Corepresentation During Joint Action in Marmoset Monkeys ( Callithrix jacchus)

Marmosets mutually compensate for differences in rhythms when coordinating vigilance

Synchronization is widespread in animals, and studies have often emphasized how this seemingly complex phenomenon can emerge from very simple rules. However, the amount of flexibility and control that animals might have over synchronization properties, such as the strength of coupling, remains underexplored. Here, we studied how pairs of marmoset monkeys coordinated vigilance while feeding. By modeling them as coupled oscillators, we noted that (1) individual marmosets do not show perfect periodicity in vigilance behaviors, (2) nevertheless, marmoset pairs started to take turns being vigilant over time, a case of anti-phase synchrony, (3) marmosets could couple flexibly; the coupling strength varied with every new joint feeding bout, and (4) marmosets could control the coupling strength; dyads showed increased coupling if they began in a more desynchronized state. Such flexibility and control over synchronization require more than simple interaction rules. Minimally, animals must estimate the current degree of asynchrony and adjust their behavior accordingly. Moreover, the fact that each marmoset is inherently non-periodic adds to the cognitive demand. Overall, our study provides a mathematical framework to investigate the cognitive demands involved in coordinating behaviors in animals, regardless of whether individual behaviors are rhythmic or not.

Chimpanzees demonstrate a behavioural signature of human joint action

The strength of human society can largely be attributed to the tendency to work together to achieve outcomes that are not possible alone. Effective social coordination benefits from mentally representing a partner's actions. Specifically, humans optimize social coordination by forming internal action models adapted to joint rather than individual task demands. To what extent do humans share the cognitive mechanisms that support optimal human coordination and collaboration with other species? An ecologically inspired joint handover-to-retrieve task was systematically manipulated across several experiments to assess whether joint action planning in chimpanzees reflects similar patterns to humans. Chimpanzees' chosen handover locations shifted towards the location of the experimenter's free or unobstructed hand, suggesting they represent the constraints of the joint task even though their individual half of the task was unobstructed. These findings indicate that chimpanzees and humans may share common cognitive mechanisms or predispositions that support joint action.

The Joint Simon task is not joint for capuchin monkeys

Human cooperation can be facilitated by the ability to create a mental representation of one's own actions, as well as the actions of a partner, known as action co-representation. Even though other species also cooperate extensively, it is still unclear whether they have similar capacities. The Joint Simon task is a two-player task developed to investigate this action co-representation. We tested brown capuchin monkeys (Sapajus [Cebus] apella), a highly cooperative species, on a computerized Joint Simon task and found that, in line with previous research, the capuchins' performance was compatible with co-representation. However, a deeper exploration of the monkeys' responses showed that they, and potentially monkeys in previous studies, did not understand the control conditions, which precludes the interpretation of the results as a social phenomenon. Indeed, further testing to investigate alternative explanations demonstrated that our results were due to low-level cues, rather than action co-representation. This suggests that the Joint Simon task, at least in its current form, cannot determine whether non-human species co-represent their partner's role in joint tasks.

Examination of the joint Simon effect in rats: Changes in task performance based on actions of the partner

Nonhuman animals have demonstrated various cooperative behaviors; however, many examples can be interpreted as individual contributions to a task rather than true behavioral coordination. In this study, we used the joint Simon task in rats to determine whether the presence of and task sharing with a partner affected performance in a joint activity. Rats were trained to discriminate between two auditory stimuli (3 and 12 kHz tones) and individually performed an auditory Simon task. They were paired with another rat and tested to perform half of the task, while the other rat performed the other half (joint task condition). The Simon effect was confirmed when the two rats completed half of a joint task. In contrast, when they were placed side by side but only one rat completed half of the task, the Simon effect was not observed. Further analyses revealed that the Simon effect observed in the joint task could not be explained by the simple addition of the two half tasks. In conclusion, task sharing affected individual performance in rats.

Putting the cart before the horse? The origin of information donation

Heintz & Scott-Phillips propose that the partner choice ecology of our ancestors required Gricean cognitive pragmatics for reputation management, which caused a tendency toward showing and expecting prosociality that subsequently scaffolded language evolution. Here, we suggest a cognitively leaner explanation that is more consistent with comparative data and posits that prosociality and eventually language evolved along with cooperative breeding.

Problem-solving in groups of common marmosets (Callithrix jacchus): more than the sum of its parts

Human hypercooperativity and the emergence of division of labor enables us to solve problems not only effectively within a group but also collectively. Collective problem-solving occurs when groups perform better than the additive performance of separate individuals. Currently, it is unknown whether this is unique to humans. To investigate the evolutionary origin of collective problem-solving and potential precursors, we propose a continuum of group effects on problem-solving, from simple to complex ones, eventually culminating in collective problem-solving. We tested captive common marmosets with a series of problem-solving tasks, either alone or in a group. To test whether the performance of a group was more than the sum of its parts, we compared real groups to virtual groups (pooled scores of animals tested alone). Marmosets in real groups were both more likely to solve problems than marmosets within the virtual groups and to do so faster. Although individuals within real groups approached the problem faster, a reduction in neophobia was not sufficient to explain the greater success. Success within real groups arose because animals showed higher perseverance, especially after a fellow group member had found the solution in complex tasks. These results are consistent with the idea that group problem-solving evolved alongside a continuum, with performance improving beyond baseline as societies move from social tolerance to opportunities for diffusion of information to active exchange of information. We suggest that increasing interdependence and the adoption of cooperative breeding pushed our ancestors up this scale.

A convergent interaction engine: vocal communication among marmoset monkeys

To understand the primate origins of the human interaction engine, it is worthwhile to focus not only on great apes but also on callitrichid monkeys (marmosets and tamarins). Like humans, but unlike great apes, callitrichids are cooperative breeders, and thus habitually engage in coordinated joint actions, for instance when an infant is handed over from one group member to another. We first explore the hypothesis that these habitual cooperative interactions, the marmoset interactional ethology, are supported by the same key elements as found in the human interaction engine: mutual gaze (during joint action), turn-taking, volubility, as well as group-wide prosociality and trust. Marmosets show clear evidence of these features. We next examine the prediction that, if such an interaction engine can indeed give rise to more flexible communication, callitrichids may also possess elaborate communicative skills. A review of marmoset vocal communication confirms unusual abilities in these small primates: high volubility and large vocal repertoires, vocal learning and babbling in immatures, and voluntary usage and control. We end by discussing how the adoption of cooperative breeding during human evolution may have catalysed language evolution by adding these convergent consequences to the great ape-like cognitive system of our hominin ancestors. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Every product needs a process: unpacking joint commitment as a process across species

Joint commitment, the feeling of mutual obligation binding participants in a joint action, is typically conceptualized as arising by the expression and acceptance of a promise. This account limits the possibilities of investigating fledgling forms of joint commitment in actors linguistically less well-endowed than adult humans. The feeling of mutual obligation is one aspect of joint commitment (the product), which emerges from a process of signal exchange. It is gradual rather than binary; feelings of mutual obligation can vary in strength according to how explicit commitments are perceived to be. Joint commitment processes are more complex than simple promising, in at least three ways. They are affected by prior joint actions, which create precedents and conventions that can be embodied in material arrangements of institutions. Joint commitment processes also arise as solutions to generic coordination problems related to opening up, maintaining and closing down joint actions. Finally, during joint actions, additional, specific commitments are made piecemeal. These stack up over time and persist, making it difficult for participants to disengage from joint actions. These complexifications open up new perspectives for assessing joint commitment across species. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

The evolutionary drivers of primate scleral coloration

The drivers of divergent scleral morphologies in primates are currently unclear, though white sclerae are often assumed to underlie human hyper-cooperative behaviours. Humans are unusual in possessing depigmented sclerae whereas many other extant primates, including the closely-related chimpanzee, possess dark scleral pigment. Here, we use phylogenetic generalized least squares (PGLS) analyses with previously generated species-level scores of proactive prosociality, social tolerance (both n = 15 primate species), and conspecific lethal aggression (n = 108 primate species) to provide the first quantitative, comparative test of three existing hypotheses. The 'self-domestication' and 'cooperative eye' explanations predict white sclerae to be associated with cooperative, rather than competitive, environments. The 'gaze camouflage' hypothesis predicts that dark scleral pigment functions as gaze direction camouflage in competitive social environments. Notably, the experimental evidence that non-human primates draw social information from conspecific eye movements is unclear, with the latter two hypotheses having recently been challenged. Here, we show that white sclerae in primates are associated with increased cooperative behaviours whereas dark sclerae are associated with reduced cooperative behaviours and increased conspecific lethal violence. These results are consistent with all three hypotheses of scleral evolution, suggesting that primate scleral morphologies evolve in relation to variation in social environment.

A prosocial function of head-gaze aversion and head-cocking in common marmosets

Gaze aversion is a behavior adopted by several mammalian and non-mammalian species in response to eye contact, and is usually interpreted as a reaction to a perceived threat. Unlike many other primate species, common marmosets (Callithrix jacchus) are thought to have a high tolerance for direct gaze, barely exhibiting gaze avoidance towards conspecifics and humans. Here we show that this does not hold for marmosets interacting with a familiar experimenter who suddenly establishes eye contact in a playful interaction (peekaboo). Video footage synchronously recorded from the perspective of the marmoset and the experimenter showed that the monkeys consistently alternated between eye contact and head-gaze aversion, and that these responses were often preceded by head-cocking. We hypothesize that this behavioral strategy helps marmosets to temporarily disengage from emotionally overwhelming social stimulation due to sight of another individual's face, in order to prepare for a new round of affiliative face-to-face interactions.

Individual differences in co-representation in three monkey species (Callithrix jacchus, Sapajus apella and Macaca tonkeana) in the joint Simon task: the role of social factors and inhibitory control

Behavioral coordination is involved in many forms of primate interactions. Co-representation is the simultaneous mental representation of one’s own and the partner’s task and actions. It often underlies behavioral coordination and cooperation success. In humans, the dyadic social context can modulate co-representation. Here, we first investigated whether individual differences in co-representation in the joint Simon task in capuchin monkeys and Tonkean macaques can be explained by social factors, namely dyadic grooming and sociality index, rank difference and eigenvector centrality. These factors did not predict variation in co-representation. However, in this specific task, co-representation reduces rather than facilitates joint performance. Automatic co-representation therefore needs to be inhibited or suppressed to maximize cooperation success. We therefore also investigated whether general inhibitory control (detour-reaching) would predict co-representation in the joint Simon task in Tonkean macaques, brown capuchin and marmoset monkeys. Inhibitory control did neither explain individual differences nor species differences, since marmosets were most successful in their joint performance despite scoring lowest on inhibitory control. These results suggest that the animals’ ability to resolve conflicts between self and other representation to increase cooperation success in this task is gradually learned due to frequent exposure during shared infant care, rather than determined by strong general inhibitory control. Further, we conclude that the joint Simon task, while useful to detect co-representation non-invasively, is less suitable for identifying the factors explaining individual differences and thus a more fruitful approach to identify these factors is to design tasks in which co-representation favors, rather than hinders cooperation success.

Watching others in a positive state does not induce optimism bias in common marmosets (Callithrix jacchus), but leads to behaviour indicative of competition

Emotional contagion is suggested to facilitate group life by enhancing synchronized responses to the environment. Cooperative breeders are an example of a social system that requires such intricate coordination between individuals. Therefore, we studied emotional contagion in common marmosets by means of a judgement bias test. Demonstrators were exposed to an emotion manipulation (i.e., positive, negative, control), and observers perceived only the demonstrator's behaviour. We predicted that the positive or negative states of the demonstrator would induce matching states in the observer, indicating emotional contagion. All subjects' emotional states were assessed through behaviour and cognition, the latter by means of a judgement bias test. Behavioural results showed a successful emotion manipulation of demonstrators, with manipulation-congruent expressions (i.e., positive calls in the positive condition, and negative calls and pilo-erect tail in the negative condition). Observers showed no manipulation-congruent expressions, but showed more scratching and arousal after the positive manipulation. Concerning the judgement bias test, we predicted that subjects in a positive state should increase their response to ambiguous cues (i.e., optimism bias), and subjects in a negative state should decrease their response (i.e., pessimism bias). This prediction was not supported as neither demonstrators nor observers showed such bias in either manipulation. Yet, demonstrators showed an increased response to the near-positive cue, and additional analyses showed unexpected responses to the reference cues, as well as a researcher identity effect. We discuss all results combined, including recently raised validation concerns of the judgement bias test, and inherent challenges to empirically studying emotional contagion.

Assessing joint commitment as a process in great apes

Many social animals interact jointly, but only humans experience a specific sense of obligation toward their co-participants, a joint commitment. However, joint commitment is not only a mental state but also a process that reveals itself in the coordination efforts deployed during entry and exit phases of joint action. Here, we investigated the presence and duration of such phases in N = 1,242 natural play and grooming interactions of captive chimpanzees and bonobos. The apes frequently exchanged mutual gaze and communicative signals prior to and after engaging in joint activities with conspecifics, demonstrating entry and exit phases comparable to those of human joint activities. Although rank effects were less clear, phases in bonobos were more moderated by friendship compared to phases in chimpanzees, suggesting bonobos were more likely to reflect patterns analogous to human “face management”. This suggests that joint commitment as process was already present in our last common ancestor with Pan.

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Great apes exchange signals and gaze before entering and exiting joint actions

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Joint action structure of both ape species resembles that of humans

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Coordinated joint action phases indicate an underlying joint commitment

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Social bonds affect joint action structure more in bonobos than in chimpanzees

Marmoset prosociality is intentional

Marmoset monkeys show high levels of proactive prosociality, a trait shared with humans, presumably because both species rely on allomaternal care. However, it is not clear whether the proximate regulation of this convergent trait is also similar, in particular with regard to intentionality, which is a defining characteristic of prosocial behavior in the human literature. The aim of this paper was to investigate whether marmoset monkeys' prosociality fulfils the criteria of intentionality developed in primate communication research. The results show that marmoset prosocial behavior (i) has some degree of flexibility, since individuals can use multiple means to reach their goal and adjust them to specific conditions, (ii) depends on the presence of an audience, i.e. potential recipients (social use), and (iii) is goal-directed, because (a) it continues exactly until the putative goal is reached, and (b) individuals check back and look at/for their partner when their prosocial actions do not achieve the putative goal (i.e. if their actions don't lead to the expected outcome, this elicits distinct reactions in the actor). These results suggest that marmoset prosociality is under some degree of voluntary, intentional control. They are in line with other findings that marmosets perceive each other as intentional agents, and only learn socially from actions that are perceived as intentional. The most parsimonious conclusion is, therefore, that prosocial behavior is fundamentally under voluntary control in marmosets, just as it is in humans, even though our more sophisticated cognitive abilities allow for a far more complex integration of prosociality into a broader variety of contexts and of behavioral goals.

How animals collaborate: Underlying proximate mechanisms

Collaboration or social interactions in which two or more individuals coordinate their behavior to produce outcomes from which both individuals benefit are common in nature. Individuals from many species hunt together, defend their territory, and form coalitions in intragroup competition. However, we still know very little about the proximate mechanisms underlying these behaviors. Recent theories of human cognitive evolution have emphasized the role collaboration may have played in the selection of socio-cognitive skills. It has been argued that the capacity to form shared goals and joint intentions with others, is what allows humans to collaborate so flexibly and efficiently. Although there is no evidence that nonhuman animals are capable of shared intentionality, there is conceivably a wide range of proximate mechanisms that support forms of, potentially flexible, collaboration in other species. We review the experimental literature with the aim of evaluating what we know about how other species achieve collaboration; with a particular focus on chimpanzees. We structure the review with a new categorization of collaborative behavior that focuses on whether individuals intentionally coordinate actions with others. We conclude that for a wider comparative perspective we need more data from other species but the findings so far suggest that chimpanzees, and possibly other great apes, are capable of understanding the causal role of a partner in collaboration. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Psychology > Comparative Psychology.

Chimpanzee Coordination and Potential Communication in a Two-touchscreen Turn-taking Game

Recent years have seen a growing interest in the question of whether and how groups of nonhuman primates coordinate their behaviors for mutual benefit. On the one hand, it has been shown that chimpanzees in the wild and in captivity can solve various coordination problems. On the other hand, evidence of communication in the context of coordination problems is scarce. Here, we investigated how pairs of chimpanzees (Pan troglodytes) solved a problem of dynamically coordinating their actions for achieving a joint goal. We presented five pairs of chimpanzees with a turn-taking coordination game, where the task was to send a virtual target from one computer display to another using two touch-screens. During the joint practice of the game some subjects exhibited spontaneous gesturing. To address the question whether these gestures were produced to sustain coordination, we introduced a joint test condition in which we simulated a coordination break-down scenario: subjects appeared either unwilling or unable to return the target to their partner. The frequency of gesturing was significantly higher in these test trials than in the regular trials. Our results suggest that at least in some contexts chimpanzees can exhibit communicative behaviors to sustain coordination in joint action.

Reflexive gaze following in common marmoset monkeys

The ability to extract the direction of the other’s gaze allows us to shift our attention to an object of interest to the other and to establish joint attention. By mapping one’s own intentions on the object of joint attention, humans develop a Theory of (the other’s) Mind (TOM), a functional sequence possibly disrupted in autism. Gaze following of both humans and old world monkeys is orchestrated by very similar cortical architectures, strongly suggesting homology. Also new world monkeys, a primate suborder that split from the old world monkey line about 35 million years ago, have complex social structures and one member of this group, the common marmosets (Callithrix jacchus) are known to follow human head-gaze. However, the question is if they use gaze following to establish joint attention with conspecifics. Here we show that this is indeed the case. In a free choice task, head-restrained marmosets prefer objects gazed at by a conspecific and, moreover, they exhibit considerably shorter choice reaction times for the same objects. These findings support the assumption of an evolutionarily old domain specific faculty shared within the primate order and they underline the potential value of marmosets in studies of normal and disturbed joint attention.

Response Coordination Emerges in Cooperative but Not Competitive Joint Task

Effective social interactions rely on humans' ability to attune to others within social contexts. Recently, it has been proposed that the emergence of shared representations, as indexed by the Joint Simon effect (JSE), might result from interpersonal coordination (Malone et al., 2014). The present study aimed at examining interpersonal coordination in cooperative and competitive joint tasks. To this end, in two experiments we investigated response coordination, as reflected in instantaneous cross-correlation, when co-agents cooperate (Experiment 1) or compete against each other (Experiment 2). In both experiments, participants performed a go/no-go Simon task alone and together with another agent in two consecutive sessions. In line with previous studies, we found that social presence differently affected the JSE under cooperative and competitive instructions. Similarly, cooperation and competition were reflected in co-agents response coordination. For the cooperative session (Experiment 1), results showed higher percentage of interpersonal coordination for the joint condition, relative to when participants performed the task alone. No difference in the coordination of responses occurred between the individual and the joint conditions when co-agents were in competition (Experiment 2). Finally, results showed that interpersonal coordination between co-agents implies the emergence of the JSE. Taken together, our results suggest that shared representations seem to be a necessary, but not sufficient, condition for interpersonal coordination.