Human and macaque pairs employ different coordination strategies in a transparent decision game.

Many real-world decisions in social contexts are made while observing a partner's actions. To study dynamic interactions during such decisions, we developed a setup where two agents seated face-to-face to engage in game-theoretical tasks on a shared transparent touchscreen display ('transparent games'). We compared human and macaque pairs in a transparent version of the coordination game 'Bach-or-Stravinsky', which entails a conflict about which of two individually-preferred opposing options to choose to achieve coordination. Most human pairs developed coordinated behavior and adopted dynamic turn-taking to equalize the payoffs. All macaque pairs converged on simpler, static coordination. Remarkably, two animals learned to coordinate dynamically after training with a human confederate. This pair selected the faster agent's preferred option, exhibiting turn-taking behavior that was captured by modeling the visibility of the partner's action before one's own movement. Such competitive turn-taking was unlike the prosocial turn-taking in humans, who equally often initiated switches to and from their preferred option. Thus, the dynamic coordination is not restricted to humans but can occur on the background of different social attitudes and cognitive capacities in rhesus monkeys. Overall, our results illustrate how action visibility promotes the emergence and maintenance of coordination when agents can observe and time their mutual actions.

To live with others is to make concessions. You may want to go to the movies tonight, but your partner may prefer the theatre: reaching a mutually desirable goal ­ that is, spending time together ­ requires adjusting your preferences to theirs. Many other social species also make such decisions, in particular monkeys that live in large groups. Conceptually, these interactions are known as coordination games. In such scenarios, two players must coordinate their actions to attain a coveted reward, but they must also resolve a conflict about who gets the larger share. This makes the joint strategy non-trivial, and different pairs of players might resort to different strategies. In the laboratory, coordination games are often tested in settings which do not allow participants to monitor each other's behaviors as they make these complex choices. In real life, however, individuals making a joint decision can often observe each other and receive immediate feedback. In response, Moeller et al. developed a new way to test coordination games that allows more realistic social interactions. In their setup, two participants face each other and use a shared see-through touchscreen to perform a task. This new design was used to test how humans and macaque monkeys solved a simplified version of the 'Bach or Stravinsky' coordination game, which involves choosing between a red and blue target on the screen. Players in a pair had been trained to 'prefer' opposite colors. In this game, collaboration is beneficial (both individuals get a better prize if they choose the same color) but also creates unfairness (the reward is higher for the participant whose 'favorite' color is selected). When paired up, both humans and monkeys learned to collaborate and to go for the same color (or, in some monkey pairs, the same side of the screen). However, only humans took turns selecting red or blue so that players could alternate getting the highest reward. Monkeys usually settled on one color throughout the game, unless they had learned the 'turn-taking' strategy from a human partner; in that case, the color chosen in each trial was typically determined by the monkey who was the faster to move. These experiments show how monkeys and humans use visual information about their partner's actions to coordinate their choices, paving the way for further decision-making studies that accurately reflect how interactions unfold in real life. Moeller et al. expect that this will help to understand how cooperation and competition emerge in these two species, including how direct face-to-face contact, or lack thereof in some aspects of our modern world, shapes our social behavior.

Emergence and suppression of cooperation by action visibility in transparent games.

Real-world agents, humans as well as animals, observe each other during interactions and choose their own actions taking the partners' ongoing behaviour into account. Yet, classical game theory assumes that players act either strictly sequentially or strictly simultaneously without knowing each other's current choices. To account for action visibility and provide a more realistic model of interactions under time constraints, we introduce a new game-theoretic setting called transparent games, where each player has a certain probability of observing the partner's choice before deciding on its own action. By means of evolutionary simulations, we demonstrate that even a small probability of seeing the partner's choice before one's own decision substantially changes the evolutionary successful strategies. Action visibility enhances cooperation in an iterated coordination game, but reduces cooperation in a more competitive iterated Prisoner's Dilemma. In both games, "Win-stay, lose-shift" and "Tit-for-tat" strategies are predominant for moderate transparency, while a "Leader-Follower" strategy emerges for high transparency. Our results have implications for studies of human and animal social behaviour, especially for the analysis of dyadic and group interactions.

Correction: Using imaging photoplethysmography for heart rate estimation in non-human primates.

[This corrects the article DOI: 10.1371/journal.pone.0202581.].

Using imaging photoplethysmography for heart rate estimation in non-human primates.

For humans and for non-human primates heart rate is a reliable indicator of an individual's current physiological state, with applications ranging from health checks to experimental studies of cognitive and emotional state. In humans, changes in the optical properties of the skin tissue correlated with cardiac cycles (imaging photoplethysmogram, iPPG) allow non-contact estimation of heart rate by its proxy, pulse rate. Yet, there is no established simple and non-invasive technique for pulse rate measurements in awake and behaving animals. Using iPPG, we here demonstrate that pulse rate in rhesus monkeys can be accurately estimated from facial videos. We computed iPPGs from eight color facial videos of four awake head-stabilized rhesus monkeys. Pulse rate estimated from iPPGs was in good agreement with reference data from a contact pulse-oximeter: the error of pulse rate estimation was below 5% of the individual average pulse rate in 83% of the epochs; the error was below 10% for 98% of the epochs. We conclude that iPPG allows non-invasive and non-contact estimation of pulse rate in non-human primates, which is useful for physiological studies and can be used toward welfare-assessment of non-human primates in research.

Change-Point Detection Using the Conditional Entropy of Ordinal Patterns.

This paper is devoted to change-point detection using only the ordinal structure of a time series. A statistic based on the conditional entropy of ordinal patterns characterizing the local up and down in a time series is introduced and investigated. The statistic requires only minimal a priori information on given data and shows good performance in numerical experiments. By the nature of ordinal patterns, the proposed method does not detect pure level changes but changes in the intrinsic pattern structure of a time series and so it could be interesting in combination with other methods.