A core element of the human social experience is sharing one’s subjective reality with others and many scholars have therefore theorized about, and empirically studied the psychology of shared reality. However, over the last couple of decades different disciplines have started to take increasingly different theoretical approaches to what it means for a reality to be shared, leading to conceptual inconsistencies (and thus confusion) within the field. In this paper, we therefore propose a unifying theory of shared reality aimed at streamlining shared reality research across different disciplines. To do so, we first provide a conceptual review of the shared reality literature in different fields. Next, we provide a conceptual analysis of shared reality, resulting in a unifying theory of shared reality containing five core principles. From these core principles, we extract two key hypotheses about the ontogeny and phylogeny of shared reality. We will then review these hypotheses in the light of the literature within the field to create a developmental timeline for the emergence of shared reality in human children, as well as a phylogenetic description of this phenomenon in non-human animals. Finally, some additional implications of the theory are discussed. Author note: The first version of the manuscript is the original MAP, defended on the 25th of April 2019.

Humans are highly skilled at establishing mental state alignment through communication during collaborative interactions. Yet there is still much debate about how they do this effectively. Recently, scholars have argued that the capacity to understand others’ communicative intent facilitates mental state alignment by constraining the meaning of communicative expressions to a domain of mutual relevance. Although this constraint is likely an important facilitator of human communication, it is unlikely to completely resolve the interpretative indeterminacy inherent to humans’ open-ended communication systems (i.e., inferring the intended meaning of arbitrary signals amid quasi-infinite interpretive possibilities). Here, I argue that understanding communicative intent facilitates mental state alignment in a crucial, previously underappreciated way. Understanding the cooperative intention underlying ostension solves the problem of ‘ambiguous affective reference’ inherent to emotional expressions in response to communicative acts. Specifically, it constrains the interpretation of these expressions to be about the communicative act’s content (i.e., ostensive feedback). Consequently, ostensive negative feedback facilitates the negotiation of mental states during perceived mental misalignment (disagreement) until both individuals use positive ostensive feedback (affirmation) to indicate that they deem their mental states sufficiently aligned for the purposes of their interaction (agreement). I argue that this capacity facilitates much of humans’ sociality.

Sharing psychological processes such as attention, intentions and emotions plays a vital role in the phenomenology, ontogeny and phylogeny of social coordination and has therefore been widely studied. Yet, discussions about how to characterize this phenomenon often remain within the boundaries of individual fields. Consequently, there is much inconsistency in how this phenomenon is conceptualized and operationalized across fields, making it difficult to assess the value of empirical work on shared psychological processes emerging in different areas. In an attempt to facilitate cross-discipline consistency we propose a novel framework of shared psychological processes, consisting of five principles. First, sharing psychological processes is construed as a cognitive capacity. Second, sharing psychological processes has intrapersonal and interactive consequences. Third, for a psychological process to be shared the overlap between individuals has to be deemed sufficient in the light of a functional criterion of shared psychological processes. Fourth, sharing psychological processes can take different forms depending on whether the recursive structure of the social information being processed allows us to construe the emerging social relationship in terms of physically causal (inter)dependency, psychological dependency, psychological interdependency, or interpersonality. Fifth, sharing psychological processes can take different forms depending on whether it is based on inferences about occurrent psychological processes in others, or assumptions about stable, latent psychological processes in others. These latter two principles culminate into a novel shared psychology typology, describing different forms of sharing in joint action (i.e. conjugate, co-experienced, shared, and joint) and disjoint social coordination (i.e. common, mutual, grounded and concordant). Author note: The first version of the manuscript is the original MAP, defended on the 25th of April 2019. This version is a paper that has been submitted to Behavioral and Brain Sciences, Psychological Review, and Perspectives on Psychological Science (all in 2020).

Abstract The study of great ape cognition offers insights into the evolutionary origins of human intelligence, but is hindered by small sample sizes and restricted access to data. To address this, we present the EVApeCognition Dataset, a publicly available resource comprising 262 experimental datasets from 150 scientific publications from the Wolfgang Köhler Primate Research Center (2004–2021) in Leipzig, Germany. Eighty-one apes participated in 150 studies, with a majority (N = 78) participating in more than one study. Publication of the dataset aims to make these unique datasets accessible for future meta-analyses and correlational analyses, helping us better understand how our great ape relatives think, learn, and behave.

The current manuscript rightly points out that non-human primates evolved complex social cognitive skills to maintain weaker social ties. However, these capacities are likely more expansive than currently proposed: research shows that apes behave more socially to those with whom they experience similar things, suggesting that they possess some precursor of humans' capacity to bond through shared experiences.

Humans have a unique capacity to bond with others through shared experiences, even in the absence of explicit communication. Yet it is unknown whether this capacity is flexible enough to accommodate the different kinds of virtual environments on which we increasingly rely. In the current pre-registered study, we examined whether this capacity still operates effectively on shared screens during non-communicative video mediated interactions, in dyads and in groups. Participants (N = 144 US participants, 71 female, 72 male, 1 non-binary) either watched a video on a shared screen together with (pre-recorded) partners or watched individually while these partners attended to something else. Equivalence tests showed that self-reported social bonding scores were practically equivalent between conditions. Thus, in contrast to several in-person studies, there was no difference in social bonding between conditions. These results show that, in the absence of explicit communication, some of humans’ most fundamental social bonding mechanisms might not operate as effectively in video mediated social interactions. As such, without sufficient active social or emotional engagement, the social costs of increasingly relying on video mediated social interactions might be greater than previously thought.

Three-year-old children normatively protest the transgression of adult rules in a variety of contexts. Five-year-olds also normatively protest the transgression of rules they have themselves created collaboratively with peers. But do children of these ages protest rules that they have created for themselves as individuals? We prompted five-year-olds (Study 1: 128 participants, 69 females) and three-year-olds (Study 2: 64 participants, 32 females) to devise a way to play with a toy in the presence of some puppet peers, after which a new puppet engaged with the toy the 'wrong' way. Results showed that five-year-olds protested at similar rates regardless of whether they came up with a way to play collaboratively with others and then played together (collaborative condition), came up with a way to play individually but then played together (two trendsetter conditions), or came up with a way to play and played totally individually (solo condition). In Study 2, three-year-olds protested self-created rules as well, albeit at lower rates than five-year-olds. Finally, neither age group's protest seemed to be influenced by instructions containing explicit cues of normativity or conventionality (e.g., creating a game with rules vs coming up with a way to play). As such, when children create norms themselves, their willingness to protest novice transgressors seems not to be impacted by the degree to which these norms were created through collaboration. Moreover, our results show that promiscuous normativity of self-created norms emerges earlier than previously thought, around the same time children become promiscuous normativists towards adult-created norms.

To understand why humans put much effort into celebrating cultural myths, it is crucial to approach this phenomenon as part of humans' broader social cognitive evolution. Specifically, humans' unique capacity to bond with others through shared/collective representations of shared experiences has likely caused individuals to use myths to assess not only coalitions' fitness interdependence, but also their cooperative prowess.

Theory of mind research has traditionally focused on the ascription of mental states to a single individual. Here, we introduce a theory of collective mind: the ascription of a unified mental state to a group of agents with convergent experiences. Rather than differentiation between one's personal perspective and that of another agent, a theory of collective mind requires perspectival unification across agents. We review recent scholarship across the cognitive sciences concerning the conceptual foundations of collective mind representations and their empirical induction through the synchronous arrival of shared information. Research suggests that representations of a collective mind cause psychological amplification of co-attended stimuli, create relational bonds, and increase cooperation, among co-attendees.

The cooperative eye hypothesis posits that human eye morphology evolved to facilitate cooperation. Although it is known that young children prefer stimuli with eyes that contain white sclera, it is unknown whether white sclera influences children's perception of a partner's cooperativeness specifically. In the current studies, we used an online methodology to present 5-year-old children with moving three-dimensional face models in which facial morphology was manipulated. Children found "alien" faces with human eyes more cooperative than faces with dark sclera (Study 2) but not faces with enlarged irises (Study 1). For more human-like faces (Study 3), children found human eyes more cooperative than either enlarged irises or dark sclera and found faces with enlarged irises cuter (but not more cooperative) than eyes with dark sclera. Together, these results provide strong support for the cooperative eye hypothesis.

Many mechanisms of social bonding are common to all primates, but humans seemingly have developed some that are unique to the species. These involve various kinds of interactive experiences-from taking a walk together to having a conversation-whose common feature is the triadic sharing of experience. Current theories of social bonding have no explanation for why humans should have these unique bonding mechanisms. Here we propose a shared intentionality account of uniquely human social bonding. Humans evolved to participate with others in unique forms of cooperative and communicative activities that both depend on and create shared experience. Sharing experience in these activities causes partners to feel closer because it allows them to assess their partner's cooperative competence and motivation toward them and because the shared representations created during such interactions make subsequent cooperative interactions easier and more effective.

After two strangers have briefly interacted with one another, both believe that they like their partner more than their partner likes them. A plausible explanation for this liking gap is that people are constantly worrying about how others are evaluating them. If so, one would expect the liking gap to emerge in young children as they become more concerned with their reputations and the impression they make on other people. The current study ( N = 241 U.S. children; age range = 4–11 years) supported this hypothesis, showing a liking gap beginning when children were 5 years old, the age at which they first become concerned with other people’s evaluations of them. Moreover, the liking gap became more pronounced as children got older. These findings provide the first developmental description of the liking gap and support the hypothesis that this phenomenon is related to individuals’ concerns for how others evaluate them.

To create social closeness, humans engage in a variety of social activities centered around shared experiences. Even simply watching the same video side by side creates social closeness in adults and children. However, perhaps surprisingly, a similar psychological mechanism was recently shown in great apes. Here we asked whether the process by which this social closeness is created is the same for children and great apes. Each participant entered a room to see an experimenter (E1) watching a video. In one condition, E1 looked to the participant at the start of the video to establish common ground that they were watching the video together. In another condition, E1 did not look to the participant in this way so that the participant knew they were watching the same video, but the participant did not know whether E1 was aware of this as well, so there was no common ground (E1 looked to the participant later in the procedure). Children, but not great apes, approached the experimenter faster after the common ground condition, suggesting that although both humans and great apes create social closeness by co-attending to something in close proximity, creating social closeness by sharing experiences in common ground may be a uniquely human social-cognitive process.

Human social relationships are often formed through shared social activities in which individuals share mental states about external stimuli. Previous work on joint attention has shown that even minimal shared experiences such as watching something together facilitates social closeness between individuals. Here, we examined whether young children already connect with others through joint attention. In the current studies, children sat next to a novel adult who either watched a film with them or was not able to see the film and read a book instead. After the video, we measured children's willingness (i.e., latency) to approach the experimenter holding out a toy. In both studies, the 2.5-year-olds who watched the film together approached more quickly than the other children. These results show that both minimally interactive shared experiences and noninteractive shared experiences lead children to feel more comfortable with a novel adult. This suggests that joint attention interactions, and shared experiences in general, play an important role not only in children's cognitive development but also in their social development and the formation of their social relationships.

Humans create social closeness with one another through a variety of shared social activities in which they align their emotions or mental states towards an external stimulus such as dancing to music together, playing board games together or even engaging in minimal shared experiences such as watching a movie together. Although these specific behaviours would seem to be uniquely human, it is unclear whether the underlying psychology is unique to the species, or if other species might possess some form of this psychological mechanism as well. Here we show that great apes who have visually attended to a video together with a human (study 1) and a conspecific (study 2) subsequently approach that individual faster (study 1) or spend more time in their proximity (study 2) than when they had attended to something different. Our results suggest that one of the most basic mechanisms of human social bonding—feeling closer to those with whom we act or attend together—is present in both humans and great apes, and thus has deeper evolutionary roots than previously suspected.

There has recently been interest in the ways in which coordinated movements encourage coactors to feel socially closer to one another, but this has generally overlooked the importance of necessary precursors to this joint action. Here we target two low-level behaviours involved in social coordination that may mediate a relationship between joint actions and social bonding, namely joint attention and shared goals. Participants engaged in a simple reaction time task while sitting next to a partner performing the same task. In a joint attention condition, both participants attended to stimuli presented on the same half of a computer screen, while in a control condition, they attended to opposite sides of the computer screen. Shared goals were manipulated by giving participants the instruction to keep below a threshold score for both individual response times and accuracy (individual goal), or their joint mean response time and accuracy (i.e., averaging their mean response time and accuracy with that of their partner: shared goal). Attending to the same side of the screen led to higher ratings on a composite social bonding index directed towards a partner, while shared goals did not cause any effects on partner ratings. Joint attention was sufficient to encourage social closeness with an interaction partner, which suggests that any activities which encourage attending to the same point in space could have some influence on how connected coactors feel about one another.

There has recently been interest in the ways in which coordinated movements encourage coactors to feel socially closer to one another, but this has generally overlooked the importance of necessary precursors to this joint action. Here we target two low-level behaviours involved in social coordination that may mediate a relationship between joint actions and social bonding, namely joint attention and shared goals. Participants engaged in a simple reaction time task while sitting next to a partner performing the same task. In a joint attention condition, both participants attended to stimuli presented on the same half of a computer screen, while in a control condition, they attended to opposite sides of the computer screen. Shared goals were manipulated by giving participants the instruction to keep below a threshold score for both individual response times and accuracy (individual goal), or their joint mean response time and accuracy (i.e., averaging their mean response time and accuracy with that of their partner: shared goal). Attending to the same side of the screen led to higher ratings on a composite social bonding index directed towards a partner, while shared goals did not cause any effects on partner ratings. Joint attention was sufficient to encourage social closeness with an interaction partner, which suggests that any activities which encourage attending to the same point in space could have some influence on how connected coactors feel about one another.

We describe Ostracism Online, a novel, social media–based ostracism paradigm designed to (1) keep social interaction experimentally controlled, (2) provide researchers with the flexibility to manipulate the properties of the social situation to fit their research purposes, (3) be suitable for online data collection, (4) be convenient for studying subsequent within-group behavior, and (5) be ecologically valid. After collecting data online, we compared the Ostracism Online paradigm with the Cyberball paradigm (Williams & Jarvis Behavior Research Methods, 38, 174–180, 2006) on need-threat and mood questionnaire scores (van Beest & Williams Journal of Personality and Social Psychology 91, 918–928, 2006). We also examined whether ostracized targets of either paradigm would be more likely to conform to their group members than if they had been included. Using a Bayesian analysis of variance to examine the individual effects of the different paradigms and to compare these effects across paradigms, we found analogous effects on need-threat and mood. Perhaps because we examined conformity to the ostracizers (rather than neutral sources), neither paradigm showed effects of ostracism on conformity. We conclude that Ostracism Online is a cost-effective, easy to use, and ecologically valid research tool for studying the psychological and behavioral effects of ostracism.