SPEECH AND LANGUAGE PROCESSING IN APHASIA

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It is the goal of this research to explore speech and language processing deficits in aphasia. A number of speech and language dimensions will be investigated including speech production and speech perception, lexical access, and sentence processing, with the broad goal of delineating the nature of language deficits in aphasia, and ultimately of developing a model of language-brain relations. In speech production, acoustic analysis of aphasic speech will be conducted to determine whether the production deficit of anterior aphasics (and particularly Broca's aphasics) reflects a global impairment in the coordination of articulatory movements or more specifically reflects an impairment in coordination only when tow independent articulators are involved. Acoustic analysis of the speech production of Wernicke's aphasics will also be conducted to investigate whether, contrary to accepted doctrine, Wernicke's aphasics display a subtle phonetic impairment that is not clinically evident and that is different in kind from the phonetic impairment of Broca's aphasics. In speech perception, a series of perception experiments using synthetic speech continua, computer-edited natural speech continua, and naturally produced exemplars will be conducted to explore the extent to which aphasic patients display speech perception deficits as a function of lexical processing demands. These studies will investigate the extent to which acoustic manipulations and phonological factors affect lexical access, and conversely, the extent to which lexical access affects the perception of the phonetic dimensions of speech. With respect to lexical access, a series of lexical decision experiments will be conducted to investigate the nature of the processing deficits involved in lexical access. It is the goal of this research to determine whether the automatic-controlled processing dichotomy elaborated in the normal literature is an appropriate characterization of lexical deficits in aphasia and to explore the extent to which the lexical access system of aphasics is sensitive to the meanings of lexical items and to the syntactic role that these words may play. Finally, on-line sentence processing in aphasia will be explored with a series of auditory and cross-modal lexical decision studies to determine whether the processing operations contributing to normal sentence comprehension are compromised. A number of dimensions shown to be sensitive to on-line processing demands in normals will be investigated including morphological, syntactic, and semantic constraints.