The goals of this project are to continue studies investigating the occurrence of syntactically-based deficits in aphasia, and to introduce experiments designed to test some specific hypotheses about the underlying mechanisms responsible for those deficits. The primary focus has been on the syndrome of agrammatic Broca's aphasia, which has been interpreted as arising from a deficit to those processes that compute and interpret the structural organization of sentences. Research completed to date supports the rational for the project as originally proposed: data concerning the co-occurrence and dissociation of symptoms in individual aphasic patients provide an important source of constraint of theories of language organization. The accumulation of additional experimental results from a wider range of patients is necessary to verify the generality of previous findings, and to continue the search for cases that support the necessary co-occurrence of particular symptoms. To that end, an additional group of aphasic patients will be tested on the extensive battery of experimental tasks that has successfully demonstrated theoretically-important dissociations of symptoms. In addition, two new sets of experiments are proposed to address specific questions that have arisen from results obtained to date. One of these issues is especially focused on defining more precisely the functional locus of the syntactic comprehension disorder in agrammatic aphasics by investigating the dissociation between their performance on auditor/comprehension tasks and on auditory sentence acceptability judgments. The second issue concerns the more general possibility that syntactic comprehension disorders might result from any one of several types of deficits within the working memory system. This latter suggestion has important implications for existing explanations of the deficit underlying agrammatic Broca's aphasia, but it is also relevant to current hypotheses concerning other syndromes of aphasia. These results are expected to provide information about the functional basis of aphasic deficits upon which principled systems of therapy can be developed.
