Aging, Divided Attention, and Processing Capacity1

The performance of young and old adults was compared in two different situations to investigate the reasons why the latter are especially poor at divided attention tasks. Although the two experimental tasks were quite different, one a single task and the other time-sharing, task difficulty was manipulated in a similar fashion in both situations. Specifically, in both tasks difficulty was varied by manipulation of number of items to be rehearsed and number of mental operations necessary for successful performance. The most salient difference in task demands, that is, divided versus nondivided attention, had little effect on results. Performance of both age groups declined as task difficulty increased, with the decline being greater and more rapid for the older subjects. Results are discussed in terms of competition for limited processing capacity in working memory. Key Words: Human aging, Divided attention, Processing capacity, Working memory C RAIK (1977) has suggested that the agingprocess leaves primary memory largely unaffected except "when the task demands reorganization of the material or a division of attention between two or more mental operations " (p. 395). Indeed, one of the most replicable findings about short-term memory changes with increasing age is that older adults' performance is affected more adversely by divided attention conditions than is that of younger adults. Despite the consistency with which this phenomenon has been observed, the variety of situations in which it has been investigated is not great. As a consequence, little is known about the variables which affect the observed age-related deficits, or about the processes or mechanisms responsible for them. It cannot even be stated with certainty that demands to divide attention necessarily result in a differential disadvantage for older individuals. The adverse effect which dividing attention has on elderly subjects is most clearly shown with dichotic listening (e.g., Clark & Knowles, 1973;Inglisetal., 1968; Parkinson etal., 1980). When asked to recall two different short strings of information presented simultaneously to the two ears, older adults recall fewer items 'This article is based on a dissertation submitted to the Graduat