The effect of illness duration on perceptual asymmetry in schizophrenia

Perceptual asymmetry in a group of schizophrenic subjects who were clinically stable and living in the community was compared with a group of normal control subjects matched for age and sex using a dichotic monitoring task of language processing. Schizophrenic subjects showed reduced target detection and slower reaction times for both left and right ear inputs. In relation to performance asymmetry, the schizophrenic subjects had a reduced speed of responding to left ear items compared to normal controls. Within the schizophrenic group differences in performance emerged according to duration of illness. Shorter duration of illness was associated with poorer target detection overall and comparatively greater magnitude of the normal right ear advantage. The latter was accounted for by a relative augmentation of the normal left ear performance decrement. These results were partly reflected in the reaction time measures. The findings suggest that as illness duration increases there may be a tendency for certain aspects of the information processing abnormality in schizophrenia to normalise, in spite of continued deficits as reflected in prolonged reaction times.