The proposed research addresses the nature of cognitive/linguistic deficits that involve impairments to morphological aspects of lexical processing, and examines the contribution of these deficits to sentence comprehension and sentence production impairments. The program of research involves testing of language impaired speakers of English and Italian. Because of the structural differences between these languages, the use of these two groups allow consideration of issues that could not be addressed with one group alone, and permits the assessment of cross-language generality of hypotheses concerning language processing. Subjects who have been screened for morphological disruptions will be tested on a series of single-word processing tasks in order to determine the variety of lexical deficit (e.g., whether the deficit is an input or output deficit and whether it effects performance in the visual or auditory modality), and to determine the variety of morphological deficity in terms of the types of lexical items affected (e.g., whether inflected words are selectively affected, or whether morphologically regular and irregular forms are similarly disrupted). These subjects will also be tested on a series of sentence processing tasks in order to evaluate the effect of morphological processing deficits in more complex language processing contexts. Information derived from these experiments will serve (a) to differentiate among varieties of morphological deficits, (b) to assess specific hypotheses about the cognitive/linguistic basis for particular deficits and further elaborate the structure of the linguistic and cognitive mechanisms that subserve morphological processing, (c) to determine the roles that various types of morphological deficit play in disorders of comprehension and production, and (d) to enable the exploration of correlations between types of lexical processing deficits and loci of brain lesions, with the aim of illuminating the relation between cognitive and neural mechanisms of language.
