Why do adult age differences increase with task complexity?

A total of 451 adults between 18 and 80 years of age participated in 2 studies conducted to investigate causes of the phenomenon that adult age differences in cognitive performance frequently increase with increased task complexity. All Ss performed 4 cognitive tasks at each of 3 levels of complexity. The strongest predictors of performance on the intermediate and complex versions of the tasks were performance on the simpler versions of the same tasks and a composite measure of working memory. It was concluded that one cause of the age-complexity phenomenon is that more complex cognitive tasks place greater demands on a working-memory resource that declines with increased age