The next step is one to which, as the reader of my chapter on hypnotism already knows, I attribute an importance much greater than is generally accorded to it. I refer to the hypnotiser's power not only of controlling but of inducing hallucinations in his subject.
As I have already said, the evocation of hallucinations is commonly spoken of as a mere example of the subject's obedience to the hypnotiser. "I tell my subject to raise his arm, and he raises it; I tell him to see a tiger in the room, and he sees one accordingly." But manifestly these two incidents are not on the same level, and only appear to be so through a certain laxity of language. The usage of speech allows me to say, "I will make my subject lift his arm," although I am of course unable to affect the motor centres in his brain which start that motion. But it is so easy for a man to lift his arm that my speech takes that familiar power for granted, and notes, only his readiness to lift it when I tell him—the hypnotic complaisance which prompts him to obey me if I suggest this trivial action. But when I say, "I will make him see a tiger," I take for granted a power on his part which is not familiar, which I have no longer a right to assume. For under ordinary circumstances my subject simply cannot see a tiger at will; nor can I affect the visual centres which might enable him to do so. All that I can ask him to do, therefore, is to choose this particular way of indicating that in his hypnotic condition he has become able to stimulate his central sensory tracts more powerfully than ever before.
And not only this. His hallucinations are in most cases elaborate products—complex images which must have needed intelligence to fashion them—although the process of their fashioning is hidden from our view. In this respect they resemble the inspirations of genius. For here we find again just what we found in those inspirations—the uprush of a complex intellectual product, performed beneath the threshold, and projected ready-made into ordinary consciousness. The uprushing stream of intelligence, indeed, in the man of genius flowed habitually in conformity with the superficial stream. Only rarely does the great conception intrude itself upon him with such vigour and such untimeliness as to bring confusion and incoherence into his ordinary life. But in the case of these induced hallucinations the incongruity between the two streams of intelligence is much more marked. When a subject, for instance, is trying to keep down some post-hypnotic hallucinatory suggestion, one can watch the smooth surface of the supraliminal river disturbed by that suggestion as though by jets of steam from below, which sometimes merely break in bubbles, but sometimes force themselves up bodily through the superficial film.
It is by considering hallucinations in this generalised manner and among these analogies, that we can best realise their absence of necessary connection with any bodily degeneration or disease. Often, of course, they accompany disease; but that is only to say that the central sensory tracts, like any other part of the organism, are capable of morbid as well as of healthful stimulus. Taken in itself, the mere fact of the quasi-externalisation of a centrally initiated image indicates strong central stimulation, and absolutely nothing more. There is no physiological law whatever which can tell us what degree of vividness our central pictures may assume consistently with health—short of the point where they get to be so indistinguishable from external preceptions that, as in madness, they interfere with the rational conduct of life. That point no well-attested case of veridical hallucinations, so far as my knowledge goes, has yet approached.
It was, of course, natural that in the study of these phantasms, as elsewhere, the therapeutic interest should have preceded the psychological, but in the newer practical study of eugenics—the study which aims at improving the human organism, instead of merely conserving it—experimental psychology is indispensable, and one branch of this is the experimental study of mental visions.
Let us consider whether, apart from such a rare and startling incident as an actual hallucination, there is any previous indication of a habit of receiving, or a power of summoning, pictures from a subliminal store-house? Any self-suggestion, conscious or unconscious, which places before the supraliminal intelligence visual images apparently matured elsewhere?
Such indications have not been wanting. In the chapter on Genius, and in the chapter on Sleep, we have traced the existence of many classes of these pictures; all of them ready, as it would seem, to manifest themselves on slight inducement. Dream-figures will rise in any momentary blur of consciousness; inspirations will respond to the concentrated desire or the mere passing emotion of the man of genius; after-images will recur, under unknown conditions, long after the original stimulus has been withdrawn; memory-images will surge up into our minds with even unwished-for vividness; the brilliant exactness of illusions hypnagogiques will astonish us in the revealing transition from waking to sleep.
All is prepared, so to say, for some empirical short-cut to a fuller control of these subjacent pictures; just as before Mesmer and Puységur all was prepared for an empirical short-cut to trance, somnambulism, suggestibility.
All that we want is to hit on some simple empirical way of bringing out the correlation between all these types of subjacent vision, just as mesmerism was a simple empirical way of bringing out the correlation between various trances and sleep-waking states.
Crystal-vision, then, like hypnotic trance, might have been gradually evolved by a series of reasoned experiments, along an unexceptionable scientific road.