Alexander Soutschek

Investigation on the improvement and transfer of dual-task coordination skills

Recent research has demonstrated that dual-task performance in situations with two simultaneously presented tasks can be substantially improved with extensive practice. This improvement was related to the acquisition of task coordination skills. Earlier studies provided evidence that these skills result from hybrid practice, including dual and single tasks, but not from single-task practice. It is an open question, however, whether task coordination skills are independent from the specific practice situation and are transferable to new situations or whether they are non-transferable and task-specific. The present study, therefore, tested skill transfer in (1) a dual-task situation with identical tasks in practice and transfer, (2) a dual-task situation with two tasks changed from practice to transfer, and (3) a task switching situation with two sequentially presented tasks. Our findings are largely consistent with the assumption that task coordination skills are non-transferable and task-specific. We cannot, however, definitively reject the assumption of transferable skills when measuring error rates in the dual-task situation with two changed tasks after practice. In the task switching situation, single-task and hybrid practice both led to a transfer effect on mixing costs.

Dissociable Networks Control Conflict during Perception and Response Selection: A Transcranial Magnetic Stimulation Study

Current models of conflict processing propose that cognitive control resolves conflict in the flanker task by enhancing task-relevant stimulus processing at a perceptual level. However, because conflicts occur at both a perceptual and a response selection level in that task, we tested the hypothesis of conflict-specific control networks for perceptual and response selection conflicts using transcranial magnetic stimulation (TMS). TMS of the presupplementary motor area selectively disrupted the processing of response selection conflict, whereas TMS of the posterior intraparietal sulcus/inferior parietal lobule interfered with perceptual conflict processing. In more detail, the presupplementary motor area seems to resolve response selection conflict mainly when no conflicts have occurred in the previous trial. In contrast, the posterior intraparietal sulcus/inferior parietal lobule may resolve perceptual conflicts selectively when a conflict has occurred in the previous trial. The current data show the need for revising models of cognitive control by providing evidence for the existence of conflict-specific control networks resolving conflict at different processing levels.

Working memory demands modulate cognitive control in the Stroop paradigm

One important task of cognitive control is to regulate behavior by resolving information processing conflicts. In the Stroop task, e.g., incongruent trials lead to conflict-related enhancements of cognitive control and to improved behavioral performance in subsequent trials. Several studies suggested that these cognitive control processes are functionally and anatomically related to working memory (WM) functions. The present study investigated this suggestion and tested whether these control processes are modulated by concurrent WM demands. For this purpose, we performed three experiments in which we combined different WM tasks with the Stroop paradigm and measured their effects on cognitive control. We found that high WM demands led to a suppression of conflict-triggered cognitive control, whereas our findings suggest that this suppression effect is rather due to WM updating than to maintenance demands. We explain our findings by assuming that WM processes interfere with conflict-triggered cognitive control, harming the efficiency of these control processes.

Motion coordination affects movement parameters in a joint pick-and-place task.

This study examined influences of social context on movement parameters in a pick-and-place task. Participants’ motion trajectories were recorded while they performed sequences of natural movements either working side-by-side with a partner or alone. It was expected that movement parameters would be specifically adapted to the joint condition to overcome the difficulties arising from the requirement to coordinate with another person. To disentangle effects based on participants’ effort to coordinate their movements from effects merely due to the others presence, a condition was included where only one person performed the task while being observed by the partner. Results indicate that participants adapted their movements temporally and spatially to the joint action situation: Overall movement duration was shorter, and mean and maximum velocity was higher when actually working together than when working alone. Pick-to-place trajectories were also shifted away from the partner in spatial coordinates. The partners presence as such did not have an impact on movement parameters. These findings are interpreted as evidence for the use of implicit strategies to facilitate movement coordination in joint action tasks.

When flanker meets the n-back: What EEG and pupil dilation data reveal about the interplay between the two central-executive working memory functions inhibition and updating

We investigated the interplay between inhibition and updating, two executive working memory (WM) functions. We applied a novel task paradigm consisting of flanker stimuli presented within an n-back task and studied the interaction between inhibitory demands and load on WM updating using behavioral measures, EEG, and pupil dilation. In contrast to studies that examine the interaction between inhibitory demands and load on WM storage components, the current task paradigm allowed testing the interaction between the executive WM components updating and inhibition. We found a reduced flanker interference effect for the highest (2-back) updating load condition compared to lower updating load conditions on most measures. We interpret these findings as indicating that inhibitory control and WM updating are closely intertwined executive functions. Increased load on updating seemed to result in an overall more activated attentional network thus enhancing inhibitory control, such that task performance is less susceptible to distracting information.

Domain-Specific Control Mechanisms for Emotional and Nonemotional Conflict Processing.

Recent neuroimaging studies suggest that the human brain activates dissociable cognitive control networks in response to conflicts arising within the cognitive and the affective domain. The present study tested the hypothesis that nonemotional and emotional conflict regulation can also be dissociated on a functional level. For that purpose, we examined the effects of a working memory and an emotional Go/Nogo task on cognitive control in an emotional and a nonemotional variant of the Stroop paradigm. The data confirmed the hypothesized dissociation: Working memory efforts selectively suppressed conflict regulation in the nonemotional Stroop task, while the demands of an emotional Go/Nogo task impaired only conflict regulation in the emotional Stroop task. We conclude that these findings support a modular architecture of cognitive control with domain-specific conflict regulation processes.

Modulation of executive control in dual tasks with transcranial direct current stimulation (tDCS).

Executive processing in dual tasks is primarily associated with activation of the lateral prefrontal cortex (lPFC), which is demonstrated in functional imaging studies (e.g., Szameitat et al., 2006). However, a causal relation between lPFC activity and executive functions in dual tasks has not been demonstrated so far. Here, we used anodal transcranial direct current stimulation (atDCS [1 mA, 20 min] vs. sham stimulation [1 mA, 30s]) over the left inferior frontal junction under conditions of random and fixed task order in dual tasks as well as in single tasks in healthy young individuals (Experiment 1). We found that atDCS, if administered simultaneously to the task, improved performance in random-order dual tasks, but not in fixed-order dual tasks and single tasks. Moreover, dual-task performance under random-order conditions did not improve if atDCS was applied prior to the task performance. The identical procedure in Experiment 2 showed no difference in dual-task performance under random-task order conditions when we compared cathodal tDCS (ctDCS) with sham stimulation. Our findings suggest that dual-task performance is causally related to lPFC activation under conditions that require task-order decisions and high demands on executive functioning. Subsequent studies may now explore if atDCS leads to sustained improvements parallel to the training of dual tasks.

Dissociable effects of motivation and expectancy on conflict processing: An fmri study

Previous studies suggest that both motivation and task difficulty expectations activate brain regions associated with cognitive control. However, it remains an open question whether motivational and cognitive determinants of control have similar or dissociable impacts on conflict processing on a neural level. The current study tested the effects of motivation and conflict expectancy on activity in regions related to processing of the target and the distractor information. Participants performed a picture–word interference task in which we manipulated the size of performance-dependent monetary rewards (level of motivation) and the ratio of congruent to incongruent trials within a block (level of conflict expectancy). Our results suggest that motivation improves conflict processing by facilitating task-relevant stimulus processing and task difficulty expectations mainly modulate the processing of distractor information. We conclude that motivation and conflict expectancy engage dissociable control strategies during conflict resolution.

Motivational and cognitive determinants of control during conflict processing

Previous studies suggest that both reward anticipation and expected or experienced conflicts activate cognitive control. The present study investigated how these factors interact during conflict processing. In two experiments, participants performed a variant of the Stroop task, receiving performance-dependent monetary rewards in some blocks. In addition, we manipulated the level of conflict-triggered reactive and expectancy-driven proactive control: In Experiment 1, we compared the Stroop effect after previously congruent and incongruent trials to examine the conflict adaptation effect (reactive control). We found that the level of motivation did not interact with conflict adaptation. In Experiment 2, we varied the proportion of congruent and incongruent trials to manipulate conflict expectancy (proactive control). The data suggest the effects of motivation to be less pronounced under conditions of high conflict expectancy. We conclude that the interaction of motivation with cognitive determinants of control depends on whether these activate proactive or reactive control processes.

Interference control in adult ADHD: No evidence for interference control deficits if response speed is controlled by delta plots

Several theoretical accounts assume that interference control deficits belong to the core symptoms of adult ADHD. However, findings of increased interference effects in adult ADHD patients compared with healthy adults may be confounded with the simultaneous finding of generally slower responses in the patient group. The current study compared the magnitude of the interference effect in the Stroop task between a group of adults with ADHD and a healthy adult control group in a procedure that accounted for differences in overall response speed by using delta plots. The amount of interference did not differ between patient and control group at comparable reaction time levels. These results challenge the conclusions of the previous studies, in that they indicate that interference control is not impaired in adult ADHD.