A five-year research program is described which is aimed at clarifying the effect of normal aging on the organization, speed and efficacy of mental operations in language processing and memory. Event-related potentials (ERPs) will be recorded from the scalp of normal human subjects between the ages of 20 and 90 in response to linguistic materials and combined with behavioral measures. The overall goals are to establish a data base and to test hypotheses about the impact of normal aging on semantic and phonological analyses, encoding and retrieval aspects of memory for language materials, and speed of categorization in the visual and auditory modalities. We plan to approach these goals via the hypothesized relationship between the N400 component and semantic/lexical search mechanisms, and the P3 component and the duration of stimulus evaluation processes.
The specific aims of the separate experiments are: (1) To use the relationship between reaction time and P3 latency for target detection in oddball paradigms of varying complexity to test the hypothesis that aging reflects a generalized slowing of CNS functioning as opposed to specific deficits for certain mental operations and materials. (2) To investigate semantic priming effects in three different tasks (lexical decision, pronunciation, delayed letter search) in the same group of subjects in order to determine whether aging effects are task independent. Moreover, to use these tasks to test the hypothesis that aging is more detrimental to attentional that automatic aspects of language processing. (3) To use tests of recognition and cued recall for congruous and incongruous words to determine the extent of information on initial presentation. (4) To examine whether aging has similar or different effects on semantic versus phonological processes. This research project will refine electrophysiological measures of important cognitive functions in relation to language processing and memory organization in normal adults throughout life. This normative data base should be of value for the future assessment of young and old individuals with disorders of language processing.
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