Global-local processing in schizophrenia: Hemispheric asymmetry and symptom-specific interference

The hypothesis of atypical functional hemispheric asymmetry in schizophreni a is tested using the directed global-local paradigm, a lateralizing measur e of visual perception. Results indicate low error rates (< 2%) for schizop hrenia and normal control groups, but longer response times for the schizop hrenia group. In the normal group, detection speed of global and local form s did not differ. In contrast, the schizophrenia group responded significan tly faster to local relative to global forms, which supports the asymmetry hypotheses of left hemisphere overactivity-right hemisphere underactivity i n schizophrenia. The normal group exhibited a global interference effect (s lowed response latency to the local target in the presence of a dissimilar global distracter). when the schizophrenia group was examined according to symptom type and severity, high positive symptom severity was associated wi th local interference (slowed response latency to the global target in the presence of dissimilar local distracters). Negative symptoms were not assoc iated with interference from the competing local or global forms. Patients with a combination of high positive and low negative symptoms showed signif icantly greater local interference than patients with high negative and low positive symptoms. Interconnected temporal and frontal systems are postula ted to contribute to this pattern of perceptual processing efficiency and d istractibility in schizophrenia.