Hallucinations by Oliver Sacks Read Free Book Online Page A

darkness: “the prisoner’s cinema.”
    Total visual deprivation is not necessary to produce hallucinations—visual monotony can have much the same effect. Thus sailors have long reported seeing things (and perhaps hearing them, too) when they spent days gazing at a becalmed sea. It is similar for travelers riding across a featureless desert or polar explorers in a vast, unvarying icescape.Soon after World War II, such visions were recognized as a special hazard for high-altitude pilots flying for hours in an empty sky, and it is a danger for long-distance truckers focused for hours on an endless road. Pilots and truckers, those who monitor radar screens for hours on end—anyone with a visually monotonous task is susceptible to hallucinations. (Similarly, auditory monotony may lead to auditory hallucinations.)
    In the early 1950s, researchers in Donald Hebb’s laboratory at McGill University designed the first experimental study of prolonged perceptual isolation, as they called it (the term “sensory deprivation” became popular later). William Bexton and his colleagues investigated this with fourteen college students immured in soundproof cubicles for several days (except for brief time out for eating and going to the toilet), wearing gloves and cardboard cuffs to reduce tactile sensation and translucent goggles which allowed only a perception of light and dark.
    At first the test subjects tended to fall asleep, but then, on awakening, they became bored and craved stimulation—stimulation not available from the impoverished and monotonous environment they were in. And at this point, self-stimulation of various sorts began: mental games, counting, fantasies, and, sooner or later, visual hallucinations—usually a “march” of hallucinations from simple to complex, as Bexton et al. described:
    In the simplest form the visual field, with the eyes closed, changed from dark to light colour; next in complexity were dots of light, lines, or simple geometrical patterns. All 14 subjects reported such imagery, and said it was a new experience to them. Still more complex forms consisted in “wall-paper patterns,” reported by 11 subjects, and isolated figures orobjects, without background (e.g., a row of little yellow men with black caps on and their mouths open; a German helmet), reported by seven subjects. Finally, there were integrated scenes (e.g., a procession of squirrels with sacks over their shoulders marching “purposefully” across a snow field and out of the field of “vision”; prehistoric animals walking about in the jungle). Three of the 14 subjects reported such scenes, frequently including dreamlike distortions, with the figures often being described as “like cartoons.”
    While these images first appeared as if projected onto a flat screen, after a time they became “compellingly three-dimensional” for some of the subjects, and parts of a scene might become inverted or pivot from side to side.
    After being initially startled, the subjects tended to find their hallucinations amusing, interesting, or sometimes irritating (“their vividness interfered with sleep”) but without any “meaning.” The hallucinations seemed external, proceeding autonomously, with little relevance or reference to the individual or situation. The hallucinations usually disappeared when the subjects were asked to do complex tasks like multiplying three-figure numbers, but not if they were merely exercising or talking to the researchers. The McGill researchers reported, as many others have, auditory and kinesthetic hallucinations as well as visual ones.
    This and subsequent studies aroused enormous interest in the scientific community, and both scientific and popular efforts were made to duplicate the results. In a 1961 paper, John Zubek and his colleagues reported, in addition to hallucination, a change in visual imagery in many of their subjects:
    At various intervals … the subjects were asked to imagine or visualize