Implicit bias and electrophysiological responses to facial anomalies

Face perception is a rapid and specialized cognitive process that plays a central role in social evaluation. The process is also highly susceptible to unconscious or implicit biases. Recent research suggests the presence of an “anomalous-is-bad” stereotype (Workman et al., 2021), whereby individuals with visible facial anomalies are subject to negative implicit judgments, reduced trustworthiness ratings, and even dehumanization (Paruzel-Czachura et al., 2024, 2025). Neuroimaging studies indicate that anomalous faces engage the amygdala, a structure thought to modulate negative emotions (such as feelings of threat) and physiological arousal. However, a direct link between implicit bias and sympathetic autonomic arousal, to our knowledge has not been demonstrated, or to our knowledge, even investigated. The amygdala plays a central role in detecting socially and biologically relevant stimuli and in modulating autonomic arousal. Sympathetic arousal more broadly can be indexed through skin conductance responses (SCRs), an indirect measure of sympathetic nervous system activation (Laine et al., 2009). Although neural responses to anomalous faces have been documented, the extent to which such faces elicit physiological arousal, and how this arousal relates to implicit bias, remains underexplored. Physiological arousal is thought to enhance cognitive appraisal, thereby facilitating the formation of automatically activated attitudes. One behavioral index of such attitudes is the Implicit Association Test (IAT), which measures the strength of automatic associations between social categories and evaluative attributes. Integrating physiological and behavioral measures may therefore clarify the mechanisms underlying implicit biases toward anomalous faces. The present study investigates whether anomalous faces elicit stronger electrophysiological arousal and more negative implicit associations than typical faces, and whether the magnitude of these responses are modulated by individual differences in explicit bias, disgust sensitivity, and empathy. We test the hypothesis that negative implicit associations to anomalous faces are associated with electrophysiologic evidence of increased sympathetic responses. We expect that anomalous faces will elicit both stronger physiological arousal and more negative implicit associations relative to typical faces. Critically, we predict that these two responses will be correlated, which means individuals showing larger SCR differences to anomalous versus typical faces will also show stronger implicit bias, suggesting that arousal and implicit evaluation are linked rather than independent responses to facial anomaly. The magnitude of both implicit associations and physiological arousal to anomalous faces is expected to vary according to individual differences in disgust sensitivity, empathic concern, and explicit attitudes. Face stimuli are selected from the Face Research Lab London Set (DeBruine, Lisa; Jones, 2017). Scarred versions of faces are created using AI image-generation tools to simulate scars from facial burns. The scars are designed to appear realistic and are placed in different locations on faces (e.g., left or right cheek). Participants will complete a laboratory session with two parts. First, they will complete an Implicit Association Test (IAT), measuring automatic associations between facial categories (typical vs. anomalous faces with burns) and evaluative attributes (positive vs. negative words), using standard protocols for IAT (Greenwald et al., 1998). They will then complete questionnaires assessing explicit bias, disgust sensitivity, and empathy. Second, participants will be fitted with an EmotiBit device (Montgomery et al., 2023) that records electrodermal activity (EDA) during an oddball paradigm (150 trials: 120 typical faces as standards, 30 anomalous faces as oddballs). This two-part design allows assessment of both implicit attitudes and physiological arousal to the same stimulus categories. Primary analyses will test: (1) implicit bias via one-sample t-test of IAT D-scores against zero, (2) physiological arousal differences via linear mixed model (LMM) with condition as a fixed effect and participant as random effects, and (3) the relationship between implicit bias and physiological arousal via correlation analysis. Exploratory analyses will use multiple regression to examine whether individual differences predict bias and arousal. This study aims to fill a notable gap in linking electrophysiologic responses to negative bias and examine whether greater sympathetic nervous system responses to anomalous faces are associated with stronger negative implicit biases. We further anticipate that the strength of this relationship is shaped by individual personality differences in sensitivity to disgust and feelings of empathy.