Discourse comprehension problems often follow right hemisphere damage, but are poorly understood. Recent evidence linking these problems with ineffective suppression of irrelevant information leads to a hypothesis that a 'suppression deficit' is one factor in poor comprehension. RHD adults also have trouble grasping nonliteral meanings and generating inferences, particularly in conditions that tax attention or working memory. Two studies are proposed with RHD and normally aging control subjects, to integrate these findings and to examine the generality of the suppression deficit hypothesis. The first study will use a dual task to evaluate the attentional demands of suppression. Subjects will hear sentences containing ambiguous words, and judge whether a spoken probe word fits the sentence meaning. The measure of suppression is the time needed to reject probes related to contextually-inappropriate meanings of the ambiguities. Subjects will perform the same task in a dual-task context, with three emphases for attention allocation. The second study will evaluate a central premise of the suppression deficit hypothesis (i.e. multiple potential meanings are activated but the irrelevant ones are then poorly suppressed) against another recent proposal (RHD adults do not activate the semantic information needed for inferencing.) Subjects will listen to passages that induce inferences to integrate ambiguous final sentences. They will make lexical decisions to target words that are related to either the intended inference, or to an alternate inference suggested by the ambiguous sentence. The suppression deficit hypothesis predicts that both inferences will be 'primed' and rapidly available. In both studies, comprehension tasks will be given to evaluate the influence of multiple meaning activation and ineffective suppression on comprehension.
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