The Trembling Hand Unraveled: Motor Dynamics and Choice Inconsistency

Extensive evidence shows that humans are inconsistent in their choices. Yet, the neural mechanism underlying inconsistent choice remains unknown. Here, we aim to show that inconsistent choice is tied to the valuation process but is also linked to motor dynamics during task execution. We report the results from two behavioral and one neuroimaging studies. Human subjects (n = 206, 117 females) completed a well validated risky-choice task to measure their inconsistency levels, followed by two novel tasks, explicitly designed to examine motor dynamics free of value computations. We record mouse trajectories during task execution and extract 34 features to examine the role of motor dynamics in choice inconsistency. We show that motor dynamics predict inconsistency levels, even when motor output is absent any sort of valuation elements, nor is it related to deliberation about the decision. These results are robust across all three studies and when using various analysis strategies. We then apply neuroimaging and show that inconsistency is represented in value brain areas but, at the same time, is also related to activity in motor brain regions. These findings suggest that inconsistent choice behavior may arise from multiple cognitive processes and invite choice theorists to examine models of inconsistent choice that include heterogeneous sources of stochasticity.