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.

为了理解他人的行为，我们通常会考虑他们可以获得哪些信息。这些信息可能来自不同的来源，包括感知和推理。与成年人一样，幼儿也会跟踪代理可以通过感知获得哪些信息：例如，如果代理直接观察事件，幼儿希望代理有关于它的信息。然而，还没有调查研究过小婴儿是否也跟踪代理可以通过推理获得的信息，通过带来相关的常识。基于大多数婴儿在 4 个月大时已经掌握了宽物体可以放入宽容器但不能放入窄容器的物理规则的发现，我们询问 5 个月大的婴儿是否会期待寻找隐藏的宽玩具的代理人在她需要一个宽盒子而不是一个窄盒子的情况下。当代理人选择窄盒子时，婴儿看起来明显更长，这表明他们希望她 (a) 分享宽物体只能放入宽容器的物理知识，以及 (b) 推断宽玩具必须隐藏在宽盒子。三个附加条件支持这种解释。总之，这些结果对早期心理推理的两个系统解释提出了质疑，它声称婴儿的早期发育系统过于僵化和封闭，无法整合来自其他认知过程的输入，例如物理推理。相反，这些结果支持单一系统的解释，并提供了新的证据，表明幼儿迅速发展的心理推理系统在性质上与年龄较大的儿童和成人相似。