Social group identity plays a central role in political polarization and inter-party conflict. Here, we use ambiguously valenced faces to measure bias in the processing of political ingroup and outgroup faces, while also accounting for inter-party differences in judgments of emotion at baseline. Participants identifying as Democrats and Republicans judged happy, angry, and surprised faces as positive or negative. Whereas happy and angry faces convey positive and negative valence respectively, surprised faces are ambiguous in that they readily convey positive and negative valence. Thus, surprise is a useful tool for characterizing valence bias (i.e., the tendency to judge ambiguous stimuli as negative). Face stimuli were assigned to the participants' political ingroup or outgroup, or a third group with an unspecified affiliation (baseline). We found a significant interaction of facial expression and group membership, such that outgroup faces were judged more negatively than ingroup and baseline, but only for surprise. There was also an interaction of facial expression and political affiliation, with Republicans judging surprise more negatively than Democrats across all group conditions. However, we did not find evidence for party differences in outgroup negativity. Our findings demonstrate the utility of judgments of surprised faces as a measure of intergroup bias, and reinforce the importance of outgroup negativity (relative to ingroup positivity) for explaining inter-party biases.

社会群体认同在政治两极分化和党际冲突中起着核心作用。在这里，我们使用模棱两可的效价面孔来衡量处理政治内群体和外群体面孔的偏见，同时还考虑了基线情绪判断中的政党间差异。被认定为民主党人和共和党人的参与者将快乐、愤怒和惊讶的面孔判断为正面或负面。快乐和愤怒的面孔分别传达正面和负面的效价，而惊讶的面孔则含糊不清，因为它们很容易传达正面和负面的信息。负价。因此，惊喜是表征价偏差的有用工具（即，将模棱两可的刺激判断为负面的倾向）。面部刺激被分配给参与者的政治内群或外群，或具有未指定隶属关系的第三组（基线）。我们发现面部表情和群体成员之间存在显着的相互作用，因此外群体的脸被判断为比内群体和基线更负面，但只是为了惊喜。面部表情和政治派别也存在相互作用，在所有群体条件下，共和党人对惊喜的判断比民主党人更负面。然而，我们没有找到证据表明党外群体消极情绪存在政党差异。我们的研究结果证明了对惊讶面孔的判断作为衡量群体间偏见的效用，