• Forty-eight schizophrenics (24 paranoids, 24 nonparanoids) and 24 matched controls (12 men and 12 women in each group) were asked to detect the differences between 30 pairs of altered pictures presented successively (15 pairs) and simultaneously (15 pairs) in a counterbalanced order. Overall performance, as measured by reaction time and response quality, was better for controls than for schizophrenics. However, schizophrenics, like right hemisphere brain-damaged patients who presumably rely on their left hemisphere, reacted faster in the successive presentation procedure while the controls reacted equally fast in both conditions. These results support the hypothesis that schizophrenics tend to overactivate their left dysfunctional hemisphere. Twenty-four depressed patients, tested in the same procedure, showed a pattern of results similar to that of controls, suggesting that the results obtained for schizophrenics are not a general characteristic of psychosis.