Eye tracking uncovered great apes' ability to anticipate that other individuals will act according to false beliefs

Head-mounted mobile eye-tracking in the domestic dog: A new method

Humans rely on dogs for countless tasks, ranging from companionship to highly specialized detection work. In their daily lives, dogs must navigate a human-built visual world, yet comparatively little is known about what dogs visually attend to as they move through their environment. Real-world eye-tracking, or head-mounted eye-tracking, allows participants to freely move through their environment, providing more naturalistic results about visual attention while interacting with objects and agents. In dogs, real-world eye-tracking has the potential to inform our understanding of cross-species cognitive abilities as well as working dog training; however, a robust and easily deployed head-mounted eye-tracking method for dogs has not previously been developed and tested. We present a novel method for real-world eye-tracking in dogs, using a simple head-mounted mobile apparatus mounted onto goggles designed for dogs. This new method, adapted from systems that are widely used in humans, allows for eye-tracking during more naturalistic behaviors, namely walking around and interacting with real-world stimuli, as well as reduced training time as compared to traditional stationary eye-tracking methods. We found that while completing a simple forced-choice treat finding task, dogs look primarily to the treat, and we demonstrated the accuracy of this method using alternative gaze-tracking methods. Additionally, eye-tracking revealed more fine-grained time course information and individual differences in looking patterns.

Canine perspective-taking

An important question in the study of canine cognition is how dogs understand humans, given that they show impressive abilities for interacting and communicating with us. In this review, we describe and discuss studies that have investigated dogs' perspective-taking abilities. There is solid evidence that dogs are not only sensitive to the gaze of others, but also their attention. We specifically address the question whether dogs have the ability to take the perspective of others and thus come to understand what others can or cannot perceive. From the latter, they may then infer what others know and use this representation to anticipate what others do next. Still, dogs might simply rely on directly observable cues and on what they themselves can perceive when they assess what others can perceive. And instead of making inferences from representations of others' mental states, they may have just learned that certain behaviours of ours lead to certain outcomes. However, recent research seems to challenge this low-level explanation. Dogs have solved several perspective-taking tasks instantly and reliably across a large number of variations, including geometrical gaze-following, stealing in the dark, concealing information from others, and Guesser/Knower differentiation. In the latter studies, dogs' choices between two human informants were strongly influenced by cues related to the humans' visual access to the food, even when the two informants behaved identically. And finally, we review a recent study that found dogs reacting differently to misleading suggestions of human informants that have either a true or false belief about the location of food. We discuss this surprising result in terms of the comprehension of reality-incongruent mental states, which is considered as a hallmark of Theory of Mind acquisition in human development. Especially on the basis of the latter findings, we conclude that pet dogs might be sensitive to what others see, know, intend, and believe. Therefore, this ability seems to have evolved not just in the corvid and primate lineages, but also in dogs.

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.

Eye-tracking as a window into primate social cognition

Over the past decade, noninvasive, restraint-free eye-tracking research with primates has transformed our understanding of primate social cognition. The use of this technology with many primate species allows for the exploration and comparison of how these species attend to and understand social agents and interactions. The ability to compare and contrast the cognitive capacities of various primate species, including humans, provides insight into the evolutionary mechanisms and selective pressures that have likely shaped social cognition in similar and divergent ways across the primate order. In this review, we begin by discussing noninvasive behavioral methods used to measure primate gaze and attention before the introduction of noninvasive, restraint-free eye-tracking methodologies. Next, we focus on findings from recent eye-tracking research on primate social cognition, beginning with simple visual and search mechanisms. We then discuss the results that have built on this basic understanding of how primates view images and videos, exploring discrimination and knowledge of social agents, following social cues, tracking perspectives and predicting behavior, and the combination of eye-tracking and other behavioral and physiological methods. Finally, we discuss some future directions of noninvasive eye-tracking research on primate social cognition and current eye-tracking work-in-progress that builds on these previous studies, investigating underexplored socio-cognitive capacities and utilizing new methodologies.

Where Is Ethology Heading? An Invitation for Collective Metadisciplinary Discussion

Many factors can impact the advancement of scientific disciplines. In the study of animal behavior and cognition (i.e., Ethology), a lack of consensus about definitions or the emergence of some current events and inventions, among other aspects, may challenge the discipline's grounds within the next decades. A collective metadisciplinary discussion may help in envisioning the future to come. For that purpose, I elaborated an online questionnaire about the level of consensus and the researchers' ways of doing in seven areas: Discipline name and concepts, species, Umwelt, technology, data, networking, and the impact of sociocultural and ecological factors. I recruited the opinion of almost a hundred of colleagues worldwide (N = 98), both junior and seniors, working both in the wild and in the lab. While the results were pitted against the literature, general conclusions should be taken with caution and considered as a first attempt in exploring the state of the discipline from the researchers' perspective: There is no unanimity for the discipline's name; 71.4% of the researchers reported there is limited consensus in the definition of relevant concepts (i.e., culture, cognition); primate species still predominate in publications whereas the species selection criteria is sometimes based on fascination, chance, or funding opportunities rather than on biocentric questions; 56.1% of the apparatuses employed do not resemble species' ecological problems, and current tech needs would be solved by fostering collaboration with engineers. Finally, embracing the Open Science paradigm, supporting networking efforts, and promoting diversity in research teams may help in gathering further knowledge in the area. Some suggestions are proposed to overcome the aforementioned problems in this contemporary analysis of our discipline.

The application of noninvasive, restraint-free eye-tracking methods for use with nonhuman primates

Over the past 50 years there has been a strong interest in applying eye-tracking techniques to study a myriad of questions related to human and nonhuman primate psychological processes. Eye movements and fixations can provide qualitative and quantitative insights into cognitive processes of nonverbal populations such as nonhuman primates, clarifying the evolutionary, physiological, and representational underpinnings of human cognition. While early attempts at nonhuman primate eye tracking were relatively crude, later, more sophisticated and sensitive techniques required invasive protocols and the use of restraint. In the past decade, technology has advanced to a point where noninvasive eye-tracking techniques, developed for use with human participants, can be applied for use with nonhuman primates in a restraint-free manner. Here we review the corpus of recent studies (N=32) that take such an approach. Despite the growing interest in eye-tracking research, there is still little consensus on "best practices," both in terms of deploying test protocols or reporting methods and results. Therefore, we look to advances made in the field of developmental psychology, as well as our own collective experiences using eye trackers with nonhuman primates, to highlight key elements that researchers should consider when designing noninvasive restraint-free eye-tracking research protocols for use with nonhuman primates. Beyond promoting best practices for research protocols, we also outline an ideal approach for reporting such research and highlight future directions for the field.

Macaques Exhibit Implicit Gaze Bias Anticipating Others' False-Belief-Driven Actions via Medial Prefrontal Cortex

The ability to infer others' mental states is essential to social interactions. This ability, critically evaluated by testing whether one attributes false beliefs (FBs) to others, has been considered to be uniquely hominid and to accompany the activation of a distributed brain network. We challenge the taxon specificity of this ability and identify the causal brain locus by introducing an anticipatory-looking FB paradigm combined with chemogenetic neuronal manipulation in macaque monkeys. We find spontaneous gaze bias of macaques implicitly anticipating others' FB-driven actions. Silencing of the medial prefrontal neuronal activity with inhibitory designer receptor exclusively activated by designer drugs (DREADDs) specifically eliminates the implicit gaze bias while leaving the animals' visually guided and memory-guided tracking abilities intact. Thus, neuronal activity in the medial prefrontal cortex could have a causal role in FB-attribution-like behaviors in the primate lineage, emphasizing the importance of probing the neuronal mechanisms underlying theory of mind with relevant macaque animal models.

A review of research in primate sanctuaries

While non-human primate studies have long been conducted in laboratories, and more recently at zoological parks, sanctuaries are increasingly considered a viable setting for research. Accredited sanctuaries in non-range countries house thousands of primates formerly used as subjects of medical research, trained performers or personal pets. In range countries, however, sanctuaries typically house orphaned primates confiscated from illegal poaching and the bushmeat and pet trafficking trades. Although the primary mission of these sanctuaries is to rescue and rehabilitate residents, many of these organizations are increasingly willing to participate in non-invasive research. Notably, from a scientific standpoint, most sanctuaries provide potential advantages over traditional settings, such as large, naturalistic physical and social environments which may result in more relevant models of primates' free-ranging wild counterparts than other captive settings. As a result, an impressive scope of research in the fields of primate behaviour, cognition, veterinary science, genetics and physiology have been studied in sanctuaries. In this review, we examine the range and form of research that has been conducted at accredited sanctuaries around the world. We also describe the potential challenges of sanctuary-based work and the considerations that external researchers may face when deciding to collaborate with primate sanctuaries on their research projects.

Great apes use self-experience to anticipate an agent's action in a false-belief test

Human social life depends on theory of mind, the ability to attribute mental states to oneself and others. A signature of theory of mind, false belief understanding, requires representing others' views of the world, even when they conflict with one's own. After decades of research, it remains controversial whether any nonhuman species possess a theory of mind. One challenge to positive evidence of animal theory of mind, the behavior-rule account, holds that animals solve such tasks by responding to others' behavioral cues rather than their mental states. We distinguish these hypotheses by implementing a version of the "goggles" test, which asks whether, in the absence of any additional behavioral cues, animals can use their own self-experience of a novel barrier being translucent or opaque to determine whether another agent can see through the same barrier. We incorporated this paradigm into an established anticipatory-looking false-belief test for great apes. In a between-subjects design, apes experienced a novel barrier as either translucent or opaque, although both looked identical from afar. While being eye tracked, all apes then watched a video in which an actor saw an object hidden under 1 of 2 identical boxes. The actor then scuttled behind the novel barrier, at which point the object was relocated and then removed. Only apes who experienced the barrier as opaque visually anticipated that the actor would mistakenly search for the object in its previous location. Great apes, therefore, appeared to attribute differential visual access based specifically on their own past perceptual experience to anticipate an agent's actions in a false-belief test.

Head-mounted sensors reveal visual attention of free-flying homing pigeons

Gaze behavior offers valuable insights into attention and cognition. However, technological limitations have prevented the examination of animals' gaze behavior in natural, information-rich contexts; for example, during navigation through complex environments. Therefore, we developed a lightweight custom-made logger equipped with an inertial measurement unit (IMU) and GPS to simultaneously track the head movements and flight trajectories of free-flying homing pigeons. Pigeons have a limited range of eye movement, and their eye moves in coordination with their head in a saccadic manner (similar to primate eye saccades). This allows head movement to act as a proxy for visual scanning behavior. Our IMU sensor recorded the 3D movement of the birds' heads in high resolution, allowing us to reliably detect distinct saccade signals. The birds moved their head far more than necessary for maneuvering flight, suggesting that they actively scanned the environment. This movement was predominantly horizontal (yaw) and sideways (roll), allowing them to scan the environment with their lateral visual field. They decreased their head movement when they flew solo over prominent landmarks (major roads and a railway line) and also when they flew in pairs (especially when flying side by side, with the partner maintained in their lateral visual field). Thus, a decrease in head movement indicates a change in birds' focus of attention. We conclude that pigeons use their head gaze in a task-related manner and that tracking flying birds' head movement is a promising method for examining their visual attention during natural tasks.

Human ostensive signals do not enhance gaze following in chimpanzees, but do enhance object-oriented attention

The previous studies have shown that human infants and domestic dogs follow the gaze of a human agent only when the agent has addressed them ostensively-e.g., by making eye contact, or calling their name. This evidence is interpreted as showing that they expect ostensive signals to precede referential information. The present study tested chimpanzees, one of the closest relatives to humans, in a series of eye-tracking experiments using an experimental design adapted from these previous studies. In the ostension conditions, a human actor made eye contact, called the participant's name, and then looked at one of two objects. In the control conditions, a salient cue, which differed in each experiment (a colorful object, the actor's nodding, or an eating action), attracted participants' attention to the actor's face, and then the actor looked at the object. Overall, chimpanzees followed the actor's gaze to the cued object in both ostension and control conditions, and the ostensive signals did not enhance gaze following more than the control attention-getters. However, the ostensive signals enhanced subsequent attention to both target and distractor objects (but not to the actor's face) more strongly than the control attention-getters-especially in the chimpanzees who had a close relationship with human caregivers. We interpret this as showing that chimpanzees have a simple form of communicative expectations on the basis of ostensive signals, but unlike human infants and dogs, they do not subsequently use the experimenter's gaze to infer the intended referent. These results may reflect a limitation of non-domesticated species for interpreting humans' ostensive signals in inter-species communication.