The purpose is to determine the brain organization and inter-dependence between speech production, speech perception and language in adults. CT scan data from the Vietnam Head Injury Study provide information on lesion topography following penetrating missile wounds. Two studies were completed this year. In persistent speech dyspraxia, the lesions all involved the primary, association motor cortices, and the pyramidal and association white matter tracts in the left hemisphere. Lesions in head injured controls without speech disorders were not as extensive and did not involve all of these structures in the left hemisphere. A study of speech perception employed a temporal resolution gap detection task between /s/ and /a/ and a temporal order task requiring /sa/ or /as/ identification at different inter-stimulus onset intervals. Deficits in temporal resolution were associated with lesions in either hemisphere and did not depend upon auditory area involvement. Deficits on the temporal order task occurred only when lesions involved the primary auditory and auditory association areas in the left hemisphere. Therefore, only temporal order perception and not temporal resolution aspects of speech perception are dependent upon the language areas of the left hemisphere.
