One does not see with the eyes; one sees with the brain, which has dozens of different systems for analyzing the input from the eyes.
— Oliver Sacks, Hallucinations (2012)
The folklore of every culture includes supernatural figures like the incubus and succubus, which assault the sleeper sexually, or the Old Hag, which paralyzes its victims and sucks their breath away. Such images seem to be universal — indeed, there is a remarkable similarity of such figures in widely disparate cultures, although there are local variations of every sort. Hallucinatory experiences, whatever their cause, generate a world of imaginary beings and abodes — heaven, hell, fairyland. Such myths and beliefs are designed to clarify and reassure and, at the same time, to frighten and warn. We make narratives for a nocturnal experience which is common, real, and physiologically based.
When traditional figures — devils, witches, or hags — are no longer believed in, new ones — aliens, visitations from “a previous life” — take their place. Hallucinations, beyond any other waking experience, can excite, bewilder, terrify, or inspire, leading to the folklore and the myths (sublime, horrible, creative, and playful) which perhaps no individual and no culture can wholly dispense with.
— Oliver Sacks, Hallucinations (2012)
But while there are neurologically determined categories of visual hallucination, there may be personal and cultural determinants, too. No one can have hallucinations of musical notation or numbers or letters, for example, if they have not actually seen these at some point in real life. Thus experience and memory may influence both imagery and hallucination — but with CBS [Charles Bonnet Syndrome], memories are not hallucinated in full or literal form. When people with CBS hallucinate people or places, they are almost never recognizable people or places, only plausible or invented ones. CBS hallucinations give one the impression that, at some lower level, in the early visual system, there is a categorical dictionary of images or part images — of generic “noses,” for example, or “headwear” or “birds,” rather than of particular noses or headwear or birds. These are, so to speak, the visual ingredients called upon and used in the recognition and representation of complex scenes — elements or building blocks which are purely visual, without context or correlation with other senses, without emotion or particular associations of place or time. (Some researchers have called them “proto-objects” or “proto-images.”) In this way, CBS images seem more raw, more obviously neurological, not personal like those of imagination or recollection.
— Oliver Sacks, Hallucinations (2012)
The last illusions we considered might fairly be called hallucinations. We must now consider the false perceptions more commonly called by that name. In ordinary parlance hallucination is held to differ from illusion in that, whilst there is an object really there in illusion, in hallucination there is no objective stimulus at all. We shall presently see that this supposed absence of objective stimulus in hallucination is a mistake, and that hallucinations are often only extremes of the perception process, in which the secondary cerebral reaction is out of all normal proportion to the peripheral stimulus which occasions the activity. Hallucinations usually appear abruptly and have the character of being forced upon the subject. But they possess various degrees of apparent objectivity. One mistake in limine must be guarded against. They are often talked of as mental images projected outwards by mistake. But where an hallucination is complete, it is much more than a mental image. An hallucination is a strictly sensational form of consciousness, as good and true a sensation as there were a real object there. The object happens not to be there, that is all.
— William James, The Principles of Psychology 1890
The full text can be found here.
I have had migraines for most of my life; the first attack I remember occurred when I was 3 or 4 years old. I was playing in the garden when a brilliant, shimmering light appeared to my left — dazzlingly bright, almost as bright as the sun. It expanded, becoming an enormous shimmering semicircle stretching from the ground to the sky, with sharp zigzagging borders and brilliant blue and orange colors. Then, behind the brightness, came a blindness, an emptiness in my field of vision, and soon I could see almost nothing on my left side. I was terrified — what was happening? My sight returned to normal in a few minutes, but these were the longest minutes I had ever experienced.
— Oliver Sacks, “Patterns. Migraine: Perspectives on a Headache”, New York Times (13 February 2008).
The full text can be found here.
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