More change in task repetition, less cost in task switching: Behavioral and event-related potential evidence.

Previous studies have shown that the probability of task switching can vary the level of cognitive control and modulate the size of switch costs. However, it is unclear whether switch costs would be affected by a task-repetition context formed by varying the degree of response (and task-relevant stimulus property) change within the task repetition sequences while the probability of task switching remains constant. In the present study, participants were presented with a string of digits (e.g., ②②②). Basing on stimulus color, they were required to indicate either the presented digit, or the number of presented digits. Before task switching, stimulus and response in consecutive task-repeat trials varied more or less frequently. Behavioral results showed that the frequent-change context elicited smaller switch costs than the rare-change context. Event-related potential (ERP) results indicated that: (1) the frequent-change context evoked greater fronto-central N2 amplitudes for both task-repeat and task-switch trials, implying that cognitive control increased due to the variation of stimulus and response associations; (2) for the task switch trials, smaller P300 amplitudes were evoked in the frequent-change context than the rare-change context, reflecting the promoted task-set reconfiguration. These findings suggest that, the more change in stimulus and response during task repetition, the higher the overall level of cognitive control and the higher efficiency of task-switching.