Developmental Psychology

Abstract

age R2 for age when it was considered alone was .158, but the value was reduced to only.035 after the variation in a composite measure of perceptual speed was controlled. These results therefore suggest that almost 807o (i.e., [. I 58 -.035 ]l I 58 = .778) ofthe age-related variance in certain measures offluid cognition is associated with variations in perceptual speed.The research reported in this article was designed with two major goals in mind. One goal was to examine the generality of the speed-mediation phenomenon by including measures of memory in addition to measures of fluid or process aspects of cognition. Extending the research in this direction is ofinterest, because less convincing support for a mediational effect of speed was found with m€asures reflecting memory functioning in the partial correlation analyses reported in Salthouse (l 985a). That is, partialing a measure ofprocessing speed had a smaller effect on the correlations between age and measures of memory than it did on the correlations between age and measures of other types of cognitive functioning. Moreover, additional analyses on the data from the Salthouse et al. (1988) project similar to those summarized in Table I also revealed weaker attenuation ofthe age relations ficr measures representing memory functioning than for measures representing other types of cognitive functioning. For example, the attenuation was only 63.8Vo for a measure of the accuracy of reproducing the identities of items in a matrix, only 4'l .59o for a measure of the accuracy of reproducing the positions of items in a matrix, and only l6.7vo for a measure of paired-associate memory.The smaller attenuation of the age-related memory differences after control of measures of speed raises the possibility that quickness of mental operations may be a less important factor in the age differences in traditional memory tests than in cognitive tests assessing reasoning or spatial abilities. Although this speculation is plausible on the basis ofthe available results, stronger evidence ofthe differential influence ofspeed on cognitive and memory measures is desirable before one can conclude that speed factors have a minimal role in the relations between age and memory. One type of evidence that would be relevant in this regard would be a discovery that substantial age-related effects remained after statistical control of a measure of perceptual speed, or equivalently, a finding that the Speed Mediation of Adult Age Differences in Cognition Timothy A. Salthouse Previous research has established that a large proportion of the adult age-related variance in various measures offluid or process cognition is reduced when statistical control procedures such as hierarchical regression are used to eliminate variation in measures ofperceptual speed. This finding was confirmed in the present study and was extended to include paired-associate and free-recall measures of memory in addition to measures of reasoning and spatial abilities. Most of the speed mediation was associated with s...