Popular Science Monthly/Volume 49/September 1896/Illusions and Hallucinations



I HAVE already had occasion more than once to speak of the development of a mental state from the stage which we term idea to that which we term sensation. Before taking up the matter in hand it will be necessary to go into this question at somewhat greater length.

We seldom have difficulty in discriminating an idea from a sensation, but it is not easy to define the difference between them. This is partly due to the fact that the differences are very complex, and partly to the fact that they vary in the respective fields of sensation, so that one can scarcely frame a definition for ideas and sensations of vision that will also prove applicable to those of sound, touch, and so on. Ideas of sound differ from the corresponding sensations chiefly in intensity, but in the case of vision a much more important distinction is drawn from the relation sustained by visual ideas to what the eye actually sees. At the present moment I am thinking of something I saw yesterday, but what I see with my eyes is not in the least affected by that. The two groups remain distinct, and it would seem as if an almost impassable gulf parted them, so seldom does a bit of one become confused with the other. This is not true of ideas of sound. If they only become intense enough they may seem to blend with real sounds—indeed, I often mistake an air of which I am thinking for the same air faintly heard.

The distinction between sense-impression and idea really rests upon intrinsic differences of this kind, but as they are so complex I shall make use of a physiological distinction which for all practical purposes coincides with it. Sense-impressions are those mental states which are primarily initiated by a current from the outlying regions or periphery of the body, especially from the organs of sense. Since these currents are usually due to the action of physical forces upon the body, sense-impressions generally give us information as to the condition of the material world. All other mental states should be classed as ideas, even though they simulate sensations so closely as to be scarcely distinguishable from them.

From this point of view the peculiar characteristics of the impressions of sense are due to some peculiarities in the cortical processes which are their physical bases—peculiarities which are usually due to the action of a peripheral current. Thus it may be that the sensation is more intense because the current acts upon the stored-up energy of the, cortical cells much as a spark acts upon gunpowder. If precisely the same kind of a cortical process could be induced in any other way than by the action of a peripheral current, we would presumably have an imitation sensation. There appears no good reason why there should not be many other kinds of cortical processes intermediate between those that underlie ideas and those that underlie sense-impressions, and to them mental states should correspond which are betwixt and between—neither fish, flesh, nor fowl.

Now, of the cortical processes we know nothing; I use them merely as symbols for mental facts. But the mental states we directly know, and it is quite certain that many different types of them exist, roughly corresponding to what we would expect if the above conception were true. We know that in different individuals ideas vary much in their clearness and in the degree to which they approach sensations. In the same individual they occasionally assume a form which is to him almost like a glimpse into a new world of experience. My own visual ideas, for example, are very vague and dim, and I shall never forget the two or three occasions in my life when they have for a while been vivid and brightly colored, somewhat as my visual sensations are. And occasionally we meet with experiences which are certainly originated largely or entirely from within and must be classed as ideas and yet resemble sensations so closely that they can be discriminated from them only upon reflection. These are what we term illusions and hallucinations; the other types, which we never mistake for realities, although they resemble sensations so closely, are termed pseudo-hallucinations. By the level or grade of a mental state I mean the degree to which it approximates that fullest and most perfect form of being which we find in the sense-impression, and by development I mean the process of becoming more like the sense-impression.

What can cause development? Well, in the first place, it can be caused in some individuals by concentration of attention. Most of my readers have heard the story of the painter who said he could at any time see again a sitter by looking at the chair in which he had once sat. I have met many such persons. Sometimes the process is slow and its several stages can be traced. Miss Z——, for example, after fixing her thoughts upon the image of a friend, sees a shadow appear before her which gradually assumes color, consistence, solidity, reality, and finally becomes the living image of the friend. But with the least distraction it vanishes like a soap bubble. In other cases the process is instantaneously completed. Rev. Mr. F—— can at any time by an act of will create an image of a friend, and after doing so finds it hard to lay the ghost which he has himself raised. Images voluntarily externalized nearly always seem subject to curious limitations. Often it is possible to externalize persons only, or only certain persons, or only in definite attitudes. The apparition rarely appears possessed of independent life, it seldom moves spontaneously, and its features reflect no play of thought; it also often disappears upon being touched. All these are common traits of ghosts, and the identity goes to show their common origin.

In the second place, the development of an idea is sometimes clearly traceable to a simultaneous but disconnected sensory stimulus. A striking illustration of this fact fell within my own experience not long ago. I had had a fatiguing and anxious day, and consequently could not sleep. As I lay in bed, dim, silhouette-like forms began to outline themselves in the darkness, as sometimes, although very rarely, happens when I am tired and excited. I was trying to make one out, when I heard a crackling sound. Instantly the shadowy image was illumined by a brilliant flash of white light, and I saw two dumb-bells lying crossed with the balls toward me. For. a moment my impression was that some one had brought a light into the room, although my eyes were closed; but upon opening them I found that my brother had entered without a light through a Japanese screen made of slender wooden rods strung lengthwise. The crackling sound made by the parted screen had raised my thought-image to sensory intensity. Parish gives another good illustration.[1] A physician, while experimenting in this line, thought of a section of liver and tried to see it, at the same time pressing on the ball of the eye. "At first he was clearly conscious that his mental image was quite dim and confused; yet suddenly an image of a section of liver stood before his eyes as if seen through a microscope, clearly outlined, and with all its arteries, veins, and gall ducts beautifully colored in red, blue, and greenish violet."

In the third place, the degree of vividness which a mental state attains seems to bear an inverse relation to the number of ideas which it suggests. I can not go into the proof of this statement here, as it would lead me too far astray into the field of normal psychology, but those who care to follow it out will find it set forth by Prof. James in his Psychology, volume ii, page 134. It is also true that hallucinations are common in states in which there seems to be an arrest of the processes of association. Such are, for example, all hypnotic states. The analogy to the forms of transmission of physical energy is striking, and has led Prof. James to conjecture that the higher development of the few ideas remaining is in some way a compensation for the arrest of association. "If," he says, "we regard association paths as paths of drainage, then the shutting off of one after another of them as the cerebral paralysis advances ought to act like the plugging of a hole in the bottom of a pail, and make the activity more intense in those systems of cells which retain any activity at all." Prof. James then quotes from Taine a vivid description of the rise in the level of the idea trains as the association paths are closed by sleep. "All external sensations are gradually effaced, or cease at any rate 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 sense of expansion and comfort. Architecture, landscapes, moving figures, pass slowly by, and sometimes remain with incomparable clearness of form and fullness 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 but 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, so as 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 to a 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 the black hearth."

In the three types which I have been discussing, the mental state was present as a thought before being externalized as a hallucination, and for many reasons hallucinations of this type are the most instructive. But very often the hallucination is not only not a mere externalization of a thought already present, but has no apparent connection with anything of which the patient is at the time thinking. Hence the theory of development needs to be supplemented by other considerations, and one may draw them from either of two quite different, although I think not inconsistent, points of view. In the first place, one may suppose that the hallucination is sometimes initiated from without, through some derangement in the mechanism of perception, and has nothing to do with what the patient is thinking of. In the second, one may have recourse to the theory of subconscious states and assume that every hallucination had a true mental existence, if not conscious, then subconscious, before being brought to the upper consciousness. The first is the old orthodox theory of illusion, and, to make it intelligible, I must say a little of the normal processes of perception.

Our sense-impressions are primarily initiated, as I have said, by currents from the periphery of the body, but their final complexion is only in part determined by the peripheral currents; it owes much to the condition in which the cortex happens to be and to the manner in which it is constituted. We may roughly compare it to a penny-in-the-slot machine. Without the penny there would be no response, but the precise character of the response is determined by the constitution of the machine. The case of the brain is similar, but infinitely more complex. Most of our sense organs send in very complex currents: from the eye, for instance, we get currents which, taken alone, would cause sensations of color, touch, and movement—the slightest change in the number and relative adjustment of these currents, even though it be so slight that we can not possibly be aware of it as a change in the simpler sensations, will totally change the character of the sense-impression. These sensory currents are like the keys and stops of an organ, and any one who knows just what stops and keys to manipulate can get any response he pleases. Thus the technical part of painting consists in so imitating the ordinary sensory determinants of vision by means of colors on a flat surface as to produce that cortical process which is usually produced by a real thing.

It is not often possible to trace the operation of these factors in our sense-impressions. Each seems an indivisible mental whole. But sometimes we can distinguish them. In the first and third of the three types of hallucination which I have already analyzed, the character of the hallucination is clearly determined by the first or central factor, and its development also seems to be due to some central factor or factors. In the second of the three the character is determined as before by the central factor, while its development to sensory intensity is due to its accidental coincidence with the arrival of a sensory current, which is a peripheral factor. These are all termed hallucinations centrally initiated, or true hallucinations. In the types which I shall now take up the character is always chiefly determined by peripheral currents, and, presumably, they are also responsible for the sensory intensity of the image. These hallucinations are termed peripherally initiated, or simply illusions.

The following account may be taken as typical of the true illusion:[2]

"One evening, at dusk, I went into my bedroom to fetch something I wanted off the mantelpiece. A street lamp threw a slanting ray of light in at the window, just sufficient to enable me to discern the dim outline of the chief articles of furniture in the room. I was cautiously feeling for what I wanted when, partially turning round, I perceived at a short distance behind me the figure of a little old lady, sitting very sedately with her hands folded in her lap, holding a white pocket handkerchief. I was much startled, for I had not before perceived any one in the room, and called out 'Who's that?' but received no answer, and, turning quite round to face my visitor, she immediately vanished from sight. 'Well' I thought, 'this is strange!' I had left all the rest of the household downstairs; it was hardly possible that any one could have followed me into the room without my being aware of it, and besides, the old lady was different from any one I had ever seen. Being very near-sighted, I began to think my eyes had played me a trick; so I resumed my search in as nearly as possible the same position as before, and having succeeded, was turning to come away, when lo! and behold! there sat the little old lady as distinct as ever, with her funny little cap, dark dress, and hands folded demurely over her white handkerchief. This time I turned round quickly and marched up to the apparition, which vanished as suddenly as before. And now being convinced that no one was playing me any trick, I determined to find out, if possible, the why and because of the mystery. Slowly resuming my former position by the fireplace, and again perceiving the figure, I moved my head slightly from side to side, and found that it did the same. I then went slowly backward, keeping my head still until I reached the place, when, deliberately turning round, the mystery was solved. A small polished mahogany stand near the window, which I used as a cupboard for various trifles, made the body of the figure, a piece of paper hanging from the partly opened door serving as the handkerchief; a vase on the top made the head and headdress, and the slanting light falling upon it and the white curtain of the window completed the illusion. I destroyed and remade the figure several times and was surprised to find how distinct it appeared when the exact relative positions were maintained."

In this case the form of the illusion seems to have been almost entirely determined by sensory stimuli, but in many cases the operation of the central factor can still be traced. For example, Parish quotes[3] from Prof. Lazarus an experience of his own. Prof. Lazarus had been wearying his eyes trying to make out a certain rock on a distant mountain side; as he turned away he saw vividly the corpse of a friend stretched out before him. Upon reflection he found that this friend had been associated with the train of ideas that had filled his mind just before he began to look for the rock. He also found that whenever he closed his eyes he saw a dull, grayish-green, corpselike color, which was the complementary after image of the dull reds, browns, and greens of the mountain side. He also found that other persons of whom he thought appeared to him of the same corpselike tint. In this case the main character of the hallucination—that is, the thought of a friend—was furnished by association of ideas, but its special form, the appearance of that friend as a corpse, as well as its sensory vividness, seems to have been due to the peripheral factor.

A closely analogous experience is reported by a Mrs. L—— in the Proceedings of the Society for Psychical Research, volume x, page 143: "About September, 1881, aged forty-six, and eighteen months after the sudden death of my mother, which had shaken my nerves very much, one night toward morning, being awake to the best of my belief, I saw a woman come through the door. Her face was sideways and I distinctly saw her features. She passed slowly from the door and went out at the window opposite, thus passing across the foot of my bed. She had on an old-fashioned bonnet and an old-fashioned caped coat, and she was carrying a basket in front of her such as country women carry their husbands dinners in. The whole figure was semi-opaque, neutraltinted, like thick smoke or cloud. A great hurricane was blowing. I was dreadfully disturbed and hysterical next day—the impression so vivid and yet unable to say who it was. About a week after, the revelation came. I sat down to dinner, became very hysterical and faint, and went into another room alone in the dark. All at once I jumped up, saying, 'It is Mrs. Peasant!' Mrs. Peasant was the pretty young bride of a farmer with whom, when about ten years old, we used to go and take tea at a farm about two or three miles from the vicarage. One day she went with her husband's dinner as usual, and he was felling a tree. She passed the wrong way, and the tree fell on her and killed her. I remember watching her funeral with my nurse, and the anguish of spirit at her death, but never remember speaking of it or the circumstance since. The day before the appearance a nurse of the name of Peasant had disturbed and annoyed me. A few months before a large elm tree had fallen in our garden and partly on the house. A hurricane was blowing at the time, and I remember thinking, 'What a lucky thing that tree can't fall on the roof!'" Clearly the storm, the falling tree, and the annoying nurse were the chief factors in determining the character of the hallucination, but as they acted through association it is not so clear to what its externalization is to be ascribed. Perhaps the hurlyburly of the storm outside had something to do with it; probably the drowsy, disordinated condition of the percipient favored the formation of the apparition, but of the details of the process one can not speak with confidence.

In the hallucinations of which the crystal vision is the type we have a form intermediate between the true hallucination and the illusion. Prolonged staring into a mirror, a glass of water, a crystal, a piece of glass, or even fixation of the gaze upon a point will induce in some persons brilliantly colored hallucinations. While they are certainly peripherally initiated by the prolonged staring, their special character is nearly always centrally determined—usually indeed, they simply reproduce old memories. Susceptibility to these hallucinations is by no means uncommon; I have tried about a hundred persons myself, and found that about one in four saw something. Similar hallucinations of hearing can be produced by listening to the "sound of waves" in a large shell, to the sound of water running from a spigot, etc. The stories of ghosts seen in mirrors probably all rest upon this principle. For example:[4]

"The first hallucination which I was in a position clearly to recognize as such occurred during the Indian mutiny. Several members of our family were in danger. One night on which we had all been talking late of them, after we had parted and gone upstairs to bed, I stood before my dressing table, plaiting my hair, when my attention was arrested by a faint spot in the center of the mirror; this, to my amazement, gradually enlarged (as a grease spot spreads with heat) till the whole surface was covered, and then, in the center of this veil, came through the face of one of the near relatives above mentioned, as plain as might have been his living reflection. I noted the day and hour, and ascertained, six weeks later, that the relative seen had incurred no sort of danger at that date." This misty discoloration of the glass is significant, for many of my subjects describe the glass as becoming milky or cloudy just before the hallucination appears. Occasionally it is possible by means of an indeterminate stimulus of this sort to raise a thought to sensory intensity. Thus Miss X—— saw in the polished surface of a piano a scene of which she was thinking,[5] I have met with one analogous experience, but it seems to be rare.

Many interesting questions arise as to the relation that exists between the hallucination and the stimulus which has generated it. It is frequently very close, any change in the stimulus either destroying the hallucination or making in it a corresponding change. In the case of crystal gazing, for example, if one looks at the image through a magnifying glass or prism, it is sometimes destroyed and sometimes magnified or doubled. Very often hallucinations originated independently appear to attach themselves in much the same way to some contiguous percept and become practically a part of it. The element to which it is attached is what the French investigators have termed the point de repère, and M. Binet has endeavored to show that without such a point de repère no hallucination can exist. The matter is still under discussion, and must be set aside with this brief allusion.

If we once admit that subconscious states exist, we are tempted in many cases of hallucination to make use of the conception to explain the facts. In the case of Mrs. Beasant's ghost, for example, it may be that the memory was revived before the apparition was seen, but remained subconscious until externalized by some obscure agencies which one can not precisely specify. An analogous experience—in this case a crystal vision—is given by Miss X——:[6]

"I find in my notebook a memorandum of August 3d as to a vision of a corner of a room, with a red carpet and walls decorated in stripes of pink, white, and green, for which for many months I was unable to account. Only a few days ago (May 10, 1889, is the date of writing) I called on a friend whom I had not visited since July, and whose house had, I observed, been newly and handsomely decorated. A letter which she had written to me before leaving town in the summer was by chance referred to, and on returning home I sought it, to settle a disputed point, and found that it was dated August 2d and contained the information that her staircase had been painted and 'looked at present like a Neapolitan ice.' This, I doubt not, supplied the coloring of my picture."

Here the development of the vision was influenced by an allusion contained in a letter read the preceding day which was no longer in mind. Now, one must suppose either that that allusion still existed in some way and was capable of influencing the vision, or that the vision had been suggested subconsciously, had existed subconsciously, and had been brought to light by the crystal, or that it had been suggested by the letter, forgotten, and then revived. Of these three suppositions the last is the most plausible, but it is difficult in other cases to resort to it. Take another case of Miss X——'s: "On March 9th I saw in the crystal a rocky coast, a rough sea, an expanse of sand in the foreground. As I watched, the picture was nearly effaced by that of a mouse, so large that I could see only a bit of cliff above his tail. Two days later I was reading a volume of poetry which I remembered having cut open, talking the while, certainly not consciously reading, on the day of my vision. As I turned over the leaves, a couple of lines struck me as somehow familiar, though the book, a volume by Aldrich, was quite new to me:

Only the sea intoning,
Only the wainscot mouse.

These, I imagine, suggested the images." Doubtless Miss X——'s eye had fallen on these lines; possibly they aroused some fleeting images in the upper consciousness which were then forgotten. But granting the existence of the subconscious, it is more easy to understand the case upon the supposition that the whole process took place outside the range of her normal consciousness.

A still more striking case of the same author's has been much quoted:

"On March 20th I happened to want the date of Ptolemy Philadelphus, which I could not recall, though feeling sure I knew it, and that I associated it with an event of some importance. When looking in the crystal some hours later, I found a picture of an old man with long, white hair and beard, dressed like a Lyceum Shylock, and busy writing in a large book with tarnished, massive clasps. I wondered much who he was and what he could possibly be doing, and thought it a good opportunity of carrying out a suggestion which had been made to me of examining objects in the crystal with a magnifying glass. The glass revealed to me that my old gentleman was writing in Greek, though the lines faded away as I looked, all but the characters he had last traced—the Latin numerals LXX. Then it flashed into my mind that he was one of the Jewish elders at work on the Septuagint, and that its date, 277 b. c., would serve equally well for Ptolemy Philadelphus. It may be worth while to add, though the fact was not in my conscious memory at the moment, that I had once learned a chronology on a mnemonic system which substituted letters for figures, and that the memoria technica for this date was, 'Now Jewish elders indite a Greek copy.'"

If this strange vision had ever been suggested to Miss X—— before by her mnemonic line, why did she not recognize it? And if it had not been suggested before, either it had been suggested in her subconsciousness or else it was suggested to her upper consciousness by a subconscious memory of the mnemonic line.

Another of Miss X——'s visions[7] is almost precisely similar to that of the sea and the mouse, save that it is still more difficult to suppose that she had any conscious knowledge of that which was revived in the crystal: "It was suggested to me, one day last September, that I should look into the crystal with the intention of seeing words, which had at that time formed no part of my experience. I was immediately rewarded by the sight of what was obviously a newspaper announcement in the type familiar to all who read the first column of the Times. It reported the death of a lady, at one time a very frequent visitor in my circle and very intimate with some of my nearest friends, an announcement, therefore, which, had I consciously seen it, would have interested me considerably. I related my vision at breakfast, quoting name, date, place, and an allusion to 'a long period of suffering' borne by the deceased lady, and added that I was sure that I had not heard any report of her illness, or even, for some months, any mention of her likely to suggest such an hallucination. I was, however, aware that I had the day before taken up the first sheet of the Times, but was interrupted before I had consciously read any announcement of death. Mrs. Henry Sidgwick, with whom I was staying, immediately sought for the paper, where we discovered the paragraph almost exactly as I had seen it." If Miss X—— had consciously seen this notice, how came she to forget it?

Cases of this kind strongly suggest, I think, what Mr. Gurney calls "an underground psychosis," but they do not demonstrate its existence; and, unfortunately, most of the cases which would seem to require the assumption of subconscious states also require the still more revolutionary assumption of such powers as telepathy and clairvoyance, which lie outside my present scheme of topics.

All these forms of hallucination are known as sensory automatism, and in my last paper I sketched the conception which underlies the term. I there also alluded to ideal automatism, and with a few words upon that point I must let the subject go.

Our thought trains usually belong to well-defined types, are of a certain average grade of development, and behave in pretty definite ways. For example, they are for the most part subservient to our will, and come and go at our bidding. But sometimes the orderly process of thought is broken up; new classes of ideas obtrude themselves, familiar types rise to a higher level without becoming full-fledged hallucinations, and, last but not least, the will finds itself unable to control them. Such disorders of ideation are often termed ideal automatism. As a very large part of our thinking is carried on in ideas of spoken words, a very common form of ideal automatism is the inner voice. A portion of the patient's word ideas rise to a higher level than usual, resist his will, and often say things which strike him as strange and foreign to his own acknowledged thoughts. For the sake of completeness I must refer to this type of automatism, although space forbids me to discuss it in detail.

  1. Ueber die Trugwahrnehmung, p. 134.
  2. Proceedings of the Society for Psychical Research, vol. x, p. 95.
  3. Op. cit., p. 135.
  4. Proceedings of the Society for Psychical Research, vol. x, p. 407.
  5. Ibid., vol. V, p. 512.
  6. Proceedings of the Society for Psychical Research, vol. v, p. 512.
  7. Op. cit., p. 508.