The role of processing speed and attentional capacity in age-related episodic and working memory change

This study compared the relative importance of attentional capacity and processing speed accounts of cognitive aging with regard to how well they predict age differences in episodic and working memory performance. Two research projects were completed involving 150 and 100 right-handed adults between the ages of 18 and 90. In Study 1, each participant was administered measures of attentional capacity, processing speed and episodic memory. In Study 2 the processing speed measures were chosen to reduce the involvement of perceptual scanning and memory ability, and multiple measures of dual-task performance were used. Two working memory tasks were also administered along with the same episodic memory measures used in Study 1. The results of the studies revealed the following: (1) Measures of attentional capacity shared relatively smaller proportions of age-related episodic memory variance (14-45%) than measures of processing speed (60-87%). (2) Measures of attentional capacity shared very small proportions of age-related episodic memory variance (1-2%) independent of speed of processing. In contrast, measures of processing speed shared substantial proportions of age-related episodic memory variance (37-76%) that were independent of attentional capacity performance. (3) Measures of attentional capacity and processing speed shared comparable proportions of age-related working memory variance (58 and 65%) as well as comparable proportions of shared variance that was independent of the other mediator (10% attentional capacity; 17% processing speed). (4) The age-attentional capacity relations were attenuated to a large extent when performance on processing speed measures was controlled for (77-88%). In contrast the age-processing speed attenuations after control of attentional capacity performance were much smaller (6-55%). Taken together, these results provide little support for any predictive utility of the attentional capacity construct independent of processing speed ability in accounting for age-episodic memory relations although they are consistent with the notion that attentional capacity might mediate aspects of age-related working memory change. In contrast, these results contribute to the large body of evidence consistent with the notion that age-related decrements in the speed of executing relatively simple processing operations might be responsible for age-related differences in several cognitive domains