Reaction time task rule congruency effects (RT-TRCEs) reflect faster responses to stimuli for which the competing task rules indicate the same correct response than to stimuli indicating conflicting responses. The authors tested the hypothesis that RT-TRCE reflects activated overlearned response category codes in long-term memory (such as up or left). The results support the hypothesis by showing that (a) RT-TRCE was absent for tasks for which there were no response codes ready beforehand, (b) RT-TRCE was present after these tasks were practiced, and (c) these practice effects were found only if the tasks permitted forming abstract response category codes. The increase in the RT-TRCE with response slowness, found only for familiar tasks, suggests that the abstract response category codes may be verbal or linguistic in these cases. The results are discussed in relation to task-switching theories and prefrontal functions.Keywords: task switching, working memory, congruency, practice, prefrontal functions Working memory (WM) and task switching are two core executive functions. Their interrelationships have been studied by means of a variety of approaches. These include examinations of WM load effects on task-switching performance (Baddeley, Chincotta, & Adlam, 2001;Emerson & Miyake, 2003), comparing WM span for tasks with WM span of items (Logan, 2004), individual differences studies (e.g., Miyake et al., 2000), and cognitive theorizing (e.g., Logan & Gordon, 2001;Mayr & Kliegl, 2000;Sohn & Anderson, 2001). The present study suggests an as-of-yet unrecognized link between these two functions by focusing on a highly replicable but poorly understood phenomenon from the task-switching literature, the task rule congruency effect (TRCE). In the remainder of the introduction, we review the literature on the TRCE and suggest a WM account for it. The experiments reported in this article provide additional crucial evidence that support our account.Task Switching and the TRCE Researchers interested in task control often use the taskswitching paradigm. The rationale for this choice is straightforward. Performance in stable conditions without task switching can be done in an "automatic pilot" mode, with little need for active control. This luxury is unavailable when there are frequent task switches. Most of the research has concentrated on the various costs associated with task switching (Fagot, 1994;Jersild, 1927; Monsell & Driver, 2000). However, additional highly replicable effects have also been found, and understanding their basis is likely to shed light on how control is accomplished (cf. Altmann, 2003). In the present work, we concentrate on the TRCE. This effect is among the most reliable found in task-switching experiments, yet relatively little work has been done to unravel its causes.To the best of our knowledge, Sudevan and Taylor (1987) were the first to demonstrate the TRCE in the context of task switching. The participants in their experiments responded to single digits and switched between two classification t...