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.

Differential visual information processing between schizophrenics and other psychiatric populations.

Deficits at the earliest stages of information processing are among the most consistent abnormalities found in schizophrenics. To better understand the deficit, the present study indirectly evaluated the functional status of two visual channels, transient and sustained, which have been implicated in early information processing. A forced-choice, two-pulse detection task was used to determine the duration that subjects required to detect a blank interval (ISI) separating a two pulse grating vs. a single pulse grating. Threshold ISI was used as the index of visible persistence. Four groups of subjects participated in the study: schizophrenics, schizoaffectives, major depressives, and normal controls. The results of the ANOVA showed a significant main effect for diagnosis, position, and spatial frequency, as well as a significant effect for diagnosis x position and diagnosis x spatial frequency. The results are discussed in terms of the differential response and retinal distribution of each channel.