HEMISPHERIC-DIFFERENCES IN GLOBAL VERSUS LOCAL PROCESSING - STILL UNCLEAR

Laterality studies examining the recognition of hierarchical letter fo rms in normal subjects have had a checkered history. Early ones report ed evidence of right hemisphere global and left hemisphere local proce ssing, but later ones found little evidence of lateralized effects. He re three reaction time experiments examine suggestions made in the lit erature that the asymmetries appear only with small stimulus eccentric ities, few experimental trials, or short stimulus exposures. No eviden ce is found to support a right-hemisphere-global and left-hemisphere-l ocal distinction. However, Experiment 3 reports a shift toward right h emisphere processing of local letters as stimulus duration is curtaile d, suggesting right hemisphere involvement when visual conditions are impoverished. These outcomes pose a challenge for clinical reports tha t differently lateralized cortical lesions have different effects on g lobal and local processing. (C) 1996 Academic Press, Inc.