The order of complexity of visuomotor learning.

Background: Learning algorithms come in three orders of complexity: zeroth-order (perturbation), first-order (gradient descent), and second-order (e.g., quasi-Newton). But which of these are used in the brain? We trained 12 people to shoot targets, and compared them to simulated subjects that learned the same task using various algorithms.

Results: Humans learned significantly faster than optimized zeroth-order algorithms, but slower than second-order ones.

Conclusions: Human visuomotor learning is too fast to be explained by zeroth-order processes alone, and must involve first or second-order mechanisms.