From trust in groups to trust individuals

Trust is central to social behaviour. When deciding to trust individualsmust arbitrate between group-based information as well asdirect information about the person they are interacting with. Here weinvestigated how trust in groups is learned and transferred to individualsusing a two-stage experiment where participants interacted withrandomly selected members of two arbitrary groups and learnt theirrelative trustworthiness. Next, they interacted with four novel individualsfrom these two groups. Two members, one from each group, actedcongruently with their group’s previous behaviour while the other twoacted incongruently. We found that while participants quickly learnedgroup characteristics they quickly abandoned these when facing individuals.Nevertheless, some bad impressions lingered in attitudes. Weexplained participants’ behaviour using reinforcement learning modelsand showing how a mix of decision biases, asymmetric learning ratesand forgetting help explain trial-by-trial variation in decisions. Weadditionally explored how variations in attention shift trust decisions,based on expectations of partners’ responses. Pro-social tendenciesand individuating information can overcome knowledge about groupbelonging.