Task sets under reconstruction: Effects of partially incorrect precues Thomas Kleinsorge, Patrick D. Gajewski, and Herbert Heuer Institut für Arbeitsphysiologie an der Universität Dortmund, Dortmund, Germany To perform a task that differs from a previously performed one, it is necessary to prepare for the new task as well as to disable the task set of the preceding task. In a series of three experi- ments we examined whether preparation for a task shift implies a direct update of the task set that is carried over from the preceding trial. To this end, in Experiments 1 and 2 we factorially varied the relation of the task in trial n, first, to the task in trial n - 1 (intertask relation) and, second, to the task that was precued for trial n (precue-to-task relation). Invalid precues resulted in substantial costs, which increased with longer precueing intervals. However, this increasing effect of the precue-to-task relation was not accompanied by a decreasing effect of the intertask relation. Furthermore, both effects had different qualitative properties. These findings suggest that two tasks can be represented concurrently but on two different levels of representation. In Experiment 3 we observed that the persistence of the effect of the intertask relation depends on the possibility that task repetitions can occur in trials in which a task shift is precued. This sug- gests that the persistence of the effect of the intertask relation is controlled in a context-sensitive way. When participants in a reaction-time (RT) experiment shift among a set of simple cognitive tasks, their speed of performance is markedly slower than when they perform the same tasks repeatedly. Recent evidence has shown that these shift costs are a very robust phenomenon. Although they can be reduced by advance preparation for a forthcoming task shift, in most studies shift costs do not disappear completely, but residual costs remain even at long prepa- ration intervals (e.g., Allport, Styles, & Hsieh, 1994; Rogers & Monsell, 1995). Among the conditions under which the largest reductions of shift costs can be observed are those in which an explicit, external precue that unambiguously specifies the next task is presented well ahead of the onset of the (usually ambiguous) imperative stimulus (e.g., Kleinsorge, Heuer, & Schmidtke, 2002; Koch, 2003; Meiran, 1996). THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2004, 57A (X), 00–000 © 2004 The Experimental Psychology Society http://www.tandf.co.uk/journals/pp/02724987.html DOI:10.1080/02724980443000034 Correspondence should be addressed to Thomas Kleinsorge, Institut für Arbeitsphysiologie an der Universität Dortmund, Ardeystraße 67, D-44139 Dortmund, Germany. Email: kleinsorge@ifado.de The research reported in this article was supported by Grant KI 1205/2-1 of the Deutsche Forschungs- gemeinschaft. We thank Gero Szepannek and Dana Lembke for assistance in running the experiments and analysing the data, and Stefan Lapp for providing the software. In addition, we thank Iring Koch and an anonymous reviewer for helpful comments on an earlier version of this article.