Inhibition of action rules

Inhibition is often proposed as an important executive-control process, but its existence is difficult to establish empirically. Recently, Mayr and Keele (2000) reported that it takes longer to switch to a recently disengaged task set (i.e., n-2 task-set repetitions) than to a less recently disengaged task set. This set-alternation cost may indicate inhibition of the disengaged task set. The primary goal of the present study was to test the inhibition account of set-alternation costs against an important alternative account based on automatic episodic retrieval. The episodic retrieval account predicts reaction time facilitation instead of costs for the special case of complete n-2 repetitions of both task sets and all stimulus-response aspects. A new task-switching paradigm, in which action rules varied on a trial-by-trial basis while the relevant stimulus dimension remained invariant, allowed the implementation of a high proportion of complete n-2 repetitions. Consistent with the inhibition view, set-alternation costs were obtained even for these constellations.