Age-related changes in task-switching components: the role of task uncertainty

The present study examined age differences in executive functioning, using an externally cued task-switching paradigm. Two components of task switching were assessed: the ability to maintain and select among task sets (general switch costs) and the ability to switch between task sets (specific switch costs). In contrast to previous findings, we found large age-related differences in specific switch costs, especially when the number of potentially relevant task sets is increased from two to four. Age-related differences in general switch costs were absent when external task cues subserved executive processing in task switching. Generally, the findings suggest that age-related impairments in task-switching components vary as a function of task uncertainty, such as the presence of environmental prompts to behavior.     

Trading off switch costs and stimulus availability benefits: An investigation of voluntary task-switching behavior in a predictable dynamic multitasking environment

In the present study, we introduce a novel, self-organized task-switching paradigm that can be used to study more directly the determinants of switching. Instead of instructing participants to randomly switch between tasks, as in the classic voluntary task-switching paradigm (Arrington & Logan, 2004), we instructed participants to optimize their task performance in a voluntary task-switching environment in which the stimulus associated with the previously selected task appeared in each trial after a delay. Importantly, the stimulus onset asynchrony (SOA) increased further with each additional repetition of this task, whereas the stimulus needed for a task switch was always immediately available. We conducted two experiments with different SOA increments (i.e., Exp. 1a = 50 ms, Exp. 1b = 33 ms) to see whether this procedure would induce switching behavior, and we explored how people trade off switch costs against the increasing availability of the stimulus needed for a task repetition. We observed that participants adapted their behavior to the different task environments (i.e., SOA increments) and that participants switched tasks when the SOA in task switches approximately matched the switch costs. Moreover, correlational analyses indicated relations between individual switch costs and individual switch rates across participants. Together, these results demonstrate that participants were sensitive to the increased availability of switch stimuli in deciding whether to switch or to repeat, which in turn demonstrates flexible adaptive task selection behavior. We suggest that performance limitations in task switching interact with the task environment to influence switching behavior.     

Unmixing the mixing cost: contributions from dimensional relevance and stimulus-response suppression

When participants repeat the same task in a context in which the task may also switch (a mixed block), performance deteriorates compared to when there is only one task repeating (a pure block). Three experiments were designed to assess how perceptual and motor transitions influenced this mixing cost. Experiment 1 provided three pure block baselines for perceptual and motor transitions. Experiments 2 and 3 examined these transitions in a mixed block. Results show that most of the mixing cost comes from two factors: (a) episodic interference in the mixed block when the stimulus changes and the response repeats, and (b) increased suppression in mixed blocks affecting trials where stimulus-response mappings repeat. We propose that these mechanisms are strategically applied when adopting a sustained "switching set" in mixed blocks. The purpose of this set would be to avoid perseveration errors in the most demanding trials (the task-switching trials), but remaining active during task-repetitions. Results regarding the mixing cost are thus relevant to the assessment of models of task-switching, which at present mainly rely on data from task switch trials.     

Aging and task switching: a meta-analysis

A meta-analysis of 26 published articles (with 36 independent participant groups) was conducted to analyze the relationship between task-switching effects and aging. Latency served as the dependent measure. Multilevel modeling was used to test for additive and multiplicative complexity effects in local and global switch costs. Global task switching was found to add 1 or more stages to processing and resulted in a marked age deficit. Local task-switching costs, on the other hand, showed a multiplicative complexity effect but no specific attention-related age deficits. Cueing or switch predictability did not affect age differences.     

The preparation effect in task switching: Carryover of SOA

A common finding in task-switching studies is switch preparation (commonly known as the preparation effect), in which a longer interval between task cue and trial stimulus (i.e., a longer stimulus onset asynchrony, or SOA) reduces the cost of switching to a different task. Three experiments link switch preparation to within-subjects manipulations of SOA. In Experiment 1, SOA was randomized within subjects, producing switch preparation that was more pronounced when the SOA switched from the previous trial than when the SOA repeated. In Experiment 2, SOA was blocked within subjects, producing switch preparation but not on the first block of trials. In Experiment 3, SOA was manipulated between subjects with sufficient statistical power to detect switch preparation, but the effect was absent. The results favor an encoding view of cognitive control, but show that any putative switching mechanism reacts lazily when exposed to only one SOA.     

Selection of objects and tasks in working memory

When people hold several objects (such as digits or words) in working memory and select one for processing, switching to a new object takes longer than selecting the same object as that on the preceding processing step. Similarly, selecting a new task incurs task- switching costs. This work investigates the selection of objects and of tasks in working memory using a combination of object-switching and task-switching paradigms. Participants used spatial cues to select one digit held in working memory and colour cues to select one task (addition or subtraction) to apply to it. Across four experiments the mapping between objects and their cues and the mapping between tasks and their cues were varied orthogonally. When mappings varied from trial to trial for both objects and tasks, switch costs for objects and tasks were additive, as predicted by sequential selection or resource sharing. When at least one mapping was constant across trials, allowing learning of long-term associations, switch costs were underadditive, as predicted by partially parallel selection. The number of objects in working memory affected object-switch costs but not task-switch costs, counter to the notion of a general resource of executive attention.     

Age equivalence in switch costs for prosaccade and antisaccade tasks

This study examined age differences in task switching using prosaccade and antisaccade tasks. Significant specific and general switch costs were found for both young and old adults, suggesting the existence of 2 types of processes: those responsible for activation of the currently relevant task set and deactivation of the previously relevant task set and those responsible for maintaining more than 1 task active in working memory. Contrary to the findings of previous research, which used manual response tasks with arbitrary stimulus-response mappings to study task-switching performance, no age-related deficits in either type of switch costs were found. These data suggest age-related sparing of task-switching processes in situations in which memory load is low and stimulus-response mappings are well learned.     

认知控制的层级性：来自任务切换的脑电证据*

认知控制的主要研究范式之一是任务切换。以往研究发现切换代价受到认知控制层级性的调节, 但鲜有研究探索这一调节过程的动态神经机制。本研究通过嵌套的线索-任务切换范式考察不同层级任务切换代价的差异及其神经机制。在实验中, 要求被试完成高低两种层级任务, 低层级任务要求被试判断数字大小(或奇偶); 高层级任务则须先加工数字的某一语义特征(如当前数字是否是偶数), 然后进行大小判断。行为结果表明, 高层级任务切换代价显著大于低层级任务切换代价。线索锁时的脑电结果表明, 层级效应最早出现于P2成分, 切换效应(切换与重复之差)在CNV成分上受到任务层级的调控, 反映了在任务目标重构阶段给予高层级任务更多的选择性注意以及更高的主动性控制。目标锁时的脑电结果表明, 在N2及慢波(SP)成分上, 高层级任务切换与重复的波幅差异相比低层级任务显著更大, 反映了在抑制旧任务集与重构新反应集的过程中增强的反应性控制。这些结果为任务设置重构论和认知控制的层级性提供了新的证据。     

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.     

Task-switching performance with 1:1 and 2:1 cue-task mappings: not so different after all

When task-switching studies use the task-cuing procedure with a 1:1 cue-task mapping, task switching and cue switching are confounded, which is problematic for interpreting switch costs. The use of a 2:1 cue-task mapping is a potential solution to this problem, but it is possible that introducing more cues may also introduce marked changes in task-switching performance. In 5 experiments involving 160 subjects, the authors compared performance with 1:1 and 2:1 mappings across several methodological changes. Differences in switch costs between mappings were small and, in most analyses, nonsignificant. In all experiments, both mappings yielded significant reductions in switch cost across cue-target interval, and there were significant cue-switching effects with the 2:1 mapping. A model of cue encoding fit the data from both mappings about equally well. Overall, task-switching performance was more similar than it was different between mappings, leading the authors to suggest that the use of a 2:1 mapping is a viable solution to the problem associated with a 1:1 mapping.     

Verbal self‐instructions in task switching: a compensatory tool for action‐control deficits in childhood and old age?

This study examined the influence of verbal self-instructions on age differences in task switching. Task-switching ability, measured as the difference between performance in single-task blocks and in mixed-task blocks in which participants switch between two tasks (mixing costs), increases during childhood and decreases in old age. To measure the influence of language on task switching, we compared conditions in which participants either (a) named the next task to be performed (i.e. task-relevant verbalization), (b) verbalized words not related to the task at hand (i.e. task-irrelevant verbalization), or (c) did not verbalize (control condition). Results indicated that mixing costs were substantially reduced under task-relevant verbalization and increased under task-irrelevant verbalization. Moreover, age-related differences in mixing costs were increased when the use of inner speech was disrupted and were reduced when participants performed task-relevant verbalization. These findings suggest that verbal self-instructions are a useful tool for retrieving the next task goal and for reducing action-control deficits in younger children and older adults.     

Task practice differentially modulates task-switching performance across the adult lifespan

Cued-trials task-switching paradigms have been used extensively to examine ageing-related changes in cognitive control. Many studies report an increase in mixing cost (i.e., cost of repeating the same task in a single-task vs. a mixed-task block) and a less reliable increase in switch cost (i.e., cost of switching vs. repeating tasks in a mixed-task block) in old as compared to young adults. However, there is substantial variability between studies in the emergence and size of age effects on mixing and/or switch cost. In this study, we examined variation in mixing cost and switch cost as a function of task practice and preparation interval across the adult lifespan (18-79 years) using a paradigm that promotes advance preparation and reduces cue encoding differences between switch and repeat trials. Both preparation interval and task practice modulated mixing cost and switch cost-but task practice mediated the effects of preparation interval and age differentially for mixing cost and switch cost. Mixing cost was consistently larger in older participants, reduced with preparation and varied little with task practice. In contrast, the effect of preparation interval on switch cost varied with task practice. Reduction in switch cost with preparation interval emerged in younger participants by the second practice session and even later in older participants. When fully practiced, older participants showed greater mixing cost but less switch cost than younger participants. Age effects on both mixing cost and switch cost were mediated by changes in processing of repeat trials, indicative of reduced differentiation between switch and repeat trials in mixed-task blocks. This is consistent with reduced cognitive flexibility with increasing age.     

Task-set reconfiguration with predictable and unpredictable task switches

Participants switched frequently between high/low and odd/even classification of a digit. The interval between a task cue and the next digit varied between blocks. In Experiment 1, the task switched predictably every two, four, or eight trials. In Experiment 2, switching predictably every four trials was compared with random switching. With predictable switching, the cost was limited to the first trial of a run. Random switching produced a more gradual approach to asymptotic performance. After one performance, control processes attenuate the resulting change in task-set bias if a further switch is likely, but this strategic modulation is soon overwhelmed by task-set priming through further performances. Preparation reduced switch costs but not interference from the irrelevant attribute: Control of interference appears to be reactive, not proactive. Switch costs did not increase with run length, suggesting that retrieval of the task set last associated with the stimulus did not contribute to switch costs.     

Age Influences on Multi-Dimensional Set Switching

Using a task switching paradigm, we investigated age effects on switch costs as a function of the number of sets to be switched. In Experiment 1, younger and older subjects determined a color or shape of an object presented on the computer screen, responding either by moving the joystick or by pressing a button on the joystick. The switch costs were assessed with differences between switch trials (task-set switch, response-set switch, and double switch) and non-switch trials. Contrary to the prediction that age would negatively influence performance on the double switch trials, age effects on switch costs were observed only for the single switch trials (i.e., response-set switch condition). Additionally, both younger and older adults were capable of preparing for task and response-set switches in parallel. In Experiment 2, we manipulated the time available to prepare for a task and response-set switch. Both younger and older adults were able to utilize extra time to reduce switch costs. Furthermore, the age deficit found in Experiment 1 for response-set switching was eliminated in the second experiment in which preparation for task and response-set switching was temporally decoupled. The data are discussed in terms of task component coordination across the adult lifespan.     

The role of attentional networks in voluntary task switching

Coordination of task choice and performance in multitask environments likely involves attentional processes. Subjects completed the Attention Network Test (ANT) and a voluntary task-switching procedure. Task choice, but not task performance, was correlated with the executive score from the ANT, with higher switch probabilities for subjects with more efficient executive control networks. Task performance was correlated with the alerting score, with larger response time switch costs for subjects with larger alerting scores. The dissociation of task choice and task performance measures in terms of the pattern of correlations with attentional networks suggests that these two measures may reflect different cognitive processes engaged in voluntary task switching.     

Switching between tasks and responses: a developmental study

Task switching requires the ability to flexibly switch between task rules and responses, and is sensitive to developmental change. We tested the hypothesis that developmental changes in task switch performance are associated with changes in the facilitating or interfering effect of the previously retrieved stimulus-response (S-R) association. Three age groups (7-8-year-olds, 10-12-year-olds and 20-25-year-olds) performed a two-choice reaction time (RT) task in which spatially compatible or incompatible responses were required. The RT costs associated with switching between tasks were larger when responses were repeated than when responses were alternated. Younger children showed a greater cost than adults when switching between tasks but repeating responses. This age difference decreased when the interval between the previous response and the upcoming stimulus increased. Switch costs were larger when switching to the compatible task than to the incompatible task, but this effect did not differ between age groups. These findings suggest that young children build up stronger transient associations between task sets and response sets, which interfere with their ability to switch to currently intended actions. A similar pattern has previously been observed for older adults (Mayr, 2001), suggesting a common contributor to task switching deficits across the life span.     

The influence of stimulus-set size on developmental changes in cognitive control and conflict adaptation

Cognitive control abilities substantially improve from early childhood to adulthood. The primary aim of this study was to examine the influence of stimulus-set size on developmental changes in cognitive control abilities such as task switching, interference control, and conflict adaptation. We assumed that a small stimulus set used in a task-switching paradigm would induce stronger task-stimulus priming that might increase the need for control, thereby amplifying age differences in cognitive control abilities. Therefore, we compared task-switching performance in a group of participants responding to a small stimulus-set (N=4) with a group responding to a large stimulus-set (N=96) in three age groups: kindergarten children (4.1-6.0 years of age), elementary school children (6.1-9.0 years of age), and young adults (21.0-28.0 years of age) on conflicting vs. non-conflicting trials (interference control) and following conflicting vs. non-conflicting trials (conflict adaptation). Results on the basis of error rates support the view that a small stimulus-set size during task switching (i.e., larger task-stimulus priming) increases the need for control as we found (a) worse conflict adaptation on task-repetition trials only for small but not for large set sizes and (b) larger interference costs under small than large set-size condition for elementary school children as compared with young adults. Kindergarten children were less sensitive to the set-size manipulation and showed major problems in interference control while being in a task-switching situation, even if no actual task switch was required, possibly reflecting their inability to represent complex higher-order task rules.     

Too much of a good thing: Stronger bilingual inhibition leads to larger lag-2 task repetition costs

Inhibitory control and monitoring abilities of Hebrew-English bilingual and English monolingual university students were compared, in a paradigm requiring participants to switch between performing three distinct tasks. Inhibitory control was gauged by lag-2 task repetition costs, namely decreased performance on the final trial of sequences of type ABA relative to CBA, due to persisting inhibition of the recently abandoned task. Bilinguals had larger lag-2 repetition costs, which reflect stronger inhibition of a no-longer relevant task to facilitate a switch into a new task. Monitoring ability was measured by the fadeout effect, which reflects adaptation to simpler task demands when a single task block immediately and unexpectedly follows mixed task blocks. Bilinguals did not differ from monolinguals in the magnitude or trajectory of the fade-out effect. Thus, results support the notion of increased bilingual inhibitory control, even when it is detrimental to performance, and do not demonstrate a specific bilingual advantage in monitoring. These findings are discussed in the context of the recent debate concerning the locus of bilingual advantages.     

An integrated model of cognitive control in task switching

A model of cognitive control in task switching is developed in which controlled performance depends on the system maintaining access to a code in episodic memory representing the most recently cued task. The main constraint on access to the current task code is proactive interference from old task codes. This interference and the mechanisms that contend with it reproduce a wide range of behavioral phenomena when simulated, including well-known task-switching effects, such as latency and error switch costs, and effects on which other theories are silent, such as with-run slowing and within-run error increase. The model generalizes across multiple task-switching procedures, suggesting that episodic task codes play an important role in keeping the cognitive system focused under a variety of performance constraints.     

Task switching and the measurement of “switch costs”

The measurement of “switch costs” is held to be of interest because, as is widely believed, they may reflect the control processes that are engaged when subjects switch between two (or more) competing tasks. [In task-switching experiments, the reaction time (RT) switch cost is typically measured as the difference in RT between switch and non-switch (repeat) trials.] In this report we focus on the RT switch costs that remain even after the subject has had some time to prepare for the shift of task, when the switch cost may be approximately asymptotic (so-called residual switch costs). Three experiments are presented. All three experiments used Stroop colour/word, and neutral stimuli. Participants performed the two tasks of word-reading and colour-naming in a regular, double alternation, using the “alternating runs” paradigm (R. D. Rogers & S. Monsell, 1995). The experiments were designed to test the hypothesis that RT switch costs depend on a form of proactive interference (PI) arising from the performance of a prior, competing task. A. Allport, E. A. Styles and S. Hsieh (1994) suggested that these PI effects resulted from “task-set inertia”, that is, the persisting activation-suppression of competing task-sets, or competing task-processing pathways. The results confirmed the existence of long-lasting PI from the competing task as a major contributor to switch costs. Non-switch trials, used as the baseline in the measurement of switch costs, were also shown to be strongly affected by similar PI effects. However, task-set inertia was not sufficient to account for these results. The results appeared inconsistent also with all other previous models of task switching. A new hypothesis to explain these between-task interference effects was developed, based on the stimulus-triggered retrieval of competing stimulus-response (S-R) associations, acquired (or strengthened) in earlier trials. Consistent with this retrieval hypothesis, switch costs were shown to depend primarily on the S-R characteristics of the preceding task (the task that was switched from) rather than the upcoming task. Further, the effects of the other, competing task were found to persist over many successive switching trials, affecting switch costs long after the stimulus overlap (and hence the principal S-R competition) between the current tasks had been removed. Switch costs were also found to be affected by recent, item-specific experience with a given stimulus, in either the same or the competing task. Finally, the results showed that switch costs were massively affected by the ratio of the number of prior trials, in response to the same stimuli, that had implemented either the currently intended or the competing S-R mappings. None of these effects are predicted by current models of residual switch costs, which appeal to the differences in control processes assumed to be engaged in switch versus non-switch trials. Received: 31 March 1999 / Accepted: 23 July 1999