Effects of global and local task repetition proportion on n - 2 repetition costs.

In task switching research, one of the most straightforward indications for the involvement of inhibitory processes are n - 2 repetition costs. The present study aimed at investigating effects of different types of repetition proportion on n - 2 repetition costs. In Experiments 1 and 2, repetition proportion was varied globally (i.e., equally for all tasks). The occurrence of 33% task repetitions reduced n - 2 repetition costs when varied within as well as between subjects, but no further decline was visible from 33% to 50% task repetitions. This result is interpreted in terms of a shift of balance between task inhibition and task activation due to the occurrence of task repetitions that is independent of the specific repetition proportion. In contrast, when repetition proportion was varied locally (i.e., by differentially manipulating the occurrence of task repetitions for the three tasks involved), n - 2 repetition costs were reduced monotonically from 0% to 50% task repetitions. This result indicates that when the utility inhibition is tied to individual tasks, the cognitive system is able to adjust the deployment of inhibition accordingly, possibly by modulating processes of overcoming inhibition, not releasing it.