Lateralization patterns of verbal stimuli processing assessed by reaction time and event-related potentials in schizophrenic patients.

Event-related potentials (ERPs), reaction time (RT), number of errors and number of omissions were recorded by using a visual target detection paradigm in which consonant pairs were presented in a central and in a lateral condition. Fourteen DSM III drug-free schizophrenics and 19 healthy subjects took part in the study. All of them were male and right-handed. Independent principal component analysis and varimax rotation were performed for each condition. Separate ANOVAs were performed on factor scores computed for each rotated principal component. In the central condition, schizophrenic patients showed a reduction of the late positive complex (LPC) peak with respect to normal controls, and this reduction was associated with a predominant negative symptomatology. No pattern of lateral asymmetry was found in either group for behavioural and ERP measures. For the lateral condition, a significant advantage of the right visual field (RVF) presentation (shorter RT and larger LPC peak for RVF stimuli) was observed in normal subjects, while no visual field effect on these two measures was detected in schizophrenics. Significant differences were found between the two groups on both behavioural and ERP measures for the RVF only. Furthermore, two ERP components showed a marked advantage of the left visual field in the patient group, associated with a predominance of positive symptoms in the clinical picture.