Many rituals are socially stipulated such that engaging in a group's rituals can fundamentally signal membership in that group. Here, we asked whether infants infer information about people's social affiliation based on whether those people perform the same ritualistic action versus different actions. We presented 16-month-old infants with two people who used the same object to achieve the same goal: turning on a light. In a first study, the actions that the actors used to turn on the light had key properties of ritual: they were not causally necessary to reach the overall goal, and there were no features of the situation that required doing the particular actions. We varied whether the two actors performed the same action or performed different actions to turn on the light. Infants expected people who used the same ritualistic action to be more likely to affiliate than people who used different actions. A second study indicated that these results were not due to perceptual similarity: when the differences in the actors' actions were not marked by properties of ritual, but were instead due to situational constraints, infants expected the actors to affiliate. Thus, infants understand the social significance of people engaging in common, potentially ritualistic actions, and expect these actions to provide information about third-party social relationships.

Language provides rich social information about its speakers. For instance, adults and children make inferences about a speaker's social identity, geographic origins, and group membership based on her language and accent. Although infants prefer speakers of familiar languages (Kinzler, Dupoux, & Spelke, 2007), little is known about the developmental origins of humans' sensitivity to language as marker of social identity. We investigated whether 9-month-olds use the language a person speaks as an indicator of that person's likely social relationships. Infants were familiarized with videos of two people who spoke the same or different languages, and then viewed test videos of those two individuals affiliating or disengaging. Results suggest that infants expected two people who spoke the same language to be more likely to affiliate than two people who spoke different languages. Thus, infants view language as a meaningful social marker and use language to make inferences about third-party social relationships.

Forming conceptually-rich social categories helps people to navigate the complex social world by allowing them to reason about the likely thoughts, beliefs, actions, and interactions of others, as guided by group membership. Nevertheless, social categorization often has nefarious consequences. We suggest that the foundation of the human ability to form useful social categories is in place in infancy: social categories guide the inferences infants make about the shared characteristics and social relationships of other people. We also suggest that the ability to form abstract social categories may be separable from the eventual negative downstream consequences of social categorization, including prejudice, discrimination, and stereotyping. Although a tendency to form inductively-rich social categories appears early in ontogeny, prejudice based on each particular category dimension may not be inevitable.

Skilled social interactions require knowledge about others' intentions and the ability to implement this knowledge in real-time to generate appropriate responses to one's partner. Young infants demonstrate an understanding of other people's intentions (e.g. Woodward, Sommerville, Gerson, Henderson & Buresh, 2009), yet it is not until the second year that infants seem to master the real-time implementation of their knowledge during social interactions (e.g. Warneken & Tomasello, 2007). The current study investigates the possibility that developments in social competence during the second year are related to increases in the speed with which infants can employ their understanding of others' intentions. Twenty- to 22-month-old infants (N = 23) viewed videos of goal-directed actions on a Tobii eye-tracker and then engaged in an interactive perspective-taking task. Infants who quickly and accurately anticipated another person's future behavior in the eye-tracking task were more successful at taking their partner's perspective in the social interaction. Success on the perspective-taking task was specifically related to the ability to correctly predict another person's intentions. These findings highlight the importance of not only being a 'smart' social partner but also a 'fast' social thinker.

Early exposure to multiple languages can enhance children's communication skills, even when children are effectively monolingual (Fan, Liberman, Keysar & Kinzler, ). Here we report evidence that the social benefits of multilingual exposure emerge in infancy. Sixteen-month-old infants participated in a communication task that required taking a speaker's perspective to understand her intended meaning. Infants were presented with two identical toys, such as two cars. One toy was mutually visible to both the infant and the speaker, but the other was visible only to the infant and was blocked from the speaker's view by an opaque barrier. The speaker requested the mutually visible toy and we evaluated whether infants understood the speaker's request. Whereas monolingual infants were at chance in choosing between the two toys, infants with multilingual exposure reliably chose the toy the speaker requested. Successful performance was not related to the degree of exposure to other languages, suggesting that even minimal multilingual exposure may enhance communication skills.

Predicting others' affiliative relationships is critical to social cognition, but there is little evidence of how this ability develops. We examined 9-month-old infants' inferences about 3rd-party affiliation based on shared and opposing evaluations. Infants expected 2 people who expressed shared evaluations to interact positively, whereas they expected 2 people who expressed opposing evaluations to interact negatively. A control condition revealed that infants' expectations could not be due to mere perceptual repetition. Thus, an abstract understanding that 3rd-party affiliation can be based on shared intentions has roots in the 1st year of life. These findings have implications for understanding humans' earliest representations of the social world.

This study explores the ways in which infants reason about h u m a n action. Although recent research supports the view that young infants' reasoning about object physics is guided by a set of core principles. there is little evidence for early principles of this sort in infants' reasoning about human action. T o explore this issue, a habituation study was done comparing 7- month-olds' reasoning about simple causal sequences involving people to their reasoning about those involving inanimate objects. Our findingssuggest that although 7-month-olds expect that the motion of inanimate objects will be constrained by the principle of contact (an object affects the motion of another object if and only if the two objects come into contact), they do not expect human motion to be constrained in this way. These findings provide preliminary evidence diat infants have principled expectations to guide their reasoning and learning about human action.

Selecting appropriate foods is a complex and evolutionarily ancient problem, yet past studies have revealed little evidence of adaptations present in infancy that support sophisticated reasoning about perceptual properties of food. We propose that humans have an early-emerging system for reasoning about the social nature of food selection. Specifically, infants' reasoning about food choice is tied to their thinking about agents' intentions and social relationships. Whereas infants do not expect people to like the same objects, infants view food preferences as meaningfully shared across individuals. Infants' reasoning about food preferences is fundamentally social: They generalize food preferences across individuals who affiliate, or who speak a common language, but not across individuals who socially disengage or who speak different languages. Importantly, infants' reasoning about food preferences is flexibly calibrated to their own experiences: Tests of bilingual babies reveal that an infant's sociolinguistic background influences whether she will constrain her generalization of food preferences to people who speak the same language. Additionally, infants' systems for reasoning about food is differentially responsive to positive and negative information. Infants generalize information about food disgust across all people, regardless of those people's social identities. Thus, whereas food preferences are seen as embedded within social groups, disgust is interpreted as socially universal, which could help infants avoid potentially dangerous foods. These studies reveal an early-emerging system for thinking about food that incorporates social reasoning about agents and their relationships, and allows infants to make abstract, flexible, adaptive inferences to interpret others' food choices.