its sensory side. Coordinate 
 with this is the highest form of function on the motor 
 side, which represents at once the control of the lower 
 centers, as already illustrated, and the effort of bring- 
 ing into relation the accumulated associations which 
 we call thinking. Thinking, or the assemblage of use- 
 ful and controlled associations, is as much effort as is 
 doing. As in all the receptive processes, there is the 
 strong sensory or presentative element, so in all motor 
 processes there is the resulting action or coordination 
 of muscles. When this represents the chief factor, as 
 in manipulations of great skill, the operation is more 
 motor than mental, though in every case it is both. 
 Thus in watching a juggler keeping many balls in the 
 
 86 
 
air, or balancing combinations of delicately arranged 
 objects, we look upen the accomplishment as largely 
 one of manual skill under visual and kinesthetic guid- 
 ance ; yet this, as do all games of skill, requires head- 
 work as well as handwork. W|hen, however, we 
 analyze the act of writing, we recognize that the 
 manual expression has become largely automatic and 
 that the operation is largely mental; the attention is 
 to what is written rather than to the strokes which 
 shape the letters. Combining these two principles we 
 realize that the function of the highest centers is to 
 get meaning out of sensory responses and to put 
 meaning into motor contractions. It is this "mean- 
 ing" element that forms the subject of many of the 
 remaining chapters of psychology. 
 
 It must now be shown that the presence or absence 
 of this element of meaning has a representation within 
 the nervous system. It must be shown that the sen- 
 sory factor may persist while its interpretation falls 
 away, or again on the motor side that the contrac- 
 tion of muscles goes on without forming significant 
 conduct. This consequence results from the concep- 
 tion of the highest type of function as that of purpose- 
 ful deliberation as well as considerate conduct. The 
 best evidence is that from mental blindness, both in 
 animals and in man. This is a condition in which the 
 eyes see, so that the animal does not blindly walk into 
 an obstacle but goes around it, but in which the 
 object is not recognized— is reacted to indifferently as 
 an object or obstacle quite irrespective of its nature. 
 This is inferred from the fact that the object does not 
 excite its normal response. Similarly there may be 
 no paralysis, but an inability to perform acquired 
 conduct owing to the falling away of the correlating 
 
 87 
 
control. This has been shown for dogs that have 
 been taught tricks. Such dogs, when certain portions 
 of the cortex have been removed, will continue to per- 
 form simple operations but can no longer coordinate 
 the movements of the acquired tricks. For man these 
 illustrations are best observed in the defects of speech, 
 for which see the text. 
 
 We thus reach the conception that the functions 
 of the cortex must all be capable of expression as 
 states of sensory reception or of motor expression. 
 The only arrangements which the brain stands for are 
 these two ; of sensory interpretation and motor ex- 
 pression. All that we know and all that we do is 
 capable of description in these terms. The nervous 
 system as such represents complex arrangements for 
 sensory reception and motor coordination. However, 
 the enormous importance of the connection between 
 reception and expression gives to the process of re- 
 direction the largest place in our psychology. While 
 we cannot describe the mental content of these asso- 
 ciative steps in any helpful terms of the nervous sys- 
 tem, it remains important to hold in mind that they 
 are bound up with nervous processes. Such examples 
 as reading, writing, speaking, copying, and even the 
 more complex language processes like translating, are 
 after all expressible in terms of sensory and motor 
 operations, together with the associations directing 
 them. Furthermore the degree of specialization within 
 the cortext represents the uses to which we have put 
 our sensory and motor centers. The visual center 
 represents the general portion of the brain at which 
 the impressions from the retina are received and inter- 
 preted; and if we come to develop a reading center, 
 this in turn is but a specialized part of the visual 
 
 88 
 
center, — specialized for the interpretation of this 
 acquired visual distinction. Similarly a certain por- 
 tion of the motor area represents the center for the 
 issuing* of impulses to the general region of the face 
 and vocal cords ; and if we have developed a speaking 
 center, this means that a special grouping of this 
 motor center specifically operates those coordinations 
 of voice and tongue, etc., which result in speaking. 
 It is well to think of the specialization of the brain in 
 terms of acquired coordinations and interpretations. 
 
 89 
 
CHAPTER VIII. 
 
 Reaction-Times. 
 
 Topic XLI. Reactions. Conduct may be thought 
 of as composed of bits of conduct, each one of which 
 conforms to the type of a reaction. The simplest re- 
 action includes the response to a stimulus, but in- 
 volves something above a reflex. It involves that the 
 response is arranged, and thus is the simplest type of 
 voluntary action. If, accordingly, I wink the eye as 
 quickly as I can I after hear a certain sound, it repre- 
 sents the minimum time for a simple reaction. The 
 average of such time is about 1 / 7 of a second. If, on the 
 other hand, the winking reflex takes place in response 
 to an actual sound or flash, it may be much quicker 
 than this, even as short as 1 / 20 of a second. In cases 
 of explosion of a glass beaker in a chemical laboratory 
 the chemist has often escaped without injury to the 
 eyes, but with fragments of glass imbedded in the 
 eyelids. It is safe to assume that if the eye had to be 
 voluntarily closed, the glass would have had time to 
 enter the eyeball, but the reflex closure was quick 
 enough to prevent it. We may thus define a simple 
 reaction as a response by a predesignated movement 
 that an expected stimulus has been received. Such 
 simple reactions hardly occur in the natural course 
 of employments, A near approach to them, where a 
 fraction of a second is important, is the starting of 
 runners for a hundred-yard dash. In that case the 
 sound of the pistol is the stimulus, and the getting off 
 
 90 
 
the reaction. Even a slight gain in promptly getting 
 under way would be of advantage. Photographs have 
 been obtained which show the smoke leaving the pistol, 
 while yet no runner has left the mark. The photo- 
 graph was instantaneous, requiring 1-40 to 1-20 of a 
 second, which is less than the time needed for even the 
 quickest runner to start. 
 
 Simple reactions are important because they set the 
 limit of all possible reactions. Every more complex 
 bit of conduct includes the simpler. The simple reac- 
 tion, in turn is conditioned by the rate of impulse in 
 the nervous system, which is about one hundred feet 
 per second. We may divide the complete reaction- 
 time into the part occupied by the ingoing impulse, by 
 the central redirection, and by the outgoing impulse. 
 The largest part is consumed by the redirection. We 
 do not know the nature of this process, but have many 
 indications of its complexity. We accordingly reach 
 the formula for the adaptive reaction that it includes 
 a simple reaction plus other factors. These other 
 factors are easily shown to be distinction and choice. 
 If, instead of making the uniform response to the 
 single signal, the signal may be one of two or more, 
 and I select the response according to the stimulus, 
 I have the formula for an adaptive reaction. As 
 demonstrated in class, to touch one 's neighbor as soon 
 as you receive a touch on the hand is a simple reac- 
 tion. To expect a touch either on the thumb or on the 
 body of the hand, and touch your neighbor at the same 
 point, is an adaptive reaction. If, in addition you 
 must touch the same finger as the one upon which you 
 were touched, it is a more complex adaptive reaction, 
 involving one of five -distinctions and one of five 
 choices. By subtracting the simple reaction-time from 
 
 91 
 
the total time necessary for these reactions, one may 
 ascertain the mental time required for distinction and 
 choice. Distinctions and choice are intimately related, 
 and are bound together by association. It is this asso- 
 ciation that must be established and which when estab- 
 lished we form a habit or memory. 
 
 "While all bits of conduct are adaptive, these adap- 
 tive reactions vary enormously in complexity. Com- 
 plexity is due not only to the number of distinctions 
 and choices, but mainly to their nature. Complexity 
 in distinction involves less addition in time than com- 
 plexity or number of choices. A larger part of the 
 additional time in making a reaction to five stimuli 
 above what is needed for two, is due to the motor 
 complexity — the choice — than to the distinction. 
 Similarity in learning to use a typewriter rapidly, the 
 training is in large part on the motor side. If we take 
 as a complex example the sorting of the outgoing mail 
 in the postoffice, the process is complex because the 
 clerk has to distinguish a large number of addresses; 
 he must associate a large number of towns each with 
 its own mail route ; he must further associate the mail- 
 route with the particular pouch in its position as it 
 hangs as one of the very many in a semi- circular rack ; 
 he must finally have skill enough to toss the letter 
 accurately into the proper pouch. This reaction shows 
 each factor of the complication: the original learning 
 of the mail routes, the memory- association of towns 
 with the route, the habit association of the town with 
 the mail pouch, and the skill or motor facility in di- 
 recting the letter accurately to its place. None the 
 less, as we compare this reaction with other complex 
 ones, we observe degrees of complexity in the associ- 
 ational process. Here lies true mental difficulty. The 
 
 92 
 
type of association may vary almost indefinitely. A 
 special type of association is that which involves 
 thinking, reasoning, judgment, comparison, etc. 
 
 Topic XLII. Association-Time. While associa- 
 tions as conditioning conduct and thinking de- 
 serve and will receive special consideration, the 
 study of association-times belongs in this con- 
 nection. When a reaction is distinctive by reason 
 of the association it involves, it is called an asso- 
 ciation-time. The association is in this sense the 
 completing process of the reaction, and the readiness 
 of associations in some sense determines the availa- 
 bility of knowledge. A large number of mental pro- 
 cesses standing for associations may thus be measured. 
 For example, if I require a subject to repeat words as 
 promptly as possible after me, I may call his average 
 time in so doing repetition-time; if I give him the task 
 of translating these simple words into German or 
 French, the additional time would stand for the time 
 of associating the English with the foreign. It is clear 
 that associations have a direction. It would take an 
 English-speaking person less time to give the English 
 of a German word than the German of an English 
 word. Thus familiarity is measured by the readiness 
 with which the knowledge that in some sense we have, 
 becomes available. I might further measure the time 
 necessary to name colors, or to name pictures, or to 
 name geometrical forms. This is something more than 
 recognition. I must both recognize the form and 
 arouse the association of its name. It is when the 
 name association is very intimate that it seemjs to 
 merge with recognition. The study of such recogni- 
 tion-times and naming : times indicates the original 
 separateness of the processes. While the study of 
 
 93 
 
these times has been very extensive, these illustrations 
 will suffice to show the principles involved. 
 
 All such associations are in a manner fixed. In 
 learning the multiplication table we learn to associate 
 63 with 7 multiplied by 9. Much of our geographical 
 knowledge is in terms of fixed memory-association. 
 We associate London with the Thames, Paris with the 
 Seine, New York with the Hudson. As we move away 
 from fixed associations, we move towards free associa- 
 tions. A considerable interest attaches to unlimited 
 associations. The type of these is that of the measure 
 of time necessary for one idea to call up another. 
 Thus if the words book, horse, tree, be suddenly 
 spoken, and the subject asked to give the first word or 
 idea called up by them, the intervening time is called 
 a free association- time. It varies considerably, but for 
 simple terms and ready associations is about 3-4 of a 
 second. Postponing further consideration of associa- 
 tions, attention is directed here merely to the place of 
 association in conduct and in preparing the knowledge 
 on the basis of which reactions take place. 
 
 Topic XLIII. Habit and Conduct, Referring to 
 Chapter X for the main points in regard to the nature 
 and workings of habit, it remains only to bring the 
 processes of habit in relation to reactions and conduct 
 and to indicate what changes habit introduce into 
 these relations. We may consider conduct as com- 
 posed of a series of reactions. Certain types of reac- 
 tions, by being done over and over again, are reduced 
 in status; actions at first voluntary become second 
 nature by habit. It is this large range of acquired 
 habits that conditions mental work, and conduct 
 alike. 
 
 94 
 
The practical effect of habit may be summed up by 
 saying that habit makes reactions easy; habit makes 
 accurate; habit makes quick; habit makes regular, 
 and habit makes proficient. The subjective accompani- 
 ment is that actions are done with diminished atten- 
 tion and this induces the sense of ease. Objectively 
 the gain in quickness is due to the close-knit associa- 
 tions between one step and another, as well as to the 
 elimination of irrelevant movements. The precision 
 is a gain in muscular control, which is again the elimi- 
 nation of the unnecessary, as well as a clear-cut con- 
 ception of processes. Regularity is but another evi- 
 dence of the same change. It is in proficiency that 
 the main utility is summed up. When this is further 
 analyzed it is probably due in the main to overlapping 
 or telescoping of the several processes. While a pro- 
 cess is new, each step must be done separately, and 
 the total time is almost the sum of the times of the 
 individual steps, facilitation enables the attention 
 to spread over a large unit, to initiate the next step 
 before the one is disposed of ; and in this condensation 
 the large gain in proficiency lies. 
 
 9o 
 
CHAPTER IX. 
 
 Attention and Mental Elaboration. 
 
 Topic XLIV. General Analysis of Mental Pro- 
 cedure. For the remaining part of the course we have 
 to consider the general elements of the process of 
 elaboration, the complex set of changes that happens 
 to the material which is the foodstuff of the mind 
 before it is transformed into the direction of conduct. 
 In general we call this thinking; but it is easy to 
 detect the common processes involved, and to give 
 them a separate standing. The most general of these 
 I rocesses is attention ; for attention represents the 
 condition of mental effort. Next come a group of 
 processes which may be called memory, perception, 
 association, imagination, and reasoning. Thought 
 consists in the orderly use of these processes in behalf 
 of a unified interest. The phases of this problem, 
 which alone we shall be able to consider, will then 
 consist in setting forth the principles determining the 
 chief relations in terms of function of attention and 
 the other processes mentioned. Viewed for the moment 
 as a whole, they represent the reaction to absent 
 stimili, to situations in the past, and direct conduct 
 towards the future. We think because we do not live 
 merely in the present, but require for thei regulation 
 of life the consideration of present stimulation in 
 terms of past experience and of future anticipation. 
 
 Topic XLV. Attention. Chapter XIII gives the 
 main facts in regard to the working of the attention 
 
 96 
 
and to the account there given need be added only 
 certain general applications and emphasis of princi- 
 ples. Let it be observed first, that attention is selec- 
 tive; that it determines which of the many invitations 
 to interest or conduct shall be in a favored position for 
 acceptance. Attention on its receptive side thus 
 selects the particular stimuli which shall enter the 
 field of consciousness. Within this field it further 
 selects by giving emphasis to some phases or parts of 
 a situation as above others. The more special problems 
 relate to the mode of action of the attention. First 
 may be considered its source and the mode of its main- 
 tenance. Here the classic distinction is that of volun- 
 tary and involuntary; while in general distinct, the 
 one merges into the other. So long as stimulations 
 have a natural interest, the attention goes out to them 
 without effort. While the acquired interests represent 
 effort and control, once established, work under ac- 
 quired interests goes on more and more along the pat- 
 tern of the involuntary type. The sense of effort 
 diminishes with familiarity and facility. The more 
 important distinction relates to the spread of atten- 
 tion as concentrated and dispersed. Here a double 
 distinction is involved, namely, the amount of avail- 
 able energy, and secondly the direction or spread in 
 which that energy is expended. Thus fatigue is the 
 most general physiological condition of attention, and 
 there is no more sensitive index of mental fatigue than 
 the wandering of the attention. One may picture the 
 distinction as that between illuminating a field, 
 whether narrow or broad, with a low illumination, or 
 illuminating it with a high illumination. The confu- 
 sion should be avoided between a change in the general 
 amount of illumination and the distribution of that 
 
 97 
 
illumination. It is the latter sense that more specially 
 attaches to the distinction between concentrated and 
 dispersed. Dispersed attention may be eager and 
 vivid, but is not allowed to play over a large field. It 
 is true that concentration and energy usually go to- 
 gether; but the mere confining of the attention to a 
 narrow area often* eases the task. It is the necessity 
 of attending to a large number of possible relations 
 that makes a task difficult. A concrete illustration 
 will help. Wjhen an author reads proof, he puts a 
 great deal of attention upon it and critically revises 
 any slips or imperfections of style, phrasing, diction, 
 syntax, grammar, as well as maintaining a general 
 look-out for at least serious misprints. The task de- 
 mands concentration in the sense of energy, but a dis- 
 persed attention in the sense that that energy is ex- 
 pended over a large number of separate relations. On 
 the other hand, the proof-reader has an easier task 
 because he is not reading for sense, but for appearance 
 only; though he, too, will detect glaring mistakes in 
 grammar or phrase at the same time that his eye and 
 mind are set for the narrower interest of the print. 
 In the end the distinction is largely that of maintain- 
 ing a consistent attention which, in turn, may be con- 
 centrated or dispersed. Goingj back to concentration 
 in the earlier sense, the main practical problem is the 
 elimination of distraction. There are ever apt to be 
 rivals for attention. The rivalry is often between an 
 acquired and a natural interest— between holding the 
 mind by force to a narrow line of thought, while yet 
 other occupations are more inviting. The ability to 
 hold the mind to a task by effort should not be con- 
 fused with, though it is related to, the distribution of 
 attention within a given task. The latter brings us 
 
 98 
 
back to the problem of habit and attention, which 
 indicates that that number of things that may be 
 attended to at the same time, provided that; they are 
 related to a common end, is really a measure of mental 
 proficiency. For remaining points see Chapter XIII. 
 
CHAPTER X. 
 Perception. 
 
 Topic XL VI. Perception. Referring to the chapter 
 on Perception for the statement of the relation of per- 
 ception and sensation, the nature of sense-illusions, 
 (including the two types and the definition of apper- 
 ception) , a few main considerations of the perceptive 
 processes in mental elaboration will be considered. In 
 general, perception is the process that makes of vague 
 or indeterminate somethings concrete definite things. 
 It breaks up great masses of mere stimuli into definite 
 arrangements and systems of objects. Naturally this 
 includes recognition. Recognition is in terms of 
 meaning acquired by past experience. The sensory 
 element persists in perception, and in all but its high- 
 est stages remains prominent. It becomes necessary 
 to distinguish between sense-perceptions with a strong 
 sensory factor, and those in which the perceptual 
 factor gradually increases in significance. The two 
 always merge; but the principle remains that as the 
 sensory element recedes, the perceptual element ad- 
 vances. The one is strong as the other is weak. 
 
 Perception interprets sensation, or better, it inter- 
 prets groups of sensory stimuli. It makes unitary 
 objects out of composite appeals to sense. Thus the 
 perception of a bell combines the sound, the shape, 
 the use, the material, all of which are not bare sense- 
 stimuli, but result from them. Particularly does per- 
 ception proceed on the basis of meaning; stimuli are 
 
 100 
 
no longer mere impressions, but composites of mean- 
 ing. In the end, interpretation gives way to infer- 
 ence,— which is but a more highly specialized form 
 of interpretation in which the steps are either a little 
 farther apart, or involve a logical quality. There is 
 very little difference between anticipation and infer- 
 ence ; but the difference emphasizes a stronger sensory 
 factor, in the former, and a logical one in the latter. 
 Thus, in the end, objects are inferred from individual 
 signs. Sensations become the signs for calling to mind 
 perceptions in terms of revived experience. 
 
 Illusions contribute apt illustrations of these dis- 
 tinctions. They are perceptions that are incorrect in 
 terms either of more critical perceptions or of judg- 
 ment or of reason. The first oder of illusions is 
 entirely objective, that is, it presents an arrangement 
 of stimuli in which the seeming appearance is not 
 that which by a critical judgment may be shown to 
 be the actual arrangement. Such illusions may be 
 called objective, in the sense that the construction of 
 the object determines the illusion. Nothing is re- 
 quired, or very little, to be added by the mind. Yet 
 such illusions are composite, and may contain stronger 
 sensory or more largely inferential elements. Of the 
 variety of distortions of lines and figures shown, it 
 may be said that most of them are strongly sensory, 
 and that the ones that illustrate perceptual elements 
 do so by including more complex experience. It is 
 a partial test, to be applied cautiously, that illusions 
 that are most marked at the first impression are 
 strongly sensory, and grow less distinct as they are 
 viewed critically, while illusions depending largely 
 upon inferential elements grow rather stronger the 
 more closely they are' attended to. The main dis- 
 
 101 
 
tinction brings in the second type of illusion: the 
 proof-reader's illusion— the mistaking of an object by 
 means of anticipation. Thus when expecting a car- 
 riage, one converts any kind of a noise into the 
 rumbling of wheels. Further illustrations are given 
 in the text. They show once more that a perception 
 starts with a sense-stimulus, but is completed from 
 within. It is when the sensory sign is mistakenly 
 completed that we call it an illusion. The working 
 of perception is evident, whether correct or incorrect. 
 
 102 
 
CHAPTER XI. 
 
 Imagination. 
 
 Topic XL VII. Imagination. Again referring to 
 the chapter on Imagination for details, it will be pos- 
 sible to further emphasize a few general relations. 
 The terms imagery and imagination are often used 
 in confusing, even in opposite senses. The main fact 
 emphasized by the word imagery is the vivid persist- 
 ence of the sense element in the revival of past ex- 
 perience. We think of the past only in so far as 
 the memory-images remain; and these are primarily 
 sensory in form. Thus images of color and form in 
 the visual field, of sound, or of movement, form the 
 real basis of revival. This is best shown in terms of 
 the dependence of different individuals upon differ- 
 ent types of imagery. The eye-minded person is 
 strongly attached to visual images; the ear-minded 
 person to auditory ones ; and the motor-mindedness, 
 while largely a support through feelings of motion, 
 contributes essentially to the composite process. 
 Illustrations in the text are adequate. Observe that 
 these show not merely a large range in accuracy, 
 in definiteness, and in scope of the visual image 
 amongst different individuals, but also different de- 
 grees of dependence upon visual, auditory, or com- 
 bined types of image. In general, the imaginative 
 person, in the sense of a person with a good visual 
 or other imagery, is one who can readily reconstruct 
 a scene, making it in imagination approximate the 
 
 103 
 
actual. (Here, again, see illustrations in the account 
 of Galton's inquiry.) The use of such a phrase as the 
 creative imagination suggests that in the absence of 
 concrete and rich imagery, it is the imagination that 
 must help out. Creative imagination thus suggests 
 the very freedom from literal sense-images, but also 
 the power to recombine vividly the elements of ex- 
 perience. Vivid imagery and vivid imagination may 
 and are apt to go together. The vivid revival of 
 actual experience suggests equally the quality of 
 vivid reconstructions from combinations that have 
 not entered into experience. None the less, the rela- 
 tions between the two is by no means necessary, 
 since the element of novelty is particularly empha- 
 sized by the term creative. The simplest combina- 
 tions are those represented in ancient mythology, 
 where a Centaur is combined of the body of a horse 
 and the head of a man; a mermaid is half woman, 
 half fish, etc. ; elements of real experience are dif- 
 ferently combined. Nothing is absolutely novel, but 
 the remoteness from experience increases as the cre- 
 ative imagination works upon its material. The 
 creative imagination is not limited to literary feat- 
 tures. There is a scientific imagination which simi- 
 larly gets away from the literal, anticipates facts, 
 constructs relations that are possible, conjectural, 
 rather than actual. Thus the larger sense of the word 
 is justified in that it represents the power to perceive 
 the absent, either constructively or pictorially. The ar- 
 chitect exercises imagination in creating in his mind 
 the building which he then reduces to drawings; 
 similarly the ability to see the building from the 
 drawings is an example of the power of imagery. 
 In a negative way, the same principle is illustrated 
 
 104 
 
by the difficulty of imagining things aivay, of realiz- 
 ing how a house would look if it were altered. The 
 power not to see what is present is similar to the 
 power to see in the mind what is absent. Observe, 
 lastly, that the second type of illusion, in which we 
 misconstrue or faultily perceive, is due to the exer- 
 cise of the imagination. It is again the subjective 
 element which is contributed by the imagination to 
 perception, that forms the largest type of serious 
 illusions. In the end these may become true hallu- 
 cinations. (This topic is touched upon in the clos- 
 ing parts of the chapter on perception.) 
 
 105 
 
CHAPTER XII. 
 
 Association. . 
 
 Topic XL VIII. Association. (The aspects of the 
 problem of association which will now be touched 
 upon in these notes is intended to supplement the 
 points given in the text. For the most part points 
 there given will not be resumed. Also observe that 
 to correctly understand this section it may be desir- 
 able to read first the lecture notes on Memory, which 
 will be given in the next and concluding section.) 
 The particular problem of association represents 
 that phase of function of mental elaboration through 
 which and by which thought advances. It repre- 
 sents the system of connections between ideas, and 
 again between perception which arouses ideas, and 
 the meanings contained in them. Association in 
 terms of experience represents the simplest side of 
 this subject. This has often been too closely re- 
 garded. The older principles brought forward as 
 types of explanatory association, association by 
 familiarity and by contiguity, either mean too much 
 or are very partial explanations. Mere contig- 
 uity, either in time or space, is a very limited 
 type of association, for it is the very business of 
 association to separate things that come together 
 and put them where they belong. Association 
 sorts experience into systematic groups, and is not 
 dependent upon mere contiguity. Likewise, simi- 
 larity does not indicate the true basis of association, 
 
 106 
 
which, would be determined by the type or quality of 
 similarity in which the succession lies. This distinc- 
 tion at once suggests that association moves in terms 
 of meaning rather than of original experience— of 
 mental situations and similarities rather than material 
 situations. Thus one of the most significant distinc- 
 tions relates to association as logical and as objective, 
 as determined by sequence in experience or in pic- 
 tures, or by sequence in logical thought. 
 
 An essential characteristic of association is its un- 
 controllable quality. "We attempt to call upon asso- 
 ciational steps, but in the end they depend upon 
 happy circumstances. Given a theme and the task 
 of expressing one's ideas, it still remains uncertain, 
 because of the uncertainty of the flow of association, 
 what the outcome will be. The preparation of a pre- 
 liminary outline is not merely an aid to memory, but 
 assures the flow of thought in a given direction. It 
 assures stopping-places from which new associations 
 may be developed. If the preparation of the paper 
 be interrupted, we are convinced that, when resumed, 
 it will not continue precisely as though further prog- 
 ress had been made at the first sitting. We can never 
 quite go over again or command the same associa- 
 tions; yet the development of thought will be similar. 
 These minor variations, while significant, yet do not 
 detract from the greater significance of the acquired 
 habits of association which stamp our individual 
 thinking and make it characteristic. The best we 
 can do to control associations is to set the mind think- 
 ing along lines of interest; to gather material, which 
 means making the data accessible; and with increas- 
 ing familiarity to concentrate directive efforts upon 
 the task. We cannot expect associations to come 
 
 107 
 
without that effort of attention which, as it were, 
 makes accessible in the outlying regions of thought, 
 those clusters of ideas which next become available 
 when relations are seen and associations are estab- 
 lished. 
 
 Association is thus considered largely on the side 
 of thought. It is equally clear that it has an import- 
 ant bearing upon sense-experience and upon habit. 
 These bearings, however, are much simpler, and are 
 directed to the explanation of the problems why and 
 how elements of experience are joined, how and why 
 sequences of behavior are more or less automatically 
 established. These topics are sufficiently covered un- 
 der Habit, and will appear again in the section on 
 Memory. 
 
 108 
 
CHAPTER XIII. 
 Memory. 
 
 Topic XL VIII. Memory. Memory in general is 
 the recalling of previous impressions or experiences 
 and referring them to one's past history. For a more 
 complete definition and its essential elements consult 
 the text, Chapter XVIII. 
 
 ■ An important distinction that needs to be specially 
 emphasized is the relation between recollection and 
 recognition. Many impressions are revived with a 
 feeling of familiarity unaccompanied by minute de- 
 tails as to time, place, and circumstances of the origi- 
 nal experience. Other impressions are revived in 
 complete detail accompanied by accurate location in 
 time and place. The former is recognition, and con- 
 sists in the identification of an impression or object 
 when that impression or object is presented again. 
 The latter is recollection and takes place without the 
 aid of the original stimulus. Obviously our range of 
 recognition is very much larger than our range of 
 recollection. "We are able to recognize a great many 
 more things than we are able to recall. In the second 
 reading of a book one is able to recognize a great 
 many incidents as having met with them in the first 
 reading, but one would be able to recall voluntarily 
 only a small percentage of the facts that can be rec- 
 ognized. 
 
 Memory may be classified on the basis of the logical 
 arrangement of the memory contents as desultory or 
 
 109 
 
systematic; or on the basis of the images employed 
 in the recalling of the impressions, as visual, auditory, 
 motor, etc. For details consult the section on the 
 Imagination. 
 
 Another important problem is, What determines 
 the order or succession in which ideas return in mem- 
 ory? Quite a number of factors and principles enter 
 into this problem. Four of the more important fac- 
 tors which determine the course of associations are 
 pramacy, recency, frequency, and vividness. Stated 
 simply, these principles are that, other things being 
 equal, the first impression or event (primacy) in a 
 series of events, or the last impression (recency), or 
 a repeated one (frequency), or an unusually vivid 
 one (vividness) in a series of items is more apt to 
 be recalled. For a more detailed statement consult 
 the text, page 267. 
 
 Physiologically the basis of memory is the same as 
 the basis of habit. Impressions once made leave a 
 more or less permanent effect or change in the ner- 
 vous system. A good memory depends therefore 
 partly upon the native retentiveness of the nervous 
 system, partly upon the number of brain paths or 
 associations and partly upon the persistence of the 
 associations. 
 
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