Human motor and economic decisions show common risk-seeking bias under asymmetric gains

Abstract To plan actions optimally, it is essential to take one’s own variability into account. The outcome of an action is determined by the target of the action plan, the variability of the action, and the gain/loss function of the outcome. In previous studies, we demonstrated that humans make risk-seeking, suboptimal motor decisions under gain functions characterized by an asymmetry, where higher gains are associated with a higher risk of zero gain. However, it remained unclear whether such suboptimal and risk-seeking behavior stems from the motor decision-making process. Here, we examined whether this bias also arises in economic decision-making which does not include a motor variance component. In Experiment 1, we investigated the response distribution in an experiment where participants pressed a key within a specified time window to earn points based on their reaction time, using a gain function characterized by the asymmetry. Consistent with previous studies, we observed risk-seeking, suboptimal decision-making in this motor task. In Experiment 2, using the same gain function, participants made a numerical selection, with the chosen number serving as the mean from which values were sampled from a normal distribution with variance similar to that in the motor task. As in Experiment 1, we observed risk-seeking, suboptimal decision-making in this economic task. Trial-by-trial analyses revealed that the compensation strategies depending on error size were similar, but a task-dependent difference emerged when the error size was large. These results indicate a robust bias in both motor and economic decision-making under gain functions with asymmetry, highlighting that optimality in human decision-making under risk is limited.