C. Nico Boehler

The Congruency Sequence Effect 3.0: A Critical Test of Conflict Adaptation

Over the last two decades, the congruency sequence effect (CSE) –the finding of a reduced congruency effect following incongruent trials in conflict tasks– has played a central role in advancing research on cognitive control. According to the influential conflict-monitoring account, the CSE reflects adjustments in selective attention that enhance task focus when needed, often termed conflict adaptation. However, this dominant interpretation of the CSE has been called into question by several alternative accounts that stress the role of episodic memory processes: feature binding and (stimulus-response) contingency learning. To evaluate the notion of conflict adaptation in accounting for the CSE, we construed versions of three widely used experimental paradigms (the colour-word Stroop, picture-word Stroop and flanker task) that effectively control for feature binding and contingency learning. Results revealed that a CSE can emerge in all three tasks. This strongly suggests a contribution of attentional control to the CSE and highlights the potential of these unprecedentedly clean paradigms for further examining cognitive control.

Pupil size directly modulates the feedforward response in human primary visual cortex independently of attention

Controversy revolves around the question of whether psychological factors like attention and emotion can influence the initial feedforward response in primary visual cortex (V1). Although traditionally, the electrophysiological correlate of this response in humans (the C1 component) has been found to be unaltered by psychological influences, a number of recent studies have described attentional and emotional modulations. Yet, research into psychological effects on the feedforward V1 response has neglected possible direct contributions of concomitant pupil-size modulations, which are known to also occur under various conditions of attentional load and emotional state. Here we tested the hypothesis that such pupil-size differences themselves directly affect the feedforward V1 response. We report data from two complementary experiments, in which we used procedures that modulate pupil size without differences in attentional load or emotion while simultaneously recording pupil-size and EEG data. Our results confirm that pupil size indeed directly influences the feedforward V1 response, showing an inverse relationship between pupil size and early V1 activity. While it is unclear in how far this effect represents a functionally-relevant adaptation, it identifies pupil-size differences as an important modulating factor of the feedforward response of V1 and could hence represent a confounding variable in research investigating the neural influence of psychological factors on early visual processing.

Motivational context for response inhibition influences proactive involvement of attention

Motoric inhibition is ingrained in human cognition and implicated in pervasive neurological diseases and disorders. The present electroencephalographic (EEG) study investigated proactive motivational adjustments in attention during response inhibition. We compared go-trial data from a stop-signal task, in which infrequently presented stop-signals required response cancellation without extrinsic incentives (“standard-stop”), to data where a monetary reward was posted on some stop-signals (“rewarded-stop”). A novel EEG analysis was used to directly model the covariation between response time and the attention-related N1 component. A positive relationship between response time and N1 amplitudes was found in the standard-stop context, but not in the rewarded-stop context. Simultaneously, average go-trial N1 amplitudes were larger in the rewarded-stop context. This suggests that down-regulation of go-signal-directed attention is dynamically adjusted in the standard-stop trials, but is overridden by a more generalized increase in attention in reward-motivated trials. Further, a diffusion process model indicated that behavior between contexts was the result of partially opposing evidence accumulation processes. Together these analyses suggest that response inhibition relies on dynamic and flexible proactive adjustments of low-level processes and that contextual changes can alter their interplay. This could prove to have ramifications for clinical disorders involving deficient response inhibition and impulsivity.

The effect of vagus nerve stimulation on response inhibition

In the current study, we explored whether vagus nerve stimulation (VNS) in patients with epilepsy, which is believed to increase norepinephrine (NE) levels via activation of the locus coeruleus, would positively affect response inhibition. Moreover, we tried to identify the dynamics of the underlying neural processes by investigating event-related potentials (ERPs) and pupil size. Patients performed a stop-signal task once when stimulation was switched on and once when it was switched off. We found a correlational pattern suggesting that patients who clinically benefit more from VNS treatment also show a larger behavioral advantage, in terms of faster response inhibition, when the vagus nerve is being stimulated. Event-related potential (ERP) results suggested more pronounced reactive inhibition when stimulation was switched on, independent of the individual amount of seizure reduction. Transient go-locked pupil size was increased from go trials to successful stop trials to unsuccessful stop trials but without displaying a clear VNS effect, which however, might relate to limited sensitivity. We conclude that VNS likely has a positive effect on response inhibition, at least in patients with epilepsy that benefit clinically from the treatment, presumably relating to enhancements of response-inhibition mechanisms and, therefore, identify enhanced response inhibition as a possible cognitive benefit of VNS.

Occipital alpha power reveals fast attentional inhibition of incongruent distractors

Recent associative models of cognitive control hypothesize that cognitive control can be learned (optimized) for task-specific settings via associations between perceptual, motor, and control representations, and, once learned, control can be implemented rapidly. Midfrontal brain areas signal the need for control, and control is subsequently implemented by biasing sensory representations, boosting or suppressing activity in brain areas processing task-relevant or task-irrelevant information. To assess the timescale of this process, we employed EEG. In order to pinpoint control implementation in specific sensory areas, we used a flanker task with incongruent flankers shown in only one hemifield (congruent flankers in the other hemifield) isolating their processing in the contralateral hemisphere. ERPs revealed fast modulations specifically in visual processing areas contralateral to the incongruent flankers. To test whether these modulations reflect increased or decreased processing of incongruent flankers, we investigated alpha power, a marker for attentional inhibition. Importantly, we show increased alpha power over visual areas processing incongruent flankers from 300 to 500 ms poststimulus onset. This suggests fast cognitive control by attentional inhibition for information disrupting goal-oriented actions. Additionally, we show that midfrontal theta earlier in the trial is also modulated by incongruency, and that theta power predicts subsequent alpha power modulations. This supports the hypothesis that midfrontal incongruency detection leads to control implementation, and reveals that these mechanisms take place on a fast, within-trial timescale.

The role of temporal predictability for early attentional adjustments after conflict

A frequently-studied phenomenon in cognitive-control research is conflict adaptation, or the finding that congruency effects are smaller after incongruent trials. Prominent cognitive control accounts suggest that this adaptation effect can be explained by transient conflict-induced modulations of selective attention, reducing congruency effects on the next trial. In the present study, we investigated these possible attentional modulations in four experiments using the Stroop and Flanker tasks, dissociating possible enhancements of task-relevant information from suppression of task-irrelevant information by varying when this information was presented. In two experiments, the irrelevant stimulus information was randomly presented shortly before, at the same time, or briefly after the presentation of the relevant dimension. In the other two, irrelevant information was always presented first, making this aspect fully predictable. Despite the central role that attentional adjustments play in theoretical accounts of conflict adaption, we only found evidence for such processes in one of the four experiments. Specifically, we found a modulation of the attention-related posterior N1 event-related potential component that was consistent with paying less attention to the irrelevant information after incongruent trials. This was accompanied by increased inter-trial mid-frontal theta power and a theta-power conflict adaptation effect. We interpret these results as evidence for an adaptive mechanism based on relative attentional inhibition. Importantly, this mechanism only clearly seems to be implemented in a very specific context of high temporal predictability, and only in the Flanker task.

Differential effects of sustained and transient effort triggered by reward : a combined EEG and pupillometry study

&NA; In instrumental task contexts, incentive manipulations such as posting reward on successful performance usually trigger increased effort, which is signified by effort markers like increased pupil size. Yet, it is not fully clear under which circumstances incentives really promote performance, and which role effort plays therein. In the present study, we compared two schemes of associating reward with a Flanker task, while simultaneously acquiring electroencephalography (EEG) and pupillometry data in order to explore the contribution of effort‐related processes. In Experiment 1, reward was administered in a block‐based fashion, with series of targets in pure reward and no‐reward blocks. The results imply increased sustained effort in the reward blocks, as reflected in particular in sustained increased pupil size. Yet, this was not accompanied by a behavioral benefit, suggesting a failure of translating increased effort into a behavioral pay‐off. In Experiment 2, we introduced trial‐based cues in order to also promote transient preparatory effort application, which indeed led to a behavioral benefit. Again, we observed a sustained pupil‐size increase, but also transient ones. Consistent with this, the EEG data of Experiment 2 indicated increased transient preparatory effort preceding target onset, as well as reward modulations of target processing that arose earlier than in Experiment 1. Jointly, our results indicate that incentive‐triggered effort can operate on different time‐scales, and that, at least for the current task, its transient (and largely preparatory) form is critical for achieving a behavioral benefit, which may relate to the temporal dynamics of the catecholaminergic systems.

Interactions between incentive valence and action information in a cued approach–avoidance task

Environmental stimuli can provoke specific response tendencies depending on their incentive valence. While some studies report positive-approach and negative-avoidance biases, others find no such mappings. To further illuminate the relationship between incentive valence and action requirement, we combined a cued monetary incentive paradigm with an approach/avoidance joystick task. Incentive type was manipulated between groups: The reward group won money, while the punishment group avoided losing money for correct and fast responses to targets following incentive cues. Depending on their orientations, targets had to be ‘approached’ or ‘avoided’. Importantly, incentive valence (signaled by cue color) was orthogonal to action requirement (target orientation). Moreover, targets could carry valence-associated information or not (target color), which was, however, task-irrelevant. First, we observed that both valence cues (reward/punishment) improved performance compared to neutral cues, independent of the required action (approach/avoid), suggesting that advance valence cues do not necessarily produce specific action biases. Second, task-irrelevant valence associations with targets promoted action biases, with valence-associated targets facilitating approach and impairing avoid responses. Importantly, this approach bias for valence-associated targets was observed in both groups and hence occurred independently of absolute valence (‘unsigned’). This rather unexpected finding might be related to the absence of a direct contrast between positive valence and negative valence within groups and the common goal to respond fast and accurately in all incentive trials. Together, our results seem to challenge the notion that monetary incentives trigger ‘hard-wired’ valence–action biases in that specific design choices seem to modulate the presence and/or direction of valence–action biases.

Smiling faces and cash bonuses: Exploring common affective coding across positive and negative emotional and motivational stimuli using fMRI.

Although it is clear that emotional and motivational manipulations yield a strong influence on cognition and behaviour, these domains have mostly been investigated in independent research lines. Therefore, it remains poorly understood how far these affective manipulations overlap in terms of their underlying neural activations, especially in light of previous findings that suggest a shared valence mechanism across multiple affective processing domains (e.g., monetary incentives, primary rewards, emotional events). This is particularly interesting considering the commonality between emotional and motivational constructs in terms of their basic affective nature (positive vs. negative), but dissociations in terms of instrumentality, in that only reward-related stimuli are typically associated with performance-contingent outcomes. Here, we aimed to examine potential common neural processes triggered by emotional and motivational stimuli in matched tasks within participants using functional magnetic resonance imaging (fMRI). Across tasks, we found shared valence effects in the ventromedial prefrontal cortex and left inferior frontal gyrus (part of dorsolateral prefrontal cortex), with increased activity for positive and negative stimuli, respectively. Despite this commonality, emotion and reward tasks featured differential behavioural patterns in that negative valence effects (performance costs) were exclusive to emotional stimuli, while positive valence effects (performance benefits) were only observed for reward-related stimuli. Overall, our data suggest a common affective coding mechanism across different task domains and support the idea that monetary incentives entail signed basic valence signals, above and beyond the instruction to perform both gain and loss trials as accurately as possible to maximise the outcome.

Neural Dynamics of Reward-Induced Response Activation and Inhibition

Reward-predictive stimuli can increase an automatic response tendency, which needs to be counteracted by effortful response inhibition when this tendency is inappropriate for the current task. Here we investigated how the human brain implements this dynamic process by adopting a reward-modulated Simon task while acquiring EEG and fMRI data in separate sessions. In the Simon task, a lateral target stimulus triggers an automatic response tendency of the spatially corresponding hand, which needs to be overcome if the activated hand is opposite to what the task requires, thereby delaying the response. We associated high or low reward with different targets, the location of which could be congruent or incongruent with the correct response hand. High-reward targets elicited larger Simon effects than low-reward targets, suggesting an increase in the automatic response tendency induced by the stimulus location. This tendency was accompanied by modulations of the lateralized readiness potential over the motor cortex, and was inhibited soon after if the high-reward targets were incongruent with the correct response hand. Moreover, this process was accompanied by enhanced theta oscillations in medial frontal cortex and enhanced activity in a frontobasal ganglia network. With dynamical causal modeling, we further demonstrated that the connection from presupplementary motor area (pre-SMA) to right inferior frontal cortex (rIFC) played a crucial role in modulating the reward-modulated response inhibition. Our results support a dynamic neural model of reward-induced response activation and inhibition, and shed light on the neural communication between reward and cognitive control in generating adaptive behaviors.