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

Abstract

Inhibition during task switching is assumed to be indexed by n - 2 repetition costs-that is, performance costs when the task in the current trial equals the task in trial n - 2 (sequences of type ABA) compared with two consecutive switches to another task each (sequences CBA). The present study examined effects of a short-term reduction of the number of candidate tasks on these costs. For this purpose, a variant of the task switching paradigm was used in which in half of the trials, a precue that preceded the task cue allowed for a short-term reduction of the number of candidate tasks. In Experiment 1, one out of three tasks could be excluded. In Experiment 2, one or two out of four tasks could be excluded. Experiment 3 served as control condition using the standard cueing paradigm. Significant n - 2 repetition costs were present with three candidate tasks. In contrast, no costs were visible when the number of candidate tasks was reduced to two. This result is interpreted in terms of a task selection mechanism based on antagonistic constraints among task representations, which operates on a rather superficial level when switching among only two tasks, thereby reducing the need for inhibition.

Keywords: Inhibition; N – 2 repetition costs; Task switching.

Fig. 1

Experiment 1: Illustration of the stimuli (A); schematic illustration of the procedure of a single trial with informative precue (B); schematic illustration of the procedure of a single trial with noninformative precue (C). Note: Precues that were colored grey in the experiment are depicted in black to allow for grey-scale copy

Fig. 2

Experiment 1: Mean LISAS as a function of task sequence, precue, lag_precue, and lag2_precue. Error bars represent SEM

Fig. 3

Illustration of the different trial types in case of an informative precue in trial n. Upper panel: Display of trial n – 2 with noninformative precue (the precue condition of this trial is not of importance): (A) initial display (B) precue display, noninformative (C) task cue (D) imperative stimulus. Lower panel: Illustration of (B) informative precue displays and (C) task cues of trial n. Note: Precues that were colored grey in the experiment are depicted in black to allow for grey-scale copy

Fig. 4

Experiment 2: Mean LISAS as a function of task sequence and number of candidate tasks in trial n. Error bars represent SEM

Fig. 5

Experiment 2: Mean LISAS as a function of task sequence, number of candidate tasks in trial n, and number of candidate tasks in trial n – 2. Error bars represent SEM

Fig. 6

Experiment 3: Mean LISAS as a function of task sequence and number of candidate tasks in trial n. Error bars represent SEM