Tracing the time course of n - 2 repetition costs in task switching.

In order to flexibly adapt to a permanently changing environment, it is necessary to inhibit previously activated but now irrelevant processing pathways. Empirically, this inhibition manifests itself only indirectly in terms of a cost of reengaging a previously inhibited pathway (n - 2 repetition costs). While imaging studies suggest an involvement of the prefrontal cortex in this type of inhibition, it has recently been argued that the underlying processes are implicated not in triggering inhibition, but in overcoming it. To disentangle these processes on a behavioral level, we investigated the time course of inhibition using a cued task switching paradigm. The response-cue interval (between the response of trial n - 1 and the cue of trial n) was varied in five steps to capture its influence on inhibition in a fine-grained manner. The results suggest that the impact of inhibitory processes increases during the first 200-300 ms after the response of the previous trial, reaches its full extent with about 300 ms, and starts to diminish after that. Therefore, future research on the neural correlates of n - 2 repetition costs should employ techniques with a high temporal resolution that are able to capture this presumed time course of inhibitory processes.