Introduction A series of studies has been planned to test the hypotheses (1) that whenever perceptual distortions are induced, by whatever means, the distorting process begins with changes in the orientational percepts—of time, space, body boundary, movement in space, and the gravity-bound feeling of weight—and that these changes proceed in a regular, orderly, predictable way; (2) that such changes are regularly associated with emotional disturbance, and, (3) finally, that the symbolic system of the mental apparatus interprets the entire experience in a characteristic way, at first by the imaginative processes, so that, presently, misinterpretations giving way to hallucinations are interpreted in a dream-like state, eventually giving way to more or less habitual delusions. At the same time, it is our intention to discover the determinance of the various thresholds involved in the course of perceptual changes. These would be as follows: (a) the threshold