Aging and random task switching: The role of endogenous versus exogenous task selection

Background/Study Context: Task switching research typically emphasizes two robust shifting effects between competing tasks: mixing costs (MCs), which indicate less efficient performance in mixed-task versus single-task conditions, and switch costs (SCs), which reflect differences between switch trials and repetition trials within mixed-task conditions. The current study examined age-related MC and SC influenced by the method of task selection in two procedures. Methods: Twenty-six young adults, 18 to 21 years of age (M=18.4, SD=1.1), and 25 older adults, 74 to 87 years of age (M=80.3, SD=5.4), participated as part of the Cognition, Health, and Aging Project (CHAP). Younger and older adults performed cued and voluntary task switching, requiring a random sequence of task changes, placing demands on externally versus internally directed processes. Results: Results indicated that SCs were not disproportionately larger for older adults during an exogenous switching condition, but large age differences in MCs were present beyond the degree predicted by differences in baseline speed. In an endogenous switching condition, small age differences were present both for MCs and SCs, although further age differences were evident in older adults reduced switch rates. Conclusion: These findings suggest that older adults are substantially slower at updating repeated task sets during exogenous switching, but partially counter these effects by adopting a more persistent within-set mode of processing during endogenous switching.