Classical Texts in Psychology
(Return to index)
William James (1890)
THE PERCEPTION OF 'THINGS.'
PERCEPTION AND SENSATION COMPARED.
A PURE sensation we saw above, p. 7, to be an abstraction never realized in adult life. Any quality of a thing which affects our sense organs does also more than that: it arouses processes in the hemispheres which are due to the organization of that organ by past experiences, and the result of which in consciousness are commonly described as ideas which the sensation suggests. The first of these ideas is that of the thing to which the sensible quality belongs. The consciousness of particular material things present to sense is nowadays called perception"  The consciousness of such things may be more or less complete; it may be of the mere name of the thing and its other essential attributes, or it may be of the thing's various remoter relations. It is impossible to draw any sharp line of distinction between the barer and the richer consciousness, because the moment we get beyond the first crude sensation all our consciousness is a matter of suggestion, and the various suggestions shade gradually into each other, being one and all products of the same psychological machinery of association. In the directer consciousness fewer, in the remoter more, associative processes are brought into play. [p. 77]
Perception thus differs from sensation by the consciousness of farther facts associated with the object of the sensation:
" When I lift my eyes from the paper on which I am writing I see the chairs and tables and walls of my room, each of its proper shape and at its proper distance. I see, from my window, trees and meadows, and horses and oxen, and distant hills. I see each of its proper size, of its proper form, and at its proper distance; and these particulars appear as immediate information of the eye, as the colors which I see by means of it. Yet philosophy has ascertained that we derive nothing from the eye whatever but sensations of color. ... How, then, is it that we receive accurate information, by the eye, of size and shape and distance? By association merely. The colors upon a body are different, according to its figure, its shape, and its size. But the sensations of color and what we may here, for brevity, call the sensations of extension, of figure, of distance, have been so often united, felt in conjunction, that the sensation of the color is never experienced without raising the ideas of the extension, the figure, the distance, in such intimate union with it, that they. not only cannot be separated, but are actually supposed to be seen. The sight, as it is called, of figure, or distance, appearing as it does a simple sensation, is in reality a complex state of consciousness -- a sequence in which the antecedent, a sensation of color, and the consequent, a number of ideas, are so closely combined by association that they appear not one idea, but one sensation."
This passage from James Mill  gives a clear statement of the doctrine which Berkeley in his Theory of Vision made for the first time an integral part of Psychology. Berkeley compared our visual sensations to the words of a language, which are but signs or occasions for our intellects to pass to what the speaker means. As the sounds called words have no inward affinity with the ideas they signify, so neither have our visual sensations, according to Berkeley, any inward affinity with the things of whose presence they make us aware. Those things are tangible; their real properties, such as shape, size, mass, consistency, position, reveal themselves only to touch. But the visible signs and the tangible significates are by long custom so "closely twisted, blended, and incorporated together, and the prejudice is so confirmed and riveted in our thoughts by a long tract of time, by the use of language, and want of reflection,"  that we think we see the whole object, tangible and visible alike, in one simple indivisible act. [p. 78]
Sensational and reproductive brain-processes combined, then, are what give us the content of our perceptions. Every concrete particular material thing is a conflux of sensible qualities, with which we have become acquainted at various times. Some of these qualities, since they are more constant, interesting, or practically important, we regard as essential constituents of the thing. In a general way, such are the tangible shape, size, mass, etc. Other properties, being more fluctuating, we regard as more or less accidental or inessential. We call the former qualities the reality, the latter its appearances. Thus, I hear a sound, and say 'a horse-car'; but the sound is not the horse-car, it is one of the horse-car's least important manifestations. The real horse-car is a feelable, or at most a feelable and visible, thing which in my imagination the sound calls up. So when I get, as now, a brown eye-picture with lines not parallel, and with angles unlike, and call it my big solid rectangular walnut library-table, that picture is not the table. It is not even like the table as the table is for vision, when rightly seen. It is a distorted perspective view of three of the sides of what I mentally perceive (more or less) in its totality and undistorted shape. The back of the table, its square corners, its size, its heaviness, are features of which I am conscious when I look, almost as I am conscious of its name. The suggestion of the name is of course due to mere custom. But no less is that of the back, the size, weight, squareness, etc.
Nature, as Reid says, is frugal in her operations, and will not be at the expense of a particular instinct to give us that knowledge which experience and habit will soon produce. Reproduced sights and contacts tied together with the present sensation in the unity of a thing with a name, these are the complex objective stuff out of which my actually perceived table is made. Infants must go through a long education of the eye and ear before they can perceive the realities which adults perceive. Every perception is an acquired perception."  [p. 79]
Perception may then be defined, in Mr. Sully's words, as that process by which the mind
"supplements a sense-impression by an accompaniment or escort of revived sensations, the whole aggregate of actual and revived sensations being solidified or 'integrated' into the form of a percept, that is, an apparently immediate apprehension or cognition of an object now present in a particular locality or region of space." 
Every reader's mind will supply abundant examples of tire process here described; and to write them down would be therefore both unnecessary and tedious. In the chapter on Space we have already discussed some of the more interesting ones; for in our perceptions of shape and position it is really difficult to decide how much of our sense of the object is due to reproductions of past experience, and how much to the immediate sensations of the eye. I shall accordingly confine myself in the rest of this chapter to certain additional generalities connected with the perceptive process.
The first point is relative to that 'solidification' or 'integration,' whereof Mr. Sully speaks, of the present with the absent and merely represented sensations. Cerebrally taken, these words mean no more than this, that the process aroused in the sense-organ has shot into various paths which habit has already organized in the hemispheres, and that instead of our having the sort of consciousness which would be correlated with the simple sensorial process, we have that which is correlated with this more complex process. This, as it turns out, is the consciousness of that more complex 'object,' the whole 'thing,' instead of being the consciousness of that more simple object, the few qualities or attributes which actually impress our peripheral nerves. This consciousness must have the unity which every 'section' of our stream of thought retains so long as its objective content does not sensibly [p.80] change. More than this we cannot say; we certainly ought not to say what usually is said by psychologists, and treat the perception as a sum of distinct psychic entities, the present sensation namely, plus a lot of images from the past, all 'integrated' together in a way impossible to describe. The perception is one state of mind or nothing -- as I have already so often said.
In many cases it is easy to compare the psychic results of the sensational with those of the perceptive process. We then see a marked difference in the way in which the impressed portions of the object are felt, in consequence of being cognized along with the reproduced portion, in the higher state of mind. Their sensible quality changes under our very eye. Take the already-quoted catch, Pas de lieu Rhone que nous: one may read this over and over again without recognizing the sounds to be identical with those of the words paddle your own canoe. As we seize the English meaning the sound itself appears to change. Verbal sounds are usually perceived with their meaning at the moment of being heard. Sometimes, however, the associative irradiations are inhibited for a few moments (the mind being preoccupied with other thoughts) whilst the words linger on the ear as mere echoes of acoustic sensation. Then, usually, their interpretation suddenly occurs. But at that moment one may often surprise a change in the very feel of the word. Our own language would sound very different to us if we heard it without understanding, as we hear a foreign tongue. Rises and falls of voice, odd sibilants and other consonants, would fall on our ear in a way of which we can now form no notion. Frenchmen say that English sounds to them like the gazouillement des oiseaux: -- an impression which it certainly makes on no native ear. Many of us English would describe the sound of Russian in similar terms. All of us are conscious of the strong inflections of voice and explosives and gutturals of German speech in a way in which no German can be conscious of them.
This is probably the reason why, if we look at an isolated printed word and repeat it long enough, it ends by assuming an entirely unnatural aspect. Let the reader try this with [p.81] any word on this page. He will soon begin to wonder if it can possibly be the word he has been using all his life with that meaning. It stares at him from the paper like a glass eye, with no speculation in it. Its body is indeed there, but its soul is fled. It is reduced, by this new way of attending to it, to its sensational nudity. We never before attended to it in this way, but habitually got it clad with its meaning the moment we caught sight of it, and rapidly passed from it to the other words of the phrase. We apprehended it, in short, with a cloud of associates, and thus perceiving it, we felt it quite otherwise than as we feel it now divested and alone.
Another well-known change is when we look at a landscape with our head upside down. Perception is to a certain extent baffled by this manoeuvre; gradations of distance and other space-determinations are made uncertain; the reproductive or associative processes, in short, decline; and, simultaneously with their diminution, the colors grow richer and more varied, and the contrasts of light and shade more marked. The same thing occurs when we turn a painting bottom upward. We lose much of its meaning, but, to compensate for the loss, we feel more freshly the value of the mere tints and shadings, and become aware of any lack of purely sensible harmony or balance which they may show.  Just so, if we lie on the floor and look up at the mouth of a person talking behind us. His lower lip here takes the habitual place of the upper one upon our retina, and seems animated by the most extraordinary an unnatural mobility, a mobility which now strikes us because (the associative processes being disturbed by the unaccustomed point of view) we get it as a naked sensation and not as part of a familiar object perceived. On a later page other instances will meet us. For the present these are enough to prove our point. Once more we find ourselves driven to admit that when qualities of an object impress our sense and we thereupon perceive object, the sensation as such of those qualities does not [p. 82] still exist inside of the perception and form a constituent thereof. The sensation is one thing and tile perception another, and neither can take place at the same time with the other, because their cerebral conditions are not the same. They may resemble each other, but in no respect are they identical states of mind.
PERCEPTION IS OF DEFINITE AND PROBABLE THINGS.
The chief cerebral conditions of perception are the paths of association irradiating from the sense-impression, which may have been already formed. If a certain sensation be strongly associated with the attributes of a certain thing, that thing is almost sure to be perceived when we get the sensation. Examples of such things would be familiar people, places, etc., which we recognize and name at a glance. But where the sensation is associated with more than one reality, so that either of two discrepant sets of residual properties may arise, the perception is doubtful and vacillating, and the most that can then be said of it is that it will be of a PROBABLE thing, of the thing which would most usually have given us that sensation.
In these ambiguous cases it is interesting to note that perception is rarely
abortive; some perception takes place. The two discrepant sets of associates
do not neutralize each other or mix and make a blur. That we more commonly
get is first one object in its completeness, and then the other in its completeness.
In other words, all brain-processes are such as give rise to what
we may call FIGURED consciousness. If paths are irradiated at all,
they are irradiated in consistent systems, and occasion thoughts of definite
objects, not mere hodge-podges of elements. Even where the brain's functions
are half thrown out of gear, as in aphasia or dropping asleep, this law of figured
consciousness holds good. A person who suddenly gets sleepy whilst reading aloud
will read wrong; but instead of emitting a mere broth of syllables, he
will make such mistakes as to read 'supper-time' instead of 'sovereign,' 'overthrow'
instead of 'opposite, or indeed utter entirely imaginary phrases, composed of
several definite words, instead of phrases of the book. So in aphasia: where
the disease is mild the patient's mis- [p. 83] takes consist in using entire
wrong words instead of right ones. It is only in grave lesions that he becomes
quite inarticulate. These facts show how subtle is the associative link; how
delicate yet how strong that connection among brain-paths which makes any number
of them, once excited together, thereafter tend to vibrate as a systematic whole.
A small group of elements, 'this,' common to two systems, A and B, may
touch off A or B according as accident decides the next step (see Fig. 47).
If it happen that a single point leading from 'this' to B is momentarily
a little more pervious than any leading from 'this' to A, then that little
advantage will upset the equilibrium in favor of the entire system B. The currents
will sweep first through that point
and thence into all the paths of B, each increment of advance making A more and more impossible. The thoughts correlated with A and B, in such a case, will have objects different, though similar. The similarity will, however, consist in some very limited feature if the 'this' be small. Thus the faintest sensations will give rise to the perception of definite things if only they resemble those which the things are wont to arouse. In fact, a sensation must be strong and distinct in order not to suggest an object and, if it is a non-descript feeling, really to seem one. The auræ of epilepsy, globes of light, fiery vision, roarings in the ears, the sensations which electric currents give rise to when passed through head, these are unfigured because they are strong. Weaker feelings of the same sort would probably suggest objects. Many years ago, after reading daury's book, Le Sommeil et lee Rêves, I began for the first time to observe ideas which faintly hit through the mind at all times ,visions, etc., disconnected with the main stream of thought, but discernible to an attention on the watch for [p. 84] them. A horse's head, a coil of rope, an anchor, are, for example, ideas which have come to me unsolicited whilst I have been writing these latter lines. They can often be explained by subtle links of association, often not at all. But I have not a few times been surprised, after noting some such idea, to find, on shutting my eyes, an after-image left on the retina by some bright or dark object recently looked at, and which had evidently suggested the idea. 'Evidently,' I say, because the general shape, size, and position of object thought -- of and of after-image were the same, although the idea had details which the retinal image lacked. We shall probably never know just what part retinal after-images play in determining the train of our thoughts. Judging by my own experiences I should suspect it of being not insignificant  [p. 85]
Note that in every illusion what is false is what is inferred, not what is immediately given. The 'this,' if it were felt by itself alone, would be all right, it only becomes misleading by what it suggests. If it is a sensation of sight, it may suggest a tactile object, for example, which Inter tactile experiences prove to be not there. The so-called 'fallacy of the senses,' of which the ancient sceptics made so much account, is not fallacy of the senses proper, but rather of the intellect, which interprets wrongly what the senses give. 
So much premised, let us look a little closer at these illusions. They are due to two main causes. The wrong object is perceived either because
1) Although not on this occasion the real cause, it is yet the habitual, inveterate, or most probable cause of 'this; ' or because
2) The mind is temporarily full of the thought of that object, and
therefore 'this' is peculiarly prone to suggest it at this moment.
I will give briefly a number of examples under each head. The first head is
the more important, because it includes a, number of constant illusions to which
all men are subject, and which call only be dispelled by much experience.
One of the oldest instances dates from Aristotle. Cross
two fingers and roll a pea, penholder, or other small object between them. It will seem double. Professor Groom Robertson has given the dearest analysis of this illusion. He observes that if the object be brought into contact first with the forefinger and next with the second finger, the two contacts seem to come in at different points of space. [p. 87] The forefinger-touch seems higher, though the finger is really lower; the second-finger-touch seems lower, though the finger is really higher. "We perceive the contacts as double because we refer them to two distinct parts of space." The touched sides of the two fingers are normally not together in space, and customarily never do touch one thing; the one thing which now touches them, therefore, seems in two places, i.e. seems two things. 
There is a whole batch of illusions which come from optical sensations interpreted by us in accordance with our usual rule, although they are now produced by an unusual object. The stereoscope is an example. The eyes see a picture apiece, and the two pictures are a little disparate, the one seen by the right eye being a, view of the object taken from a point slightly to the right of that from which the left eye's picture is taken. Pictures thrown on the two eyes by solid objects present this identical disparity. Whence we react on the sensation in our usual way, and perceive a solid. If the pictures be exchanged we perceive a hollow mould of the object, for a hollow mould would cast just such disparate pictures as these. Wheatstone's instrument, the pseudoscope, allows us to look at solid objects and see with each eye the other eye's picture. We then perceive the solid object hollow, if it be an object which might probably be hollow, but not otherwise. A human face, e.g., never appears hollow to the pseudoscope. In this irregularity of reaction on different objects, some seem hollow, others not; the perceptive process is true to its ,which is always to react on the sensation, in a determinate and figured fashion if possible, and in as probable fashion as the case admits. To couple faces and hollow [p. 87] ness violates all our habits of association. For the same reason it is very easy to make an intaglio cast of a face, or the painted inside of a pasteboard mask, look convex, instead of concave as they are.
Our sense of the position of things with respect to our eye consists in suggestions of how we must move our hand to touch them. Certain places of the image on the retina, certain actively-produced positions of the eyeballs, are normally linked with the sense of every determinate position which an outer thing may come to occupy. Since we perceive the usual position, even if the optical sensation be artificially brought from a different part of space. Prisms warp the light-rays in this way, and throw upon the retina the image of an object situated, say, at spot a of space in the same manner in which (without the prisms) an object situated at spot b would cast its image [sic] Accordingly we feel for the object at b instead of a. If the prism be before one eye only we see the object at b with that eye, and in its right position a with the other -- in other words, we see it double. If both eyes be armed with prisms with their angle towards the right, we pass our hand to the right of all objects when we try rapidly to touch them. And this illusory sense of their position lasts until a new association is fixed, when on removing the prisms a contrary illusion at first occurs. Passive or unintentional changes in the position of the eyeballs seem to be no more kept account of by the mind than prisms are; so we spontaneously make no allowance for them in our perception of distance and movements. Press one of the eyeballs into a strained position with the anger, and objects move and are translocated accordingly, just as when prisms are used.
Curious illusions of movement in objects occur whenever the eyeballs move without our intending it. We shall learn in the following chapter that the original visual feeling of movement is produced by any image passing over the retina. Originally, however, this sensation is definitely referred neither to the object nor to the eyes. Such definite reference grows up later, and obeys certain simple laws. We believe objects to move: 1) whenever we get the retinal movement-feeling, but think our eyes are still; and 2) when- [p. 89] ever we think that our eyes move, but fail to get the retinal movement-feeling. We believe objects to be still, on the contrary, 1) whenever we get the retinal movement-feeling, but think our eyes are moving; and 2) whenever we neither think our eyes are moving, nor get the retinal movement-feeling. Thus the perception of the object's state of motion or rest depends on the notion we frame of our own eye's movement. Now many sorts of stimulation make our eyes move without our knowing it. If we look at a waterfall, river, railroad train, or any body which continuously passes in front of us in the same direction, it carries our eyes with it. This movement can be noticed in our eyes by a by-stander. If the object keep passing towards our left, our eyes keep following whatever moving bit of it may have caught their attention at first, until that bit disappears from view. Then they jerk back to the right again, and catch a new bit, which again they follow to the left, and so on indefinitely. This gives them an oscillating demeanor, slow involuntary rotations leftward alternating with rapid voluntary jerks rightward. Put the oscillations continue for a while after the object has come to a standstill, or the eyes are carried to a new object, and this produces the illusion that things now move in the opposite direction. For are unaware of the slow leftward automatic movements our eyeballs, and think that the retinal movement-sensations thereby aroused must be due to a rightward motion the object seen; whilst the rapid voluntary rightward movements of our eyeballs we interpret as attempts to pursue and catch again those parts of the object which have been slipping away to the left.
Exactly similar oscillations of the eyeballs are produced giddiness, with exactly similar results. Giddiness is easiest produced by whirling on our heels. It is a feeling of movement of our own head and body through space, is now pretty well understood to be due to the irritation of the semi-circular canals of the inner ear.  When, [p. 90] after whirling, we stop, we seem to be spinning in the reverse direction for a few seconds, and then objects appear to continue whirling in the same direction in which, a moment previous, our body actually whirled. The reason is that our eyes normally tend to maintain their field of view. If we suddenly turn our head leftwards it is hard to make the eyes follow. They roll in their orbits rightwards, by a, sort of compensating inertia. Even though we falsely think our head to be moving leftwards, this consequence occurs, and our eyes move rightwards -- as may be observed in any one with vertigo after whirling. As these movements are unconscious, the retinal movement-feelings which they occasion are naturally referred to the objects seen. And the intermittent voluntary twitches of the eyes towards the left, by which we ever and anon recover them from the extreme rightward positions to which the reflex movement brings them, simply conform and intensify our impression of a leftward-whirling field of view: we seem to ourselves to be periodically pursuing and overtaking the objects in their leftward flight. The whole phenomenon fades out after a few seconds. And it often ceases if we voluntarily fix our eyes upon a given point. 
0ptical vertigo, as these illusions of objective movement are called, results sometimes from brain-trouble, intoxications, paralysis, etc. A man will awaken with a, weakness of one of his eye-muscles. An intended orbital rotation will then not produce its expected result in the way of retinal movement-feeling-whence false perceptions, of which one of the most interesting cases will fall to be discussed in later chapters. There is an illusion of movement of the opposite sort, with which every one is familiar at railway stations. Habitually, when we ourselves move forward, our entire field of view glides backward over our retina. When our movement is due to that of the windowed carriage, car, or boat [p. 91] in which we sit, all stationary objects visible through the window give us a sensation of gliding in the opposite direction. Hence, whenever we get this sensation, of a window with all objects visible through it moving in one direction, we react upon it in our customary way, and perceive a stationary field of view, over which the window, and we ourselves inside of it, are passing by a motion of our own. Consequently when another train comes alongside of ours in a station, and fills the entire window, and, after standing still awhile, begins to glide away, we judge that it is our train which is moving, and that the other train is still. If, however, we catch a glimpse of any part of the station through the windows, or between the cars, of the other train, the illusion of our own movement instantly disappears, and we perceive the other train to be the one in motion. This, again, is but making the usual and probable inference from our sensation. 
Another illusion due to movement is explained by Helmholtz. Most wayside objects, houses, trees, etc., look small when seen out of the windows of a swift train. This is because we perceive them in the first instance unduly near. And we perceive them unduly near because of their extra-ordinarily rapid parallactic flight backwards. When we ourselves more forward all objects glide backwards, as aforesaid; but the nearer they are, the more rapid is this apparent translocation. Relative rapidity of passage back-wards is thus so familiarly associated with nearness that when we feel it we perceive nearness. But with a given size of retinal image the nearer an object is, the smaller do judge its actual size to be. Hence in the train, the faster we go, the nearer do the trees and houses seem, and nearer they seem, the smaller do they look. 
Other illusions are due to the feeling of convergence being interpreted. When we converge our eyeballs we an approximation of whatever thing we may be at. Whatever things do approach whilst we look [p. 92] at them oblige us, so long as they are not very distant, to converge our eyes. Hence approach of the thing is the probable objective fact when we feel our eyes converging. Now in most persons the internal recti muscles, to which convergence is due, are weaker than the others; and the entirely passive position of the eyeballs, the position which they assume when covered end looking at nothing in particular, is either that of parallelism or of slight divergence. Make a person look with both eyes at some near object, and then screen the object from one of his eyes by a card or book. The chances are that you will see the eye thus screened turn just a little outwards. Remove the screen, and you will now see it turn in as it catches sight of the object again. The other eye meanwhile keeps as it was at first. To most persons, accordingly, all objects seem to come nearer when, after looking at them with one eye, both eyes are used; and they seem to recede during the opposite change. With persons whose external recti muscles are insufficient, the illusions may be of the contrary kind. The size of the retinal image is a fruitful source of illusions. Normally, the retinal image grows larger as the object draws near. But the sensation yielded by this enlargement is also given by any object which really grows in size without changing its distance. Enlargement of retinal image is therefore an ambiguous sign. An opera-glass enlarges the moon. But most persons will tell you that she looks smaller through it, only a great deal nearer and brighter. They read the enlargement as a sign of approach; and the perception of approach makes them actually reverse the sensation which suggests it-by an exaggeration of our habitual custom of making allowance of the apparent enlargement of whatever object approaches us, and reducing it in imagination to its natural size. Similarly, in the theatre the glass brings the stage near, but hardly seems to magnify the people on it.
The well-known increased apparent size of the moon on the horizon is a result of association and probability. It is seen through vaporous air, and looks dimmer and duskier than when it rides on high; and it is seen over fields, trees, [p. 93] hedges, streams, and the like, which break up the intervening space and make us the better realize the latter's extent Both these causes make the moon seem more distant from us when it is low; and as its visual angle grows no less, deem that it must be a larger body, and we so perceive it. It looks particularly enormous when it comes up directly behind some well-known large object, as a house or tree distant enough to subtend an angle no larger than that the moon itself. 
The feeling of accommodation also gives rise to false perceptions of size. Usually we accommodate our eyes for an object as it approaches us. Usually under these circumstances the object throws a larger retinal image. But believing the object to remain the same, we make allowance for this and treat the entire eye-feeling which we receive significant of nothing but approach. When we relax accommodation and at the same time the retinal image grows smaller, the probable cause is always a receding object. The moment we put on convex glasses, however, the accommodation relaxes, but the retinal image grows larger instead of less. This is what would happen if object, whilst receding, grew. Such a probable object we accordingly perceive, though with a certain vacillation as to the recession, for the growth in apparent size is also a probable sign of approach, and is at moments interpreted accordingly. -- Atropin paralyzes the muscles of accommodation. It is possible to get a dose which will weaken these muscles without laming them altogether. When a known near object is then looked at we have to make the voluntary strain to accommodate, as if it were a great deal nearer; but as its retinal image is not enlarged in proportion to this suggested approach, we deem that it must have grown smaller than usual. In consequence of this so-called micropsy, Aubert relates that he saw a man apparently no larger then a photograph. But the small made the man seem farther off. The real distance [p. 94] was two or three feet, and he seemed against the wall of the room.  Of these vacillations we shall have to speak again in the ensuing chapter. 
Mrs. C. L. Franklin has recently described and explained with rare acuteness
an illusion of which the most curious thing is that it was never noticed before.
Take a single pair of crossed lines (Fig. 49), hold them in a horizontal plane
before the eyes, and look along them, at such a distance that with the right eye shut, 1, and with the left eye shut, 2, looks like the projection of a vertical line. Look steadily now at the point of intersection of the lines with both eyes open, and you will see a third line sticking up like a pin through the paper at right angles to the plane of the two first lines. The explanation of this illusion is very simple, but so circumstantial that I must refer for it to Mrs. Franklin's own account.  Suffice it that images of the two lines fell on 'corresponding' rows of retinal points, and that the illusory vertical line is the only object capable of throwing such images. A variation of the experiment is this:
"In Fig. 50 the lines are all drawn so as to pass through a common point. With
a little trouble one eye can be put into the position of this point -- it is
only necessary that the paper be held so that, with one eye shut, the other
eye sees all the lines leaning neither to the right nor to the left. After a
moment one can fancy the lines to be vertical staffs standing out of the plane
of the paper. ... This illusion [says Mrs. Franklin] 
I take to be of purely mental origin. When a line lies anywhere in a plane passing
through the apparent vertical meridian of one eye, and is looked at with
that eye only.... we have no very good means of knowing how it is directed in
that plane. ... Now of the lines in nature which lie anywhere within
such a plane, by far the [p. 95] a number are vertical lines. Hence we are peculiarly
inclined to think that a line which we perceive to be in such a plane is a vertical
line. But to see a lot of lines at once, all ready to throw their images
upon the vertical meridian, is a thing that has hardly ever happened to except when they all have been vertical lines. Hence when that happens we have a still stronger tendency to think that what we see before us is a group of vertical lines."
In other words, we see, as always, the most probable object. The foregoing
may serve as examples of the first type illusions mentioned on page 86. I could
cite of course many others, but it would be tedious to enumerate all the thaumatropes
and zoetropes, dioramas, and juggler's tricks which they are embodied. In the
chapter on Sensation sew that many illusions commonly ranged under this are,
physiologically considered, of another sort altogether, and that associative
processes, strictly so called, · nothing to do with their production.
Illusions of the Second Type.
We may now turn to illusions of the second of the two type discriminated on page 86. In this type we perceive a wrong object because our mind is full of the thought of it time, and any sensation which is in the least degree connected with it touches off, as it were, a train already laid and gives us a sense that the object is really before us. Here is a familiar example:
"a sportsman, while shooting woodcock in cover, sees a bird ;the size and color of a woodcock get up and By through the foli- [p. 95] age, not having time to see more than that it is a bird of such a size and color, he immediately supplies by inference the other qualities of a woodcock, and is afterwards disgusted to find that he has shot a thrush. I have done so myself, and could hardly believe that the thrush was the bird I had fired at, so complete was my mental supplement to my visual perception." 
As with game, so with enemies, ghosts, and the like Anyone waiting in a dark place and expecting or fearing strongly a certain object will interpret any abrupt sensation to mean that object's presence. The boy playing 'I spy,' the criminal skulking from his pursuers, the superstitious person hurrying through the woods or past the church-yard at midnight, the man lost in the woods, the girl who tremulously has made an evening appointment with her swain, all are subject to illusions of sight and sound which make their hearts beat till they are dispelled. Twenty times a day the lover, perambulating the streets with his preoccupied fancy, will think he perceives his idol's bonnet before him.
The Proof-reader's Illusion. I remember one night in Boston, whilst waiting for a, 'Mount Auburn' car to bring me to Cambridge, reading most distinctly that name upon the signboard of a car on which (as I afterwards learned) 'North Avenue' was painted. The illusion was so vivid that I could hardly believe my eyes had deceived me. All reading is more or less performed in this way.
"Practised novel -- or newspaper-readers could not possibly get on so fast if they had to see accurately every single letter of every word in order to perceive the words. More than half of the words come out of their mind, and hardly half from the printed page. Were this not so, did we perceive each letter by itself, typographic errors in well-known words would never be overlooked. Children, whose ideas are not yet ready enough to perceive words at a glance, read them wrong if they are printed wrong, that is, right according to the way of printing. In a foreign language, although it may Be printed with the same letters, we read by so much the more slowly as we do not understand, or are unable promptly to perceive the words. But we notice misprints all the more readily. For this reason Latin and Greek and, still better, Hebrew works are more correctly printed, because the proofs are better corrected, than in German works. Of two friends of mine, one knew much Hebrew, the other little ; the latter, however, gave instruction in [p. 97] Hebrew in a gymnasium; and when he called the other to help correct his pupils' exercises, it turned out that he could find out all sorts little errors better than his friend, because the latter's perception of the words as totals was too swift." 
Testimony to personal identity is proverbially fallacious for similar reasons. A man has witnessed a rapid crime or accident, and carries away his mental image. Later he is fronted by a prisoner whom he forthwith perceives in light of that image, and recognizes or 'identifies' as participant, although he may never have been near that spot. Similarly at the so-called 'materializing seéances which fraudulent mediums give: in a dark room a man sees a gauze-robed figure who in a whisper tells him she is the spirit of his sister, mother, wife, or child, and falls upon is neck. The darkness, the previous forms, and the expectancy have so filled his mind with premonitory images that it is no wonder he perceives what is suggested. These fraudulent 'séances' would furnish most precious documents to the psychology of perception, if they could only satisfactorily inquired into. In the hypnotic trance any suggested object is sensibly perceived. In certain subject happens more or less completely after waking from the trance. It would seem that under favorable conditions somewhat similar susceptibility to suggestion may exit certain persons who are not otherwise entranced at all. This suggestibility is greater in the lower senses than the higher. A German observer writes:
"We know that a weak smell or taste may he very diversely interpreted by us, and that the same sensation will now be named as one thing and the next moment as another. Suppose an agreeable smell of flowers in a room: A visitor will notice it, seek to recognize what it is, [p. 98] and at last perceive more and more distinctly that it is the perfume of roses -- until after all he discovers a bouquet of violets. Then suddenly he recognizes the violet-smell, and wonders how he could possibly have hit upon the roses. -- Just so it is with taste. Try some meat whose visible characteristics are disguised by the mode of cooking, and you will perhaps begin by taking it for venison, and end by being quite certain that it is venison, until you are told that it is mutton; where- upon you get distinctly the mutton flavor. -- In this wise one may make a person taste or smell what one will, if one only makes sure that he shall conceive it beforehand as we wish, by saying to him: 'Doesn't that taste just like, etc.?' or 'Doesn't it smell just like, etc.?' One call cheat whole companies in this way; announce, for instance at a meal, that the meat tastes 'high,' and almost every one who is not animated by a spirit of opposition will discover a flavor of putrescence which in reality is not there at all.
"In the sense of feeling this phenomenon is less prominent, because we get so close to the object that our sensation of it is never incomplete. Still, examples may be adduced from this sense. On superficially feeling of a cloth, one may confidently declare it for velvet, whilst it is perhaps a long-haired cloth; or a person may perhaps not be able to decide whether he has put on woolen or cotton stockings, and, trying to ascertain this by the feeling on the skin of the feet, he may become aware that he gets the feeling of cotton or wool according as he thinks of the one or the other. When the feeling in our fingers is somewhat blunted by cold, we notice many such phenomena, being then more ex- posed to confound objects-of touch with one another." [ 21]
High authorities have doubted this power of imagination to falsify present impressions of sense.  Yet it unquestionably exists. Within the past fortnight I have been annoyed by a smell, faint but unpleasant, in my library. My annoyance began by an escape of gas from the furnace below stairs. This seemed to get lodged in my imagination as a sort of standard of perception; for, several days after the furnace had been rectified, I perceived the 'same smell' again. It was traced this time to a new pair of India rubber shoes which had been brought in from the shop and laid on a table. It persisted in coming to me for several days, however, in spite of the fact that no other member of the family or visitor noticed anything unpleasant. My impression during part of this time was one of uncertainty whether [p. 99] the smell was imaginary or real; and at last it faded out. Everyone must be able to give instances like this from the smell-sense. When we have paid the faithless plumber pretending to mend our drains, the intellect inhibits nose from perceiving the same unaltered odor, until perhaps several days go by. As regards the ventilation heating of rooms, we are apt to feel for some time as we think we ought to feel. If we believe the ventilator is shut, we feel the room close. On discovering it open, the oppression disappears.
An extreme instance is given in the following extract:
"A patient called at my office one day in a state of great excitement from the effects of an offensive odor in the horse-car she had come and which she declared had probably emanated from some very sick person who must have been just carried in it. There could be no doubt that something had affected her seriously, for she was very pale, with nausea, difficulty in breathing, and other evidences of bodily and mental distress. I succeeded, After some difficulty and time, in quieting her, and she left, protesting that the smell was unlike anything she had before experienced and was something dreadful. Leaving my office soon after, it so happened that I found her at the street-corner, waiting for a car: we thus entered the car together. She immediately cal attention to the same sickening odor which she had experienced other car, and began to be affected the same as before, when I pointed out to her that the smell was simply that which always emanates from the straw which has been in stables. She quickly recognized it as the same, when the unpleasant effects which arose while she was possessed with another perception of its character at once passed away." 
It is the same with touch. Everyone must have felt the sensible quality change under his hand, as sudden con tact with something moist or hairy, in the dark, awoke a shock of disgust or fear which faded into calm recognition of some familiar object? Even so small a thing as a crumb of potato on the table-cloth, which we pick up, thinking it a crumb of bread, feels horrible for a few moments to our fancy, and different from what it is.
Weight or muscular feeling is a sensation; yet who heard the anecdote of some one to whom Sir Humphry Davy showed the metal sodium which he had just discovered? "Bless me, how heavy it is!" said the man; [p. 100] showing that his idea of what metals as a, class ought to be had falsified the sensation he derived from a very light substance. In the sense of hearing, similar mistakes abound. I have already mentioned the hallucinatory effect of mental images of very faint sounds, such as distant clock-strokes (above, p. 71). But even when stronger sensations of sound have been present, everyone must recall some experience in which they have altered their acoustic character as soon as the intellect referred them to a different source. The other day a friend was sitting in my room, when the clock, which has a rich low chime, began to strike. "Hollo!" said he, "hear that hand-organ in the garden," and was surprised at finding the real source of the sound. I had myself some years ago a very striking illusion of the sort. Sitting reading late one night, I suddenly heard a most formidable noise proceeding from the upper part of the house, which it seemed to fill. It ceased, and in a moment renewed itself. I went into the hall to listen, but it came no more. Resuming my seat in the room, however, there it was again, low, mighty, alarming, like a rising flood or the avant-courier of an awful gale. It came from all space. Quite startled, I again went into the hall, but it had already ceased once more. On returning a second time to the room, I discovered that it was nothing but the breathing of a little Scotch terrier which lay asleep on the door. The note-worthy thing is that as soon as I recognized what it was, I was compelled to think it a different sound, and could not then hear it as I had heard it a moment before.
In the anecdotes given by Delbœuf and Reid, this was probably also the case, though it is not so stated. Reid says:
" I remember that once lying abed, and having been put into a fright, I heard my own heart beat; but I took it to be one knocking at the door, and arose and opened the door oftener than once, before I discovered that the sound was in my own breast." (Inquiry, chap. Iv. Delbœuf's story is as follows: 'The illustrious P. J. van Beneden, senior, was walking one evening with a friend along a moody hill near Chaudfontaine. 'Don't you [p. 101] ,hear,' said the friend, 'the noise of a hunt on the mountain?' M. van Beneden listens and distinguishes in fact the giving-tongue of the dogs. They listen some time, expecting from one moment to another to see a deer bound by; but the voice of the dogs seems neither to recede nor approach. At last a countryman comes by, and they ask him who it is that can be hunting at this late hour. But he, pointing to some puddles of water near their feet, replies: 'Yonder little animals are what you hear.' And there were in fact a number of toads of the species Bombinator igneus. ... This batrachian emits at the pairing season a silvery or rather crystalline note. ... Sad and pure, it is a voice no wise resembling that of hounds giving chase." 
The sense of sight, as we have seen in studying Space is pregnant with illusions of both the types considered. No sense gives such fluctuating impressions of the s object as sight does. With no sense are we so apt to treat the sensations immediately given as mere signs; with none is the invocation from memory of a thing, and the consequent perception of the latter, so immediate. The' thing' which we perceive always resembles, as we have seen, the object of some absent object of sensation, usually another optical figure which in our mind has come to be the standard of reality; and it is this incessant reduction of our optical objects to more 'real' forms which has led some authors into the mistake of thinking that the sensation which first apprehend them are originally and natively of any form at all. 
Of accidental and occasional illusions of sight amusing examples might be given. Two will suffice. One is a reminiscence of my own. I was lying in my berth steamer listening to the sailors holystone the deck outside; when, on turning my eyes to the window, I perceived perfect distinctness that the chief-engineer of the vessel had entered my state-room, and was standing looking through the window at the men at work upon the guards. Surprised at his intrusion, and also at his intentness and [p. 102] immobility, I remained watching him and wondering how long he would stand thus. At last I spoke; but getting no reply, sat up in my berth, and then saw that what I had taken for the engineer was my own cap and coat hanging on a peg beside the window. The illusion was complete; the engineer was a peculiar-looking mall; and I saw him unmistakably; but after the illusion had vanished I found it hard voluntarily to make the cap and coat look like him at all.
The following story, which I owe to my friend Prof. Hyatt, is of a probably not uncommon class:
"During the winter of 1858, while in Venice, I had the somewhat peculiar illusion which you request me to relate. I remember the circumstances very accurately because I have often repeated the story, and have made an effort to keep all the attendant circumstances clear of exaggeration. I was travelling with my mother, and we had taken rooms at a hotel which had been located in an old palace. The room in which I went to bed was large and lofty. The moon was shining brightly, and I remember standing before a draped window, thinking of the romantic nature of the surroundings, remnants of old stories of knights and ladies, and the possibility that even in that room itself love-scenes and sanguinary tragedies might have taken place. The night was so lovely that many of the people were strolling through the narrow lanes or so-called streets, singing as they went, and I laid awake for some time listening to these patrols of serenaders, and of course finally fell asleep. I became aware that some one was leaning over me closely, and that my own breathing was being interfered with; a decided feeling of an unwelcome presence of some sort awakened me. As I opened my eyes I saw, as distinctly as I ever saw any living person, a draped head about a foot or eighteen inches to the right, and just above my bed. The horror which took possession of my young fancy was beyond anything I have ever experienced. The head was covered by a long black veil which floated out into the moonlight, the face itself was pale and beautiful, and the lower part swathed in the white band commonly worn by the nuns of Catholic orders. My hair seemed to rise up, and a profuse perspiration attested the genuineness of the terror which I felt. For a time I lay in this way, and then gradually gaining more command over my superstitious terrors, concluded to try to grapple with the apparition. It remained perfectly distinct until I reached at it sharply with my hand, and then disappeared, to return again, however, as soon as: I sank back into the pillow. The second or third grasp which I made at the head was not followed by a reappearance, and I then saw that the ghost was not a real presence, but depended upon the position of my head. If I moved my eyes either to the left [p. 103] or right of the original position occupied by my head when I awakened, the ghost disappeared, and by returning to about the same position, I could make it reappear with nearly the same intensity as at first. I presently satisfied myself by these experiments that the illusion arose from the effect of the imagination, aided by the actual figure made by a visual section of the moonbeams shining through the lace curtains of the window. If I had given way to the first terror of the situation and covered up my head, I should probably have believed in the reality of the apparition, since I have not by the slightest word, so far as I know, exaggerated the vividness of my feelings."
At bottom this is only one case (and that the simples case) of the general fact that our nerve-centres are an organ for reacting on sense-impressions, and that our hemisphere in particular, are given us in order that records of our private past experience may co-operate in the reaction. Of course such a general way of stating the fact is vague; and all the those follow the current theory of ideas will be prompt throw this vagueness at it as a reproach. Their way of describing the process goes much more into detail. The sensation they say, awakens 'images' of other sensations associated with it in the past. These images 'fuse,' or are 'combined' by the Ego with the present sensation into a new product, the percept, etc., etc. Something so indistinguishable from this in practical outcome is what really occurs, one may seem fastidious in objecting to such a state, specially if have no rival theory of the elementary processes to propose. And yet, if this notion of images rising and flocking and fusing be mythological (and we have along so considered it), why should we entertain it unless confessedly as a mere figure of speech? As such, of course is convenient and welcome to pass. But if we try to put an exact meaning into it, all we find is that the brain react paths which previous experiences have worn, and make usually perceive the probable thing, i.e., the thing by [p. 104] which on previous occasions the reaction was most frequently aroused. But we can, I think, without danger of being too speculative, be a little more exact than this, and conceive of a physiological reason why the felt quality of an object changes when, instead of being apprehended in a mere sensation, the object is: perceived as a thing. All consciousness seems to depend on a certain slowness of the process in the cortical cells. The rapider currents are, the less feeling they seem to awaken. If a region A, then, be so connected with another region B that every current which enters A immediately drains off into B, we shall not be very strongly conscious of the sort of object that A can make us feel. If B, on the contrary, has no such copious channel of discharge, the excitement will linger there longer ere it diffuses itself elsewhere, and our consciousness of the sort of object that B makes us feel will be strong. Carrying this to an ideal maximum, we may say that if A offer no resistance to the transmission forward of the present, and if the current terminate in B, then, no matter what causes may initiate the current, we shall get no consciousness of the object peculiar to A, but on the contrary a vivid sensation of the object peculiar to B. And this will be true though at other times the connection between A and B might lie less open, and every current then entering A might give us a strong consciousness of A's peculiar object. In other words, just in proportion as associations are habitual, mill the qualities of the suggested thing tend to substitute themselves in consciousness for those of the thing immediately there; or, more briefly, just in proportion as an experience is probable will it tend to be directly felt. In all such experiences the paths lie wide open from the cells first affected to those concerned with the suggested ideas. A circular after-image on the receding wall or ceiling is actually seen as an ellipse, a square after-image of a cross there is seen as slant-legged, etc., because only in the process correlated with the vision of the latter figures do the inward currents find a pause (see the next chapter).
We must remember this when, in dealing with the eye, we come to point oat the erroneousness of the principle laid [p. 105] down by Reid and Helmholtz that true sensations can never be changed by the suggestions of experience.
A certain illusion of which I have not yet spoken affords additional illustration of this. When we will to execute a movement and the movement for some reason does not occur, unless the sensation of the part's NOT moving is a strong one, we are apt to feel as if the movement had actually taken place. This seems habitually to be the case in anæesthesia of the moving parts. Close the patient's eyes, hold his anæesthetic a still, and tell him to raise his hand to his head; and when he opens his eyes he will be astonished to find that movement has not taken place. All reports of anaesthetic cases seem to mention this illusion. Sternberg who wrote on a subject in 1885, lays it down as a law that the intention move is the same thing as the feeling of the motion. We will later see that this is false (Chapter XXV); but it certainly may suggest the feeling of the motion with hallucinatory intensity. Sternberg gives the following experiment, which I find succeeds with at least half of those who it: Rest your palm on the edge of the table with your forefinger hanging over in a position of extreme flexion, and then exert your will to flex it still more. The position the other fingers makes this impossible, and yet if we do not look to see the finger, we think we feel it move. He quotes from Exner a similar experiment with the jaws: Put some hard rubber or other unindentable obstacle between [p. 106] your back teeth and bite hard: you think you feel the jaw move and the front teeth approach each other, though in the nature of things no movement can occur.  -- The visual suggestion of the path traversed by the finger-tip as the locus of the movement-feeling in the joint, which we discussed on page 41, is another example of this semi-hallucinatory power of the suggested thing. Amputated people, as we have learned, still feel their lost feet, etc. This is a necessary consequence of the law of specific energies, for if the central region correlated with the foot give rise to any feeling at all it must give rise to the feeling of a foot.  But the curious thing is that many of these patients can will the foot to move, and when they have done so, distinctly feel the movement to occur. They can, to use their own language, 'work' or 'wiggle' their lost toes. 
Now in all these various cases we are dealing with data which in normal life are inseparably joined. Of all possible experiences, it is hard to imagine any pair more uniformly and incessantly coupled than the volition to move, on the one hand, and the feeling of the changed position of the parts, on the other. From the earliest ancestors of ours which had feet, down to the present day, the movement of the feet must always have accompanied the will to move them; and here, if anywhere, habit's consequences ought to be found.  The process of the willing ought, then, to pour into the process of feeling the command effected, and ought to awaken that feeling in a maximal degree provided no other positively contradictory sensation come in at the same time. In most of us, when the will fails of its effect there is a, contradictory sensation. We discern a resistance or the unchanged position of the limb. But neither in anæsthesia nor in amputation can there be any contradictory sensation in the foot to correct us; so imagination has all the force of fact. [p. 107]
Professor H. Steinthal has analyzed apperceptive processes with a, sort of detail which is simply burdensome.  [p. 108] His introduction of the matter may, however, be quoted. He begins with an anecdote from a comic paper.
"In the compartment of a railway-carriage six persons unknown to each other sit in lively conversation. It becomes a matter of regret that one of the company must alight at the next station. One of the others says that he of all things prefers such a meeting with entirely unknown persons, and that on such occasions he is accustomed neither to ask who or what his companions may be nor to tell who or what he is. Another thereupon says that he will undertake to decide this question, if they each and all will answer him an entirely disconnected question. They began. He drew five leaves from his note-book, wrote a question on each, and gave one to each of his companions with the request that he write the answer below. When the leaves were returned to him, he turned, after reading them, without hesitation to the others, and said to the first, 'You are a man of science'; to the second, 'You are a soldier'; to the third, 'You are a philologer'; to the fourth, 'You are a journalist'; to the fifth, 'You are a farmer.' All admitted that he was right, whereupon he got out and left the five behind. Each wished to know what question the others had received; and behold, he had given the same question to each. It ran thus:
"What being destroys what it has itself brought forth?
"To this the naturalist had answered, 'natural force'; the soldier, 'war'; the philologist, 'Kronos'; the publicist, 'revolution'; the farmer, 'a boar'. This anecdote, methinks, if not true, is at least splendidly well invented. Its narrator makes the journalist go on to say : 'Therein consists the joke. Each one answers the first thing that occurs to him,  and that is whatever is most newly related to his pursuit in life. Every question is a hole-drilling experiment, and the answer is an opening through which one sees into our interiors.' ... So do we all. We are all able to recognize the clergyman, the soldier, the scholar, the business man, not only by the cut of their garments and the attitude of their body, but by what they say and how they express it. We guess the place in life of men by the interest which they show and the way in which they show it, by the objects of which they speak, by the point of view from which they regard things, judge them, conceive them, in short by their mode of apperceiving. ...
"Every man has one group of ideas which relate to his own person and interests, and another which is connected with society. Each has his group of ideas about plants, religion, law, art, etc., and more especially about the rose, epic poetry, sermons, free trade, and the like. Thus the mental content of every individual, even of the uneducated [p. 109] and of children, consists of masses or circles of knowledge of which each lies within some larger circle, alongside of others similarly included, and of which each includes smaller circles within itself. ... The perception of a thing like a horse ... is a process between the present horse's picture before our eyes, on the one hand, and those fused or interwoven pictures and ideas of all the horses we have ever seen, on the other; ... a process between two factors or momenta, of which one existed before the process and was an old possession of the mind (the group of ideas, or concept, namely), whilst the other is but just presented to the mind, and is the immediately supervening factor (the sense-impression). The former apperceives the latter; the latter is apperceived by the former. Out of their combination an apperception- product arises: the knowledge of the perceived being as a horse. The earlier factor is relatively to the later one active and a prori; the supervening factor is given, a posteriori, factor passive. ... We may then define Apperception as the movement of two masses of consciousness (Vorstellungsmassen) against each other so as to produce a cognition.
"The a priori factor we called active, the a posteriori factor passive, but this is only relatively true. ... Although the a priori moment commonly shows itself to be the more powerful, apperception-processes can perfectly well occur in which the new observation transforms or en- riches the apperceiving group of ideas. A child who hitherto has seen - none but four-cornered tables apperceives a round one as a table; but by this the apperceiving mass ('table') is enriched. To his previous knowledge of tables comes this new feature that they need not be four- cornered, but may be round. In the history of science it has happened often enough that some discovery, at the same time that it was apperceived, i.e. brought into connection with the system of our knowledge, transformed the whole system. In principle, however, we must maintain that, although either factor is both active and passive, the a priori factor is almost always the more active of the two." 
This account of Steinthal's brings out very clearly the difference between our psychological conceptions and what are called concepts in logic. In logic a concept is unalterable; but what are popularly called our 'conceptions of things' alter by being used. The aim of 'Science' is to attain conceptions so adequate and exact that we shall never need to change them. There is an everlasting struggle in every mind between the tendency to keep unchanged, and the tendency to renovate, its ideas. Our education is a cease-less compromise between the conservative and the progressive factors. Every new experience must be disposed [p.110] of under some old head. The great point is to find the head which has to be least altered to take it in. Certain Polynesian natives, seeing horses for the first time, called them pigs, that being the nearest head. My child of two played for a week with the first orange that was given him, calling it a 'ball.' He called the first whole eggs he saw 'potatoes' having been accustomed to see his 'eggs' broken into a glass, and his potatoes without the skin. A folding pocket-corkscrew he unhesitatingly called 'bad-scissors.' Hardly any one of us can make new heads easily when fresh experiences come. Most of us grow more and more enslaved to the stock conceptions with which we have once become familiar, and less and less capable of assimilating impressions in any but the old ways. Old-fogyism, in short, is the inevitable terminus to which life sweeps us on. Objects which violate our established habits of 'apperception' are simply not taken account of at all; or, if on some occasion we are forced by dint of argument to admit their existence, twenty-four hours later the admission is as if it were not, and every trace of the unassimilable truth has vanished from our thought. Genius, in truth, means little more than the faculty of perceiving in an unhabitual way.
On the other hand, nothing is more congenial, from babyhood to the end of life, than to be able to assimilate the new to the old, to meet each threatening violator or burster of our well-known series of concepts, as it comes in, see through its unwontedness, and ticket it off as an old friend in disguise. This victorious assimilation of the new is in fact the type of all intellectual pleasure. The lust for it is curiosity. The relation of the new to the old, before the assimilation is performed, is wonder. We feel neither curiosity nor wonder concerning things so far beyond us that we have no concepts to refer them to or standards by which to measure them. The Fuegians, in Darwin's voy- [p. 111] age, wondered at the small boats, but took the big ship as a 'matter of course.' Only what we partly know already inspires us with a desire to know more. The more elaborate textile fabrics, the vaster works in metal, to most of us are like the air, the water, and the ground, absolute existences which awaken no ideas. It is a matter of course that an engraving or a copper-plate inscription should possess that degree of beauty. But if we are shown a pen-drawing of equal perfection, our personal sympathy with the difficulty of the task makes us immediately wonder at the skill. The old lady admiring the Academician's picture, says to him: "And is it really all done by hand?"
IS PERCEPTION UNCONSCIOUS INFERENCE?
A widely-spread opinion (which has been held by such men as Schopenhauer, Spencer, Hartmann, Wundt, Helmholtz, and lately interestingly pleaded for by M. Binet ) will have it that perception should be called a sort of reasoning operation, more or less unconsciously and automatically performed. The question seems at first a verbal one, depending on how broadly the term reasoning is to be taken. If, every time a present sign suggests an absent reality to our mind, we make an inference; and if every time we make an inference we reason ; then perception is indubitably reasoning. Only one sees no room in it for any unconscious part. Both associates, the present sign and the contiguous things which it suggests, are above-board, and no intermediary [p. 112] ideas are required. Most of those who have upheld the thesis in question have, however, made a more complex supposition. What they have meant is that perception is a mediate inference, end that the middle term is unconscious. When the sensation which I have called' this ' (p. 83, supra) is felt, they think that some process like the following runs through the mind:
'This' is M;
but M is A;
therefore 'this' is A 
Now there seem no good grounds for supposing this additional wheel work in the mind. The classification of 'this' as M is itself an act of perception, and should, if all perception were inference, require a still earlier syllogism for its performance, and so backwards in infinitum. The only extrication from this coil would be to represent the process in altered guise, thus:
'This' is like those;
Those are A;
Therefore 'this' is A.
The major premise here involves no association by contiguity, no naming of those as M, but only a suggestion of unnamed similar images, a recall of analogous past sensations with which the characters that make up A were habitually conjoined. But here again, what grounds of fact are there for admitting this recall? We are quite unconscious of any such images of the past. And the conception of all the forms of association as resultants of the elementary fact of habit-worn paths in the brain makes such images entirely superfluous for explaining the phenomena in point. Since the brain-process of 'this,' the sign of A, has repeatedly been aroused in company with the process of the full object A, direct paths of irradiation from the one to the other must be already established. And although roundabout paths may also be possible, as from 'this' to 'those,' and then [p. 113] from 'those' to 'A' (paths which would lead to practically the same conclusion as the straighter ones), yet there is no ground whatever for assuming them to be traversed now, especially since appearances point the other way. In explicit reasoning, such paths are doubtless traversed in perception they are in all probability closed. So far, then, from perception being a species of reasoning properly so called, both it and reasoning are co-ordinate varieties of that deeper sort of process known psychologically as the association of ideas, and physiologically as the law of habit in the brain. To call perception unconscious reasoning is thus either a useless metaphor, or a positively misleading confusion between two different things.
One more point and we may leave the subject of Perception. Sir Wm. Hamilton thought that he had discovered a 'great law' which had been wholly overlooked by psychologists, and which, 'simple and universal,' is this: "Knowledge and Feeling, -- Perception end Sensation, though always coexistent, are always in the inverse ratio of each other." Hamilton wrote as if perception and sensation were two coexistent elements entering into a single state of consciousness. Spencer refines upon him by contending that they are two mutually exclusive states of consciousness, not two elements of a single state. If sensation be taken, as both Hamilton and Spencer mainly take it in this discussion, to mean the feeling of pleasure or pain, there is no doubt that the law, however expressed, is true; and that the mind which is strongly conscious of the pleasantness or painfulness of an experience is ipso facto less fitted to observe and analyze its outward cause.  Apart from pleasure and pain, however, the law seems but a corollary of the fact that the more concentrated a state of consciousness is, the more vivid it is. When feeling a color, or listening to a tone per se, we get it more intensely, notice it better, than when we are aware of it merely as one among many other properties of a total object. The more diffused cerebral excitement of the perceptive state is probably incompatible [p. 114] with quite as strong an excitement of separate parts as the sensational state comports, So we come back here to our own earlier discrimination between the perceptive and the sensational processes, and to the examples which we gave on pp, 80, 81 
"In carelessly questioning a patient we may confound his pseudo-hallucinatory perceptions with hallucinations. But to the unconfused consciousness of the patient himself, even though he be imbecile, the identification of the two phenomena is impossible, at least in the sphere of vision. At the moment of having a pseudo-hallucination of sight, the patient feels himself in an entirely different relation to this subjective sensible appearance, from that in which he finds himself whilst subject to a true visual hallucination. The latter is reality itself; the former, on the contrary, remains always a subjective phenomenon which the individual commonly regards either as sent to him as a sign of God's grace, or as artificially induced by his secret persecutors ... If he knows by his own experience what a genuine hallucination is, it is quite impossible for him to mistake the pseudo-hallucination for it. ... A concrete example will make the difference clear:
"Dr. N. L....heard one day suddenly amongst the voices of his persecutors ('coming from a hollow space in the midst of the wall') a rather loud voice impressively saying to him: 'Change your national allegiance.' Understanding this to mean that his only hope consisted in ceasing to be subject to the Czar of Russia, he reflected a moment what allegiance would be better, and resolved to become an English subject. At the same moment he saw a pseudo-hallucinatory lion of natural size, which appeared and quickly laid its fore-paws on his shoulders. He had a lively feeling of these paws as a tolerably painful local pressure (complete hallucination of touch). Then the same voice from the wall said: 'Now you have a lion -- now you will rule,' whereupon the patient recollected that the lion was the national emblem of England. The lion appeared to L. very distinct and vivid, but he nevertheless remained conscious, as he afterwards expressed it, that he saw the animal, not with his bodily but with his mental eyes. (After his recovery he called analogous apparitions by the name of 'expressive-plastic ideas.') Accordingly he felt no terror, even though he felt the contact of the claws. ... Had the lion been a complete hallucination, the patient, as he himself remarked after recovery would have felt great fear, and very likely screamed or taken to flight. Had it been a simple image of the fancy he would not have connected it with the voices, of whose objective reality he was at the time quite convinced." 
From ordinary images of memory and fancy, pseudo-hallucinations differ in being much more vivid, minute, de- [p. 117] tailed, steady, abrupt, and spontaneous, in the sense that all feeling of our own activity in producing them is lacking. Dr. Kandinsky had a patient who, after taking opium or haschisch, had abundant pseudo-hallucinations and hallucinations. As he also had strong visualizing power and was an educated physician, the three sorts of phenomena could be easily compared. Although projected outwards (usually not farther than the limit of distinctest vision, a foot or so) the pseudo-hallucinations lacked the character of objective reality which the hallucinations possessed, but, unlike the pictures of imagination, it was almost impossible to produce them at will, most of the 'voices' which people hear (whether they give rise to delusions or not) are pseudo-hallucinations. They are described as 'inner' voices, although their character is entirely unlike the inner speech of the subject with himself. I know two persons who hear such inner voices making unforeseen remarks whenever they grow quiet and listen for them. They are a very common incident of delusional insanity, and at last grow into vivid hallucinations. The latter are comparatively frequent occurrences in sporadic form; end certain individuals are liable to have them often. From the results of the 'Census of Hallucinations,' which was begun by Edmund Gurney, it would appear that, roughly speaking, one person at least in every ten is likely to have had a vivid hallucination at some time in his life.  The following cases from healthy people will give an idea of what these hallucinations are:
"When a girl of eighteen, I was one evening engaged in a very painful discussion with an elderly person. My distress was so great that I took up a thick ivory knitting-needle that was lying on the mantelpiece of the parlor and broke it into small pieces as I talked. In the midst of the discussion I was very wishful to know the opinion of a brother with whom I had an unusually close relationship. I turned round and saw him sitting at the further side of a centre-table, with his arms folded (an unusual position with him), but, to my dismay, I per- [p. 118] ceived from the sarcastic expression of his mouth that he was not in sympathy with me, was not 'taking my side,' as I should then have expressed it. The surprise cooled me, and the discussion was dropped.
"Some minutes after, baring occasion to speak to my brother, I turned towards him, but he was gone. I inquired when he left the room, and was told that he had not been in it, which I did not believe, thinking that he had come in for a minute and had gone out without being noticed. About an hour and a half afterwards he appeared, and convinced me, with some trouble, that he had never been near the house that evening. He is still alive and well."
Here is another case:
"One night in March 1873 or '74, I cannot recollect which year, I was attending on the sick-bed of my mother. About eight o'clock in the evening I went into the dining room to fix a cup of tea, and on turning from the sideboard to the table, on the other side of the table before the fire, which was burning brightly, as was also the gas, I saw standing with his hand clasped to his side in true military fashion a soldier of about thirty years of age, with dark, piercing eyes looking directly into mine. He wore a small cap with standing feather; his costume was also of a soldierly style. He did not strike me as being a spirit, ghost, or anything uncanny, only a living man; but after gazing for fully a minute I realized that it was nothing of earth, for he neither moved his eyes nor his body, and in looking closely I could see the fire beyond. I was of course startled, and yet did not run out of the room. I felt stunned. I walked out rapidly, however, and turning to the servant in the hall asked her if she saw anything. She said not. I went into my mother's room and remained talking for about an hour, but never mentioned the above subject for fear of exciting her, and finally forgot it altogether, returning to the dining-room, still in forgetfulness of what had occurred, but repeating, as above, the turning from sideboard to table in act of preparing more tea. I looked casually towards the fire, and there I saw the soldier again. This time I was entirely alarmed, and fled from the room in haste. I called to my father, but when he came he saw nothing."
Sometimes more than one sense is affected. The following is a case:
"In response to your request to write out my experience of Oct. 30, 1888, I will inflict on you a letter.
"On the day above mentioned, Oct. 30, 1888, I was in -------, where I was teaching. I had performed my regular routine work for the day, and was sitting in my room working out trigonometrical for- [p. 119] mulae. I was expecting every day to hear of the confinement of my wife, and naturally my thoughts for some time had been more or less with her. She was, by the way, in B ----, some fifty miles from me.
"At the time, however, neither she nor the expected event was in my mind; as I said, I was working out trigonometrical formulæ, and I had been working on trigonometry the entire evening. About eleven o'clock, as I sat there buried in sines, cosines, tangents, cotangents, secants, and cosecants, I felt very distinctly upon my left shoulder a touch, and a slight shake, as if somebody had tried to attract my attention by other means and had failed. Without rising I raised my head, and there between me and the door stood my wife, dressed exactly as I last saw her, some five weeks before. As I turned she said: 'It is a little Herman; he has come.' Something more was said, but this is the only sentence I can recall. To make sure that I was not asleep and dreaming, I rose from the chair, pinched myself and walked toward the figure, which disappeared immediately as I rose. I can give no information as to the length of time occupied by this episode, but I know I was awake, in my usual good health. The touch was very distinct, the figure was absolutely perfect, stood about three feet from the door. which was closed, and had not been opened during the evening. The sound of the voice was unmistakable, and I should have recognized it as my wife's voice even if I had not turned and had not seen the figure at all. The tone was conversational, just as if she would have said the same words had she been actually standing there.
"In regard to myself, I would say, as I have already intimated, I was in my usual good health; I had not been sick before, nor was I after the occurrence, not so much as a headache having afflicted me.
"Shortly after the experience above described, I retired for the night and, as I usually do, slept quietly until morning. I did not speculate particularly about the strange appearance of the night before, and though I thought of it some, I did not tell anybody. The following morning I rose, not conscious of having dreamed anything, but I was very firmly impressed with the idea that there was something for me at the telegraph-office. I tried to throw off the impression, for so far as I knew there was no reason for it. Having nothing to do, I went out for a walk; and to help throw off the impression above noted, I walked away from the telegraph-office. As I proceeded, however, the impression became a conviction, and I actually turned about and went to the very place I had resolved not to visit, the telegraph-office. The first person I saw on arriving at said office was the telegraph-operator, who being on terms of intimacy with me, remarked: 'Hello, papa, I've got a telegram for you.' The telegram announced the birth of a boy, weighing nine pounds, and that all were doing well. Now, then, I have no theory at all about the events narrated above; I never had any such experience before nor since; I am no believer in spiritualism, am not in the least superstitious, know very little about ' thought-transference,' [p. 120] 'unconscious cerebration;' etc., etc., but I am absolutely certain about what I have tried to relate.
"In regard to the remark which I heard, 'It is a little Herman,' etc., I would add that we had previously decided to call the child, if a boy, Herman -- my own name, by the way." 
The hallucination sometimes carries a change of the general consciousness with it, so as to appear more like a sudden lapse into a dream. The following case was given me by a man of 43, who bad never anything resembling it before:
"While sitting at my desk this A. M. reading a circular of the Loyal Legion a very curious thing happened to me, such as I have never experienced. It was perfectly real, so real that it took some minutes to recover from. It seems to me like a direct intromission into some other world. I never had anything approaching it before sale when dreaming at night. I was wide awake, of course. But this was the feeling. I had only just sat down and become interested in the circular, when I seemed to love myself for a minute and then found myself in the top story of a high building very white and shining and clean, with a noble window immediately at the right of where I sat. Through this window I looked out upon a marvellous reach of landscape entirely new. I never had before such a sense of infinity in nature, such superb stretches of light and color and cleanness. I know that for the space of three minutes I was entirely lost, for when I began to come to, so to speak, -- sitting in that other world, I debated for three or four minutes more as to which was dream and which was reality. Sitting there I forgot a faint sense of C.... [the town in which the writer was] , away off and dim at first. Then I remember thinking 'Why, I used to live in C....; perhaps I am going back.' Slowly C.... did come back, and I found myself at my desk again. For a few minutes the process of determining where I was was very funny. But the whole experience was perfectly delightful, there was such a sense of brilliancy and clearness and lightness about it. I suppose it lasted in all about seven minutes or ten minutes."
The hallucinations of fever-delirium are a mixture of pseudo-hallucination, true hallucination, and illusion. Those of opium, hasheesh, and belladonna resemble them [p. 121] in this respect. The following vivid account of a fit of hasheesh-delirium has been given me by a friend:
"I was reading a newspaper, and the indication of the approaching delirium was an inability to keep my mind fixed on the narrative. Directly I lay down upon a sofa there appeared before my eyes several rows of human hands, which oscillated for a moment, revolved and then changed to spoons. The same motions were repeated, the objects changing to wheels, tin soldiers, lamp-posts, brooms, and countless other absurdities. This stage lasted about ten minutes, and during that time it is safe to say that I saw at least a thousand different objects. These whirling images did not appear like the realities of life, but had the character of the secondary images seen in the eye after looking at some brightly-illuminated object. A mere suggestion from the person who was with me in the room was sufficient to call up an image of the thing suggested, while without suggestion there appeared all the common objects of life and many unreal monstrosities, which it is absolutely impossible to describe, and which seemed to be creations of the brain.
"The character of the symptoms changed rapidly. A sort of wave seemed to pass over me, and I became aware of the fact that my pulse was beating rapidly. I took out my watch, and by exercising considerable will-power managed to time the heart-beats, 135 to the minute.
"I could feel each pulsation through my whole system, and a curious twitching commenced, which no effort of the mind could stop.
"There were moments of apparent lucidity, when it seemed as if I could see within myself, and watch the pumping of my heart. A strange fear came over me, a certainty that I should never recover from the effects of the opiate, which was as quickly followed by a feeling of great interest in the experiment, a certainty that the experience was the most novel and exciting that I had ever been through.
"My mind was in an exceedingly impressionable state. Any place thought of or suggested appeared with all the distinctness of the reality. I thought of the Giant's Causeway in Staffa, and instantly I stood within the portals of Fingal's Cave. Great basaltic columns rose on all aides, while huge wares rolled through the chasm and broke in silence upon the rocky shore. Suddenly there was a roar and blast of sound, and the word 'Ishmaral' was echoing up the cave. At the enunciation of this remarkable word the great columns of basalt changed into Whirling clothes pins and I laughed aloud at the absurdity. "(I may here state that the word 'Ishmaral' seemed to haunt my other hallucinations, for I remember that I heard it frequently there after.) I next enjoyed a sort of metempsychosis. Any animal or thing that I thought of could be made the being which held my mind. I thought of a fox, and instantly I was transformed into that animal. I could distinctly feel myself a fox, could see my long ears and bushy [p. 122] tail, and by a sort of introvision felt that my complete anatomy was that of a fox. Suddenly the point of vision changed. My eyes seemed to be located at the back of my mouth; I looked out between the parted lips, saw the two rows of pointed teeth, and, closing my mouth with a snap, saw --nothing.
"I was next transformed into a bombshell, felt my size, weight, and thickness, and experienced the sensation of being shot up out of a giant mortar, looking down upon the earth, bursting and falling back in a shower of iron fragments.
"Into countless other objects was I transformed, many of them so absurd that I am unable to conceive what suggested them. For example, I was a little china doll, deep down in a bottle of olive oil, next moment a stick of twisted candy, then a skeleton inclosed in a whirling coffin, and so on ad infinitum.
"Towards the end of the delirium the whirling images appeared again, and I was haunted by a singular creation of the brain, which reappeared every few moments. It was an image of a double-faced doll, with a cylindrical body running down to a point like a peg-top. It was always the same, having a sort of crown on its head, and painted in two colors, green and brown, on a background of blue. The expression of the Janus-like profiles was always the same, as were the adornments of the body. After recovering from the effects of the drug I could not picture to myself exactly how this singular monstrosity appeared, but in subsequent experiences I was always visited by this phantom, and always recognized every detail of its composition. It was like visiting some long-forgotten spot and seeing some sight that had faded from the memory, but which appeared perfectly familiar as soon as looked upon.
"The effects of the drug lasted about an hour and a half, leaving me a trifle
tipsy and dizzy; but after a ten-hour sleep I was myself again, save for a slight
inability to keep my mind fixed on any piece of work for any length of time,
which remained with me during most of the next day."
THE NEURAL PROCESS IN HALLUCINATION.
Examples of these singular perversions of perception might be multiplied indefinately, but I have no more space. Let us turn to the question of what the physiological process may be to which they are due. It must, of course, consist of an excitement from within of those centres which are active in normal perception, identical in kind and degree with that which real external objects are usually needed to induce. The particular process which cur- [p. 123] rents from the sense-organs arouse would seem under normal circumstances to be arousable in no other way. On p. 72 if. above, we saw that the centres aroused by incoming peripheral currents are probably identical with the centres used in mere imagination; and that the vividness of the sensational kind of consciousness is probably correlated with a discrete degree of intensity in the processes therein aroused. Referring the reader back to that pal sage and to what was more lately said on p. 103 ff., I no proceed to complete my theory of the perceptive process by an analysis of what may most probably be believed take place in hallucination strictly so called.
We have seen (p. 75) that the free discharge of into each other through associative paths is a likely reason why the maximum intensity of function is not reached when the cells are excited by their neighbors in the cortex. At the end of Chapter XXV we shall return to this conception, and whilst making it still more precise, use it for explaining certain phenomena connected with the will. The idea is that the leakage forward along these paths is too rapid for the inner tension in any centre to accumulate the maximal explosion-point, unless the exciting currents are greater than those which the various portions of cortex supply to each other. Currents from the periphery are (as it seems) the only currents whose energy can vanquish the supra-ideational resistance (so to call it) of the cells, and cause the peculiarly intense sort of disintegration with which the sensational quality is linked. If, however, the leakage forward were to stop, the tension inside certain cells might reach the explosion-point, even though the influence which excited them came only from neighboring cortical parts. Let an empty pail with a leak in its bottom, tipped up against a support so that if it ever became full of water it would upset, represent the resting condition of the centre for a certain sort of feeling. Let water poured into it stand for the currents which are its natural stimulus then the hole in its bottom will, of course, represent the 'paths' by which it transmits its excitement to other associated cells. Now let two other vessels have the fun [p. 124] of supplying it with water. One of these vessels stands any more water than goes out by the leak. The pail consequently never upsets in consequence of the supply from this source. A current of water passes through it and does work elsewhere, but in the pail itself nothing but what stands for ideational activity is aroused. The vessel, however, stands for the peripheral sense-organ, and supplies a stream of water so copious that the pail promptly fills up in spite of the leak, and presently upsets; in other words sensational activity is aroused. But it is obvious that if the leak were plugged, the slower stream of supply would also end by upsetting the pail.
To apply this to the brain and to thought, if we take a series of processes A B CD E, associated together in that order, and suppose that the current through them is very fluent there will be little intensity anywhere until, perhaps, a pause occurs at E. But the moment the current is, blocked "anywhere, say between C and D, the process in C must grow more intense, and might even be conceived to explode so as to produce a sensation in the mind instead of an idea. It would seem that some hallucinations are best to be explained in this way. We have in fact a regular series of facts which can all be formulated under the single law that the substantive strength of a state of consciousness bears an inverse proportion to its suggestiveness. It is the halting-places of our thought which are occupied with distinct imagery. Most of the words we utter have no time to awaken images at all; they simply awaken the following words. But when the sentence stops, an image dwells for awhile before the mental eye (see Vol. I. p, 243). Again, whenever the associative processes are reduced and impeded by the approach of unconsciousness, as in falling asleep, or growing faint, or becoming narcotized, we find a concomitant increase in the intensity of whatever partial consciousness may survive. In some people what M. Maury has called 'hypnagogic'  hallucinations are the regular concomitant of the process of [p. 125]. falling asleep. Trains of faces, landscapes, etc., pass before the mental eye, first as fancies, then as pseudo-hallucinations, finally as full-hedged hallucinations forming dreams. If we regard association-paths as paths of drainage, then the shutting off of one after another of them as the encroaching cerebral paralysis advances ought to act like the plugging of the hole in the bottom of the pail, and make the activity more intense in those systems of cells that retain an activity at all. The level rises because the currents are not drained away, until at last the full sensational explosion may occur.
The usual explanation of hypnagogic hallucinations that they are ideas deprived of their ordinary reductives. In somnolescence, sensations being extinct, the mind, it is said, then having no stronger things to compare its ideas with ascribes to these the fulness of reality. At ordinary times the objects of our imagination are reduced to the status subjective facts by the ever-present contrast of our sensations with them. Eliminate the sensations, however, this view supposes, and the 'images' are forthwith 'projected' into the outer world and appear as realities, Thus is the illusion of dreams also explained. This, indeed, after fashion gives an account of the facts.  And yet it certainly fails to explain the extraordinary vivacity and completeness of so many of our dreams-fantasms. The process of 'imagining' must (in these cases at least ) be not merely relatively, but absolutely and in itself more intense than at other times. The fact is, it is not a process of imaging, but genuine sensational process; and the theory in question therefore false as far as that point is concerned.
Dr. Hughlings Jackson's explanation of the epileptic seizure is acknowledged to be masterly. It involves [p. 126] principles exactly like those which I am bringing forward here. The 'loss of consciousness' in epilepsy is due to the most highly organized brain-processes being exhausted and thrown out of gear. The less organized (more instinctive) processes, ordinarily inhibited by the others, are then exalted, so that we get as a mere consequence of relief from the inhibition, the meaningless or maniacal action which so often follows the attack. 
Similarly the subsultus tendinorum or jerking of the muscles which so often startles us when we are on the point [p. 127] of falling asleep, may be interpreted as due to the rise (in certain lower motor centres) of the ordinary 'tonic' tension to the explosion-point, when the inhibition commonly exerted by the higher centres falls too suddenly away.
One possible condition of hallucination then stands revealed, whatever other conditions there may be. When the normal paths of association between a centre and other centres are thrown out of gear, any activity which may exist in the first centre tends to increase in intensity until finally the point may be reached at which the last inward resistance is overcome, and the full sensational process explodes.  Thus it will happen that causes of an amount of activity in brain-cells which would ordinarily result in a weak consciousness may produce a very strong consciousness when the overflow of these cells is stopped by the torpor of the rest of the brain. A slight peripheral irritation, then, if it reaches the centres of consciousness at all during sleep, will give rise to the dream of a violent sensation. All the books about dreaming are full of anecdotes which illustrate this. For example, M, Maury's nose and lips are tickled with a feather while he sleeps. He dreams he is being tortured by having a pitch-plaster applied to his face, torn off, lacerating the skin of nose and lips. Descartes, on being bitten by a flea, dreams of being run through by a sword. A friend tells me, as I write this, of his hair changing its position in his forehead just as he 'dozed off' in his chair a few days since. Instantly he dreamed that some one had struck him a blow. Examples can be quoted ad libitum, but these are enough.  [p. 128]
We seem herewith to have an explanation for a certain number of hallucinations. Whenever the normal forward irradiation of intra-cortical excitement through association-paths is checked, any accidental spontaneous activity or ally peripheral stimulation (however inadequate at other times) by which a brain- centre may be visited, sets up a process off full sensational intensity therein.
In the hallucinations artificially produced in hypnotic subjects, some degree of peripheral excitement seems usually to be required. The brain is asleep as far as its own spontaneous thinking goes, and the words of the 'magnetizer' then awaken a cortical process which drafts off into itself any currents of a related sort which may come in from the periphery, resulting in a vivid objective perception of the suggested thing. Thus, point to a dot on a sheet of paper, and call it 'General Grant's photograph,' and your subject will see a photograph of the General there instead of the dot. The dot gives objectivity to the appearance, and the suggested notion of the General gives it form. Then magnify the dot by a lens; double it by a, prism or by nudging the eyeball; reflect it in a mirror; turn it upside down; or wipe it out; and the subject will tell you that the 'photograph' has been enlarged, doubled, reflected, turned about, or made to disappear. In M. Binet's language,  the dot is the outward point de repère which is needed to give objectivity to your suggestion, and without which the latter will only produce a conception in the subject's mind.  M. Binet has shown that such a periphe- [p. 129]. ral point de repère is used in an enormous number, not only of hypnotic hallucinations, but of hallucinations of the insane. These latter are often unilateral; that is, the patient bears the voices always on one side of him, or sees the figure only when a certain one of his eyes is open. In many of these cases if has been distinctly proved that a morbid irritation in the internal ear, or an opacity in the humors of the eye, was the starting point of the current which the patient's diseased acoustic or optical centres clothed with their peculiar products in the way of ideas. Hallucinations produced in this way are 'ILLUSIONS'; and M. Binet's theory, that all Hallucinations must start in the periphery, may be called an attempt to reduce hallucination and illusion to one physiological type, the type, namely, to which normal perception belongs. In every case, according to M. Binet, whether of perception, of hallucination, or of illusion, we get the sensational vividness by means of a current from the peripheral nerves. It may be a mere trace of a current. But that trace is enough to kindle the maximal or supra ideational process so that the object perceived will have the character of externality. What the nature of the object shall be will depend wholly on the particular system of paths in which the process is kindled. Part of the thing in all cases comes from the sense-organ, the rest is furnished by the mind. But we cannot by introspection distinguish between these parts; and our only formula for the result is that the brain has reacted on the impression in the normal way. Just so in the dreams which we have considered, and in the hallucinations of which M. Binet tells, we can only say that the brain has reacted in an abnormal way.
Binet's theory accounts indeed for a multitude of casts, but certainly not for all. The prism does not always double [p. 130] the false appearance, nor does the latter always disappear when the eyes are closed. Dr. Hack Tuke  gives several examples in sane people of well-exteriorized hallucinations which could not respond to Binet's tests; and Mr. Edmund Gurney  gives a number of reasons why intensity in a cortical process may be expected to result from local pathological activities just as much as its peculiar nature does. For Binet, an abnormally exclusively active part of the cortex gives the nature of what shall appear, whilst a peripheral sense-organ alone can give the intensity sufficient to make it appear projected into real space. But since this intensity is after all but a matter of degree, one does not see why, under rare conditions, the degree in question might not be attained by inner causes exclusively. In that case we should have certain hallucinations centrally initiated alongside of the peripherally initiated hallucinations, which are the only sort that M. Binet's theory allows. It seems plausable on the whole, therefore, that centrally initiated hallucinations can exist. How often they do exist is another question. The existence of hallucinations which affect more than one sense is an argument for central initiation. For grant that the thing seen may have its starting point in the outer world, the voice which it is heard to utter must be due to an influence from the visual region, i.e. must be of central origin.
Sporadic cases of hallucination, visiting people only once in a lifetime (which seem to be by far the most frequent type), are on any theory hard to understand in detail. They are often extraordinarily complete; and the fact that many of them are reported as veridical, that is, as coinciding with real events, such as accidents, deaths, etc., of the persons seen, is an additional complication of the phenomenon. The first really scientific study of hallucination [p. 131] in all its possible bearings, on the basis of a large mass of empirical material, was begun by Mr. Edmund Gurney and is continued by other members of the Society for Psychical Research; and the 'Census' is now being applied to several countries under the auspices of the International Congress of Experimental Psychology. It is to be hoped that out of these combined labors something solid will eventually grow. The facts shade off into the phenomena of motor automatism, trance, etc.; and nothing but a wide comparative study can give really instructive results. 
The part played by the peripheral sense-organ in hallucination is just as obscure as we found it in the case of imagination. The things seen often seem opaque and hide the background upon which they are projected. It does not follow from this, however, that the retina is actually involved in the vision. A contrary process going on in the visual centres would prevent the retinal impression made by the outer realities from being felt, and this would in mental terms be equivalent to the hiding of them by the imaginary figure. The negative after-images of mental pictures reported by Meyer and Féré, and the negative after-images of hypnotic hallucinations reported by Binet and others so far constitute the only evidence there is for the retina being involved. But until these after-images a explained in some other way we must admit the possibility of a centrifugal current from the optical centres downwards into the peripheral organ of sight, paradoxical as the co of such a current may appear.
The time which the perceptive process occupies has been inquired into by various experimenters. Some call it perception-time, some choice-time, some discrimination-time. The results have been already given in Chapter XIII (vol., p. 623 ff.), to which the reader is consequently referred. [p. 132] Dr. Romanes gives an interesting variation of these time-measurements. He found 
"an astonishing difference between different individuals with respect to the rate at which they are able to read. Of course reading implies enormously intricate processes of perception both of the sensuous and of the intellectual order; but if we choose for these observations persons who have been accustomed to read much, we may consider that they are all very much on a par with respect to the amount of practice which they have had, so that the differences in their rates of reading may fairly be attributed to real differences in their rates of forming complex perceptions in rapid succession, and not to any merely accidental differences arising from greater or less facility acquired by special practice.
"My experiments consisted in marking a brief printed paragraph in a book which had never been read by any of the persons to whom it was to be presented. The paragraph, which contained simple statements of simple facts, was marked on the margin with pencil. The book was then placed before the reader open, the page, however, being covered with a sheet of paper. Having pointed out to the reader upon this sheet of paper what part of the underlying page the marked paragraph occupied, I suddenly removed the sheet of paper with one hand, while I started a chronograph with the other. Twenty seconds being allowed for reading the paragraph (ten lines octave), as soon as the time was up I again suddenly placed the sheet of paper over the printed page, passed the book on to the next render, and repeated the experiment as before. Meanwhile, the first reader, the moment after the book had been removed, wrote down all that he or she could remember having read. End so on with all the other readers.
"Now the results of a number of experiments conducted on this method were to
show, as I have said, astonishing differences in the maximum, rate of
reading which is possible to different individuals, all of whom have been accustomed
to extensive reading. That is to say, the difference may amount to 4 to 1; or,
otherwise stated, in a given time one individual may be able to read four times
as much as another. Moreover, it appeared that there was no relationship between
slowness of reading and power of assimilation; on the contrary, when all the
efforts are directed to assimilating as much as possible in a given time, the
rapid readers (as shown by their written notes) usually give a better account
of the portions of the paragraph which have been compassed by the slow readers
than the latter are able to give; and the most rapid reader I have found is
also the best at assimilating. I should further say that there is no relationship
between rapidity of perception as thus tested and intellectual activity as tested
by the general results of intellectual work; for I have tried the experiment
with [p. 133] server highly distinguished men in science and literature, most
whom I found to be slow readers." 
 The word Perception. however, has been variously used. For historical notices, see Hamilton's Lectures on Metaphysics, ii. 96. For Hamilton perception is the consciousness of external objects (ib. 28). Spencer defines it oddly enough as "a discerning of the relation or relations between states of consciousness partly presentative and partly representative; which states of consciousness must be themselves known to the extent involved in the knowledge of their relations" (Psychol., 355).
 The educative process is particularly obvious in the case of the ear, for all sudden sounds seem alarming to babies. The familiar noises of house and street keep them in constant trepidation until such time as they either learned the objects which emit them, or have become blunted to them by frequent experience of their innocuity.
 The more or less geometrically regular phantasms which are produced by pressure on the eyeballs. congestion of the head inhalation of anæsthetics, etc., might again be cited to prove that feint and vague excitements of sense-organs are transformed into figured objects by the brain. only the facts are not quite clearly interpretable; and the figuring may possibly be due to some retinal peculiarity, as yet unexplored. Beautiful patterns, which would do for wall-papers, succeed each other when the eyeballs are long pressed. Goethe's account of his own phantasm of a flower is well known. It came in the middle of his visual held whenever he closed his eyes and depressed his head, ''unfolding itself and developing from its interior new flowers, formed of colored or sometimes green leaves, not natural but of fantastic forms, and symmetrical as the rosettes of sculptors," etc. (quoted in Müler's Physiology, Baly's tr., p. 1397). The fortification -- and zigzag-patterns, which are well-known appearances in the held of view in certain functional disorders, have characteristics (steadiness, coerciveness, blotting out of other objects) suggestive of a retinal origin -- this is why the entire class of phenomena treated of in this note seem to me still doubtfully connected with the cerebral factor in perception of which the text treuts.-- I copy from Taine's book on Intelligence (vol. I. p. 61) the translation of an interesting observation by Prof. M. Lazarus, in which the same effect of an after-image is seen. Lazarus himself proposes the name of 'visionary illusions' for such modifications of ideal pictures by peripheral stimulations (Lehre von den Sinnestiluschunjien, 1867, p. 19). "I was on the Kaltbad terrace at Rigi, on a very clear afternoon, and attempting to make out the Waldbruder, a rock which stands out from the midst of the gigantic wall of mountains surrounding it, on whose summits we see like a crown the glaciers of Titlis, Uri-Rothsdock, etc. I was looking alternately with the naked eye and with a spy-glass ; but could not distinguish it with the naked eye. For the space of six to ten minutes I had gazed steadfastly upon the mountains, whose color varied according to their several altitudes or declivities between violet, brown, and dark green, and I had fatigued myself to no purpose, when I ceased looking and turned away. At that moment I saw before me (I cannot recollect whether my eyes were shut or open) the figure of an absent friend, like a corpse. ... I asked myself at once how I had come to think of my absent friend. -- In a few seconds I regained the thread of my thoughts, which my looking for the Waldbruder had interrupted, and readily found that the idea of my friend had by a very simple necessity introduced itself among them. My recollecting him was thus naturally accounted for. -- But in addition to this, he had appeared as a corpse. How was this? -- At this moment, whether through fatigue or in order to think, I closed my eyes, and found at once the whole field of sight, over a considerable extent, covered with the same corpse-like hue, a greenish-yellow gray. I thought at once that I had here the principle of the desired explanation, and attempted to recall to memory the forms of other persons. And, in fact, these forms too appeared like corpses; standing or sitting, as I wished, all had a corpse-like tint. The persons whom I wished to see did not all appear to me as sensible phantoms; and again, when my eyes were open. I did not see phantoms, or at all events only saw them faintly, of no determined color. -- I then inquired how it was that phantoms of persons were affected by and colored like the visual held surrounding them, how their lines were traced, and if their faces and clothes were of the same color. But it was then too late or perhaps the influence of reflection and examination had been too powerful. All grew suddenly pale, and the subjective phenomenon which might have lasted some minutes longer had disappeared. -- It is plain that here an inward reminiscence, arising in accordance the laws of association, had combined with an optical after-image. excessive excitation of the periphery of the optic nerve. I mean the long-continued preceding sensation of my eyes when contemplating the color of the mountain, had indirectly provoked a subjective and durable sensation, that of the complemenatry color; and my reminiscence, incorporating itself with this subjective sensation, became the corpse-like phantom I have described."
 Cf. Th. Reid's Intellectual Powers, essay ii. chap. xxii, and A. Binet. in Mind, Ix. 206. M. Binet points out the fact that what is fallaciously inferred is always an object of some other sense than the 'this.' 'Optics' illusions' are generally errors of touch and muscular sensibility, and the fallaciously perceived object and the experiences which correct it are both tactile in these cases
 The converse illusion is hard to bring about. The points a and b. being normally in contact, mean to us the same space, and hence it might be supposed that when simultaneously touched, as by a pair of callipers, we should feel but one object, whilst as a matter of fact we feel two. It should be remarked in explanation of this that an object placed between ,fingers in their normal uncrossed position always awakens the sense of two contacts. When the fingers are pressed together we feel one object to be between them. And when the fingers are crossed, and their corresponding points a and b simultaneously pressed, we do get something like the of singleness -- that is, we get a very doubtful doubleness.
 Purkinje, Mach, and Breuer are the authors to whom we mainly owe the explanation of the feeling of vertigo. I have found (American Journal of Ontology, Oct. 1882) that in deaf-mutes (whose semi-circular canals are auditory nerves must often be disorganized) there very frequently exists no susceptibility to giddiness or whirling
 The involuntary continuance of the eye's motions is not the only cause of the false perception in these cases. There is also a true negative after-image of the original retinal movement-sensations, as we shall see in Chapter XX.
 It seems likely that the strains in the recti muscles have something to do with the vacillating judgment in these atropin cases. The internal recti contract whenever we accommodate. They squint and produce double vision when the innervation for accommodation is excessive. To see singly, when straining the atropinized accommodation, the contraction of our internal reci must be neutralized by a correspondingly excessive contraction of the external reci. But this is a sigh of the object's recession, etc.
 M. Lazarus: Das Leben d. Seele, ii (1857), p. 32. In the ordinary hearing of speech half the words we seem to hear are supplied out of our head. A language with which we are perfectly familiar is understood, even when spoken in low tones and far off. An unfamiliar language is unintelligible under these conditions. If we do not get a very good seat foreign theatre, we fail to follow the dialogue; and what gives trouble to most of us when abroad is not only that the natives speak so fast, but they speak so indistinctly and so low. The verbal objects for interpreting the sounds by lire not alert and ready made in our minds, as they are in our familiar mother-tongue, and do not start up at so faint a cue.
 Compare A. W Volkmann's essay 'Ueber Ursprüngliches und Erworbenes in den Raumanschauungen,' on p. 139 of his Untersuchungen re der Optik; and Chapter xiii of Hering's contribution to Hermann's Handbuch der Physiologie, vol. III
 In the Proceedings of the American Society for Psychical Research, pp. 253-4. I have tried to account for some of the variations in this conscious Out of 140 persons whom I found to feel their lost foot, some did so dubiously. " Either they only feel it occasionally, or only when it pa or only when they try to move it; or they only feel it when they 'think a good deal about it' and make an effort to conjure it up. When they 'grow inattentive,' the feelings 'flies back' or 'jumps back,' to the stump. Every degree of consciousness, from complete and permanent hallucination down to something hardly distinguishable from ordinary fancy represented in the sense of the missing extremity which these patients say they have. Indeed I have seldom seen a more plausible lot, for the view that imagination and sensation are but differences of vividness in an identical process than these confessions, taking them altogether, contain. Many patients say they can hardly tell whether or fancy the limb."
 Compare the historical reviews by K. Lange: Ueber Apperception (Plauen, 1879), pp. 12-14; by Staude in Wundt's Philosophische Studien, i. 149; and by Marty in Vierteljsch. f. wiss. Phil., x. 347 ff. ,
 One of my colleagues, asking himself the question after reading the anecdote, tells me that he replied 'Harvard College,' the faculty of that body having voted, a few days previously, to keep back the degrees of members of the graduating class who might be disorderly on class-day night.
 The great maxim in pedagogy is to knit every new piece of knowledge on to a pre-existing curiosity -- i.e., to assimilate its matter in some way to what is already known. Hence the advantage of 'comparing all that is far off and foreign to something that is near home, of making the unknown plain by the example of the known, slid of connecting all the instruction with the personal experience of the pupil. ... If the teacher is to explain the distance of the sun from the earth, let him ask ... 'If anyone there in the sun fired off a cannon straight at you, what should you do?' 'Get out of the way' should be the answer. 'No need of that,' the teacher might reply. 'You may quietly go to sleep in your room, and get up again, you may wait till your confirmation-day, you may learn a trade, and grow as old as I am, -- then only will the cannon-ball be getting near, then you may jump to one side! See, so great as that is the sun's distance!"' (K. Langue, Ueber Apperception, 1879, p. 76 -- a charming though prolix little work.)
 A. Schopenhauer, Satz vom Grunde, chap. iv. H. Spencer, Psychol., part vi. chaps. ix, x. E. v. Hartmann. Phil. of the Unconscious (B), chaps. vii, viii. W. Wundt. Beiträge, pp,. 422 ff.; Vorlesungen, iv, xii. H. Helmholtz, Physiol Optik, pi,. 430, 447. A. Binet, Psychol. du Raisonnement, chaps. iii, v. Wundt and Helmholtz have more recently 'recanted.' See above, vol i. p. 169 note.
 When not all M, but only some M, is A, when, in other words, M is 'undistributed' the conclusion is liable to error. Illusions would thus be logical fallacies, if true perceptions were valid syllogisms. They would draw false conclusions front undistributed middle terms.
"The sight of a man walking is a familiar spectacle to us. We perceive it as a connected whole, and at most notice the most striking of its peculiarities. Strong attention is required, and a special choice of the point of
view, in order to feel the perpendicular and lateral oscillations of such a walking figure. We must choose fitting points or lines in the background with which to compare the positions of its head. But if a distant walking man be looked at through all astronomical telescope (which inverts the object), what a singular hopping and rocking appearance he presents! No difficulty now in seeing the body's oscillations, and many other details of the gait. ... But, on the other hand, its total character, whether light or clumsy, dignified or graceful, is harder to perceive than in the upright position."
 Illusions and hallucinations must both be distinguished
from delusions. A delusion is a false opinion about a matter
of fact, which need not necessarily involve, though it often does involve,
false perceptions of sensible things. We may, for example, have religions delusions,
medical delusions, delusions about our own importance, about other peoples'
characters, etc., ad libitum. The delusions of the insane are apt to
affect certain typical forms, often very hard to explain. But in many cases
they are certainly theories which the patients invent to account for their abnormal
bodily sensations. In other cases they are due to hallucinations of hearing
and osight. Dr. Clouston (Clinical Lectures on Mental Disease, lecture ii ad
fin.) gives the following special delusions as having been found in about
a hundred melancholy female patients who were afflicted in this way. There were
|general persecution;||being destitute;|
|general suspicion;||being followed by the police;|
|being poisoned;||being very wicked;|
|being killed;||impending death;|
|being conspired against;||impending calamity;|
|being defrauded;||the soulbeing lost;|
|being preached against in church;||having no stomach;|
|being pregnant;||having no inside;|
|having a bone in the throat;||having neither stomach nor brains;|
|having lost much money;||being covered with vermin;|
|being undt to live;||letters being written about her;|
|that she will not recover;||property being stolen;|
|that she is to be murdered;||her children being killed;|
|that she is to be boiled alive;||having committed theft;|
|that she is to be starved;||the legs being made of glass;|
|that the flesh is boiling;||having helms on the head;|
|that the head is severed from the body;||being chloroformed;|
|that children are burning;||having committed murder;|
|that murders take place around;||fear of being hanged;|
|that it is wrong to take food;||being called names by persons;|
|being in hell;||being acted on by spirits;|
|being tempted of the devil;||being a man;|
|being possessed of the devil;||the body being transformed;|
|having committed an unpardonable sin;||insects coming from the body;|
|unseen agencies working;||rape being practised on her;|
|her own identity;||having a venereal disease;|
|being on fire;||being a fish;|
|having committed 'suicide of the soul.'|
 See Proceedings of Sec. for Psych. Research, Dec. 1859, pp. 7, 183. a International Congress for Experimental Psychology has now charge the Census, and the present writer is its agent for America.
 For a full account of Jackson's theories, see his 'Croonian Lectures' published in the Brit. Med. Journ. for 1884. Cf. also his remarks in the Discussion of Dr. Mercier's paper on Inhibition in 'Brain,' xi. 381.
The loss of vivacity in the images in the process of waking, as well as the gain of it in falling asleep, are both well described by M. Taine, who writes (on Intelligence, i. 50, 58) that often in the daytime, when fatigued and seated in a chair; it is sufficient for him to close one eye with a handkerchief when, "by degrees, the sight of the other eye becomes vague, and it closes. All external sensations are gradually effaced, or cease, at all events, to be remarked; the internal images, on the other hand, feeble and rapid during the state of complete wakefulness, become intense, distinct, colored, steady, and lasting : there is a sort of ecstasy, accompanied by a feeling of expansion and of comfort. Warned by frequent experience, I know that sleep is coming on, and that I must not disturb the rising vision; I remain passive, and in a few minutes it is complete. Architecture, landscapes, moving figures, pass slowly by, and sometimes remain, with incomparable clearness of form and fulness of being; sleep comes on, and I know no more of the real world I am in. Many times, like M. Maury, I have caused myself to be gently roused at different moments of this state, and have thus been able to mark its characters. -- The intense image which seems an external object is hut a more forcible continuation of the feeble image which an instant before I recognized as internal some scrap of a forest, some house, some person which I vaguely imagined on closing my eyes, has in a minute become present to me with full bodily details, seas to change into a complete hallucination. Then, waking up on a hand touching me, I feel the figure decay, lose color and evaporate; what had appeared a substance is reduced toe shadow. ... In such a case, I have often seen, for a passing moment, the image grow pale, waste away and evaporate; sometimes, on opening the eyes, a fragment of landscape or the skirt of a dress appears still to float over the fire-irons or on the black hearth." This persistence of dream objects for a few moments after the eyes are oppened seems to be no extremely rare experience. Many cases of it have been reported to me directly Compare Muuml;ller's Physiology, Baly's tr., p. 945
 I say the 'normal 'paths. bectlnse hallucinations are not incompatible with some paths of association being left. Some hypnotic patients will not only have hallucinations of objects suggested to them, but will amplify them and act out the situation. But the paths here seem excessively narrow, and the reductions which ought to make the hallucination incredible do not occur to the subject's mind. In general, the narrower a train of 'ideas' is, the wider the consciousness is of each. Under ordinary circumstances, the entire brain probably plays a part in draining any centre which may be ideationally active. When the drainage is reduced in any way it probably makes the active process more intense.
 M. Binet's highly important experiments, which were first published in vol. xvii of the Revue Philosophique (1884), ale also given in full in chapter rx of his and Férŕ work on 'Animal Magnetism' in the International Scientific Series. Where there is no dot on the paper, nor any other visible mark, the subject's judgment about the 'portrait' would seem to be guided by what he sees happening to the entire sheet
 It is a difficult thing to distinguish in a hypnotic patient between a genuine sensorial hallucination of something suggested and a conception of it merely, coupled with belief that it is there. I have been surprised at the vagueness with which such subjects will often trace upon blank paper the outlines of the pictures which they say they 'see' thereupon. On the other hand, you will hear them say that they find no difference between a real flower which you show them and an imaginary flower which you tell them is beside it. When told that one is imaginary and that they must pick out the real one, they sometimes say the choice is impossible, and sometimes they point to the imaginary flower.
 Literature. The best example of perception with which I am acquainted is that in Mr. James Sully's book on 'Illusions' in the International Science Series. On hallucinations the literature is large. Gurney, Kandinsky (as already cited), and some articles by Kraepelin in the Vierteljahrschrift für Wissenachaftliche Philosophie, vol. v (1881), the most systematic studies recently made. All the works on Insanity treat of them. Dr. W. W. Ireland's works, 'The Blot upon the Brain' (1886); 'Through the Ivory Gate' (1890) have much information on the subject. Gurney gives pretty complete references to older literature. The most important thing on the subject from the point of view of theory is the article by Mr. Myers on the Demon of Socrates in the Proceedings of the Society for Psychical Research for 1889, p. 522.