Testing stimulus generalisation as a mechanism for impression formation

People readily judge trustworthiness based on others' facial appearance, but less is known about how our prior experiences shape who we find trustworthy. Stimulus generalisation is one mechanism which may explain how experience influences impressions of strangers. This fundamental learning principle argues that learning about one stimulus generalises to stimuli that resemble the original stimulus. Here, we asked whether stimulus generalisation, specifically, based on facial resemblance, can influence impressions of trustworthiness. We used a novel face resemblance paradigm to test whether naturally acquired attitudes held towards known individuals (celebrities) predict trustworthiness impressions of strangers' faces that were manipulated to resemble these identities. Across three studies (Total N = 283) and two countries (UK, Australia), we confirmed that pre-existing attitudes towards known individuals significantly predicted trustworthiness impressions of strangers' faces that merely resemble these individuals. Importantly, pre-existing attitudes remained significant after multi-level modelling accounted for variation in both facial appearance and participant differences. We found strong support for stimulus generalisation, demonstrating that social learning in the real world predicts individuals' impressions of trustworthiness. Therefore, impression formation involves integrating visual appearance with prior experiences to help us decide which people we trust. Our work demonstrates an important but neglected theoretical overlap between person perception, attitude formation, and learning principles.