Decision urgency invigorates movement in humans

Recent work in highly trained monkeys suggests that decision-making and motor control are linked processes whose regulation by urgency allows reward rate optimization. However, such urgency-based mechanism might be species-specific and/or a consequence of practice. Here I show that the unified regulation hypothesis exists in naïve human subjects. Seventeen volunteers performed a reach decision task in which blocks of trials encouraged either risky or conservative choices. Participants performed at least two sessions in which they were indirectly motivated to maximize their reward rate. Results show that subjects' accuracy criterion decreased over time within each trial, and that decisions were earlier and less accurate in fast than slow blocks, with a larger difference in session #2 compared to session #1. A simple model in which sensory information is combined with a growing urgency signal captured these effects. Crucially, arm and eye movement vigor systematically increased as decision duration increased within blocks and the block-dependent decision policy strongly predicted the kinematics of reaching movements. These results suggest a practice-independent mechanistic link for establishing the unified control of human decision timing and action vigor in order to optimize the rate of reward.