Task switching is not cue switching

Contextual Features of the Cue Enter Episodic Bindings in Task Switching

Evidence suggests that the features of a stimulus and the actions performed on it are bound together into a coherent mental representation of the episode, which is retrieved from memory upon reencountering at least one of these features. Effects of such binding and retrieval processes emerge in action control, such as in multitasking situations like task switching. In the task-switching paradigm, response-repetition benefits are observed in task repetitions, but response-repetition costs in task switches. This interaction of task repetition (vs. switch) with response repetition (vs. switch) may be explained in terms of task-response binding. In two experiments, we included a task-irrelevant contextual feature in a cued task-switching paradigm using word identification tasks. In Experiment 1, the cue modality could vary between visual and auditory; in Experiment 2, the cue language could vary between English and Spanish, while the target stimulus was always presented visually and in German. We predicted that repeating the contextual feature in the subsequent trial would retrieve the features of the previous trial, even though cue modality or cue language did not afford any response and were not associated with either task. The results showed that response repetition-benefits in task repetitions were observable when the context (i.e., the modality or the language of the cue) repeated but disappeared when the context switched from the previous trial. These results are consistent with context-specific binding and retrieval processes in task switching.

Evidence for a multicomponent hierarchical representation of dual tasks

Recent dual-task studies observed worse performance in task-pair switches than in task-pair repetitions and interpreted these task-pair switch costs as evidence that the identity of the two individual tasks performed within a dual task is jointly represented in a single mental representation, termed “task-pair set.” In the present study, we conducted two experiments to examine (a) whether task-pair switch costs are due to switching cues or/and task pairs and (b) at which time task-pair sets are activated during dual-task processing. In Experiment 1, we used two cues per task-pair and found typical dual-task interference, indicating that performance in the individual tasks performed within the dual task deteriorates as a function of increased temporal task overlap. Moreover, we observed cue switch costs, possibly reflecting perceptual cue priming. Importantly, there were also task-pair switch costs that occur even when controlling for cue switching. This suggests that task-pair switching per se produces a performance cost that cannot be reduced to costs of cue switching. In Experiment 2, we employed a go/no-go-like manipulation and observed task-pair switch costs after no-go trials where subjects prepared for a task-pair, but did not perform it. This indicates that task-pair sets are activated before performing a dual task. Together, the findings of the present study provide further evidence for a multicomponent hierarchical representation consisting of a task-pair set organized at a hierarchically higher level than the task sets of the individual tasks performed within a dual task.

Switch-Independent Task Representations in Frontal and Parietal Cortex

Alternating between two tasks is effortful and impairs performance. Previous fMRI studies have found increased activity in frontoparietal cortex when task switching is required. One possibility is that the additional control demands for switch trials are met by strengthening task representations in the human brain. Alternatively, on switch trials, the residual representation of the previous task might impede the buildup of a neural task representation. This would predict weaker task representations on switch trials, thus also explaining the performance costs. To test this, male and female participants were cued to perform one of two similar tasks, with the task being repeated or switched between successive trials. Multivoxel pattern analysis was used to test which regions encode the tasks and whether this encoding differs between switch and repeat trials. As expected, we found information about task representations in frontal and parietal cortex, but there was no difference in the decoding accuracy of task-related information between switch and repeat trials. Using cross-classification, we found that the frontoparietal cortex encodes tasks using a generalizable spatial pattern in switch and repeat trials. Therefore, task representations in frontal and parietal cortex are largely switch independent. We found no evidence that neural information about task representations in these regions can explain behavioral costs usually associated with task switching.SIGNIFICANCE STATEMENT Alternating between two tasks is effortful and slows down performance. One possible explanation is that the representations in the human brain need time to build up and are thus weaker on switch trials, explaining performance costs. Alternatively, task representations might even be enhanced to overcome the previous task. Here, we used a combination of fMRI and a brain classifier to test whether the additional control demands under switching conditions lead to an increased or decreased strength of task representations in frontoparietal brain regions. We found that task representations are not modulated significantly by switching processes and generalize across switching conditions. Therefore, task representations in the human brain cannot account for the performance costs associated with alternating between tasks.

The contribution of task-choice response selection to the switch cost in voluntary task switching

Mental flexibility not only enables us to switch between tasks but also to select the tasks we want to perform. The latter scenario is central to voluntary task switching, in which participants are free to select on each trial which task to perform. The present study argues that voluntary task switching also includes and additional component, namely task-choice response selection. Task-choice response selection refers to the whole chain of processes involved in the overt report or indication of the task that was selected by emitting an arbitrary response. Task-choice response selection is not required to voluntarily switch between tasks, but serves the measurement of participants' covert task selection. The results of two experiments indicate that the contribution of task-choice response selection to switch performance in voluntary task switching is substantial. It is proposed that task-choice response selection delays the top-down retrieval of task rules in voluntary task switching.

Components of task switching: a closer look at task switching and cue switching

Research using the diffusion model to decompose task-switching effects has contributed to a better understanding of the processes underlying the observed effect in the explicit task cueing paradigm: Previous findings could be reconciled with multiple component models of task switching or with an account on compound-cue retrieval/repetition priming. In the present study, we used two cues for each task in order to decompose task-switch and cue-switch effects. Response time data support previous findings that comparable parts of the switching effect can be attributed to cue-switching and task-switching. A diffusion model analysis of the data confirmed that non-decision time is increased and drift rates are decreased in unpredicted task-switches. Importantly, it was shown that non-decision time was selectively increased in task-switching trials but not in cue-switching trials. Results of the present study specifically support the notion of additional processes in task-switches and can be reconciled with broader multiple component accounts.

Positive affect facilitates task switching in the dimensional change card sort task: implications for the shifting aspect of executive function

Using the modified Dimensional Change Card Sort task, we examined the influence of positive affect on task switching by inspecting various markers for the costs, including restart cost, switch cost and mixing cost. Given that the executive-control processes that underlie switching performance--i.e., inhibition or shifting--are distinct from the component processes that underlie non-switching performance--i.e., stimulus evaluation, resource allocation or response execution--we hypothesised that if positive affect facilitates task switching via executive-control processes, rather than via component processes, positive affect would reduce both switch and restart costs, but not mixing cost, because both switch and restart costs rely on executive processes, while mixing cost imposes only minimal demands on executive processes. We found beneficial effects of positive affect on both restart and switch costs, but not on mixing costs. These results suggest that positive affect improves switching abilities via executive processes rather than via component processes.

A Review of the Role of Cue Processing in Task Switching

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.

Fine-Grain Episodic Memory Processes in Cognitive Control

Previous task-switching research raises a question concerning the role of episodic memory processes in cognitive control. The question is framed by the contrast between two procedures, explicit cuing and randomized runs, one of which presents a task cue perceptually on every trial and the other of which involves uncued trials. The present study compares performance across these procedures. Performance errors sensitive to errors in focusing on the correct task were higher under explicit-cuing conditions than under randomized-runs conditions, consistent with a high level of proactive interference from old task information. The results support an account in which control codes stored in episodic memory play an integral role in cognitive control, even under conditions in which all information needed for performance is perceptually available.

Differential effects of articulatory suppression on cue-switch and task-switch trials in random task cueing with 2:1 mapping

Recent studies have revealed that verbal representations play an important role in various task-switching situations. This study examined whether verbal representations contribute to the actual switching process using random task cueing with two cues per task. This procedure allowed us to produce a trial in which the cue switched, but the task repeated, thereby separating the cue-switching process from the actual task-switching process. Participants performed colour or shape judgements that were initiated by an arbitrary symbol cue (Experiments 1 and 2) or a kanji cue (Experiment 3) under control, articulatory-suppression, and foot-tapping conditions. In Experiments 1 and 2 with the arbitrary cues, articulatory suppression impaired performance in only the cue-switch condition. In Experiment 3, in which a kanji cue indicated the upcoming task name, articulatory suppression did not have any effects. These results suggest that the involvement of verbal representations in random task cueing is based on the cue-switching process rather than on the task-switching process.

Cognitive control in cued task switching with transition cues: cue processing, task processing, and cue-task transition congruency

We investigated the processes underlying performance during cued task switching with transition cues. To this end, transition cueing and explicit cueing were compared in a design controlling for sequential effects in the two preceding trials in order to further examine the contribution of cue processes, task processes, and cue-task transition congruency during transition cueing. The study confirmed that the task-switch cost in transition cueing is larger than the task-switch cost in explicit cueing and showed that this larger switch cost is mainly due to cue processing. We also successfully decomposed performance in transition cueing into cue processing, task processing, and cue-task transition congruency on both a theoretical (Experiment 1) and an empirical basis (Experiments 2-3). Our empirical dissociation also demonstrates that cue-task transition congruency affects performance during both cue processing and task processing. We discuss the importance of our findings in relation to the different theories on task switching.

Two mechanisms for task switching in the prefrontal cortex

Measuring the cognitive and neural sequelae of switching between tasks permits a window into the flexible functioning of the executive control system. Prolonged reaction times (RTs) after task switches are accompanied by increases in brain activity in the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (dlPFC), but the contribution made by these regions to task level control remains controversial. Here, subjects performed a hybrid spatial Stroop/task-switching paradigm, requiring them to respond with a joystick movement to congruent or incongruent spatial/verbal cues. Relative to the previous trial, the active task either switched or remained the same. Calculating switch costs as a function of current and previous trial congruency, we observed both a general RT increase on every switch trial, and additional slowing and impairment to performance when the switch occurred on the second of two successive incongruent trials (iI trials). Imaging data revealed corresponding neural concomitants of these two switch costs: the ACC was activated by task switches regardless of trial type (including congruent trials in which task-relevant and task-irrelevant information did not clash), whereas the caudal dlPFC exhibited a switch cost that was unique to iI trials. We argue that the ACC configures the priorities associated with a new task, whereas the dlPFC tackles interference from recently active, rivalrous task sets. These data contribute to a literature arguing that human cognitive flexibility benefits from the setting of new priorities for future action as well as the overcoming of interference from previously active task sets.

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.

Influence of display type and cue format on task-cuing effects: dissociating switch cost and right-left prevalence effects

In previous studies of task switching and of the right-left prevalence effect, researchers have used a procedure in which the stimulus on each trial occurs in one of four quadrants, and responses are made by pressing one of two diagonally arranged response keys. Across these studies, discrepant effects of cuing interval have been reported. These discrepancies need clarification because cue-based preparation effects are frequently interpreted as reflecting cognitive control processes. In Experiment 1, we compared performance with display formats used by Meiran (1996; Meiran, Chorev, & Sapir, 2000; small display, cues located at sides of quadrants and displayed until response) to study task switching and by Proctor and colleagues (Proctor, Koch, & Vu, 2006; large display, cues located at center of display and shown until target onset) to study right-left prevalence. We found a decrease in task-switch cost with increasing cuing interval with the Meiran display, but not with the Proctor display, but the right-left prevalence effect was of similar size for the two display formats and was relatively unaffected by cuing interval. To determine the basis of the discrepant task-switch results, we used small and large displays in Experiments 2 and 3, respectively, with cue type and cue offset varied. With the side cues, the task-switch cost decreased in all cases at the longer cuing interval, but with the centered cues, it decreased only when the display size was small. Thus, the effects of cuing interval on switch costs are sensitive to variations of display characteristics, whereas cuing interval and display characteristics have little influence on the right-left prevalence effect, suggesting that prevalence effect is due to processes that are independent from those producing the switch cost.