There is, then, at the basis of dreaming a seemingly spontaneous procession of dream imagery which is always undergoing transformation into something different, yet not wholly different, from that which went before. It seems a mechanical flow of images, regulated by associations of resemblance, which sleeping consciousness recognises without either controlling or introducing foreign elements. This is probably the most elementary form of dreaming, that which is nearest to waking consciousness, and that in which the peripheral and retinal element of dreaming plays the largest part.
The fundamental character of this spontaneous self-evolving procession of imagery is indicated by the significant fact that it tends to take place whenever the more retinal and peripheral part of the visual apparatus is affected by the exhaustion of undue stimulation, or even when the organism generally is disturbed or run down, as in neurasthenic conditions.[19] The most obtrusive and familiar example of visual imagery is furnished by the procession of perpetually shifting and changing after-images which continue to evolve for a considerable time after we have looked at the sun or other brilliant object.[20] Less striking, but more intimately akin to the imagery of dreams, are the hypnagogic visions occurring as we fall asleep, especially after a day during which vision has been unusually stimulated and fatigued, though they do not seem necessarily dependent on such fatigue. Most vivid and instructive of all is the procession of visual imagery evoked by certain drugs. Of these the most remarkable and potent, as well as the best for study, is probably mescal, which happens also to be the only one with which I am myself well acquainted.[21] This substance provokes a constant succession of self-evolving visual imagery which constantly approaches and constantly eludes the semblance of real things; in the earlier stages these images closely resemble those produced by the kaleidoscope, and they change in a somewhat similar manner. Such spontaneous evolution of imagery is evidently a fundamental aptitude of the visual apparatus which many very slightly abnormal conditions may bring into prominence.
The power of opium is somewhat similar, and, as DeQuincey long since pointed out, such power is simply a revival of a faculty usually possessed by children, although, judging from my own experiences with mescal, drugs exert it in a far more vivid and potent degree than that in which it usually occurs in the child. The psychologists of childhood have not often investigated this phenomenon,[22] but so far as my own inquiries go, all or nearly all persons have possessed, when children, the power of seeing visions in the dark on the curtain of the closed eyelids, perhaps the representation of fairy tales they had read, perhaps merely commonplace processions of individuals or events, a tendency sometimes appearing for the same figure to recur again and again. I think it is fairly certain that the so-called 'lies' of children, told in good faith, are in part due to the occasional eruption of this faculty into daylight life. People who deny that they ever possessed this power have, almost certainly, only forgotten. I should myself be inclined to deny that I had ever had any such visionary faculty if it were not that I can recall one occasion of its presence, at about the age of seven, when sleeping with a cousin of the same age; we amused ourselves by burying our heads in the pillows and watching a connected series of pictures which we were both alike able to see, each announcing any change in the picture as soon as it took place. This fact of community of vision served to impress on my mind the existence of a faculty of which otherwise I can recall no trace.[23]
Of these various groups of allied phenomena, that which more especially concerns us in the investigation of dreams is the group of phenomena most strictly called hypnagogic, belonging, that is to say, to the ante-chamber of sleep, when the senses are in repose and waking consciousness is slipping away, or else when, as we leave the world of dreams, waking consciousness is flowing back again. This state has been known from very ancient times. Aristotle referred to it, and in the dawn of modern scientific thought Hobbes described allied phenomena.[24] The strictly psychological study of hypnagogic visions seems to have begun with Baillarger.[25] Then, some years later, Maury, who had a rich personal experience of such phenomena, devoted a chapter to the hypnagogic state, and gave it its recognised name.[26]
Hypnagogic imagery, there can be little doubt, is not a purely ocular phenomenon, even when it is stimulated by ocular fatigue. It is a mixed phenomenon, partly retinal and partly central. That is to say that the eye supplies entoptic glimmerings, and the brain, acting on the suggestions thus received, superposes mental pictures to those glimmerings.[27] They are thus analogous to the pictures we may see in the fire or in the clouds. It must be added that the other senses also furnish corresponding rudiments which are filled in by the central activity; this is notably the case with faint buzzings and sounds in the ear, and in addition, muscular twitches and internal visceral sensations, all these becoming more prominent as the attentive activity of waking life subsides.[28]
What is the relation of hypnagogic imagery to dreams? Johannes Müller, the great physiologist, long ago identified them, as previously had Gruithuisen and Burdach, while Maury—who himself possessed, however, a somewhat abnormal and irritable nervous system—regarded hypnotic imagery as furnishing the whole of the formative element of dreams, as being 'the embryogeny of dreams'; he frequently found that images which appeared to him in this way before going to sleep reappeared in dreams. This is supported by Mourly Vold, who made experiments on himself, and by fixing images as he fell asleep dreamed of the same images. Goblot, however, while regarding hypnagogic imagery as analogous with dream imagery, denies that it is identical. Since the hypnagogic state is the porch to sleep and dreams—the praedormitium, as Weir Mitchell terms it—we can scarcely fail to admit with Maury that hypnagogic imagery presents us with the germinal stuff of dreams. If it is not identical with the fully formed dream, it is still the early stage of dreaming. This is certainly the view suggested by my own experience, even though I have never definitely recognised a dream as related to a previous hypnagogic image. It has, however, occasionally happened to me that as I have begun to lose waking consciousness a procession of images has drifted before my vision, and suddenly one of the figures I see has spoken. This hallucinatory voice occurring before I was fully asleep has startled me into full waking consciousness, and I have realised that, while yet in the hypnagogic stage, I was assisting at the birth of a dream.
There is one point, it may be noted in passing, at which dreams do not usually correspond with some of the phenomena with which we may most naturally compare them. I refer to their presentation of colour. In the dreams of most people colour is rare. We seem usually, from this point of view, to remember a dream as we would remember a photograph, or, if any colour at all is present, a tinted drawing. Judging from my own experience, I should say that it is difficult to decide whether the absence of colour is due to its actual absence from the dream imagery, or merely to its failure to make any impression on memory. Some careful observers have, however, stated that the colour of their dream imagery is definitely grey. Thus Beaunis states that his dream imagery is usually en grisaille, like an image recalled in the waking state, though occasionally the colour is vivid, and Dr. Savage says that in his dreams colour is rarely or never present. 'I see landscapes of black and white, and flowers assume their true form, but not their colours.'[29] This greyness of dream imagery corresponds to the disappearance of colour under chloroform anaesthesia. 'So long as the eyes could be held open voluntarily,' says Elmer Jones, 'vision seemed quite normal, save that the colours of the spectrum faded out into a grey band.' Even in the early stage of some insanities also, as Stoddart has found, some degree of colour-blindness is present.[30] Grace Andrews states, indeed, that in nearly half of her own visual dreams colour sensations were included. This seems to me exceptional. In my own experience, the emergence of a single colour, which usually strikes me as beautiful, is not rare. I see, for instance, a friend drinking wine copiously from a large goblet, and I judge by the colour of the wine that it is hock, or I am impressed by the shimmering grey tone of the poplin dresses worn by a group of ladies, which seems to indicate that the tone of the whole picture was not grey. I am inclined to think that when colour in a dream becomes more pronounced than this, the dream is not normal, but is associated with some degree of cerebral disturbance, and especially the presence of headache. This would agree with the fact that persons subject to migraine are liable to visual colour phenomena. As an example of a vivid colour dream associated with headache, I may bring forward the following: I dreamed that an artist of note, with whom I am acquainted, was painting my portrait. (The pose of the portrait was standing, but I was lying down; this, however, caused me no surprise.) I saw the colours of the picture with great vividness, and I noted the extreme rapidity with which the artist painted; thus the red and black pattern of the necktie he had given me was suddenly changed to a totally different blue pattern, and the whole picture then appeared as a harmony of blues, the rapidity with which the artist effected these changes impressing me as very remarkable. In another dream in which I saw a painter occupied on a picture, a landscape representing sunrise, memory recalled the effect of light as vivid, but no definite sense of colour remained. This seems to me the normal condition of things in the ordinary dreams of most persons, colour, when it occurs, or when it is remembered, being for the most part confined to a single object or a single tint, and often being associated with a feeling of aesthetic pleasure.
In ordinary dreaming there is usually something more than a spontaneous procession of related imagery. There is a more definitely central and psychic element. There is association, not only by obvious resemblance, but by contiguity, usually the casual contiguity of images received during the previous day, which forces together images related to each other indeed, but by no means obviously. Dreaming consciousness embodies and actively co-ordinates definite, and not merely random, images. The passive and spontaneous flow of imagery is thus modified in its course.
The image of the magic lantern well illustrates this character of dream experiences. The movement of the cinematograph, indeed, scarcely corresponds to that fusion of heterogeneous images which marks dream visions. Our dreams are like dissolving views in which the dissolving process is carried on swiftly or slowly, but always uninterruptedly, so that at any moment two (often, indeed, more) incongruous pictures are presented to consciousness, which strives to make one whole of them, and sometimes succeeds, and is sometimes baffled. Or we may say that the problem presented to dreaming consciousness resembles that experiment in which psychologists pronounce three wholly unconnected words and require the subject to combine them at once in a connected sentence. It is unnecessary to add that such analogies fail to indicate the subtle complexity of the apparatus which is at work in the manufacture of dreams.