Effects of task relevance and attention on P3 in schizophrenic patients.

The P3 component of the event-related potentials (ERPs) to auditory task-relevant and task-irrelevant stimuli in 'Attend Auditory' (i.e., reaction time task) and 'Attend Visual' (i.e., when the auditory stimuli were being ignored) conditions was investigated in 13 RDC/DSM-III diagnosed schizophrenic patients. ERPs were recorded from Fz, Cz, and Pz. Compared to controls, schizophrenics had a significantly smaller P3 in the Attend Auditory than in the Attend Visual condition and to the task-relevant than to the task-irrelevant stimuli. Furthermore, the patients' P3 response to the most salient task-irrelevant stimuli in the Attend visual condition was normal. The results are discussed as suggesting that schizophrenics either allocate relatively more resources to task-irrelevant than task-relevant stimuli or that they fail to habituate to task-irrelevant stimuli.