We know that we don't know: Children's understanding of common ignorance in a coordination game.

Common ground is the knowledge, beliefs, and suppositions shared between partners in an interaction. Previous research has focused extensively on what partners know they know together, that is, "common knowledge." However, another important aspect of common ground is what partners know they do not know together, that is, "common ignorance." A new coordination game was designed to investigate children's use of common ignorance. Without communicating or seeing each other's decisions, 4- to 8-year-olds needed to make the same decision as their partner about whether to try to retrieve a reward. To retrieve it, at least one of them needed to know a secret code. The knowledge/ignorance of both partners was ostensively manipulated by showing one partner, both partners, or neither partner the secret code in four conditions: common knowledge (both knew the code), common ignorance (neither partner knew the code), common privileged self knowledge (only children knew the code), and common privileged other knowledge (only their partner knew the code). Children's decisions, latency, and uncertainty were coded. Results showed that the common ignorance states were generally more difficult than the common knowledge states. Unexpectedly, children at all ages had difficulty with coordinating when their partner knew the code but they themselves did not (common privileged other knowledge). This study shows that, along with common knowledge, common ignorance and common privileged self knowledge and other knowledge also play important roles in coordinating with others but may develop differently.

Young children use imitation communicatively.

There is growing evidence that children imitate not just to learn from others but also to affiliate socially with them. However, although imitation can convey a wealth of affiliative information to others, it is not yet known whether imitators intend for this to be the case. In particular, we do not know whether children imitate communicatively in some contexts, expending extra effort to make sure that the demonstrator sees their imitation. Here, in two experiments (N = 20 and N = 48, respectively), we tested whether preschool-age children modify their imitation when needed to ensure that the demonstrator sees it. In each trial, children were shown a demonstration. Then, for their response, in one condition a barrier obscured the demonstrator's view of children's imitation unless children raised their arms above the barrier while imitating. In the other condition the demonstrator was able to see children's imitation without any additional effort from children. Results from both experiments showed that children were significantly more likely to imitate with their arms raised when their actions would otherwise be obscured from view. In the second experiment, we also coded for other communicative behaviors (e.g., social smiles, eye contact, showing gestures) and found that children often displayed communicative behaviors while imitating, as expected, in both conditions. Thus, young children actively use imitation communicatively in some contexts.

Showing and giving: from incipient to conventional forms.

Understanding humans' motivation and capacity for social interaction requires understanding communicative gestures. Gestures are one of the earliest means that infants employ to communicate with others, and showing and giving are among the earliest-emerging gestures. However, there are limited data on the processes that lead up to the emergence of conventional showing and giving gestures. This study aimed to provide such data. Twenty-five infants were assessed longitudinally at monthly intervals from 6 to 10 months of age using a variety of methods (elicitation procedures, free play observations and maternal interviews), as well as via questionnaires conducted at 11-12 months. A particular focus was on pre-conventional, incipient gestures, behaviours that involved some components of conventional gestures, but lacked other important components. We present observational evidence that at least some of these behaviours (observed as early as 7 months of age) were communicative and make the case for how conventional showing and giving may emerge gradually in the context of social interactions. We also discuss the influence of maternal interpretations of these early behaviours on their development. Overall, the study seeks to draw attention to the importance of understanding the cognitive, motor and interactional processes that lead to the emergence of infants' earliest communicative gestures. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

When does it pay to follow the crowd? Children optimize imitation of causally irrelevant actions performed by a majority.

Cultural evolutionary theory posits that human cultural complexity rests on a set of adaptive learning biases that help to guide functionality and optimality in social learning, but this sits in contrast with the commonly held view that children are unselective "over-imitators." Here, we tested whether 4- and 6-year-old children use social learning biases flexibly to fine-tune their copying of irrelevant actions. Children watched a video of a majority demonstrating causally irrelevant actions and a minority demonstrating only causally relevant actions. In one condition observers approved of the majority and disapproved of the minority, and in the other condition observers watched the majority and minority neutrally. Results showed that both 4- and 6-year-olds copied the inefficient majority more often than the efficient minority when the observers had approved of the majority's actions, but they copied the efficient minority significantly more when the observers had watched neutrally. We discuss the implications of children's optimal selectivity in copying and the importance of integrating social approval into majority-biased learning when acquiring norms and conventions and in broader processes of cultural evolution.

Young children share more under time pressure than after a delay.

Adults under time pressure share with others generously, but with more time they act more selfishly. In the current study, we investigated whether young children already operate in this same way, and, if so, whether this changes over the preschool and early school age years. We tested 144 children in three age groups (3-, 5-, and 7-year olds) in a one-shot dictator game: Children were given nine stickers and had the possibility to share stickers with another child who was absent. Children in the Time Pressure condition were instructed to share quickly, whereas children in the Delay condition were instructed to take time and consider their decision carefully. Across ages, children in the Time Pressure condition shared significantly more stickers than children in the Delay condition. Moreover, the longer children waited, the less they shared. Thus, children, like adults, are more prosocial when acting spontaneously than after considering their decision more carefully.

Common knowledge that help is needed increases helping behavior in children.

Although there is considerable evidence that at least some helping behavior is motivated by genuine concern for others' well-being, sometimes we also help solely out of a sense of obligation to the persons in need. Our sense of obligation to help may be particularly strong when there is common knowledge between the helper and the helpee that the helpee needs help. To test whether children's helping behavior is affected by having common knowledge with the recipient about the recipient's need, 6-year-olds faced a dilemma: They could either collect stickers or help an experimenter. Children were more likely to help when they and the experimenter had common knowledge about the experimenter's plight (because they heard it together) than when they each had private knowledge about it (because they heard it individually). These results suggest that already in young children common knowledge can heighten the sense of obligation to help others in need.

A new look at joint attention and common knowledge.

Everyone agrees that joint attention is a key feature of human social cognition. Yet, despite over 40 years of work and hundreds of publications on this topic, there is still surprisingly little agreement on what exactly joint attention is, and how the jointness in it is achieved. Part of the problem, we propose, is that joint attention is not a single process, but rather it includes a cluster of different cognitive skills and processes, and different researchers focus on different aspects of it. A similar problem applies to common knowledge. Here we present a new approach: We outline a typology of social attention levels which are currently all referred to in the literature as joint attention (from monitoring to common, mutual, and shared attention), along with corresponding levels of common knowledge. We consider cognitive, behavioral, and phenomenological aspects of the different levels as well as their different functions, and a key distinction we make in all of this is second-personal vs. third-personal relations. While we focus mainly on joint attention and common knowledge, we also briefly discuss how these levels might apply to other 'joint' mental states such as joint goals.

Communicative eye contact signals a commitment to cooperate for young children.

Making commitments to cooperate facilitates cooperation. There is a long-standing theoretical debate about how promissory obligations come into existence, and whether linguistic acts (such as saying "I promise") are a necessary part of the process. To inform this debate we experimentally investigated whether even minimal, nonverbal behavior can be taken as a commitment to cooperate, as long as it is communicative. Five- to 7-year-old children played a Stag Hunt coordination game in which they needed to decide whether to cooperate or play individually. During the decision-making phase, children's partner made either ostensive, communicative eye contact or looked non-communicatively at them. In Study 1 we found that communicative looks produced an expectation of collaboration in children. In Study 2 we found that children in the communicative look condition normatively protested when their partner did not cooperate, thus showing an understanding of the communicative looks as a commitment to cooperate. This is the first experimental evidence, in adults or children, that in the right context, communicative, but not non-communicative, looks can signal a commitment.

The Whistleblower's Dilemma in Young Children: When Loyalty Trumps Other Moral Concerns.

When a group engages in immoral behavior, group members face the whistleblower's dilemma: the conflict between remaining loyal to the group and standing up for other moral concerns. This study examines the developmental origins of this dilemma by investigating 5-year-olds' whistleblowing on their in- vs. outgroup members' moral transgression. Children (n = 96) watched puppets representing their ingroup vs. outgroup members commit either a mild or a severe transgression. After the mild transgression, children tattled on both groups equally often. After the severe transgression, however, they were significantly less likely to blow the whistle on their ingroup than on the outgroup. These results suggest that children have a strong tendency to act on their moral concerns, but can adjust their behavior according to their group's need: When much is at stake for the ingroup (i.e., after a severe moral transgression), children's behavior is more likely to be guided by loyalty.

Selective copying of the majority suggests children are broadly "optimal-" rather than "over-" imitators.

Human children, in contrast to other species, are frequently cast as prolific "over-imitators". However, previous studies of "over-imitation" have overlooked many important real-world social dynamics, and may thus provide an inaccurate account of this seemingly puzzling and potentially maladaptive phenomenon. Here we investigate this topic using a cultural evolutionary approach, focusing particularly on the key adaptive learning strategy of majority-biased copying. Most "over-imitation" research has been conducted using consistent demonstrations to the observer, but we systematically varied the frequency of demonstrators that 4- to 6-year-old children observed performing a causally irrelevant action. Children who "over-imitate" inflexibly should copy the majority regardless of whether the majority solution omits or includes a causally irrelevant action. However, we found that children calibrated their tendency to acquire the majority behavior, such that copying did not extend to majorities that performed irrelevant actions. These results are consistent with a highly functional, adaptive integration of social and causal information, rather than explanations implying unselective copying or causal misunderstanding. This suggests that our species might be better characterized as broadly "optimal-" rather than "over-" imitators.

Great apes distinguish true from false beliefs in an interactive helping task.

Understanding the behavior of others in a wide variety of circumstances requires an understanding of their psychological states. Humans' nearest primate relatives, the great apes, understand many psychological states of others, for example, perceptions, goals, and desires. However, so far there is little evidence that they possess the key marker of advanced human social cognition: an understanding of false beliefs. Here we demonstrate that in a nonverbal (implicit) false-belief test which is passed by human 1-year-old infants, great apes as a group, including chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and orangutans (Pongo abelii), distinguish between true and false beliefs in their helping behavior. Great apes thus may possess at least some basic understanding that an agent's actions are based on her beliefs about reality. Hence, such understanding might not be the exclusive province of the human species.

What Is a Group? Young Children's Perceptions of Different Types of Groups and Group Entitativity.

To date, developmental research on groups has focused mainly on in-group biases and intergroup relations. However, little is known about children's general understanding of social groups and their perceptions of different forms of group. In this study, 5- to 6-year-old children were asked to evaluate prototypes of four key types of groups: an intimacy group (friends), a task group (people who are collaborating), a social category (people who look alike), and a loose association (people who coincidently meet at a tram stop). In line with previous work with adults, the vast majority of children perceived the intimacy group, task group, and social category, but not the loose association, to possess entitativity, that is, to be a 'real group.' In addition, children evaluated group member properties, social relations, and social obligations differently in each type of group, demonstrating that young children are able to distinguish between different types of in-group relations. The origins of the general group typology used by adults thus appear early in development. These findings contribute to our knowledge about children's intuitive understanding of groups and group members' behavior.

The Early Emergence of Guilt-Motivated Prosocial Behavior.

Guilt serves vital prosocial functions: It motivates transgressors to make amends, thus restoring damaged relationships. Previous developmental research on guilt has not clearly distinguished it from sympathy for a victim or a tendency to repair damage in general. The authors tested 2- and 3-year-old children (N = 62 and 64, respectively) in a 2 × 2 design, varying whether or not a mishap caused harm to someone and whether children themselves caused that mishap. Three-year-olds showed greatest reparative behavior when they had caused the mishap and it caused harm, thus showing a specific effect of guilt. Two-year-olds repaired more whenever harm was caused, no matter by whom, thus showing only an effect of sympathy. Guilt as a distinct motivator of prosocial behavior thus emerges by at least 3 years.

I won't tell: Young children show loyalty to their group by keeping group secrets.

Group loyalty is highly valued. However, little is known about young children's loyal behavior. This study tested whether 4- and 5-year-olds (N=96) remain loyal to their group even when betraying it would be materially advantageous. Children and four puppets were allocated to novel groups. Two of these puppets (either in-group or out-group members) then told children a group secret and urged them not to disclose the secret. Another puppet (not assigned to either group) then bribed children with stickers to tell the secret. Across ages, children were significantly less likely to reveal the secret in the in-group condition than in the out-group condition. Thus, even young children are willing to pay a cost to be loyal to their group.

The effects of collaboration and minimal-group membership on children's prosocial behavior, liking, affiliation, and trust.

Recent theoretical work has highlighted potential links between interpersonal collaboration and group membership in the evolution of human sociality. Here we compared the effects of collaboration and minimal-group membership on young children's prosocial behavior (i.e., helping and resource allocation), liking, affiliation, and trust. In a design that matched as closely as possible these two ways of connecting with others, we showed that 5-year-olds' behavior was affected similarly by collaboration and minimal-group membership; both increased children's preference for their partners on multiple dimensions and produced overall effects of a similar magnitude. In contrast, 3.5-year-olds did not have a strong preference for either collaborators or minimal in-group members. Thus, both collaboration and minimal-group membership are similarly effective in their influence on children's prosocial behavior and social preferences.

Children draw more affiliative pictures following priming with third-party ostracism.

Humans have a strong need to belong. Thus, when signs of ostracism are detected, adults often feel motivated to affiliate with others in order to reestablish their social connections. This study investigated the importance of affiliation to young children following priming with ostracism. Four- and 5-year-old children were primed with either ostracism or control videos and their understanding of, and responses to, the videos were measured. Results showed that children were able to report that there was exclusion in the ostracism videos, and that they recognized that the ostracized individual felt sad. Most interestingly, when subsequently asked to draw a picture of themselves and their friend, children primed with ostracism depicted relationships that were significantly more affiliative. Children drew themselves and their friend standing significantly closer together and adults rated their drawings as more affiliative overall. These findings introduce drawing as a useful new method for measuring social motivations and processes following an experimental manipulation, and demonstrate that affiliation is particularly important to children following even a vicarious experience of social exclusion.

Young children show the bystander effect in helping situations.

Much research in social psychology has shown that otherwise helpful people often fail to help when bystanders are present. Research in developmental psychology has shown that even very young children help and that the presence of others can actually increase helping in some cases. In the current study, in contrast, 5-year-old children helped an experimenter at very high levels when they were alone but helped significantly less often in the presence of bystanders who were potentially available to help. In another condition designed to elucidate the mechanism underlying the effect, children's helping was not reduced when bystanders were present but confined behind a barrier and thus unable to help (a condition that has not been run in previous studies with adults). Young children thus show the bystander effect, and it is due not to social referencing or shyness to act in front of others but, rather, to a sense of a diffusion of responsibility.

Children infer affiliative and status relations from watching others imitate.

We investigated whether young children are able to infer affiliative relations and relative status from observing others' imitative interactions. Children watched videos showing one individual imitating another and were asked about the relationship between those individuals. Experiment 1 showed that 5-year-olds assume that individuals imitate people they like. Experiment 2 showed that children of the same age assume that an individual who imitates is relatively lower in status. Thus, although there are many advantages to imitating others, there may also be reputational costs. Younger children, 4-year-olds, did not reliably make either inference. Taken together, these experiments demonstrate that imitation conveys valuable information about third party relationships and that, at least by the age of 5, children are able to use this information in order to infer who is allied with whom and who is dominant over whom. In doing so, they add a new dimension to our understanding of the role of imitation in human social life.

Young children create iconic gestures to inform others.

Much is known about young children's use of deictic gestures such as pointing. Much less is known about their use of other types of communicative gestures, especially iconic or symbolic gestures. In particular, it is unknown whether children can create iconic gestures on the spot to inform others. Study 1 provided 27-month-olds with the opportunity to inform a novice how to perform a task. The majority of children created appropriate iconic gestures, and they did so significantly more than in a control condition in which the need to inform someone was removed. In Study 2, some of the 21-month-olds tested also created novel iconic gestures but to a lesser extent. Results are discussed in relation to children's symbolic, linguistic, and social-cognitive development.

Limitations to the cultural ratchet effect in young children.

Although many animal species show at least some evidence of cultural transmission, broadly defined, only humans show clear evidence of cumulative culture. In the current study, we investigated whether young children show the "ratchet effect," an important component of cumulative culture--the ability to accumulate efficient modifications across generations. We tested 16 diffusion chains--altogether consisting of 80 children--to see how they solved an instrumental task (i.e., carrying something from one location to another). We found that when the chain was seeded with an inefficient way of solving the task, 4-year-olds were able to innovate and transmit these innovations so as to reach a more efficient solution. However, when it started out with relatively efficient solutions already (i.e., the ones that children in a control condition discovered for themselves), there were no further techniques invented and/or transmitted beyond that. Thus, young children showed the ratchet effect to a limited extent, accumulating efficient modifications but not going beyond the inventive level of the individual.