Dissociating retention and access in working memory: An age-comparative study of mental arithmetic

In two experiments, young and older adults solved arithmetic chain tasks wi th single-digit operands, with or without a concurrent memory load of three or six digits. Variables in the arithmetic tasks had to be replaced by dig its from the screen or from the memory set. A task-irrelevant concurrent lo ad impaired neither speed nor accuracy of arithmetic in younger adults. In Experiment 2, this was also true for older adults. A large decrease in arit hmetic performance was observed, however, when variables in the arithmetic task had to be substituted by digits from the memory list. Older adults had specific problems with this condition in Experiment 1, where the substitut ion involved two successive steps, but not in Experiment 2, where the subst itution from memory could be done in a single step. The results are difficu lt to reconcile with models assuming a common resource for storage and proc essing. Rather, they are compatible with the hypothesis that a concurrent m emory load interferes with a processing task only during the points of acce ss to working memory. Further, even though access to working memory was fou nd to be the critical source of concurrent-load interference, it was found to be insensitive to the effects of adult aging.