Abstract

With the increasing proportion of older adults in the population, the maintenance of autonomy in everyday functioning is of growing importance. To this end, cognitive aging researchers have identified executive functions, including attentional switching, inhibition, and updating, to be key factors in everyday functioning. A current model of cognitive control, Dual Mechanisms of Control theory (DMC; Braver, Gray, & Burgess, 2007) postulates two basic mechanisms. Proactive control involves goal maintenance and conflict resolution based upon preceding cue information, whereas reactive control resolves conflicts based upon immediate stimulus characteristics. The prior research indicates age-related variance in executive functions is related to age-related declines in proactive control. The overall aim of this dissertation is to examine DMC processes in one particular executive function, task switching, which is essential for efficient multi-tasking and entails task-set inhibition (TSI) to smoothly transition from one task to the next (Mayr & Keele, 2000; Mayr, 2001). Previous work suggests that TSI requires proactive control (Mayr, 2007), which declines with aging, yet the empirical support for age differences in TSI is mixed. Therefore, in Study 1, healthy young (n = 28) and older adults (n = 22) were compared on a task switching paradigm, in which TSI was assessed under high (flanker trials) and low (unflanked trials) reactive control task contexts. The results show age-equivalent TSI effects in low reactive control, but young adults showed larger TSI in high reactive control. In Study 2 (Expt. 1: nYA = 25, nOA = 25; Expt. 2: nYA = 25, nOA = 25), age-related TSI effects were examined across four conditions that varied along a proactive-reactive control continuum. A key aspect of this design was that the four task contexts were intermixed, thereby compelling participants to adopt a global control strategy that was either reactive (Expt. 1) or proactive (Expt. 2). In line with Study 1, the overall results of Study 2 indicate that TSI effects are observable in reactive control task contexts. Additionally, young and older adults showed differential modulation of the dual control processes to match the global task context. In Experiment 2 when the task context was more proactive, older adults exhibited more TSI than young adults. Taken together, these results suggest that age-related TSI effects are contingent on the age-related utilization of the dual control processes, which in turn are influenced by the global task context.