Though, as a race, we are eye-minded, individually we differ much with regard to the rôle that sight plays in our psychic life. In one direction a good index of its importance is to be found in the perfection of the visualizing faculty, of which Mr. Galton has given an interesting account. He asked various persons to describe, amongst other things, the vividness of their mental picture when calling to mind the morning's breakfast-table. To some the mental scene was as clear and as natural as reality, lacking none of the details of form or color; to others the resulting mental image was tolerably distinct, with the conspicuous features well brought out, but the rest dim and ill-defined; while a third group could only piece together a very vague, fragmentary, and unreliable series of images, with no distinct or constant picture.
Similar differences are observable with regard to memories. Some persons firmly retain what they read, while the memory forte of others is in what they hear; and pathology supports this subdivision of the sense-memories by showing, for example, that all remembrance for seen objects may be lost while that for sounds remains intact. A case, remarkable in several aspects, is recorded by M. Charcot. The subject in question could accurately call up, in full detail, all the scenes of his many travels, could repeat pages of his favorite authors from the mental picture of the printed page, and by the same means could mentally add long columns of numbers. The mere mention of a scene in a play, or of a conversation with a friend, immediately brought up a vivid picture of the entire circumstance. Through nervous prostration he lost this visual memory. An attempt to sketch a familiar scene now resulted in a childish scrawl; he remembered little of his correspondence, forgot the appearance of his wife and friends, and even failed to recognize his own image in a mirror. Yet his eyesight was intact and his intellect unimpaired. In order to remember things he had now to have them read aloud to him, and thus bring into play his undisturbed auditory centre--to him an almost new experience.
The function of vision in dreams is doubtless subject to similar individual variations, though probably to a less extent. Seeing, with rare exceptions, constitutes the typical operation in dreams; it is this sense, too, that, under the influence of drugs or of other excitement, is most readily stimulated into morbid action, and most easily furnishes the basis of delusions and hallucinations to a disordered mind. The dependence of the nature and content of dreams upon the waking experiences is so clearly proven that it would be surprising not to find in them the individual characteristics of our mental processes; and if Aristotle is right in saying that in waking life we all have a world in common but in dreams each has a world of his own, we may look to the evidence of dream-life for indications of unrestrained and distinctive psychological traits.