The relationship between habitual control and markers of motor automaticity

<p>Habits are a central example of automatic behavior, expressed at the level of action selection: with repeated practice, people may inflexibly continue selecting an action even when its outcome is no longer valuable, reflecting a shift from goal-directed choice toward habitual control. Repeated practice can also produce features associated with automatic behavior at the level of action execution, including markers of motor automaticity such as faster, more regular, and more stereotyped motor execution. Although both selection-level habitual control and execution-level motor automaticity markers are commonly associated with repeated practice and often treated as convergent features of automaticity, their relationship remains largely untested. Here, using a novel paradigm designed to enhance and measure habit expression (assessed via outcome devaluation), alongside established markers of motor automaticity (including timing consistency and execution speed of action sequences), we tested this relationship. We found an inverse relationship: individuals with stronger markers of motor automaticity at the end of training, before devaluation, showed less habitual responding after devaluation. This finding was replicated in a pre-registered confirmatory study and generalized across three independent datasets spanning different paradigms, training durations, action types, reinforcement schedules, and laboratories (total N=1,065 across all five datasets). This inverse relationship converged across multiple markers of motor automaticity. Additionally, we found that motor automaticity during habitual errors was preserved after extensive training but disrupted after limited training, offering a potential window into habit consolidation. Together, these findings suggest that habitual control is not simply aligned with markers of motor automaticity, but can vary in the opposite direction across individuals. More broadly, they indicate that automaticity at the levels of action selection and action execution can diverge, with implications for understanding how practice shapes adaptive skill and maladaptive rigidity in healthy and clinical populations.</p>