Fourteen- to Eighteen-Month-Old Infants Use Explicit Linguistic Information to Update an Agent's False Belief

Five-month-old infants attribute inferences based on general knowledge to agents

To make sense of others' actions, we generally consider what information is available to them. This information may come from different sources, including perception and inference. Like adults, young infants track what information agents can obtain through perception: If an agent directly observes an event, for example, young infants expect the agent to have information about it. However, no investigation has yet examined whether young infants also track what information agents can obtain through inference, by bringing to bear relevant general knowledge. Building on the finding that by 4 months of age most infants have acquired the physical rule that wide objects can fit into wide containers but not narrow containers, we asked whether 5-month-olds would expect an agent who was searching for a wide toy hidden in her absence to reach for a wide box as opposed to a narrow box. Infants looked significantly longer when the agent selected the narrow box, suggesting that they expected her (a) to share the physical knowledge that wide objects can fit only into wide containers and (b) to infer that the wide toy must be hidden in the wide box. Three additional conditions supported this interpretation. Together, these results cast doubt on two-system accounts of early psychological reasoning, which claim that infants' early-developing system is too inflexible and encapsulated to integrate inputs from other cognitive processes, such as physical reasoning. Instead, the results support one-system accounts and provide new evidence that young infants' burgeoning psychological-reasoning system is qualitatively similar to that of older children and adults.

Infant expectations of instant or delayed gratification

Choices between immediate gratification and long-term (but larger) gains are prevalent in human life, which is why the decision-making processes to delay gratification have been studied extensively throughout different developmental ages. Children's delay-of-gratification behaviors have been examined in the well-known "marshmallow test," in which 3- to 5-year-olds are given a marshmallow and told by an experimenter that they can eat it immediately or wait for an unspecified duration of time (which can be capped at 15 min) until the experimenter returns so that they can receive another marshmallow. Children's wait time has been viewed as a good indicator of their later development. Here we show that a group of 22-month-old infants (N = 32) already held expectations about others' choices in a violation-of-expectation looking-time task modeled after the marshmallow test. The infants expected an agent to defer gratification based on a speaker's promise of the second marshmallow available in the future, but to eat the currently attainable marshmallow when the speaker made no such promise. Our findings indicate an early-emerging understanding of others' choices of delayed or instant gratification and shed new light on the development of delay-of-gratification behaviors.