Heavy Matters

People can reliably infer various traits, states, and group memberships from minimal cues. Despite impressive demonstrations of the breadth of social perception, however, few studies have critically examined the sensitivity and limits of social perception in specific quantitative terms. Here, we investigated the just noticeable difference for perceptions of a facial trait with profound consequences for social behavior, that is, facial attractiveness. Building on research examining facial adiposity, we determined the changes in body mass index needed to meaningfully alter perceivers’ judgments of weight and attractiveness. Although perceivers recognized differences as small as 1.33 kg/m2, changes of roughly twice that size (2.38 kg/m2 and 2.59 kg/m2 for women and men, respectively) were necessary to alter attractiveness. These findings contribute to a greater basic understanding of the precision and limits of social perception and may provide information of value to medical practitioners and individuals seeking to manage changes in weight.