Performance on the Stroop task reflects two types of conflict—informational (between the incongruent word and font color) and task (between the contextually relevant color-naming task and the irrelevant, but automatic, word-reading task). According to the dual mechanisms of control theory (DMC; Braver, 2012), variability in Stroop performance can result from variability in the deployment of a proactive task-demand control mechanism. Previous research has shown that when proactive control (PC) is diminished, both increased Stroop interference and a reversed Stroop facilitation (RF) are observed. Although the current DMC model accounts for the former effect, it does not predict the observed RF, which is considered to be behavioral evidence for task conflict in the Stroop task. Here we expanded the DMC model to account for Stroop RF. Assuming that a concurrent working memory (WM) task reduces PC, we predicted both increased interference and an RF. Nineteen participants performed a standard Stroop task combined with a concurrent n-back task, which was aimed at reducing available WM resources, and thus overloading PC. Although the results indicated common Stroop interference and facilitation in the low-load condition (zero-back), in the high-load condition (two-back), both increased Stroop interference and RF were observed, consistent with the model’s prediction. These findings indicate that PC is modulated by concurrent WM load and serves as a common control mechanism for both informational and task Stroop conflicts.
Bibliographical noteFunding Information:
The first two authors contributed equally to this research. We thank Desiree Meloul for critical reading of the manuscript, and Alexander Soutschek for allowing us access to his data. M.U. is supported by the Israeli Science Foundation (Grant No. 743/12) and the German–Israel Foundation (Grant No. 158/2011) and by a Visiting Professorship at the University of Oxford from the Leverhulme Trust.
© 2014, Psychonomic Society, Inc.
- Dual mechanism of control
- Executive control
- Task conflict
- Working memory