UC San Diego

Syntactic processing is widely held to be a left hemisphere (LH) phenomenon, a view influenced by a large body of research showing lesions to certain LH areas are far more devastating than are lesions to corresponding right hemisphere (RH) areas. Although few studies have examined whether RH damage causes subtle syntactic processing deficits, there is evidence it does. This dissertation investigated the relative contribution of each hemisphere to syntactic processing in neurologically normal individuals using event-related potential (ERP) and behavioral studies in combination with the visual half- field paradigm. Central presentation ERP studies were conducted as a baseline against which to compare the results of the lateralized studies. The first experiment series (chapters two, three) examined processing of (in)correct grammatical number agreement marked either lexically or morphologically. Both behavioral and ERP results suggested the hemispheres are equally able to appreciate lexically marked agreement. In contrast, the RH appears to have greater difficulty than the left in processing morphologically marked agreement. The second experiment series (chapters four, five) investigated whether this LH advantage for morphologically-marked agreement errors reflects a language-specific difference in hemispheric processing or a low level, perceptually- based difference. Stimuli included both morphological and lexical conditions; salience of lexical markings was manipulated to adjudicate between these alternatives. Behavioral results suggested that the observed processing differences were based at the perceptual level. However, the ERP results obtained were not in accord with the predictions and did not lend themselves to any clear conclusions with respect to the hypothesis investigated. The central presentation studies in chapter two also investigate how aging affects syntactic processing. ERPs from elderly compared to young participants showed no evidence of an age-related delayed or diminished P600 effect, although there were changes in its scalp distribution, suggesting a qualitative, rather than any strictly quantitative, age-related change in speed of processing. Chapter four provides data relevant to the debate concerning the mental representation(s) of regular and irregular words, and the mental processes underlying the left anterior negativity component. Overall, we find that the RH is sensitive to certain grammatical manipulations, although not always in the same manner as the LH