Front Page Titles (by Subject) CHAPTER XIII.: THE PERCEPTION OF SPACE. - The Principles of Psychology
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CHAPTER XIII.: THE PERCEPTION OF SPACE. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE PERCEPTION OF SPACE.
§ 61. By implication something has been said in the last chapter, respecting our perception of Space. The consideration of occupied space cannot be dissociated from the consideration of unoccupied space. Body and Space being distinguished as resistant extension and non-resistant extension, it is impossible to treat of extension in any of its modes, without virtually treating of them both. Substantially, therefore, the inquiry on which we are now to enter, must be a continuation of the one just concluded. Before commencing it, however, there seems a need for some comments on the position of those who, holding that Space is a form of thought, consider all attempts to analyze our cognition of it as absurd.
Foremost among these, is Sir William Hamilton; who says that, “it is truly an idle problem to attempt imagining the steps by which we may be supposed to have acquired the notion of extension; when in fact we are unable to imagine to ourselves the possibility of that notion not being always in our possession.”
Granting, for argument's sake, this alleged impossibility of conceiving ourselves ever to have been without the notion of extension, it does not necessarily follow either that extension is a form of thought, or that we are disabled from analyzing the notion we have of it. In a preceding criticism of the Kantian doctrine (§ 12), it was pointed out that our inability to banish from our minds the idea of space, was readily to be accounted for on the experience-hypothesis: seeing that if space be an universal form of the non-ego, it must produce some corresponding universal form in the ego—a form which, as being the constant element of all impressions presented in experience, and therefore of all impressions represented in thought, is independent of every particular impression; and consequently remains when every particular impression is banished. And then, to the argument that whether extension is a form of thought or not, our inability to conceive ourselves as ever being without it, disables us from analyzing it, I reply, that though we may be disabled from analyzing it directly, we may still remain able to analyze it indirectly. Though, in any subjective examination of our mental processes, we may fail in finding any anterior elements of thought out of which to construct the idea; yet, by examining mental processes objectively, we may gain the means of conceiving how our own consciousness of space was originally constructed.
But what is here granted for argument's sake, may be denied. This alleged impossibility of conceiving ourselves ever to have been without the notion of extension, I, for one, do not admit. It appears to me quite possible for a man to think of himself as having possessed states of consciousness not involving any notion of extension; or, what is the same thing—it is quite possible to imagine trains of thought in which space is not implied. And indeed, it would be strange that the contrary should be asserted, were it not that we are so tyrannized over by the almost indissoluble associations which experience establishes, and so habitually carry them with us in all our thinkings, as to be constantly in danger of attributing to the undeveloped mind, ideas which only the developed mind possesses. It needs, however, but to figure ourselves as devoid of certain perceptions that are known to be acquired, and it at once becomes easy to conceive ourselves as having thoughts that do not imply space. Remembering that, as Sir William Hamilton expresses it, “we are never aware even of the existence of our organism, except as it is somehow affected;” let any one imagine a human being in that early stage in which he is yet unacquainted with his own body—in which he has had no experiences. It is admitted by Kantists that space being but a form of thought cannot exist before thought—cannot be known in itself antecedently to experience; but that it is disclosed to consciousness in the act of receiving experiences. They assert that the matter of perception being given by the non-ego, and the form by the ego, the form and the matter come into consciousness simultaneously. In the supposed case, therefore, there is yet no idea of space. Let now the first impressions received, be those of sound. No one will allege that sound as an affection of consciousness, has any space-attributes. And even those who have little considered such questions, will admit that our knowledge of sound as coming from this or that point in space, is a knowledge gained by experience—is a knowledge quite separate from the sound itself—is a knowledge inferred from certain modifications of the sound; and that primarily the sound is known only as a pure undecomposable sensation. Further, let it be observed that the sensation of sound is of a kind that does not in itself make us “aware of the existence of our organism, as somehow affected.” Only by experience do we learn that we hear through the ears. Aural impressions are so indistinctly localized, that, in spite of their associations, most adults even will perceive that were it not for their acquired knowledge, they would not know whereabouts on the surface of the body they were sentient. Hence, in the supposed state of nascent intelligence, sensations of sound, not having in themselves any space-attributes, and not in themselves disclosing any part of the organism as affected, would be nothing more than simple affections of consciousness, having no space implications; and would admit of being remembered and compared, without any idea of extension being involved. Having duly contemplated the case thus objectively presented, any one ordinarily endowed with imagination, will, I think, by closing his eyes, arranging his body so as to give as few disturbing sensations as possible, and banishing as much as he can all remembrance of surrounding things, be enabled to conceive the possibility of a state in which a varied series of sounds known as severally like and unlike, and thought of solely in respect to their mutual relations, should be the entire contents of consciousness.
With such further reasons for holding that Space is not a form of thought, but a form of the non-ego disclosed to us by experience, we may be encouraged to continue that analysis of our perception of it collaterally entered upon in the last chapter.
§ 62. Starting afresh from the conclusions there reached—that, whether visual or tactual, every perception of the space-attributes of body is decomposable into perceptions of relative position; that all perceptions of relative position are decomposable into perceptions of the relative position of subject and object; and that these relations of position are knowable only through motion—the firszt question that arises is—How, through experiences of occupied extension, or body, can we ever gain the notion of unoccupied extension, or space? How, from the perception of a relation between resistant positions, do we progress to the perception of a relation between non-resistant positions? If all the space-attributes of body are resolvable into relations of position between subject and object, disclosed in the act of touch—if, originally, relative position is only thus knowable—if therefore position is, to the nascent intelligence, incognizable except as the position of something that produces an impression on the organism; how is it possible for the idea of position ever to be dissociated from that of body? how can the germinal notion of empty extension ever be gained?
This problem, though apparently difficult of solution, is really a very easy one. If, after some particular motion of a limb there invariably came a sensation of softness; after some other, one of roughness; after some other, one of hardness—or if, after those movements of the eye needed for some special act of vision, there always came a sensation of redness; after some others, a sensation of blueness; and so on—it is manifest that, in conformity with the known laws of association, there would be established a constant relation between such motions and such sensations. If positions were conceived at all, they would be conceived as invariably occupied by things producing special impressions; and it would be impossible to dissociate the positions from the things. But as, in our experience, we find that a certain movement of the hand which once brought the finger in contact with something hot, now brings it in contact with something sharp, and now with nothing at all; and that a certain movement of the eye which once was followed by the sight of a black object, is now followed by the sight of a white object, and now by the sight of no object; it results that the idea of the particular position accompanying each one of these movements, is, by accumulated experiences, dissociated from objects and impressions, and comes to be conceived by itself; it results that as there are endless such movements, there come to be endless such positions conceived as existing apart from body; and it results that as in the first and in every subsequent act of perception, each position is known as coexistent with the subject, there arises a consciousness of endless such coexistent positions; that is—of Space. This is by no means offered as an ultimate analysis, or rather synthesis, of the idea; for, as before admitted, the difficulty is to account for our notion of relative position. All that is here attempted is, partially to explain, how, from that primitive notion may be derived the materials of which our cognition of Space in its totality is built.
Carrying with us this idea, and calling to mind the description given in the last chapter of the mode in which the retina is constructed, and the relations among its elements established, it will, I think, become possible to conceive how that wonderful perception which we have of visible space, is generated. It is a peculiarity of sight, as contrasted with all the other senses, that it makes us partially conscious of many things at once. On now raising my head, I take in at one glance, desk, papers, table, books, chairs, walls, carpet, windows, and sundry objects outside; all of them simultaneously impressing me with various details of colour, which more or less tend to suggest surface and structure. It is true that I am not equally conscious of all these things at the same time. I find that some one object to which my eyes are directed, is more distinctly present to my mind than any other; and that the one point in this object on which the visual axes converge, is more vividly perceived than the rest. In fact, I have a perfect perception of scarcely more than an infinitesimal portion of the whole visual area. Nevertheless, I find that even while concentrating my attention on this infinitesimal portion, I am in some degree aware of the whole. My complete consciousness of a particular letter in the title on the back of a book at the other side of the room, does not seem to exclude a consciousness that there are accompanying letters—does not seem to exclude a consciousness of the book—does not even seem to exclude a consciousness of the table on which the book lies—nay, does not even seem entirely to exclude a consciousness of the wall against which the table stands. Of all these things I feel myself conscious in different degrees of intensity—degrees that become less, partly in proportion as the things are unobtrusive in colour and size, and partly in proportion as they recede from the centre of the visual field. Not that these various surrounding things occupy consciousness in the sense of being definitely known as such or such; for I find, on experiment, that while keeping my eyes fixed on one object, I cannot make that assertory judgment respecting any adjacent object which a real cognition of it implies, without becoming, for the moment, imperfectly conscious even of the object on which my eyes are fixed. But notwithstanding all this, it remains true that these various objects are in some sense present to my mind—are incipiently perceived—are severally tending to fill the consciousness—are each of them partially exciting the various mental states that would arise were it to be distinctly perceived.
This peculiarity in the faculty of sight—to which there is nothing analogous in the faculties of taste and smell; which, in the faculty of hearing, is vaguely represented by our appreciation of harmony; and which is but very imperfectly paralleled in the tactile faculty by the ability we have to discern numerous irregularities in a rough surface on which the hand is laid—is clearly due to the structure of the retina. Consisting of an immense number of separate sensitive elements, each of them capable of independent stimulation, it results that when, as in any ordinary act of vision, a cluster of images is simultaneously cast on the retina, all of those numberless sensitive elements upon which the variously modified rays of light fall, are severally thrown into a state of greater or less excitement. Each of them, as it were, touches some particular part of one of the images; and conveys to the sensorium the feeling produced by the touch. But now, let it be remembered that, in the manner before explained, each retinal element has come to have a certain known relation to every one of those which surround it—a relation such that their synchronous excitation serves to represent their serial excitation. Lest this symbolism should not have been fully understood, I will endeavour yet further to elucidate it. Suppose a minute dot to be looked at—a dot so small that the image of it, cast upon the retina, covers only one of these sensitive elements, A. Now suppose the eye to be so slightly moved that the image of this dot falls upon the adjacent element B. What results? Two slight changes of consciousness: the one proceeding from the new retinal element affected; and the other from the muscles producing the motion. Let there be another motion, such as will transfer the image of the dot to the next element C. Two other changes of consciousness result. And so on continuously: the consequence being that the relative positions in consciousness of A and B, A and C, A and D, A and E, &c., are known by the number of intervening states. Imagine now that instead of these minute motions separately made, the eye is moved with ordinary rapidity; so that the image of the dot passes successively over the whole series A to Z, in an extremely brief space of time. What results? It is a familiar fact that all impressions on the senses, and visual ones among the number, continue for a certain brief period after they are made. Hence, when the series of retinal elements A to Z, are excited in rapid succession, the excitation of Z commences before that of A has ceased; and for a short time the whole series A to Z remains in a state of excitement together. This being understood, suppose a line to be looked at whose image is long enough to cover the whole series A to Z. What results? There is a simultaneous excitation of the series A to Z, differing from the last in this; that it is continuous, and that it is unaccompanied by sensations of motion. But does it not follow from the known laws of mental suggestion, that as the simultaneous excitation is common to both cases, it will, in the last case, tend to arouse in consciousness that series of states that accompanied it in the first? Will it not as it were tend to consolidate the entire series of such states into one state? and will it not insensibly come to be taken as the equivalent of such series? There cannot I think be a doubt of it. And if not, then it becomes comprehensible how an excitement of consciousness by the coexistent positions constituting a line, serves as the representative of that serial excitement of it which accompanies motion along that line. Returning now to the above described state of the retina as occupied by a cluster of images—remembering that the relations of coexistent position which we have here considered in respect to a particular linear series, are similarly established throughout countless such series in all directions over the retina, so as to put each element in relation with every other—remembering further that in virtue of a process analogous to that described, the state of consciousness produced by the adjustment of the eyes to a particular focus has become a symbol of the series of coexistent positions between the eyes and the point to which they are directed—remembering all this, the genesis of our visual perception of space will begin to be vaguely comprehensible. Every one of the retinal elements simultaneously thrown into a state of partial excitement, producing as it does a partial consciousness not only of itself as excited, but also of the many relations of coexistent position established between it and the rest, which are all of them similarly excited and similarly suggestive; there tends to arise a consciousness of a whole area of coexistent positions. Meanwhile the state of consciousness produced by the focal adjustment of the eyes, calling up as it does the line of coexistent positions lying between the subject and the object specially contemplated; and each of the things, and parts of things not in the centre of the field, producing, by the greater or less definiteness of its image, an incipient consciousness of its distance, that is, of the coexistent positions lying between the eye and it; there arises an indistinct consciousness of a whole volume of coexistent positions—of Space in three dimensions. Along with a complete consciousness of the one position to which the visual axes converge, arises a nascent consciousness of an infinity of other positions—a consciousness that is nascent in the same sense that our consciousness of the various objects out of the centre of the visual field is nascent. To all which it may be added, that as the innumerable relations subsisting between these coexistent positions were originally established by motion; as each of these relations of coexistent positions came by habit to stand for the series of mental states accompanying the motion which measured it; as every one of such relations must, when presented to consciousness, still tend to call up, in an indistinct way, that train of feelings, that sense of motion, which it represents; and as the simultaneous presentation of an infinity of such relations will tend to suggest an infinity of such experiences of motion, which, as being in all directions, must so neutralize each other as to prevent any particular motion being thought of; there will arise, as their common resultant, that sense of ability to move, that sense of freedom for motion, which forms the remaining constituent in our idea of Space.
Should any still find it difficult to conceive how, by so elaborate a process as the one described, there should be reached an idea apparently so simple, so homogeneous, as that which we have of Space; they will perhaps feel the difficulty somewhat diminished on remembering:—first, that this process commences at birth; second, that every day throughout our lives, and throughout the whole of each day, we are, from moment to moment, repeating our experiences of these innumerable coexistences of position and their several equivalences to the serial states of feeling accompanying motions; and third, that these experiences invariably agree—that these relations of coexistent position are unchangeable—are ever the same towards each other and the subject—are ever equivalent to the same motions. By duly contemplating this early commencement of these experiences, this infinite repetition of them, and their absolute uniformity; and at the same time remembering the power which, in virtue of its structure, the eye possesses of partially suggesting to the mind countless such experiences at the same moment; it will become possible to conceive how we acquire that consolidated idea of space in its totality, which at first seems so inexplicable. And if, to develop somewhat further a late illustration, we call to mind the mode in which we regard long used symbols—how by habit each of the groups of letters now before the reader has acquired a seemingly inherent meaning—has ceased to be a mere series of straight and bent strokes, and has actually, as it were, absorbed some of the thought for which it stands; and if further we remember how, in our intellectual operations, these words have come to be the elements with which we think—how we cannot definitely realize to ourselves any proposition without putting it into words—and how the words are so habitually thought of to the exclusion of the things they signify, as to cause frequent mistakes; if we call to mind these facts, it will not be difficult to understand how, with symbols learnt much earlier, symbols incomparably more simple, uniform, and exact, symbols used every instant of our waking lives, a like transformation should have been carried much further. And this being understood, it may also be understood how the state of consciousness answering to any group of coexistent positions made known by the senses, has supplanted in our minds the series of states of consciousness to which it was equivalent; and how, consequently, our space-perceptions have become a language in which we think of surrounding things, without at all thinking of those experiences of motion which this language expresses.
§ 63. Strong confirmations of this analysis may be drawn from certain peculiarities in our perception of space. If the reader whilst looking at his hand, or any equally close object, will consider what kind of knowledge he has of the space lying between it and his eyes, he will perceive that his knowledge of it is, as it were, exhaustive. He is conscious of the minutest differences of position in it. He has an extremely complete or detailed perception of it. If now he will direct his eyes to the farther side of the room, and contemplate an equal portion of that more remote space, he will find that he has but a comparatively vague cognition of it. He has nothing like so intimate an acquaintance with its constituent parts. If, again, he will look through the window, and observe what consciousness he has of a space that is a hundred yards away, he will discover it to be a still less specific consciousness. And on gazing at the distant horizon he will perceive that he has scarcely any perception of that far off space—has rather an indistinct conception than a distinct perception. This now is exactly the kind of knowledge that would result from the organized experiences above described. Of the space that is so close to us as to be within the range of our hands, we have the most complete perception, because we have had myriads of experiences of relative positions within that space. And of space as it recedes from us we have a less and less complete perception, because our experiences of the relative positions contained in it have been fewer and fewer.
The disordered feelings accompanying certain abnormal states of the nervous system, furnish similar evidence. De Quincey, describing some of his opium-dreams, says that “buildings and landscapes were exhibited in proportions so vast as the bodily eye is not fitted to receive. Space swelled, and was amplified to an extent of unutterable infinity.” It is not at all an uncommon thing with nervous subjects to have illusive perceptions in which the body seems enormously extended: even to the covering an acre of ground. Now the state in which these phenomena occur, is one of exalted nervous activity—a state in which De Quincey depicts himself as seeing in their minutest details the long-forgotten events of his childhood. And if we consider what effect must be produced upon the consciousness of space, by an excitement during which forgotten experiences are revived in extreme abundance and vividness, we shall see that it will cause the illusion of which he speaks. Of the myriad experiences of surrounding positions accumulated throughout life, we manifestly remember but a part. In common with all other experiences they severally tend to fade from the mind; and the perception of space would in the end become indistinct, were it not that they are day by day refreshed, or replaced by new ones. Imagine now, that these innumerable experiences of relative positions, which have been hourly registered in the mind from infancy upwards, and of which the earliest are quite effaced, while intermediate ones continue in various degrees of faintness—imagine these innumerable fading experiences suddenly to revive, and become definitely present to consciousness. What must result? It must result that space will be known in comparatively microscopic detail. Within any portion of space ordinarily thought of as containing a certain quantity of positions, an immensely greater quantity of positions will be thought of. Between the eye and each point looked at, whose distance is commonly conceived as equivalent to a certain series of positions, a far more extensive series will be conceived; and as the length of each such series is the mind's measure of the distance, all distances will appear increased, all points will appear more remote, and it will seem that space has “swelled,” as De Quincey expresses it.
Yet another fact having the same implication, is supplied by that striking change in our cognition of space which results during a temporary inability to see. Any one guided into a totally dark place with which he is unacquainted, and of which there are consequently no recollected visual impressions to occupy his imagination, will find that he almost loses his ordinary idea of space—that he almost ceases to be conscious of it as an infinity of coexistent positions, and remains conscious of it only as permitting freedom of movement. Even on merely closing the eyes for a few minutes, and, as far as may be, excluding from the mind all recollection of adjacent objects, it will be perceived that distant space cannot be thought of at all, except by remembering the cognition of it gained through the eyes; and that the space near at hand, is presented to the mind more as a negation of resistance than anything else. Most persons on several times repeating this experiment, and critically observing their ideas, will, I think, find, that could they move their limbs without imagining the visible changes accompanying the motions, this negation of resistance would be almost their sole cognition of space; and that until, after the manner of the blind, they had developed their tactual experiences of positions, they would be unable to think of space as they at present think of it. Now these are just the mental conditions to which the foregoing analysis points. The infinity of coexistent positions suggested by any visual impression, having become by habit the language in which we think of space, to the exclusion of those motor experiences which this language represents; it results that in proportion as we are deprived of this language, are we disabled from thinking of space: just as we should be almost incapacitated for reasoning, by the loss of our words.
And here let it be further observed, that while these several phenomena perfectly conform to the experience-hypothesis, they are irreconcilable with the antagonist one. The fact that our idea of adjacent space differs in completeness from our idea of remote space, is wholly at variance with the hypothesis that space is a form of thought; which implies a perfect homogeneity in our idea of space. That in morbid states of the brain, space should appear “swelled,” is, on the Kantian theory, unaccountable: seeing that the form of thought should remain constant, whether the thought itself be normal or abnormal. And similarly inconsistent with his theory, is the change in our cognition of space caused by a temporary privation of vision; which, if space were a subjective condition, would cause no change.
§ 64. Leaving here the inquiry into our perception of space in its totality, a few further words are called for respecting that relation of two coexistent positions, in our consciousness of which, the problem ultimately centres. From time to time in the progress of the argument, something has been done towards explaining the nature of this consciousness—towards showing that it is a state of consciousness serving to symbolize a series of states to which it is found equivalent. But, as before said, it is desirable to postpone the more definite analysis of this perception of coexistent positions, until the perception of motion is dealt with. At present the only reason for recurring to it, is to point out the indissoluble union between the cognition of space and the cognition of coexistence; and afterwards what is implied by this.
Not only is it that the idea of space involves the idea of coexistence; but it is that the idea of coexistence involves the idea of space. Fundamentally, space and coexistence are two sides of the same cognition. On the one hand space cannot be thought of without coexistent positions being thought of: on the other hand coexistence cannot be thought of without at least two points in space being thought of. A relation of coexistence implies two somethings that coexist. Two somethings cannot occupy absolutely the same point in space. And hence coexistence implies space. If it be said that one body can have coexistent attributes, and that therefore two attributes can coexist in the same place; the reply is, that body itself is unthinkable except as presenting coexistent positions—a top and a bottom, a right and a left. Body cannot be so diminished, even in imagination, as to present only one position; or, in other words—in ceasing to present in thought more than one position, it ceases to be body. And as attributes imply body—as a mere position in space can have no other attribute than that of position, it follows that a relation of coexistence, even between attributes, is inconceivable without an accompanying conception of space. Space can be known only as presenting relations of coexistence: relations of coexistence can be known only as presented in space.
If now it should turn out under an ultimate analysis, that a relation of coexistence is not directly cognizable, but is cognizable only by a duplex act of thought—only by a comparison of experiences; the question between the transcendentalists and their opponents will be set finally at rest. When, after it has been shown, as above, that our cognition of space in its totality is explicable upon the experience-hypothesis, and that all the peculiarities of the cognition confirm that hypothesis, it comes to be shown that the ultimate element into which that cognition is decomposable—the relation of coexistence—can itself be gained only by experience; the utter untenableness of the Kantian doctrine will become manifest. That this will be so shown, the reader must at present take for granted. I am obliged thus to forestall the argument, because it would be inconvenient, during an analysis of the several orders of relations, to recur at any length to the controversy respecting space.
§ 65. To complete the chapter it needs but to say, that the process of organic classification, shown in previous cases to constitute the act of perception, is very clearly exhibited in the perception of space. The materials of the perception having been gained in the way described, the co-ordination of them into any particular perception, consists in the assimilation of each relation of position to the like before-known relations. In every glance we cast around, the distinct consciousness of the distance of each thing specially looked at, and the nascent consciousness of the distances of various neighbouring things, alike imply a classing of present distances with remembered distances. These distances being one and all unknowable under any other condition, there is no alternative but to admit this. And the seemingly incomprehensible fact that numberless such classings should be simultaneously made by us without attracting our attention, simply shows to what perfection the process of automatic classification is brought by infinite repetition.