任务切换理论争议新证据

任务切换是研究认知控制的主要范式之一。大量研究发现切换试次比重复试次的反应时更长,错误率更高,这种差异称为切换代价。任务切换时所产生切换代价的理论解释主要有惯性论、重构论和联结论。近十年来,这些理论均获得新的实验支持和发展,但其争议依旧,没有哪一理论能成功解释任务切换的所有效应。未来研究可以建立整合模型,以准确描述切换代价产生的认知机制。     

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。     

执行控制研究的重要范式——任务切换

任务切换是当前研究执行控制的重要范式。被试完成切换任务要慢于完成重复任务,并且往往有更高的错误率,这种差异称为切换损失。该文对此领域的研究进行了回顾,介绍了任务切换研究范式的发展,重点阐述了对切换损失来源的三种主要解释：任务重建、联结竞争和任务设置的惯性;指出任务切换与其他范式的结合是更深入地了解执行控制的可行途径。最后进行了简要的总结与展望。     

任务切换中的反应重复效应

在任务重复试次中反应的重复对反应有促进作用，而在任务切换试次中反应的重复对反应有阻碍作用，此现象即为反应重复效应（response repetition effects, RRE）。RRE普遍存在不同任务切换范式中，是一种抽象反应编码重复效应，受刺激效价和一致性、反应编码重复度和准备时间等因素影响。其理论解释主要有重构论、启动-抑制论、以及情境检索说。现有研究初步表明前额叶皮层是RRE的关键脑区，但RRE的认知神经机制及理论解释还有待进一步探讨。     

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。     

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     

延迟时间与反应设置对任务切换的影响

采用任务线索范式,探讨了在不同反应设置条件下,延迟时间对任务切换的影响,以揭示在延迟时间内之前任务设置延迟的认知加工。以切换代价为主要测量指标,结果表明,反应设置和延迟时间的主效应均不显著,但是二者的交互作用显著。简单效应分析发现,在双向设置条件下,切换代价随着延迟时间的延长而显著减少,但是在单向设置条件下无显著差异。这说明,在任务切换中反应设置对延迟时间的影响效应具有调节作用。由此可见,在延迟时间内之前任务设置延迟的是反应设置。     

抑制控制在被动与主动语码切换中的作用

本研究探讨被动与主动语码切换过程中的语码切换代价及抑制控制的作用。该实验以阿拉伯数字为实验材料,随机选取高校汉-英双语大学生为被试,要求被试完成数字命名任务。结果表明,被动语码切换过程存在语码切换代价且代价对称,这一现象既可以用特定语言选择假说解释,也可以用抑制控制模型来解释,但未能直接支持抑制控制真正参与被动语码切换,有待进一步研究; 主动语码切换过程中,目标语言为汉语时存在语码切换代价,而目标语言为英语时不存在语码切换代价,可能是抑制控制机制与词汇选择策略共同参与的结果。     

延迟时间与预先信息对任务切换的作用

对切换代价的本质存在任务设置惯性和任务设置重构两种观点。为揭示二者在切换代价中的关系, 研究了不同延迟时间条件下预先信息对任务切换的作用, 结果发现：(1)延迟时间对切换代价有显著影响, 100 ms的切换代价显著高于1000 ms的切换代价, 而600 ms分别与100 ms、1000 ms之间的切换代价无显著差异; (2)预先信息对切换代价的影响显著, 全部信息的切换代价显著低于无信息和部分信息的切换代价, 而后二者之间无显著差异; (3)延迟时间与预先信息无交互作用。这表明, 延迟时间与预先信息分别作用于任务设置惯性和任务设置重构, 切换代价反映了这两种具有相加效应的加工过程。     

通道呈现方式与感知学习风格的匹配性对粤-普双言切换代价的影响

选取不同感知学习风格的熟练粤-普双言者被试, 比较在不同通道呈现方式下他们刺激命名任务的表现, 由此考察感知学习风格与通道呈现方式的匹配性对熟练双言者双言切换代价的影响。结果发现, 被试在视觉线索呈现条件下要比在听觉线索条件下的切换代价小; 当感知学习风格与通道呈现方式匹配时, 双言切换代价更低。表明感知学习风格与通道呈现方式的匹配性对于双言切换代价有调节作用。     

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.     

Reward enhances backward inhibition in task switching

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

Executive control of thought and action: in search of the wild homunculus

Executive control is studied in many areas of psychological research using a wide variety of procedures. This article focuses on studies of the executive processes involved in switching between tasks. The experiments discussed were designed to isolate and measure the duration of the executive processes required to switch from one task to another. However, the research is open to alternative interpretations that do not hypothesize executive processes, suggesting that task-switching procedures may not measure the duration of executive control. Further research is required to determine whether or not behavioral effects reflect the involvement of executive processes.     

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.     

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.     

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.     

Self-regulatory strategy and executive control: implementation intentions modulate task switching and Simon task performance

Two tasks where failures of cognitive control are especially prevalent are task-switching and spatial Simon task paradigms. Both tasks require considerable strategic control for the participant to avoid the costs associated with switching tasks (task-switching paradigm) and to minimize the influence of spatial location (Simon task). In the current study, we assessed whether the use of a self-regulatory strategy known as "implementation intentions" would have any beneficial effects on performance in each of these task domains. Forming an implementation intention (i.e., an if-then plan) is a self-regulatory strategy in which a mental link is created between a pre-specified future cue and a desired goal-directed response, resulting in facilitated goal attainment (Gollwitzer in European Review of Social Psychology, 4, 141-185, 1993, American Psychologist, 54, 493-503, 1999). In Experiment 1, forming implementation intentions in the context of a task-switching paradigm led to a reduction in switch costs. In Experiment 2, forming implementation intentions reduced the effects of spatial location in a Simon task for the stimulus specified in the implementation intention. Results supported the prediction that the need for high levels of cognitive control can be alleviated to some degree by making if-then plans that specify how one responds to that critical stimuli.     

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.