Syntactic and semantic processing in the healthy and aphasic human brain

A syntactic and a semantic task were performed by German-speaking healthy s ubjects and aphasics with lesions in the dominant left hemisphere. In both tasks, pictures of objects were presented that had to be classified by pres sing buttons. The classification was into grammatical gender in the syntact ic task (masculine or feminine gender?) and into semantic category in the s emantic task (man- or nature made?). Behavioral data revealed a significant Group by Task interaction, with aphasics showing most pronounced problems with syntax. Brain event-related potentials 300-600 ms following picture on set showed different task-dependent laterality patterns in the two groups. In controls, the syntax task induced a left-lateralized negative ERR wherea s the semantic task produced more symmetric responses over the hemispheres. The opposite was the case in the patients, where, paradoxically, stronger laterality of physiological brain responses emerged in the semantic task th an in the syntactic task. We interpret these data based on neuro-psycholing uistic models of word processing and current theories about the roles of th e hemispheres in language recovery.