Automatic, but not autonomous: Implicit adaptation is modulated by goal-directed attentional demands

Implicit adaptation recalibrates movements based on sensory prediction errors. It is often characterized as automatic and resource-independent, suggesting that it is insulated from cognitive influence. Here, we asked whether implicit adaptation is sensitive to goal-directed attentional demands imposed by a concurrent visual task. Across two experiments, we used clamped visual feedback to measure implicit adaptation while human adults monitored a rapidly changing visual stream for targets. In Experiment 1, participants performing the visual task showed modest early enhancement in implicit adaptation relative to a single-task control condition. In Experiment 2, adding response-contingent feedback to the visual task led to stronger and more sustained enhancement. Visual task accuracy and implicit adaptation were uncorrelated, arguing against resource competition. Model-based analyses revealed elevated error sensitivity under dual-task conditions, with individual differences reflecting an inverse relationship between error sensitivity and retention. These patterns are compatible with arousal-mediated modulation of cerebellar error processing and hierarchical models of cerebellar learning. These findings suggest that implicit adaptation is automatic but not autonomous: while it operates outside voluntary control, it appears open to the physiological states in which errors are experienced.