Lynn Hasher - US grants

The proposed research is motivated by a new model of age-related declines in cognitive functioning. The model assumes that (a) control over the contents of Working Memory (WM) is central to efficient cognitive processing; (b) such control involves the inhibition of irrelevant streams of thought and (c) because of reduced or sluggish inhibitory mechanisms older adults are less able than younger adults to keep task-unrelated thoughts out of WM. In broad outline, this model is applicable to many areas of cognitive functioning. In this proposal, we hope to both establish the general validity of the model and its usefulness for understanding age-related differences in components of discourse processing. As such, two types of studies are processed: ones focusing on major assumptions of the model (especially the assumption of an age-related decline in the efficiency of inhibitory mechanisms), and ones which apply the model to differences between young and old adults in discourse processing. For the latter, the model suggests that when listening to or reading texts, older adults are hindered by a greater activation into WM, and by a slower removal there from, of thoughts that are not central to the formation of a detailed and integrated representation of the text. These task-irrelevant thoughts compete with task-relevant thoughts in various ways, including, crucially, impeding the retrieval into WM of antecedent and general knowledge information necessary for inference generation and other integrative processes. Repeated experience with retrieval failure may set the stage for the development of compensatory strategies of comprehension. The proposed experiments will use cross- sectional designs to compare the performance of younger (18-30 yrs) and older (63-75 yrs) adults on a variety of experimental paradigms and measures. These will include both direct (e.g., recall and recognition) and indirect (e.g., fragment completion) measures of memory, as well as measures of processing speed. To the extent that the proposed model is confirmed, the findings will, by adding to such concepts as reduced capacity and mental slowing, extend our general understanding of cognitive deficits in aging. Also, to the extent that the results increase our understanding of older adults' limitations in processing discourse, they will have direct application to daily life, especially with respect to the question of how best to present important information (e.g., about health, safety, and legal matters) to older adults.

age difference; memory; attention; neural information processing; cognition; stimulus /response; language; young adult human (21-34); human old age (65+); speech; performance; mathematical model; psychological tests; data collection; human subject;

Cognitive performance varied across the day as a function of the synchrony between the time of testing and an individual's optimal period; best performance occurs at the time that coincides with optimal arousal. There are dramatic age differences in peak arousal: The majority of older adults are at their peak in the morning (when few college-attending younger adults are); many younger adults are at their peak late in the day (when virtually no older adults are). Thus, if experiments comparing younger and older adults are conducted in the afternoon, age differences will be exaggerated on tasks vulnerable to synchrony effects. The broad goals of the present project are to determine (1) the range of cognitive tasks and processes vulnerable to synchrony effects; (2) the degree to which there are age differences in the synchrony effect; and (3) the extent to which age differences have been exaggerated in the cognitive literature. Of central interest is the exploration of the behavioral and potential neurobiological mechanisms that are presumed to be particularly responsible for synchrony effects. Preliminary results strongly suggest that these mechanisms may be inhibitory in nature, and, as a result a general inhibitory theory of attention and its control over the contents of working memory is used to guide task selection. Because of recent suggestions implicating the role of the frontal lobes in aging and inhibitory control, the vulnerability of a number of neuropsychological tests to synchrony are explored. Three presumed functions of behavioral inhibition are tested: (1) access to working memory, (2) activation within working memory, and (3) preventing premature production of strong but unevaluated candidates for response. Consequences of diminished inhibition including heightened retrieval interference and increased reliance on heuristic decision rules will also be explored. The materials and tasks used are quite varied. These choices ensure (1) that a converging operations criterion will be used to assess the usefulness of the theoretical model and (2) that an extensive picture of the deficits of older adults at their nonoptimal times of day would emerge from the project. We explore the existence of circadian effects on frontal lobe functioning for both younger and older adults, in an attempt to link behavior and age differences to their underlying neurobiology. At a practical behavioral level, this work should reveal tasks that are relatively unimpaired by asynchrony and age as well as others which are severely impaired. Guidelines for maximizing older adults' performance on difficult tasks (e.g., making medical and legal decisions) are expected to emerge from this work.