I judge you by your profit: Judgments of effort exerted by self and others are influenced by received rewards

Effort constitutes a major part of cost-benefit calculations underlying decision making. Therefore, estimating the effort someone has spent on a task is a core dimension for evaluating own and others’ actions. It has been previously shown that self-judgments of effort are influenced by the magnitude of obtained rewards. It is unclear, however, whether the influence of reward on effort estimations is limited to self-judgments or whether reward incorporation represents a general computational principle when judging effort. Here we show that people also integrate reward magnitude when judging the effort exerted by others. Participants (N=48) performed an effortful sensorimotor task interleaved with a partner, while rating either their own or the other person’s effort. After each trial but before the effort rating, both participants were informed about the obtained reward. We found that higher rewards led to higher estimations of exerted effort, in self-as well as other-judgments, and this effect was more pronounced for other-judgments. In both types of judgment, computational modelling revealed that reward information and the perceived level of exertion were combined in a Bayes optimal manner to form effort estimates. Remarkably, the extent to which rewards influenced effort judgments was positively correlated with conservative world-views, indicating that the basic computations underlying this behavioural phenomenon might be related to more general beliefs about the association between effort and reward in the society. The integration of reward information into retrospective effort judgments underscores the convergence of multiple information sources that supports adaptive learning and decision making in social contexts.