The impact of stimulus-specific practice and task instructions on response congruency effects between tasks

Preparing auditory task switching in a task with overlapping and non-overlapping response sets

We used a variant of cued auditory task switching to investigate task preparation and its relation to response-set overlap. Previous studies found increased interference with overlapping response sets across tasks relative to non-overlapping motor response sets. In the present experiments, participants classified either pitch or loudness of a simple tone as low or high, hence, both tasks were constructed around common underlying integrated semantic categories ranging from low to high. Manual responses overlapped in both category and modality for both tasks in Experiment 1A, whereas each task was related to a specific response category and response modality (manual vs. vocal) in Experiment 1B. Focusing on the manual responses in both experiments, the data showed that non-overlapping response sets (Experiment 1B) resulted in a decreased congruency effect, suggesting reduced response-based crosstalk and thus better task shielding, but at the same time switch costs were increased, suggesting less efficient switching between task sets. Moreover, varying preparation time (cue-stimulus interval, CSI) showed that long CSI led to better performance overall. Our results thus suggest that when non-overlapping response sets share common semantic categories across tasks, there is no general benefit over overlapping response sets.

Control dilemma: Evidence of the stability-flexibility trade-off

Cognitive control can be applied flexibly when task goals or environments change (i.e., cognitive flexibility), or stably to pursue a goal in the face of distraction (i.e., cognitive stability). Whether these seemingly contradictory characteristics have an inverse relationship has been controversial, as some studies have suggested a trade-off mechanism between cognitive flexibility and cognitive stability, while others have not found such reciprocal associations. This study investigated the possible antagonistic correlation between cognitive flexibility and stability using a novel version of the flexibility-stability paradigm and the classic cued task switching paradigm. In Experiment 1, we showed that cognitive flexibility was inversely correlated with cognitive stability, as increased distractor proportions were associated with decreased cognitive flexibility and greater cognitive stability. Moreover, cognitive flexibility and stability were regulated by a single control system instead of two independent control mechanisms, as the model selection results indicated that the reciprocally regulated model with one integration parameter outperformed all other models, and the model parameter was inversely linked to cognitive flexibility and stability. We found similar results using the classic cued task switching paradigm in Experiment 2. Therefore, a trade-off between cognitive flexibility and stability was observed from the paradigms used in this study.

The role of response set overlap for flexibility and cognitive control in auditory multitasking

We developed a new variant of auditory task-switching in order to systematically investigate shifting and cognitive control in auditory task-switching and their relation to motor response overlap in a comprehensive way. In two experiments, participants classified either pitch or loudness of a simple tone as either low or high, hence, both tasks were constructed around a common underlying dimension ranging from low to high. In Experiment 1, response sets overlapped in both category and motor modality (both manual), whereas each task was related to a specific response category and motor response modality (manual vs. vocal) in Experiment 2. The data revealed reliable switch costs that were, contrary to our expectations, not reduced with reduced response set overlap. In addition, we found reliable congruency effects and their sequential modulation in both experiments with manual as well as vocal responses, and in the absence of competing motor activation (i.e., without motor response overlap). Congruency effects after auditory task switches were smaller when response sets did not overlap. Our data thus provides an important empirical generalization of known effects to auditory stimuli as well as with both manual and vocal responses. In addition, we demonstrated that reduced congruency effects after switches for non-overlapping response sets were due to the extent of overlap between different response sets in task-switching.

Further Evidence for the Binding and Retrieval of Control-States From the Flanker Task

In response-interference tasks, congruency effects are reduced in trials that follow an incongruent trial. This congruence sequence effect (CSE) has been taken to reflect top-down cognitive control processes that monitor for and intervene in case of conflict. In contrast, episodic-memory accounts explain CSEs with bottom-up retrieval of stimulus-response links. Reconciling these opposing views, an emerging perspective holds that memory stores instances of control - abstract control-states - creating a shortcut for effortful control processes. Support comes from a study that assessed CSEs in a prime-target task. Here, repeating an irrelevant context feature boosted CSEs, possibly by retrieving previously stored control-states. We present a conceptual replication using the Eriksen flanker task because previous research found that CSEs in the flanker task reflect different control mechanisms than CSEs in the prime-target task. We measured CSEs while controlling for stimulus-response memory effects and manipulated contextual information (vertical spatial location) independently from the stimulus information, which introduced the conflict (horizontal spatial location). Results replicate previous findings - CSEs increased for context-repetition compared to context-changes. This study shows that retrieval of control-states is not limited to a specific task or context feature and therefore generalizes the notion that abstract control parameters are stored into trial-specific event files.

Contextual Adaptation of Cognitive Flexibility is driven by Task- and Item-Level Learning

Adaptive behavior requires finding, and adjusting, an optimal tradeoff between focusing on a current task-set (cognitive stability) and updating that task-set when the environment changes (cognitive flexibility). Such dynamic adjustments of cognitive flexibility are observed in cued task-switching paradigms, where switch costs tend to decrease as the proportion of switch trials over blocks increases. However, the learning mechanisms underlying this phenomenon, here referred to as the list-wide proportion switch effect (LWPSE), are currently unknown. We addressed this question across four behavioral experiments. Experiment 1 replicated the basic LWPSE reported in previous studies. Having participants switch between three instead of two tasks, Experiment 2 demonstrated that the LWPSE is preserved even when the specific alternate task to switch to cannot be anticipated. Experiments 3a and 3b tested for the generalization of list-wide switch-readiness to an unbiased "transfer task," presented equally often as switch and repeat trials, by intermixing the transfer task with biased tasks. Despite the list-wide bias, the LWPSE was only found for biased tasks, suggesting that the modulations of switch costs are task set and/or task stimulus (item)-specific. To evaluate these two possibilities, Experiment 4 employed biased versus unbiased stimuli within biased task sets and found switch-cost modulations for both stimuli sets. These results establish how people adapt their stability-flexibility tradeoff to different contexts. Specifically, our findings show that people learn to associate context-appropriate levels of switch readiness with switch-predictive cues, provided by task sets as well as specific task stimuli.

Rule Perseveration during Task-Switching in Brain Tumor: A Severe Form of Task-Setting Impairment

It has been proposed that at least two distinct processes are engaged during task-switching: reconfiguration of the currently relevant task-set and interference resolution arising from the competing task-set. Whereas in healthy individuals the two are difficult to disentangle, their disruption is thought to cause different impairments in brain-damaged patients. Yet, the observed deficits are inconsistent across studies and do not allow drawing conclusions regarding their independence. Forty-one brain tumor patients were tested on a task-switching paradigm. We compared their performance between switch and repeat trials (switch cost) to assess rule reconfiguration, and between trials requiring the same response (congruent) and a different response for the two tasks (incongruent) to assess interference control. In line with previous studies, we found the greatest proportion of errors on incongruent trials, suggesting an interference control impairment. However, a closer look at the distribution of errors between two task rules revealed a rule perseveration impairment: Patients with high error rate on incongruent trials often applied only one task rule throughout the task and less frequently switched to the alternative one. Multivariate lesion-symptom mapping analysis unveiled the relationship between lesions localized in left orbitofrontal and posterior subcortical regions and perseveration scores, measured as absolute difference in accuracy between two task rules. This finding points to a more severe task-setting impairment, not reflected as a mere switching deficit, but instead as a difficulty in creating multiple stable task representations, in line with recent accounts of OFC functions suggesting its critical role in representing task states.

Task switching in old participants: A potential interplay between strategy and cognitive ability

Task-switching cost is highly reliable in old participants. However, in a Stroop-switching paradigm that compared old musicians with old non-musicians (Experiment 1A), task-switching costs were not consistent. For non-musicians, the task-switching costs were significant in the congruent and neutral trials, but not in the incongruent trials. For musicians, the task-switching costs disappeared completely. We suspected that besides following task rules, old participants might also apply a stimulus-based strategy called the target-first strategy. In Experiment 1B and 2, participants in Experiment 1A were invited again to perform two more Stroop-switching paradigms. To encourage the participants to use task rules, in Experiment 1B we removed the neutral trials but found the same results as in Experiment 1A. In Experiment 2, when inserting a cue-target interval in the Stroop-switching paradigm, both musicians and non-musicians produced reliable task-switching costs in all trial conditions. Note that younger participants had reliable task-switching costs in Experiment 1B and 2. We suggest that older participants preferred the target-first strategy to the task rules-based strategy because the former was easy to implant although it was less flexible. Besides task-switching costs, we found that old musicians had less interference effect than old non-musicians in Experiment 1B. In all three experiments, old musicians had shorter RTs than old non-musicians, which might be due to differences in strategies apart from cognitive abilities. We propose that without considering the strategy preference, some previous studies might misestimate the difference between old and young participants in terms of task-switching performance and interference control.

An Episodic Model of Task Switching Effects: Erasing the Homunculus from Memory

The Parallel Episodic Processing (PEP) model is a neural network for simulating human performance in speeded response time tasks. It learns with an exemplar-based memory store and it is capable of modelling findings from various subdomains of cognition. In this paper, we show how the PEP model can be designed to follow instructions (e.g., task rules and goals). The extended PEP model is then used to simulate a number of key findings from the task switching domain. These include the switch cost, task-rule congruency effects, response repetition asymmetries, cue repetition benefits, and the full pattern of means from a recent feature integration decomposition of cued task switching (Schmidt & Liefooghe, 2016). We demonstrate that the PEP model fits the participant data well, that the model does not possess the flexibility to match any pattern of results, and that a number of competing task switching models fail to account for key observations that the PEP model produces naturally. Given the parsimony and unique explanatory power of the episodic account presented here, our results suggest that feature-integration biases have a far greater power in explaining task-switching performance than previously assumed.

Time for a true display of skill: Top players in League of Legends have better executive control

Research into the effects of action video gaming on cognition has largely relied on self-reported action video game experience and extended video game training. Only a few studies have focused on participants' actual gaming skills. However, whether superior players and average players have different executive control is still not fully demonstrated. This study had top-ranking League of Legends players (global top 0.17%; N = 35) and average-ranking League of Legends players (N = 35) perform two cognitive tasks that aimed to measure three aspects of executive functioning: cognitive flexibility, interference control, and impulsive control. We controlled self-reported gaming experience, so that top-ranking players and average-ranking players had similar years of play and hours of play per week. We found that compared to a group of average players, top players showed smaller task-switching costs and smaller response-congruency effects in a Stroop-switching test. In a continuous performance test, top players indicated higher hit rates and lower false alarm rates as compared to average players. These findings suggest that top players have better cognitive flexibility and more accurate control of interference in the context of task-switching. Moreover, top players exhibit better impulsive control. The present study provides evidence that players' gaming skills rather than gaming experience are related to cognitive abilities, which may explain why previous studies on self-reported gaming experience and those assessing supervised training and cognitive performance have shown inconsistent results.

Mood state and conflict adaptation: an update and a diffusion model analysis

The present study investigated the affective modulation of conflict adaptation. In a first step, we conducted a direct replication of a previous study (Schuch & Pütz, 2018). Positive vs. negative mood state was induced by a success-failure manipulation (between-groups, N = 40 per group). In a subsequent task-switching experiment, the congruency sequence effect was assessed in task repetitions and task switches, measuring conflict adaptation within tasks and between tasks, respectively. We found conflict adaptation (averaged across task repetitions and task switches) to be enhanced in negative mood. We did not replicate our previous finding of enhanced conflict adaptation in task switches in positive mood. In a second step, we combined the replication data with the original data set, yielding a larger database with N = 80 per mood group. Using diffusion modeling, we explored the affective modulation of conflict adaptation in task repetitions. Conflict adaptation was reflected in drift rate, consistent with the idea that response conflict triggers an increase in processing selectivity, thereby attenuating the influence of the irrelevant stimulus dimension. Conflict adaptation was also reflected in boundary separation, suggesting that response conflict on the previous trial triggered an increase in response caution. The mood manipulation did not seem to affect processing selectivity (as captured by drift rate) but affected the setting of response caution (as captured by the boundary separation parameter), with faster and more error-prone responding in the negative than positive mood group. We discuss theoretical implications of these findings, and also briefly consider the affective modulations of other cognitive control measures.

Error-preceding brain activity links neural markers of task preparation to cognitive stability and flexibility

Balancing stability and flexibility is required to facilitate successful task selection in situations with competing stimuli. Research suggests a set of counteracting control processes that maintains this balance. In the present study, we investigate how two neural correlates of task preparation in event-related potentials (ERPs), the mixing positivity and the switch positivity, can be linked to stability and flexibility in task selection. In a cued task switching paradigm, we analyzed deviations of these ERPs when task confusions occurred, that is, when participants erroneously executed the currently irrelevant task. We found a reduced mixing positivity to be a main source of task confusions in a task environment that required ongoing switches between competing tasks, whereas the switch positivity was uninvolved here. However, an overabundance of this latter component was a source of task confusions in a task environment that required the repetitive execution of the same task, although task switches were not required at all in this condition. These results not only highlight the distinct functional significance of the two preparatory ERPs and show that control processes can be maladaptive in certain contexts. They can also be utilized to locate the mixing positivity and the switch positivity on the stability-flexibility spectrum. Our results are in line with accounts that suggest that a balance between stability and flexibility is facilitated by the concurrent involvement of two control processes. One that manages the top-down bias of the relevant task set and one that increases or decreases competition between alternatively available stimuli.

On the Role of Attention in Working Memory for Response Selection in Task Switching

Oberauer's (2019) analysis and related research on how working memory and attention are linked can provide insight regarding how responses are selected in task-switching situations. One mechanism for response selection-the mediated route-categorizes stimuli with respect to both tasks, then activates responses based on instructed category-response associations. The author discusses two proposals for how these associations are represented in working memory, both of which seem consistent with the idea that attention selects or prioritizes the relevant-task associations, enabling accurate response selection. A broader implication of the representation and operation of the mediated route is that nominal task switching might reflect concurrent multitasking within the cognitive system (constrained by attention in working memory), raising the issue of how task switching should be characterized.

Exploring the Limitations of the Shielding Function of Categorization Rules in Task-Switching

Applying categorization rules narrows attention toward the relevant features of a target and helps participants to ignore the irrelevant features of the target. This is called the shielding function of categorization rules. Here we explored the limitation of the shielding function in two task-switching experiments. In Experiment 1, we assigned each target a single digital numeral as an additional feature in addition to conventional bivalent features as in the previous task-switching experiments with bivalent tasks. In the first two stages of Experiment 1, half of the participants learned the numeral-response associations and the other half used an alternative numeral-categorization rule to infer the response. Without participants applying conventional task-switching rules, the switching costs disappeared. Moreover, when participants performed tasks by numeral-response associations the bivalent features interfered with response retrieval and caused response-congruency effects, whereas when participants applied the numeral-categorization rule, the bivalent features were shielded away and thereby the response-congruency effects disappeared. In the third stage, in which all participants applied task-switching rules by discriminating between bivalent features (i.e., filling and orientations), we found task-switching costs and response-congruency effects. In Experiment 2, new bivalent features produced stronger interference compared to Experiment 1. As a consequence, participants in both the association group and the numeral-categorization rule group showed significant response-congruency effects in the first two stages, where task-switching rules were not introduced. It follows that the shielding function of categorization rules has limits—strong interference from bivalent features can break down the shielding function. In addition, participants in the association group showed task-switching costs without being informed about the task-switching rules. We propose that strong proactive interference can produce task-switching costs even without the use of task-switching rules.

Target-Response Associations Can Produce Response-Congruency Effects Without Task-Switching Costs

In task-switching experiments with bivalent target stimuli, conflicts during response selection give rise to response-congruency effects. Typically, participants respond more slowly and make more errors in trials with incongruent targets that require different responses in the two tasks, compared to trials with congruent targets that are associated with the same response in both tasks. Here we investigate whether participants show response-congruency effects when task rules are not made explicit. In two experiments, we assigned task-irrelevant features to each bivalent target. When participants were instructed to apply the task rules, they showed significant task-switching costs as well as response-congruency effects. Importantly, when the same participants did not know the task rules and responded without applying the task rules, they showed response-congruency effects but no switch costs. The significant congruency effects suggest that associations between bivalent target features and responses can be formed passively, even when participants do not follow the task rules and use task-irrelevant target features to make a response.

Categorization difficulty modulates the mediated route for response selection in task switching

Conflict during response selection in task switching is indicated by the response congruency effect: worse performance for incongruent targets (requiring different responses across tasks) than for congruent targets (requiring the same response). The effect can be explained by dual-task processing in a mediated route for response selection, whereby targets are categorized with respect to both tasks. In the present study, the author tested predictions for the modulation of response congruency effects by categorization difficulty derived from a relative-speed-of-processing hypothesis. Categorization difficulty was manipulated for the relevant and irrelevant task dimensions in a novel spatial task-switching paradigm that involved judging the locations of target dots in a grid, without repetition of dot configurations. Response congruency effects were observed and they varied systematically with categorization difficulty (e.g., being larger when irrelevant categorization was easy than when it was hard). These results are consistent with the relative-speed-of-processing hypothesis and suggest that task-switching models that implement variations of the mediated route for response selection need to address the time course of categorization.

How long is long-term priming? Classification and action priming in the scale of days

Previous research has shown that stimulus–response associations comprise associations between the stimulus and the task (a classification task in particular) and the stimulus and the action performed as a response. These associations, contributing to the phenomenon of priming, affect behaviour after a delay of hundreds of trials and they are resistant against overwriting. Here, we investigate their longevity, testing their effects in short-term (seconds after priming) and long-term (24 hr and 1 week after priming) memory. Three experiments demonstrated that both stimulus–classification (S-C) and stimulus–action (S-A) associations show long-term memory effects. The results also show that retrieval of these associations can be modulated by the amount of engagement on the same task between encoding and retrieval, that is, how often participants performed this task between prime and probe sessions. Finally, results show that differences in processing time during encoding are linked to the amount of conflict caused during retrieval of S-C, but not S-A associations. These findings add new information to the existing model of priming as a memory system and pose questions about the interactions of priming and top-down control processes.

Dissociation of binding and learning processes

A single encounter of a stimulus together with a response can result in a short-lived association between the stimulus and the response [sometimes called an event file, see Hommel, Müsseler, Aschersleben, & Prinz, (2001) Behavioral and Brain Sciences, 24, 910-926]. The repetition of stimulus-response pairings typically results in longer lasting learning effects indicating stimulus-response associations (e.g., Logan & Etherton, (1994) Journal of Experimental Psychology: Learning, Memory, and Cognition, 20, 1022-1050]. An important question is whether or not what has been described as stimulus-response binding in action control research is actually identical with an early stage of incidental learning (e.g., binding might be seen as single-trial learning). Here, we present evidence that short-lived binding effects can be distinguished from learning of longer lasting stimulus-response associations. In two experiments, participants always responded to centrally presented target letters that were flanked by response irrelevant distractor letters. Experiment 1 varied whether distractors flanked targets on the horizontal or vertical axis. Binding effects were larger for a horizontal than for a vertical distractor-target configuration, while stimulus configuration did not influence incidental learning of longer lasting stimulus-response associations. In Experiment 2, the duration of the interval between response n - 1 and presentation of display n (500 ms vs. 2000 ms) had opposing influences on binding and learning effects. Both experiments indicate that modulating factors influence stimulus-response binding and incidental learning effects in different ways. We conclude that distinct underlying processes should be assumed for binding and incidental learning effects.

More than Attentional Tuning - Investigating the Mechanisms Underlying Practice Gains and Preparation in Task Switching

In task switching, participants perform trials of task repetitions (i.e., the same task is executed in consecutive trials) and task switches (i.e., different tasks are executed in consecutive trials) and the longer reaction times in switch trials in comparison to these times in repetition trials are referred to as switch costs. These costs are reduced by lengthening of an interval following a cue that indicates the upcoming task; this effect demonstrated effective task preparation. To investigate the role of task switching practice for these preparation effects and task switch costs, we applied a task switching paradigm, involving two digit classification tasks, in six successive practice sessions and varied the length of the preparation interval. To further examine practice-related processing alterations on preparation, particularly concerning the focusing of visual attention and control of response competition, we added an Eriksen flanker task in the initial and the final session. Unlike the two digit tasks, which were always validly cued, the Eriksen flanker task occurred randomly after a cue that indicated one of the other two tasks (i.e., invalid task cuing). The results showed that, in the initial session, task switch costs for the digit tasks were reduced after a long preparation interval but this reduction disappeared after practice. This finding is consistent with the assumption of practice-related enhancement of preparation efficiency concerning non-perceptual task processes. Flanker interference was larger after preparation for a task repetition than for a task switch and (regarding error rates) larger in the final than in the initial session. Possible mechanisms underlying these attentional modulations evoked by task-sequence-dependent preparation and by task switching practice are discussed.

Learning a nonmediated route for response selection in task switching

Two modes of response selection--a mediated route involving categorization and a nonmediated route involving instance-based memory retrieval--have been proposed to explain response congruency effects in task-switching situations. In the present study, we sought a better understanding of the development and characteristics of the nonmediated route. In two experiments involving training and transfer phases, we investigated practice effects at the level of individual target presentations, transfer effects associated with changing category-response mappings, target-specific effects from comparisons of old and new targets during transfer, and the percentages of early responses associated with task-nonspecific response selection (the target preceded the task cue on every trial). The training results suggested that the nonmediated route is quickly learned in the context of target-cue order and becomes increasingly involved in response selection with practice. The transfer results suggested that the target-response instances underlying the nonmediated route involve abstract response labels coding response congruency that can be rapidly remapped to alternative responses, but not rewritten when category-response mappings change after practice. Implications for understanding the nonmediated route and its relationship with the mediated route are discussed.

Modulation of Executive Control in the Task Switching Paradigm With Transcranial Direct Current Stimulation (tDCS)

Abstract. Executive processing in the task switching paradigm is primarily associated with activation of the lateral prefrontal cortex (lPFC), demonstrated in numerous functional imaging studies (e.g., Brass & von Cramon, 2002 ). However, there are only very few attempts to modulate neural activation related with executive functions and to investigate the effects of this modulation on the performance in this paradigm. To modulate lPFC activity here, we used the non-invasive transcranial Direct Current Stimulation (tDCS; atDCS [1 mA, 20 min] vs. ctDCS [1 mA, 20 min] vs. sham stimulation [1 mA, 30 s]) over the left inferior frontal junction under conditions of single tasks, task repetitions, and task switches in the task switching paradigm. We assessed the performance effects of online tDCS on mixing costs (single tasks vs. task repetitions) as well as on switching costs (task repetitions vs. task switches). In a within-subjects design across three sessions, there was no evidence of stimulation on the magnitude of these cost types. However, when taking a between-subjects perspective in the first session (i.e., after excluding dominant effects of task experience), atDCS showed an increase in mixing costs in contrast to ctDCS and sham. We interpreted this finding in the context of task switching theories on task activation and task inhibition and their neural localizations.

Proactive control of irrelevant task rules during cued task switching

In task-switching paradigms, participants are often slower on incongruent than congruent trials, a pattern known as the task-rule congruency effect. This effect suggests that irrelevant task rules or associated responses may be retrieved automatically in spite of task cues. The purpose of the present study was to examine whether the task-rule congruency effect may be modulated via manipulations intended to induce variation in proactive control. Manipulating the proportion of congruent to incongruent trials strongly influenced the magnitude of the task-rule congruency effect. The effect was significantly reduced in a mostly incongruent list relative to a mostly congruent list, a pattern that was observed for not only biased but also 50 % congruent items. This finding implicates a role for global attentional control processes in the task-rule congruency effect. In contrast, enhancing the preparation of relevant (cued) task rules by the provision of a monetary incentive substantially reduced mixing costs but did not affect the task-rule congruency effect. These patterns support the view that there may be multiple routes by which proactive control can influence task-switching performance; however, only select routes appear to influence the automatic retrieval of irrelevant task rules.

Modeling graded response congruency effects in task switching

Compound cue retrieval is a computational model of a mediated route for response selection in task-switching situations. In previous studies, the model has been shown to account for response congruency effects when switching between two tasks, where response congruency reflects the degree of match between relevant and irrelevant task responses associated with a target stimulus. In the present study, the author derived a model prediction of graded response congruency effects in situations involving three tasks. The predicted pattern was observed for both response time and error rate in an experiment in which numerical categorization tasks were performed on single-digit targets. Implications for understanding response congruency effects and for developing models of task-switching performance are discussed.

Modelling response selection in task switching: testing the contingent encoding assumption

The contingent encoding assumption is the idea that response selection in task-switching situations does not begin until the cue and the target have both been encoded. The authors tested the assumption by manipulating response congruency, stimulus order, and stimulus onset asynchrony (SOA) in two experiments. They found evidence of response selection prior to cue encoding for congruent targets with target-cue order at a long SOA, indicating that the contingent encoding assumption is invalid. The authors describe how contingent encoding can be removed from an existing task-switching model by introducing baseline evidence--task-neutral evidence that serves as a baseline for response selection prior to stimulus encoding. Simulations revealed that the modified model could reproduce the full pattern of response time data and generate responses prior to cue encoding. The authors conclude by discussing directions for further model development.

Irrelevant Stimulus Processing When Switching Between Tasks

Frequent switching between two tasks afforded by the same stimuli is associated with between-task congruency effects, that is, relatively impaired performance when a stimulus affords different responses as compared to the same responses in both tasks. These congruency effects indicate some form of application of the stimulus-response (S-R) rules of the currently irrelevant task. Between-task congruency effects are usually enhanced on task switch trials compared with task repetition trials. Here we investigate whether this interaction reflects stronger proactive interference from the irrelevant task on switch trials or whether performance on switch trials is characterized by generally enhanced susceptibility to task-irrelevant information processing. To this end, we contrasted between-task congruency effects with interference exerted from flanker stimuli taken from the current task (Experiment 1) and from spatial-numerical association of response codes (SNARC; Experiment 2). In both experiments, between-task congruency effects were larger on switch trials than on repetition trials, whereas interference from the other source remained constant, thus demonstrating that switch trials are not characterized by generally increased distractibility.

Analogous mechanisms of selection and updating in declarative and procedural working memory: experiments and a computational model

The article investigates the mechanisms of selecting and updating representations in declarative and procedural working memory (WM). Declarative WM holds the objects of thought available, whereas procedural WM holds representations of what to do with these objects. Both systems consist of three embedded components: activated long-term memory, a central capacity-limited component for building structures through temporary bindings, and a single-element focus of attention. Five experiments test the hypothesis of analogous mechanisms in declarative and procedural WM, investigating repetition effects across trials for individual representations (objects and responses) and for sets (memory sets and task sets), as well as set-congruency effects. Evidence for analogous processes was obtained from three phenomena: (1) Costs of task switching and of list switching are reduced with longer preparation interval. (2) The effects of task congruency and of list congruency are undiminished with longer preparation interval. (3) Response repetition interacts with task repetition in procedural WM; here we show an analogous interaction of list repetition with item repetition in declarative WM. All three patterns were reproduced by a connectionist model implementing the assumed selection and updating mechanisms. The model consists of two modules, an item-selection module selecting individual items from a memory set, or responses from a task set, and a set-selection module for selecting memory sets or task sets. The model codes the matrix of binding weights in the item-selection module as a pattern of activation in the set-selection module, thereby providing a mechanism for building chunks in LTM, and for unpacking them as structures into working memory.

Top-down versus bottom-up: when instructions overcome automatic retrieval

Research on human action has extensively covered controlled and automatic processes in the transformation of stimulus information into motor action, and how conflict between both types of processes is solved. However, the question of how automatic stimulus-response (S-R) translation per se depends on top-down control states remains unanswered. The present study addressed this issue by manipulating top-down control state (instructed S-R mapping) and automatic bottom-up processing (retrieval of S-R memory traces) independently from each other. Using a color/shape task-switching paradigm, we compared cross-talk triggered by distractor stimuli, for which the instructed S-R mapping and the S-R associations compiled at the beginning of the experiment matched, with the cross-talk triggered by distractor stimuli, for which (re-)instructed mapping and compiled S-R associations did not match. We show that the latter distractors do not yield any cross-talk in RTs and even reversed cross-talk in error rates, demonstrating that automatic S-R retrieval is modulated by top-down control states.

The stressed prefrontal cortex and goal-directed behaviour: acute psychosocial stress impairs the flexible implementation of task goals

Goals are often at the basis of human actions. As an essential mechanism of behavioural adaptation, individuals need to be able to flexibly implement new task goals so as to alter their actions (switch tasks) in response to contextual changes. The present study investigated the effect of acute psychosocial stress on cognitive control processes of flexible task-goal implementation with temporal focus on the occurrence interval of the hypothalamus-pituitary-adrenal (HPA) stress response. For this, forty-eight healthy volunteers were either challenged with a standardised stress-induction protocol (the Trier Social Stress Test) or underwent a standardised control situation. Subsequently, they were exposed to a task-switching procedure with two tasks alternating in random order. Participants of the stress group displayed increased salivary α-amylase activity immediately after stress exposure as well as elevations of salivary cortisol from 10 min after stress cessation, reflecting the typical stress-related activity increases in the sympathetic nervous system and the HPA axis, respectively. At the time interval of elevated cortisol levels, stressed individuals persistently showed larger performance differences between task switches and task repetitions (switch costs) than controls. This effect was reliably evident when tested 5-20 min as well as 25-40 min following treatment cessation. These results indicate that acute psychosocial stress impairs cognitive control processes of flexible task-goal implementation essential for voluntary goal-directed behaviour.

Task switching: effects of practice on switch and mixing costs

In the task-switching paradigm, mixing costs indicate the performance costs to mix two different tasks, while switch costs indicate the performance costs to switch between two sequentially presented tasks. Applying tasks with bivalent stimuli and responses, many studies demonstrated substantial mixing and switch costs and a reduction of these costs as a result of practice. The present study investigates whether extensive practice of a task-switching situation including tasks with univalent stimuli eliminates these costs. Participants practiced switching between a visual and an auditory task. These tasks were chosen because they had shown eliminated performance costs in a comparable dual-task practice study (Schumacher et al. Psychol Sci 12:101-108, 2001). Participants either performed the tasks with univalent responses (i.e., visual-manual and auditory-verbal stimulus-response mappings) or bivalent responses (i.e., visual-manual and auditory-manual stimulus-response mappings). Both valence conditions revealed substantial mixing and switch costs at the beginning of practice, yet, mixing costs were largely eliminated after eight practice sessions while switch costs were still existent.

The reaction-time task-rule congruency effect is not affected by working memory load: further support for the activated long-term memory hypothesis

Previous studies claimed that task representation is carried out by the activated long-term memory portion of working memory (WM; Meiran and Kessler in J Exp Psychol Human Percept Perform 34:137-157, 2008). The present study provides a more direct support for this hypothesis. We used the reaction-time task-rule congruency effect (RT-TRCE) in a task-switching setup, and tested the effects of loading WM with irrelevant task rules on RT-TRCE. Experiment 1 manipulated WM load in a between-subject design. WM participants performed a color/shape task switching, while having 0, 1 or 3 numerical task rules as WM load. Experiment 2 used a similar load manipulation (1 or 3 rules to load WM) in a within-subject design. Experiment 3 extended these results by loading WM with perceptual tasks that were more similar to the shape/color tasks. The results show that RT-TRCE was not affected by WM load supporting the activated long-term memory hypothesis.

Unbewusste Wahrnehmung

Zusammenfassung. Die Wirkungsweise unbewusster Reize wird unter anderem mit der Methode des subliminalen Primings untersucht. Subliminal präsentierte Prime-Reize beeinflussen die Verarbeitung eines Targets, wenn ihre Verarbeitung intendiert ist und diese Reize im Experimentalkontext erwartet werden können. Zur Erklärung dieser Befunde haben wir existierende Konzepte zur Handlungsvorbereitung weiterentwickelt. Das Erklärungskonzept der handlungsdeterminierenden Reizerwartungen postuliert einen zweistufigen Prozess für Vorbereitung und Ausführung intendierter Handlungen. Zunächst werden handlungsdeterminierende Reizerwartungen spezifiziert entsprechend der aktuell instruierten Aufgabe bzw. des erlebten Aufgabenkontextes. Als zweiter Prozess findet ein Abgleich des tatsächlichen Reizes mit den Reizerwartungen statt. Stimmt der Reiz mit den handlungsdeterminierenden Reizerwartungen überein, wird die entsprechende Reaktion automatisch aktiviert. Dieser Ansatz kann viele Befunde zum subliminalem Priming erklären, die bisher widersprüchlich erschienen. Er ist nicht nur auf übliche Experimentalkontexte mit Zweifachwahlreaktionen anwendbar, sondern gilt auch für Aufgabenkontexte mit mehrfachen Handlungsbereitschaften und für die freie Wahl zwischen zwei Handlungsalternativen. Ob das Erklärungskonzept der handlungsdeterminierenden Reizerwartungen ausreicht, um alle Arten des subliminalen Primings zu erklären ist unklar. Hier ist weitere Forschung notwendig um zu klären ob und gegebenenfalls unter welchen Bedingungen unbewusste Reize komplexere Verarbeitungsprozesse, wie semantische Verarbeitung oder exekutive Kontrollprozesse beeinflussen.

Selecting a response in task switching: testing a model of compound cue retrieval

How can a task-appropriate response be selected for an ambiguous target stimulus in task-switching situations? One answer is to use compound cue retrieval, whereby stimuli serve as joint retrieval cues to select a response from long-term memory. In the present study, the authors tested how well a model of compound cue retrieval could account for a complex pattern of congruency effects arising from a procedure in which a cue, prime, and target were presented on each trial. A comparison of alternative models of prime-based effects revealed that the best model was one in which all stimuli participated directly in the process of retrieving a response, validating previous modeling efforts. Relations to current theorizing about response congruency effects and models of response selection in task switching are discussed.