Infants understand deceptive intentions to implant false beliefs about identity: New evidence for early mentalistic reasoning

• We used a novel deception situation to test the minimalist claim that infants cannot represent false beliefs about identity.
• In each experiment, a thief attempted to secretly steal a rattling toy in its owner’s absence by substituting a silent toy.
• 17-month-olds understood the conditions under which the thief could successfully lure the owner into holding a false belief.
• When these conditions were met, infants expected the owner to hold a false belief about the identity of the silent toy.
• These results support the mentalistic view that the ability to represent false beliefs is already present in infancy.

Are infants capable of representing false beliefs, as the mentalistic account of early psychological reasoning suggests, or are they incapable of doing so, as the minimalist account suggests? The present research sought to shed light on this debate by testing the minimalist claim that a signature limit of early psychological reasoning is a specific inability to understand false beliefs about identity: because of their limited representational capabilities, infants should be unable to make sense of situations where an agent mistakes one object for another, visually identical object. To evaluate this claim, three experiments examined whether 17-month-olds could reason about the actions of a deceptive agent who sought to implant in another agent a false belief about the identity of an object. In each experiment, a thief attempted to secretly steal a desirable rattling toy during its owner’s absence by substituting a less desirable silent toy. Infants realized that this substitution could be effective only if the silent toy was visually identical to the rattling toy (Experiment 1) and the owner did not routinely shake her toy when she returned (Experiment 2). When these conditions were met, infants expected the owner to be deceived and to mistake the silent toy for the rattling toy she had left behind (Experiment 3). Together, these results cast doubt on the minimalist claim that infants cannot represent false beliefs about identity. More generally, these results indicate that infants in the 2nd year of life can reason not only about the actions of agents who hold false beliefs, but also about the actions of agents who seek to implant false beliefs, thus providing new support for the mentalistic claim that an abstract capacity to reason about false beliefs emerges early in human development.