sensory_deprivation.htmlTEXTUm6l5B5D# Sensory deprivation

Starve your senses and you reap the consequences

©Robert Sekuler 1999
Sensory starvation can come from accidental causes. When a functioning human brain is cut off from sensory input, the result is usually experiences called hallucinations -- perceptual experiences that seem real to the perceiver but occur without normal stimulation of the sense organ. Hallucinations, which can occur when someone has taken a psychoactive drug such as LSD, are usually signs of mental disturbance, such as that associated with schizophrenia. However, hallucinations also can occur in normal people when they suffer sensory starvation.

In surveying this phenomenon, Geoffrey Schultz and Ronald Melzack (1991) examined reports of visual hallucinations in apparently normal people, dating back to the mid-eighteenth century. In nearly all the 60 case reports they studied, the h allucinations followed some severe impairment of vision. In one early report, Charles Bonnet, a French physician, described an elderly uncle who began to experience complex visual hallucinations some years after having cataract surgery. These images - -of men, women, horsedrawn carriages, and buildings-- lasted from a few seconds to several days. Though Bonnet's elderly uncle knew that the objects he saw were not real, his experiences were still quite powerful. Other cases described by Schultz and Melzack involved bizarre imagery: tiny giraffes or miniature hippopotamuses, an entire circus troupe that burst through the window, large chickens wearing shoes, or people with outsized heads. In honor of the first person to describe this condition, these hallucinations are called "Charles Bonnet syndrome."

When they examined fourteen new cases of Charles Bonnet syndrome, Schultz and Melzack (1993) verified that the hallucinations were not the result of drugs or mental conditions such as dementia, depression or anxiety. Instead, as in the historical cases they had examined previously, the hallucinations were consistently associated with damage to the visual system. These hallucinations in normal, healthy persons, followed diseases or accidents that interfered with the normal flow of information from the eyes to the brain. Schultz and Melzack (1991) suggested that the hallucinations occur when regions of the brain that normally receive and process information from the eyes are stimulated indirectly, in the absence of input from the eyes. Schultz and Melzack note that this explanation contradicts the notion "that people who experience the syndrome are 'going crazy'. These people must be assured that their experiences are a natural consequence of deteriorating eyesight" (1991; p. 823).

In the Charles Bonnet syndrome, the sensory starvation that set the stage for the hallucinations was accidental --the result of a naturally occurring vision impairment. But in special conditions it is possible to produce sensory starvation intentionally, though temporarily. One study of intentional sensory starvation was done in the mid-1950's at McGill University (Heron 1957). Undergraduate student volunteers were recruited through an advertisement that offered people good pay, the equivalent of more than $100 (U.S.) per day in today's U.S. dollars, to do nothing but lie on a comfortable bed in a lighted cubicle 24 hours a day for as long as they wanted to. This may sound like pretty easy money, but the volunteers discovered that doing nothing was far harder than they could have believed possible.

Volunteers were deprived of normal sensory input. Their eyes were covered with translucent plastic goggles that diffused whatever was seen, thereby eliminating pattern vision. Subjects' heads were cradled in a foam rubber pillow that covered their ears in order to block out most external sounds (the steady hum of an air conditioner and fan masked other sounds). Their arms were wrapped in tubes that kept them from touching anything with their hands. These conditions were maintained around the clock, except when the volunteers were being tested, fed or had to go to the bathroom. After a very short time of this arrangement, volunteers started to bail. Most quit the experiment after just two or three days; one volunteer managed to stick it out fo r as long as six days. Deprivation of sensory input produced dramatic effects including striking visual hallucinations. These usually started with hallucinations of simple forms --dots of light or simple patterns.

"Then the visions became more complex, with abstract patterns repeated like a design on wallpaper, or recognizable figures, such as rows of little yellow men with black caps on and their mouths open. Finally there were integrated scenes, e.g. , a procession of squirrels with sacks over their shoulders marching 'purposefully' across the visual field, prehistoric animals walking about in a jungle, processions of eyeglasses marching down a street...The subjects had little control over the content of the hallucinations. Some kept seeing the same type of picture no matter how hard they tried to change it. One man could see nothing but dogs, another nothing but eyeglasses of various types, and so on... The hallucinations were not confined to visio n. Occasionally a subject heard people in the 'scene' talking, and one many heard a music box playing. Another saw the sun rising over a church and heard a choir singing 'in full stereophonic sound.' Several subjects reported sensations of movement or touch. One had a feeling of being hit in the arm by pellets fired from a miniature rocket ship he saw; another, reaching out to touch a doorknob in his vision, felt an electric shock." (Heron, 1957; p.54)

Schultz and Melzack (1993) proposed a single explanation for hallucinations that are experienced by volunteers in sensory deprivation experiments and for hallucinations experienced by people with damaged sensory systems (as in Charles Bonnet syndrome). These hallucinations may spring from the normal, ongoing activity of the brain, which under ordinary conditions is kept under control by sensory activity triggered by sensory stimuli.