The overall goal of this project is to analyze the nature of short-term memory deficits in aphasic patients and their relation to bask cognitive functions and to language comprehension and production. Short-term memory tasks will be administered to identify deficits in retaining input phonological representations, output phonological representations, and semantic representations. The patterns of short-term memory deficits will be related to patients' performance on simple cognitive tasks designed to tap components of executive functioning - specifically inhibition, set shifting, and updating. The pattern of short-term memory deficits will also be related to patients' ability to understand sentences in which integration of word meanings is immediate or requires the reactivation of material from earlier in the sentence. It is predicted that patients with semantic short-term memory deficits, but not those with phonological retention deficits, will have difficulty with the sentences involving delayed integration. We will also assess patients' ability to process grammatical structure for sentences that should place heavy demands on a capacity from maintaining syntactic information. These experiments will test whether syntactic retention capacity is separate from the capacities involved in retaining semantic and phonological information. The studies on speech production will obtain further evidence on whether patients with a semantic retention deficit, but not those with a phonological retention deficit, have difficulty producing phrases containing several lexical-semantic representation preceding the head of the phrase. We will carry out studies designed to test between a phrasal scope of speech production planning versus word-by-word planning. We will also develop tests for assessing speech-production planning at the phonological level and determine whether patients with output phonological retention deficits on memory span tasks are impaired on phonological planning aspects of sentence production. Anatomical MRI data will be obtained for all the patients and lesion localization will be related to the pattern of short-term memory deficits and performance on the basic cognitive tasks. These studies will have important implications concerning whether short-term deficits are the source of the patients' other language deficits and will provide valuable information on the neural circuitry underlying the components of verbal short-term memory.
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