Infants expect friends, but not rivals, to be happy for each other when they succeed.

A friend telling you good news earns them a smile while witnessing a rival win an award may make you wrinkle your nose. Emotions arise not just from people's own circumstances, but also from the experiences of friends and rivals. Across three moderated, online looking time studies, we asked if human infants hold expectations about others' vicarious emotions and if they expect those emotions to be guided by social relationships. Ten- and 11-month-old infants (N = 154) expected an observer to be happy rather than sad when the observer watched a friend successfully jump over a wall; infants looked longer at the sad response compared to the happy response. In contrast, infants did not expect the observer to be happy when the friend failed, nor when a different, rival jumper succeeded; infants' looking times to the two emotion responses in these conditions were not reliably different. These results suggest that infants are able to integrate knowledge across social contexts to guide expectations about vicarious emotional responses. Here infants connected an understanding of agents' goals and their outcomes with knowledge of social relationships to infer an emotion response. Biased concern for friends but not adversaries is not just a descriptive feature of human relationships, but an expectation about the social world present from early in development. Further, the successful integration of these information types welcomes the possibility that infants can jointly reason about goals, emotions, and social relationships under an intuitive theory of psychology. RESEARCH HIGHLIGHTS: 11-month-old infants use knowledge of relationships to make inferences about others' vicarious emotions. In Experiment 1 infants expected an observer to respond happily to a friend's success but not their failure. Experiments 2 and 3 varied the relationship between the observer and actor and found that infants' expectation of vicarious happiness is strongest for positive relationships and absent for negative relationships. The results may reflect an intuitive psychology in which infants expect friends to adopt concern for one another's goals and to thus experience one another's successes as rewarding.

"Yay! Yuck!" toddlers use others' emotional responses to reason about hidden objects.

Young children show sensitivity to others' emotions, discriminating between facial expressions and using them to help guide their behavior. Beyond providing information about how others are feeling, emotional expressions also can support inferences about the non-social world. Here, in four experiments, we investigated 18- to 28-month-old children's ability to use others' emotional responses to reason about physical objects. We found that 24- to 26-month-old children successfully used an agent's incongruent emotional responses ("Yay! Yuck!"), but not congruent emotional responses ("Yay! Wow!") to infer the presence of multiple hidden objects (Experiment 1). When two different agents produced the incongruent emotional responses, children did not infer that multiple objects must be present (Experiment 2), implicating early recognition that different people can have different emotional reactions towards the same entity. Younger, 20-month-old children failed to use incongruent emotional responses to make inferences about hidden objects (Experiment 3), although they succeeded at using contrasting words in an otherwise identical task ("A blick! A fep!"; Experiment 4). These results show that young children can use other people's emotional responses to reason about the physical world-an ability that develops in the second year of life.

Online measures of looking and learning in infancy.

Infants in laboratory settings look longer at events that violate their expectations, learn better about objects that behave unexpectedly, and match utterances to the objects that likely elicited them. The paradigms revealing these behaviors have become cornerstones of research on preverbal cognition. However, little is known about whether these canonical behaviors are observed outside laboratory settings. Here, we describe a series of online protocols that replicate classic laboratory findings, detailing our methods throughout. In Experiment 1a, 15-month-old infants (N = 24) looked longer at an online support event culminating in an Unexpected outcome (i.e., appearing to defy gravity) than an Expected outcome. Infants did not, however, show the same success with an online solidity event. In Experiment 1b, 15-month-old infants (N = 24) showed surprise-induced learning following online events-they were better able to learn a novel object's label when the object had behaved unexpectedly compared to when it behaved expectedly. Finally, in Experiment 2, 16-month-old infants (N = 20) who heard a valenced utterance ("Yum!") showed preferential looking to the object most likely to have generated that utterance. Together, these results suggest that, with some adjustments, online testing is a feasible and promising approach for infant cognition research.

When Not Choosing Leads to Not Liking: Choice-Induced Preference in Infancy.

The question of how people's preferences are shaped by their choices has generated decades of research. In a classic example, work on cognitive dissonance has found that observers who must choose between two equally attractive options subsequently avoid the unchosen option, suggesting that not choosing the item led them to like it less. However, almost all of the research on such choice-induced preference focuses on adults, leaving open the question of how much experience is necessary for its emergence. Here, we examined the developmental roots of this phenomenon in preverbal infants (N = 189). In a series of seven experiments using a free-choice paradigm, we found that infants experienced choice-induced preference change similar to adults'. Infants' choice patterns reflected genuine preference change and not attraction to novelty or inherent attitudes toward the options. Hence, choice shapes preferences-even without extensive experience making decisions and without a well-developed self-concept.

Children's Reasoning About Empathy and Social Relationships.

Across the lifespan, empathic and counter-empathic emotions are shaped by social relationships. Here we test the hypothesis that this connection is encoded in children's intuitive theory of psychology, allowing them to predict when others will feel empathy versus counter-empathy and to use vicarious emotion information to infer relationships. We asked 4- to 7-year-old children (N = 79) to make emotion predictions or relationship inferences in response to stories featuring two characters, an experiencer and an observer, and either a positive or negative outcome for the experiencer. In the context of positive outcomes, we found that children engaged in robust joint reasoning about relationships and vicarious emotions. When given information about the characters' relationship, children predicted empathy from a friendly observer and counter-empathy from a rival observer. When given information about the observer's response to the experiencer, children inferred positive and negative relationships from empathic and counter-empathic responses, respectively. In the context of negative outcomes, children predicted that both friendly and rival observers would feel empathy toward the experiencer, but they still used information about empathic versus counter-empathic responses to infer relationship status. Our results suggest that young children in the US have a blanket expectation of empathic concern in response to negative outcomes, but otherwise expect and infer that vicarious emotions are connected to social relationships. Future research should investigate if children use this understanding to select social partners, evaluate their own relationships, or decide when to express empathy toward others.

Children's understanding of economic demand: A dissociation between inference and choice.

Adults infer that resources that become scarce over time are in higher demand, and use this "demand inference" to guide their own economic decisions. However, it is unclear when children begin to understand and use economic demand. In six experiments, we investigated the development of demand inference and demand-based economic decisions in 4- to 10-year-old children and adults in the United States. In Experiments 1-5, we showed children two boxes with the same number of compartments but containing different numbers of face-down stickers and varied the information provided about how those differences arose (e.g. that other children had taken the stickers). In separate experiments, we asked children to buy or trade to get a sticker for themselves or to predict what other children would do. We also asked them which set of stickers they thought the other children had preferred to assess their ability to make a demand inference separately from their own choice. Across experiments, children were able to make a demand inference about children's past preferences by 6 years of age. However, children did not use this demand information when making choices for themselves or when predicting what another child would select in the future. In Experiment 6, we adapted the task for adults and found that adult participants inferred that the set containing fewer resources was in higher demand, and selected the higher demand resource for themselves at rates significantly above chance. The overall pattern of results suggests a dissociation between economic inference and economic decisions during early-to-middle childhood. We discuss implications for our understanding of the development of economic reasoning.