Readout of confidence from kinematics shapes collective decision-making

A central challenge in decision-making is deciding when to trust one’s own judgement and when to rely on others. Because subjective confidence correlates with objective accuracy, a sensible strategy is to follow the choice made with higher confidence. Crucially, however, this strategy depends on accessing others’ confidence. Here, we show that humans spontaneously ‘read out’ confidence from others’ movements and use this information to guide collective decisions. Dyads performed a collective perceptual decision-making task. In each trial, one participant—the arbitrator—first made an individual decision by reaching toward one of two targets, then observed their partner doing the same, and finally made the collective decision on behalf of the dyad, confirming or revising their initial choice. When own confidence was low or high, arbitrators relied on simple heuristics—revising their choice when uncertain and confirming it when certain. At intermediate confidence levels, however, they extracted confidence from their partner's movement kinematics to guide revision. Computational simulations demonstrated that integrating the partner’s encoded confidence improved collective accuracy. Our findings highlight the importance of bodily motion for the social transmission of confidence information in collective decision-making.