The number of chances affects motor decision-making under risk

We execute scoring movements by taking the uncertainty of motor outcomes into account for maximization of reward rates. In many sports, the winning point could be determined by proximity to high gain or failure, and in such situations, the preference for high gain is evident. However, findings were constrained when individuals planned a movement to increase the average reward over a large number of trials under the same conditions. Here, we examined the effects of the number of chances, one of the essential contexts for decision-making, on the planning of aiming points. The results showed that when there was only one chance in a set, aiming points were more conservative than when there were more chances (5, 10, or 15). We proposed a risk-sensitive decision model that accounts for the modulation in aiming points, depending on the number of chances. Fitting the model to participants' observed data showed that participants tended to be risk-averse and to underestimate their motor variability in general. The current study provides behavioral and computational evidence that number of chances is one of the variables to account for in motor variability.