Executive control in the Simon task: A dual-task examination of response priming and its suppression

Executive control processes are supposed to regulate behaviour and to resolve conflicts in information processing. Recently, Stürmer and colleagues (Stürmer et al., 2002; Stürmer & Leuthold, 2003) reported electrophysiological findings in a Simon task that indicated control over a location-based processing route that mediates response priming. Importantly, when a response conflict occurred on a given trial, a suppression of response priming on the immediately following trial was demonstrated. The present study examines boundary conditions of such control in the Simon paradigm by comparing single-task with dual-task performance. In four experiments a second task, alternating trial-by-trial with the Simon task, was systematically manipulated in its control demands. Whereas reaction time (RT) analysis of single-task conditions revealed the absence of location-based response priming in the Simon task, such priming reappeared when the second task required an overt response. In contrast, working memory load as such did not touch the Simon effect. Therefore, not the response conflict itself but capacity-limited response monitoring processes seem to be critical for executive control in the Simon task and the suppression of response priming.