People evaluate a stranger’s trustworthiness from their facial features in a fraction of a second, despite common advice “not to judge a book by its cover.” Evaluations of trustworthiness have critical and widespread social impact, predicting financial lending, mate selection, and even criminal justice outcomes. Consequently, understanding how people perceive trustworthiness from faces has been a major focus of scientific inquiry, and detailed models explain how consensus impressions of trustworthiness are driven by facial attributes. However, facial impression models do not consider variation between observers. Here, we develop a sensitive test of trustworthiness evaluation and use it to document substantial, stable individual differences in trustworthiness impressions. Via a twin study, we show that these individual differences are largely shaped by variation in personal experience, rather than genes or shared environments. Finally, using multivariate twin modeling, we show that variation in trustworthiness evaluation is specific, dissociating from other key facial evaluations of dominance and attractiveness. Our finding that variation in facial trustworthiness evaluation is driven mostly by personal experience represents a rare example of a core social perceptual capacity being predominantly shaped by a person’s unique environment. Notably, it stands in sharp contrast to variation in facial recognition ability, which is driven mostly by genes. Our study provides insights into the development of the social brain, offers a different perspective on disagreement in trust in wider society, and motivates new research into the origins and potential malleability of face evaluation, a critical aspect of human social cognition.

Despite warnings not to "judge a book by its cover", people rapidly form facial impressions. In Oosterhof and Todorov's (2008) two-dimensional model of facial impressions, trustworthiness and dominance underlie impressions and primarily function to signal the potential threat of others. Here, we test a key assumption of these models, namely that these dimensions are functional, by evaluating whether the adult-face dimensions apply to young children's faces. Although it may be functional for adults to judge adult faces on dimensions that signal threat, adults associate different social goals with children, and these goals are likely to impact the impressions adults make of such faces. Thus, a functional approach would predict that the dimensions for children's faces are not threat focused. In Studies 1-2, we build a data-driven model of Caucasian adults' impressions of Caucasian children's faces, finding evidence for two dimensions. The first dimension, niceness, is similar (although not identical) to the adult dimension of trustworthiness. However, we find a second dimension, shyness, that is clearly dissociable from dominance (Study 3), and critically, is not focused on threat. We demonstrate that adults are sensitive to subtle facial manipulations of these dimensions (Studies 4-5) and that these impressions impact adults' behavioral expectations of children (Study 6). Finally, we show that niceness and shyness dimensions generalize to an independent sample of ambient images, demonstrating their robustness (Study 7). Our results suggest that social goals have the power to drive functional impressions and highlight the flexibility of our visual system when forming such inferences.

Lay wisdom warns against “judging a book by its cover.” However, facial first impressions influence people’s behaviour towards others, so it is critical that we understand whether these impressions are at all accurate. Understanding impressions of children’s faces is particularly important because these impressions can have social consequences during a crucial time of development. Here, we examined the accuracy of two traits that capture the most variance in impressions of children’s faces, niceness and shyness. We collected face images and parental reports of actual niceness/shyness for 86 children (4–11 years old). Different images of the same person can lead to different impressions, and so we employed a novel approach by obtaining impressions from five images of each child. These images were ambient, representing the natural variability in faces. Adult strangers rated the faces for niceness (Study 1) or shyness (Study 2). Niceness impressions were modestly accurate for different images of the same child, regardless of whether these images were presented individually or simultaneously as a group. Shyness impressions were not accurate, for images presented either individually or as a group. Together, these results demonstrate modest accuracy in adults’ impressions of niceness, but not shyness, from children’s faces. Furthermore, our results reveal that this accuracy can be captured by images which contain natural face variability, and holds across different images of the same child’s face. These results invite future research into the cues and causal mechanisms underlying this link between facial impressions of niceness and nice behaviour in children.

The well-known other-race effect in face recognition has been widely studied, both for its theoretical insights into the nature of face expertise and because of its social and forensic importance. Here we demonstrate an other-race effect for the perception of a simple visual signal provided by the eyes, namely gaze direction. In Study 1, Caucasian and Asian participants living in Australia both showed greater perceptual sensitivity to detect direct gaze in own-race than other-race faces. In Study 2, Asian (Chinese) participants living in Australia and Asian (Chinese) participants living in Hong Kong both showed this other-race effect, but Caucasian participants did not. Despite this inconsistency, meta-analysis revealed a significant other-race effect when results for all 5 participant groups from corresponding conditions in the 2 studies were combined. These results demonstrate a new other-race effect for the perception of the simple, but socially potent, cue of direct gaze. When identical morphed-race eyes were inserted into the faces, removing race-specific eye cues, no other-race effect was found (with 1 exception). Thus, the balance of evidence implicated perceptual expertise, rather than social motivation, in the other-race effect for detecting direct gaze. (PsycINFO Database Record