ORIGINAL ARTICLE Working memory demands modulate cognitive control in the Stroop paradigm Alexander Soutschek • Tilo Strobach • Torsten Schubert Received: 23 December 2011 / Accepted: 25 February 2012 Ó Springer-Verlag 2012 Abstract One important task of cognitive control is to regulate behavior by resolving information processing conflicts. In the Stroop task, e.g., incongruent trials lead to conflict-related enhancements of cognitive control and to improved behavioral performance in subsequent trials. Several studies suggested that these cognitive control processes are functionally and anatomically related to working memory (WM) functions. The present study investigated this suggestion and tested whether these con- trol processes are modulated by concurrent WM demands. For this purpose, we performed three experiments in which we combined different WM tasks with the Stroop paradigm and measured their effects on cognitive control. We found that high WM demands led to a suppression of conflict- triggered cognitive control, whereas our findings suggest that this suppression effect is rather due to WM updating than to maintenance demands. We explain our findings by assuming that WM processes interfere with conflict-trig- gered cognitive control, harming the efficiency of these control processes. Introduction In everyday life, we often focus our attention on behav- iorally relevant stimuli while ignoring distracting ones. For example, we are concentrating on writing an article in our office and, at the same time, ignoring the noise outside the window. One basic mechanism behind these phenomena is cognitive control. According to many theoretical approa- ches, cognitive control is defined as a collection of pro- cesses allowing humans to modify their behavior to achieve their action goals (e.g., Baddeley, 1986; Norman & Shallice, 1986). Recent studies have shown that humans may enhance cognitive control and improve its operation after the occurrence of information processing conflicts. The oper- ation of such enhanced cognitive control is especially reflected by improved conflict resolution in interference tasks in which participants process conflicting response information. In these situations, processing improvements usually occur in an actual trial if participants processed a conflict compared to no conflict in the preceding trial (Botvinick, Braver, Barch, Carter, & Cohen, 2001; Kerns et al., 2004; Stu ¨rmer, Leuthold, Soetens, Schro ¨ter, & Sommer, 2002; Wu ¨hr & Kunde, 2008; but see Mayr, Awh, & Laurey, 2003). Such trial-to-trial modulations were reported by Kerns et al. (2004) for the case of the Stroop task, in which participants name the ink color of a color word and in which reaction times (RT) are increased in incongruent (I) conditions (e.g., the word ‘‘RED’’ in green ink) compared to congruent (C) ones (e.g., ‘‘RED’’ in red ink). Kerns et al. have shown that the interference effect (i.e., the RT difference between I and C trials; Stroop effect) is smaller in trials which are preceded by a conflict trial compared to a non-conflict trial. Similar trial-to-trial modulations were also observed for other interference tasks A. Soutschek (&) Á T. Strobach Á T. Schubert Department of Psychology, Ludwig-Maximilians-Universita ¨t Munich, Leopoldstr. 13, 80802 Munich, Germany e-mail: Alexander.Soutschek@psy.lmu.de A. Soutschek Munich Center for Neurosciences-Brain and Mind, Munich, Germany T. Schubert Department of Psychology, Humboldt-Universita ¨t zu Berlin, Berlin, Germany 123 Psychological Research DOI 10.1007/s00426-012-0429-9