The influence of perceptual load on gaze perceptual adaptation aftereffect
收稿日期: 2015-10-19 网络出版日期: 2018-06-01
Received: 2015-10-19 Online: 2018-06-01
结合知觉负载任务和注视适应范式, 考察了知觉负载(高、低知觉负载)对不同注视线索(偏离注视与直视)适应后效的影响。结果发现：(1)偏离注视在低负载条件存在显著的适应后效, 而在高负载条件仅存在微弱的适应后效, 并且前者显著大于后者; (2)直视在低负载和高负载条件都出现了显著的适应后效, 并且二者不存在显著差异; (3)注意资源对偏离注视知觉的调节作用大于对直视知觉的作用。这说明, 偏离注视知觉受到注意资源紧张程度的调节, 而直视知觉不受注意资源的调节, 注意资源对直视与偏离注视的调节作用存在差异, 推测二者可能存在不同的加工机制。
结合知觉负载任务和注视适应范式, 考察了知觉负载(高、低知觉负载)对不同注视线索(偏离注视与直视)适应后效的影响。结果发现：(1)偏离注视在低负载条件存在显著的适应后效, 而在高负载条件仅存在微弱的适应后效, 并且前者显著大于后者; (2)直视在低负载和高负载条件都出现了显著的适应后效, 并且二者不存在显著差异; (3)注意资源对偏离注视知觉的调节作用大于对直视知觉的作用。这说明, 偏离注视知觉受到注意资源紧张程度的调节, 而直视知觉不受注意资源的调节, 注意资源对直视与偏离注视的调节作用存在差异, 推测二者可能存在不同的加工机制。
During social communication, eyes gaze indicates the focus of people's attention. There are two types of gaze cue: direct gaze (straight) and averted gaze (left or right), which have different social functions. Previous researchers assume that gaze perception involves two different processing stages. The first stage refers to earlier visual feature analysis of eyes such as luminance contrast and geometry of white sclera and iris. The second stage involves the perceptual integration of eyes’ features and the extraction of gaze direction. However, this assumption ignores the differences in processing mechanism between direct gaze and averted gaze. Other researchers hypothesize that perception of direct gaze is mediated by a fast-track pathway via subcortical face processing route. Direct gaze perception has characteristics of automatic process, such as capturing attention and being processed unconsciously. Its automaticity shows that direct gaze has a processing advantage over averted gaze. We inferred that direct gaze perception was independent of attentional resources, while averted gaze perception required more attentional resources. The present study aimed at investigating how attentional resources affect perception of averted and direct gaze. We combined Lavie’s perceptual load task and a short-term gaze adaptation paradigm to investigate how attentional resources influence the gaze adaptation aftereffect of direct gaze and averted gaze. Participants attended to a letter string superimposed on gaze adaptor (200 ms), and identified the target letter (X or N) embedded in the letter string of either 6 identical letters (low load) or 6 different letters (high load). Subsequently, a gaze probe was presented for 200 ms. Participants had to make judgements concerning the direction of probe (i.e. leftward, straight, or rightward). Sixteen naïve participants (8 females) were tested in Experiment 1, which measured the modulation of averted gaze adaptation effect by perceptual loads. And twenty-two naïve observers (11 females) participated in Experiment 2, which explored the effects of perceptual loads on direct gaze adaptation effect. The results of Experiment 1 revealed that a significant aftereffect of averted gaze directed toward the adapted side in the low load condition. However, such gaze adaptation effect was eliminated under high load condition. Crucially, the gaze adaptation effect in low load condition was significantly greater than that in high load condition. It was suggested that the extraction of averted gaze direction (leftward or rightward) was modulated by attentional resources (perceptual load). When a demanding competing task has exhausted all available processing capacity, the direction of averted gaze could not be extracted. While the load was low, “spill over” capacity was available to the processing of task-irrelevant gaze direction. Results of Experiment 2 showed a significant direct gaze adaptation effect both under low and high load conditions, which were not significantly different from each other. These results indicated that the perceptual adaptation of direct gaze was not influenced by attentional resources. Although limited processing capacity was fully consumed by a high load task, direct gaze could be processed as well. Compared with averted gaze, processing of direct gaze required fewer attentional resources. Therefore, requirements to attentional resources were different between processing of averted and direct gaze. In conclusion, the current study demonstrates that the processing of averted gaze direction is not mandatory automatic and it requires some degree of attentional resources. But gaze perception does not require attentional resources for direct gaze. Our findings indicated that processing of averted and direct gaze may be mediated by different underlying mechanisms, although distinct gaze directions are coded by a similar multichannel system with separate channels coding left, direct, and right gaze. Our results replicate and extend recent findings of different processing mechanisms between averted and direct gaze. Moreover, it may promote integration between different gaze perception models, such as multichannel system and fast-track modulator model.
During social communication, eyes gaze indicates the focus of people's attention. There are two types of gaze cue: direct gaze (straight) and averted gaze (left or right), which have different social functions. Previous researchers assume that gaze perception involves two different processing stages. The first stage refers to earlier visual feature analysis of eyes such as luminance contrast and geometry of white sclera and iris. The second stage involves the perceptual integration of eyes’ features and the extraction of gaze direction. However, this assumption ignores the differences in processing mechanism between direct gaze and averted gaze. Other researchers hypothesize that perception of direct gaze is mediated by a fast-track pathway via subcortical face processing route. Direct gaze perception has characteristics of automatic process, such as capturing attention and being processed unconsciously. Its automaticity shows that direct gaze has a processing advantage over averted gaze. We inferred that direct gaze perception was independent of attentional resources, while averted gaze perception required more attentional resources. The present study aimed at investigating how attentional resources affect perception of averted and direct gaze.
We combined Lavie’s perceptual load task and a short-term gaze adaptation paradigm to investigate how attentional resources influence the gaze adaptation aftereffect of direct gaze and averted gaze. Participants attended to a letter string superimposed on gaze adaptor (200 ms), and identified the target letter (X or N) embedded in the letter string of either 6 identical letters (low load) or 6 different letters (high load). Subsequently, a gaze probe was presented for 200 ms. Participants had to make judgements concerning the direction of probe (i.e. leftward, straight, or rightward). Sixteen naïve participants (8 females) were tested in Experiment 1, which measured the modulation of averted gaze adaptation effect by perceptual loads. And twenty-two naïve observers (11 females) participated in Experiment 2, which explored the effects of perceptual loads on direct gaze adaptation effect.
The results of Experiment 1 revealed that a significant aftereffect of averted gaze directed toward the adapted side in the low load condition. However, such gaze adaptation effect was eliminated under high load condition. Crucially, the gaze adaptation effect in low load condition was significantly greater than that in high load condition. It was suggested that the extraction of averted gaze direction (leftward or rightward) was modulated by attentional resources (perceptual load). When a demanding competing task has exhausted all available processing capacity, the direction of averted gaze could not be extracted. While the load was low, “spill over” capacity was available to the processing of task-irrelevant gaze direction. Results of Experiment 2 showed a significant direct gaze adaptation effect both under low and high load conditions, which were not significantly different from each other. These results indicated that the perceptual adaptation of direct gaze was not influenced by attentional resources. Although limited processing capacity was fully consumed by a high load task, direct gaze could be processed as well. Compared with averted gaze, processing of direct gaze required fewer attentional resources. Therefore, requirements to attentional resources were different between processing of averted and direct gaze.
In conclusion, the current study demonstrates that the processing of averted gaze direction is not mandatory automatic and it requires some degree of attentional resources. But gaze perception does not require attentional resources for direct gaze. Our findings indicated that processing of averted and direct gaze may be mediated by different underlying mechanisms, although distinct gaze directions are coded by a similar multichannel system with separate channels coding left, direct, and right gaze. Our results replicate and extend recent findings of different processing mechanisms between averted and direct gaze. Moreover, it may promote integration between different gaze perception models, such as multichannel system and fast-track modulator model.
赵亚军, 张智君, 刘志方, 刘炜, 严璘璘, 唐溢.
ZHAO Yajun, ZHANG Zhijun, LIU Zhifang, LIU Wei, YAN Linlin, TANG Yi.
眼睛注视线索(eyes gaze cue)是指他人的目光注视方向, 用于传递注意兴趣和行为意图等信息(Frischen, Bayliss, & Tipper, 2007)。在社会交往中, 当两人面对面交流时, 他人的注视线索可分为直视(direct gaze)和偏离注视(averted gaze)两种, 前者为相互注视, 后者指两人中一人注视着另外一人, 而另外那人却注视着其他人或物, 即转向左边或右边。对他人眼睛注视方向的知觉称为“注视知觉” (gaze perception) (Teufel, Fletcher, & Davis, 2010)。Teufel等研究者认为, 注视知觉包括两个加工阶段：第一, 识别眼睛虹膜与巩膜之间的明度对比和几何形状等特征信息(Frischen et al., 2007); 第二, 整合以上特征信息, 并抽取和编码注视方向(Materna, Dicke, & Thier, 2008; Shepherd, 2010; Teufel et al., 2010)。其中, 第二个阶段反映了从低级特征信息中抽取出注视方向的过程。
对注视方向抽取过程的探讨来自于注视知觉适应的研究。Jenkins, Beaver和Calder (2006)发现, 在对某一特定方向的偏离注视适应一段时间后, 被试倾向于将与适应方向相同的注视线索方向判断为直视(Jenkins et al., 2006)。这种对注视方向进行适应所导致的知觉扭曲称为“注视知觉适应后效” (gaze perceptual adaptation aftereffect), 它表明人脑中存在对不同注视方向(向左或向右)进行选择性编码的两类神经元群。Calder, Jenkins, Cassel和Clifford (2008)采用注视适应范式揭示了注视线索的编码方式(Calder et al., 2008)。他们发现, 对直视的适应也会导致被试注视知觉的扭曲, 表现为倾向于将直视知觉为偏离注视(向左或向右), 而偏离注视则更不易知觉为直视。这说明, 人脑中也存在专门对直视进行编码的神经元群。据此, Calder等(2008)提出注视方向编码的“多通道编码模型” (multichannel system), 认为人脑中存在三类神经元群分别对不同的注视方向(向左、直视或向右)进行编码。
研究表明, 直视较偏离注视存在加工优势(Senju & Johnson, 2009)。在行为层面, 直视更容易捕获注意, 能被更快速地检测到(胡中华, 刘强, 赵光, 李红, 2013; 胡中华, 赵光, 刘强, 李红, 2012; Von Grünau & Anston, 1995), 直视知觉不需要集中注意的参与(Yokoyama, Sakai, Noguchi, & Kita, 2014), 直视比偏离注视更容易在无意识条件下得到知觉(Chen & Yeh, 2012; Rothkirch, Madipakkam, Rehn, & Sterzer, 2015; Stein, Senju, Peelen, & Sterzer, 2011; Yokoyama, Noguchi, & Kita, 2013)。在神经层面, 直视的加工依赖于皮层下杏仁核等神经组织, 杏仁核的损伤会导致患者在人际会话中避免目光接触(Burra et al., 2013; Spezio, Huang, Castelli, & Adolphs, 2007)。这些证据支持了Senju和Johnson (2009)的“快通道调制器模型” (fast-track modulator model)。该模型认为, 大脑中存在一个皮层下的快速通道加工直视线索, 直视知觉具有自动化加工的特点：加工快速、能捕获注意、存在无意识知觉、对认知资源依赖程度较低等(Burra et al., 2013)。因此, 可以进一步推测, 直视对注意资源的需求较低(Yokoyama et al., 2014)。
关于注意影响注视知觉的研究表明, 偏离注视的知觉需要集中注意(focused attention)的参与(Burton, Bindemann, Langton, Schweinberger, & Jenkins, 2009; Ricciardelli & Turatto, 2011; Yokoyama et al., 2014)。Burton等(2009)采用目标-分心物干扰范式发现, 当被试的注意焦点集中在视野中央的目标刺激上时, 外周视野的分心物刺激(偏离注视线索)不会干扰目标刺激的加工, 说明作为分心物的注视方向没有得到知觉。可见, 偏离注视方向的知觉需要集中注意的参与。然而, 直视知觉不需要集中注意的参与(Yokoyama et al., 2014)。Yokoyama等(2014)采用双任务范式, 让处于视野中心的字母辨别任务(主任务)占据被试的注意焦点, 考察处于外周视野的注视方向辨别任务(次任务)是否受到集中注意的影响。结果发现, 在非集中注意状态下, 被试能够区分出直视和偏离注视, 却不能辨别不同方向的偏离注视(向左或向右)。Yokoyama等认为, 直视知觉不需要集中注意的参与, 而偏离注视知觉需要集中注意。但在该研究中, 位于视野中央的字母辨别任务不仅让注视线索远离空间注意的中心, 也会消耗被试的注意资源, 因而不清楚是集中注意(空间注意)还是注意资源影响了注视方向的辨别。
可见, 以往关于“注意影响注视知觉”的研究还存在一些不足。比如, 这些研究探讨的是空间注意(通过操纵被试的注意中心)对注视知觉的影响, 它们尚未系统地探讨注意资源对直视与偏离注视知觉编码的影响。注意资源(attentional resources)与空间注意(spatial attention)的概念不一样(Ricciardelli & Turatto, 2011)。为此, 本研究打算从“注意资源影响注视知觉”的角度去揭示不同注视线索的知觉编码机制。
根据前文分析, 直视与偏离注视对注意资源的需求可能不同。那么, 探讨注意资源对注视适应效应的调节情况, 将能揭示出直视和偏离注视的知觉编码机制及其差异。对注意资源与知觉关系的研究通常依据知觉负载理论(the perceptual load theory) (Lavie, 2005; Murphy, Groeger, & Greene, 2016)。该理论认为, 认知加工的注意资源是有限的, 当前任务的知觉负载高低决定了选择性注意过程中的资源分配。如果当前任务的知觉负载较低, 则多余的注意资源会自动溢出, 去加工干扰刺激, 从而产生干扰效应; 如果当前任务的知觉负载较高, 有限的注意资源被消耗尽, 那么与任务无关的干扰刺激无法得到知觉加工, 从而不会产生干扰效应。若结合知觉负载任务与注视知觉适应范式, 将能考察不同注视线索对注意资源的需求程度, 从而区分直视与偏离注视的知觉编码机制。可以预测, 偏离注视需要较多的注意资源, 将受到知觉负载的调节, 而直视对注意资源的需求较低, 将不受知觉负载的调节。
本研究结合知觉负载任务和注视适应范式, 考察注意资源对不同注视线索(直视与偏离注视)适应后效的影响。研究包含两个实验：实验1考察不同知觉负载条件下偏离注视的知觉适应效应; 实验2考察不同知觉负载条件下直视的知觉适应效应。结合两个实验的结果, 考察知觉负载对直视和偏离注视适应后效的影响是否存在差异。
需说明的是, 本研究对注视适应范式做了一些修改。研究者们在探讨注视适应效应中均采用长时程-适应范式, 适应刺激呈现的时间较长(几秒至数十秒) (Jenkins et al., 2006)。本研究旨在探讨知觉负载任务占用大量注意资源时被试能否抽取出注视方向, 如果适应刺激和知觉负载刺激呈现时间过长, 被试有充足的时间和资源加工适应刺激, 就达不到操纵注意资源的目的。因此, 本研究采用短时程-适应范式(Fang, Murray, & He, 2007; Neumann & Schweinberger, 2008), 适应刺激的呈现时间仅为200 ms, 使得被试在完成知觉负载任务时很难将注意分配到适应刺激上去。
16名(男、女各8人)浙江大学大学生参加实验。所有被试视力或矫正视力正常, 均为右利手, 平均年龄约为23岁(19~26岁)。实验结束后被试可获得一定的报酬。
在暗室环境下, 采用17英寸纯平CRT显示器呈现刺激, 屏幕背景为灰色(RGB: 128, 128, 128), 分辨率为1024×768, 刷新率为85 Hz。被试眼睛距离屏幕中心约57 cm。实验程序的编写和数据采集均采用E-Prime 1.1。
注视刺激是由10名大学生(男、女各5人)作为模特拍摄而成的彩色人脸照片。拍摄时要求模特将头部朝向正前方静止不动, 同时转动眼睛注视特定的参考点(Jenkins et al., 2006)。其中, 探测刺激(probe)包括5种不同注视方向的人脸照片：左10° (L10)、左5° (L5)、直视前方0° (D0)、右5° (R5)和右10° (R10), 共50张; 适应刺激(adaptor)包括3种不同的注视方向：左25° (L25)、右25° (R25)和直视前方0° (D0), 共30张。用一个椭圆截取每张人脸图片, 去除头发、耳朵及脖子等无关信息。采用Photoshop7.0将探测刺激的视角大小处理成6.0°×8.2°, 将适应刺激处理成7.4°×10.0° (约为探测刺激的1.5倍), 示例见图1。
采用组内设计, 自变量为负载水平(低负载, 高负载)、适应条件(适应前基线, 适应L25, 适应R25)和探测刺激(L10, L5, D0, R5, R10)。实验结合知觉负载任务与注视适应范式, 包括三个部分：(1)适应前的注视辨别测试, 简称适应前基线; (2)低知觉负载水平下的适应及适应后的注视辨别测试, 简称低负载适应; (3)高知觉负载水平下的适应及适应后的注视辨别测试, 简称高负载适应(见图2)。
在适应前基线部分(图2a), 50张探测人脸刺激随机呈现, 每张重复3次, 共150次。单次试验流程为：(1)在屏幕中央呈现0.75 s的注视点; (2)呈现探测刺激0.2 s, 要求被试做出反应; (3)呈现空屏, 持续时间最长为1.5 s, 若被试在1.5 s内作出反应, 便立即进入下一次trial, 若被试在1.5 s没有反应, 也进入下一次trial。两次试验的间隔时间为0.75 s。被试的任务是辨别探测刺激的注视方向, 用右手按键盘上的“H”、“J”、“K”键分别对向左(L10, L5)、直视(D0)、向右(R5, R10)的注视方向进行反应。指导语要求被试在每次试验时注视屏幕中央, 并尽可能准确地做出反应。正式实验分为3个block, 之间各休息30 s。正式实验前, 被试先进行30次的练习trials, 练习阶段给予反馈。适应前基线的实验约需15 min。
在低负载适应部分(图2b), 每次试验都包括两个任务：第一个是知觉负载任务, 第二个是注视方向辨别任务。实验流程为：(1)在屏幕中央呈现注视点0.75 s; (2)屏幕中央呈现一张适应人脸刺激和目标字母串0.2 s (字母串重叠在适应人脸上面, 字母串不会掩盖住人脸的眼睛); (3)呈现空屏2.0 s, 此时被试执行第一个任务, 即判断字母串是X还是N (此时, 字母串的6个字母相同), 分别按“H”或“SPACE”键进行反应, X或N各占50%可能性, 要求被试尽可能准确地反应, 不做反应时要求(2.0 s内反应即可), 并告知人脸与任务无关; (4)按键后, 进入第二个任务, 该任务的实验流程与适应前基线基本相同, 稍作改变的是：探测刺激消失后, 呈现空屏2.0 s以便被试尽可能准确地做反应。适应刺激与探测刺激在人脸身份和图片尺寸上均不相同, 用以排除人脸身份信息或低级水平特征的适应。低负载适应部分包括L25和R25两种适应刺激情境, 约需30 min。
高负载适应部分(图2b)与低负载适应部分流程基本相同, 不同的是第一个任务改为高负载任务, 被试需在6个不同字母串(1个目标：X或N; 5个非目标：H, K, M,W, Z)中搜索目标字母, X或N各占50%可能性。高负载适应部分的实验约需30 min。
所有被试先完成适应前基线, 以确定对注视方向辨别的基线水平。然后, 半数被试先做低负载适应再做高负载适应, 另一半被试的顺序则相反。同时, 一部分被试先做向左适应刺激(L25)的实验并完成适应后测试, 再做向右适应刺激(R25)的实验, 另一部分被试的顺序相反。在每种条件的正式实验之前, 被试先进行练习, 并给予反应时和正确率的反馈。
对知觉负载任务中的目标字母搜索正确率进行分析。被试在低负载下的正确率(98.4%)显著高于高负载下的正确率(87.7%), t(15) = 6.34, p < 0.001; 低负载下的反应速度(664.30 ms)显著快于高负载下的反应速度(948.34 ms), t(15) = 7.53, p < 0.001。这说明, 本实验对被试知觉负载水平的操作是成功的。下面仅对正确完成负载任务后的注视方向辨别数据进行分析。
|向左||0.93 (0.08)||0.58 (0.18)||0.10 (0.08)||0.01 (0.02)||0.01 (0.02)|
|直视||0.06 (0.07)||0.40 (0.18)||0.78 (0.14)||0.31 (0.17)||0.04 (0.04)|
|向右||0.01 (0.01)||0.02 (0.04)||0.12 (0.11)||0.68 (0.17)||0.95 (0.05)|
|向左||0.85 (0.12)||0.42 (0.18)||0.08 (0.09)||0.03 (0.04)||0.00 (0.00)|
|直视||0.12 (0.10)||0.53 (0.18)||0.73 (0.19)||0.22 (0.13)||0.02 (0.03)|
|向右||0.03 (0.05)||0.05 (0.07)||0.19 (0.16)||0.75 (0.13)||0.98 (0.03)|
|向左||0.95 (0.09)||0.68 (0.20)||0.18 (0.11)||0.08 (0.08)||0.02 (0.03)|
|直视||0.04 (0.08)||0.30 (0.20)||0.75 (0.18)||0.50 (0.20)||0.07 (0.06)|
|向右||0.01 (0.02)||0.02 (0.04)||0.07 (0.12)||0.42 (0.18)||0.91 (0.07)|
|向左||0.91 (0.16)||0.51 (0.17)||0.08 (0.06)||0.02 (0.03)||0.00 (0.01)|
|直视||0.07 (0.13)||0.44 (0.17)||0.73 (0.18)||0.21 (0.12)||0.02 (0.02)|
|向右||0.02 (0.06)||0.05 (0.10)||0.19 (0.17)||0.77 (0.11)||0.98 (0.02)|
|向左||0.94 (0.08)||0.64 (0.23)||0.15 (0.16)||0.06 (0.06)||0.01 (0.02)|
|直视||0.05 (0.07)||0.32 (0.22)||0.73 (0.25)||0.36 (0.22)||0.05 (0.77)|
|向右||0.01 (0.02)||0.04 (0.08)||0.12 (0.14)||0.58 (0.20)||0.94 (0.76)|
对基线条件下注视方向的辨别正确率进行分析。在基线水平下, 被试对注视方向有较为准确的辨别能力：对直视0°的辨别平均正确率为78%, 对眼睛向左或向右10°的平均正确率为94%, 对眼睛向左或向右5°的平均正确率为63%。单因素重复测量方差分析发现, 探测刺激主效应显著, F(2, 30) = 33.10, p < 0.001, ηp2 = 0.688。事后检验发现, 被试对5°注视方向的辨别不及0°和10°准确、对0°的辨别不及10°准确(ps < 0.05)。
被试对每种刺激可能存在3种反应(向左、直视或向右)。为使分析更简洁, 只采用“直视反应”作为指标对适应前基线与适应后的反应进行比较。图3中呈现了不同实验条件下被试做出“直视反应” 的比例, 即将探测刺激的注视方向判断为直视的 情况。
(1)低负载条件下的注视适应后效分析图3a可以发现, 被试在适应后更容易将与适应刺激方向相同的探测刺激判断为直视, 而在未适应刺激方向的探测刺激以及直视D0则较不容易判断为直视。采用3(适应条件：适应前, 适应L25, 适应R25)×5(探测刺激：L10, L5, D0, R5, R10)的重复测量方差分析显示：适应条件的主效应不显著, F(2, 30) = 0.23, p = 0.790; 探测刺激的主效应显著, F(4, 60) = 141.79, p < 0.001, ηp2 = 0.904;两者的交互作用显著, F(8, 120) = 19.66, p < 0.001, ηp2 = 0.567, 即不同适应条件下对不同探测刺激的反应存在差异。
与适应前基线相比, 适应L25后, 在适应的方向上, 被试更容易将注视向左的探测刺激判断为直视, 两者在探测刺激L10 (t(15) = 3.21, p = 0.006)和L5 (t(15) = 2.44, p = 0.028)上的差异均显著。对D0的正确率没有发生变化, t(15) = 1.48, p = 0.160。在未适应的方向上, 被试对向右的探测刺激更不容易判断为直视, 在探测刺激R5上的差异边缘显著, t(15) = 1.99, p = 0.065; 在R10上的差异显著, t(15) = 2.43, p = 0.028。
与适应前基线相比, 适应R25后, 在适应的方向上, 被试更容易将注视方向向右的探测刺激判断为直视, 两者在探测刺激R10 (t(15) = 2.44, p = 0.028)和R5上(t(15) = 3.85, p = 0.002)上的差异均显著。对D0的正确率没有发生变化, t(15) = 1.22, p = 0.241。在未适应的方向上, 被试对向左的探测刺激更不容易判断为直视, 在探测刺激L5上的差异显著, t(15) = 2.22, p = 0.042, 但在L10上不显著, t(15) = 1.53, p = 0.147。
分析图3b可以发现, 被试在适应前后对探测刺激的判断变化较小。采用3(适应条件：适应前, 适应L25, 适应R25)×5(探测刺激：L10, L5, D0, R5, R10)的重复测量方差分析。结果显示：适应条件的主效应不显著, F(2, 30) = 0.64, p = 0.476; 探测刺激的主效应显著, F(4, 60) = 145.83, p < 0.001, ηp2 = 0.907; 两者的交互作用显著, F(8, 120) = 4.41, p = 0.002, ηp2 = 0.227。
与适应前基线相比, 适应L25后, 在适应的方向(L10, L5)和D0上, 被试的正确率没有发生变化(ps > 0.10)。而在未适应的方向上, 被试对向右的探测刺激的反应更不容易判断为直视(在R5上, t(15) = 2.17, p = 0.047; 在R10上, t(15) = 2.16, p = 0.047)。
与适应前基线相比, 适应R25后, 在L10、L5、D0、R5和R10上, 被试的反应判断均没有发生变化(ps > 0.10)。
对适应效应量进行2(负载水平：低负载, 高负载)×2(适应条件：适应L25, 适应R25)×5(探测刺激：L10, L5, D0, R5, R10)的重复测量方差分析。结果显示：负载水平主效应显著, F(1, 15) = 6.29, p = 0.024, ηp2 = 0.295, 而适应条件主效应和探测刺激主效应均不显著(ps > 0.50); 负载水平与适应条件的交互作用不显著(p = 0.997), 负载水平与探测刺激交互作用显著(F(4, 60) = 3.48, p = 0.013, ηp2 = 0.188), 适应条件与探测刺激交互作用显著(F(4, 60) = 36.31, p < 0.001, ηp2 = 0.708), 负载水平、适应条件与探测刺激三者交互作用显著(F(4, 60) = 4.96, p = 0.008, ηp2 = 0.248)。三阶交互作用显著说明被试在不同知觉负载任务中的注视适应效应模式存在差异。下面从适应L25和R25两方面解析三阶交互作用。
首先, 分析被试在不同负载水平下适应L25后的注视适应效应的差异(图4a)。采用2(负载水平：低负载, 高负载)×5(探测刺激：L10, L5, D0, R5, R10)重复测量方差分析。结果显示：负载水平主效应显著, F(1, 15) = 11.17, p = 0.004, ηp2 = 0.427; 探测刺激主效应显著, F(4, 60) = 6.17, p = 0.002, ηp2 = 0.291; 两者的交互作用显著, F(4, 60) = 2.86, p = 0.031, ηp2 = 0.160。采用配对t检验, 对不同探测刺激在低负载与高负载任务中的适应效应进行比较发现：在探测刺激L10上, 低负载的适应量显著大于高负载的适应量, t(15) = 3.13, p = 0.007; 在L5上, 低负载的适应量也显著大于高负载的适应量, t(15) = 2.58, p = 0.021; 而在D0、R5和R10上差异均不显著(ps > 0.50)。
然后, 分析被试在不同负载水平下适应R25后的注视适应效应的差异(图4b)。采用2(负载水平：低负载, 高负载)×5(探测刺激：L10, L5, D0, R5, R10)重复测量方差分析。结果显示：负载水平主效应不显著, F(1, 15) = 2.33, p = 0.148; 探测刺激主效应显著, F(4, 60) = 6.25, p = 0.002, ηp2 = 0.294; 两者的交互作用显著, F(4, 60) = 5.76, p = 0.002, ηp2 = 0.278。采用配对t检验, 对不同探测刺激在低负载与高负载任务中的适应效应进行比较发现：在探测刺激R5上, 低负载的适应量显著大于高负载的适应量, t(15) = 3.45, p = 0.004; 在L10、L5、D0和R10上差异均不显著(ps > 0.40)。
实验1发现, 在不同知觉负载条件下, 注视适应效应表现出差异：低负载条件下的适应效应显著大于高负载条件下的效应, 即偏离注视适应后效受到知觉负载的调节。具体地, 低负载条件下存在显著的注视适应效应, 在适应某个方向的注视刺激后, 被试倾向于将与适应方向相同的探测刺激知觉为直视, 即对适应刺激的知觉适应影响了随后对探测刺激的辨别, 注视方向得到了抽取。但是, 高负载条件下仅存在微弱的注视适应效应, 这说明当知觉负载较高时, 有限的注意资源被消耗尽, 与任务无关的适应刺激的注视方向很难得到知觉。因此, 偏离注视的方向抽取是需要注意资源参与的, 这一过程依据注意资源占用情况而定。
考察不同知觉负载条件下直视的知觉适应效应, 以探讨直视注视方向的抽取对注意资源的需求程度。由于直视适应与偏离注视适应的效应存在相互影响, 因此实验1与实验2不便于采用组内设计(Stein, Peelen, & Sterzer, 2012)。其中, 实验1探讨知觉负载对偏离注视知觉适应后效的影响, 实验2探讨知觉负载对直视注视适应后效的影响, 结合二者的结果, 考察知觉负载(注意资源的紧张程度)对直视和偏离注视的影响是否存在差异。
22名(男、女各11人)浙江大学大学生参加实验。所有被试视力或矫正视力正常, 均为右利手, 平均年龄约为21岁(19~24岁)。实验结束后被试可获得一定的报酬。
实验装置和环境同实验1, 知觉负载任务、探测刺激跟实验1完全相同, 但适应刺激采用直视D0, 共10张人脸(见图1b)。
采用组内设计, 自变量为负载水平(低负载, 高负载)、适应条件(适应前基线, 适应D0)和探测刺激(L10, L5, D0, R5, R10)。实验程序同实验1, 包括适应前基线、低负载适应、高负载适应三个部分, 不同的是将适应刺激改为直视D0。整个实验约需40 min。
被试在低负载条件下的目标字母辨别正确率(96.91%)显著高于高负载下的正确率(85.45%), t(21) = 11.17, p < 0.001; 低负载下的反应速度(671.98 ms)显著快于高负载下的反应速度(979.26 ms), t(21) = 13.39, p < 0.001。这说明, 本实验对被试知觉负载水平的操作是成功的。仅对正确完成负载任务后的注视方向辨别数据进行分析。
被试在实验1与实验2的知觉负载任务中, 正确率不存在显著差异(低负载任务：t(36) = 1.89, p = 0.067; 高负载任务：t(36) = 1.22, p = 0.232), 反应时不存在显著差异(低负载任务：t(36) = 0.20, p = 0.841; 高负载任务：t(36) = 0.69, p = 0.492)。这说明两个实验中知觉负载任务所占用的注意资源基本相同。因而实验1与实验2结果的差别与注意资源的差异无关。
|向左||0.94 (0.11)||0.65 (0.18)||0.14 (0.10)||0.04 (0.06)||0.00 (0.01)|
|直视||0.06 (0.10)||0.33 (0.16)||0.75 (0.16)||0.39 (0.16)||0.06 (0.06)|
|向右||0.00 (0.01)||0.02 (0.04)||0.11 (0.12)||0.57 (0.18)||0.94 (0.07)|
|向左||0.98 (0.04)||0.78 (0.14)||0.19 (0.10)||0.05 (0.05)||0.00 (0.01)|
|直视||0.02 (0.04)||0.21 (0.14)||0.70 (0.18)||0.28 (0.18)||0.05 (0.08)|
|向右||0.00 (0.01)||0.01 (0.02)||0.11 (0.12)||0.67 (0.20)||0.95 (0.08)|
|向左||0.97 (0.06)||0.78 (0.18)||0.13 (0.06)||0.04 (0.04)||0.00 (0.01)|
|直视||0.02 (0.04)||0.20 (0.16)||0.73 (0.18)||0.31 (0.23)||0.04 (0.05)|
|向右||0.01 (0.05)||0.02 (0.05)||0.14 (0.19)||0.65 (0.24)||0.96 (0.06)|
对基线条件下注视方向的辨别正确率进行分析。结果发现, 被试对5°注视方向的辨别不及0°和10°准确、对0°的辨别不及10°准确(ps < 0.05)。
以“直视反应”为指标, 对被试在适应前基线与适应后的反应进行比较。从表2可见, 被试在适应后更不容易将探测刺激判断为直视。
分析图5发现, 被试在适应直视后更不容易将探测刺激判断为直视。采用2(适应条件：适应前基线, 适应D0)×5(探测刺激：L10, L5, D0, R5, R10)的重复测量方差分析显示：适应条件的主效应显著, F(1, 21) = 13.91, p = 0.001, ηp2 = 0.398; 探测刺激的主效应显著, F(4, 84) = 137.33, p < 0.001, ηp2 = 0.867; 两者的交互作用显著, F(4, 84) = 4.68, p = 0.006, ηp2 = 0.182, 即不同适应条件下对不同探测刺激的反应存在差异。
为揭示交互作用, 采用配对t检验对适应后反应与适应前基线进行比较。与适应前相比, 适应D0后被试对L10更不容易知觉直视, t(21) = 2.13, p = 0.046; 对L5更不容易知觉为直视, t(21) = 3.74, p = 0.001; 对D0知觉变化不显著, t(21) = 1.68, p = 0.108; 对R5更不容易知觉为直视, t(21) = 3.70, p = 0.001; 而对R10知觉无显著变化, t(21) = 0.78, p = 0.443。
分析图5发现, 被试在适应直视后更不容易将探测刺激判断为直视。采用2(适应条件：适应前基线, 适应D0)×5(探测刺激：L10, L5, D0, R5, R10)的重复测量方差分析显示：适应条件的主效应显著, F(1, 21) = 13.31, p = 0.002, ηp2 = 0.388; 探测刺激的主效应显著, F(4, 84) = 119.77, p < 0.001, ηp2 = 0.851; 两者的交互作用显著, F(4, 84) = 3.22, p = 0.017, ηp2 = 0.133, 即不同适应条件下对不同探测刺激的反应存在差异。
为揭示交互作用, 采用配对t检验对适应后反应与适应前基线进行比较。与适应前相比, 适应D0后被试对L10较不容易知觉直视, 边缘显著, t(21) = 1.74, p = 0.096; 对L5更不容易知觉为直视, t(21) = 3.95, p = 0.001; 对D0知觉变化不显著, t(21) = 0.73, p = 0.477; 对R5更不容易知觉为直视, t(21) = 2.28, p = 0.033; 而对R10知觉无显著变化, t(21) = 1.19, p = 0.248。
对适应效应量进行2(负载水平：低负载, 高负载)×5(探测刺激：L10, L5, D0, R5, R10)的重复测量方差分析。结果显示：负载水平主效应不显著, F(1, 21) = 0.75, p = 0.395; 探测刺激主效应显著, F(4, 84) = 4.66, p = 0.008, ηp2 = 0.182; 负载水平与探测刺激交互作用不显著, F(4, 84) = 0.62, p = 0.574。采用配对t检验对不同探测刺激在低负载与高负载条件下的适应量进行比较发现：在探测刺激L10, L5, D0, R5, R10上均不存在显著差异(ps > 0.20)。
首先, 比较适应L25(实验1)与D0(实验2)在高、低知觉负载条件下的适应后效之差(即知觉负载对适应后效的调节量, 简称注意调节量)是否存在差异(图7a)。采用2(适应条件：L25, D0)×5(探测刺激：L10, L5, D0, R5, R10)重复测量方差分析。结果显示：适应条件主效应不显著, F(1, 36) = 2.42, p = 0.129; 探测刺激主效应不显著, F(4, 144) = 1.16, p = 0.326; 两者的交互作用显著, F(4, 144) = 2.60, p = 0.039, ηp2 = 0.067。采用独立样本t检验, 对不同探测刺激在L25与D0适应条件下的注意调节量进行比较发现：在探测刺激L10和L5上, L25适应的注意调节量均显著大于D0适应的注意调节量(t(36) = 2.92, p = 0.006; t(36) = 2.10, p = 0.043), 而在D0、R5和R10上差异均不显著(ps > 0.40)。
然后, 比较适应R25(实验1)与D0(实验2)在高、低知觉负载条件下的适应后效之差(注意调节量)是否存在差异(图7b)。采用2(适应条件：R25, D0)×5(探测刺激：L10, L5, D0, R5, R10)重复测量方差分析。结果显示：适应条件主效应不显著, F(1, 36) = 1.13, p = 0.295; 探测刺激主效应显著, F(4, 144) = 5.18, p = 0.002, ηp2 = 0.126; 两者的交互作用边缘显著, F(4, 144) = 2.41, p = 0.052, ηp2 = 0.063。采用独立样本t检验, 对不同探测刺激在R25与D0适应条件下的注意调节量进行比较发现：在探测刺激R5上, R25适应的注意调节量显著大于D0适应的注意调节量(t(36) = 2.42, p = 0.021), 而在L10、L5、D0和R10上差异均不显著(ps > 0.30)。
以上结果表明, 知觉负载对L25和R25适应后效的调节量均大于其对D0适应的调节量(表现在探测刺激L10, L5和R5上), 这说明知觉负载(注意资源)对偏离注视与直视知觉适应的影响不同, 知觉负载对偏离注视存在影响(实验1), 而知觉负载对直视不存在影响(实验2), 并且知觉负载对偏离注视知觉的影响作用大于对直视知觉的影响(实验1与实验2的比较)。
实验2发现, 在低负载和高负载条件下都出现了显著的直视知觉适应后效, 即适应直视注视方向后, 被试倾向于将直视探测刺激判断为偏离注视, 而对偏离注视的判断更为准确。这说明, 在不同知觉负载条件下, 被试都能抽取出适应刺激D0的方向信息。更重要的是, 低负载和高负载条件下的直视适应效应不存在显著差异, 这说明直视知觉适应不受知觉负载水平(注意资源紧张程度)的影响。实验1发现, 低负载条件下的偏离注视适应效应显著大于高负载条件下的效应, 偏离注视知觉受到注意资源的调节。结合实验1和实验2的结果可以发现, 偏离注视的知觉受到注意资源的调节, 直视的知觉不受注意资源的调节, 并且注意资源对偏离注视知觉的调节作用大于对直视知觉的作用。由于直视与偏离注视受到注意资源的影响不同, 因而它们可能存在不同的加工机制。
本研究结合知觉负载任务和注视知觉适应范式, 探讨了知觉负载水平(注意资源紧张程度)对注视知觉适应的影响。实验1发现, 低负载条件下存在显著的注视适应效应, 高负载条件下仅存在微弱的注视适应效应, 低负载条件下的适应效应显著地大于高负载条件下的效应, 说明偏离注视方向的抽取受注意资源的调节。而实验2发现, 在低负载和高负载条件下都出现了显著的直视知觉适应后效, 并且二者之间不存在显著差异, 说明直视注视方向的抽取不受注意资源的影响。比较实验1与实验2的结果可以发现, 注意资源对偏离注视知觉的调节作用大于对直视知觉的作用。尽管直视与偏离注视在人脑中存在相似的注视方向表征(向左、直视或向右) (Calder et al., 2008), 但由于它们受到注意资源的影响不同, 因而可能存在不同的加工机制(Senju & Johnson, 2009)。
在高知觉负载条件下, 直视能够被抽取出方向, 而偏离注视受到注意资源的影响而很难抽取出方向。这说明, 直视较偏离注视存在加工优势, 不论注意资源的多寡, 其注视方向都能得到抽取。这跟以往发现直视与偏离注视加工机制存在不同的研究是一致的。研究发现, 直视加工具有自动化的特点：直视能捕获注意, 能被更快速地检测到(胡中华等, 2012, 2013; Von Grünau & Anston, 1995), 直视知觉不需要集中注意的参与(Yokoyama et al., 2014), 直视比偏离注视更容易在无意识条件下得到知觉(Rothkirch et al., 2015; Stein et al., 2011; Yokoyama et al., 2013), 直视依赖皮层下杏仁核等神经组织得到加工(Burra et al., 2013; Spezio et al., 2007)。这些证据说明, 直视存在一定的加工优势, 大脑中存在一个皮层下的快速通道加工直视线索(Johnson, Senju, & Tomalski, 2015; Senju & Johnson, 2009)。可以推测, 直视能在注意资源紧张的情况下得到知觉, 得益于它独特的认知加工特点：直视容易捕获注意; 直视对注意资源的需求较少。这两个加工特点可能分别作用于直视知觉的不同加工阶段, 对注意的捕获优势使得直视能被快速检测到, 对注意资源需求低使得它能够被更容易地知觉出具体的方向。当然, 这种推测还需进一步的研究加以检验。
Xu等(2011)采用注视线索范式, 该范式探讨偏离注视能否引发注意转移, 从而证明其得到知觉加工。本研究采用的是注视知觉适应范式, 考察适应注视线索是否影响探测注视线索的方向辨别, 从而证明适应注视线索的方向得到了抽取。虽然注视线索效应和注视适应效应都能说明偏离注视得到了加工, 但它们涉及的注视知觉加工的心理过程不同。研究表明, 这两个效应存在不同的加工机制, 在儿童发展、知觉表征、神经基础等方面表现出不同的特点(Doherty, McIntyre, & Langton, 2015; Insch, Slessor, Warrington, & Phillips, 2017; Jenkins et al., 2006; Nummenmaa & Hietanen, 2009; Shepherd, 2010)。Doherty (2006)认为, 存在两个加工注视线索的认知系统：一个是基于巩膜和虹膜明度对比信息加工的注视追随系统, 其信息加工迅速; 另一个是基于巩膜和虹膜几何形状的注视知觉系统, 其信息加工复杂、精细。事实上, 注视线索效应比注视适应效应的加工更加自动化, 注视适应效应则涉 及更加精细复杂的知觉系统(Doherty et al., 2015; Shepherd, 2010)。比如, 阈下的偏离注视能够引发注视线索效应(陈艾睿, 董波, 方颖, 于长宇, 张明, 2014; 张美晨, 魏萍, 张钦, 2015; Sato, Kochiyama, Uono, & Toichi, 2016; Sato, Okada, & Toichi, 2007; 但见Al-Janabi & Finkbeiner, 2014), 而偏离注视在无意识条件下不能产生注视适应效应(Stein et al., 2012)。Xu等(2011)的研究采用注视线索范式, 发现注视线索效应不受知觉负载影响, 而我们采用注视适应范式, 发现注视适应后效受到知觉负载影响。由于注视线索效应与注视适应后效涉及的心理过程不同, 这两个结果并不矛盾, 它可能反映了在注意资源紧张条件下, 注视线索效应与注视知觉适应的加工机制不同。
既然注意资源对直视与偏离注视的调节作用存在差异, 那么这种调节发生在注视知觉过程的哪一阶段呢?以往研究者认为, 注视线索经过特征 分析和方向抽取两个阶段而形成注视方向的表征(Bayliss et al., 2011; Calder et al., 2008; Shepherd, 2010; Teufel et al., 2010)。而本研究发现注意资源对直视与偏离注视适应后效(反映注视方向的编码或抽取阶段)的调节作用存在不同。研究表明, 注视适应后效是一种高级的知觉适应过程, 它是对注视线索的方向进行的选择性适应, 不是对其特征信息(明度对比、几何形状)的适应, 也就是说特征信息的适应不足以产生注视适应后效(Calder et al., 2008; Jenkins et al., 2006; Stein et al., 2012), 因而注视适应后效反映了注视线索特异性的知觉编码过程(Bayliss et al., 2011; Duchaine, Jenkins, Germine, & Calder, 2009)。可以推测, 注意资源对注视知觉的影响可能发生在注视方向抽取阶段。
需要注意的是, 本研究采用知觉负载水平的高低来操纵注意资源的分配, 知觉负载只是引起了知觉水平上的差异, 还是也引起了其它认知加工过程(如任务难度、决策与反应阶段等)的差异呢?由于高知觉负载水平会增加任务的难度, 并导致反应时的延长和正确率的降低。那么, 知觉负载带来的实验效应是不是由于任务难度的增加(而非注意资源的分配)引起的呢?在不增加知觉负载水平的条件下, 研究者们通过降低任务刺激的呈现质量(如降低对比度、缩短呈现时间、施加掩蔽刺激等)来增加任务的难度(Lavie & de Fockert, 2003; Yeshurun & Marciano, 2013)。然而, 单纯地增加任务难度而不增加知觉负载水平, 并不能减少干扰效应。相反地, 增加当前任务的知觉负载水平, 使其对注意资源的需求与消耗增加, 则能导致干扰效应减少甚至消失。也就是说, 增加任务难度与提高知觉负载水平对干扰刺激加工的影响是不同的。因此, 高知觉负载条件下干扰效应的减少不能归结为任务难度的增加, 而应归结为任务加工负荷的增加(即注意资源消耗过多)。只有当增加任务的加工负载、并消耗更多的注意资源时, 与任务无关的干扰刺激的干扰效应才会减少。可见, 任务难度并不能解释知觉负载所引起的实验效应(Murphy et al., 2016)。
另外, 目前没有证据表明知觉负载任务会影响决策和反应阶段(Cave & Chen, 2016)。脑电研究表明, 增加知觉负载水平能够增强目标刺激的加工(N1波幅的增加, 潜伏期约为180~220 ms), 并减弱对干扰刺激的加工(N1波幅的减小) (Rorden, Guerrini, Swainson, Lazzeri, & Baylis, 2008)。由于视觉N1成分是知觉辨别加工的指标, 因此知觉负载影响的是早期的知觉信息加工阶段(Murphy et al., 2016; Rorden et al., 2008)。综上所述, 本研究中知觉负载引起的实验效应是由注意资源的分配所引起的(罗禹等, 2017; Lavie & de Fockert, 2003; Murphy et al., 2016; Yeshurun & Marciano, 2013)。
Teufel等(2010)的“社会知觉与心理理论交互模型”、Shepherd (2010)的注视追随“双通路模型”以及Calder等人(2008)的“多通道模型”在解释注视知觉时忽略了直视与偏离注视在加工机制上的不同, 而Senju和Johnson (2009)的“快通道调制器模型”虽强调直视与偏离注视的不同, 却没有探讨其特异性的知觉编码方式。本研究通过考察注意资源对直视与偏离注视知觉产生不同的影响, 能揭示出直视与偏离注视具有不同的加工机制。而且, 采用注视适应效应对注视知觉进行测量, 能明确地反映注视线索加工的认知阶段, 也能用于推测注视方向编码的神经表征机制。因此, 本研究既能有效地揭示出直视与偏离注视加工机制上的不同, 又能揭示注视线索特有的知觉编码机制(Bayliss et al., 2011)。这样的研究结果能够促进不同注视知觉模型的整合。
同时, 本研究采用最常用的知觉负载任务操纵注意资源, 考察注意资源对不同注视线索知觉的调节作用, 避免了将注意资源与空间注意混到一起操纵。另外, 本研究的结果是在短时程-适应范式中获得的, 仅需200 ms的适应时间就能诱导出显著的注视适应后效, 这具有一定的方法学意义。减少适应时长便于研究者设计更简洁的实验, 缩短实验时间。并且, 结合了知觉负载任务与知觉适应效应的范式具有广泛的用途, 可用于探讨面孔身份、面孔表情和面孔朝向等其它社会线索的加工机制。
本研究探讨了知觉负载(高、低知觉负载)对不同注视线索(偏离注视与直视)适应后效的影响, 获得以下结论：偏离注视的知觉受到注意资源紧张程度的调节, 而直视的知觉不受注意资源的调节, 注意资源对二者知觉编码的调节存在不同。尽管直视与偏离注视在人脑中存在相似的注视方向表征(向左、直视或向右), 但由于受注意资源的影响不同, 推测它们可能存在不同的加工机制。
感谢Andrew J. Calder教授、审稿专家对本文提出的宝贵意见。
Responding to the direction of the eyes: In search of the masked gaze-cueing effect. Attention, Perception,,
A direct link between gaze perception and social attention,
Abstract How information is exchanged between the cognitive mechanisms responsible for gaze perception and social attention is unclear. These systems could be independent; the "gaze cueing" effect could emerge from the activation of a general-purpose attentional mechanism that is ignorant of the social nature of the gaze cue. Alternatively, orienting to social gaze direction might be directly determined by the operation of cognitive mechanisms specifically dedicated to gaze perception. This second notion is the dominant assumption in the literature, but there is little direct support for this account. Here, we systematically manipulated observers' perception of gaze direction by implementing a gaze adaptation paradigm. Gaze cueing was reduced only in conditions where perception of specific averted gaze stimuli was impaired (Experiment 1). Adaptation to a pointing stimulus failed to impact gaze cueing (Experiment 2). Overall, these data suggest a direct link between the specific operation of gaze perception mechanisms and the consequential orienting of attention.
Amygdala activation for eye contact despite complete cortical blindness,
Cortical blindness refers to the loss of vision that occurs after destruction of the primary visual cortex. Although there is no sensory cortex and hence no conscious vision, some cortically blind patients show amygdala activation in response to facial or bodily expressions of emotion. Here we investigated whether direction of gaze could also be processed in the absence of any functional visual cortex. A well-known patient with bilateral destruction of his visual cortex and subsequent cortical blindness was investigated in an fMRI paradigm during which blocks of faces were presented either with their gaze directed toward or away from the viewer. Increased right amygdala activation was found in response to directed compared with averted gaze. Activity in this region was further found to be functionally connected to a larger network associated with face and gaze processing. The present study demonstrates that, in human subjects, the amygdala response to eye contact does not require an intact primary visual cortex.
Gaze perception requires focused attention: Evidence from an interference task,
Abstract The direction of another person's gaze is difficult to ignore when presented at the center of attention. In 6 experiments, perception of unattended gaze was investigated. Participants made directional (left-right) judgments to gazing-face or pointing-hand targets, which were accompanied by a distractor face or hand. Processing of the distractor was assessed via congruency effects on target response times. Congruency effects were found from the direction of distractor hands but not from the direction of distractor gazes (Experiment 1). This pattern persisted even when distractor sizes were increased to compensate for their peripheral presentation (Experiments 2 and 5). In contrast, congruency effects were exerted by profile heads (Experiments 3 and 4). In Experiment 6, isolated eye region distractors produced no congruency effects, even when they were presented near the target. These results suggest that, unlike other facial information, gaze direction cannot be perceived outside the focus of attention. Copyright 2009 APA, all rights reserved.
Visual representation of eye gaze is coded by a nonopponent multichannel system,
To date, there is no functional account of the visual perception of gaze in humans. Previous work has demonstrated that left gaze and right gaze are represented by separate mechanisms. However, these data are consistent with either a multichannel system comprising separate channels for distinct gaze directions (e.g., left, direct, and right) or an opponent-coding system in which all gaze directions are coded by just 2 pools of cells, one coding left gaze and the other right, with direct gaze represented as a neutral point reflecting equal activation of both left and right pools. In 2 experiments, the authors used adaptation procedures to investigate which of these models provides the optimal account. Both experiments supported multichannel coding. Previous research has shown that facial identity is coded by an opponent-coding system; hence, these results also demonstrate that gaze is coded by a different representational system to facial identity.
Identifying visual targets amongst interfering distractors: Sorting out the roles of perceptual load, dilution, and attentional zoom.,
Abstract Visual selection is imperfect; whenever a complex array of objects is processed, representations of multiple objects are likely to be active simultaneously. A full account of attentional processing must explain how these representations affect one another and how they interact to produce a response. Evidence on these interactions comes from measures of distractor interference and from dilution of distractor effects by other nontargets. Based on these data, different principles have been proposed to help understand target-distractor interactions, including accounts based on perceptual load and on dilution among nontargets. We review evidence from a number of experiments, including some using Yantis and Jonides's (Journal of Experimental Psychology: Human Perception and Performance, 10, 601-621, 1984, Journal of Experimental Psychology: Human Perception and Performance, 16, 121-134, 1990) methods for preventing abrupt onsets, which can disrupt spatial attention. The results underscore spatial constraints on the allocation of attention to include targets and exclude distractors. Selection is most effective when a single region can be selected that includes all possible target locations and excludes possible distractor locations. This region can be expanded or contracted as needed for the task, as suggested by C. W. Eriksen and St. James's (Perception & Psychophysics, 40, 225-240, 1986) zoom lens model. This attentional zoom setting is probably affected by a number of factors, including the number of nontargets, the similarity among stimulus elements, the discriminability of the possible targets, and the discrimination difficulty of a concurrent task. A narrower attentional zoom setting that excludes a distractor will prevent interference from that distractor. Interference from a distractor will be diluted by nontargets, but only if they are within the attentional zoom region.
The role of cue type in the subliminal gaze-cueing effect
Look into my eyes and I will see you: Unconscious processing of human gaze,
This study examines whether human gaze lacking the confounding factor of eye whites can be processed unconsciously and explores the critical aspects for such process. Utilizing the continuous flash suppression paradigm, a schematic face—with direct or averted gaze, and with neutral, fearful or happy expressions—was presented to one eye while dynamic masks rendered it invisible to the other eye. Schematic faces were used to avoid unwanted influence from salient eye whites. Participants’ detection time of anything other than the masks was used as an index of unconscious processing time. Faster detection was found for faces with direct gaze than those with averted gaze. However, there was no difference between detection times for different facial expressions (Experiment 1) and upright-face, inverted-face, and eyes-only conditions (Experiment 2). These results confirm that, with schematic faces, gaze can be processed unconsciously regardless of facial expression, and eyes alone are sufficient for such process.
The development of mentalistic gaze understanding,
Very young infants are sensitive to and follow other people’s gaze. By 18 months old children, like chimpanzees, apparently represent the spatial relationship between viewer and object viewed: they can follow eye-direction alone, and react appropriately if the other’s gaze is blocked by occluding barriers. This paper assesses when children represent this relationship as psychological in nature. Studies examining sensitivity to gaze, gaze following, and explicit judgement of gaze direction are reviewed. The evidence suggests that neither infants nor chimpanzees represent gaze as psychological. It is concluded that mentalistic gaze understanding develops from the age of 3 years.
Developmentally distinct gaze processing systems: Luminance versus geometric cues,
Two experiments examined how the different cues to gaze direction contribute to children鈥檚 abilities to follow and make explicit judgements about gaze. In each study participants were shown blurred images of faces containing only luminance cues to gaze direction, line-drawn images containing only fine-grained detail supporting a geometric analysis of gaze direction, and unmanipulated images. In Experiment 1a, 2- and 3-year olds showed gaze-cued orienting of attention in response to unmanipulated and blurred faces, but not line-drawn faces. Adult participants showed cueing effects to line drawn faces as well as the other two types of face cue in Experiment 1b. In Experiment 2, 2-year-olds were poor at judging towards which of four objects blurred and line-drawn faces were gazing, whereas 3- and 4-year-olds performed above chance with these faces. All age groups performed above chance with unmanipulated images. These findings are consistent with an early-developing luminance-based mechanism, which supports gaze following, but which cannot initially support explicit judgements, and a later-developing mechanism, additionally using geometric cues in the eye, which supports explicit judgements about gaze.
Normal gaze discrimination and adaptation in seven prosopagnosics,
Sensitive gaze perception is critical for social interactions. Neuroimaging and neurophysiological results and the unique demands of gaze processing have led to suggestions that gaze is processed by different mechanisms than other aspects of faces. Neuropsychological data however provides little support for this possibility. We administered gaze discrimination tasks to six developmental prosopagnosics and one acquired prosopagnosic who exhibit identity perception deficits. First we examined whether the prosopagnosic participants could discriminate between straight and averted gaze normally. The performance of the control and prosopagnosic groups was very similar, and all of the prosopagnosics scored in the normal range. To assess whether the prosopagnosics represented gaze information like the controls, participants were tested on the discrimination task following adaptation to leftward and rightward gaze. The control and prosopagnosic groups both showed strong adaptation in the expected direction, and each prosopagnosic showed normal post-adaptation performance. These results indicate that gaze discrimination and representation is normal in these prosopagnosics. Their dissociation between impaired identity perception and normal gaze perception provides support for models of face processing suggesting that these aspects of face processing involve separate mechanisms.
Duration-dependent fMRI adaptation and distributed viewer-centered face representation in human visual cortex,
Abstract Two functional magnetic resonance imaging (fMRI) face viewpoint adaptation experiments were conducted to investigate whether fMRI adaptation in high-level visual cortex depends on the duration of adaptation and how different views of a face are represented in the human visual system. We found adaptation effects in multiple face-selective areas, which suggest a distributed, viewer-centered representation of faces in the human visual system. However, the nature of the adaptation effects was dependent on the length of adaptation. With long adaptation durations, face-selective areas along the hierarchy of the visual system gradually exhibited viewpoint-tuned adaptation. As the angular difference between the adapter and test stimulus increased, the blood oxygen level-dependent (BOLD) signal evoked by the test stimulus gradually increased as a function of the amount of 3-dimensional (3D) rotation. With short adaptation durations, however, face-selective areas in the ventral pathway, including the lateral occipital cortex and right fusiform area, exhibited viewpoint-sensitive adaptation. These areas showed an increase in the BOLD signal with a 3D rotation, but this signal increase was independent of the amount of rotation. Further, the right superior temporal sulcus showed little or very weak viewpoint adaptation with short adaptation durations. Our findings suggest that long- and short-term fMRI adaptations may reflect selective properties of different neuronal mechanisms.
Gaze cueing of attention: Visual attention, social cognition, and individual differences,
During social interactions, people's eyes convey a wealth of information about their direction of attention and their emotional and mental states. This review aims to provide a comprehensive overview of past and current research into the perception of gaze behavior and its effect on the observer. This encompasses the perception of gaze direction and its influence on perception of the other person, as well as gaze-following behavior such as joint attention, in infant, adult, and clinical populations. Particular focus is given to the gaze-cueing paradigm that has been used to investigate the mechanisms of joint attention. The contribution of this paradigm has been significant and will likely continue to advance knowledge across diverse fields within psychology and neuroscience.
The measurement of detection superiority of direct gaze affected by stimuli component information
直视的探测优势效应被认为是一 种普遍存在的现象,但近期的几个研究发现,在头为正面的情况下,直视的探测优势将消失。本研究将通过三个实验,探究在头为正面的情况下直视探测优势消失的 原因到底是源于斜视在结构信息上的特异性还是其在特征信息上的特异性。本研究采用两种刺激图片:眼睛图片(实验1、2)和面孔图片(实验3),三种斜视偏 转角度:10°、20°、30°,两种刺激呈现方式:直立、倒置。结果显示:斜视对直视加工优势的抵消主要来自于斜视在特征信息上的突显,直视探测优势是 一种普遍存在的社会现象,但在实验室的测量中容易受到实验材料特征信息的影响。
直视的探测优势效应被认为是一 种普遍存在的现象,但近期的几个研究发现,在头为正面的情况下,直视的探测优势将消失。本研究将通过三个实验,探究在头为正面的情况下直视探测优势消失的 原因到底是源于斜视在结构信息上的特异性还是其在特征信息上的特异性。本研究采用两种刺激图片:眼睛图片(实验1、2)和面孔图片(实验3),三种斜视偏 转角度:10°、20°、30°,两种刺激呈现方式:直立、倒置。结果显示:斜视对直视加工优势的抵消主要来自于斜视在特征信息上的突显,直视探测优势是 一种普遍存在的社会现象,但在实验室的测量中容易受到实验材料特征信息的影响。
The detection superiority of perceived direct gaze in visual search task: Evidence from eye movements
Gaze detection and gaze cuing in Alzheimer’s disease,
People with Alzheimer’s disease (AD) show problems with social processing in tasks which require the understanding of others’ mental states. However traditional social processing tasks are cognitively complex, which may influence the effects of AD. Less is known about how AD influences more basic aspects of social perception, such as the ability to decode eye gaze direction or follow the gaze of another. The current research assessed whether those with AD showed difficulty in both explicitly decoding subtle manipulations of gaze direction (Study 1), and reflexively following another’s eye gaze (Study 2). Those with AD were more impaired than a matched control group when making explicit discrimination distinctions between direct and averted gaze. In contrast people with Alzheimer’s disease performed comparably to a control group when following gaze. This pattern indicates that more automatic aspects of social perception such as gaze following are unaffected by AD. In contrast, more controlled processes such as deciding whether someone is looking towards you are impaired in AD. This has implications for socially engaging with other people and interpreting their focus of interest.
I thought you were looking at me: Direction-specific aftereffects in gaze perception,
Abstract Gaze direction is an important social signal in humans and other primates. In this study, we used an adaptation paradigm to investigate the functional organization of gaze perception in humans. Adaptation to consistent leftward or rightward gaze produced a powerful illusion that virtually eliminated observers' perception of gaze in the adapted direction; gaze to that side was seen as pointing straight ahead, though perception of gaze to the opposite side was unimpaired. This striking dissociation held even when retinotopic mapping between adaptation and test stimuli was disrupted by changes in size or head orientation, suggesting that our findings do not reflect adaptation to low-level visual properties. Moreover, adaptation to averted gaze did not affect judgments of line bisection, illustrating that our findings do not reflect a general spatial bias. Our findings provide evidence that humans have distinct populations of neurons that are selectively responsive to particular directions of seen gaze.
Recognition memory for distractor faces depends on attentional load at exposure,
Incidental recognition memory for faces previously exposed as task-irrelevant distractors was assessed as a function of the attentional load of an unrelated task performed on superimposed letter strings at exposure. In Experiment 1, subjects were told to ignore the faces and either to judge the color of the letters (low load) or to search for an angular target letter among other angular letters (high load). A surprise recognition memory test revealed that despite the irrelevance of all faces at exposure, those exposed under low-load conditions were later recognized, but those exposed under high-load conditions were not. Experiment 2 found a similar pattern when both the high- and low-load tasks required shape judgments for the letters but made differing attentional demands. Finally, Experiment 3 showed that high load in a nonface task can significantly reduce even immediate recognition of a fixated face from the preceding trial. These results demonstrate that load in a nonface domain (e.g., letter shape) can reduce face recognition, in accord with Lavie load theory. In addition to their theoretical impact, these results may have practical implications for eyewitness testimony.
The two-process theory of face processing: Modifications based on two decades of data from infants and adults,
Johnson and Morton (1991. Biology and Cognitive Development: The Case of Face Recognition. Blackwell, Oxford) used Gabriel Horn's work on the filial imprinting model to inspire a two-process theory of the development of face processing in humans. In this paper we review evidence accrued over the past two decades from infants and adults, and from other primates, that informs this two-process model. While work with newborns and infants has been broadly consistent with predictions from the model, further refinements and questions have been raised. With regard to adults, we discuss more recent evidence on the extension of the model to eye contact detection, and to subcortical face processing, reviewing functional imaging and patient studies. We conclude with discussion of outstanding caveats and future directions of research in this field.
Gaze direction aftereffects are surprisingly long-lasting,
Adaptation to gaze direction induces aftereffects in the perception of gaze in subsequently presented faces. Gaze adaptation calibrates neural responses to the most frequently occurring gaze signals and therefore frees up capacity to respond to more novel signals, likely enhancing gaze discrimination and supporting novelty detection. The longevity of aftereffects can provide some insight into the temporal window over which this calibration occurs. Since gaze direction is a rapidly changing signal in the face, one might expect gaze aftereffects to also be very short-lived. Here we show that this is not the case. In Experiment 1, we measured participants' aftereffects immediately after gaze adaptation and 24 h later. We found significant aftereffects at both times. In Experiment 2, we tested whether long-term adaptation also occurred when aftereffects were measured only once, 24 h after adaptation. Again, we found significant long-term aftereffects. These results demonstrate that gaze adaptation can integrate information over remarkably long periods. We discuss the implications of the longevity of gaze direction aftereffects on our understanding of their functionality, and the functionality of face aftereffects more generally. (PsycINFO Database Record(c) 2016 APA, all rights reserved).
Absence of sex-contingent gaze direction aftereffects suggests a limit to contingencies in face aftereffects,
Face aftereffects (e.g., expression aftereffects) can be simultaneously induced in opposite directions for different face categories (e.g., male and female faces). Such aftereffects are typically interpreted as indicating that distinct neural populations code the categories on which adaptation is contingent, e.g., male and female faces. Moreover, they suggest that these distinct populations selectively respond to variations in the secondary stimulus dimension, e.g., emotional expression. However, contingent aftereffects have now been reported for so many different combinations of face characteristics, that one might question this interpretation. Instead, the selectivity might be generated during the adaptation procedure, for instance as a result of associative learning, and not indicate pre-existing response selectivity in the face perception system. To alleviate this concern, one would need to demonstrate some limit to contingent aftereffects. Here, we report a clear limit, showing that gaze direction aftereffects are not contingent on face sex. We tested 36 young Caucasian adults in a gaze adaptation paradigm. We initially established their ability to discriminate the gaze direction of male and female test faces in a pre-adaptation phase. Afterwards, half of the participants adapted to female faces looking left and male faces looking right, and half adapted to the reverse pairing. We established the effects of this adaptation on the perception of gaze direction in subsequently presented male and female test faces. We found that adaptation induced pronounced gaze direction aftereffects, i.e., participants were biased to perceive small gaze deviations to both the left and right as direct. Importantly, however, aftereffects were identical for male and female test faces, showing that the contingency of face sex and gaze direction participants experienced during the adaptation procedure had no effect.
Distracted and confused?: Selective attention under load,
The ability to remain focused on goal-relevant stimuli in the presence of potentially interfering distractors is crucial for any coherent cognitive function. However, simply instructing people to ignore goal-irrelevant stimuli is not sufficient for preventing their processing. Recent research reveals that distractor processing depends critically on the level and type of load involved in the processing of goal-relevant information. Whereas high perceptual load can eliminate distractor processing, high load on ‘frontal’ cognitive control processes increases distractor processing. These findings provide a resolution to the long-standing early and late selection debate within a load theory of attention that accommodates behavioural and neuroimaging data within a framework that integrates attention research with executive function.
Contrasting effects of sensory limits and capacity limits in visual selective attention,
Abstract The effects of perceptual load and those of target-stimulus degradation on distractor processing were contrasted. Targets either had to be found among several nontargets (high perceptual load) or were presented alone and were intact (low perceptual load), had reduced size and contrast (Experiment 1), had reduced duration and were followed by a mask (Experiment 2), or had reduced visual acuity owing to position eccentricity (Experiment 3) in the degraded low-load condition. The results showed that both high perceptual load and target degradation increased general task difficulty, as is reflected by overall reaction times and accuracy. However, whereas high perceptual load reduced response-competition effects of irrelevant distractors, target degradation increased distractor effects. These results support the hypothesis that distractor processing depends on the extent to which high perceptual load exhausts attention in relevant processing and provide a dissociation between perceptual load and general task difficulty and processing speed.
The effect of perceptual load on processing and memorizing negative facial distractor
Dissociable roles of the superior temporal sulcus and the intraparietal sulcus in joint attention: A functional magnetic resonance imaging study,
Abstract Previous imaging work has shown that the superior temporal sulcus (STS) region and the intraparietal sulcus (IPS) are specifically activated during the passive observation of shifts in eye gaze [Pelphrey, K. A., Singerman, J. D., Allison, T., & McCarthy, G. Brain activation evoked by perception of gaze shifts: The influence of context. Neuropsychologia, 41, 156-170, 2003; Hoffman, E. A., & Haxby, J. V. Distinct representations of eye gaze and identity in the distributed human neural system for face perception. Nature Neuroscience, 3, 80-84, 2000; Puce, A., Allison, T., Bentin, S., Gore, J. C., & McCarthy, G. Temporal cortex activation in humans viewing eye and mouth movements. Journal of Neuroscience, 18, 2188-2199, 1998; Wicker, B., Michel, F., Henaff, M. A., & Decety, J. Brain regions involved in the perception of gaze: A PET study. Neuroimage, 8, 221-227, 1998]. Are the same brain regions also involved in extracting gaze direction in order to establish joint attention? In an event-related functional magnetic resonance imaging experiment, healthy human subjects actively followed the directional cue provided by the eyes of another person toward an object in space or, in the control condition, used a nondirectional symbolic cue to make an eye movement toward an object in space. Our results show that the posterior part of the STS region and the cuneus are specifically involved in extracting and using detailed directional information from the eyes of another person to redirect one's own gaze and establish joint attention. The IPS, on the other hand, seems to be involved in encoding spatial direction and mediating shifts of spatial attention independent of the type of cue that triggers this process.
Twenty years of load theory—Where are we now, and where should we go next?,
Selective attention allows us to ignore what is task-irrelevant and focus on what is task-relevant. The cognitive and neural mechanisms that underlie this process are key topics of investigation in cognitive psychology. One of the more prominent theories of attention is perceptual load theory, which suggests that the efficiency of selective attention is dependent on both perceptual and cognitive load. It is now more than 20 years since the proposal of load theory, and it is a good time to evaluate the evidence in support of this influential model. The present article supplements and extends previous reviews (Lavie, Trends in Cognitive Sciences, 9, 75-82. doi: 10.1016/j.tics.2004.12.004 , 2005, Current Directions in Psychological Science, 19, 143-148. doi: 10.1177/0963721410370295 , 2010) by examining more recent research in what appears to be a rapidly expanding area. The article comprises five parts, examining (1) evidence for the effects of perceptual load on attention, (2) cognitive load, (3) individual differences under load, (4) alternative theories and criticisms, and (5) the future of load theory. We argue that the key next step for load theory will be the application of the model to real-world tasks. The potential benefits of applied attention research are numerous, and there is tentative evidence that applied research would provide strong support for the theory itself, as well as real-world benefits related to activities in which attention is crucial, such as driving and education.
N250r and N400 ERP correlates of immediate famous face repetition are independent of perceptual load,
It is a matter of considerable debate whether attention to initial stimulus presentations is required for repetition-related neural modulations to occur. Recently, it has been assumed that faces are particularly hard to ignore, and can capture attention in a reflexive manner. In line with this idea, electrophysiological evidence for long-term repetition effects of unattended famous faces has been reported. The present study investigated influences of attention to prime faces on short-term repetition effects in event-related potentials (ERPs). We manipulated attention to short (20002ms) prime presentations (S1) of task-irrelevant famous faces according to Lavie's Perceptual Load Theory. Participants attended to letter strings superimposed on face images, and identified target letters “X” vs. “N” embedded in strings of either 6 different (high load) or 6 identical (low load) letters. Letter identification was followed by probe presentations (S2), which were either repetitions of S1 faces, new famous faces, or infrequent butterflies, to which participants responded. Our ERP data revealed repetition effects in terms of an N250r at occipito-temporal regions, suggesting priming of face identification processes, and in terms of an N400 at the vertex, suggesting semantic priming. Crucially, the magnitude of these effects was unaffected by perceptual load at S1 presentation. This indicates that task-irrelevant face processing is remarkably preserved even in a demanding letter detection task, supporting recent notions of face-specific attentional resources.
How attentional systems process conflicting cues: The superiority of social over symbolic orienting revisited,
Abstract We investigated orienting of attention by social and symbolic cues presented inside/outside the locus of attention. Participants responded to laterally presented targets preceded by simultaneously presented gaze and arrow cues. Participants' attention was allocated to either of the cues and the other cue served as a distractor. In Experiments 1-4 nonpredictive cues were employed. The validity of the attended cue and distractor were varied orthogonally. Valid cues and distractors produced additive facilitation to reaction times when compared to invalid cues and distractors. The effects of gaze and arrow distractors were similar. When the cue was 100% valid and the distractor 50% valid (Experiment 5), distractor validity had no effect on reaction times. When realistic gaze and arrow cues were employed (Experiment 6), arrow but not gaze distractors influenced the reaction times. The results suggest that social and symbolic directional information can be integrated for attention orienting. The processing of social and symbolic directional information can be modulated by top-down control, but the efficiency of the control depends on the visual saliency of the cues.
Is attention necessary for perceiving gaze direction? It depends on how you look at it: Evidence from the locus-of-slack method,
Several researchers have studied how we process and perceive gaze direction. However, it is still unclear at which perceptual stage of gaze processing (encoding or/and categorization), attention is required to judge gaze direction. We report a study in which we manipulated the difficulty of gaze perceptual judgements (easy vs. difficult) and used the locus-of-slack method to test the role of different types of attention (spatial and central) in the encoding and categorization of gaze direction. In Experiment 1 we used the spatial cueing paradigm to investigate if gaze direction judgements can be carried out while spatial attention is diverted. In Experiment 2 we used the psychological refractory period (PRP) paradigm to determine whether judgement of gaze direction involves central attention processes. The findings demonstrate that gaze judgements require input attention (both for the encoding and categorization stage) but not central attention. The implications of the results are discussed.
Event related potentials reveal that increasing perceptual load leads to increased responses for target stimuli and decreased responses for irrelevant stimuli,
Lavie (1995) have suggested that perceptual processing is influenced by perceptual load. Specifically, relevant information receives additional processing in high load situations exhausting the available capacity. On the other hand, irrelevant information receives less processing with increasing load on a relevant task, as there is a reduced amount of residual processing available. Rees et al. (1997) provided the first physiological evidence for this model, showing this pattern in a functional magnetic resonance imaging study. Likewise, Handy et al. (2001) offered supporting evidence measuring event related potentials (ERPs). Both of these studies presented irrelevant information in peripheral vision. Here we manipulated load while using the identical stimuli and the same task (a peripheral gap judgment task) with centrally presented irrelevant stimuli. ERPs show the pattern predicted by Lavie and colleagues, specifically for the N1 component. This work offers further evidence that visual attention modulates relatively early processing of perceptual information. Specifically, increasing load resulted in stronger N1 responses to relevant information and weaker N1 responses to irrelevant information.
Making eye contact without awareness,
Direct gaze is a potent non-verbal signal that establishes a communicative connection between two individuals, setting the course for further interactions. Although consciously perceived faces with direct gaze have been shown to capture attention, it is unknown whether an attentional preference for these socially meaningful stimuli exists even in the absence of awareness. In two experiments, we recorded participants’ eye movements while they were exposed to faces with direct and averted gaze rendered invisible by interocular suppression. Participants’ inability to correctly guess the occurrence of the faces in a manual forced-choice task demonstrated complete unawareness of the faces. However, eye movements were preferentially directed towards faces with direct compared to averted gaze, indicating a specific sensitivity to others’ gaze directions even without awareness. This oculomotor preference suggests that a rapid and automatic establishment of mutual eye contact constitutes a biological advantage, which could be mediated by fast subcortical pathways in the human brain.
Neural mechanisms underlying conscious and unconscious attentional shifts triggered by eye gaze,
Behavioral studies have shown that eye gaze triggers attentional shifts both with and without conscious awareness. However, the neural substrates of conscious and unconscious attentional shifts triggered by eye gaze remain unclear. To investigate this issue, we measured brain activity using event-related functional magnetic resonance imaging while participants observed averted or straight eye-gaze cues presented supraliminally or subliminally in the central visual field and then localized a subsequent target in the peripheral visual field. Reaction times for localizing the targets were shorter under both supraliminal and subliminal conditions when eye-gaze cues were directionally congruent with the target locations than when they were directionally neutral. Conjunction analyses revealed that a bilateral cortical network, including the middle temporal gyri, inferior parietal lobules, anterior cingulate cortices, and superior and middle frontal gyri, was activated more in response to averted eyes than to straight eyes under both supraliminal and subliminal conditions. Interaction analyses revealed that the right inferior parietal lobule was specifically active when participants viewed averted eyes relative to straight eyes under the supraliminal condition; the bilateral subcortical regions, including the superior colliculus and amygdala, and the middle temporal and inferior frontal gyri in the right hemisphere were activated in response to averted versus straight eyes under the subliminal condition. These results suggest commonalities and differences in the neural mechanisms underlying conscious and unconscious attentional shifts triggered by eye gaze.
Attentional shift by gaze is triggered without awareness,
Reflexive attentional shift in response to another individual’s gaze direction has been reported, but it remains unknown whether this process can occur subliminally. We investigated this issue using facial stimuli consisting of drawings (Experiment 1) and photographs (Experiment 2). The gaze direction was expressed by the eye gaze direction (Experiment 1), and the eye gaze and head direction (Experiment 2). The gaze cue was presented either supraliminally or subliminally in the center of the visual field, before target presentation in the periphery. The task for participants was to localize the target as soon as possible. The reaction time needed to localize the target was consistently shorter for valid than invalid gaze cues for both types of gaze cues in both subliminal and supraliminal conditions. These findings indicate that attentional shift can be triggered even without awareness in response to another individual’s eye gaze or head direction.
The eye contact effect: Mechanisms and development,
Abstract The 'eye contact effect' is the phenomenon that perceived eye contact with another human face modulates certain aspects of the concurrent and/or immediately following cognitive processing. In addition, functional imaging studies in adults have revealed that eye contact can modulate activity in structures in the social brain network, and developmental studies show evidence for preferential orienting towards, and processing of, faces with direct gaze from early in life. We review different theories of the eye contact effect and advance a 'fast-track modulator' model. Specifically, we hypothesize that perceived eye contact is initially detected by a subcortical route, which then modulates the activation of the social brain as it processes the accompanying detailed sensory information.
Following gaze: Gaze-following behavior as a window into social cognition,
In general, individuals look where they attend and next intend to act. Many animals, including our own species, use observed gaze as a deictic (“pointing”) cue to guide behavior. Among humans, these responses are reflexive and pervasive: they arise within a fraction of a second, act independently of task relevance, and appear to undergird our initial development of language and theory of mind. Human and nonhuman animals appear to share basic gaze-following behaviors, suggesting the foundations of human social cognition may also be present in nonhuman brains.
Amygdala damage impairs eye contact during conversations with real people,
The role of the human amygdala in real social interactions remains essentially unknown, although studies in nonhuman primates and studies using photographs and video in humans have shown it to be critical for emotional processing and suggest its importance for social cognition. We show here that complete amygdala lesions result in a severe reduction in direct eye contact during conversations with real people, together with an abnormal increase in gaze to the mouth. These novel findings from real social interactions are consistent with an hypothesized role for the amygdala in autism and the approach taken here opens up new directions for quantifying social behavior in humans.
Eye gaze adaptation under interocular suppression,
The perception of eye gaze is central to social interaction in that it provides information about another person's goals, intentions, and focus of attention. Direction of gaze has been found to reflexively shift the observer's attention in the corresponding direction, and prolonged exposure to averted eye gaze adapts the visual system, biasing perception of subsequent gaze in the direction opposite to the adapting face. Here, we tested the role of conscious awareness in coding eye gaze directions. To this end, we measured aftereffects induced by adapting faces with different eye gaze directions that were presented during continuous flash suppression, a potent interocular suppression technique. In some trials the adapting face was rendered fully invisible, whereas in others it became partially visible. In Experiment 1, the adapting and test faces were presented in identical sizes and to the same eye. Even fully invisible faces were capable of inducing significant eye gaze aftereffects, although these were smaller than aftereffects from partially visible faces. When the adapting and test faces were shown to different eyes in Experiment 2, significant eye gaze aftereffects were still observed for the fully invisible faces, thus showing interocular transfer. Experiment 3 disrupted the spatial correspondence between adapting and test faces by introducing a size change. Under these conditions, aftereffects were restricted to partially visible adapting faces. These results were replicated in Experiment 4 using a blocked adaptation design. Together, these findings indicate that size-dependent low-level components of eye gaze can be represented without awareness, whereas object-centered higher-level representations of eye gaze directions depend on visual awareness.
Eye contact facilitates awareness of faces during interocular suppression,
Eye contact captures attention and receives prioritized visual processing. Here we asked whether eye contact might be processed outside conscious awareness. Faces with direct and averted gaze were rendered invisible using interocular suppression. In two experiments we found that faces with direct gaze overcame such suppression more rapidly than faces with averted gaze. Control experiments ruled out the influence of low-level stimulus differences and differential response criteria. These results indicate an enhanced unconscious representation of direct gaze, enabling the automatic and rapid detection of other individuals making eye contact with the observer.
Seeing other minds: Attributed mental states influence perception,
The detection of gaze direction: A stare-in-the-crown effect,
Abstract A visual-search paradigm was used to explore the relative ease with which the direction of gaze can be detected. Straight-gaze stimuli were presented as targets within a variable number of distractors with left-averted or right-averted gaze. Reaction time in this case was compared with that when either the left-averted or right-averted gaze stimuli were the targets among distractors of the two remaining gaze directions. The data were examined for the existence of a search asymmetry favoring the straight-gaze targets. Such an asymmetry was found with stimuli that were realistically drawn renditions of pairs of human eyes, as well as with similar schematic stimuli representing pairs of human eyes. The asymmetry, however, was not found with geometric control stimuli, which also presented the critical feature in the central, the left-lateral, or the right-lateral position within the stimulus, but were not eyelike. It was also not found for schematic stimuli consisting of only one eye. It was concluded that the straight gaze direction is a special stimulus with eyelike stimuli, which the visual system is set up to process faster and with fewer errors than averted gaze directions. The results are discussed in terms of the evolutionary significance of the straight gaze direction.
Gaze-induced joint attention persists under high perceptual load and does not depend on awareness,
The automaticity of gaze-induced joint attention is well known in relatively easy cognitive tasks; but its role in harder tasks had never been examined. This encouraged us to study automaticity in hard tasks, tasks presenting the subjects with high perceptual loads. The Rapid Serial Visual Presentation (RSVP) paradigm was used to present participants with two streams of bilaterally displayed digit-flows while they fixated at the center of a synthetic representation of a human face. The face was presented both above (Experiments 1 and 2) and below (Experiment 3) the face’s visual threshold (henceforth called “supraliminal” and “subliminal”, respectively). Interocular suppression was used to make the face stimulus invisible (subliminal). In the critical trials of all three experiments, the gaze direction shown on the face was randomly diverted to either the left or to the right. This directed the participant’s gaze either towards or away from the location of a target in the RSVP. The perceptual load was always relatively high. It was either set (Experiments 1 and 3) or manipulated (Experiment 2) during the experiment. In all three experiments, an appreciably higher and significant level of target detection was found when an uninformative gaze-cue was congruent with the location of the target. This result, which had only been reported with relatively easy tasks previously, is called the “gaze-cueing effect”. Our novel findings include showing that: (i) the attentional effect of gaze persists under high perceptual loads, and (ii) awareness of the gaze stimuli is not required to obtain the gaze-cueing effect. They also serve to validate prior support for an important role of automaticity in gaze-induced joint attention.
Degraded stimulus visibility and the effects of perceptual load on distractor interference,
In this study we examined whether effects of perceptual load on the attentional selectivity are modulated by degradation of the visual input. According to the perceptual load theory, increasing task difficulty via degradation of stimulus visibility should not alter the typical effect of perceptual load. In previous studies only the target was degraded, resulting in increased distractor saliency. Here we combined manipulation of perceptual load with a more systematic degradation of visual information. Experiment 1 included five conditions. Three conditions involved low perceptual load + contrast reduction of: (A) only the target; (B) only the distractor; (C) both target and distractor. The other two conditions included non-degraded stimuli with low or high perceptual load. In Experiment 2 visibility degradation was established via manipulation of exposure duration. It included two exposure durations 100 and 150 ms or each load level (low vs. high). The results of both experiments demonstrated reliable distractor interference of a similar magnitude with both degraded and non-degraded stimuli. This finding suggests that task difficulty, when manipulated via degradation of stimulus visibility, does not play a critical role in determining the efficiency of the attentional selectivity. However, contrary to the predictions of the perceptual load theory, in both experiments distractor interference emerged under the high load condition. In Experiment 2 the high-load interference was of the same magnitude as that of the low load condition. This high-load interference is not due to the presence of a mask (Experiment 3) or a mixed design (Experiment 4). These findings suggest that perceptual load may also play a lesser role in attentional selectivity than that assigned to it by the perceptual load theory.
Unconscious processing of direct gaze: Evidence from an ERP study,
Humans detect faces with direct gaze more rapidly than they do faces with averted gaze. Evidence suggests that the visual information of faces with direct gaze reaches conscious awareness faster than that of faces with averted gaze. This suggests that faces with direct gaze are effectively processed in the brain before they reach conscious awareness; however, it is unclear how the unconscious perception of faces with direct gaze is processed in the brain. To address this unanswered question, we recorded event-related potentials while observers viewed faces with direct or averted gaze that were either visible or rendered invisible during continuous flash suppression. We observed that invisible faces with direct gaze elicited significantly larger negative deflections than did invisible faces with averted gaze at 200, 250, and 350 ms over the parietofrontal electrodes, whereas we did not observe such effects when facial images were visible. Our results suggest that the visual information of faces with direct gaze is preferentially processed in the brain when they are presented unconsciously.
Perception of direct gaze does not require focus of attention,
Previous research using averted (e.g., leftward or rightward) gaze indicates that gaze perception requires a focus of attention. However, direct gaze, compared with averted gaze, is processed in the brain preferentially and enhances cognitive functions. Thus, it is necessary to use direct gaze to investigate whether gaze perception is possible without focused attention. We conducted a dual-task paradigm in which attention was drawn away from gaze. Results showed performance on gaze-direction discrimination (direct vs. averted gaze) in the dual-task condition was only slightly lower than in the single-task condition; participants were able to discriminate direct from averted gaze without focusing their attention in a similar manner to when they did focus their attention. In contrast, when participants discriminated between averted gazes (leftward and rightward), performance dropped to near-chance levels. It was concluded that gaze perception does not require a focus of attention for direct gaze.
The impact of supra- and sub-liminal facial expressions on the gaze-cueing effect
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