Backward versus forward visual masking deficits in schizophrenic patients: centrally, not peripherally, mediated?

OBJECTIVE: Schizophrenic patients have repeatedly demonstrated the inability to rapidly process information when tasks are timed or the processing load is relatively high. Schizophrenic patients show consistent deficits in the visual backward masking paradigm. In visual backward masking, an informational target stimulus is presented, followed after an interstimulus interval by a masking stimulus that interferes with or interrupts target identification.
METHOD: In order to clarify whether the visual backward masking deficits of schizophrenic patients are indeed central rather than peripheral in origin, the authors compared visual backward masking to psychometrically matched visual forward masking performance in 35 normal comparison subjects and then 35 schizophrenic patients. In visual forward masking, the mask precedes the target, and visual forward masking mechanisms are felt to be more peripheral (retinal) than are visual backward masking mechanisms.
RESULTS: For psychometrically matched forward and backward masking tasks, the schizophrenic patients had a selective and differential deficit in the backward masking condition.
CONCLUSIONS: These results support the interpretation that the observed visual backward masking deficits of schizophrenic patients are centrally mediated.