Bilateral hemispheric processing deficits in schizophrenia.

Schizophrenics are known to have an early visual processing deficit, but the exact nature of that deficit is unclear. The present research was undertaken in order to establish the difference between schizophrenic and normal subjects in their processing of visual stimuli. Previous studies have shown that short duration stimuli activate a transient visual system which is associated with the right hemisphere, while longer duration stimuli activate the sustained system associated with the left hemisphere. The present study was designed to determine the effects of activation/inactivation of both the sustained and transient channels on hemispheric processing in normal compared to schizophrenic patients. The task was a forced choice continuity of form. The subject was required to detect two grating pulses, separated by a blank interval (interstimulus interval-ISI) vs. a single grating pulse, which was shown for the same total duration as the two pulse condition. Threshold ISI was obtained and used as the index of visible persistence/speed of visual processing, 19 schizophrenics, 12 depressives, 6 schizoaffectives, and 11 controls participated in the study. Stimuli were sinusoidal spatial frequency (SF) gratings of 0.9 and 15 c/degrees presented independently to the left and right hemisphere for durations of 50 and 250 ms. The results revealed statistical significance for Diagnosis, Diagnosis x SF, and Position x Diagnosis. Normal controls and depressed subjects did not statistically differ from each other, while schizophrenic and schizoaffectives differed from both control groups and on some conditions from each other. No hemispheric asymmetries were observed for any group. The results are discussed in terms of differential deficits in schizophrenics in the absence of early occurring asymmetries.