Hard choices: Children's understanding of the cost of action selection

When predicting or explaining another person's actions, we often appeal to the physical effort they require; a person who works hard for something, for instance, must really like it (Liu, Ullman, Tenenbaum, & Spelke, 2017). But people are not only motivated to avoid physical effort; they also seek to avoid mental effort (Shenhav et al., 2017; Kool & Botvinick, 2018). Here, we ask whether mental effort enters into preschoolers' understanding of other people's actions. Across 4 experiments (N=112), we presented 4- and 5-year-old children with an agent (naive in Exp 1, 2 and 4, and knowledgeable in Exp 3) who can either move through a simple or complex maze environment with a specific goal (in Exp 1-3, to reach a play structure beyond the mazes, and in Exp 4, to practice solving the mazes). We found that children were sensitive to the physical and mental effort associated with more complex mazes, and to the trade-offs between effort and gain in skill. The intuition that choices impose costs on our bodies and minds appears to guide children's understanding of other people.