Mediation of Adult Age Differences in Cognition by Reductions in Working Memory and Speed of Processing

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Abstract
Three studies, involving a total of 672 adults between 20 and 84 years of age, were conducted to evaluate the relative importance of working memory and perceptual comparison speed in the age-related differences in selected measures of cognitive functioning. The same measures of working memory and comparison speed were used in each study, but the studies differed in the specific cognitive measures examined. A common finding across all studies was that the magnitude of the age-related cognitive differences was greatly reduced by statistically controlling measures of working memory and perceptual comparison speed. Many of the age differences in process or fluid aspects of cognition therefore appear to be mediated by age-related reductions in working memory, which may in turn be largely mediated by age-related reductions in the speed of executing simple processing operations.