Differential effects of left-and right-hemisphere brain damage on the ability to use context in lexical ambiguity resolution

Recent research has argued that the intact functioning of both the left (LH) and right cerebral hemispheres (RE) is integral for comprehending lexically ambiguous words (Chiarello, 1998; Faust & Chiarello, 1998; Faust & Gemsbacher, 1996). While studies of neurologically intact individuals have attributed specific functions to the LH and RH, studies of brain-damaged patients have failed to provide complementary evidence for these hemispheric abilities. In addition, the majority of studies have focused on ambiguity resolution in single-sentence (local) contexts, and, as such, do not address whether each hemisphere is sensitive to different types of context, a factor which could potentially serve to modulate brain-damaged patients' ability to resolve ambiguity. To illuminate the role of the cerebral hemispheres in ambiguity resolution and to explore the sensitivity of each hemisphere to different types of context, three studies were undertaken in this thesis. The first study examined left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects' ability to use a single-sentence local context to resolve lexically ambiguous words. Results indicated that both patient groups were unable to use this type of context. While LHD patients activated both meanings regardless of context at a short (0 ms) ISI and no meanings at a longer (750 ms) ISI, RHD patients only activated more frequent first meanings at both ISIs. The second study explored these same groups' ability to use a two-sentence global context. Results of this experiment in part paralleled those of the previous one, showing that LHD patients were unable to activate any meanings at either ISI, whereas RHD patients, at both ISIs, again activated more frequent meanings regardless of context. The final study investigated these individuals' ability to use a four-sentence discourse context. Findings of this study, across all groups