The social cost of gathering information for trust decisions.

Trust decisions are inherently uncertain, as people usually have incomplete information about the trustworthiness of the other person prior to their decision to trust or not trust. Therefore, it is typically beneficial to gather information about a trustee's past behaviour before deciding whether or not to trust them. However, elaborate inquiries about a trustee's behaviour may change the trustee's willingness to reciprocate, causing either a decrease due to the trustee's negative impressions of the investor or an increase because the investor appears to be highly betrayal-averse to the trustee. In turn, such a change could cause the investor to gather less or more information, respectively. Here, we examine how information acquisition is modulated by social context, monetary cost, and the trustee's trustworthiness. We gave participants the opportunity to sequentially sample information about a trustee's reciprocation history before they decided whether or not to invest. Participants sampled less when there was a monetary cost and when the gathered information was more conclusive. On some trials, we induced a social context by telling the participant that the trustee would learn how much the participant sampled ("overt sampling"). Crucially, when sampling was free, participants sampled less when sampling was overt than when it was covert, suggesting that they avoided leaving negative impressions. We find that the data were well accounted for by a Bayesian heuristic model, in which the agent continues sampling until uncertainty about trustworthiness-as measured by the width of the posterior belief-drops below a level that they find tolerable. This study opens the door to broader applications of the tools and models of information sampling to social decision-making.