Inhibition and shifting capacities mediate adults' age-related differences in strategy selection and repertoire.

Young and older adults differ in how many strategies they use to accomplish cognitive tasks. They also differ in how often they select the best strategy on each problem. Two experiments were run to determine whether two executive functions-inhibition and shifting capacities-mediate age-related differences in strategy repertoire and in strategy selection. Both experiments were run in arithmetic problem solving. In Experiment 1, young and older adults' strategy repertoire was assessed on a problem-by-problem basis while participants solved two-digit addition problems (e.g., 42+76). In Experiment 2, young and older participants had to select the best strategy on each problem to find estimates of two-digit multiplication problems (e.g., 43×72). In both experiments, individuals' inhibition and shifting capacities were assessed with the Trail Making Test and the Stroop Test. The main results showed that (a) older adults used a smaller strategy repertoire (Expt. 1) and selected the best strategy on each problem less frequently (Expt. 2) than young adults, (b) inhibition and shifting capacities mediated age-related differences in strategy repertoire and strategy selection, and unique age effects were no longer significant in strategy repertoire but were still significant in strategy selection after statistical control of inhibition and shifting capacities. We discuss important implications of these findings to further our understanding of strategic variations during cognitive aging.