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LSD GRATIShttp://www.encyclopedia.com/doc/1G1-20522809.html

Sensory isolation has been the subject of numerous research projects showing that individuals began to hallucinate after only a few hours in a sensory isolation chamber that removes all stimulation from touching, hearing and seeing. It has been hypothesized that the hallucination is the person's attempt to provide self-stimulation - a form of communication, if you will.