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It is well-known that alcohol impairs behavioral control and motor response inhibition, but it has remained rather unclear whether it also impairs cognitive inhibition. As automatized behavior is less vulnerable towards the detrimental effects of alcohol than cognitive control processes, potential cognitive inhibition deficits might however improve with training. We investigated the effect of an acute, binge-like alcohol intoxication in a balanced within-subjects design, asking n=32 healthy young males to perform a backward inhibition paradigm once sober and once while intoxicated (~1.1 ‰). To identify the underlying neurophysiological mechanisms, we analyzed stimulus- and response selection-related processes in neurophysiological data after Residue Iteration Decomposition (RIDE). Alcohol generally impaired behavioral task performance (accuracy and response times) during task switching. This was associated with impaired attentional processing of the task-relevant cue (reflected by reduced P1 and N1 amplitudes), which likely resulted in a larger need for reactive control at the later stage of response selection and control (reflected by increased fronto-central theta power). Without prior practice (~30 minutes), the intoxicated participants further struggled to overcome the cognitive inhibition of a previously relevant task set (reflected by a larger backward inhibition effect). This was linked to reduced posterior theta power, which reflects alcohol-induced impairments in working memory capacity and task set-relevant memory retrieval. As individuals with ~30 min task practice did not show the same alcohol-related deficit, it may be deduced that (partial) task set automatization via stimulus-response associations may help to reduce the detrimental effects of alcohol on cognitive inhibition during task switching.

Perseverative cognition (PC), that is, the continuous cognitive representation of uncontrollable threats, is known to dampen executive control processes in experimental paradigms. Similarly, PC has been shown to impair sleep and to be implicated in the exacerbation of insomnia, which may in turn contribute to the disruption of executive functions. The interactions between PC and insomnia in influencing executive functions, however, have never been tested to date. In the present study, we explored whether insomnia symptoms may moderate the associations between PC and disrupted executive functions, with the hypothesis to find a stronger relationship between these variables at increasing levels of insomnia. Fifty participants completed measures of trait PC and insomnia severity in the previous month and also completed a computerized task-switching paradigm assessing backward inhibition, switch cost, and accuracy. Prior to the task switching, participants completed a measure of state rumination in order to control for the effects of state PC on cognitive performance. Results show that trait PC was significantly correlated with higher insomnia symptoms and state rumination and marginally correlated with lower backward inhibition and longer switch cost. Moreover, insomnia severity moderated the relationship between trait PC and backward inhibition after controlling for the effects of state rumination; that is, the relationship between PC and inhibitory deficits was stronger in those with higher versus lower levels of insomnia symptoms. Findings suggest the need to better elucidate the associations between PC, insomnia, and executive functioning in clinical samples and longitudinal designs.

Ignoring or withholding a response from a stimulus causes it to become affectively devalued. Leading accounts posit that this is due to negative affect elicited by neurocognitive inhibition when it is applied to resolve conflict from distracting or otherwise inappropriate stimulus/response representations. Other research, however, suggests that stimulus/response conflict may itself elicit negative affect and devalue stimuli, raising questions about whether effects previously attributed to inhibition may instead reflect the emotional impact of conflict, per se. To address this, we measured affective ratings of art-like patterns that previously appeared on critical trials of a task-switching paradigm (ABA vs. CBA task sequences) known for its capacity to distinguish behavioural effects of inhibition and conflict. Stimuli from the ABA-sequence experimental condition showing behavioural evidence of backward inhibition (n-2 repetition costs) received more negative ratings than those from the CBA-sequence control condition. This stimulus-devaluation effect was not impacted by the level of conflict associated with high uncertainty or low uncertainty about upcoming task order. Moreover, the response-time index of inhibition was larger on ABA trials in which the associated stimuli later received negative ratings than on trials preceding relatively positive ratings. Inhibition therefore appears to have negative affective consequences that exceed any emotional impact of conflict, with fluctuations in inhibition linked to subsequent stimulus evaluations.

Previous studies have found that inhibiting a task set plays an important role in task switching. However, the impact of stimulus–response (S–R) complexity on this inhibition processing has not been explored. In this study, we applied the backward inhibition paradigm (switching between tasks A, B, and C, presented in sets of three) in order to investigate inhibition performance under different S–R complexities caused by corresponding S–R mappings. The results showed that the difficult condition resulted in a greater switch cost than the moderate and easy conditions. Furthermore, we found a significant n−2 repetition cost under the easy S–R complexity that was reversed under the difficult S–R complexity. To verify stability of the reversed n−2 repetition cost in the difficult condition, we recruited another independent sample to conduct an additional experiment with the difficult condition. These results replicated the reversed n−2 repetition cost. These findings suggest that S–R complexity affects task-set inhibition in task switching because the effect of the task-set inhibition was insignificant when the S–R complexity increased; it was only significant under the easy condition. This result was caused by the different cognitive resource assignments.

The inhibitory mechanism named backward inhibition (BI) counteracts interference of previous tasks supporting task switching. For instance, if task set A is inhibited when switching to task B, then it should take longer to immediately return to task set A (as occurring in an ABA sequence), as compared to a task set that has not been just inhibited (as occurring in a CBA sequence), because extra time will be needed to overcome the inhibition of task set A. The evidenced prefrontal and cerebellar role in inhibitory control suggests their involvement even in BI. Here, for the first time, we modulated the excitability of multiple brain sites (right presupplementary motor area (pre-SMA), left and right cerebellar hemispheres) through continuous theta burst stimulation (cTBS) in a valuable sham-controlled order-balanced within-subject experimental design in healthy individuals performing two domain-selective (verbal and spatial) task-switching paradigms. Verbal BI was abolished by prefrontal or cerebellar stimulations through opposite alterations of the basal pattern: cTBS on pre-SMA increased CBA reaction times, disclosing the current prefrontal inhibition of any interfering old task. Conversely, cerebellar cTBS decreased ABA reaction times, disclosing the current cerebellar recognition of sequences in which it is necessary to overcome previously inhibited events.

BackgroundPoor executive functions are associated with dysregulated eating and greater caloric intake in healthy samples. In parallel, findings suggested that sleep deprivation impairs executive functions.MethodsWe investigated whether partial sleep deprivation impairs executive functions in individuals reporting binge eating (BE,N = 14) and healthy controls (C,N = 13). Switch cost and backward inhibition were measured using the Task Switching Paradigm after a habitual night of sleep and after a night of partial sleep deprivation.ResultsResults showed a Night by Group interaction on the backward inhibition. The two groups differed in the habitual night, evidencing higher inhibitory control in BE compared to C. Additionally, after partial sleep deprivation, compared to the habitual night, backward inhibition decreased in BE group. This preliminary study was the first to explore the impact of sleep deprivation on executive functions in participants reporting binge eating and healthy controls, thus highlighting their potential role in influencing eating behavior.

Task inhibition (also known as backward inhibition) is an hypothesised form of cognitive inhibition evident in multi-task situations, with the role of facilitating switching between multiple, competing tasks. This article presents a novel cognitive computational model of a backward inhibition mechanism. By combining aspects of previous cognitive models in task switching and conflict monitoring, the model instantiates the theoretical proposal that backward inhibition is the direct result of conflict between multiple task representations. In a first simulation, we demonstrate that the model produces two effects widely observed in the empirical literature, specifically, reaction time costs for both (n-1) task switches and n-2 task repeats. Through a systematic search of parameter space, we demonstrate that these effects are a general property of the model's theoretical content, and not specific parameter settings. We further demonstrate that the model captures previously reported empirical effects of inter-trial interval on n-2 switch costs. A final simulation extends the paradigm of switching between tasks of asymmetric difficulty to three tasks, and generates novel predictions for n-2 repetition costs. Specifically, the model predicts that n-2 repetition costs associated with hard-easy-hard alternations are greater than for easy-hard-easy alternations. Finally, we report two behavioural experiments testing this hypothesis, with results consistent with the model predictions.

Backward inhibition may aid our ability to switch between tasks by counteracting the tendency to repeat a recently performed task. Current theory asserts that conflict between tasks during performance plays a key role in inducing the effect. However, a study by Costa and Friedrich suggests that backward inhibition might occur without this type of conflict being present. To better understand the mechanisms underlying backward inhibition, we investigated the roles of between-task conflict, task-based instructions, and task cues. Experiment 1 tentatively supported the view that conflict between tasks is not necessary for backward inhibition to be present, and suggested that either the use of task-based instructions or the provision of specific task cues might be sufficient to generate the effect. Experiment 2 ruled out task-based instruction as a likely cause of backward inhibition in this context. Experiment 3 showed that the provision of task cues was sufficient to drive a significant backward inhibition effect, but only when stimuli and responses (as well as tasks) repeated. Overall, these results indicate that between-task conflict during performance is not necessary for backward inhibition to be applied, and that task cues have a key role in generating the effect.

In task switching, a conflict between competing task-sets is resolved by inhibiting the interfering task-set. Recent models have proposed a framework of the task-set as composed of two hierarchical components: abstract task identity (e.g., respond to quantity) and more concrete task rules (e.g., category-response rules mapping the categories "one" and "three" to the left and right keys, respectively). The present study explored whether task-set inhibition is the outcome of a general control process or whether it reflects multiple inhibitory processes, each targeting a different component of the competing task-set. To this end, two effects of task-set inhibition were examined: backward inhibition (BI), reflecting the suppression of a just-performed task-set that is no longer relevant; and, competitor rule suppression (CRS), reflecting the suppression of an irrelevant task-set that generates a response conflict. In two task switching experiments, each involving three tasks, we asked participants to make two responses: a cue response, indicating the identity of the relevant task (e.g., "Color"), and a target response requiring the implementation of the task rule (e.g., "Red"). The results demonstrate that BI, but not CRS, appears in cue responses, and thus, suggests that BI reflects inhibition that influences representations related to abstract task identity, rather than (just) competing responses or response rules. These results support a dissociation between inhibitory processes in task switching. The current findings also provide further evidence for a multi-component conceptualization of task-set and task-set inhibition.

Background and objectives The aim of the present study was to investigate the effects of a partial sleep deprivation night on executive functions in participants reporting chronic insomnia and good sleepers using a Task Switching paradigm. Methods Sixteen participants reporting symptoms of chronic insomnia and sixteen good sleepers were tested after a night of habitual sleep and after a night of partial sleep deprivation (5 h of sleep allowed). The Switch Cost (SC) and the Backward Inhibition (BI) were computed as measures of switching attention and response inhibition, respectively. Results We observed a marginally significant interaction Night × Group on SC (F(1,29) = 4.06, p = 0.053), η2 = 0.123. Fisher's least significant difference (LSD) post-hoc revealed a smaller SC after the sleep deprived night relative to the habitual night for the good sleepers (p = 0.027; M = 192.23 ± 201.81 vs M = 98.99 ± 141.16). Differently, participants with insomnia did not show any change after the two nights. Limitations Several limitations must be acknowledged including the use of a convenient sample of university students and the use of a single task of cognitive performance. Conclusions We found that SC was smaller in the good sleepers after a night of partial sleep deprivation compared to a habitual night, indicating a better switching performance. The insomnia group showed no differences in performance after the two experimental nights. Several factors may account for these results, including increased levels of arousal and cognitive effort during task execution.

In task-switching experiments, participants switch between task rules, and each task rule describes how responses are mapped to stimulus information. Importantly, task rules do not pertain to any specific response but to all possible responses. This work examined the hypothesis that task rules, as wholes, rather than (just) specific responses are primed by their execution, such that, in the following trial, response conflicts are exacerbated when the competing responses are generated by these recently primed rules, and performance becomes relatively poor. This hypothesis was supported in two task-switching experiments and re-analyses of additional three published experiments, thus indicating Competitor Rule Priming. Importantly, the Competitor Rule-Priming effect was independent of response repetition vs. switch, suggesting that it reflects the priming of the entire task rule rather than the priming (or suppression) of specific responses. Moreover, this effect was obtained regardless of Backward Inhibition, suggesting these effects are unrelated.

Recently, effects of reward incentives on interference-induced cognitive adjustments have drawn much attention. It has been demonstrated that reward can reduce or eliminate switch costs which occurred when alternating between different tasks. However, it still remains a question how reward affects inhibitory processes underlying task switching. The present study examined this issue by combining a task-switching paradigm with performance-contingent reward. Results showed that the inhibitory processes were modulated by reward, with n-2 repetition costs incremented after reward delivery. Data suggest that reward-triggered reduction or elimination of switch costs may reflect enhancing inhibitory processes which are motivated by reward signals and targeted at the irrelevant task set. These findings shed new light on the role of reward in cognitive control.

In task switching, a common result supporting the notion of inhibitory processes as a determinant of switch costs is the occurrence of n - 2 repetition costs. Evidence suggests that this effect is not affected by preparation. However, the role of preparation on preceding trials has been neglected so far. In this study, evidence for an influence of preparatory processes on n - 2 repetition costs is provided by focusing on the cue-target interval on trials n - 1 and n - 2. N - 2 repetition costs were affected by an interaction of both n - 1 and n - 2 preparation time, being more pronounced when both preparatory intervals were long. The results provide support for the notion of active preparation processes involved in backward inhibition.

The role of cue processing has become a controversial topic in research on cognitive control using task-switching procedures. Some authors suggested a priming account to explain switch costs as a form of encoding benefit when the cue from the previous trial is repeated and hence challenged theories that attribute task-switch costs to task-set (re)configuration. A rich body of empirical evidence has evolved that indeed shows that cue-encoding repetition priming is an important component in task switching. However, these studies also demonstrate that there are usually substantial “true” task-switch costs. Here, we review this behavioral, electrophysiological, and brain imaging evidence. Moreover, we describe alternative approaches to the explicit task-cuing procedure, such as the usage of transition cues or the task-span procedure. In addition, we address issues related to the type of cue, such as cue transparency. We also discuss methodological and theoretical implications and argue that the explicit task-cuing procedure is suitable to address issues of cognitive control and task-set switching.

The n-2 repetition cost seen in task switching is the effect of slower response times performing a recently completed task (e.g. an ABA sequence) compared to performing a task that was not recently completed (e.g. a CBA sequence). This cost is thought to reflect cognitive inhibition of task representations and has been well replicated (Koch, Gade, Schuch, & Philipp, 2010). As such, the n-2 repetition cost has started to be used as a measure of individual differences in inhibitory control (e.g. Whitmer & Banich, 2007); however, the reliability of this measure has not been investigated in a systematic manner. The current study addressed this important issue. Seventy-two participants performed three task switching paradigms; participants were also assessed on rumination traits and processing speed-measures of individual differences potentially modulating the n-2 repetition cost. We found significant n-2 repetition costs for each paradigm. However, split-half reliability tests revealed that this cost was not reliable at the individual-difference level. Neither rumination tendencies nor processing speed predicted this cost. We conclude that the n-2 repetition cost is not reliable as a measure of individual differences in inhibitory control.

In an investigation of task-set reconfiguration, participants switched between 2 tasks on every 2nd trial in 5 experiments and on every 4th trial in a final experiment. The tasks were to classify either the digit member of a pair of characters as even/odd or the letter member as consonant/vowel. As the response-stimulus interval increased up to 0.6 s, the substantial cost to performance of this predictable task-switch fell: Participants could partially reconfigure in advance of the stimulus. However, even with 1.2 s available for preparation, a large asymptotic reaction time (RT) cost remained, but only on the 1st trial of the new task. This is attributed to a component of reconfiguration triggered exogenously, i. e., only by a task-relevant stimulus. That stimuli evoke associated task-sets also explains why RT and switch costs increased when the stimulus included a character associated with the currently irrelevant task. © 1995 American Psychological Association.

The ability to flexibly switch between tasks is an important faculty in daily life. One process that has been suggested to be an important aspect of flexible task switching is the inhibition of a recently performed task. This is called backward inhibition. Several studies suggest that task switching performance can be enhanced by rewards. However, it is less clear in how far backward inhibition mechanisms are also affected by rewards, especially when it comes to the neuronal mechanisms underlying reward-related modulations of backward inhibition. We therefore investigated this using a system neurophysiological approach combining EEG recordings with source localization techniques. We demonstrate that rewards reduce the strength of backward inhibition processes. The neurophysiological data shows that these reward-related effects emerge from response and/or conflict monitoring processes within medial frontal cortical structures. Upstream processes of perceptual gating and attentional selection, as well as downstream processes of context updating and stimulus-response mapping are not modulated by reward, even though they also play a role in backward inhibition effects.

The n–2 repetition cost (Mayr & Keele, 2000) seen in task switching is the effect of slower response times performing a recently completed task (e.g. an ABA sequence) compared to performing a task that was not recently completed (e.g. a CBA sequence). This cost is thought to reflect cognitive inhibition of task representations and has been well replicated (Koch, Gade, Schuch, & Philipp, 2010). As such, the n–2 repetition cost has started to be used as a measure of individual differences in inhibitory control (e.g. Whitmer & Banich, 2007); however, the reliability of this measure has not been investigated in a systematic manner. The current study addressed this important issue. Seventy-two participants performed three task switching paradigms, alongside the Rumination Responses Scale and the Digit-Symbol substitution processing speed task — which measures individual differences potentially modulating the n–2 repetition cost. We found significant n–2 repetition costs for each paradigm. However, split-half reliability tests revealed that this cost was not reliable. Neither rumination nor processing speed predicted this cost. We conclude that the n–2 repetition cost is not reliable as a measure of individual differences in inhibitory control.

The concept of inhibition plays a major role in cognitive psychology. In the present article, we review the evidence for the inhibition of task sets. In the first part, we critically discuss empirical findings of task inhibition from studies that applied variants of the task-switching methodology and argue that most of these findings— such as switch cost asymmetries—are ambiguous. In the second part, we focus on n-22 task-repetition costs, which currently constitute the most convincing evidence for inhibition of task sets. n-22 repetition costs refer to the performance impairment in sequences of the ABA type relative to CBA, which can be interpreted in terms of persisting inhibition of previously abandoned tasks. The available evidence suggests that inhibition is primarily triggered by conflict at selection of stimulus attributes and at the response level. Author Note

The task-switching paradigm is being increasingly used as a tool for studying cognitive control and task coordination. Different procedural variations have been developed. They have in common that a comparison is made between transitions in which the previous task is repeated and transitions that involve a change toward another task. In general, a performance switch cost is observed such that switching to a new task results in a slower and more error-prone execution of the task. The present article reviews the theoretical explanations of the switch cost and the findings collected in support of those explanations. Resolution and protection from interference by previous events explain part of the switching cost, but processes related to task setting and task preparation also play a prominent role, as testified by faster execution and lower switch costs when the preparation time is longer. The authors discuss the evidence in favor of each of these sets of accounts and raise a number of questions that situate task switching in a broader context of cognitive control processes. The role of several aspects of the task set, including task variations, task-set overlap, and task-set structure, is addressed, as is the role of knowledge about probability of task changes and about the structure of task sequences.

Task-switching has proved to be a fruitful paradigm for studying cognitive control mechanisms. Interestingly, this avenue of study has revealed that subjects are, to some degree, able to bring about a change in task-set prior to the performance of that task (provided that they are given advance warning of the upcoming task, for instance in the form of a cue). Event-related potentials (ERPs) have proved to be a good way of measuring these rapid anticipatory control processes. To explore these processes further, the current study examined the relationship between the availability of spatial information and cue-locked task-switching ERP effects. Two groups of subjects were compared: one group could separate the task-sets on the basis of the targets’ colour (the ‘colour’ group), the second on the basis of the targets’ location (the ‘spatial’ group). The performance of both groups benefited to the same extent from advance cueing of task-transitions (switches or repeats), yet the ERP data revealed cue-locked (but not target-locked) differences between the two groups. The most striking of these differences was the absence of both a late positivity over posterior scalp and a late negativity over frontal scalp when the spatial group switched between tasks. Thus, it seems unlikely that these effects index stimulus-response ‘reconfiguration’ per se – as the mappings were identical for both groups of subjects – but rather that these taskswitching processes are sensitive to how the mappings are represented.

Performance after a shifting of task is supported by the inhibition of the executed task, as revealed by slower reaction times (RTs) on alternating compared to nonalternating task sequences (ABA vs CBA). In the present study we investigated the role of stimulus processing in the establishment of task inhibition during task switching, irrespective of the response selection process. Comparing performance on AbA and CbA task sequences within a procedure in which the b-task only involved stimulus encoding processes for later comparison but response selection did not occur, we found slower RTs on AbA compared to CbA task sequences. This revealed that inhibition of the executed task can be triggered at the stimulus processing stage of the new task. In accordance, inhibition only emerged when interference between tasks occurred at the stimulus level, due to stimuli having features relevant for both the executed and the upcoming task.

A feature of human cognition is the ability to monitor and adjust one's own behavior under changing circumstances. A dynamic balance between controlled and rapid responding is needed to adapt to a fluctuating environment. We suggest that cognitive control may include, among other things, two distinct processes. Incongruent stimuli may drive top-down facilitation of task-relevant responses to bias performance toward exploitation vs. exploration. Task or response switches may generally slow responses to bias toward accuracy vs. speed and exploration vs. exploitation. Behavioral results from a task switching study demonstrate these two distinct processes as revealed by higher-order sequential effects. A computational model implements the two conflict-control mechanisms, which allow it to capture many complex and novel sequential effects. Lesion studies with the model demonstrate that the model is unable to capture these effects without the conflict-control loops and show how each monitoring component modulates cognitive control. The results suggest numerous testable predictions regarding the neural substrates of cognitive control.

A task set may need to be inhibited to facilitate the switch to another task. This event-related potential (ERP) study determined (1) whether backward inhibition (BI) is exerted preferentially in high interference environments, and (2) whether ERPs locked to critical time points reflect BI during cue preparation and/or response stages. High interference (HI) and low interference (LI) were created by manipulating task difficulty. A reaction time (RT) BI effect (i.e., BI>control trials) was shown only during HI tasks. Cue-locked ERPs on LI tasks suggest increased attentional resources were allocated during the reactivation of a recently inhibited task. For HI tasks, BI versus control trial differences were reflected in a response-locked ERP negativity only after response selection (indexed by the response-locked lateralized readiness potential), indicating that BI is a lateral inhibition mechanism exerted during response preparation.

The aim of the present study was to examine the contribution of overlapping response sets to the occurrence of task inhibition, measured as n-2 task repetition cost. We had subjects switch among four tasks. Three tasks overlapped on both stimulus set and response set. A fourth, neutral, univalent task never overlapped on the stimulus set but, across three experiments, varied in terms of the degree of overlap in the response set. We found that overlap in response set affects task inhibition. We suggest that response set overlap increases the competition among tasks and, thus, triggers task inhibition to resolve this competition.

The present study used a go/no-go signal delay (GSD) to explore the role of response-related processes in task switching. A go/no-go signal was presented at either 100 ms or 1,500 ms after the stimulus. Participants were encouraged to use the GSD for response selection and preparation. The data indicate that the opportunity to select and prepare a response (i.e., long GSD) resulted in a substantial reduction of task-shift costs (Experiment 1) and n-2 task-repetition costs (i.e., backward inhibition; Experiment 2) in the current trial. These results suggest that interference from the preceding trial can be resolved during response selection and preparation. Furthermore, the shift costs and the n-2 repetition costs after no-go trials with long GSD (i.e., response selection but no execution) were markedly smaller than after go trials. These findings suggest that the interference that gives rise to shift costs and n-2 repetition costs is related not solely to response selection but also to response execution. Thus, the present study demonstrates dissociable contributions of response selection and response execution to interference effects in task switching.

Task switching is regularly required in our everyday life. To succeed in switching, it is important to inhibit the most recently performed task and instead activate the currently relevant task. The process that inhibits a recently performed task when a new task is to be performed is referred to as 'backward inhibition' (BI). While the BI effect has been subject to intense research in cognitive psychology, little is known about the neuronal mechanisms that are related to the BI effect and those that relate to differences in the magnitude of the BI effect. In the current study, we examined the system neurophysiological basis of BI processes using event-related potentials (ERPs) and sLORETA by also taking inter-individual differences in the magnitude of the BI into account. The results suggest that BI processes and inter-individual differences in them strongly depend upon attentional selection mechanisms (reflected by N1-ERP modulations in the current task/trial) mediated via networks consisting of extrastriate occipital areas, the temporo-parietal junction and the inferior frontal gyrus. Other processes and mechanisms related to conflict monitoring, response selection, or the updating, organization and implementation of a new task-set (i.e. N2 and P3 processes) were not shown to be modulated by BI processes and differences in their magnitude, as evoked with a common BI paradigm.

Effective task switching is supported by the inhibition of the just executed task, so that potential interference from previously executed tasks is adaptively counteracted. This inhibitory mechanism, named Backward Inhibition (BI), has been inferred from the finding that switching back to a recently executed task (A-B-A task sequence) is harder than switching back to a less recently executed task (C-B-A task sequence). Despite the fact that BI effects do impact performance on everyday life activities, up to now it is still not clear whether the BI represents an amodal and material-independent process or whether it interacts with the task material. To address this issue, a group of individuals with Williams syndrome (WS) characterized by specific difficulties in maintaining and processing visuo-spatial, but not verbal, information, and a mental age- and gender-matched group of typically developing (TD) children were subjected to three task-switching experiments requiring verbal or visuo-spatial material to be processed. Results showed that individuals with WS exhibited a normal BI effect during verbal task-switching, but a clear deficit during visuo-spatial task-switching. Overall, our findings demonstrating that the BI is a material-specific process have important implications for theoretical models of cognitive control and its architecture.

Parkinson's disease has been associated with executive dysfunction, especially task-switching deficits. One factor contributing to task-switching costs is backward inhibition, as measured by less efficient performance when switching back to a task from which one has recently switched away. This alternating-switch cost is considered to be due to persisting inhibition of elements of the previous task set after a switch. In this study, patients with mild to moderate Parkinson's disease and controls performed three tasks (A-C) in an intermixed fashion. Patients with mild to moderate Parkinson's disease and controls showed equivalent response times. However, the patients made significantly more errors during an alternating switch (i.e., ABA) than did control participants. In contrast, there was no group difference in accuracy in the comparable condition of two consecutive switches between different tasks (i.e., CBA). In addition, accuracy for the two groups was similar for trials in which the task was repeated. These data suggest that Parkinson's disease is associated with either increased backward inhibition, or a reduced ability to overcome this inhibition when reactivating a recently abandoned task set.