Why we dive deep: A momentum-based account of depth-first persistence in hierarchically organized goals

Humans can flexibly organize their behavior to pursue hierarchically structured goals, dynamically updating their commitment to goals and their concomitant subgoals in response to changes in environmental contingencies. Through a novel hierarchical goal selection paradigm, we investigate human persistence patterns in goal and subgoal pursuit, especially in the presence of varying subgoal prospects. We observe that humans exhibit a depth-first commitment to hierarchical goals, preferring to persist on a goal--subgoal pair until termination rather than the breadth-first approach of alternating between subgoals within a goal. We also show that this depth-first persistence in goals and subgoals is modulated by goal and subgoal progress, respectively. We further demonstrate that a momentum-based account that parsimoniously estimates the values of ongoing goals explains depth-first patterns of persistence in hierarchically organized goals. We explicitly dissociate the effects of momentum computations from switching costs on goal persistence, and show that momentum computations drive persistence choices above and beyond dynamic costs imposed by switching goals and subgoals.