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Title:
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Effects of Working Memory and Semantic Impairment on Speech in Alzheimer's Disease
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Author:
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Lori Altmann
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Email:
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click here to access email
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Degree Awarded:
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University of Southern California
, Department of Linguistics
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Degree Date:
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1998
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Linguistic Subfield(s):
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Applied Linguistics
Cognitive Science
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Director(s):
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Elaine Andersen
Daniel Kempler
Maryellen MacDonald
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Abstract:
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This dissertation evaluates the relative adequacy of modular versus interactive theories of language processing to explain speech production patterns exhibited by patients with Alzheimer's Disease (AD) patients. Two aspects of modularity are explored: 1) the view that language processing is encapsulated from the effects of individual differences in extra-linguistic resources, such as working memory (WM); and 2) the claim that syntax and semantics are independent or autonomous components of grammar. Because claims of selective impairment of semantic and/or memory abilities in AD have been cited as support for modular accounts, the current study investigated whether speech production data support such claims by comparing the performance of mild-moderate AD patients and healthy elderly controls on a range of language and cognitive tasks.
The findings indicated that AD subjects exhibited impairments in several aspects of speech production usually considered part of syntactic processing, (e.g., closed class word use and sentence construction ability), and that the frequency of both the syntactic and semantic errors in their speech was related to the severity of their semantic impairment. In addition, individual differences in WM accounted for significant portions of the variance in several types of errors by both AD patients and healthy elderly people.
These results, therefore, are incompatible with any theoretical account that assumes a completely modular language system in which semantic and syntactic processing proceed independently, and in which WM has no effect on speech production processes. Instead, they support a more interactive account of language processing in which semantic and WM abilities interact during the production of speech. In order to account for the range of findings reported in this thesis, I propose a model of speech production based on connectionist principles, which specifies that: WM plays a major role in the activation of the words that comprise an utterance, all words (both open and closed class) are semantically represented, and the syntactic information associated with words is either part of or activated from their semantic representations.
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