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Abstract
Social interactions require quick perception, interpretation, and categorization of faces, with facial features offering cues to emotions, intentions, and traits. Importantly, reactions to faces depend not only on their features but also on their processing fluency, with disfluent faces suffering social devaluation. The current research used electrophysiological (EEG) and behavioral measures to explore at what processing stage and under what conditions emotional ambiguity is detected in the brain and how it influences trustworthiness judgments. Participants viewed male and female faces ranging from pure anger, through mixed expressions, to pure happiness. They categorized each face along the experimental dimension (happy vs. angry) or a control dimension (gender). In the emotion-categorization condition, mixed (ambiguous) expressions were classified relatively slower, and their trustworthiness was rated relatively lower. EEG analyses revealed that early brain responses are independent of the categorization condition, with pure faces evoking larger P1/N1 responses than mixed expressions. Some late (728- 880 ms) brain responses from central-parietal sites also were independent of the categorization condition and presumably reflect familiarity of the emotion categories, with pure expressions evoking larger central-parietal LPP amplitude than mixed expressions. Interestingly, other late responses were sensitive to both expressive features and categorization task, with ambiguous faces evoking a larger LPP amplitude in frontal-medial sites around 560-660 ms but only in the emotion categorization task. Critically, these late responses from the frontal-medial cluster correlated with the reduction in trustworthiness judgments. Overall, the results suggest that ambiguity detection involves late, top-down processes and that it influences important social impressions.
Keywords Processing fluency . Trustworthiness . EEG/ERP . Face processing
Introduction
Social interactions often require quick perception, interpretation, and categorization of faces (Todorov, 2017). Facial features offer cues to a target's emotional states, personality, and behavioral intentions, as documented by decades of work on facial displays (Knutson, 1996; Russel, Bachorowski, & Fernadez-Doz, 2003). Facial features also allow people to form rapid judgments about important social traits, including trustworthiness-a major element in relationships, trade, and politics (Rezlescu, Duchaine, Olivola, & Chater, 2012; Todorov, Pakrashi, & Oosterhof, 2009; Wojciszke, Bazinska, & Jaworski, 1998). Interestingly, the processes involved in emotion perception and impression formation seem tightly intertwined (Ambady & Skowronski, 2008). For example, people judge a face as more trustworthy when it has features resembling smiles...