A PERSON cut off from meaningful sensory stimulation is literally on his own. What significance he puts into his experience comes largely from him. Perceptual or sensory deprivation can be, in Goldberger's phrase, a walk-in inkblot. Reactions vary from something very like psychosis to pleasant enjoyment. It has been suggested that deprivation, like the hallucinogens, offers an experimental analogue of psychosis. As with the LSD experience much depends upon the atmosphere in which the experiment takes place. But under standard conditions almost every worker has found substantial variation in how his individual subjects react. Would deprivation be a useful tool in individual assessment? Does it measure the individual's potential for psychosis? Does the variability of individual reactions shed any light upon the theoretical explanations of the effects of deprivation? Lindsley1 links the effects of deprivation to the need of the reticular activating