'Unwilling' versus 'unable': Tonkean macaques' understanding of human goal-directed actions

Unwilling or unable? Using three-dimensional tracking to evaluate dogs' reactions to differing human intentions

The extent to which dogs (Canis familiaris) as a domesticated species understand human intentions is still a matter of debate. The unwilling-unable paradigm has been developed to examine whether nonhuman animals are sensitive to intentions underlying human actions. In this paradigm, subjects tended to wait longer in the testing area when presented with a human that appeared willing but unable to transfer food to them compared to an unwilling (teasing) human. In the present study, we conducted the unwilling-unable paradigm with dogs using a detailed behavioural analysis based on machine-learning driven three-dimensional tracking. Throughout two preregistered experiments, we found evidence, in line with our prediction, that dogs reacted more impatiently to actions signalling unwillingness to transfer food rather than inability. These differences were consistent through two different samples of pet dogs (total n = 96) and they were evident also in the machine-learning generated three-dimensional tracking data. Our results therefore provide robust evidence that dogs distinguish between similar actions (leading to the same outcome) associated with different intentions. However, their reactions did not lead to any measurable preference for one experimenter over the other in a subsequent transfer phase. We discuss different cognitive mechanisms that might underlie dogs' performance in this paradigm.

The evolutionary origins of syntax: Event cognition in nonhuman primates

Languages tend to encode events from the perspective of agents, placing them first and in simpler forms than patients. This agent bias is mirrored by cognition: Agents are more quickly recognized than patients and generally attract more attention. This leads to the hypothesis that key aspects of language structure are fundamentally rooted in a cognition that decomposes events into agents, actions, and patients, privileging agents. Although this type of event representation is almost certainly universal across languages, it remains unclear whether the underlying cognition is uniquely human or more widespread in animals. Here, we review a range of evidence from primates and other animals, which suggests that agent-based event decomposition is phylogenetically older than humans. We propose a research program to test this hypothesis in great apes and human infants, with the goal to resolve one of the major questions in the evolution of language, the origins of syntax.

Come with me: experimental evidence for intentional recruitment in Tonkean macaques

Recruitment is a process by which animals can initiate collective movements: the action of an individual prompts conspecifics to follow. Although it has been hypothesized that animals may be able to intentionally recruit others, there is no experimental evidence of this to date. We tested this hypothesis in two pairs of Tonkean macaques in a situation requiring the subjects to find a food site in a 2800 m² area, and approach the site together to release rewards. Each subject was informed of the location of either highly or little-valued rewards. We recorded attention-action sequences in which an individual checked that his partner was attending to him before moving, and also simple departures (i.e., not preceded by eye contact). Analyses showed that sequences were more often followed by recruitment and leading the partner to a baited site than simple departures were. Moreover, subjects used attention-action sequences more frequently when informed of the location of the highly valued reward. This may be explained by the fact that the more motivated they were by the expected rewards, the more likely they were to actively recruit their partner. No such effect was found when subjects performed simple departures. We conclude that Tonkean macaques are capable of intentional recruitment because the subjects voluntarily behaved with the goal of influencing their partner's movement: they checked that the partner was paying attention to them and prompted him to follow by moving. Such performances can be accounted for either by associative learning or by intentional communication.

Dogs distinguish human intentional and unintentional action

When dogs interact with humans, they often show appropriate reactions to human intentional action. But it is unclear from these everyday observations whether the dogs simply respond to the action outcomes or whether they are able to discriminate between different categories of actions. Are dogs able to distinguish intentional human actions from unintentional ones, even when the action outcomes are the same? We tested dogs' ability to discriminate these action categories by adapting the so-called "Unwilling vs. Unable" paradigm. This paradigm compares subjects' reactions to intentional and unintentional human behaviour. All dogs received three conditions: In the unwilling-condition, an experimenter intentionally withheld a reward from them. In the two unable-conditions, she unintentionally withheld the reward, either because she was clumsy or because she was physically prevented from giving the reward to the dog. Dogs clearly distinguished in their spontaneous behaviour between unwilling- and unable-conditions. This indicates that dogs indeed distinguish intentional actions from unintentional behaviour. We critically discuss our findings with regard to dogs' understanding of human intentional action.

No evidence that monkeys attribute mental states to animated shapes in the Heider-Simmel videos

Human Theory of Mind (ToM) is so automatic and pervasive that we spontaneously attribute mental states to animated abstract shapes, as evidenced by the classic Heider-Simmel findings. The extent to which this represents a fundamental characteristic of primate social cognition is debated. Prior research suggests that monkeys spontaneously predict behavior and attribute basic goals to conspecifics, but it remains unclear whether, like humans, they spontaneously ascribe mental states to animated shapes. Here, we address this question by analyzing rhesus monkeys' viewing patterns of the classic Heider-Simmel animations. We hypothesized that if rhesus monkeys also spontaneously attribute mental states to animated shapes, then, like humans, they would have the longest fixation durations for theory of mind animations, medium duration fixation for goal-directed animations, and shortest fixations for animations with random motion. In contrast, if attributing mental states to animations is specific to humans and perhaps other apes, then we predict no differences in looking time across animation categories. Unlike humans, monkeys did not fixate longer on ToM videos. Critically, monkeys' viewing patterns did not correlate with humans' viewing patterns or intentionality ratings from previously published research. The only major difference in viewing patterns between animation categories tracked differences in low-level visual motion. Thus, monkeys do not view the classic Heider-Simmel animations like humans do and we found no evidence that they spontaneously attribute mental states to animated shapes.

Unwilling or willing but unable: can horses interpret human actions as goal directed?

Social animals can gain important benefits by inferring the goals behind the behavior of others. However, this ability has only been investigated in a handful of species outside of primates. In this study, we tested for the first time whether domestic horses can interpret human actions as goal directed. We used the classical "unwilling versus unable" paradigm: an experimenter performed three similar actions that have the same outcome, but the goal of the experimenter differed. In the unwilling condition, the experimenter had no intention to give a piece of food to a horse and moved it out of reach when the horse tried to eat it. In the two unable conditions, the experimenter had the intention to give the food to the horse but was unable to do so, either because there was a physical barrier between them or because of the experimenter's clumsiness. The horses (n = 21) reacted differently in the three conditions: they showed more interest in the unable conditions, especially in the unable clumsy condition, than in the unwilling condition. These results are similar to results found in primates with the same paradigm and suggest that horses might have taken the experimenter's goal, or even intentions, into account to adapt their behavior. Hence, our study offers more insights into horse interspecific social cognition towards humans.

Pragmatics and social meaning: Understanding under-informativeness in native and non-native speakers

Foreign-accented non-native speakers sometimes face negative biases compared to native speakers. Here we report an advantage in how comprehenders process the speech of non-native compared to native speakers. In a series of four experiments, we find that under-informative sentences are interpreted differently when attributed to non-native compared to native speakers. Specifically, under-informativeness is more likely to be attributed to inability (rather than unwillingness) to say more in non-native as compared to native speakers. This asymmetry has implications for learning: under-informative teachers are more likely to be given a second chance in case they are non-native speakers of the language (presumably because their prior under-informativeness is less likely to be intentional). Our results suggest strong effects of non-native speech on social-pragmatic inferences. Because these effects emerge for written stimuli, they support theories that stress the role of expectations on non-native comprehension, even in the absence of experience with foreign accents. Finally, our data bear on pragmatic theories of how speaker identity affects language comprehension and show how such theories offer an integrated framework for explaining how non-native language can lead to (sometimes unexpected) social meanings.

Death among primates: a critical review of non-human primate interactions towards their dead and dying

For the past two centuries, non-human primates have been reported to inspect, protect, retrieve, carry or drag the dead bodies of their conspecifics and, for nearly the same amount of time, sparse scientific attention has been paid to such behaviours. Given that there exists a considerable gap in the fossil and archaeological record concerning how early hominins might have interacted with their dead, extant primates may provide valuable insight into how and in which contexts thanatological behaviours would have occurred. First, we outline a comprehensive history of comparative thanatology in non-human primates, from the earliest accounts to the present, uncovering the interpretations of previous researchers and their contributions to the field of primate thanatology. Many of the typical behavioural patterns towards the dead seen in the past are consistent with those observed today. Second, we review recent evidence of thanatological responses and organise it into distinct terminologies: direct interactions (physical contact with the corpse) and secondary interactions (guarding the corpse, vigils and visitations). Third, we provide a critical evaluation regarding the form and function of the behavioural and emotional aspects of these responses towards infants and adults, also comparing them with non-conspecifics. We suggest that thanatological interactions: promote a faster re-categorisation from living to dead, decrease costly vigilant/caregiving behaviours, are crucial to the management of grieving responses, update position in the group's hierarchy, and accelerate the formation of new social bonds. Fourth, we propose an integrated model of Life-Death Awareness, whereupon neural circuitry dedicated towards detecting life, i.e. the agency system (animate agency, intentional agency, mentalistic agency) works with a corresponding system that interacts with it on a decision-making level (animate/inanimate distinction, living/dead discrimination, death awareness). Theoretically, both systems are governed by specific cognitive mechanisms (perceptual categories, associative concepts and high-order reasoning, respectively). Fifth, we present an evolutionary timeline from rudimentary thanatological responses likely occurring in earlier non-human primates during the Eocene to the more elaborate mortuary practices attributed to genus Homo throughout the Pleistocene. Finally, we discuss the importance of detailed reports on primate thanatology and propose several empirical avenues to shed further light on this topic. This review expands and builds upon previous attempts to evaluate the body of knowledge on this subject, providing an integrative perspective and bringing together different fields of research to detail the evolutionary, sensory/cognitive, developmental and historical/archaeological aspects of primate thanatology. Considering all these findings and given their cognitive abilities, we argue that non-human primates are capable of an implicit awareness of death.

The Pertinence of Studying Neuroethology in Nonhuman Primates for Human Behavior in Groups and Organizations

Are we the only living beings endowed with a complex communicative system and sharp sociocognitive skills? How did these remarkable abilities develop? Even raised several centuries ago, those questions are still nourishing the current research and debates. A relevant approach for identifying the dynamics in the evolution of humans’ social and communicative abilities appears to study our closest living relatives, the nonhuman primates. In this article I focus on two abilities that drove the building of our unique sociality and are still playing a crucial role in daily human behaviors in groups and organizations: (a) the origins of human language, through the study of nonhuman primates gestures, vocalizations, and facial expressions and (b) the precursors and underpinning neural mechanisms of our ability to assess others’ mental states, that is, theory of mind. In each part, examples illustrate the advantages and limitations of the different methodological approaches used in research on nonhuman primates’ communication and social abilities and discuss the results in light of the current hypotheses and still open debates on what make the singularity of our species.

Action Categorization in Rhesus Monkeys: discrimination of grasping from non-grasping manual motor acts

The ability to recognize others’ actions is an important aspect of social behavior. While neurophysiological and behavioral research in monkeys has offered a better understanding of how the primate brain processes this type of information, further insight with respect to the neural correlates of action recognition requires tasks that allow recording of brain activity or perturbing brain regions while monkeys simultaneously make behavioral judgements about certain aspects of observed actions. Here we investigated whether rhesus monkeys could actively discriminate videos showing grasping or non-grasping manual motor acts in a two-alternative categorization task. After monkeys became proficient in this task, we tested their ability to generalize to a number of untrained, novel videos depicting grasps or other manual motor acts. Monkeys generalized to a wide range of novel human or conspecific grasping and non-grasping motor acts. They failed, however, for videos showing unfamiliar actions such as a non-biological effector performing a grasp, or a human hand touching an object with the back of the hand. This study shows the feasibility of training monkeys to perform active judgements about certain aspects of observed actions, instrumental for causal investigations into the neural correlates of action recognition.

Factors influencing deceptive behaviours in Tonkean macaques (Macaca tonkeana)

The complex social environments of primates create opportunities for engaging in tactical deception, especially for subordinate individuals. We analysed the behaviour of subordinate Tonkean macaques with dominant conspecifics in an experimental food competition context. The subordinate macaque could see two pieces of food in a test area, but only one piece was visible to the dominant. Both individuals were released into the test area at the same time or with the subordinate given a short head start on the dominant. Here, based on video analysis of the subordinates’ behaviours, we describe and classify functionally deceptive behaviours displayed by subordinates, and report factors that influenced these behaviours. Subordinates used several types of tactical deception, including concealment and distraction, especially when paired with competitors of much higher social rank, and they obtained the hidden food more frequently when they used a combination of tactics rather than only one.