Fig. 1: Experimental design and model space.

a, Participants were entered into a double-blind, placebo-controlled, within-subject experimental design. ECG, electrocardiogram. b, Participants engaged in a three-partner version of the sharing game (inset). Here, partners were assigned the role of Dictator and, on each trial, could either take £0.10 for themselves (unfair outcome), or take £0.05 and give the participant £0.05 (fair outcome). Participant reported two types of attributional intent concerning the motivations of the partner after each outcome. These included harmful intent attributions and self-interest attributions. Partner order was randomized, and partner change was signalled. c, Model space used to test whether dopamine manipulations were best explained by the full model (M1), a model that constrained policy updating to a single sensitivity parameter for each attribution (M2), or a model that constrained prior uncertainty to a single parameter (M3; Table 1). Although filled objects are free parameters. Grey shaded objects are probability distributions.