Time, space and feature similarity determine attractive and repulsive serial biases in trustworthiness impressions

Facial trustworthiness impressions influence important social decisions, including economic choices, decisions to hire and criminal justice outcomes. Most research has focused on the face attributes associated with various impressions, implicitly regarding these impressions as stable over time. However, our perception is dynamically shaped by past visual experience through two opposite serial effects: negative aftereffects (bias away from the past) and serial dependence (bias towards the past). Here, we investigated how first impressions of trustworthiness are biased by our past visual experience. Specifically, we tested how basic stimulus properties such as exposure duration to previous face, feature similarity, and spatial proximity to previous faces determine the direction and strength of the biases. We found that (1) exposure duration determined the direction of the bias with negative aftereffects following prolonged adaptor exposure and (positive) serial dependence after brief adaptor exposure. Furthermore, (2) increased identity similarity between previous and current faces enhanced attractive biases, whereas different identities led to repulsion. Finally, (3) relative spatial distance in world-centre coordinates between adaptor and test faces modulated the strength of serial dependence but not negative aftereffects. Our paradigm enabled us to provide evidence for, and to dissociate, attractive and repulsive serial biases in trustworthiness impressions. Our findings demonstrate the specific conditions under which these impressions can be dynamically shaped by past experience, depending on time, space, and feature similarity. Importantly, the fact that serial effects are determined by basic stimulus properties of time, space, and feature similarity indicates that these biases cannot be entirely explained by high-level factors such as decision or memory.