Psychology
Chapter 7: Perception of Spatial
and
Temporal Relations
James Rowland Angell
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I. SPACE
The objects which we have mentioned in our analysis of sensory consciousness are all objects perceived by us as parts of a spatial and temporal order; and it is evident that our account of them would be extremely defective if we altogether omitted a study of these time and space relations. We shall consider space first.
Two Fundamental Problems.-- Psychologists are divided in opinion upon two fundamental problems concerning our space perceptions. It is maintained in the first place by some of them, the nativists, that space perception is primarily an innate hereditary attainment possessed by us in a rude form prior to, and independent of, all experience. Others, the empiricists, maintain that spatial judgments are as much the results of experience, are as truly acquired, as piano playing or the liking for caviar. We shall not discuss the question, for this would require more time than we can give it. But we may register the dogmatic opinion that both parties to the controversy are in a measure correct. We hold that the crude, vague feeling of extension, of volume, is a genuinely innate experience, unlike any other experience, and underived by mere experience from non-spatial psychical elements. So far we are nativists. On the other hand, we are confident that all accurate knowledge of the meaning of the space relations in our space world, all practically precise
(142) perception of direction, position, contour, size, etc., is a result of experience, and could never be gained without it. So far we are empiricists, holding to a genetic point of view regarding the development of our adult space consciousness. The analyses and discussions which follow will serve to furnish some of the evidence upon which this view rests.
Sensory Basis of Spatial Perception. --The second main point upon which psychologists are unable to agree concerns the sensory sources from which we gain our spatial judgments, a matter to which we made cursory reference in Chapter V. The majority of psychologists maintain that vision and touch are the only real avenues of spatial perception whereas certain others, like James, boldly maintain that all forms of sensory consciousness are " voluminous," -- smell and taste and audition, as well as sight and touch. The doctrine maintained in this book is that all forms of sensations are immediately suggestive of spatial attributes, e. g., position, size, distance, etc. ; but that only sight and touch possess intrinsically and completely the full spatial characteristics. We include in touch, when thus mentioned, all the cutaneous sensations and the motor, or kinaesthetic, sensations. As a matter of fact, however, the temperature and pain sensations, considered apart from pressure and sensations of movement, are ordinarily negligible elements. When involved in conjunction with pressure, they often modify our perceptions materially.
Doubtful Cases.-- Taste and smell and hearing are really the debatable sensations. Taste we throw out of court at once, because taste stimuli practically involve invariably the stimulation of cutaneous sensations of contact and temperature. We cannot, therefore, submit the matter to unambiguous introspective analysis. Smells we undoubtedly classify at times in ways suggesting spatial attributes. The smell of illuminating gas seems somehow a more massive, extensive sort of thing than the odour of lemon peel. But if
(143) one lessens the disparity in the intensity of the two odours, by getting just the merest whiff of the gas and inhaling freely and deeply of the lemon odour, the spatial difference between the two begins to evaporate. There can be no question but that we tend to think of the more intense and more widely diffused odour as the larger. Nor is this remarkable, since we find in it actually occupying more of the atmospheric space about us. But when we note that with mild intensities of odours their spatial suggestiveness wanes; when we further note that we have no definite impressions of size, much less of shape, under any conditions; and finally when we remark that even our ability to localise odours is extremely imperfect, we may well question whether smell has itself any properly space quality.
The case of auditory space is similar to that of smell. We are told, for instance, that the tones of the lowest organ pipes are far larger, far more voluminous, than those of the high shrill pipes. A base drum sounds bigger than a pennywhistle, a lion's roar than the squeaking of a mouse, etc. Such illustrations, when adduced as evidence of the spatial character of sounds, evidently contain three possible sources of error. In the first place, we often know something about the causes of these sounds, and we tend to transfer the known size of the producing object to the supposed size of the sound. Secondly, and of far more consequence, sounds affect other organs than those of the internal ear, especially when they are loud or of deep pitch. Powerful tones thus jar the whole body, and are felt all over. Moreover, vibrations of the drum membrane of the middle-ear undoubtedly set up crude sensations of pressure, or strain, to which we may come to attach a spatial significance associated with the sound. Add to this, thirdly, the fact that we readily convert judgments based upon the intensity of sounds into judgments about their extensity just as in the case of smell, and one has a large mass of considerations leading to scepticism concerning the
(144) genuineness of intrinsic auditory space relations. Of course , one doubts that we localise sounds, and of the factors involved in this process we shall have more to say presently. But the fact that certain sounds are located within the head (e. g., when two telephone receivers are placed against the ears and an induction shock sent through them) has been cited to prove the native possession of a true auditory space; for here apparently experience from the other senses, such as vision, would give no direct assistance. But these cases are certainly capable of explanation by means of the intra-cranial sensations set up in pressure nerves by bone vibrations, and by the effect of the imagination, visual and otherwise. Taken alone, such evidence could hardly be conclusive. If we come back, then, to ordinary introspection, we find that all which the most ardent partisans of an auditory space can claim is a much emaciated form of the visual and tactual article. A vague sense of volume, or mass, much vaguer even than that given by mere temperature, with some crude sense of position, would seem to be the utmost capacity. Any sense of contour or shape or exact size, any ability to measure, is lacking. Clearly such a space, even if genuine, which we doubt, would ill deserve to be ranked beside the space of sight and touch. The manner in which we localise sound may best be described after we have analysed visual and tactual space.
Growth of Space Perception. -- Our adult cognition of space relations is generally so immediate and unreflective, the feeling for space values so compelling and seemingly inevitable, that we find it difficult to believe that these reactions are the results of a slow process of growth and learning. Nevertheless, this is unquestionably the fact. Babies evidently have no precise perceptions of space until they have acquired a considerable degree of motor control; and even then their appreciation of large expanses and distances is often ludicrously inexact. The child reaching in good faith for the moon is the stock illustration of this sort of thing.
(145) That we have no precise appreciation of visual space relations until experience has brought it to us is abundantly proven by the cases of persons born blind and successfully operated upon for the restoration of sight. Immediately after the operation such persons are almost wholly at a loss for impressions of size, shape, or distance. After the hands have explored the objects seen, and the eyes have been allowed to pass freely to and fro over them, these spatial impressions gradually begin to emerge and take on definiteness. By the use of properly arranged lenses and prisms experiments of various kinds have been made on normal persons, showing that we can speedily accommodate ourselves to the most unusual inversions and distortions of our visual space. We can thus learn to react properly, although all the objects, as we see them, are upside down and turned about as regards their right and left relations. The new relations soon come to have the natural feeling of ordinary perceptions.
These observations show very strikingly that there is noth. ing rigidly fixed and innate about the form of our space perceiving; that it is a function of experience and can be changed by changing the conditions of the experience. Moreover, it is easy to demonstrate that the space relations, as we perceive them by different senses, are far from homogeneous. Indeed, the impressions which we gain from the same sense are often far from being in agreement. Nevertheless, we feel our space relations to be objectively homogeneous, a result which could hardly come about under such circumstances of sensory disparity without the harmonising effects of experience. To illustrate the edge of a card pressed gently upon the forearm will feel to the skin shorter than it looks. The same card, if the finger tip is allowed to run slowly along it, will feel longer than it looks. The disappointing disparity between the cavity of a tooth, as it feels to the tongue and appears to the eye, or feels to the finger-tip, is a notorious instance of the same thing. The
(146) tongue and the finger-tip both give us pressure sensations. Yet they give a very different report of the same object. Similarly, objects seen upon the periphery of the retina appear smaller than when seen by the fovea; and often they undergo a certain distortion in form. That we should perceive, amid all these possible sources of confusion, a fairly stable and well-ordered space world betokens unmistakably the systematising effects of experience, controlled no doubt by the exigencies of our practical interests in effective orientation.
Part Played by Movement.-- Even though we recognise the fact that experience brings order and precision and effectiveness into our space perceptions, the general manner by which these results are achieved is not yet clear; much less what factors are chiefly employed in their attainment. It requires only the most cursory examination to convince oneself that the all-important element in the building up and correlating with one another of our various spatial sensations is movement. In acquiring accurate touch perceptions, for instance, the finger-tips and hands move over the object, grasp it now in this way and now in that, until a complex set of tactual impressions has been gained from it. Without such movement our touch perceptions are vague in the extreme. If we close our eyes and allow another person to put a series of small objects -upon our outstretched hands we receive only the most indefinite impressions of form and size and texture. But allow us to manipulate the same objects in our fingers, and we can give a highly accurate account of them. Similarly, if we wish to compare visually the magnitude and contours of two objects we must allow our eyes to move freely from one to the other. Indeed, reflection must assure us that the vital meaning of all space relations is simply a given amount and direction of movement. To pass toward the right means to make a certain kind of movement; to pass upward means to make another kind, etc. To be
(147) sure, we assign arbitrary measures to these relations, and we say an object is a mile away, or is a foot thick and six inches high. But the meaning to us of the mile, the foot, and the inch must always remain ultimately expressible in movement. Were it possible to get at the exact stages in the process by which the child acquires its control over space relations, we should thus secure the most penetrating possible insight into our adult space perceptions. But as this is at present impracticable, we must content ourselves with an analysis of the factors which seem clearly involved in these adult conditions, without regard to their genetic features.
Touch and Vision.-- It is certain that touch and vision practically cooperate from the beginning, and we shall isolate them from one another only to point out their respective peculiarities, and not because their operation is independent. The most important, and for practical purposes the most accurate, part of our touch perceptions comes from the hands and finger-tips. By moving the bands over, the various parts of the body we come to have a fairly accurate notion of their touch characteristics in terms of the hand as a standard. Moreover, each hand touches the other, and we thus get a kind of check from touch on the tactual standard itself. Generally speaking, when two parts of our body touch each other we feel the one which is quiet with the one which is moving. Thus, if we stroke the forehead with the fingers we feel the forehead; but if we bold the hand steady and move the bead, we feel the fingers. Now in order that we should be able to learn in these ways that a certain amount of sensation in the finger-tips means a certain area on the forehead, and, much more, that we should be able to tell with so much accuracy when we are touched what part of the body the sensation comes from, seems to depend upon what Lotze calls the "local sign."
Local Signs.-- If one is touched upon the palm and upon the back of the hand, one obtains from both stimulations
(148) sensations of pressure; but however much alike they may be as regards duration, intensity, and extensity, we promptly feel a difference in them, which leads us to refer each to its appropriate region. Now this something about touch sensa. tions which permits us to recognise them as locally distinct, although we recognise all of them as being cases of contact, is what is meant by the local sign. These local signs, then, are the relatively fixed elements in our space-perceiving processes. It is by learning to correlate one group of them with another group that we can develop by experience the accuracy of our perceptions. Thus, for example, we come to learn that the stimulation of one series of local signs in the order a-b-c means a special movement of one hand over the other, say the downward movement of the right hand over the left. The same series stimulated in the order c-b-a means the reverse movement. It must be remembered very explicitly at this point that we are including the kinaesthetic sensations of movement under the general heading of touch: since we doubtless have local signs of movement distinct from those of the cutaneous pressure sense, and they doubtless play a very important part here. But they are commonly fused in an inextricable way with the pressure sensations, so that a separate treatment of them seems hardly necessary in a sketch of this kind.
A Caution.-- A warning must be held out at this point against the fallacy of supposing that in learning his space world a child uses these local signs in any very reflective way. He does not say to himself : "That movement of localisation was inaccurate because I used the wrong local sign to control it." He generally employs the " try, try again method," until he hits the mark. But his success carries with it a recollection of the total feeling of the successful experience, and in this total feeling the local sign element is an indispensable part, even though the child is not himself definitely cognisant of the fact.
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The simultaneous stimulation of a group of these local signs gives us the extensity feeling of touch, and when the impressions come from three-dimensional objects we get, through our motor reactions upon them, experiences of change of motion in three cardinal directions. This seems to be the basis of our tactual tridimensionalitv.
Delicacy of Touch.-- In normal persons touch falls far behind vision in its spatial nicety of function, and far behind its possible capacities, as is shown by the astonishing accuracy of blind persons, who do not, however, seem to be notably more accurate than seeing persons as regards the parts of the body which are not used for tactual exploration, e. g., the forearms and the back. But despite its lesser delicacy, touch-movement undoubtedly plays an important role during childhood in furnishing interpretative checks upon our visual estimates of large areas and great distances. The visual perception of a mile, for instance, gets a practical meaning for us largely through our walking over the distance. Moreover, although vision so largely displaces touch in our actual spatial judgments, touch always retains a sort of refereeship. When we doubt the accuracy of our visual perceptions we are likely' whenever possible, to refer the case to touch, and the verdict of this sense we commonly accept uncritically.
Peculiarities of Vision. -- Vision resembles the non-spatial senses of smell and hearing in one particular which marks it off characteristically from touch. Touch sensations we commonly refer to the surface of the body itself, although when we tap with a cane, or a pencil, we seem to have a curious kind of projection of part of our sensations out to the farther tip of the object. Visual objects we always place outside ourselves. Even our after-images gotten with closed eyes often seem to float in a space vaguely external to ourselves.
It seems necessary to assume a system of local signs for vision, comparable to those of touch-movement, although doubtless more complex. It must be admitted, however, that
(150) introspection is much more uncertain in its deliverances here, than in the case of touch, and we shall be on somewhat speculative ground in assuming the nature of this visual local signature. It seems probable that this attribute of sensations from the Periphery of the retina consists primarily in reflex impulses, or tendencies, to movement toward the fovea, the fovea itself furnishing a peculiar feeling which serves more or less as a fixed point of reference. Certain it is that stimulation of any part of the retina tends to release movements turning the fovea toward the stimulus. The incessant and complicated movements of the eyes over the visual field must speedily render the relation of the various retinal points, as conjoined by movements, intricate in the highest degree. But such relations as exist must pretty clearly rest on the intermediation of movements with their motor and retinal effects upon consciousness; and it seems probable, therefore, that the space value of any retinal point comes to be determined by the position it occupies in such a system of movements. Thus, a point 20' to the right of the fovea in the visual field comes to mean to us a definite kind of motor impulse. One 20' to the left, another kind of impulse, etc. Whether the visual local -sign is actually this sort of a fused retinal-kinaesthetic affair or Dot, there can be no doubt that as adults, we have a remarkably accurate sense of the general space relations of the objects in the field of view, and that we can turn our eyes with unhesitating accuracy to any part of this field.
The Third Dimension.-- Psychologists have always been especially interested in the problem of the visual perception of distance, or the third dimension. Bishop Berkeley maintained in his celebrated work entitled " Essay Toward a New Theory of Vision " (1709), that the eye cannot give us any direct evidence of distance, because any point in the visual field must affect one point and one only in the retina, and it can affect this no differently when it is two feet away from
(151) what it does when four feet away. Therefore, Berkeley concluded that our perception of visual distance is dependent upon our tactual-motor experiences. This view overlooks several important facts, including its plain contradiction of our common feeling about the matter. In the first place, we have two eyes, and each eve sees a part of solid objects varying slightly from that seen by the other. The psychical percept of such objects appears to be a fusion of the factors supplied by the two eyes, and we get from this source the visual feeling of solidity. The stereoscope employs this principle, and by giving us pictures which exaggerate somewhat the disparity in the point of view of the right and left eve affords us a most startling impression of distance and volume. Furthermore, we converge our eyes more upon near points than upon far, and the muscular strain thus, brought about may serve to inform us of differences in distance. Similarly, the muscles controlling the ](,uses contract with varying degrees of intensity in the effort properly to focus rays of light from objects at different distances. How far our consciousness of these focussing movements is significant for our judgments of distance it is difficult to say. But it is at least clear that there are factors operative other than those Berkeley had in mind, and the genuineness of the optical sense of distance can hardly be seriously questioned. The eye is, in short, not merely a retina, it is a binocular motor organ as well. Normally, therefore, visual perceptions are always fused stereoscopic binocular-motor experiences.
We use in actual practice other forms of criteria for distance. Thus, the apparent size of the object is used as a clue to its distance. By the apparent size of a man we may judge whether he be a mile or a hundred yards away. Conversely, when we know the distance, we can employ it to form an estimate of the size of an object at that distance. Thus, if we know the approximate distance, we can be fairly sure whether the person we see is a man or a boy.
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The seeming size of objects runs roughly, but not percisely, (sic) parallel with the size of the retinal image. We make a certain compensation for objects at considerable distances.[1]
The distinctness of the perceptual image is another criterion. Things seen dimly, other things equal, are judged to be far away. Objects near at hand seen dimly in this way, as during a fog, seem much magnified in size. We have dimness, the sign of distance, conjoined with a large image, and we consequently judge the object to be much larger than it is, because of its seeming distance. The contrary form of this confusion is experienced by persons going into the mountains for the first time. The unaccustomed atmospheric clearness renders distant objects unwontedly distinct, and so they are misjudged as much nearer and much smaller than they really are. Our judgments of distance are seriously disturbed, also, when deprived of the assistance of familiar intermediary objects. Persons unacquainted with the sea are wholly unable to guess accurately the distance of vessels or other objects across the water. Light and shadow give us many trustworthy indications of contour, and even the absolute brightness of the light seems to affect our judgment, bright objects seeming to be nearer than those which are less bright.
Inaccuracies of Space Perception.-- Despite its general accuracy, our visual perception is subject to sundry eccentric-
(153) -ities, the precise causes of which we cannot pause to discuss. In many cases, indeed, the reasons for them are far from cer. tain. Thus vertical lines are commonly judged longer than objectively equal horizontal lines. The upper portions of vertically symmetrical figures look larger than the lower portions. The printed letter S and the figure 8 illustrate the supplementary principle, that to make the top and bottom parts appear of equal size the bottom one must be made larger. The seeming size of objects is affected by their surroundings, a kind of spatial contrast evidently existing. Figure 54 illustrates this. We might mention many other instances, but space forbids.
In the establishment of effective correlations among our
several sources of space perception, there can be no question, as we have previously insisted, that movement is the great factor. Objects touched are, by the movement of the eyes, at the same time seen. The superposition of one object upon another, and the successive passing of one hand after the other over the things we touch, must rapidly serve to build up elaborate space perceptions upon the foundation of local signs, some of which are visual and some tactual. Our space, as we know it in adult consciousness, is, then, a distinctly synthetic affair, developed from two or three distinct sensory
(154) sources, through the intermediation of localising and exploring movements.
Space Limen.-- We may add for those who are interested in the quantitative aspect of these matters, that the limen for space perception in vision has generally been given at 60", this being the angular distance at which two lines can just be distinguished as two. Recent experimenters report a far smaller angle, one observer finding the limen at 15", another at 2.5". In touch, the threshold for the detecting of two points as two is, for the finger-tips, roughly, 2 mm. The tongue is even more sensitive. But this can hardly be called the space limen with propriety, for single points are felt as having some extension. Apart from the tongue, the finger-tips are the most delicate tactual surfaces. Speaking generally, the delicacy of tactual space perception seems to be a function, first, of the richness of nervous innervation (those places which are most richly innervated being generally most sensitive), and second, of practice, or use.
Localization of Sound.-Although we may not admit that auditory sensations are themselves spatial, we cannot question that we localise sounds with considerable accuracy. In our view, however, this localisation occurs in the space world of vision-touch-movement. The two most important factors in the localisation of sound are, first; the relative amplitude of the sound waves distributed to the two ears, and, second, the acoustic complexity of the sound waves. If the right ear is more violently stimulated than the left, we locate the stimulus on the right side of the body. If the two ears are stimulated equally, we judge the so-Lind to be somewhere in the median vertical plane, at right angles to the line joining the ears. But of the precise point in this plane we are very uncertain.
With sounds that have many partial tones, these tones, especially the higher ones, are so affected by the bones of the head and by the external ear, that they reach the two ears in
(155) distinctly different condition, save when they occur in the median plane. In consequence the timbre of complex sounds differs with their direction; and it seems quite certain that we employ these differences in our auditory localisation of direction, and possibly also of distance. Our auditory estimates of distance, however, are highly inexact. To put it graphically, a sound on the right side may be heard as a fusion of tones a-b-c-d-e-f by the right ear, whereas by the left ear it could only be heard as a fusion of a-b-c. Now if the sound be moved to a point a little to the right of straight back, the right ear gets a-b-c-d-e, the left ear a-b-c-d. Our perception of the sound is of course always a fusion of the increment coming from the two ears. But our illustration may serve to show how these differences in timbre may act as local indices. Most persons seem to make their localisation of sounds either in the form of visual imagery, or in the form of quasi-reflex localising movements of head and eye. It is possible that cutaneous sensations from the drum membrane are of some consequence in certain localisations, but the evidence for this is hardly conclusive.
II. TIME
Space and Time.-- Although certain of our sensations may not, perhaps, contribute directly to our consciousness of space, all of them participate in furnishing us our sense of time. We are probably never wholly oblivious to the feeling of passling time, and now and then it monopolises our entire attention. Unlike our perception of space, however, our direct perception of time is a very limited, cramped sort of an affair. The eye permits us to range over the vast distances of interstellar space, but our perception of time, so far as it is an immediate sensory process, never gets far beyond the present moment It seems to be based upon our awareness of the changes occurring in consciousness itself.
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Primary Characteristics of Time Perception -- We may perceive the passing of time, either in the form of a mere vague duration, or as an interval, depending upon whether we give our attention to the filling of the period, or to its limiting stimuli. In either case what we become aware of is never a mere point of time, sharply marked off from that which has gone before and that which follows. It is always a consciousness of an extent of time which confronts us, however limited this extent may be.
The Specious Present.-- This consciousness of the sensibly present moment is often referred to as the "specious present" -a phrase suggested by E. R. Clay. This specious present seems to owe its extended nature to the fact that objects which have once been in consciousness do not drop out in. stantaneously, but fade out often somewhat slowly. We are at any given moment, therefore, aware in the fringe of consciousness not only of that which a moment ago engaged our attention, but also of that which a moment hence is more fully to occupy us. This period of waning which our thoughts display before passing entirely out of the field of consciousness is often entitled the period of "primary memory." In any case our direct perception of the passing of time is simply this process in which from moment to moment we become aware of the coming and going among our conscious activities. Evidently the scope of such a perceptual process must be very circumscribed. As a matter of fact our direct, as distinguished from our indirect and inferred, consciousness of time never exceeds a few seconds. Under favourable conditions it may mount up to twelve seconds or thereabouts, but ordinarily it is much shorter.
Factors in Direct Perception of Time.-Although all the senses may be employed for this purpose, hearing is the sense from which we gain our most accurate direct perception of time relations. Touch and the motor sensations rank next, and in actual practice generally operate with hearing. If we
(157) are attempting to judge accurately the length of two time intervals we tend strongly to tap, or make other rhythmical movements, and our judgment is much assisted by these movements. The shortest interval which we can feel as a time period between two sounds is about 1-50 to 1-80 of a second. Sounds succeeding one another more rapidly than this we may distinguish as qualitatively different from absolutely simultaneous sounds, but we hardly recognise them as temporally separate. Furthermore, we may feel as successive two stimuli which are objectively simultaneous. This is said to be true of the combination of a noise and a light sensation.
When the auditory stimuli follow each other at the rate of less than 1-2 second, we seem to sense the sequence in one way. When they come at intervals of 1-2 second to 3 seconds, we have a different mode of reaction. These latter cases we feel distinctly as durations. Probably the sensory content of these durations is largely made up of kinaesthetic sensations, especially from the respiratory muscles. The shorter intervals first mentioned we sense more as "moments," although they may vary considerably in actual length. They are in no true sense, therefore, felt as mere points in time. If we compare intervals longer than three seconds we find ourselves beginning to employ our consciousness of the number of sensations, or ideas, which come into the mind. We tend to overestimate very small intervals and to underestimate long intervals. The region of relatively correct judgment may be called the indifference zone. This is about 6-10 to 7-10 of a second.
Much as in the case of space perception, we judge richly filled intervals as longer than relatively vacant intervals. " Empty time " is a myth. We always have some consciousness of change, so long as we are conscious at all. We are also subject to illusions and to the effect of contrast, as in spatial processes. An interval seems shorter when preceded by a long interval than when preceded by a short one, and
(158) vice versa. An interval bounded by intense stimuli seems shorter than one with more moderate limiting stimuli. Ifour attention is very much engaged upon some expected event we may perceive it as coming before another event which it actually follows.
Generally speaking, our consciousness of time, as such, is proportional to our interest and absorption in the occupation of the moment. When we are bored, as in waiting for a train, or when ill, time drags outrageously. We may be conscious of every loathsome increment in it. When, on the, other hand, we are thoroughly interested, long intervals may pass as in a flash. Certain drugs, such as hashish, have a curious effect upon our time perception, lending a vastly magnified perspective to it, so that events of a moment since seem ages remote. Dreams often display a similar distortion.
Indirect Time Perception.-- Clearly our practical -use of time relations depends largely on other processes than those of direct perception. For our consciousness of the hour, the day, and the year we resort to the sun and moon, to clocks, watches, calendars and other indirect means of information. Despite the fact that the subject does not bear immediately upon perception, it will be convenient to add a few words at this point upon one or two general features of our time consciousness.
General Characteristics of the Apprehension of Time Relations.-- When we recall intervals of time which belong to the more or less remote past, we immediately remark a, seeming paradox. Intervals which actually passed very slowly for us, appear retrospectively to have been very brief. Thus, a tedious illness, when time palled upon us almost beyond
:endurance, may in recollection seem very short, although we actually know it occupied weeks. Conversely' intervals which passed in a twinkling appear to us in memory as long drawn out. The reason for the paradox is obvious. Our feeling for the length of these remembered intervals depends upon
(159) the amount of content, the number of events, which we can read back into them. The interesting intervals are full of such things, whereas the tedious periods are characterised by a depressing sameness, which affords our memory little or nothing to lay hold upon.
The change which comes over our feeling for the various intervals of time as we grow older is an interesting and familiar phenomenon. In childhood the year seems interminable, the month majestic, the week momentous, and even the day important, to say nothing of the hour. In adult years all these periods shrink, the longest ones most markedly. Our feelings for very short intervals, like the second and the minute, undergo no change of which we can speak confidently.
Our notion of very remote times, whether thought of as past or future, is gotten in an almost wholly symbolic way, like our notion of vast numbers. The difference between 2000 B. C. and 6000 B. C. is a thing for which we have a cold intellectual apprehension, quite distinct from our feeling for the difference between 1776 and 1860.
Neural Basis of Time Perception.-- We can say very little about the neural basis of time perception, and that little is largely of an inferential and speculative character. If the awareness of passing time rests, as we have maintained, upon our consciousness of the waxing and waning of the thought processes, there should be some fairly constant phase of the cortical activity corresponding to this conscious metabolism. We may suppose this to exist in the rising and falling of the pulses of neural activity throughout the various regions of the cortex. Time consciousness would depend, therefore, upon the overlapping of the activity of various groups of neurones. Beyond some such vague formulation as this we cannot go. Let it be remarked, however, that the conception, though vague, is wholly intelligible.
Physiological Time Sense.-- In closing this subject, we may mention two striking and perplexing peculiarities which many
(160) persons possess. One of these is the capacity for telling with great accuracy the precise hour, whether by day or by night, without any recourse to watch or clock, and without any deliberate computation or estimate. The other is the ability to awaken exactly at any given hour, without any preliminary disturbance of the soundness of sleep. Both of these per. formances probably rest upon some sort of recognition by the cortical centres of the rhythm of physiological activities constantly in progress in the body. But after all is said, the matter remains something of a mystery, a mystery which is enhanced, rather than removed, by the familiar attempt to find an explanation in " subconscious " activities. It suggests certain of the experiences met with in post-hypnotic suggestion. Of hypnotism itself we shall have something to say in the final chapter of this book.
