Task preparation and task repetition: two-component model of task switching.

The switch cost (the disadvantage of performing a new task vs. a repeated task) has been attributed to lack of preparation for the switched task or priming of the repeated task. These sources were examined by manipulating foreknowledge of task transition (repeat or switch), response-to-stimulus interval (RSI), and practice level. Regardless of foreknowledge, the cost decreased with RSI and practice. The reduction was greater with foreknowledge than with no foreknowledge, and the amount of switch cost did not depend on foreknowledge. These results suggest that the switch cost with foreknowledge may consist of both inadequate preparation and repetition benefit but the switch cost with no foreknowledge may reflect repetition benefit only. An ACT-R (adaptive control of thought-rational) model was proposed, accommodating both preparation and priming effect with 2 independent processes: conflict resolution among productions and decay of chunk activation.     

准备时间和预先信息对任务切换的影响

两个实验采用任务线索范式,考察了准备时间和预先信息对任务切换的影响。实验1的准备时间为可预测,实验2的为不可预测,以考察准备时间的可预测性对任务切换的影响。以被试执行重复任务、切到任务和切离任务的正确反应时为主要指标,结果：（1）在准备时间可预测和不可预测两种条件下,准备时间和预先信息之间存在显著交互作用。在可预测条件中,重复和切到任务的反应时随着准备时间的增加而减少,但切到代价无显著变化,切离任务的反应时不受准备时间的影响,切离代价表现出反准备效应;不可预测条件下,三种任务的反应时都随着准备时间的增加而减少,但是切到和切离代价表现出反准备效应;（2）切离任务的反应时和代价显著高于切到任务的反应时和代价;（3）在这两种条件下,都没有出现切换代价的准备效应     

Task switching and response correspondence in the psychological refractory period paradigm

Three experiments examined the effects of task switching and response correspondence in a psychological refractory period paradigm. A letter task (vowel-consonant) and a digit task (odd-even) were combined to form 4 possible dual-task pairs in each trial: letter-letter, letter-digit, digit-digit, and digit-letter. Foreknowledge of task transition (repeat or switch) and task identity (letter or digit) was varied across experiments: no foreknowledge in Experiment 1, partial foreknowledge (task transition only) in Experiment 2, and full foreknowledge in Experiment 3. For all experiments, the switch cost for Task 2 was additive with stimulus onset asynchrony, and the response-correspondence effect for Task 2 was numerically smaller in the switch condition than in the repeat condition. These outcomes suggest that reconfiguration for Task 2 takes place after the central processing of Task 1 and that the crosstalk correspondence effect is due to response activation by way of stimulus-response associations.     

Stimulus-related priming during task switching

Task switch cost (the deficit of performing a new task vs. a repeated task) has been partly attributed to priming of the repeated task, as well as to inappropriate preparation for the switched task. In the present study, we examined the nature of the priming effect by repeating stimulus-related processes, such as stimulus encoding or stimulus identification. We adopted a partial-overlap task-switching paradigm, in which only stimulus-related processes should be repeated or switched. The switch cost in this partial-overlap condition was smaller than the cost in the full-overlap condition, in which the task overlap involved more than stimulus processing, indicating that priming of a stimulus is a component of a switch cost. The switch cost in the partial-overlap condition, however, disappeared eventually with a long interval between two tasks, whereas the cost in the full-overlap condition remained significant. Moreover, the switch cost, in general, did not interact with foreknowledge, suggesting that preparation on the basis of foreknowledge may be related to processes beyond stimulus encoding. These results suggest that stimulus-related priming is automatic and short-lived and, therefore, is not a part of the persisting portion of switch cost.     

刺激类型与预先信息对任务切换的影响

为揭示联结竞争与任务设置重构在切换加工过程中的关系,以切换代价为指标,研究了刺激类型与预先信息对任务切换的影响效应,结果发现:(1)无信息的切换代价显著高于部分信息和全部信息的切换代价,而后二者之间无显著差异;(2)单向刺激的切换代价显著高于双向刺激的切换代价;(3)预先信息和刺激类型对切换代价的影响无交互作用。这表明任务设置重构与联结竞争是两个具有相加效应的序列认知活动。     

工作记忆中转换加工的内源性准备 和外源性调节

考察工作记忆中转换加工的控制过程。采用“任务转换”范式,探究预知条件（实验一）和未预知条件（实验二）下的转换加工。结果发现：（1）任务重复与任务转换是两个不同的过程;无论是在预知条件还是未预知条件下都出现任务重复效应显著大于任务转换效应;（2）验证了转换加工包括内源性准备和外源性调节两个不同的加工过程, 内源性准备只是任务设置重建的一部分;（3）对先后呈现的两个任务（任务1—任务2 ：任务重复或任务转换）在预知重复、预知转换和未预知条件下,任务2对任务1的影响不同,存在前瞻性记忆效应。由此推断转换加工的心理过程是：在预知情况下,任务1呈现后即启动内源性准备,直到任务2呈现时,通过外源性调节最终完成任务转换;而在未预知情况下,只能依赖外源性调节来实现     

The costs of crossing paths and switching tasks between audition and vision

Switching from one functional or cognitive operation to another is thought to rely on executive/control processes. The efficacy of these processes may depend on the extent of overlap between neural circuitry mediating the different tasks; more effective task preparation (and by extension smaller switch costs) is achieved when this overlap is small. We investigated the performance costs associated with switching tasks and/or switching sensory modalities. Participants discriminated either the identity or spatial location of objects that were presented either visually or acoustically. Switch costs between tasks were significantly smaller when the sensory modality of the task switched versus when it repeated. This was the case irrespective of whether the pre-trial cue informed participants only of the upcoming task, but not sensory modality (Experiment 1) or whether the pre-trial cue was informative about both the upcoming task and sensory modality (Experiment 2). In addition, in both experiments switch costs between the senses were positively correlated when the sensory modality of the task repeated across trials and not when it switched. The collective evidence supports the independence of control processes mediating task switching and modality switching and also the hypothesis that switch costs reflect competitive interference between neural circuits.     

Persisting activation in voluntary task switching: It all depends on the instructions

We tested the hypothesis that persisting activation from a previous task execution does not contribute to the switch cost in voluntary task switching. We reasoned that voluntary task switching requires the selection of random task sequences, which necessitates the active inhibition of previously executed tasks. The asymmetric switch cost was used as a marker for persisting activation. Participants switched voluntarily between color naming and word naming. One group was instructed to select unpredictable task sequences. The other group was not instructed to do so. When participants were instructed to be unpredictable, no asymmetric switch cost was observed. When participants were not instructed to be unpredictable, an asymmetric switch cost was observed. We conclude that the amount of persisting activation in voluntary task switching is limited and that the switch cost in voluntary task switching reflects the time needed for reconfiguring the cognitive system from one task to another rather than the time needed to compensate for persisting activation.     

Task switching based on externally presented versus internally generated information

A number of observations from the task switching literature suggest that task preparation based on internally generated knowledge is less efficient than task preparation based on externally presented information. In the present study, we investigated task switching based on internally generated versus externally presented information and additionally varied the reliability of foreknowledge. Source and reliability of foreknowledge were varied between groups of participants. With reliable foreknowledge, the relevant task always conformed to foreknowledge, even when the features of the imperative stimulus called for an alternative task. With unreliable foreknowledge, the relevant task was determined by the imperative stimulus and foreknowledge was sometimes misleading. Apart from measuring switch costs, we examined the effectiveness of establishing a task set by measuring interference exerted by conflicting stimuli (conditions with reliable foreknowledge) or misled expectancies (conditions with unreliable foreknowledge). In terms of switch costs, we observed a slight superiority of externally presented over internally generated information when foreknowledge was reliable, but this relationship strongly reversed with unreliable foreknowledge. This conclusion was corroborated by observations regarding the effectiveness of task-set establishment in terms of proneness to interference.

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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.     

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.     

任务切换中切换代价产生的机制

关于任务切换中切换代价的来源和本质,目前主要有三种观点:任务设置惯性、任务设置重构和联结竞争。为揭示三者的关系,研究了在不同延迟时间条件下,预先信息与刺激类型对切换代价的影响机制。结果发现:延迟时间、预先信息和刺激类型对切换代价均有显著的作用,但是,三者之间的二次和三次交互作用均不显著。这表明,切换代价反映了任务设置惯性、任务设置重构和联结竞争三种成分,并且三者的关系是具有可加性的序列认知加工。     

Backward inhibition as a means of sequential task-set control: evidence for reduction of task competition

Endogenously initiated transitions between tasks are associated with inhibition of the attentional set for the task preceding the transition, as demonstrated by slowed reactions to a task most recently switched away from (U. Mayr & S. W. Keele, 2000). Using an altered methodological approach, the authors found that this backward inhibition counteracts perseverative tendencies when switching to a new task in that it selectively reduces interference exerted by the preceding task set. The reduction of interference was dependent on endogenous preparation for the new task and did not occur for unpredictable task switches or for task switches that were precued without information about the identity of the new task.     

预先信息的不确定性与准备时间对任务切换的影响

为揭示任务切换中切换代价的本质, 考察了预先信息与准备时间对任务切换的影响, 结果发现: (1) 预先信息对任务切换有显著的影响效应, 全部信息的反应时和切换代价显著低于无信息和部分信息的反应时和切换代价, 而后二者之间无显著差异; (2) 预先信息的影响效应受到准备时间的调节作用, 在准备时间为100ms时, 预先信息无显著的影响效应, 而在准备时间达到600ms以后, 预先信息的准备效应显著。这说明, 预先信息影响的认知加工是任务设置重构, 并且这种影响效应受到准备时间的调节作用。     

Current task activation predicts general effects of advance preparation in task switching

Two experiments investigated the way that beforehand preparation influences general task execution in reaction-time matching tasks. Response times (RTs) and error rates were measured for switching and nonswitching conditions in a color- and shape-matching task. The task blocks could repeat (task repetition) or alternate (task switch), and the preparation interval (PI) was manipulated within-subjects (Experiment 1) and between-subjects (Experiment 2). The study illustrated a comparable general task performance after a long PI for both experiments, within and between PI madipulations. After a short PI, however, the general task performance increased significantly for the between-subjects manipulation of the PI. Furthermore, both experiments demonstrated an analogous preparation effect for both task switching and task repetitions. Next, a consistent switch cost throughout the whole run of trials and a within-run slowing effect were observed in both experiments. Altogether, the present study implies that the effects of the advance preparation go beyond the first trials and confirms different points of the activation approach (Altmann, 2002) to task switching.     

Effects of deviant trials on precue-based versus memory-based switching among two or four tasks

In two experiments, the effects of an introduction of deviant trials on precue-based and memory-based task switching were investigated. Deviant trials were trials that deviated from task foreknowledge as induced either by precues or memory of the task sequence. The experiments differed with respect to the number of tasks to be switched among (two in Experiment 1, four in Experiment 2). In Experiment 1, the introduction of deviant trials had a detrimental effect on precue-based task preparation, but had little impact on memory-based preparation. The latter observation was due to the fact that there was little evidence for memory-based preparation at the outset. In Experiment 2, introducing deviant trials had little effect on either precue-based or memory-based preparation. In contrast to Experiment 1, in Experiment 2 memory-based preparation was as effective as precue-based preparation.     

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.     

Executive control in set switching: residual switch cost and task-set inhibition.

Executive processes necessary for flexibly switching between different tasks were studied using a set switching paradigm that requires participants to rapidly switch between different tasks across consecutive trials. Switch cost reflects poorer performance for task-switch trials than for consecutive same-task trials. Significant switch cost was observed even with considerable preparation time before a task-switch, an effect known as residual switch cost. This study tested the hypothesis that one process underlying residual switch cost is inhibition of the previous task-set. We used semantic categorization tasks to compare switch cost between alternating task series (ABA) and nonalternating series (ABC) in order to test the generality of a task-set inhibition effect previously observed with perceptual judgment tasks (Mayr & Keele, in press). The results yielded significant switch cost only for alternating tasks, in both response times and errors resulting from performance of the wrong task. Thus, resolving inhibition associated with previously abandoned task-sets may be the main process underlying residual switch costs, suggesting that task-set inhibition is an important executive control process.     

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.     

Exploring task-set reconfiguration with random task sequences

Switching between two different tasks normally results in an impairment in people's performance known as a switch cost, typically measured as an increase in reaction time (RT) and errors compared to a situation in which no task switch is required. Researchers in task switching have suggested that this switch cost is the behavioural manifestation of the task set reconfiguration processes that are necessary to perform the upcoming task. However, an examination of the literature in task switching reveals apparently contradictory results about the nature of task set reconfiguration processes. In Experiment 1, we addressed this issue by comparing participants' performance in two different experimental conditions: predictable task switching and random task switching. In the predictable switch condition the switch cost completely vanished after the first repetition of the new task. However, in the random switch condition, while the difference between switch and repetition trials was not significant, we observed a significant reduction in RT between the first and second repetition of the new task. In Experiment 2, we further investigated the pattern of task set reconfiguration in the random switch situation. The results showed a progressive reduction of participants' response latencies across repetitions of the same task. The present study demonstrates that, whereas the results in predictable switching conditions are compatible with an exogenous-reconfiguration hypothesis, random task switching produces a more gradual, decay-like switch cost reduction with task repetition.