Collinear contextual suppression in schizophrenic patients.

Schizophrenic patients show aberrancies of contextual processing over a broad range. Of particular importance are low level contextual deficiencies since they might cause higher level processing deficits. It was previously found that schizophrenic patients reveal diminished contextual facilitation in visual detection tasks taken as an indication of a modified neural circuitry. Here, we show that contextual suppression is not affected. Sixteen schizophrenic patients and sixteen healthy controls participated in a backward masking task in which a vernier target was followed by a masking grating. In accordance with a previous publication, schizophrenic patients needed longer SOAs between the vernier and the grating onset to obtain a performance level comparable to healthy controls. To study contextual processing we added single collinear lines to the grating. These lines yielded a strong impairment of performance in patients and controls. This impairment is comparable between the two groups if SOAs were individually adjusted. Hence, whereas contextual facilitation is deficient, contextual suppression seems to be intact in schizophrenic patients.