Hemispheric differences in global versus local processing: still unclear

Laterality studies examining the recognition of hierarchical letter forms in normal subjects have had a checkered history. Early ones reported evidence of right hemisphere global and left hemisphere local processing, but later ones found little evidence of lateralized effects. Here three reaction time experiments examine suggestions made in the literature that the asymmetries appear only with small stimulus eccentricities, few experimental trials, or short stimulus exposures. No evidence is found to support a right-hemisphere-global and left-hemisphere-local distinction. However, Experiment 3 reports a shift toward right hemisphere processing of local letters as stimulus duration is curtailed, suggesting right hemisphere involvement when visual conditions are impoverished. These outcomes pose a challenge for clinical reports that differently lateralized cortical lesions have different effects on global and local processing.