Humans are primarily model-based and not model-free learners in the two-stage task

Abstract

Distinct model-free and model-based learning processes are thought to drive both typical and dysfunctional behaviors. Data from two-stage decision tasks have seemingly shown that human behavior is driven by both processes operating in parallel. However, in this study, we show that more detailed task instructions lead participants to make primarily model-based choices that show little, if any, model-free influence. We also demonstrate that behavior in the two-stage task may falsely appear to be driven by a combination of model-based/model-free learning if purely model-based agents form inaccurate models of the task because of misunderstandings. Furthermore, we found evidence that many participants do misunderstand the task in important ways. Overall, we argue that humans formulate a wide variety of learning models. Consequently, the simple dichotomy of model-free versus model-based learning is inadequate to explain behavior in the two-stage task and connections between reward learning, habit formation, and compulsivity.