A five year research program is proposed which is aimed at clarifying the extent to which the organization of semantic memory and semantic analyses, as used in language comprehension, are indeed relatively spared from the normal aging process, as is commonly believed. We assess this belief by examining effects of aging on different subprocesses;more specifically, by (1) comparing and contrasting processing of different modes of sensory input that refer to the same concepts--words and pictures;(2) examining two distinct contributors to semantic processing in language-the semantic integration of an item within its context and the various semantic constraints that accrue as context taps semantic memory to make sense of incoming stimuli prior to an item's appearance;(3) comparing the whole brain's response to word &picture processing when one hemisphere has a slight processing headstart;(4) examining individual differences in brain/behavioral measures in tasks tapping processing speed, inhibition, &working memory, an anti-saccade task accenting sensorimotor inhibition, a reading span task, and a sentence congruity reading rate task. To these ends we analyze event-related brain potentials (ERPs) recorded from the scalp of (brain) intact humans between 18-90 yrs of age and concomitant behavior as they process words or pictures. Twenty four experiments manipulate stimulus (visual, pictorial) and context modality (verbal, pictorial), the nature of relations among stimuli (categorical, antonymic), the probability that a particular item will be encountered (cloze probability), whether or not and, if so, how well an item fits within its context, how constrained and thus predictable an item is and at what level (lexical, semantic), visual field of input, and task, or combinations thereof.
The specific aims are to determine whether or not and if so, how, normal aging changes what lexical, semantic, and contextual cues the two hemispheres are sensitive to and how each uses them to access semantic memory and to make sense of language. In so doing, we test (1) our hypothesis that though everyone benefits from context, most older adults, unlike younger ones, do not use it to predict features of upcoming stimuli, though greater verbal proficiency may compensate for this, (2) Cabeza's hypothesis that older adults are more likely to use both cerebral hemispheres to perform cognitive functions that were in their younger years the primary responsibility of just one, and (3) links between well-known ERP effects and age-related changes in processing speed and cognitive functions. This research project will refine ERP markers of important cognitive functions in language processing and memory use throughout the lifespan. This normative database will be of value for the assessment of adults of all ages with semantic/language processing disorders.
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