Cognitive control across the adult lifespan: a combined cognitive modelling and event-related potential approach

Executive functioning allows us to adapt behaviour flexibly in response to continually changing environmental demands. Many studies report age-differences in tasks of executive function, however, the tasks used do not typically allow identification of the specific processes contributing to this decline in performance. The task-switching paradigm has been used previously to study selective aspects of cognitive control decline in aging. We used a cued-trials task switching paradigm, where preparation time was manipulated (Experiment 1: short vs. long preparation interval; Experiment 2: non-informative vs. informative cues) and multiple methodologies (evidence accumulation modelling and event-related potentials) to examine which processing differences underlying changes in task-switching performance across the lifespan. We provide evidence that the amount of task practice differentially affects performance between young and older adult groups. When participants are highly practiced and well prepared, young adults are able to flexibly adjust the use of proactive and reactive control strategies between mixed-repeat and switch trials. In this group, residual mixing cost is due to overcoming stimulus-based interference, whereas residual switch costs are attributable to prolonged response-selection. In contrast, older adults do not show evidence of flexibly adjusting performance between trials within a mixed-task block. As a result, older adults show significant mixing cost effects (prolonged response-selection and execution), with minimal switch cost effects. These effects are not affected by changes in experimental design, suggesting that performance in mixed-task blocks is unlikely to reflect a strategy implemented by older adults. We discuss these results in relation to theories of task-switching performance, and also discuss how models of cognitive aging may account for the findings reported. We propose that aging is associated with increased engagement of proactive and reactive control processes, at lower levels of demand.