[Deficit in suppression of interference in visual information processing by schizophrenic subjects]

Although many studies have indicated information processing deficits in schizophrenic patients, the precise nature and underlying causes of these deficits remain largely uncertain. One prominent hypothesis is that these patients show insufficient attentional inhibition. This deficit to inhibition has been linked to certain cognitive disorders in schizophrenic patients, including attention deficits, as well as to some clinical symptoms, especially those involving delusional thought, hallucinations,and poor contact with reality. The hypothesis of deficient attentional inhibition, although attractive in some ways, is difficult to work with, because it is not easy to directly measure "attentional inhibition". Several studies involving normal subjects have linked attentional inhibition with performance on a task demanding the suppression of distracting information: the presumption is that efficient attentional inhibition will permit rapid responses because the distracting information will be quickly suppressed, allowing undistracted processing of the target information. The present study measures schizophrenic patients' performance on a task demanding suppression of rapidly-presented visual information. An important methodological feature of this study is that performance is measured in terms of "percent correct responses" rather than the reaction time measures typically used in tasks demanding distractor suppression, such as Stroop-like selective attention tasks. Since reaction times are not considered, the results cannot be interpreted in terms of deficient response organization and execution. Schizophrenic (18) and normal (18) subjects underwent trials in which a visual target was the second of two stimuli presented in rapid succession. Interference produced by a non-target significantly impaired perception of the target for schizophrenic patients. This effect persisted longer in the schizophrenic subjects possibly because of deficient attentional inhibition.