Preferential looking studies of trustworthiness detection confound structural and expressive cues to facial trustworthiness

On encountering a stranger, we spontaneously attribute to them character traits (e.g., trustworthiness, intelligence) based on their facial appearance. Participants can base impressions on structural face cues—the stable aspects of facial appearance that support identity recognition–or expression cues, such as the presence of a smile. It has been reported that 6- to 8-month-old infants attend to faces that adults judge to be trustworthy in preference to faces judged untrustworthy. These results are striking because the face stimuli employed were ostensibly emotion neutral. Consequently, these preferential looking effects have been taken as evidence for innate sensitivity to structural face cues to trustworthiness. However, scrutiny of the emotion rating procedure used with adults suggests that the face stimuli employed may have been judged emotion neutral only when interleaved with more obvious examples of facial affect. This means that the faces may vary in emotional expression when compared to each other. Here, we report new evidence obtained from adult raters that the stimuli used in these studies confound trustworthiness and untrustworthiness with the presence of happiness and anger, respectively. These findings suggest that the preferential looking effects described in infants are compatible with a preference for positive facial affect and may not reflect early sensitivity to structural face cues to trustworthiness.