Despite widespread cortical degeneration in Alzheimer's Disease, the dissolution of cognitive abilities over the course of the disease is not diffuse. Rather, the loss of cognitive abilities is a selective process. Therefore, it is important on both neurological and psychological grounds to specify factors which determine the extent to which the representation and processing of knowledge is relatively impaired or preserved in the dementia of Alzheimer's Disease (AD). With this goal in view, the project will explore two kinds of knowledge in AD patients: 1) lexical-semantic knowledge, i.e., knowledge of conceptual referents of lexical items, and 2) """"""""schematic"""""""" or """"""""script-like"""""""" knowledge for causally related (temporarily constrained) event sequences. One part of the project will employ a series of reaction-time experiments to study the specific ways in which active lexical- semantic representations change in the early to moderate stages of AD. For example, property verification and modified stroop paradigms will be used for a property- or feature-level analysis of word concept representations in AD patients and age-matched control subjects. In particular, the experiments are designed to answer the following questions: 1) What kinds of properties are likely to be maintained (activated, accessed, instantiated), or lost in AD patients' functional representations of word concepts? 2) Is there a restructuring of dominance relations of properties of concepts in AD? 3) How does context affect the active lexical- semantic representations of AD patients? 4) How do particular task demands affect abilities of AD patients to process lexical-semantic knowledge? A second set of experiments will employ a variety of free recall and event-sequencing paradigms to assess the degree to which AD patients maintain schematically organized knowledge of story structure and familiar, script-like event sequences. A particular emphasis will be placed on determining the extent to which AD patients are able to exploit such knowledge to facilitate the processing of new information. In addition to advancing our knowledge of cognitive processes in AD, and thereby, in normal processors, the proposed project has important clinical and practical implications. For example, the specification of predictable lexical-semantic changes in early AD patients may lead to the development of standardized tests to aid in early detection and differential diagnosis of Alzheimer's Disease. Furthermore, the investigation of schematically represented knowledge in AD may suggest potential methods for self- management training of Alzheimer's patients.
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