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.

Primate origins of corepresentation and cooperative flexibility: A comparative study with common marmosets (Callithrix jacchus), brown capuchins (Sapajus apella), and Tonkean macaques (Macaca tonkeana).

Human joint action is generally facilitated by the tendency to represent not only one's own task and behavior but also the partner's. Yet, under some conditions, such as in the joint Simon task, corepresentation can cause interference and hampers, rather than facilitates, joint performance. A competent cooperator should thus also be able to flexibly inhibit corepresentation if that is conducive to cooperation success. To investigate the evolutionary origin of corepresentation, as well as the cooperative flexibility to inhibit it when necessary, we tested brown capuchins and Tonkean macaques in the joint Simon task and compared them with the previously tested marmosets. Corepresentation was present in all 3 species, but its strength and the cooperation success varied substantially. The cooperatively breeding marmosets showed the weakest corepresentation effect and, therefore, highest cooperation success, and they were the only ones to use mutual gaze when coordination with the partner was necessary. Cooperative flexibility was therefore not correlated with brain size but with the prevalence of cooperation in nature. This conclusion was corroborated by species differences in gazing patterns and suggests that the drivers of cooperative flexibility in humans were not solely cognitive. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Corepresentation During Joint Action in Marmoset Monkeys ( Callithrix jacchus).

Behavioral coordination is a fundamental element of human cooperation. It is facilitated when individuals represent not only their own actions but also those of their partner. Identifying whether action corepresentation is unique to humans or also present in other species is therefore necessary to fully understand the evolution of human cooperation. We used the auditory joint Simon task to assess whether action corepresentation occurs in common marmosets, a monkey species that engages extensively in coordinated action during cooperative infant care. We found that marmosets indeed show a joint Simon effect. Furthermore, when coordinating their behavior in the joint task, they were more likely to look at their partner than in a joint control condition. Corepresentation is thus not unique to humans but also present in the cooperatively breeding marmosets. Since marmosets are small-brained monkeys, our results suggest that routine coordination in space and time, rather than complex cognitive abilities, plays a role in the evolution of corepresentation.