Proceedings of the Annual Meeting of the Cognitive Science Society

When faced with a complex problem, people naturally break it up into several simpler problems. This hierarchical decom-position of an ultimate goal into sub-goals facilitates planning by reducing the number of factors that must be consideredat one time. However, it can also lead to suboptimal decision-making, obscuring opportunities to make progress towardsmultiple subgoals with a single action. Is it possible to take advantage of the hierarchical structure of problems withoutsacrificing opportunities to kill two birds with one stone? We propose that people are able to do this by representing andpursuing multiple subgoals at once. We present a formal model of planning with compositional goals, and show that itexplains human behavior better than the standard ”one-at-a-time” subgoal model as well as non-hierarchical limited-depthsearch models. Our results suggest that people are capable of representing and pursuing multiple subgoals at once; how-ever, there are limitations on how many subgoals one can pursue concurrently. We find that these limitations vary byindividual.