Comparison of two Simon tasks: Neuronal correlates of conflict resolution based on coherent motion perception Matthias Wittfoth, a,c, * Daniela Buck, a Manfred Fahle, b,c and Manfred Herrmann a,c a Department of Neuropsychology and Behavioral Neurobiology, Institute for Cognitive Neuroscience, University of Bremen, Grazer Strasse 6, D-28359 Bremen, Germany b Department of Human Neurobiology, Center for Cognitive Sciences, University of Bremen, Bremen, Germany c Center for Advanced Imaging—CAI Bremen, University of Bremen, Bremen, Germany Received 4 November 2005; revised 17 March 2006; accepted 22 March 2006 Available online 3 May 2006 The present study aimed at characterizing the neural correlates of conflict resolution in two variations of the Simon effect. We introduced two different Simon tasks where subjects had to identify shapes on the basis of form-from-motion perception (FFMo) within a randomly moving dot field, while (1) motion direction (motion-based Simon task) or (2) stimulus location (location-based Simon task) had to be ignored. Behavioral data revealed that both types of Simon tasks induced highly significant interference effects. Using event- related fMRI, we could demonstrate that both tasks share a common cluster of activated brain regions during conflict resolution (pre- supplementary motor area (pre-SMA), superior parietal lobule (SPL), and cuneus) but also show task-specific activation patterns (left superior temporal cortex in the motion-based, and the left fusiform gyrus in the location-based Simon task). Although motion-based and location-based Simon tasks are conceptually very similar (Type 3 stimulus – response ensembles according to the taxonomy of [Korn- blum, S., Stevens, G. (2002). Sequential effects of dimensional overlap: findings and issues. In: Prinz, W., Hommel., B. (Eds.), Common mechanism in perception and action. Oxford University Press, Oxford, pp. 9 –54]) conflict resolution in both tasks results in the activation of different task-specific regions probably related to the different sources of task-irrelevant information. Furthermore, the present data give evidence those task-specific regions are most likely to detect the relationship between task-relevant and task-irrelevant information. D 2006 Elsevier Inc. All rights reserved. Keywords: Response conflict; fMRI; Simon task; Coherent motion perception Introduction The Simon task has been widely used to study conflict resolution in cognitive psychology (Simon, 1969). When stimulus and res- ponse sides (right/left) do not correspond even though stimulus location is task-irrelevant, the resulting increase in reaction time (RT) is referred to as the Simon effect. This robust phenomenon is interpreted as resulting from the automatic generation of a spatial code in response to stimulus location. Since the spatial code overlaps with the relevant response code derived from the nonspatial dimen- sion (e.g., shape), it interferes with the speed of correct response selection. The Dimensional Overlap (DO) model by Kornblum (e.g., Kornblum and Stevens, 2002) provides a theoretical framework to differentiate between the various conflict effects. It accounts for stimulus – stimulus (S – S) and stimulus – response (S – R) compati- bility effects based on perceptual, conceptual or structural similarity between the relevant and the irrelevant stimulus dimensions on one side, and the response dimension of the task on the other side. According to the DO model, the Simon effect results from a direct stimulus – response conflict induced by a prepotent association bet- ween the stimulus and a response on the same side (Type 3 sti- mulus – response ensemble). Although advances in neuroimaging methods over the past decade have opened new windows into human cognitive functions, the neural mechanism of cognitive control processes underlying experimental procedures, such as the Simon, Stroop, or Eriksen flanker tasks, remains largely unexplained. Up to now, only few studies compared in some detail neural networks activated by different conflict tasks within the same experimental session with event-related fMRI (Fan et al., 2003; Liu et al., 2004; Peterson et al., 2002; Wager et al., 2005). These studies reported numerous brain regions being activated during the conflict task condition as compared to the no-conflict task condition. Among these are the posterior frontomedian cortex (pFMC; in particular the anterior cingulate cortex (ACC), the pre-supplementary and the supplemen- tary motor areas (pre-SMA/SMA)), the middle frontal cortex, the anterior insula/frontal operculum, anterior prefrontal, superior and 1053-8119/$ - see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2006.03.034 * Corresponding author. Department of Neuropsychology and Behav- ioral Neurobiology, Institute for Cognitive Neuroscience, University of Bremen, Grazer Strasse 6, D-28359 Bremen, Germany. Fax: +49 421 218 4408. E-mail address: mwittfoth@uni-bremen.de (M. Wittfoth). Available online on ScienceDirect (www.sciencedirect.com). www.elsevier.com/locate/ynimg NeuroImage 32 (2006) 921 – 929