Backward masking in schizophrenia: Relationship to medication status, neuropsychological functioning, and dopamine metabolism

Patients with schizophrenia have deficits in early information processing, which have been demonstrated on several tasks, including the backward paradigm (Braff et al 1991). On this task, patients with schizophrenia, asked to identify a first stimulus, followed by a second masking stimulus (a cross of Xs), need longer interstimulus intervals (ISis) between target and mask than controls to successfully identify the target stimulus (Braff et al 1991). This deficit in initial processing could lead to faulty intake of information resulting in clinical symptomatology. One recent study indicates that the backward deficit in patients with schizophrenia is related to thought disorder (Perry and Braff 1994). The goal of this study is to further examine potential correlates of backward dysfunction. First, we examined whether or not backward deficits are due to a medication effect. Unmedicated patients show a deficit (Braff and Saccuzzo 1982; Harvey et al 1990), but most studies have examined medicated patients. This pilot study is the first study to our knowledge to utilize a within-subjects design to test patients on and off medication, thus providing a more rigorous test of the