Do Infants Really Expect Agents to Act Efficiently? A Critical Test of the Rationality Principle

Rose M. Scott, Renée Baillargeon

Research output: Contribution to journalArticlepeer-review


Recent experiments have suggested that infants' expectations about the actions of agents are guided by a principle of rationality: In particular, infants expect agents to pursue their goals efficiently, expending as little effort as possible. However, these experiments have all presented infants with infrequent or odd actions, which leaves the results open to alternative interpretations and makes it difficult to determine whether infants possess a general expectation of efficiency. We devised a critical test of the rationality principle that did not involve infrequent or odd actions. In two experiments, 16-month-olds watched events in which an agent faced two identical goal objects; although both objects could be reached by typical, everyday actions, one object was physically (Experiment 1) or mentally (Experiment 2) more accessible than the other. In both experiments, infants expected the agent to select the more-accessible object. These results provide new evidence that infants possess a general and robust expectation of efficiency.

Original languageEnglish (US)
Pages (from-to)466-474
Number of pages9
JournalPsychological Science
Issue number4
StatePublished - Apr 2013


  • cognitive development
  • efficiency
  • goals
  • infant cognition
  • infant development
  • psychological reasoning
  • rationality
  • social cognition

ASJC Scopus subject areas

  • General Psychology


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