N-2 Repetition Costs in Task Switching: Task Inhibition or Interference Between Task Episodes?

A prominent behavioral marker of inhibition in task switching is the “N-2 repetition cost” that denotes the decrement in performance in task sequences with an N-2 task repetition (ABA), relative to task sequences without an N-2 task repetition (CBA). Recently, it has been critized that N-2 repetition costs at least partially reflect interference between task episodes, rather than persisting inhibition, raising doubts about the interpretation of N-2 repetition costs as a measure of inhibition. Here, we aim to generalize these conclusions in two ways. First, we define episodic effects in task switching with respect to the last episode of the same task, which might have occurred several trials back (e.g., in trial N-2, N-3, etc.). Second, we distinguish between episodic interference caused by task-relevant and task-irrelevant features. We present a re-analysis of previously published data, and a new pre-registered experiment, where we manipulated the degree of interference between task episodes in three levels (episodic match of both task-relevant and task-irrelevant features, episodic match of only task-relevant features, episodic mismatch of both kinds of features). We observed empirical evidence for both cognitive mechansims: Episodic interference was indicated by a main effect of episodic condition; task-level inhibition was indicated by N-2 repetition costs, and by a performance benefit with increasing task lag in an exploratory task-lag analysis. We did not observe any significant modulation of N-2 repetition costs by episodic condition, suggesting that if there was such a modulation, this effect appears to be smaller than the individual contributions of episodic interference and inhibition to task performance.