The extent to which the six basic human facial expressions perceptually differ from one another remains controversial. For instance, despite the importance of rapidly decoding fearful faces, this expression often is confused with other expressions, such as Surprise in explicit behavioral categorization tasks. We quantified implicit visual discrimination among rapidly presented facial expressions with an oddball periodic visual stimulation approach combined with electroencephalography (EEG), testing for the relationship with behavioral explicit measures of facial emotion discrimination. We report robust facial expression discrimination responses bilaterally over the occipito-temporal cortex for each pairwise expression change. While fearful faces presented as repeated stimuli led to the smallest deviant responses from all other basic expressions, deviant fearful faces were well discriminated overall and to a larger extent than expressions of Sadness and Anger. Expressions of Happiness did not differ quantitatively as much in EEG as for behavioral subjective judgments, suggesting that the clear dissociation between happy and other expressions, typically observed in behavioral studies, reflects higher-order processes. However, this expression differed from all others in terms of scalp topography, pointing to a qualitative rather than quantitative difference. Despite this difference, overall, we report for the first time a tight relationship of the similarity matrices across facial expressions obtained for implicit EEG responses and behavioral explicit measures collected under the same temporal constraints, paving the way for new approaches of understanding facial expression discrimination in developmental, intercultural, and clinical populations.

六种基本人类面部表情在感知上的差异程度仍然存在争议。例如，尽管快速解码可怕的面孔很重要，但这种表达经常与其他表达相混淆，例如显式行为分类任务中的惊喜。我们使用古怪的周期性视觉刺激方法结合脑电图 (EEG) 来量化快速呈现的面部表情之间的隐性视觉辨别力，测试与面部情绪辨别的行为外显测量的关系。对于每个成对的表情变化，我们在枕颞皮层双边报告了强大的面部表情辨别反应。虽然作为重复刺激呈现的恐惧面孔导致所有其他基本表情的最小异常反应，离经叛道的可怕面孔在整体上得到了很好的区分，而且在更大程度上比悲伤和愤怒的表情更容易区分。在脑电图中，幸福的表达在数量上没有行为主观判断那么大，这表明幸福和其他表达之间的明显分离，通常在行为研究中观察到，反映了高阶过程。然而，这种表达在头皮地形方面与所有其他表达不同，表明存在定性而不是定量的差异。尽管存在这种差异，总体而言，我们首次报告了在相同时间约束下收集的隐式 EEG 响应和行为显式测量所获得的面部表情之间的相似性矩阵的紧密关系，