When giving an account of the mechanism of perception, I spoke of an independent action of the imagination which tends to antic.i.p.ate the process of suggestion from without. Thus, when expecting a particular friend, I recognize his form much more readily than when my mind has not been preoccupied with his image.
A little consideration will show that this process must be highly favourable to illusion. To begin with, even if the preperception be correct, that is to say, if it answer to the perception, the mere fact of vivid expectation will affect the exact moment of the completed act of perception. And recent experiment shows that in certain cases such a previous activity of expectant attention may even lead to the illusory belief that the perception takes place before it actually does.[47]
A more palpable source of error resides in the risk of the formation of an inappropriate preperception. If a wrong mental image happens to have been formed and vividly entertained, and if the actual impression fits in to a certain extent with this independently formed preperception, we may have a fusion of the two which exactly simulates the form of a complete percept. Thus, for example, in the case just supposed, if another person, bearing some resemblance to our expected friend, chances to come into view, we may probably stumble into the error of taking one person for another.
On the physical side, we may, agreeably to the hypothesis mentioned above, express this result by saying that, owing to a partial ident.i.ty in the nervous processes involved in the antic.i.p.atory image and the impression, the two tend to run one into the other, const.i.tuting one continuous process.
There are different ways in which this independent activity of the imagination may falsify our perceptions. Thus, we may voluntarily choose to entertain a certain image for the moment, and to look at the impression in a particular way, and within certain limits such capricious selection of an interpretation is effectual in giving a special significance to an impression. Or the process of independent preperception may go on apart from our volitions, and perhaps in spite of these, in which case the illusion has something of the irresistible necessity of a pa.s.sive illusion. Let us consider separately each mode of production.
_Voluntary Selection of Interpretation._
The action of a capricious exercise of the imagination in relation to an impression is ill.u.s.trated in those cases where experience and suggestion offer to the interpreting mind an uncertain sound, that is to say, where the present sense-signs are ambiguous. Here we obviously have a choice of interpretation. And it is found that, in these cases, what we see depends very much on what we wish to see. The interpretation adopted is still, in a sense, the result of suggestion, but of one particular suggestion which the fancy of the moment determines. Or, to put it another way, the caprice of the moment causes the attention to focus itself in a particular manner, to direct itself specially to certain aspects and relations of objects.
The eye"s interpretation of movement, already referred to, obviously offers a wide field for this play of selective imagination. When looking out of the window of a railway carriage, I can at will picture to my mind the trees and telegraph posts as moving objects. Sometimes the true interpretation is so uncertain that the least inclination to view the phenomenon in one way determines the result. This is ill.u.s.trated in a curious observation of Sinsteden. One evening, on approaching a windmill obliquely from one side, which under these circ.u.mstances he saw only as a dark silhouette against a bright sky, he noticed that the sails appeared to go, now in one direction, now in another, according as he imagined himself looking at the front or at the back of the windmill.[48]
In the interpretation of geometrical drawings, as those of crystals, there is, as I have observed, a general tendency to view the flat delineation as answering to a raised object, or a body in relief, according to the common run of our experience. Yet there are cases where experience is less decided, and where, consequently, we may regard any particular line as advancing or receding. And it is found that when we vividly imagine that the drawing is that of a convex or concave surface, we see it to be so, with all the force of a complete perception. The least disposition to see it in the other way will suffice to reverse the interpretation. Thus, in the following drawing, the reader can easily see at will something answering to a truncated pyramid, or to the interior of a cooking vessel.
[Ill.u.s.tration: FIG. 5.]
Similarly, in the accompanying figure of a transparent solid, I can at will select either of the two surfaces which approximately face the eye and regard it as the nearer, the other appearing as the hinder surface looked at through the body.
[Ill.u.s.tration: FIG. 6.]
Again, in the next drawing, taken from Schroeder, one may, by an effort of will, see the diagonal step-like pattern, either as the view from above of the edge of an advancing piece of wall at _a_, or as the view from below of the edge of an advancing (overhanging) piece of wall at _b_.
[Ill.u.s.tration: FIG. 7.]
These last drawings are not in true perspective on either of the suppositions adopted, wherefore the choice is easier. But even when an outline form is in perspective, a strenuous effort of imagination may suffice to bring about a conversion of the appearance. Thus, if the reader will look at the drawing of the box-like solid (Fig. 3, p. 79), he will find that, after a trial or two, he succeeds in seeing it as a _concave_ figure representing the coyer and two sides of a box as looked at from within.[49]
Many of my readers, probably, share in my power of variously interpreting the relative position of bands or stripes on fabrics such as wall-papers, according to wish. I find that it is possible to view now this stripe or set of stripes as standing out in relief upon the others as a ground, now these others as advancing out of the first as a background. The difficulty of selecting either interpretation at will becomes greater, of course, in those cases where there is a powerful suggestion of some particular local arrangement, as, for example, the case of patterns much brighter than the ground, and especially of such as represent known objects, as flowers. Yet even here a strong effort of imagination will often suffice to bring about a conversion of the first appearance.
A somewhat similar choice of interpretation offers itself in looking at elaborate decorative patterns. When we strongly imagine any number of details to be elements of one figure, they seem to become so; and a given detail positively appears to alter in character according as it is viewed as an element of a more or less complex figure.
These examples show what force belongs to a vivid preconception, if this happens to fit only very roughly the impression of the moment, that is to say, if the interpretative image is one of the possible suggestions of the impression. The play of imagination takes a wider range in those cases where the impression is very indefinite in character, easily allowing of a considerable variety of imaginative interpretation.
I referred at the beginning of this account of sense-illusions to the readiness with which the mind deceives itself with respect to the nature and causes of the vague sensations which usually form the dim background of our mental life. A person of lively imagination, by trying to view these in a particular way, and by selectively attending to those aspects of the sensation which answer to the caprice of the moment, may give a variety of interpretations to one and the same set of sensations. For example, it is very easy to get confused with respect to those tactual and motor feelings which inform us of the position of our bodily members. And so, when lying in bed, and attending to the sensations connected with the legs, we may easily delude ourselves into supposing that these members are arranged in a most eccentric fashion. Similarly, by giving special heed to the sensations arising in connection with the condition of the skin at any part, we may amuse ourselves with the strangest fancies as to what is going on in these regions.
Again, when any object of visual perception is indistinct or indefinite in form, there is plainly an opening for this capricious play of fancy in transforming the actual. This is ill.u.s.trated in the well-known pastime of discovering familiar forms, such as those of the human head and animals, in distant rocks and clouds, and of seeing pictures in the fire, and so on. The indistinct and indefinite shapes of the ma.s.ses of rock, cloud, or glowing coal, offer an excellent field for creative fancy, and a person of lively imagination will discover endless forms in what, to an unimaginative eye, is a formless waste. Johannes Muller relates that, when a child, he used to spend hours in discovering the outlines of forms in the partly blackened and cracked stucco of the house that stood opposite to his own.[50] Here it is plain that, while experience and a.s.sociation are not wholly absent, but place certain wide limits on this process of castle-building, the spontaneous activity of the percipient mind is the great determining force.
So much as to the influence of a perfectly unfettered voluntary attention on the determination of the stage of preperception, and, through this, of the resulting interpretation. Let us now pa.s.s to cases in which this direction of preperception follows not the caprice of the moment, but the leading of some fixed predisposition in the interpreter"s mind. In these cases attention is no longer free, but fettered, only it is now fettered rather from within than from without; that is to say, the dominating preperception is much more the result of an independent bent of the imagination than of some suggestion forced on the mind by the actual impression of the moment.
_Involuntary Mental Preadjustment._
If we glance back at the examples of capricious selection just noticed, we shall see that they are really limited not only by the character of the impression of the time, but also by the mental habits of the spectator. That is to say, we find that his fancy runs in certain definite directions, and takes certain habitual forms. It has already been observed that the percipient mind has very different att.i.tudes with respect to various kinds of impression. Towards some it holds itself at a distance, while towards others it at once bears itself familiarly; the former are such as answer to its previous habit and bent of imagination, the latter such as do not so answer.
This bent of the interpretative imagination a.s.sumes, as we have already seen, two forms, that of a comparatively permanent disposition, and that of a temporary state of expectation or mental preparedness. Illusion may arise in connection with either of these forms. Let us ill.u.s.trate both varieties, beginning with those which are due to a lasting mental disposition.
It is impossible here to specify all the causes of illusion residing in organized tendencies of the mind. The whole past mental life, with its particular shade of experience, its ruling emotions, and its habitual direction of fancy, serves to give a particular colour to new impressions, and so to favour illusion. There is a "personal equation"
in perception as in belief--an amount of erroneous deviation from the common average view of external things, which is the outcome of individual temperament and habits of mind. Thus, a naturally timid man will be in general disposed to see ugly and fearful objects where a perfectly unbiased mind perceives nothing of the kind; and the forms which these objects of dread will a.s.sume are determined by the character of his past experience, and by the customary direction of his imagination.
In perfectly healthy states of mind this influence of temperament and mental habit on the perception of external objects is, of course, very limited; it shows itself more distinctly, as we shall see, in modifying the estimate of things in relation to the aesthetic and other feelings.
This applies to the mythical poetical way of looking at nature--a part of our subject to which we shall have to return later on.
Pa.s.sing now from the effect of such permanent dispositions, let us look at the more striking results of temporary expectancy of mind.
When touching on the influence of such a temporary mental att.i.tude in the process of correct perception, I remarked that this readiness of mind might a.s.sume an indefinite or a definite form. We will examine the effect of each kind in the production of illusion.
_Action of Sub-Expectation._
First of all, then, our minds may at the particular moment be disposed to entertain any one of a vaguely circ.u.mscribed group of images. Thus, to return to the example already referred to, when in Italy, we are in a state of readiness to frame any of the images that we have learnt to a.s.sociate with this country. We may not be distinctly antic.i.p.ating any one kind of object, but are nevertheless in a condition of _sub-expectation_ with reference to a large number of objects.
Accordingly, when an impression occurs which answers only very roughly to one of the a.s.sociated images, there is a tendency to superimpose the image on the impression. In this way illusion arises. Thus, a man, when strolling in a cathedral, will be apt to take any kind of faint hollow sound for the soft tones of an organ.
The disposition to antic.i.p.ate fact and reality in this way will be all the stronger if, as usually happens, the mental images thus lying ready for use have an emotional colouring. Emotion is the great disturber of all intellectual operations. It effects marvellous things, as we shall presently see, in the region of illusory belief, and its influence is very marked in the seemingly cooler region of external perception. The effect of any emotional excitement appears to be to give a preternatural vividness and persistence to the ideas answering to it, that is to say, the ideas which are its excitants, or which are otherwise a.s.sociated with it. Owing to this circ.u.mstance, when the mind is under the temporary sway of any feeling, as, for example, fear, there will be a special readiness to interpret objects by help of images congruent with the emotion. Thus, a man under the control of fear will be ready to see any kind of fear-inspiring object whenever there is any resemblance to such in the things actually present to his vision. The state of awe which the surrounding circ.u.mstances of a spiritualist _seance_ inspires produces a general readiness of mind to perceive what is strange, mysterious, and apparently miraculous.
It is worth noting, perhaps, that those delightful half-illusions which imitative art seeks to produce are greatly favoured by such a temporary att.i.tude of the interpreting imagination. In the theatre, for example, we are prepared for realizing the semblance of life that is to be unfolded before us. We come knowing that what is to be performed aims at representing a real action or actual series of events. We not improbably work ourselves into a slightly excited state in antic.i.p.ation of such a representation. More than this, as the play progresses, the realization of what has gone before produces a strong disposition to believe in the reality of what is to follow. And this effect is proportionate to the degree of coherence and continuity in the action. In this way, there is a c.u.mulative effect on the mind. If the action is good, the illusion, as every play-goer knows, is most complete towards the end.
Were it not for all this mental preparation, the illusory character of the performance would be too patent to view, and our enjoyment would suffer. A man is often aware of this when coming into a theatre during the progress of a piece before his mind accommodates itself to the meaning of the play. And the same thing is recognizable in the fact that the frequenter of the theatre has his susceptibility to histrionic delusion increased by acquiring a habit of looking out for the meaning of the performance. Persons who first see a play, unless they be of exceptional imagination and have thought much about the theatre--as Charlotte Bronte, for instance--hardly feel the illusion at all. At least, this is true of the opera, where the departure from reality is so striking that the impression can hardly fail to be a ludicrous one, till the habit of taking the performance for what it is intended to be is fully formed.[51]
A similar effect of intellectual preadjustment is observable in the fainter degrees of illusion produced by pictorial art. Here the undeceiving circ.u.mstances, the flat surface, the surroundings, and so on, would sometimes be quite sufficient to prevent the least degree of illusion, were it not that the spectator comes prepared to see a representation of some real object. This is our state of mind when we enter a picture gallery or approach what we recognize as a picture on the wall of a room. A savage would not "realize" a slight sketch as soon as one accustomed to pictorial representation, and ready to perform the required interpretative act.[52]
So much as to the effect of an indefinite state of sub-expectation in misleading our perceptions. Let us now glance at the results of definite preimagination, including what are generally known as expectations.
_Effects of Vivid Expectation._
Such expectations may grow out of some present objective facts, which serve as signs of the expected event; or they may arise by way of verbal suggestion; or, finally, they may be due to internal spontaneous imagination.
In the first place, then, the expectations may grow out of previous perceptions, while, nevertheless, the direction of the expectation may be a wrong one. Here the interpreting imagination is, in a large sense, under the control of external suggestion, though, with respect to the particular impression that is misconstrued, it may be regarded as acting independently and spontaneously.
Ill.u.s.trations of this effect in producing illusion will easily occur to the reader. If I happen to have heard that a particular person has been a soldier or clergyman, I tend to see the marks of the cla.s.s in this person, and sometimes find that this process of recognition is altogether illusory. Again, let us suppose that a person is expecting a friend by a particular train. A pa.s.senger steps out of the train bearing a superficial resemblance to his friend; in consequence of which he falls into the error of false identification.
The delusions of the conjuror depend on a similar principle. The performer tells his audience that he is about to do a certain thing, for example, take a number of animals out of a small box which is incapable of holding them. The hearers, intent on what has been said, vividly represent to themselves the action described. And in this way their attention becomes bribed, so to speak, beforehand, and fails to notice the inconspicuous movements which would at once clear up the mystery.
Similarly with respect to the illusions which overtake people at spiritualist _seances_. The intensity of the expectation of a particular kind of object excludes calm attention to what really happens, and the slightest impressions which answer to signs of the object antic.i.p.ated are instantly seized by the mind and worked up into illusory perceptions.
It is to be noted that even when the impression cannot be made to tally exactly with the expectation, the force of the latter often effects a grotesque confusion of the perception. If, for example, a man goes into a familiar room in the dark in order to fetch something, and for a moment forgets the particular door by which he has entered, his definite expectation of finding things in a certain order may blend with the order of impressions experienced, producing for the moment a most comical illusion as to the actual state of things.
When the degree of expectation is unusually great, it may suffice to produce something like the counterfeit of a real sensation. This happens when the present circ.u.mstances are powerfully suggestive of an immediate event. The effect is all the more powerful, moreover, in those cases where the object or event expected is interesting or exciting, since here the mental image gains in vividness through the emotional excitement attending it. Thus, if I am watching a train off and know from all the signs that it is just about to start, I easily delude myself into the conviction that it has begun to start, when it is really still.[53] An intense degree of expectation may, in such cases, produce something indistinguishable from an actual sensation. This effect is seen in such common experiences as that the sight of food makes the mouth of a hungry man water; that the appearance of a surgical instrument produces a nascent sensation of pain; and that a threatening movement, giving a vivid antic.i.p.ation of tickling, begets a feeling which closely approximates to the result of actual tickling.
One or two very striking instances of such imagined sensations are given by Dr. Carpenter.[54] Here is one. An officer who superintended the exhuming of a coffin rendered necessary through a suspicion of crime, declared that he already experienced the odour of decomposition, though it was afterwards found that the coffin was empty.[55]
It is, of course, often difficult to say, in such cases as these, how far elements of actual sensation co-operate in the production of the illusions. Thus, in the case just mentioned, the odour of the earth may have been the starting-point in the illusion. In many cases, however, an imaginative mind appears to be capable of transforming a vivid expectation into a nascent stage of sensation. Thus, a mother thinking of her sick child in an adjoining room, and keenly on the alert for its voice, will now and again fancy she really hears it when others hear nothing at all.
_Transition to Hallucination._