Hypothesis testing governs strategic motor learning

How do people discover an effective movement strategy when the environment abruptly changes-such as when using the trackpad on an unfamiliar laptop? Strategic adaptation is often described as a reinforcement learning process characterized by two key features: random exploration followed by gradual error reduction. We propose a different view in which strategic adaptation operates through hypothesis testing: learners generate specific action-outcome hypotheses about the environmental change, discount those that conflict with feedback, and continue testing alternatives until they discover the correct rule. To adjudicate between these accounts, we conducted two large-scale experiments using a visuomotor rotation task designed to isolate strategic adaptation under different target arrangements (N = 560). Individual learning trajectories showed pronounced exploration but were far from random, exhibiting structured, multimodal error distributions. Moreover, participants did not converge on the solution gradually; instead, they discovered it abruptly. Critically, strategic adaptation depended on target arrangement: some configurations steered participants toward the correct rotational hypothesis, whereas others led them to alternate between rotational and translational hypotheses. Together, these findings position hypothesis testing as a core mechanism governing strategic motor learning.