This research examines changes that occur in lexical-semantic processing, as a function of normal aging and as a side effect of Alzheimer's Disease (AD), a progressive neurological disorder. The experiments focus on the perception and manipulation of separate meanings in ambiguous words, such as bark or safe. Historically, such conceptual factors have been studied in word perception only as a between-words manipulation, as in semantic priming. However, recent studies show that semantic factors within words also affect perception, even in the earliest stages of processing. Specifically, ambiguous words with unrelated meanings (e.g., the dog and tree interpretations of bark) are processed differently than words with related meanings (e.g., the protected and box interpretations of safe). It appears that unrelated meanings compete with each other, slowing down word perception. Related meanings, on the other hand, have little effect on processing speed, but they strongly inhibit attempts to individuate separate senses of a word. These conceptual dynamics will be further assessed in healthy young adults, healthy older adults, and older adults diagnosed with early-stage AD. The proposed experimental tasks (lexical decision, standard and primed ambiguity decision, sentence verification) all require access or manipulation of ambiguous words. Due to deficits in working memory and executive functions, it is predicted that AD patients will experience extra difficulty processing such ambiguous words. Moreover, this impairment should increase (or decrease) in a principled manner across priming manipulations. Taken together, these experiments will: (1) elucidate the organization and processes of semantic memory in younger and older adults, (2) assess semantic processing changes in AD, and (3) assess the role of working memory in fluent semantic processing.
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