心理科学进展, 2018, 26(11): 1969-1975 doi: 10.3724/SP.J.1042.2018.01969

研究前沿

双价效应及其认知机制

杜玮玮1, 宋婷1, 李富洪,2

1 辽宁师范大学脑与认知神经科学研究中心, 大连 116029

2 江西师范大学心理学院, 南昌 330022

Bivalency effect and its cognitive mechanism

DU Weiwei1, SONG Ting1, LI Fuhong,2

1 Research Center of Brain and Cognitive Science, Liaoning Normal University, Dalian 116029, China

2 School of Psychology, Jiangxi Normal University, Nanchang 330022, China

通讯作者: 李富洪 E-mail: lifuhong@jxnu.edu.cn;宋婷和杜玮玮为共同第一作者。

第一联系人:

收稿日期: 2017-11-13   网络出版日期: 2018-11-15

基金资助: * 国家自然科学基金项目资助.  31571118

Received: 2017-11-13   Online: 2018-11-15

摘要

任务转换时, 如果一个刺激不仅包含当前任务的特征还包含另一任务的关联特征, 这样的刺激被称为双价刺激。双价刺激能影响个体对单价刺激的加工, 使个体对后续所有单价刺激的反应减慢, 这种现象被称为双价效应(bivalency effect)。研究者发现双价效应具有一定的普遍性和稳定性。对双价效应的理论解释主要有情境捆绑说和基于经验的预测模型。双价效应的产生与额外视觉特征的提取及自上而下的认知控制调整有关, 前者主要与颞-顶联合区的激活有关, 后者主要与背侧前扣带回以及前辅助运动区的激活相关。

关键词: 双价效应 ; 冲突 ; 认知控制 ; 背侧前扣带回 ; 认知机制

Abstract

In task switching, a stimulus containing the features of the current task and the associated features of another task is defined as a bivalent stimulus. Exposure to bivalent stimuli affects the processing of univalent stimuli, slowing the response to all subsequent univalent stimuli. This phenomenon is called the bivalency effect. Researchers have found that the bivalency effect is generally and stably observed among various tasks. The theoretical explanation of the bivalency effect mainly comprises episodic context binding and the history-dependent predictive model. The generation of the bivalency effect is related to the extraction of additional visual features and top-down adjustment of cognitive control. The former is mainly related to activation of the temporal-parietal junction, while the latter is mainly related to activation of the dorsal anterior cingulate cortex and the pre-supplementary motor regions.

Keywords: bivalency effect ; conflict ; cognitive control ; dorsal anterior cingulate cortex ; cognitive mechanism

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本文引用格式

杜玮玮, 宋婷, 李富洪. (2018). 双价效应及其认知机制. 心理科学进展, 26(11), 1969-1975

DU Weiwei, SONG Ting, LI Fuhong. (2018). Bivalency effect and its cognitive mechanism. Advances in Psychological Science, 26(11), 1969-1975

任务转换是执行控制领域中一种主要的研究范式。任务转换研究中, 通常使用多种实验刺激探究转换代价的加工机制。最常用的刺激仅具有单一的维度特征, 如颜色、字母大小写等, 这种刺激被称之为单价刺激(univalent stimuli)。具有两个任务相关维度特征的刺激(图1)被称为双价刺激(bivalent stimuli)。研究表明, 在任务转换过程中, 双价刺激比单价刺激的反应时更长, 且表现出更大的转换代价(Allport, Styles, & Hsieh, 1994), 且双价刺激会影响后续单价刺激的加工(Egner & Hirsch, 2005; Woodward, Meier, Tipper, & Graf, 2003)。

图1

图1   混合block中刺激呈现示例
注:要求被试判断几何图形的颜色、数字奇偶、字母大小写; 图中的字母a具有“颜色”与“小写”两个属性, 是双价刺激; 刺激上方的文字为正确答案(在实验中并不出现)。彩图见电子版。


Woodward等人于2003年首先研究了双价刺激对单价刺激的影响。研究者依次呈现数字(1~9)、红色或蓝色的符号(如###)和字母三种单价刺激, 要求被试判断数字奇偶性、符号颜色和字母大小写。双价刺激为书写红色或蓝色的字母, 被试需要忽略字母的颜色, 判断其大小写。实验包含单价block和混合block:单价block中是三种单价刺激; 而混合block中, 数字、颜色以及80%的字母任务为单价刺激, 其余字母任务为双价刺激。实验按照单价block、混合block、单价block的顺序进行。结果表明, 混合block中单价刺激的反应时显著长于两个单价block中单价刺激的平均反应时, Woodward等人(2003)将这种现象定义为双价代价(bivalency cost), 后来又被称为双价效应(Meier, Woodward, Rey-mermet, & Graf, 2009)。

1 双价效应的特点

1.1 双价效应的普遍性和稳定性

Meier等人(2009)采用与Woodward等人(2003)相同的实验范式, 使用不同的任务和材料也发现了双价效应。在其实验1中, 研究者将数字(1~8)、彩色符号(#,$,%,&)以及字母(p, n, s, d)作为单价刺激, 要求被试判断数字奇偶性、符号颜色和字母大小写。字母任务中的20%以红色或蓝色的字体呈现作为双价刺激, 被试需要忽略字母的颜色, 判断其大小写。同时, 研究者设置了1000 ms和2000 ms的刺激间隔考察其对双价效应的影响。结果表明, 三种任务都存在双价效应且两种间隔条件下不存在显著差异。为了防止颜色信息对数字任务的影响, 在实验2中, 研究者将数字任务以听觉形式呈现, 不改变其它两种任务的呈现方式。结果表明, 数字任务依然存在双价效应, 说明双价效应不受刺激呈现方式的影响。为了进一步验证双价效应的普遍性, Meier等人(2009)在实验3中将实验任务和材料做了改变, 将符号(#, $, %, &)、数字以及字母作为单价刺激, 要求被试判断符号字体大小(20号或180号字体)、数字奇偶性以及元音或辅音字母。双价刺激为字体是20号或180号的字母, 被试需要忽略字母的字号, 判断其为元音或辅音。同样研究者设置了1000 ms、3000 ms和5000 ms的刺激间隔考察其对双价效应的影响, 结果表明, 不同实验任务和刺激间隔条件下都存在双价效应。

双价效应除了不受材料和呈现方式的影响外, 还不受按键设置以及年龄的影响。例如, Rey-Mermet和Meier (2012b)将数字、颜色和字母作为刺激材料, 并设置了反应按键重叠和非重叠两种条件。在按键重叠的条件下, 要求被试对数字、颜色和字母三种任务按b或n键; 非重叠条件下, 要求被试对数字任务按b或n键, 颜色任务按v或m键, 字母任务按c或“, ”键。结果显示, 反应键重叠和非重叠条件下, 三种任务都存在双价效应且大小相似。此外, 双价效应还存在于不同的年龄群体中。对双价效应的研究大都以大学生为对象, 而在Meier, Rey-Mermet, Woodward, Müri和Gutbrod (2013)以老年人为被试的研究中, 也发现了双价效应, 说明双价效应在年轻人以及老年人群体中都是普遍存在的。

后续研究者采用相同的范式以及不同的实验材料, 都发现了稳定的双价效应(Grundy & Shedden, 2014a; Grundy et al, 2013; Rey-Mermet & Meier, 2012a, 2014; Rey-Mermet, Koening, & Meier, 2013)。综上所述, 双价效应具有普遍性和稳定性, 不受刺激特征、呈现方式、反应键以及年龄的影响。

1.2 非冲突性和时间持久性

双价效应的非冲突性指不仅与双价刺激有冲突特征的单价刺激(如图1中的字母和颜色刺激)存在双价效应, 与双价刺激没有冲突特征的单价刺激(图1中的数字刺激)也存在双价效应。双价效应的另一重要特点是具有时间持久性。Meier等人(2009)在研究中设置了1000 ms、2000 ms、3000 ms以及5000 ms的刺激间隔, 结果显示, 即使刺激之间的间隔为5000 ms时, 双价效应依然存在并可以持续20 s。

双价效应的非冲突性和时间持久性主要表现在双价刺激产生的后效应(after-effect)。为了验证对新异刺激的朝向反应是否可以解释双价效应, Rey-Mermet和Meier (2013)在研究中对比了新异单价刺激和新异双价刺激引起的后效应之间的差异。研究者采用的单价刺激是数字、红色或蓝色的符号以及字母, 要求被试判断数字奇偶性、符号颜色以及字母大小写。在新异单价block中, 新异刺激为绿色或黄色的字母; 而新异混合block中, 新异刺激为红色或蓝色的字母, 要求被试忽略字母的颜色, 只判断其大小写。结果显示, 新异单价和新异双价刺激的反应时不存在显著差异, 说明二者引起的朝向反应相似。尽管如此, 两种新异刺激引发了不同的后效应。主要表现为, 与单价block中单价刺激相比, 新异双价刺激引发了三种单价任务反应的持续减慢, 出现了典型的双价效应。新异单价刺激最初也引起了三种任务的反应减慢, 而随后反应时减慢只表现在与新异单价刺激有共同特征(字母任务)的任务中。Rey-Mermet和Meier (2013)认为这些结果说明, 双价效应的时间持久性和非冲突性并非源于个体对新异刺激的朝向反应。

2 影响双价效应的因素

2.1 冲突特性对双价效应的影响

2.1.1 按键冲突

冲突数量是反映冲突特征的一个重要方面。在双价效应的研究中, 操纵冲突数量的一种方法是呈现按键一致和不一致的双价刺激。前者指双价刺激的两个特征对应的按键相同, 后者指双价刺激的两个特征对应不同的按键(如图1, 要求被试对红色图形按F键, 蓝色图形按J键; 大写字母按F键, 小写字母按J键。图中的双价刺激a具有红色和小写两个特征且对应不同的按键, 即为不一致的双价刺激)。为此, 我们不难发现, 与一致的双价刺激相比, 不一致的双价刺激还包含了按键冲突。

关于按键冲突对双价效应的影响, 不同研究者得出了不同结论。有的研究者认为, 双价效应不受按键冲突(即冲突数量)的影响。如:Rey-Mermet和Meier (2014)对一致和不一致双价刺激的研究显示, 虽然不一致双价刺激的反应时显著长于一致的双价刺激, 但二者之后的单价刺激存在相似的双价效应。而Grundy和Shedden (2014a)的研究则发现, 相对于一致的双价刺激, 不一致双价刺激引起了更大的双价效应。因此Grundy和Shedden认为, 对冲突数量的操纵会影响双价效应的大小, 冲突越大, 引发的双价效应越大。虽然两个研究得出了完全相反的结论, 但是, 我们发现, 与Rey-Mermet和Meier (2014)的实验相比, Grundy和Shedden (2014a)在实验中将双价刺激的位置进行了伪随机且双价刺激后有较多的单价trial, 同时对按键做了平衡, 这些操作显然能更好地控制额外变量。因此, 我们认为其结论可能更加可靠。

2.1.2 任务转换冲突

冲突的来源是冲突的另一特征。除了按键冲突, 任务转换冲突也是冲突的重要来源。Rey-Mermet和Meier (2012a)考察了任务转换和任务重复对双价效应的影响。在其实验中, 将符号(#, %, &, $)、数字(1~4)和字母(A, P, T, U)作为刺激材料并按照AABBCC的形式呈现, 要求被试分别判断符号的字体大小、数字奇偶性和字母的大小写。实验1中, 刺激呈现顺序为符号、数字和字母。其中, 双价刺激为字体或大或小的字母, 要求被试忽略字母的字体大小(20号或180号字体), 判断其大小写(如A或a)。实验2的任务呈现顺序为符号、字母和数字。此外, 双价刺激为字体或大或小的数字, 要求被试忽略数字的字体大小, 判断数字奇偶性。实验3的刺激呈现顺序为字母、数字和符号, 而双价刺激则为字体或大或小的数字, 且要求被试忽略数字奇偶性关注字体大小。实验中呈现了包含两种冲突的单价刺激(转换条件下且与双价刺激有共同特征), 一种冲突的单价刺激(重复条件下与双价刺激有共同特征或转换条件下与双价刺激没有共同特征)以及没有冲突的单价刺激(重复条件下与双价刺激没有共同特征)。结果显示, 在三个实验中, 符号、数字和字母三种任务在转换条件下的反应时显著长于重复条件, 证明存在转换代价。更重要的是, 与双价刺激有相关特征的单价刺激(如实验1中的字母和符号刺激)在转换和重复的条件下存在相似的双价效应。但是, 与双价刺激没有相关特征的单价刺激(如实验1中的数字刺激), 仅仅在转换条件下出现了双价效应, 而在重复条件下双价效应则有所减小。这些结果说明冲突对双价效应的产生是必要的, 但是冲突数量和冲突的来源并不能影响双价效应的大小。

2.2 练习对双价效应的影响

练习也是影响双价效应的重要因素之一。Grundy等人(2013)将颜色、数字和字母的实验材料作为单价刺激, 有颜色的字母材料为双价刺激, 结合事件相关电位技术(ERP)研究了双价效应及练习对双价效应的影响。行为和电生理结果都显示, 双价效应随着练习的增多而减小。此外, 行为结果表明颜色任务存在最大的双价效应且较不容易受练习的影响。

练习对一致和不一致的双价刺激产生的双价效应有不同的影响。Grundy和Shedden (2014a)对一致和不一致的双价刺激的研究显示, 一致和不一致的双价效应随着练习增多都会减小。但随着练习增加, 个体能够准确区分两种双价效应并以不同的方式适应它们, 主要表现为不一致的双价刺激引起的双价效应较不易受到练习的影响。

3 双价效应的理论解释

3.1 情境捆绑说

情境捆绑理论(Episodic context binding)认为, 情境的捆绑不仅包含刺激、反应和任务特征, 还包括刺激、反应以及任务加工的情境, 是通过记忆过程形成的关于刺激、反应以及任务加工的复杂情境表征(Allport & Wylie, 2000; Meier et al., 2009; Meier et al, 2013)。Rey-Mermet和Meier (2012b)的研究证明了情境捆绑说在双价效应中的合理性。在双价效应的研究中, 所有任务都使用相同的两个按键, 因此对单价刺激的按键反应可能会启动双价刺激的加工, 从而引发认知冲突。为了排除反应按键对双价效应的影响, Rey- Mermet和Meier (2012b)在研究中设置了反应键重叠和非重叠两种条件。在重叠的条件下, 所有任务使用相同的两个按键, 非重叠条件下, 每个任务对应独立的按键。结果表明, 在按键重叠与非重叠条件下的所有任务都存在双价效应且大小相似, 说明双价效应不受单价和双价刺激之间反应键设置的影响, 而是受任务(或刺激)本身的特征所影响。

根据情境捆绑说, 双价刺激出现的情境形成的复杂表征干扰了后面所有单价任务的加工, 个体为了应对这种复杂的情境就减慢反应速度, 从而引起双价效应。Meier等人(2013)的研究进一步支持了情境捆绑说在双价效应中的加工机制。研究者以严重失忆症病人和正常人为被试, 将颜色、数字和字母任务作为单价刺激, 红色或蓝色的字母为双价刺激, 对比了两组被试在双价刺激后的表现。结果显示与单价block相比, 正常组被试在混合block内三种任务上都表现出反应时持续减慢, 存在典型的双价效应。而失忆症病人只在双价刺激后的第一个任务中表现出反应减慢, 持续时间较短。研究者认为, 由于失忆症病人的记忆缺陷, 导致任务与情境之间的捆绑受到了破坏。

3.2 基于经验的预测模型

基于经验的预测模型(History-dependent predictive model)认为, 双价效应反映了认知控制系统根据当前认知负荷对未来行为的调节过程(Grundy & Shedden, 2014a)。Grundy和Shedden (2014a)使用一致和不一致的双价刺激考察了认知负荷对双价效应的影响, 结果显示, 与一致的双价刺激相比, 不一致双价刺激后引发了更大的双价效应且一致和不一致的双价效应之间存在显著差异。根据基于经验的预测模型, 相对于一致的双价刺激, 不一致的双价刺激还包含反应按键的冲突, 因此会引发较大的认知负荷从而产生更大的双价效应。

Grundy和Shedden (2014b)利用ERP技术为基于经验的预测模型提供了实验证据。研究者使用新异单价刺激和新异双价刺激(一致和不一致的双价刺激)考察了刺激新异性和认知负荷在双价效应中的作用。研究者以颜色、数字和字母任务作为单价刺激, 红色或蓝色的字母为双价刺激, 古英语字体书写的字母为新异单价刺激。行为结果显示, 不一致的双价刺激引发了最大的双价效应。脑电结果表明, 不一致双价刺激引起的脑电差异的时间窗口最长, 并在背侧前扣带回(Dorsal anterior cingulate cortex)的激活水平最高。由此不难认为, 双价效应反映了认知控制系统根据当前认知需求对行为的调节过程。当认知需求增加或减小时, 认知控制会随之改变(Grundy & Shedden, 2014a, 2014b; Sheth et al., 2012)。

综上, 我们发现情境捆绑说和基于经验的预测模型之间并不互相排斥。情境捆绑假说强调自上而下的认知控制在个体对“复杂”情景反应调整中的作用。当出现双价刺激时, 以往的反应经验(即刚刚对某一任务刺激的加工, 如对符号颜色的判断)会影响被试对双价刺激的反应, 要求被试抑制先前加工的反应惯性, 保持对双价刺激任务相关特征的注意集中。双价刺激之后, 个体并不能立刻从刚刚发生的复杂情景中脱离, 对后续刺激的加工依然表现出一种“谨慎”的反应。基于经验的预测模型强调认知控制系统对干扰特征的抑制负荷随冲突增大而增大, 从而导致双价效应增大。这一理论可以解释反应按键冲突对双价效应的影响, 但并不能很好地解释双价效应的产生。可见, 两个理论都提及任务经验在双价效应中的作用, 都认为双价效应反映了认知控制对行为的调节。两者的主要区别是情境捆绑假说认为这种调节是自上而下的过程, 是认知控制系统对“复杂”情景的适应性调节, 与反应键的冲突无关。而基于经验的预测模型则认为双价效应与反应键冲突有关, 正是反应冲突的存在改变了后续trial的认知负荷, 从而产生双价效应。

4 双价效应的生理机制

4.1 双价效应的脑区:背侧前扣带回的调控作用

背侧前扣带回(dACC)在双价效应中有重要的调控作用。Woodward, Metzak, Meier和Holroyd (2008)使用功能性磁共振成像技术(fMRI)研究了双价效应的脑机制。首先研究者将混合block内的单价刺激与单价block内的单价刺激对比, 结果显示, 混合block中的单价刺激激活了dACC以及前辅助运动区(Pre-supplementary motor regions)。同时研究者将混合block内双价刺激与单价block中对应位置的单价刺激进行对比, 发现双价刺激也激活了dACC, 并与双价效应(即混合block中的单价刺激)引起的dACC的激活没有显著差异。Kerns等人(2004)Woodward, Ruff和Ngan (2006b)使用fMRI对Stroop任务中色-词一致和不一致刺激的研究表明, 之前的冲突刺激会影响当前的任务并引起dACC的激活。Sheth等人(2012)使用fMRI和单神经元记录相结合的方法也证明了这一结果, 即冲突刺激以及冲突后的任务中都引起了dACC的激活。由此可知, 双价效应与dACC的激活密切相关。在任务转换过程中, dACC的作用之一是监控环境中的冲突, 通过发出打破任务惯性的信号来适应新情境(Woodward et al, 2008)。此外, Woodward等人(2008)的研究结果是对冲突监控理论的延伸, 当冲突存在于之前的任务中(冲突不是由当前的任务引起)同样能引起dACC的显著激活。

除了ACC在双价效应显著激活外, 侧颞-顶叶联合区(Temporal-parietal junction)也与双价效应有关。Grundy等人(2013)发现在100~120 ms的时间窗口, 混合block中的单价刺激比单价block中的刺激波幅更负, 源分析显示, 这个成分或许反映了TPJ的活动。TPJ在早期视觉加工中有重要作用(Evans, Shedden, Hevenor, & Hahn, 2000), 这说明双价刺激的出现也影响了认知控制系统对后续单价刺激的物理特征的注意与知觉过程。

4.2 双价效应的时间进程:冲突解决之后效

fMRI的研究清楚表明了dACC在双价效应中的重要作用。基于此, 一些研究将dACC在双价效应中的时间进程进行了进一步探究。

首先, 研究者考察了大脑对双价刺激的新异性及双价效应的早期加工, 以确定新异刺激是否为诱发双价效应的直接原因(Metzak, Meier, Graf, & Woodward, 2013; Rey-Mermet & Meier, 2013)。Grundy和Shedden (2014b)研究了新异单价刺激, 一致以及不一致的双价刺激引起的脑电成分的差异。结果发现在刺激呈现后100~120 ms, 混合block中的单价刺激比单价block中的刺激波幅更正, 这个成分反映了TPJ的激活。在刺激呈现后300~550 ms, 混合/新异单价block中的单价刺激比单价block中的单价刺激波幅更正, 这个成分与dACC的激活相联系。新异单价刺激只引起了dACC的活动, 并没有发现TPJ的激活。可能的原因是, 在混合block中, 对双价刺激两个线索的同时加工加强了对后续单价刺激特征的注意引起了TPJ的活动。这说明大脑在双价效应产生的早期阶段(即注意调节阶段)并未关注双价刺激的新异性, 相反, 可能由于认知控制系统自上而下的作用关注后续单价刺激的物理特征。此外, 不一致的双价刺激之后的单价刺激引起的dACC的激活更强烈, 且脑电差异的时间窗口最长。因此这一结果支持了基于经验的预测模型。

其次, 研究表明双价效应与持续性电位(Sustained potential)对应的冲突解决过程有关。Rey-Mermet等(2013)的研究显示, 双价效应与刺激呈现之后650 ms引发的持续的顶叶正波和额叶负波相关。研究者认为这个神经信号反映了SP成分, 而SP成分主要与冲突的解决有关(Larson, Kaufman, & Perlstein, 2009; Wylie, Javitt, & Foxe, 2003)。在另外两个经典的任务, Simon和Flanker任务中也存在冲突解决, 但这两个任务的冲突解决过程通常与N2成分相联系, N2成分主要与反应冲突的干扰有关(Clayson & Larson, 2012; Spapé, Band, & Hommel, 2011)。而在双价效应的研究中, 并没有发现N2成分的存在(Rey-Mermet & Meier, 2012a), 这也间接说明反应冲突对双价效应的出现不是决定性的, 双价效应可能反映了冲突解决的控制过程。

再次, 在双价效应的研究中, 由于双价刺激出现的次数太少(n < 20), 研究者没有直接将双价刺激与单价刺激的脑电结果进行对比。Poulsen, Luu, Davey和Tucker (2005)在任务转换的范式中发现, 在300~600 ms的时间窗口内, 双价刺激比单价刺激的波幅更正。Grundy等人(2013)在同样的时间窗口, 发现混合block中的单价刺激比单价block中的单价刺激波幅更正。双价刺激与混合block中的单价刺激引发的ERP成分的相似性说明, 双价刺激和双价效应引起的冲突之间有重叠的加工过程。双价刺激引起的冲突可能继续存在于后面的单价刺激中, 说明认知控制的调整不仅会影响当前冲突加工的表现, 也会影响冲突后的加工(Botvinick et al., 2001; Egner, 2008), 体现冲突解决的后效。

5 小结与展望

双价效应具有普遍性和持久性, 会受到冲突特性以及练习的影响。对双价效应的理论解释主要有情境捆绑说和基于经验的预测模型, 两个理论之间并不互相矛盾。双价效应的产生与额外视觉特征的提取及自上而下的认知控制的调整有关。前者主要与TPJ, 后者主要与dACC以及pre-SMA的激活有关。尽管当前对于双价效应的产生机制及可能涉及的脑区已形成一些认识, 但依然存在一些需要进一步探索的问题。

首先, 双价效应的来源尚不清楚。双价效应指的是双价刺激后混合block内所有单价刺激的反应时减慢。以往研究者对比单价block和混合block内单价刺激的差异, 而至今没有研究将混合block内即双价刺激前后的单价刺激进行比较。因此不能确定双价效应是由于双价刺激本身还是单价和混合block之间的差异引起的。将来的研究可以比较混合block内双价刺激前后的单价刺激, 不仅有利于确定双价效应的来源, 亦可探索认知控制系统在block内和block间对冲突刺激的不同加工过程。

其次, 双价刺激与不一致刺激所产生的冲突后效应有何不同?以往研究表明双价刺激引起的冲突后减慢具有非冲突性和时间持久性, 双价效应可以持续长达20 s。Rey-Mermet和Meier (2016)对不一致刺激(Stroop、Flanker以及Simon任务)的研究显示, 不一致刺激引起的冲突后减慢也具有非冲突性和时间持久性, 但随着任务进行仅影响与冲突刺激有相关特征的刺激。可见两种冲突刺激引发的冲突后效应极其相似。ERP研究表明, 对冲突刺激的反应会引起dACC的激活。Stroop、Simon和Flanker任务涉及的冲突解决过程通常与N2成分相关, 而对双价刺激的研究尚未发现N2成分的存在。这说明认知控制对双价刺激与不一致刺激的调整可能不同。但目前未见研究者在同一实验中对比这两种冲突刺激及其后效应。

最后, 双价效应关联的脑区激活和时间进程还需要进一步研究。Woodward等人(2008)使用fMRI研究发现, 双价效应显著激活了dACC。在任务转换中dACC对于打破任务惯性以调整反应风格有重要作用。而根据Meier等人(2013)提出的情境捆绑理论, 记忆对情境捆绑的形成有重要作用, 那么双价效应的产生应该会引起记忆相关脑区的激活。因此, 未来研究有必要结合fMRI和ERP技术研究海马等与记忆相关的脑区在双价效应中的激活情况, 以考察情境捆绑理论的合理性。如果关于刺激、反应以及任务加工的情境捆绑存在, 那么双价效应涉及的认知控制过程将不受冲突来源和冲突数量的影响, 这一发现是对认知控制理论的重要扩展和延伸。

The authors have declared that no competing interests exist.
作者已声明无竞争性利益关系。

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When switching tasks, if stimuli are presented that contain features that cue two of the tasks in the set (i.e., bivalent stimuli), performance slowing is observed on all tasks. This generalized slowing extends to tasks in the set which have no features in common with the bivalent stimulus and is referred to as the bivalency effect. In previous work, the bivalency effect was invoked by presenting occasionally occurring bivalent stimuli; therefore, the possibility that the generalized slowing is simply due to surprise (as opposed to bivalency) has not yet been discounted. This question was addressed in two task switching experiments where the occasionally occurring stimuli were either bivalent (bivalent version) or merely surprising (surprising version). The results confirmed that the generalized slowing was much greater in the bivalent version of both experiments, demonstrating that the magnitude of this effect is greater than can be accounted for by simple surprise. This set of results confirms that slowing task execution when encountering bivalent stimuli may be fundamental for efficient task switching, as adaptive tuning of response style may serve to prepare the cognitive system for possible future high conflict trials.

Poulsen, C., Luu, P., Davey, C., & Tucker, D. M. ( 2005).

Dynamics of task sets: evidence from dense-array event- related potentials

Cognitive Brain Research, 24( 1), 133-154.

URL     PMID:15922166      [本文引用: 1]

Prior research suggests that task sets facilitate coherent, goal-directed behavior by providing an internal, contextual frame that biases selection toward context-relevant stimulus attributes and responses. Questions about how task sets are engaged, maintained, and shifted have recently become a major focus of research on executive control processes. We employed dense-array (128-channel) event-related potential (ERP) methodology to examine the dynamics of brain systems engaged during the preparation and implementation of task switching. The EEG was recorded while participants performed letter and digit judgments to pseudorandomly-ordered, univalent (#3, A%) and bivalent (G5) stimulus trials, with the appropriate task cued by a colored rectangle presented 450 ms before target onset. Results revealed spatial and temporal variations in brain activity that could be related to preparatory processes common to both switch and repeat trials, switch-specific control processes engaged to reconfigure and maintain task set under conflict, and visual priming benefits of task repetition. Despite extensive practice and improvement, both behavioral and ERP results indicated that subjects maintained high levels of executive control processing with extended task engagement. The patterns of ERP activity obtained in the present study fit well with functional neuroanatomical models of self-regulation of action. The frontopolar and right-lateralized frontal switch effects obtained in the present study are consistent with the role of these regions in adapting to changing contextual contingencies. In contrast, the centroparietal P3b and N384 effects related to the contextual ambiguity of bivalent trials are consistent with the context monitoring and updating functions associated with the posterior cingulate learning circuit.

Rey-Mermet, A., & Meier, B.( 2012a).

The bivalency effect: Evidence for flexible adjustment of cognitive control

Journal of Experimental Psychology: Human Perception and Performance, 38( 1), 213-221.

URL     [本文引用: 3]

Rey-Mermet, A., & Meier, B.( 2012b).

The bivalency effect: adjustment if cognitive control without response set priming

. Psychological Research, 76( 1), 50-59.

[本文引用: 3]

Rey-Mermet, A., & Meier, B.( 2013).

An orienting response is not enough: Bivalency not infrequency causes the bivalency effect

Advances in Cognitive Psychology, 9( 3), 146-155.

[本文引用: 3]

Rey-Mermet, A., & Meier, B.( 2014).

More conflict does not trigger more adjustment of cognitive control for subsequent events: A study of the bivalency effect

Actapsychologica, 145, 111-117.

[本文引用: 3]

Rey-Mermet, A., & Meier, B.( 2016).

Post-conflict slowing after incongruent stimuli: from general to conflict-specific

Psychological Research, 81( 3), 611-628.

[本文引用: 1]

Rey-Mermet, A., Koenig, T., & Meier, B. ( 2013).

The bivalency effect represents an interference-triggered adjustment of cognitive control: An ERP study

Cognitive, Affective, & Behavioral Neuroscience, 13( 3), 575-583.

[本文引用: 2]

Sheth, S. A., Mian, M. K., Patel, S. R., Asaad, W. F., Williams, Z. M., Dougherty, D. D., … Eskandar, E. N. ( 2012).

Human dorsal anterior cingulate cortex neurons mediate ongoing behavioral adaptation

Nature, 488( 7410), 218-221.

URL     [本文引用: 2]

Spapé, M. M., Band, G. P. H., & Hommel, B. ( 2011).

Compatibility-sequence effects in the Simon task reflect episodic retrieval but not conflict adaptation: Evidence from LRP and N2

Biological Psychology, 88( 1), 116-123.

[本文引用: 1]

Woodward, T. S., Meier, B., Tipper, C., & Graf, P. ( 2003).

Bivalency is costly: Bivalent stimuli elicit cautious responding

Experimental Psychology, 50( 4), 233-238.

[本文引用: 4]

Woodward, T. S., Metzak, P. D., Meier, B., & Holroyd, C. B. ( 2008).

Anterior cingulate cortex signals the requirement to break inertia when switching tasks: A study of the bivalency effect

NeuroImage, 40( 3), 1311-1318.

[本文引用: 4]

Woodward, T. S., Ruff, C. C., & Ngan, E. T. C.( 2006b).

Short- and long-term changes in anterior cingulate activation during resolution of task-set competition

Brain Research, 1068( 1), 161-169.

[本文引用: 1]

Wylie, G. R., Javitt, D. C., & Foxe, J. J. ( 2003).

Task switching: a high-density electrical mapping study

Neuroimage, 20( 4), 2322-2342.

URL     PMID:14683733      [本文引用: 1]

Flexibly switching between tasks is one of the paradigmatic functions of so-called “executive control” processes. Neuroimaging studies have implicated both prefrontal and parietal cortical regions in the processing necessary to effectively switch task. Beyond their general involvement in this critical function, however, little is known about the dynamics of processing across frontal and parietal regions. For instance, it remains to be determined to what extent these areas play a role in preparing to switch task before arrival of the stimulus to be acted upon and to what extent they play a role in any switching processes that occur after the stimulus is presented. Here, we used the excellent temporal resolution afforded by high-density mapping of brain potentials to explore the time course of the processes underlying (1) the performance of and (2) the preparation for a switch of task. We detail the contributions of both frontal and parietal processes to these two aspects of the task-switching process. Our data revealed a complex pattern of effects. Most striking was a period of sustained activity over bilateral parietal regions preceding the switch trial. Over frontal regions, activity actually decreased during this same period. Strongest sustained frontal activity was in fact seen for trials on which no switch was required. Further, we find that the first differential activity associated with switching task was over posterior parietal areas (220 ms), whereas over frontal scalp, the first differential activity is found more than 200 ms later. These and other effects are interpreted in terms of a “competition” model in which preparing to switch task is understood as the beginning of a competition between the potentially relevant tasks that is resolved during the switch trial. Our findings are difficult to account for with models that posit a strong role for frontal cortical regions in “reconfiguring” the system during switches of task.

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