Outgroup members are often perceived as threating and untrustworthy, and this is particularly true for judgments of outgroup males. As race influences perceptions of group membership, male racial outgroup faces (MROFs) are judged as less trustworthy than male racial ingroup faces (MRIFs). Neurologically, this effect is mediated by amygdala activation, a brain region central to the processing of fear-related stimuli, threat detection, vigilance regulation and facial trustworthiness. As acute stress up regulates amygdala activity and promotes hyper-vigilance towards threatening stimuli, we hypothesised that acute stress would result in increased vigilance and lower trustworthiness judgements towards MROFs. In contrast, we expected that stress would have no effect on MRIFs. Using a within-subjects design, White-Dutch male participants rated the perceived trustworthiness of White males (ingroup) and Arab males (outgroup) under stress and during the absence of stress (baseline). Stress significantly reduced trust towards racial outgroup members, whilst trust towards racial ingroup members was maintained. Understanding the mechanisms by which stress differentially affects social behaviors towards outgroups is of theoretical and practical relevance to our understanding of the biological basis of ethnocentrism and xenophobia.
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