The role of inhibitory functioning in age-related working memory decline and the moderating effect of time course changes in inhibitory functioning with age

The current thesis investigated whether and how inhibitory and working memory functioning change with age in the context of a sequential action paradigm. The approach taken was guided by (1) propositions that inhibitory functions decline with age and negatively impact higher order abilities, and (2) the utility of better understanding cognitive mechanisms underlying sequential activities. In Study 1, I examined the extent to which age-related decline in deletion-type inhibition (suppression of no-longer-relevant information) accounted for age differences in working memory performance. Unlike much of the prior research, I examined inhibitory changes with respect to working memory components (processing and storage). I observed that reduced deletion-type inhibition with age accounted for sizable proportions of age differences in working memory components, with significant findings in storage and marginal findings in processing components. This finding indicates that changes in executive function with age, such as inhibitory control, have direct implications for working memory functioning at the componential level. Moreover, given the observation of age-related decline in deletion-type inhibition in Study 1, a finding that has been inconsistent in the literature, in two subsequent studies I examined the nature of inhibitory changes with age. In particular, I examined whether compared to younger adults, older adults’ have reduced ability to engage deletion-type inhibition in a timely manner, beyond the effects of age-related general slowing. In Study 2, I did not observe age differences in the time course of deletion-type inhibition when I examined erroneous responses to the prior, no-longer-relevant, item (n - 1 repeat). However, this finding may have been limited by low error rates obtained. Thus, in Study 3, response latencies on n - 1 repeats were examined for changes in low-level (unintentional) deletion-type inhibition across variable numbers of distractors, corresponding to variable time delays. Compared to younger adults, older adults had difficulty engaging deletion-type inhibition. This finding suggests that more detailed specification of inhibitory changes with age might depend on examining the temporal dynamics of inhibitory functioning in young and older adults. Taken together, this work highlights the important role of inhibitory functioning with age in higher order cognition (working memory) and emphasizes the utility of examining age effects in the time course of cognitive functions in sequential tasks