Cognitive Control of coherent motion perception:functional MRI studies of response selection

Executive control is a human ability that allows to overcome automatic stimulus-responsemappings and to act appropriate in the context of a task where the selection of relevant stimuliand the suppression of interfering information are crucial. The first study (Chapter 2) aimed atcharacterizing the neural correlates of conflict resolution in two variations of the Simoneffect. Two different Simon tasks were introduced where subjects had to identify shapes onthe basis of form-from-motion perception (FFM) within a randomly moving dot field, while(1) motion direction (motion-based Simon task) or (2) stimulus location (location-basedSimon task) had to be ignored. Behavioral data revealed that both types of Simon tasksinduced highly significant interference effects. Using event-related fMRI we coulddemonstrate that both tasks share a common cluster of activated brain regions during conflictresolution (pre-supplementary motor area (pre-SMA), superior parietal lobule (SPL), andcuneus) but also show task-specific activation patterns (left superior temporal cortex in themotion-based, and the left fusiform gyrus in the location-based Simon task). Althoughmotion-based and location-based Simon tasks are conceptually very similar (Type-3 stimulusresponseensembles according to the taxonomy of Kornblum&Stevens (2002)) conflictresolution in both tasks results in the activation of different task-specific regions probablyrelated to the different sources of task-irrelevant information. The second experiment(Chapter 3) aimed at investigating the influence of the degree of interfering information onerror processing. The ability to detect errors is a crucial prerequisite for the appropriateadjustment of behavior to future situations. By means of fMRI, we provide evidence for theexistence of different error-related networks within the human brain. While errors related toincompatible trials were mainly associated with activation of the rostral anterior cingulatecortex (rACC) and the precuneus / posterior cingulate, errors related to trials without preresponseconflict showed specific activation in right inferior parietal cortex. Despite thisfunctional dissociation of brain networks, conjunction analysis revealed common clusters ofactivation in the medial wall (dorsal anterior cingulate cortex (dACC) and medial superiorfrontal cortex (msFC)), and bilateral inferior frontal gyrus / insula, consistent with earlierreports of error-related BOLD-signal increases. The results support the view that despite of anoverlapping core system of error processing, additional brain areas come into play dependingon the existence or absence of cognitive conflict. In order to address the question which brainareas are involved in the detection and processing of two simultaneously operating sources ofinterference derived from a spatial incompatibility task, we used fMRI to directly contrastneural activity related to a double conflict situation to single incompatibility conditions(Chapter 6). Results show signal increase of left dorsolateral prefrontal cortex whenmonitoring simultaneously presented conflict. There was no additional activity in the medialprefrontal cortex or anterior cingulate cortex although these regions are expected to play animportant role in all types of conflict monitoring. Further analyses also suggest a major rolefor the basal ganglia during error detection and resolution.