  People often plan hierarchically. That is, rather than planning over a
monolithic representation of a task, they decompose the task into simpler
subtasks and then plan to accomplish those. Although much work explores how
people decompose tasks, there is less analysis of why people decompose tasks in
the way they do. Here, we address this question by formalizing task
decomposition as a resource-rational representation problem. Specifically, we
propose that people decompose tasks in a manner that facilitates efficient use
of limited cognitive resources given the structure of the environment and their
own planning algorithms. Using this model, we replicate several existing
findings. Our account provides a normative explanation for how people identify
subtasks as well as a framework for studying how people reason, plan, and act
using resource-rational representations.
