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

Schuch, Stefanie; Keppler, Emily · 2022 · OpenAlex-citations

DOI: 10.5334/joc.244

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Summary

This paper investigates the cognitive mechanisms underlying N-2 repetition costs in task-switching paradigms, specifically addressing the debate between task-level inhibition and episodic interference. N-2 repetition costs refer to the performance decrement observed when a task is repeated after one intervening trial (ABA sequence) compared to sequences where the task has not appeared recently (CBA sequence). While traditionally interpreted as evidence of backward inhibition—where the previously active task set is suppressed to facilitate switching—recent research suggests these costs may also reflect interference between memory episodes of past trials. The authors aim to disentangle these two mechanisms by generalizing previous findings and distinguishing between interference caused by task-relevant and task-irrelevant features. To address this, the authors propose a novel methodological approach termed the “N-X contrast.” Unlike previous methods that only considered the immediate N-2 trial, this approach defines episodic interference relative to the last occurrence of the same task, regardless of lag (e.g., N-2, N-3, or further back). The study combines a re-analysis of previously published data with a new pre-registered experiment. In the new experiment, participants switched between three face categorization tasks (gender, age, and emotion). The researchers manipulated the degree of episodic interference across three levels: full episodic match (both task-relevant and task-irrelevant features matched), partial match (only task-relevant features matched), and full mismatch (neither feature type matched). This design allowed for a rigorous test of whether episodic retrieval effects, driven by specific feature overlaps, contribute to N-2 costs independently of inhibition. The results provided empirical evidence for both cognitive mechanisms. Episodic interference was indicated by a significant main effect of the episodic condition, demonstrating that performance varied depending on the degree of feature overlap with previous episodes. Task-level inhibition was evidenced by the presence of N-2 repetition costs and a performance benefit with increasing task lag in an exploratory analysis. Crucially, the study did not observe a significant modulation of N-2 repetition costs by the episodic condition. This suggests that while both inhibition and episodic interference influence task performance, their effects appear additive rather than interactive; the contribution of episodic interference does not significantly alter the magnitude of the inhibition-based N-2 cost. These findings imply that N-2 repetition costs are not a pure measure of task inhibition, as they are partially confounded by episodic interference. However, the lack of interaction suggests that the two mechanisms operate independently. The authors conclude that while episodic interference contributes to the observed costs, it does not fully account for them, supporting the existence of persisting task inhibition. This distinction is significant for clinical and cognitive research, as it highlights the need to control for episodic effects when using N-2 costs as a marker of inhibitory control in populations such as those with psychiatric or neurological conditions.

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• task switching