Reaching reflects ongoing deliberation prior to a decision


We constantly make choices while moving, such as when navigating a crowded hallway. Studies that examine the interplay between decision-making and movement employ sudden target changes to evoke a rapid decision and motor response, whereas perceptual decision-making studies manipulate sensory evidence over time to influence the timing of a decision. In both cases, deliberation is hidden. Here we tested the hypothesis that decision-making and motor circuitry continuously interact during deliberation. We predicted that lateral hand movement would reflect the ongoing deliberation, prior to a decision. We extended the “tokens task” (Cisek, 2009) to require active forward movement prior to the final decision. Participants were required to move forward from a start position towards two potential targets. Once they left the start position, 15 tokens individually moved into one of the two targets. We manipulated the token patterns to influence the ongoing deliberation. Participants indicated the target expected to finish with the most tokens by both hitting the selected target with their reaching hand and pushing a button with their other hand. Critically, we measured the unconstrained lateral hand position, prior to the decision, to determine the influence of deliberation on movement. Across two experiments, the token patterns differentially impacted the lateral hand position prior to a decision (p < 0.003 for all comparisons), demonstrating that hand movements reflect a continuous readout of the ongoing deliberation. Our results support the idea that there is a continuous interaction between decision-making and motor circuitry.