Perceptual and attentional asymmetries in schizophrenia: further evidence for a left hemisphere deficit.

Increasing evidence suggests the presence of a lateralizing attentional deficit in schizophrenia. In the present study, 23 unmedicated patients with schizophrenia (mean age = 32.1 years) and 14 age- and sex-matched normal subjects were studied with the Global/Local Task to provide converging evidence for the presence of a left-hemisphere-associated attentional deficit in schizophrenia. This task is sensitive to the integrity of mechanisms involved in discriminating local and global elements of stimuli. Previous research has linked the discrimination of local targets to left hemispheric processes and the discrimination of global targets to right hemispheric processes. As predicted, patients were impaired in the detection of local level targets, consistent with a left hemispheric deficit. The degree of impairment correlated with the patient's level of auditory hallucinations. These results are consistent with previous studies showing an asymmetrical attentional deficit in schizophrenia and left hemispheric dysfunction. The correlation between this deficit and auditory hallucinations is consistent with a hypothesized relationship between this symptom in schizophrenia and left temporal pathology.