The influence of repeating stimuli on task set inhibition following task execution and mere task preparation

In task switching, participants often switch between a limited number of stimuli, e.g., the digits 1-9 (except 5). Presenting stimuli repeatedly in different task contexts may induce interference due to different tasks (/cues) and responses becoming associated with the same stimulus. Here, we investigated whether inhibitory processes measured by n-2 repetition costs rely on such interference on the level of cue-stimulus-response associations, or if mere task set conflict suffices. To manipulate interference at the level of stimuli, we generated a unique stimulus set, in which stimuli were only presented once, and contrasted it with a stimulus set where stimuli were highly repeated across tasks. The results revealed significant mean n-2 repetition costs in the unique set, indicating that highly repeated stimuli are not required for n-2 repetition costs to emerge. In Experiment 2, we additionally investigated n-2 repetition costs following mere task preparation in cue-only trials, which are considered to be independent of stimulus processing due to the complete lack of a task episode. Like in Experiment 1, no pronounced influence of the stimulus set on n-2 repetition costs was observed. However, Experiment 2 revealed that mere task preparation in trial n-1 is not sufficient to trigger n-2 repetition costs, while there was some mixed evidence for such costs following a cue-only in trial n-2. This suggests that n-2 repetition costs are reactively triggered during task processing in trial n-1, be it that the processed stimulus was previously performed in different task contexts or not.