The results of a study conducted at University College London said when a group of people are placed in a dark, silent room, many start hallucinating after just a few minutes.
The study, which was published in the "Journal of Nervous and Mental Disease," attempted to differentiate the subjective experience of different people undergoing sensory deprivation, depending on how predisposed they were to hallucinating.
Celia Morgan, a research fellow at the university, described the process of the investigation.
Morgan said participants were first given a questionnaire to determine psychotic personality expressions and other unusual perceptions.
From the results of the questionnaire, researchers selected two groups, those who were more prone to hallucinations in daily life and those who were not. None of the participants were institutionalized or mentally disabled. They were all members of the normal population.
The selected participants were then closed inside an anechoic chamber, a room designed specifically to eliminate all light, sound and echoes.
"(Sensory deprivation chambers) are used to study thinking, emotions, memory and so forth when there is minimal environmental stimuli," said Peter Suedfeld, psychologist at the University of British Columbia in Vancouver who has done research on sensory deprivation for 30 years.
Participants in UCL's study rated their expressions before and after 15 minutes in the chamber.
"Hallucination-prone people had weird experiences," Morgan said.
However, even some of the participants who were not prone to hallucinations still had unpleasant experiences in the quarter hour they spent in the chamber, Morgan said.
"Healthy people can get hallucinations under sensory deprivation," Morgan said. "They experienced less (perceptual distortion) than hallucination-prone people, but still experienced some."
Morgan, who has done research on hallucinogenic drugs, noted the similarity in hallucinations produced by drugs and those produced in the anechoic chamber.
"What we saw for sensory deprivation hallucinations is that when there's not information coming in (the brain)," Morgan said, "our brain predicts what's supposed to be there. same thing happens when you take hallucinogenic drugs."
Morgan explained that different drugs cause different kinds of hallucinations, but that the serious hallucinations reported in the anechoic chamber were comparable to the effects of LSD.
Initially explored by researchers in the '50s and '60s, sensory deprivation has become a controversial topic. The CIA has implemented it as a form of torture, while others have discovered it has therapeutic value.
Suedfeld called sensory deprivation "an obsolete term used for what is now referred to as Restrictive Environmental Stimulation Therapy."
Sensory deprivation tanks, or flotation tanks, have been greatly popularized by Suedfeld's research.
There is no light inside the tank, and a person can float in a pool of Epsom salt that is heated precisely to body temperature. The Epsom salt is particularly useful because of its properties that absorb sound and scents.
The combined effect is almost a complete elimination of sensation.
The Harmony Learning Center in Atlanta is a therapeutic center that specializes in flotation therapy.
"I've seen a lot of people have different experiences," said Marilyn Morrison, the owner of the therapeutic center. "At first, the mind goes frantic. It takes about 25 minutes for that chatter to subside."
Morrison said it is helpful for participants to focus on breathing until the mind relaxes.
Once the "chatter" goes away, it should be a pleasant experience, Morrison said.
Flotation chambers have numerous health benefits, Suedfeld said.
Suedfeld denied that REST flotation tanks could prove psychologically harmful, contrary to UCL's research.
"People who have hallucinations are people who are prone to have hallucinations," Suedfeld said. "It is dependent on personality."
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