Forward and backward visual masking of contour by light in positive- and negative-symptom schizophrenia.

Forward and backward masking of contour by light was investigated with stimulus onset asynchronies from 20 to 180 ms in a group of 22 schizophrenic patients and 22 matched normal controls. Individuals with schizophrenia were selected using American Psychiatric Association (1987) criteria and were also assessed using the Andreasen scales for the presence of positive and negative symptoms (N.C. Andreasen, 1981, 1983). The Andreasen scales were used to divide schizophrenic patients into 2 subgroups (positive and negative symptoms). Positive-symptom schizophrenic patients showed no differences in their target duration thresholds or in their backward masking functions. Negative-symptom schizophrenic patients showed significantly longer target duration thresholds and experienced significantly more backward masking. There was no difference between schizophrenic patients and controls in forward masking.