Model-free or muddled models 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. In this study, however, 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 the standard methods of analyzing the two-stage task may falsely classify purely model-based agents that misunderstood the task as hybrid model-based/model-free actors. 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.