Inhibition during task switching is affected by the number of competing tasks

Scheil, Juliane; Kleinsorge, Thomas · 2024 · Crossref

DOI: 10.3758/s13421-023-01456-w

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Summary

This study investigates how the number of competing tasks influences inhibitory processes during task switching, specifically examining n–2 repetition costs. These costs—performance deficits when a task repeats after two intervening trials (ABA sequence)—are traditionally interpreted as evidence of task-set inhibition. The authors hypothesize that reducing the number of candidate tasks allows for simpler "antagonistic constraints" between tasks, thereby reducing the need for inhibition and diminishing n–2 repetition costs. The research comprised three experiments using a task-switching paradigm with informative precues that allowed participants to exclude certain tasks before the trial began. Experiment 1 involved three tasks, where precues reduced the candidate set to two in half of the trials. Experiment 2 expanded to four tasks, with precues reducing candidates to three or two. Experiment 3 served as a control using standard cueing without precues. Participants performed perceptual judgments (e.g., size, color, shape) based on visual cues. Data were analyzed using linear integrated speed–accuracy scores (LISAS) to account for speed–accuracy trade-offs. In Experiment 1, significant n–2 repetition costs were observed only when all three tasks remained candidates (noninformative precues). When the precue reduced the candidate set to two tasks, n–2 repetition costs vanished, regardless of whether the reduction occurred in the current or preceding trials. Supplementary analyses confirmed that participants engaged in genuine task-set activation rather than simple stimulus-response mapping, evidenced by task-shielding effects and stimulus congruency interactions. Experiment 2 replicated these findings: reducing candidates from four to two eliminated n–2 costs, while reducing them to three maintained significant costs. Notably, the four-task baseline condition in Experiment 2 showed an n–2 repetition benefit, which the authors attribute to the specific paradigm variant rather than the core inhibition mechanism. The findings suggest that n–2 repetition costs are not a fixed property of task switching but are sensitive to the complexity of the task environment. When only two tasks compete, discrimination relies on simple antagonistic constraints, minimizing the need for lateral inhibition. In contrast, environments with three or more tasks require more complex interrelations among task representations, necessitating stronger inhibitory control. This challenges the assumption that the absence of n–2 costs implies an absence of inhibition, proposing instead that inhibition levels scale with the discriminability and number of competing tasks.

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Topics

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• task switching
• dual task performance