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。     

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     

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。     

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。     

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。     

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。     

不同熟练程度藏汉双语者言语理解中的语码切换及其代价

以母语为藏语,第二语言为汉语的熟练和非熟练藏汉双语者为被试,采用词汇判断任务,在无切换、预期切换和无预期切换三种条件下,考察藏汉两种语言之间的语码切换及其切换代价。结果表明：（1）在三种条件下,熟练和非熟练藏汉双语者对汉语词的反应时均显著短于对藏语词的反应时,汉语词的错误率也显著低于藏语词;（2）切换条件下的反应速度显著慢于无切换条件,切换条件下的错误率显著高于无切换条件,存在显著的切换代价;（3）熟练藏汉双语者对汉语词的反应时显著短于非熟练藏汉双语者,熟练藏汉双语者对汉语词反应的错误率也显著低于非熟练藏汉双语者。本研究表明,藏汉双语语码切换过程中存在切换代价,支持抑制说;熟练藏汉双语者语码切换代价更小。     

藏-汉-英双语者字词识别中的语码切换及其代价

以母语为藏语、汉语熟练、英语不熟练的藏-汉-英双语者为被试,采用词汇判断的研究范式,在无切换、预期切换和无预期切换三种条件下,考察了藏-汉-英三种语言之间的语码切换及其代价。结果表明：⑴在三种条件下,被试对汉语词和藏语词的反应时和错误率的差异不显著,藏语词和汉语词的切换代价差异不显著。⑵在无切换条件下,对藏语词和英语词的反应时和错误率的差异不显著;在切换条件下,对英语词反应时长,错误率也高;英语词的切换代价显著大于藏语词的切换代价。⑶在无切换条件下,对汉语词和英语词的反应时和错误率的差异不显著;在切换条件下,对英语词反应时长,错误率也高;英语词的切换代价显著大于藏语词的切换代价。整个研究表明,藏-汉-英双语者在字词识别中的语码切换代价主要受语言的熟练程度影响     

任务切换的老化效应

采用任务线索范式(task-cueing paradigm),考察年龄对两个不同来源的切换损失的影响。实验一操控准备时间考察内源性切换损失,实验二操控首尾任务的异同考察外源性切换损失。以被试执行切换任务和重复任务的正确反应时为主要指标,结果发现:(1)在执行不同类型的任务时,老化效应极其明显,青年人反应速度普遍快于老年人,错误率普遍低于老年人;(2)内源性任务范式中重复任务和切换任务老化速度不一致,老化对切换任务影响更大,而外源性任务范式中CBA和ABA任务老化速度基本一致;(3)青年人和老年人在内源切换损失、外源切换损失上不存在显著差异。结果表明,整体上老年人的任务切换成绩差于年轻人,与外源性任务相比,内源性切换任务的成绩更易受老化的影响。     

汉-英双语者言语理解中语码切换的机制——来自亚词汇水平的证据

以汉字义符和英文词后缀为对象,考察了汉-英双语者语码切换的机制及切换代价的来源。结果表明:(1)在亚词汇水平上,汉字义符和英文词后缀影响字词认知的过程,但对语码切换代价的影响不显著,支持语码切换与任务转换的发生机制相同的观点。(2)语言熟练程度是影响语码切换代价及切换代价不对称性的主要原因。整个研究表明,在亚词汇水平上,语码切换与任务转换的实质相同。参考任务转换中切换代价的来源,归纳了语码切换代价的可能来源。     

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.     

任务切换机制研究的理论争议与整合

任务切换是执行控制的一种重要功能。切换代价是量化执行控制持续时间的指标。并广泛应用于各个研究领域。但是切换代价在多大程度上体现了执行控制的作用,仍然还存在争论．当前主要存在任务设置重构、任务设置惯性和联结竞争三种理论。本文首先介绍了三种理论的基本观点和实验证据,以及对任务切换加工机制的分析;其次阐明了对三种理论进行整合的相关研究;最后分析了进一步研究的方向。     

Joint task switching

The present study investigates the representation of task-sets in a joint dual-task setting. To this end, a task-switching approach is used. Task switching is associated with a switch cost, which can be decomposed in several markers of task-set coordination. These markers can be used to investigate whether participants represent the co-actor's task-set in a joint dual-task setting. A joint task-switching procedure was used in which two participants performed a distinct task and the participants’ turn to respond could switch or repeat on a trial-by-trial basis. The results indicate that joint task switching also elicits a switch cost. However, this switch cost does not seem to be related to the representation of the co-actor's task-set. It is suggested that the switch cost observed in joint task switching is based on processes of task monitoring, which increase the saliency of task-irrelevant stimulus information.     

The effects of recent practice on task switching

Four experiments investigated the effect of recent selective practice on the cost of switching between 2 tasks afforded by letter-digit pairs: alphabet arithmetic and shape comparison. Experiments 1 and 2 found a greater cost associated with switching to the more recently practiced task: evidence that task-set inertia contributes to switching costs. Experiment 3 found this effect to be limited to trials on which a recently trained stimulus followed another such stimulus: a result problematic for all current theories of task-set priming. Experiment 4 showed that the effect of recent practice was eliminated by active preparation for a task switch: It appears that endogenous task-set preparation reduces the effects of task-set inertia. ((c) 2003 APA, all rights reserved)     

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.     

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。     

Asymmetric switch cost and backward inhibition: Carryover activation and inhibition in switching between tasks of unequal difficulty.

Asymmetric switch cost, observed when switching between tasks varying in difficulty, shows that the difference between repeat and switch trials is greater when switching to the easier task. Early explanations of this effect attributed this pattern to both positive priming of the difficult task and negative priming of the easier task, but more recent models have focused only on activation processes. The role of inhibition in asymmetric switch cost was examined using backward inhibition, a more direct measure of task-set inhibition. The results indicated asymmetric backward inhibition, with greater sequential inhibition of the easier task (i.e., easy-difficult-easy sequences). Switch costs, however, showed both typical and reversed asymmetry (greater cost when switching from the easy to the difficult task), depending on the relative difficulty of task pairs. This pattern of results indicates that switch costs are attributable to both activation and inhibition processes.     

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。