Although right hemisphere brain damage (RHD) typically does not cause aphasic language disorders, specific discourse comprehension impairments often follow RHD. These studies are proposed to investigate several possible mechanisms of discourse comprehension inadequacies in RHD adults. The approach has been guided by a current theoretical perspective on comprehension, the structure building framework. This framework emphasizes two comprehension mechanisms: suppression, which inhibits information that is inappropriate or irrelevant to a final interpretation; and enhancement, which heightens the activation of contextually-relevant meanings. The potential contribution of inefficient suppression and/or enhancement mechanisms to discourse comprehension impairment in RHD adults provides the impetus for this proposal. Much of the existing descriptive literature on discourse comprehension deficits can be interpreted from this perspective, and in-effective suppression could account for various observations about other aspects of communication behavior following RHD as well. Two studies are proposed to examine the efficiency of suppression and enhancement mechanisms after RHD. The first focuses on lexical ambiguity, using a speeded probe judgment task. Subjects will hear probe words at several points after a spoken context sentence, and judge whether each probe fits with the meaning of an ambiguous word in that sentence. The second study focuses on inference revision, using similar methods. Subjects will judge whether probes that represent (a) initial, eventually incompatible inferences or (b) revised inferences fit with the meaning of a prior context. Two comprehension tasks will be given to examine the influence of inefficient suppression and/or enhancement mechanisms on comprehension performance. Left hemisphere-damaged and nonneurologically impaired adults will form comparison groups. It is expected that RHD adults will suppress inappropriate meanings of lexical ambiguities and contextually-incompatible inferences less efficiently than non-brain-damaged control subjects. In addition, it is expected that these inefficiencies will contribute to predicting RHD adults' discourse comprehension performance, even after controlling for other important factors such as education and visual neglect.
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