Control in context: The theta rhythm provides evidence for reactive control but no evidence for proactive control.

A prime goal of psychological science is to understand how humans can flexibly adapt to rapidly changing contexts. The foundation of this cognitive flexibility rests on contextual adjustments of cognitive control, which can be tested using the list-wide proportion congruency effect (LWPC). Blocks with mostly incongruent (MI) trials show smaller conflict interference effects compared to blocks with mostly congruent (MC) trials. A critical debate is how proactive and reactive control processes drive contextual adjustments. In this preregistered study (N = 30), we address this conundrum, by using the theta rhythm as a key neural marker for cognitive control. In a confound-minimized Stroop paradigm with short alternating MC and MI blocks, we tested reaction times, error rates, and participants' individualized theta activity (2-7 Hz) in the scalp-recorded electroencephalogram. An LWPC effect was found for both, reaction times and error rates. Importantly, the results provided clear evidence for reactive control processes in the theta rhythm: Theta power was higher in rare incongruent compared with congruent trials in MC blocks, but there was no such modulation in MI blocks. However, regarding proactive control, there were no differences in sustained theta power between MC and MI blocks. A complementary analysis of the alpha activity (8-14 Hz) also revealed no evidence for sustained attentional resources in MI blocks. These findings suggest that contextual adjustments rely mainly on reactive control processes in the theta rhythm. Proactive control, in the present study, may be limited to a flexible attentional shift but does not seem to require sustained theta activity.

Global patterns of tropical forest fragmentation.

Remote sensing enables the quantification of tropical deforestation with high spatial resolution. This in-depth mapping has led to substantial advances in the analysis of continent-wide fragmentation of tropical forests. Here we identified approximately 130 million forest fragments in three continents that show surprisingly similar power-law size and perimeter distributions as well as fractal dimensions. Power-law distributions have been observed in many natural phenomena such as wildfires, landslides and earthquakes. The principles of percolation theory provide one explanation for the observed patterns, and suggest that forest fragmentation is close to the critical point of percolation; simulation modelling also supports this hypothesis. The observed patterns emerge not only from random deforestation, which can be described by percolation theory, but also from a wide range of deforestation and forest-recovery regimes. Our models predict that additional forest loss will result in a large increase in the total number of forest fragments-at maximum by a factor of 33 over 50 years-as well as a decrease in their size, and that these consequences could be partly mitigated by reforestation and forest protection.

Embodied cognition in multitasking: increased hand-specific task shielding when stimuli are presented near the hand.

The proximity of hand position alters the processing of visual stimuli. Stimuli presented close (proximal) to hands receive an enhanced allocation of visual attention compared to stimuli presented far (distal) from hands. In the present dual-task study we studied the consequences of this preferential processing when the stimulus for Task 1 (S1) and the stimulus for Task 2 (S2) were presented together and were assigned to specific response hands (R1 and R2) located proximal (at the monitor) versus distal (in the lap) to the stimuli. In two experiments, we tested whether stimulus-hand proximity affected the extent of between-task interference (i.e., influence of additional Task 2 processing on primary Task 1 processing). In Experiment 1, results showed that stimulus-hand proximity reduced the amount of between-task interference compared to the distal stimulus-hand condition. Extending these findings, in Experiment 2 a further reduction of between-task interference was obtained when a single hand was located at the monitor instead of two hands. These results are inconsistent with the assumption of a generally increased attentional processing benefit for multiple stimuli within hand space. Instead, these findings speak for a hand-specific processing benefit that supports more separate processing of two tasks. Together these findings demonstrate that stimulus-hand proximity affects the quality of multiple task performance, which is discussed in the context of both, basic and applied cognitive research.

Lianas in silico, ecological insights from a model of structural parasitism.

Tropical forests are a critical component of the Earth system, storing half of the global forest carbon stocks and accounting for a third of terrestrial photosynthesis. Lianas are structural parasites that can substantially reduce the carbon sequestration capacity of these forests. Simulations of this peculiar growth form have only recently started and a single vegetation model included lianas so far. In this work we present a new liana implementation within the individual based model Formind. Initial tests indicate high structural realism both horizontal and vertical. In particular, we benchmarked the model against empirical observations of size distribution, mean liana cluster size and vertical leaf distribution for the Paracou site in French Guiana. Our model predicted a reduction of above-ground biomass between 10% for mature stands to 45% for secondary plots upon inclusion of lianas in the simulations. The reduced biomass was the result of a lower productivity due to a combination of lower tree photosynthesis and high liana respiration. We evaluated structural metrics (LAI, basal area, mean tree-height) and carbon fluxes (GPP, respiration) by comparing simulations with and without lianas. At the equilibrium, liana productivity was 1.9t C ha - 1 y - 1 , or 23% of the total GPP and the forest carbon stocks were between 5% and 11% lower in simulations with lianas. We also highlight the main strengths and limitations of this new approach and propose new field measurements to further the understanding of liana ecology in a modelling framework.

Contextual recruitment of cognitive control in preadolescent children and young adults.

The ability to use contextual cues to adjust cognitive control according to situational demands is a hallmark of flexible and adaptive behavior. We investigated the development of three different types of contextual control recruitment in children (9- and 12-year-olds) and young adults. First, we implemented a list-wide proportion congruence manipulation in which conflict trials were frequently/infrequently presented within a list of trials. Second, we implemented a location-specific proportion congruence manipulation in which conflict trials were frequently/infrequently presented at one of two locations. Both types of contextual control recruitment are based on the formation of high-level associations between context features (lists and locations) and the respective cognitive control set. Contextual recruitment of control is observed in reduced interference at contexts with high conflict frequencies. Finally, we investigated a trial-by-trial, conflict-triggered recruitment of cognitive control. Here, the experience of a conflict in the previous trial is expected to reduce subsequent conflict. In all three forms of control recruitment, distinct contextual cues reveal information about the required extent of cognitive control. Young adults showed reliable adjustments of control for all types of contextual cues. Children were able to demonstrate contextual control recruitment based on stable context-control associations (lists and locations). However, using single conflict signals turned out to challenge children in that they were able to adapt control resources only for error reduction, not for reaction times. Altogether, the results indicated that children can learn and use high-level associations between context and control sets. Implications regarding proactive and reactive mechanisms of cognitive control are discussed.

Transcutaneous vagus nerve stimulation (tVNS) enhances conflict-triggered adjustment of cognitive control.

Response conflicts play a prominent role in the flexible adaptation of behavior as they represent context-signals that indicate the necessity for the recruitment of cognitive control. Previous studies have highlighted the functional roles of the affectively aversive and arousing quality of the conflict signal in triggering the adaptation process. To further test this potential link with arousal, participants performed a response conflict task in two separate sessions with either transcutaneous vagus nerve stimulation (tVNS), which is assumed to activate the locus coeruleus-noradrenaline (LC-NE) system, or with neutral sham stimulation. In both sessions the N2 and P3 event-related potentials (ERP) were assessed. In line with previous findings, conflict interference, the N2 and P3 amplitude were reduced after conflict. Most importantly, this adaptation to conflict was enhanced under tVNS compared to sham stimulation for conflict interference and the N2 amplitude. No effect of tVNS on the P3 component was found. These findings suggest that tVNS increases behavioral and electrophysiological markers of adaptation to conflict. Results are discussed in the context of the potentially underlying LC-NE and other neuromodulatory (e.g., GABA) systems. The present findings add important pieces to the understanding of the neurophysiological mechanisms of conflict-triggered adjustment of cognitive control.

Conflict and disfluency as aversive signals: context-specific processing adjustments are modulated by affective location associations.

Context-specific processing adjustments are one signature feature of flexible human action control. However, up to now the precise mechanisms underlying these adjustments are not fully understood. Here it is argued that aversive signals produced by conflict- or disfluency-experience originally motivate such context-specific processing adjustments. We tested whether the efficiency of the aversive conflict signal for control adaptation depends on the affective nature of the context it is presented in. In two experiments, high vs. low proportions of aversive signals (Experiment 1: conflict trials; Experiment 2: disfluent trials) were presented either above or below the screen center. This location manipulation was motivated by existing evidence that verticality is generally associated with affective valence with up being positive and down being negative. From there it was hypothesized that the aversive signals would lose their trigger function for processing adjustments when presented at the lower (i.e., more negative) location. This should then result in a reduced context-specific proportion effect when the high proportion of aversive signals was presented at the lower location. Results fully confirmed the predictions. In both experiments, the location-specific proportion effects were only present when the high proportion of aversive signals occurred at the more positive location above but were reduced (Experiment 1) or even eliminated (Experiment 2) when the high proportion occurred at the more negative location below. This interaction of processing adjustments with affective background contexts can thus be taken as further hint for an affective origin of control adaptations.

The test of both worlds: identifying feature binding and control processes in congruency sequence tasks by means of action dynamics.

Cognitive control processes enable us to act flexibly in a world posing ever-changing demands on our cognitive system. To study cognitive control, conflict tasks and especially congruency sequence effects have been regarded as a fruitful tool. However, for the last decade a dispute has arisen whether or not congruency sequence effects are indeed a valid measure of cognitive control processes. This debate has led to the development of increasingly complex paradigms involving numerous, intricately designed experimental conditions which are aimed at excluding low-level, associative learning mechanisms like feature binding as an alternative explanation for the emergence of congruency sequence effects. Here, we try to go beyond this all-or-nothing thinking by investigating the assumption that both cognitive control processes as well as feature binding mechanisms occur within trials of the same task. Based on a theoretical dual-route-model of behavior under conflict, we show that both classes of cognitive mechanisms should affect behavior at different points of the decision process. By comparing these predictions to continuous mouse movements from an adapted Simon task, we find evidence that control processes and feature binding mechanisms do indeed coexist within the task but that they follow distinct timing patterns. We argue that this dynamic approach to cognitive processing opens up new ways to investigate the diversity of co-existing processes that contribute to the selection of behavior.

Acute stress shifts the balance between controlled and automatic processes in prospective memory.

In everyday life we frequently rely on our abilities to postpone intentions until later occasions (prospective memory; PM) and to deactivate completed intentions even in stressful situations. Yet, little is known about the effects of acute stress on these abilities. In the present work we investigated the impact of acute stress on PM functioning under high task demands. (1) Different from previous studies, in which intention deactivation required mostly low processing demands, we used salient focal PM cues to induce high processing demands during intention-deactivation phases. (2) We systematically manipulated PM-monitoring demands in a nonfocal PM task that required participants to monitor for either one or six specific syllables that could occur in ongoing-task words. Eighty participants underwent the Trier Social Stress Test, a standardized stress induction protocol, or a standardized control situation, before performing a computerized PM task. Our primary interests were whether PM performance, PM-monitoring costs, aftereffects of completed intentions and/or commission-error risk would differ between stressed and non-stressed individuals and whether these effects would differ under varying task demands. Results revealed that PM performance and aftereffects of completed intentions during subsequent performance were not affected by acute stress induction, replicating previous findings. Under high demands on intention deactivation (focal condition), however, acute stress produced a nominal increase in erroneous PM responses after intention completion (commission errors). Most importantly, under high demands on PM monitoring (nonfocal condition), acute stress led to a substantial reduction in PM-monitoring costs. These findings support ideas of selective and demand-dependent effects of acute stress on cognitive functioning. Under high task demands, acute stress might induce a shift in processing strategy towards resource-saving behavior, which seems to increase the efficiency of PM performance (reduced monitoring costs), but might increase initial susceptibility to automatic response activation after intention completion.

Activation of context-specific attentional control sets by exogenous allocation of visual attention to the context?

Different contexts with high versus low conflict frequencies require a specific attentional control involvement, i.e., strong attentional control for high conflict contexts and less attentional control for low conflict contexts. While it is assumed that the corresponding control set can be activated upon stimulus presentation at the respective context (e.g., upper versus lower location), the actual features that trigger control set activation are to date not described. Here, we ask whether the perceptual priming of the location context by an abrupt onset of irrelevant stimuli is sufficient in activating the context-specific attentional control set. For example, the mere onset of a stimulus might disambiguate the relevant location context and thus, serve as a low-level perceptual trigger mechanism that activates the context-specific attentional control set. In Experiment 1 and 2, the onsets of task-relevant and task-irrelevant (distracter) stimuli were manipulated at each context location to compete for triggering the activation of the appropriate control set. In Experiment 3, a prior training session enabled distracter stimuli to establish contextual control associations of their own before entering the test session. Results consistently showed that the mere onset of a task-irrelevant stimulus (with or without a context-control association) is not sufficient to activate the context-associated attentional control set by disambiguating the relevant context location. Instead, we argue that the identification of the relevant stimulus at the respective context is a precondition to trigger the activation of the context-associated attentional control set.

Intention deactivation: effects of prospective memory task similarity on aftereffects of completed intentions.

Recent prospective memory (PM) studies indicate that intentions are not always directly deactivated after completion, but that they entail aftereffects in terms of slower ongoing-task performance and/or commission errors on repeated (no-longer relevant) PM trials. In four experiments, we investigated whether aftereffects depend on the similarity between completed and currently performed PM-tasks. Aftereffects were reduced when PM-cues differed between the two PM-tasks (symbols vs. words) compared to when PM-cues belonged to the same category (symbols vs. symbols). This could be explained by the new dissimilar PM-task shifting spatial attention away from repeated PM-cues and, thus, attenuating processing of these cues. Moreover, a switch of the PM-response (to or within the manual modality) did not result in erroneous retrieval of the no-more-relevant PM-response (i.e., commission errors) but in erroneous retrieval of the currently relevant PM-response (i.e., false alarms). In addition, aftereffects vanished in conditions, in which participants did not perform a new PM-task. This finding indicates that forming a new PM-task set might be a prerequisite for aftereffects when the ongoing task changes between the two subsequent PM-tasks. Finally, we did not find evidence that forming a new, dissimilar PM-task representation led to overwriting of the completed intention representation, and thus to a change of the content or destabilization of its activation level.

Sampling Motif-Constrained Ensembles of Networks.

The statistical significance of network properties is conditioned on null models which satisfy specified properties but that are otherwise random. Exponential random graph models are a principled theoretical framework to generate such constrained ensembles, but which often fail in practice, either due to model inconsistency or due to the impossibility to sample networks from them. These problems affect the important case of networks with prescribed clustering coefficient or number of small connected subgraphs (motifs). In this Letter we use the Wang-Landau method to obtain a multicanonical sampling that overcomes both these problems. We sample, in polynomial time, networks with arbitrary degree sequences from ensembles with imposed motifs counts. Applying this method to social networks, we investigate the relation between transitivity and homophily, and we quantify the correlation between different types of motifs, finding that single motifs can explain up to 60% of the variation of motif profiles.

Individual Differences in the Context-Dependent Recruitment of Cognitive Control: Evidence From Action Versus State Orientation.

The ability to flexibly adapt to deviations from optimal performance is an important aspect of self-control. In the present study, the authors present first evidence that the personality trait action versus state orientation (Kuhl, 2000) modulates the ability of adaptive control adjustments in response to experienced conflicts. Sixty-two German individuals with extreme scores on the action-state dimension performed a response interference task, that is, 31 extreme action-oriented individuals (30 females; Mage = 20.35 years) and 31 extreme state-oriented individuals (20 females; Mage = 23.23 years), respectively. Action-oriented individuals displayed a stronger conflict adaptation effect as evidenced by a stronger reduction of interference on trials following conflict. These results were further corroborated by a correlational analysis including a sample of 105 participants: the higher the score on the action-state dimension, the lower the interference effect following conflict (i.e., stronger conflict adaptation). The results provide evidence that even low-level, bottom-up-driven processes of self-control such as conflict adaptation are systematically moderated by individual differences in control modes and provide insights into the cognitive mechanisms underlying action versus state orientation.

Subthalamic deep brain stimulation restores automatic response activation and increases susceptibility to impulsive behavior in patients with Parkinson's disease.

Repeatedly reported deficits of patients with Parkinson's disease (PD) in selecting an appropriate action in the face of competing response alternatives has led to the conclusion of a basal ganglia (BG) involvement in response selection and impulse control. Despite capacious research, it remains elusive how BG dysfunction affects processes subserving goal-directed behavior. Even more problematically, since PD pathology transcends a BG dysfunction due to dopamine depletion in the nigrostriatal DA system (by also comprising alterations in extrastriatal dopamine availability and other neurotransmitter systems), it is not yet clear which aspects of these deficits are actually caused by BG dysfunction. To address this question, the present study investigated 13 off-medication PD patients with bilateral therapeutic subthalamic deep brain stimulation (DBS) both with and without stimulation (DBSON and DBSOFF, respectively) and 26 healthy controls. All participants performed a task that tests the relation between automatic response impulses and goal-directed action selection. Results show an improvement of automatic response activation under DBSON, increasing the susceptibility to impulsive responses, and a reduced impact of automatic response activation under DBSOFF. We argue that the BG determine the efficiency of the regulation and transmission of stimulus-driven bottom-up response activation required for efficient response selection.

The difficulty of letting go: moderators of the deactivation of completed intentions.

Recent studies showed that prospective memory (PM) intentions might not be deactivated directly after completion. The residual activation leads to aftereffects which are reflected as interference in performance when former PM cues of old intentions are interspersed in the new task (i.e., intention deactivation failure, Walser et al., J Exp Psychol Learn Mem Cogn 38(4):1030-1044, 2012). In the present study, we investigated potential mechanisms that might support the deactivation process of completed intentions by manipulating the task demands (e.g., working memory load) between intention completion and measurement of aftereffects. Aftereffects on repeated PM-cue trials were found when working memory load was low (control condition), but were reduced when available resources were sparse (working memory load condition). When participants were asked to reflect upon the to-be-deactivated PM cue, subsequent aftereffects were increased. Further, overall aftereffects were larger for participants low in self-reported action control. Results show that the nature of the filler-task activity determines whether the representation of the completed intention is destabilized (working memory load) or strengthened (intention reflection). The (at least partial) overwriting of completed intention representations by new working memory task representations seems therefore to reflect a supporting factor for the deactivation of completed intentions.

The role of temporal delay and repeated prospective memory cue exposure on the deactivation of completed intentions.

Previous studies have shown that completed prospective memory (PM) intentions entail aftereffects in terms of ongoing-task-performance decrements in trials containing repeated PM cues which previously served as PM cues triggering the intended action. Previous research reported that PM aftereffects decrease over time, thus revealing a specific time course of PM aftereffects. In the present study, we tested two accounts for this pattern, assuming either that the decline of aftereffects is related to the temporal distance to PM task completion or may be a result of the repeated exposure of repeated PM cues in the ongoing task. In three experiments, we manipulated both the temporal distance to PM task completion and the frequency of repeated PM cues and demonstrated that aftereffects of completed intentions declined with repeated exposure of formerly relevant PM cues. In addition, effects of repeated exposure were not only limited to the repetition of specific PM-cue exemplars but also generalized to other semantically related PM cues within the PM-cue category. Together, findings show that decreased aftereffects of completed intentions are not related to the temporal duration of the subsequent test block, but crucially depend on the repeated exposure of the previously relevant PM cues.

EXPRESS: The affective consequences of response inhibition determine no-go based crosstalk effects in dual tasks.

Backward crosstalk effects (BCE) are observed in dual-task studies when characteristics of Task 2 influence Task 1 performance. When Task 2 is a go/no-go task, responses in Task 1 are slower when Task 2 is a no-go as compared to a go trial. This no-go BCE has been argued to be due to response inhibition spilling over from Task 2 to Task 1. Growing evidence shows that response inhibition elicits negative affect leading to affective devaluation of associated stimuli. We tested for a functional role of the negative affective consequence of response inhibition in the no-go BCE by investigating its interaction with affective processing in Task 1. In four experiments, Task 1 was a valence categorization task, and Task 2 a go/no-go task. In all experiments, the no-go BCE strongly depended on affective processing in Task 1. While this modulation could be attributed to an affective (mis)match between stimulus features in both tasks in Experiments 1 and 2, Experiments 3 and 4 provided evidence for an affective (mis)match between stimulus valence in Task 1 and affective consequences of Task 2 response inhibition. Results are discussed in the context of current theories of no-go BCE in dual tasks.

Transfer of task-probability-induced biases in parallel dual-task processing occurs in similar, but is constraint in distinct task sets.

Although humans often multitask, little is known about how the processing of concurrent tasks is managed. The present study investigated whether adjustments in parallel processing during multitasking are local (task-specific) or global (task-unspecific). In three experiments, participants performed one of three tasks: a primary task or, if this task did not require a response, one of two background tasks (i.e., prioritized processing paradigm). To manipulate the degree of parallel processing, we presented blocks consisting mainly of primary or background task trials. In Experiment 1, the frequency manipulation was distributed equally across the two background tasks. In Experiments 2 and 3, only one background task was frequency-biased (inducer task). The other background task was presented equally often in all blocks (diagnostic task) and served to test whether processing adjustments transferred. In all experiments, blocks with frequent background tasks yielded stronger interference between primary and background tasks (primary task performance) and improved background task performance. Thus, resource sharing appeared to increase with high background task probabilities even under triple task requirements. Importantly, these adjustments generalized across the background tasks when they were conceptually and visually similar (Experiment 2). Implementing more distinct background tasks limited the transfer: Adjustments were restricted to the inducer task in background task performance and only small transfer was observed in primary task performance (Experiment 3). Overall, the results indicate that the transfer of adjustments in parallel processing is unrestricted for similar, but limited for distinct tasks, suggesting that task similarity affects the generality of resource allocation in multitasking. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Investigating the neural mechanisms of transcranial direct current stimulation effects on human cognition: current issues and potential solutions.

Transcranial direct current stimulation (tDCS) has been studied extensively for its potential to enhance human cognitive functions in healthy individuals and to treat cognitive impairment in various clinical populations. However, little is known about how tDCS modulates the neural networks supporting cognition and the complex interplay with mediating factors that may explain the frequently observed variability of stimulation effects within and between studies. Moreover, research in this field has been characterized by substantial methodological variability, frequent lack of rigorous experimental control and small sample sizes, thereby limiting the generalizability of findings and translational potential of tDCS. The present manuscript aims to delineate how these important issues can be addressed within a neuroimaging context, to reveal the neural underpinnings, predictors and mediators of tDCS-induced behavioral modulation. We will focus on functional magnetic resonance imaging (fMRI), because it allows the investigation of tDCS effects with excellent spatial precision and sufficient temporal resolution across the entire brain. Moreover, high resolution structural imaging data can be acquired for precise localization of stimulation effects, verification of electrode positions on the scalp and realistic current modeling based on individual head and brain anatomy. However, the general principles outlined in this review will also be applicable to other imaging modalities. Following an introduction to the overall state-of-the-art in this field, we will discuss in more detail the underlying causes of variability in previous tDCS studies. Moreover, we will elaborate on design considerations for tDCS-fMRI studies, optimization of tDCS and imaging protocols and how to assure high-level experimental control. Two additional sections address the pressing need for more systematic investigation of tDCS effects across the healthy human lifespan and implications for tDCS studies in age-associated disease, and potential benefits of establishing large-scale, multidisciplinary consortia for more coordinated tDCS research in the future. We hope that this review will contribute to more coordinated, methodologically sound, transparent and reproducible research in this field. Ultimately, our aim is to facilitate a better understanding of the underlying mechanisms by which tDCS modulates human cognitive functions and more effective and individually tailored translational and clinical applications of this technique in the future.