Birgit Stürmer

Control Over Location-Based Response Activation in the Simon Task: Behavioral and Electrophysiological Evidence

In 4 Simon experiments the authors examined control over 2 routes of sensorimotor processing: response priming in the unconditional route and response selection via the conditional route. The Simon effect diminished as the frequency of noncorresponding trials increased. Location-based response priming was observed only when the stimulus followed a corresponding event but not after a noncorresponding trial. Therefore, the unconditional route appears to be suppressed whenever the task context indicates priming as potentially disadvantageous. Moreover, the task-irrelevant stimulus location was used for response selection as a function of correspondence probability. Although exact repetitions of stimulus-response sequences caused a marked speed-up of responses, this 3rd mechanism is independent of unconditional route suppression and frequency-based adjustments in the conditional route.

Correspondence effects with manual gestures and postures: A study of imitation

In this study, the authors applied methods and theories from research of stimulus-response compatibility (SRC) to action imitation. In 6 experiments, they adopted the logic of the Simon paradigm (B. Hommel & W. Prinz, 1996) to explore interference between task-relevant symbolic stimulus features (color) and task-irrelevant iconic stimulus features (2 hand gestures and 2 postures). The same 2 hand gestures served as responses. Pronounced correspondence effects for both gestures and postures showed up throughout. In line with theories of SRC, the authors account for these correspondence effects in terms of overlap arising between stimulus and response features in a common representational domain. As a specific extension of this approach, they propose 2 functionally independent mechanisms: One operates movement-based when dynamic information is provided, and the other operates state-based with static postures as stimuli. Implications for theories of both SRC and action imitation are discussed.

Theta power as a marker for cognitive interference

OBJECTIVE The present study aimed at investigating whether theta activity within medio-frontal cortex (MFC) serves as a marker for increased cognitive control demands such as performance monitoring. METHODS We confronted participants with at least two incompatible sources of information in a Simon task, a flanker task, and a NoGo task to assess whether changes in EEG theta activity correspond to executive control demands across different sources of cognitive interference. RESULTS Overall, increases of theta power were to a different extent observed in all interference situations: (1) differences in theta power were largest between successful response inhibition in NoGo events compared to Go responses, (2) incongruent and congruent events in the flanker task differed to a lesser extent, and (3) differences in theta power were smallest comparing incompatible and compatible Simon events. Scalp-topographies and dipole modeling of theta activity pointed to different sources across interference conditions that encompassed various MFC areas within anterior cingulate cortex and (pre-) supplementary motor areas. CONCLUSIONS Our results indicate that theta power amplitude is sensitive to the recruitment of executive control in interference situations, whereas the MFC sources of theta power varied across different interference situations. SIGNIFICANCE This study shows for the first time theta power enhancement related to the recruitment of cognitive control across different types of conflicts in the stream of information processing.

Explicit and implicit learning of event sequences: Evidence from event-related brain potentials

Event-related brain potentials (ERPs) were recorded during a serial reaction time (RT) task, where single deviant items seldom (Experiment 1) or frequently (Experiment 2) replaced 1 item of a repeatedly presented 10-item standard sequence. Acquisition of sequence knowledge was reflected in faster RTs for standard as compared with deviant items and in an enhanced negativity (N2 component) of the ERP for deviant items. Effects were larger for participants showing explicit knowledge in their verbal reports and in a recognition test. The lateralized readiness potential indicated that correct responses were activated with shorter latencies after training. For deviant items, participants with explicit knowledge showed an initial activation of the incorrect but expected response. These findings suggest that the acquisition of explicit and implicit knowledge is reflected in different electrophysiological correlates and that sequence learning may involve the anticipatory preparation of responses.

Theta dynamics reveal domain-specific control over stimulus and response conflict

Cognitive control allows us to adjust to environmental changes. The medial frontal cortex (MFC) is thought to detect conflicts and recruit additional resources from other brain areas including the lateral prefrontal cortices. Here we investigated how the MFC acts in concert with visual, motor, and lateral prefrontal cortices to support adaptations of goal-directed behavior. Physiologically, these interactions may occur through local and long-range synchronized oscillation dynamics, particularly in the theta range (4–8 Hz). A speeded flanker task allowed us to investigate conflict-type-specific control networks for perceptual and response conflicts. Theta power over MFC was sensitive to both perceptual and response conflict. Interareal theta phase synchrony, however, indicated a selective enhancement specific for response conflicts between MFC and left frontal cortex as well as between MFC and the presumed motor cortex contralateral to the response hand. These findings suggest that MFC theta-band activity is both generally involved in conflict processing and specifically involved in linking a neural network controlling response conflict.

Control over response priming in visuomotor processing: a lateralized event-related potential study.

In a typical Simon task responses are faster when the task-irrelevant stimulus location corresponds to the response location than when it does not. In the case of noncorrespondence it is assumed that externally triggered and internally selected responses are in conflict. Crucially, such conflict appears to be subject to contextual modulations as induced by the immediately preceding event, i.e., the Simon effect was found to be absent when a conflict trial preceded the current event (Stürmer et al. 2002, JEP:HPP). Here, we examined two possible accounts of this context effect in terms of early suppression of externally triggered S-R coding at a premotoric level versus late suppression at a motoric level. Lateralized event-related brain potentials (L-ERPs) were recorded in a Simon task and analyzed as a function of the correspondence sequence. L-ERP activity started earliest over occipito-parietal brain areas and revealed location-based S-R priming irrespective of the prior correspondence context. By contrast, when a noncorresponding trial preceded, such location-based priming was absent in L-ERP activity over the motor cortex (MC). Thus, in support of the late suppression view L-ERPs suggest a clear dissociation in function between externally triggered visuomotor functions within the dorsal stream and the MC reflecting context-controlled response activation.

Reward and Punishment Effects on Error Processing and Conflict Control

Recently, positive affect has been reported to reduce cognitive conflicts and adaptations related to conflict control. van Steenbergen et al. (2009) proposed that the aversive quality of conflicts drives short-term adaptations following a conflict. They reasoned that monetary gain and its positive emotional consequences might counteract the aversive quality of conflict and hence reduce subsequent adaptations. In two experiments, we combined Simon-type conflicts with monetary gains and losses in between trials and analyzed event-related brain potentials. In Experiment 1, gains and losses occurred randomly between trials as a lottery, whereas in Experiment 2 gains and losses were contingent upon performance, either rewarding the 25% fastest responses or penalizing the 25% slowest responses. In Experiment 1, conflict adaptation was completely unaffected by gains or losses; contrary to predictions, in Experiment 2, conflict adaptation in reward blocks was more pronounced after a gain. In Experiment 2 we also investigated the error-related negativity (ERN) – a brain signal proposed to be related to performance monitoring. The ERN and behavioral post-error slowing were enlarged in the context of reward; therefore, reward increases error adaptation, possibly by enhancing the subjective value of errors. In conclusion, affective modulations of conflict adaptations seem to be much more limited than previously asserted and adaptive mechanisms triggered by errors and conflicts dissociate.

Chunking processes in the learning of event sequences : Electrophysiological indicators

The present study investigated whether effects of implicit learning (IL) are due to well-learned and explicitly represented parts of the stimulus material (“chunks”). To this purpose, event-related brain potentials (ERPs) were recorded during an oddball-version of a serial reaction time (RT) task: At unpredictable positions within a 16-item letter sequence, single deviant items replaced an item of the repeatedly presented standard sequence. After acquisition, the “process dissociation procedure” (Jacoby, 1991) was adopted to identify explicitly learned sequence parts for each participant. Acquisition of sequence knowledge was reflected in faster RTs for standard items than for deviant items and in enhanced N2b and P3b components for deviant items. While the ERP effects were obtained for explicitly represented sequence parts only, RT effects were independent of subsequent reproduction performance. These results indicated that (1) ERPs are a valid measure of explicit knowledge, (2) implicit and explicit knowledge coexist in serial RT tasks, and (3) chunking processes play a major role in the acquisition of explicit knowledge about event sequences.

Response priming in the Simon paradigm: A transcranial magnetic stimulation study

Abstract. The Simon effect refers to the finding of faster responses when stimulus and response locations correspond than when they do not, although a nonspatial stimulus feature is task-relevant. These performance differences are usually accounted for by response priming processes directly induced by the task-irrelevant stimulus location. The present study investigated neural mechanisms of response priming in a Simon task at the level of the motor cortex with the help of transcranial magnetic stimulation (TMS) and motor evoked potentials (MEPs) in both arms. A single TMS was applied contralateral or ipsilateral to the requested response at the time point where response priming was at a maximum. The MEP effects depended on the stimulated hemisphere. Over the left hemisphere, MEP areas were larger when TMS was applied over the primed motor cortex. However, reduced MEPs for the nonprimed hemisphere fell short of significance. Over the right hemisphere, only a MEP reduction for nonprimed left-hand responses was present. Therefore, we conclude that mainly excitatory activation underlies response priming in a Simon task, whereas the role of inhibitory processes is tentative.

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.