Model-based learning protects against forming habits

Abstract Studies in humans and rodents have suggested that behavior can at times be Bgoal-directed^—that is, planned, and purposeful—and at times Bhabitual^—that is, inflexible and automatically evoked by stimuli. This distinction is cen-tral to conceptions of pathological compulsion, as in drug abuse and obsessive-compulsive disorder. Evidence for the distinction has primarily come from outcome devaluation studies, in which the sensitivity of a previously learned behav-ior to motivational change is used to assay the dominance of habits versus goal-directed actions. However, little is known about how habits and goal-directed control arise. Specifically, in the present study we sought to reveal the trial-by-trial dy-namics of instrumental learning that would promote, and pro-tect against, developing habits. In two complementary exper-iments with independent samples, participants completed a sequential decision task that dissociated two computational-learning mechanisms, model-based and model-free. We then tested for habits by devaluing one of the rewards that had reinforced behavior. In each case, we found that individual differences in model-based learning predicted the participants’ subsequent sensitivity to outcome devaluation, suggesting that an associative mechanism underlies a bias toward habit for-mation in healthy individuals