The backward masking procedures that have been used in psychopathology research have confounded two types of masking mechanisms (integration and interruption) and two types of visual channels (transient and sustained). In an earlier study, we attempted to limit the masking mechanism to interruption. The current study limited the role of sustained (parvocellular) visual channels to masking performance.
Masking procedures were altered in the following two ways to reduce reliance on sustained visual channels: (1) the spatial frequency was lowered by blurring the target and (2) a location task was used instead of an identification task. Manic patients were included to examine the specificity of deficits on these tasks to schizophrenia and to test the hypothesis that mania is associated with abnormalities on visuospatial tasks.
Schizophrenic patients differed significantly from normal controls on both masking conditions. Manic patients also showed deficits relative to normal controls. Manic patients showed a significantly different masking function from that of schizophrenic patients on the location condition.
Schizophrenic deficits within masking paradigms may involve abnormalities in transient, as opposed to sustained, visual channels. Masking performance deficits were also found in manic patients, but the underlying processes are probably different. A reformulation is offered concerning the nature of early visual processing deficits in schizophrenia.