Dissociating the impact of movement time and energy costs on decision-making and action initiation in humans

Abstract

Recent theories and data suggest that adapted behavior involves economic computations during which multiple trade-offs between reward value, accuracy requirement, energy expenditure and elapsing time are solved so as to obtain rewards as soon as possible while spending the least possible amount of energy. However, the relative impact of movement energy and duration costs on perceptual decision-making and movement initiation is poorly understood. Here, we tested 31 healthy subjects on a perceptual decision-making task in which they executed reaching movements to report probabilistic choices. In three distinct blocks of trials, the reaching time and energy costs were independently varied while decision difficulty was maintained similar at the block level. Participants also performed a fully instructed delayed-reaching (DR) task in each motor condition. Results in that DR task show that time-consuming movements extended reaction times (RTs) in most subjects, whereas energy-consuming movements led to mixed effects on RTs. In the choice task, about half of the subjects decreased their decision durations (DDs) in the time consuming condition, while the impact of energy costs on DDs were again mixed across subjects. Decision accuracy was overall similar across motor conditions. These results indicate that movement duration and, to a lesser extent, energy expenditure, idiosyncratically affect perceptual decision-making and action initiation. We propose that subjects who shortened their decisions in the time consuming condition of the choice task did so to limit a drop of their rate of reward.