§ 41. The Development of Perception. — Before we Pure percep- go on to deal with special perceptions, however, we must notice the fact that perception, like sensation, shows different strata or levels of development. In the early days of mental evolution, perception was wholly dominated by the object of perception, the material thing perceived. But as experience grew, and the store of ideas increased, the mind became ready to meet the material thing half-way; a full and complete perception could be touched-off by some single aspect of the thing, and the other aspects supplied by sensations aroused within the brain. The perception now includes not only outside sen- assimilation sations, but in addition to these a large — perhaps an overwhelming — number of inside sensations. And lastly, as language developed, and men came to have more and more thoughts that they wished to com- municate to each other, the thing perceived degen- erated into a mere symbol or sign of the idea, and symbolic the group of central sensations, that its perception p^^^^p^°"- brought into consciousness: the perceived thing was actually attended froin^ and the central sensations that clustered round the outside sensations were attended to. So we have a development in three stages: first the pure perception, made up entirely of outside sensations; then the mixed perception, — or assimilation, as it is technically named, — made up partly of inside and partly of outside sensations; and lastly the symbolic perception, in which the Perception Instances of the three sorts of perception.
only service done by outside sensations is that of arousing the important, inside processes.
We have instances of the original form of perception in our own experience, when we are brought into contact with something altogether new and strange to us. Suppose, e,g,^ that a friend shows you a photograph, consisting of a circle, scrawled all over with random zigzag marks, mounted on a cabinet-sized card, and dated. What is it? You do not know: you have a pure perception, — all that the thing means to you is just that which it is, a circular photograph of scrawls. — Then your friend says: ** What happened on that date? " A light flashes across you: '* The great earth- quake! " you say. Now the thing is not a photograph of scrawls; it is the record of an earthquake, a seismogram. Your perception has become mixed; a mass of central sen- sations has been awakened, and gives the photograph a different and a more definite meaning.
All our everyday perceptions are of this mixed sort, /.<f., are assimilations, unless indeed they have advanced to the symbolic stage. Thus I say that I * see ' my table. What I see, however, is merely a surface of a certain colour, dis- torted by perspective as I approach it from this side or from that. When I perceive the table, I have in mind a good deal more than the sensations coming in through the eye. I have ideas of hardness and smoothness, ideas of the uses of the table as a piece of furniture, perhaps the idea of the word * table.* The perception is mixed.
Chief among our symbolic perceptions are those of written and spoken words. As you have read this book, have you thought of the form of the words, the character of the type, the blackness of the letters? Your aim has rather been to ' understand ' the words. You have instinctively attended from the material of perception, and attended to the ideas which that material called up.
The result of this evolution is (i) that the psychologist has no easy task when he tries to find out how a particular percep- § 42. Perceptions of Qtcality 103 tion was first formed, and (2) that his enquiry is likely to end in the discovery of quite unexpected facts. Our minds are so well stocked with ideas, and our nervous tendencies have given us so many short cuts from fact to meaning (from pure to symbolic perception), that we hardly recognise our perceptions when they are dissected and laid out before us free from their central asso- ciates. Hence the reader must not be surprised if he cannot easily verify some of the following statements by an appeal to his own consciousness.
§ 42. Perceptions of ftuality. — Qualitative percep- Qualitative tions have undergone less change than perceptions ^re formed of time and of space. This is natural: for if a thing to-day as is sufficiently itself to impress its nature upon us, have been, there is no reason why this impression should be lost or modified; indeed, the perception would cease to be of value as a perception of the thing's nature, if it were liable to change and modification. Percep- tions of time and space, on the other hand, once ac- quired slowly and laboriously, with continual testing and retesting, have changed much, and gained much by the change. It would be a great waste of time and energy if we were obliged to go through all the steps that our ancestors took, when we are called upon to judge of movement or rhythm, distance or direction; but quality is the same for us as it was for them.
All qualitative perceptions are formed upon the same plan. A number of sensation qualities are run by fusion together, fused or blended together; and the result of the fusion or blending is the perception of the nature or character of some material object.
Notice that the qualitative perception is not the sum of (not by sum- ^ y- ^ mation) of the sensation qualities contained in it. That would be the sensations.
104 Perception case if the sensations were things, bits of mind in the hteral sense. It cannot be the case when they are processes: processes run into each other, interfere with each other. Hence the quaUtative perception is something less, and something more, than the sum of its sensation quaUties: less, because some of the sensations cancel or check or in- terfere with others; more, because the result of the mixture is novel, — is a perception, a process that?neans something, a concrete process with a specific character of its own.
Taste. We will take three illustrations, (i) Consider the ' taste ' of coffee. This is a qualitative perception. It contains the sensations of bitter, the real taste of the coffee-berry; of warmth; of pressure, the * feel ' of the liquid in the mouth; a peculiar fragrance, the coffee odour; and a sight, the clear brown or cloudy brown of the coffee in the cup. These are the necessary, essential elements in the perception. There may be others: the sight sensation may bring with it a space idea, an idea of the position of cup and saucer upon the spread table, etc.; and the word * coffee ' may, very likely, be added. In this case the perception is of the mixed sort: but it may quite well be a pure perception of quality. In either case it is not the simple process that at first it seems to Resistance, be. (2) Consider the perception of resistance. Here we have the qualities of pressure on the skin; of strain in the tendons, say, of the arm; and of press- ure from the jamming together of joints and the contraction of muscles. Usually, a space suggestion is added: the form and direction of the door that resists us, or of the obstacle that we are trying to Clang. remove; but the addition is not necessary. (3) Suppose that a note is sounded upon some instrument § 42. Perceptions of Qitality 105 which we cannot see. Most people would tell us that the note is a single sensation; and yet we are able to say at once that it is a piano note, or a violin or trumpet or banjo note. As a matter of fact, every note is a mixture of tones and noises. There is one loud tone, which gives its name to the note {c, d, e^ etc.); there are a number of weaker tones, higher in the scale than the loud note, and therefore called ^ overtones '; and there are a number of noise quali- ties {H.^ 237; N., ch. XXXV.)., All these sensations fuse into the single note, the perception. But the same note sounds different on different instruments, because {a) the overtones are different, and {b) the noises are different. In the piano the noise is a dull thud; in the violin a harsh scrape; in the banjo a click or pluck, etc. In the piano certain overtones are strong, in the violin others, etc. The trained ear can pick out the separate overtones and noises; the untrained ear can do no more than hear * the same note differently' « « The notes of a musical instrument are an excellent in- stance of qualitative perception. The space idea of the instrument, piano or violin, is not apt to combine with them; and the result of the mixture of sensations is so different from a mere sum of tones and noises, so much ' itself,' that unmusical persons have difficulty in realising its complex nature.
The chief reason why music employs no more than 90 Music out of the possible 11,000 tones (§ 18) is that the musical scale began as a voice-scale, a succession of tones sung. The range of the human voice is limited; hence the musical scale is cut short at both ends. And our power to adjust the larynx is limited; hence the unit of the musical scale pressure 1 06 Perception (the musical ^ semitone ') is much larger than the unit of hearing (the ' tone ' of § 18). Other reasons are the neces- sity of keeping a keyboard small enough for easy handling, the unpleasant shrillness of very high tones, the faintness of very low tones, etc.
The 'local § 43. Perceptions of Space: Place or Locality upon Dfe^sure^ the Skin. — If you are passing through a room in the dark, and bump your knee against something, you are quite sure that it is your knee that is hurt: more, you are sure that it is your right (or left) knee: and more still, you know that it is hurt just in one par- ticular place, above or below, to right or left, of the knee-cap. How do you know this? What tells you that the bump is a knee-bump?
One might suppose, perhaps, that a knee-pressure is different, in quality, from a pressure elsewhere. But that is not the case: all pressure sensations are alike in quality. Regarded as pressures, knee-bump and shin-bump — to say nothing of right and left knee-bumps — are precisely the same. So we must look elsewhere for an explanation.
We have two facts to notice. The first is that, although skin and joint are able to give us space perceptions (their pressure sensations having the attribute of extent), yet, in actual m.ental history, their development as * space organs ' does not keep anything like even pace with the development of the eye. Doubtless there are perceptions of space in the animal kingdom before there are eyes; but when the eyes have arrived, they make haste to take upon themselves the burden of supplying these perceptions. The eye, then, is the ' space organ.' The second § 44- Perceptions of Space: Position 107 fact is that primitive man must have come into con- scious contact with things, for the most part, in the daytime; in the dark he would have been sleeping. That is, he would see what struck him, and where it struck him. — Putting these facts together, we can is usually a understand what introspection shows: that most of ™^ ^^^ " us know where we are pressed or struck by having 2^ picture of the place flash up in our minds, a picture which is very accurate at the centre, though very hazy in the surrounding parts. ^ We can say, in the dark, '* I have bumped my knee! " because a picture of the knee comes up at the moment of the bump: we can say, with our eyes shut, **You are touching my cheek! " because a picture of the cheek arises at the touch. The perception is a mixed perception.
Not everybody has this picture, however. Those who do not have it ^ place ' the bump or pressure by means of a word. The word ' knee ' or ' cheek ' occurs to them, as they are touched. They or their ancestors must have gone through the picture stage: but now their mental constitu- tion is such that the picture does not arise. The word, originally used to name the picture, has taken the picture's place altogether, by one of those mental ' short cuts ' of which we spoke in § 41.
§ 44. Perceptions of Space: Position. — The percep- tion of an object in space includes two perceptions: those of place and of distance. We have seen that place on the skin is perceived by sight: how, now, is place in the field of vision perceived } We see where we are touched: do we see where we see } Partly yes, partly no. {a) If a red patch be moved over the retina, from the centre outwards, — the eye io8 Perception The percep- being kept steady during the movement, — it will be tion of place, ^ c i..• xtti where 'by Seen as red only tor a short time. When it gets to a the eye. certain distance from the centre, it becomes bluish; and as it travels still further, passes over into black.^ Here, then, we have differences of sensation quality, corresponding to differences of place in the field of vision. Knowing that the patch was red, and seeing it bluish, we should know approximately where it was: the eye could see wJiere it saw, though the skin (all pressures being alike) cannot 'feel' where \t 'feels.' But {U) it is needful for us to see things, to apprehend qualities, as they are; and we therefore always move the eyes, so as to bring the object upon the centre of the retina. We do not allow a red to remain bluish, by remaining away from the centre; we look directly at it. Now plainly, the more we have to move the eye to get the object to the centre, the stronger will be the pressure and strain sensations from the mus- cles and tendons which turn the eye in its socket. So each ' look ' of the object gets welded together with a special group of muscle and tendon sensa- tions; and the whole sensation-mass tells us where the object is. Partly, the eye sees ivJiere it sees, for itself; partly, sensations of pressure and strain, a4ded to the look of the object, tell us where the object is in the field of vision.
This, then, is the way in which we are able to 'place' an object in the field of vision. But how do we come to see it as a solid object t And how do we know its distance from us } ^ This is Experiment 6, p. 52 above.
§ 45- Peixeptions of Space: Bodily Posture 109 The perception of solidity is the result of our Thepercep- having two eyes. The eyes take two pictures of the solidity object, from two slightly different points of view. These pictures are laid over each other; and their combination into a single picture results. But if a single picture is to be formed from two dissimilar pictures, the object which the picture represents must appear solid.
So much, again, the eyes do for themselves; and, andofdis- again, the rest is done for them by the muscles and tendons around them. If an object is very near us, we must turn the eyes strongly inwards, towards each other, to see it. If it is far off, we can let the eyes swing outwards; until, if the object is at the horizon, they are both looking straight forward, par- allel with each other. The nearer the object, then, the greater is the pressure and strain about the eye; the farther off the object, the less this pressure and strain. In every case of our looking at something in space, a special sensation-mass from muscle and tendon appears to tell us of the distance of the thing from us.
§45. Perceptions of Space: Bodily Posture. — Our Bodily post- perception of the posture or attitude of our own body cdved^^^ is, in general, a perception of sight. We see how we ^^^>' are sitting or lying or standing. Even when we are in the dark, we call up a mental picture of ourselves to tell us of our position; and in thinking how our legs are disposed under the table, we call up a like picture of the lower part of the body.
At the same time, sensations from skin and joint VISUno Perception play a very considerable part in this perception of our andtactuaiiy. own position. If the soles of our feet were rendered insensible, we should not walk as confidently as we do with sensations constantly coming in from the skin of ball and heel. If the hips became insensible to the weight of the body, we should make grievous mistakes in estimating our position. Moreover, we have seen (§ i8) that a special sense-organ, the shake-organ in the ear, is set apart to give us warn- ing of any loss of balance or of command of ourselves in space.
Suppose that you are lying full-length, your eyes shut, on a board which can be tilted uj-) and down like a seesaw. Your head is lowered, and you are to call out when you are * standing on your head.' You call out much too soon: as soon as the weight of the body begins to tell upon the back of the neck, jamming the vertebrae together, you think that you are vertical. — Now you are brought back to the horizontal; you are to call out when you are lying perfectly flat. You call too late; not till the weight gets well off the neck, and you ^ feel your feet,' do you think that you are level. Evidently, then, the distribution of the weight of the body, the jamming of some joints and the free play of others, has something to do with our percep- tion of the posture of the body.
§ 46. Perceptions of Space: Movement. — Movement can be perceived in two ways: by touch (sensations from skin, muscle, tendon and joint) and by sight.
(i) If we are carried through space at an even rate, without jar, we have no perception of move- ment. The earth rotates on its axis; it revolves round the sun; it rushes forward with the sun into space. We ' feel ' nothing of all this movement, Tactual per- ception of movement.
because it is quite even and uniform. So you do not know that you are rising in a balloon, until you look over the side of the car and see the trees and houses getting smaller beneath you; you do not ' feel ' the motion. One may have the same experience, of ignorance of movement, on a sail-boat or in a well- hung and rubber-tired carriage.
As soon as the movement slows or quickens, how- ever, wx perceive it. When the brake is put on the carriage, you are thrown forward; as the speed increases, you are forced back against the cushions. This throwing backward and forward means a shift of the weight of your body, a change in the press- ures upon your skin, a stretching of certain muscles and tendons and a tightening of others, a jamming of this joint and a pulling-apart of that. The mass of sensations thus aroused gives you the percep- tion of movement.
We can perceive the movement of a single limb (arm or leg) by the help of joint sensations alone. The turning of the joint in its socket tells us both that the limb is moving and how far it has gone. We might be blind, and have no sensations from skin, muscle or tendon; and we should still know when, and how far, our limbs moved.
The sensations from skin, joint, tendon and muscle that give us the perception of movement are sometimes called, for that reason, uiotor sensations. But we do not sense movement. — there is no peculiar movement organ; we perceive it. Hence it is best not to use the phrase ' motor sensations.'
(2) The earliest perception of movement by the visual per- eye consisted in seeing something ' in two places at Movement once.' Think of the fall of a shooting star down the sky. The star leaves a trail of light behind it as it 112 Perception drops; so that you see it, so to speak, at the place it started from, and at the place where it disappears, all in the same moment. Seeing it thus, you perceive that it has moved.
We do not need now to see the moving object in two places at once; but we must remember that it was in a different place a little while ago, if we are to perceive its movement. We * see ' that the train moves across the landscape, because we remember that a second ago it was at that tree, and a second before at that other tree, and so on. If the whole landscape moved, trees and train and all, — ourselves and our standing-ground included, — we should not perceive the movement.
We said just now that the solar system is rushing on into space. We do not ' feel ' the movement, because it is even and uniform; we do not see it, because everything is mov- ing: there is no ' tree ' from which the movement starts, no fixed point which we can remember having passed so many seconds or minutes or hours ago. Just as we perceive the movement of the body by touch only when the rate of move- ment changes, so we see movement only when an object changes its position among other, fixed objects.
§ 47. Perceptions of Time: Rhythm. — All sejasa- tions have the attribute of duration, of lasting a little while; so that any class of sensations can give rise. to perceptions of time. For the particular time-per- ception that we have chosen for discussion here, however, — for the perception of rhythmy — two sen- sation-groups are of especial importance: the tactual group, made up of sensations from skin, muscle, tendon and joint; and the tactual-auditory group.
§ 47- Perceptions of Time: Rliythn 113 made up of these sensations and of sensations of hearing.
(i) The four limbs are, so to speak, four pendu- Tactual lums, attached to the trunk of the body. As we run ^ ^ "^' or walk, the legs swing alternately, and with each leg swings the arm of the opposite side. Here we have the basis of the idea of rhythm; a strong sensa- tion-mass from the leg whose foot rests upon the ground, the leg that carries the weight of the body, followed at equal intervals by a weak sensation-mass from the leg that swings through the air before its foot is set down. As the leg swings, the arm swings; and at the moment that the foot is set down, the arm pulls with its full weight upon the shoulder; so that the strong leg-sensations are rein- forced by strong arm-sensations, and the weak by weak. The rhythm is thus still further accented.
(2) This movement-rhythm, as we may call it, — Tactuai- the alternation of strong and weak sensation-masses rhythm^ from some moving part of the body, arm or hand or foot, — plays a part in every perception of rhythm. But pure movement-rhythm has not been nearly so highly developed as the compound rhythm of move- ment and hearing. The reason is that the limbs are fixed to the body; they can do no more than oscillate to and fro, up and down; while sounds are free^ not attached to anything, and so can be divided up into rhythmical groups at pleasure. Movement can give us nothing but one-two rhythms; sound and move- ment together give us the one-two-three rhythms of music and dancing.
We are so accustomed to regard rhythm as something to 114 Perception hear that the reader may never have thought of walking or running as a movement-rhythm (/r^j-^-swing, /r^j-j"- swing), but only as a hearing rhythm {tramp-XxdSii^^ tramp-trsimp). But close your ears with cotton-wool and walk across the room, letting your arms swing naturally with the movement of the legs. You can easily get into the movement-rhythm: one-3ind one-Sind one. Notice the strong jerk or pull of the heavy arm at each one^ i.e., at each pressure of a foot upon the floor.
When next you listen to music, notice that you ^keep time ' not by the ear only, but by some movement (of head, finger, etc.) as well.
§ 48. What Perception Means. — We cannot here discuss more of the perceptions that fall under the three heads of quality, space and time; the examples chosen must suffice. These few instances, however, are enough to show the reader what the value of per- ception is, and what * perceiving' means to us. Perception Plainly, perception means a breaking-up of the the outside world around us. To the primitive animal and to world. "the human infant the world must be, in Professor James' language, '' one big blooming buzzing Confu- sion." As the sense-organs grow, as the channels through which the world gains entry into mind be- come more numerous and more complicated^^ this Confusion is broken up into parts: quality parts, space parts, time parts. Mind is never fully able to cope with the world: there are stars that our best telescopes cannot find, and animal structures too deli- cate for our finest microscopes to reveal. But the farther perception goes, the more concrete processes we have that mean different parts or aspects of the material universe, the better do we understand the § 49- Illusions of Perception 115 world. With perception comes knowledge: without perception we should be without science. Just as the course of animal evolution runs from creatures made up of a single sort of tissue to creatures of many tissues, — blood and nerves and muscles and bone and the rest, — so does mental evolution run from the confused one-tissue knowledge of the infant to the many-sided, differentiated knowledge of the scientific man. We saw in § 41 that perception itself under- goes transformation and development; but no one of the three steps there mentioned is so important as the first step of all, — the step from the single world of confusion to the ordered world of perception.
§ 49. Illusions of Perception. — Mind, however, is illusory per- not wholly adequate to the world; we do not always ^^^ ^°"^' perceive aright. For one thing, the sense-organs are not always equal to the demands laid upon them: a bird may be ^too far off to be seen,' and yet it would be wrong to say that there is no bird in the sky. For another, we are biassed in our outlook over nature; our nervous tendencies, which lead us to apperceive objects rather than to perceive them, are likely to lead us astray, to make us see what is not there, or to fail in seeing what is. So there arise what are called illnsions^ perceptions in which the world is ' playing with ' us (Lat. btdns^ game) instead of telling us the truth about itself.
The most important and most instructive illusions are those of space perception, in its various forms.
Illusions oi Form. — Draw a perfect square. Notice that of form, it looks higher than it is broad. The reason is that the Il6 Perception muscles around the eyes can move them out and in more easily than they can move them up and down. Since it requires more effort to look up and down the square than to look across it, the distance up and down is taken to be greater.
Draw a number of ' squares ' which are a little lower than they are broad. Note which of them looks to be exactly right, a real square. Measure the height and subtract it from the breadth. The result gives you the amount of the illusion, of size, Illusions of Size, — It is a curious fact that, if a thing be estimated by touch (that is, by the skin wnth the assistance of muscle, tendon and joint) it seems to be larger than it does to the eye \ whereas, if it be estimated by the skin alone, it seems smaller than it does to sight. Thus a hollow tooth ' feels ' much larger, both to tongue and finger, than it looks in the mirror. Since we have learned to trust our eyes, we regard the tactual perception as illusory.
We read, however, that men born blind, and restored to sight by a surgical operation, are surprised at the largeness of the objects about them. This does not mean, as it might seem to do, that tactual space is smaller than the space of sight. The things seen appear to the patient to press in upon him, he remaining passive; just as solid bodies press down upon the passive skin. It is skin-space, then, that he compares with the space of sight: and it is this skin-space, not tactual space, that seems to him to be smaller than the sight-space. ^ The facts mean, evidently, that we live in three distinct spaces: skin-space, touch-space and eye-space. The three do not altogether agree: there is^ no real reason why they should, since the organs are different. We have learned always to believe the eye, however, and so look upon the skin-size and touch-size of things as illusory. — An illusion of size is given in Fig. ii. The vertical line looks longer in the upper figure than in the lower. This is because the eyes are tempted to run on, beyond the vertical.
§ 49' Illusions of Perception Apperceptive illusions.
in the one case; while they are checked, held back, at the ends of the vertical in the other.
Illusions of Direction, — The laws of perspective are largely of direction, based upon illusions of direction. Look out along a railway track: the lines seem to meet at the horizon, though you know that they do not. Look at your table, from one corner of the room: it seems to be a trapezoid, though you know that it is a parallelogram. The seen direction of the lines is illusory.
These illusions are all illusions of the first class; due to the inabiHty of the sense-organs to meet the requirements laid upon them. Apperceptive illusions are equally common. Thus if we are walking after a shower on a moonlight evening, we may take the shadow of a tree-trunk for a runnel of water, and step over it. Our mind is full of ideas of wetness. — Or in traversing a lonely spot at night-time we may see a ghost, which proves on nearer examination to be a white birch-trunk or a white post. Our mind is full of ghost-stories.
— Cf. H., Lesson X.