| Older adults demonstrate impaired inhibitory function on some cognitive tasks (e.g., Hasher, Zacks, & May, 1999; Kane, Hasher, Stoltzfus, Zacks, & Connelly, 1994; Zacks & Hasher, 1997) but not others (e.g., Connelly & Hasher, 1993; Kramer, Humphrey, Larish, Logan, & Strayer, 1994). Despite the abundance of research on the relation between aging and inhibitory function, no theories have proposed specific mechanistic explanations for why older adults demonstrate inhibitory deficits on some tasks but not others. This dissertation proposed a formulation that combined findings from the literature on age differences in episodic memory with that on prefrontal cortex theories of cognitive aging in order to make specific predictions about the types of tasks most likely to reveal age-related deficits in inhibitory function. Specifically the hypothesis predicted that age-related deficits in inhibitory function should be largest on tasks with greater demands for endogenous (e.g., self-initiated) processing and smallest on tasks providing greater environmental support to engage inhibition. To test this primary hypothesis, older and younger adults completed a computerized battery of inhibitory tasks: Stroop, A/X version of the Continuous Performance Test (A/X-CPT), garden path sentences, go no-go, and the stop-signal paradigm. Participants also completed a simple processing speed task. Results demonstrated significant age differences in performance on the A/X-CPT, the Stroop and the Stop-signal, although the magnitude of the group differences for the Stroop and the stop-signal were relatively small. Results did not support the hypothesis that age differences in inhibition occur as a function of increased demand for endogenous control during task processing. The A/X-CPT was designed to measure the ability to use context information within a task situation. The fact that the A/X-CPT revealed the largest age differences in performance implies that older and younger adults may differ in how they use contextual information within a task situation. More specifically, the pattern of A/X-CPT data obtained suggests that qualitative differences in the use of context information may be related to age differences in inhibition. |
