Sensorimotor communication fosters trust and generosity: The role of effort and signal utility

Previous research has shown that a co-actor's willingness to bear the monetary costs of prior cooperative activities influences our cooperative behaviour towards them. But what about when such information is lacking? In addition to monetary costs, people routinely engage in joint actions in which they incur effort costs in order to help each other achieve their goals, for example by adapting their goal-directed actions in order to send informative signals. We aimed to investigate whether people act more cooperatively towards those who are willing to bear the effort costs of an interaction by adapting their movements to send informative signals. We find that the effort that a co-actor invests in order to produce informative movement adaptations increases a participant's trust towards that co-actor, and that both the effort and utility of these informative movement adaptations increase generosity towards that co-actor. This demonstrates that we may base decisions about cooperation with a person on their willingness to bear the effort costs of interaction. These findings are discussed with respect to the role that effort investment plays in sustained cooperation.