Fumihiro Kano

Great apes anticipate that other individuals will act according to false beliefs

Apes understand false beliefs We humans tend to believe that our cognitive skills are unique, not only in degree, but also in kind. The more closely we look at other species, however, the clearer it becomes that the difference is one of degree. Krupenye et al. show that three different species of apes are able to anticipate that others may have mistaken beliefs about a situation (see the Perspective by de Waal). The apes appear to understand that individuals have different perceptions about the world, thus overturning the human-only paradigm of the theory of mind. Science, this issue p. 110; see also p. 39 Apes recognize that others may have false beliefs. [Also see Perspective by de Waal] Humans operate with a “theory of mind” with which they are able to understand that others’ actions are driven not by reality but by beliefs about reality, even when those beliefs are false. Although great apes share with humans many social-cognitive skills, they have repeatedly failed experimental tests of such false-belief understanding. We use an anticipatory looking test (originally developed for human infants) to show that three species of great apes reliably look in anticipation of an agent acting on a location where he falsely believes an object to be, even though the apes themselves know that the object is no longer there. Our results suggest that great apes also operate, at least on an implicit level, with an understanding of false beliefs.

How chimpanzees look at pictures: a comparative eye-tracking study

Surprisingly little is known about the eye movements of chimpanzees, despite the potential contribution of such knowledge to comparative cognition studies. Here, we present the first examination of eye tracking in chimpanzees. We recorded the eye movements of chimpanzees as they viewed naturalistic pictures containing a full-body image of a chimpanzee, a human or another mammal; results were compared with those from humans. We found a striking similarity in viewing patterns between the two species. Both chimpanzees and humans looked at the animal figures for longer than at the background and at the face region for longer than at other parts of the body. The face region was detected at first sight by both species when they were shown pictures of chimpanzees and of humans. However, the eye movements of chimpanzees also exhibited distinct differences from those of humans; the former shifted the fixation location more quickly and more broadly than the latter. In addition, the average duration of fixation on the face region was shorter in chimpanzees than in humans. Overall, our results clearly demonstrate the eye-movement strategies common to the two primate species and also suggest several notable differences manifested during the observation of pictures of scenes and body forms.

Face scanning in chimpanzees and humans: continuity and discontinuity

How do chimpanzees, Pan troglodytes, the species with the closest evolutionary connection to humans, view faces? This study is the first to use the eye-tracking method to perform direct comparisons between humans and chimpanzees with regard to face scanning. Members of both species viewed the same sets of photographs representing conspecific and nonconspecific faces under the same experimental conditions. Chimpanzees and humans showed systematic and similar patterns of face scanning, including intensely viewing main facial features (i.e. eyes, nose and mouth) and inspecting the eyes and mouth, in that order. However, several differences between the species were also evident. For example, humans were more likely to show sequential refixations on the eye regions than were chimpanzees, whereas chimpanzees were more likely to engage in quick, vertical scanning over the eyes and mouth. Such species similarities and differences were consistent across conspecific and nonconspecific faces and were thus independent of the external morphologies of species-specific faces. Furthermore, when presented with facial expressions, chimpanzees changed their scanning patterns in response to those facial actions, whereas humans maintained intense eye viewing across the expressions. Finally, we discuss how these face-scanning patterns are related to species-specific forms of facial communication in chimpanzees and humans, and suggest that both species have unique eye movement strategies for interactions with conspecifics.

Great Apes Generate Goal-Based Action Predictions An Eye-Tracking Study

To examine great apes’ on-line prediction of other individuals’ actions, we used an eye-tracking technique and an experimental paradigm previously used to test human infants. Twenty-two great apes, including bonobos, chimpanzees, and orangutans, were familiarized to movie clips of a human hand reaching to grasp one of two objects. Then the objects’ locations were swapped, and in the test event, the hand made an incomplete reach between the objects. In a control condition, a mechanical claw performed the same actions. The apes predictively looked at the familiarized goal object rather than the familiarized location when viewing the hand action in the test event. However, they made no prediction when viewing the claw action. These results are similar to those reported previously for human infants, and predictive looking did not differ among the three species of great apes. Thus, great apes make on-line goal-based predictions about the actions of other individuals; this skill is not unique to humans but is shared more widely among primates.

Social attention in the two species of Pan: : bonobos make more eye contact than chimpanzees

Humans’ two closest primate living relatives, bonobos and chimpanzees, differ behaviorally, cognitively, and emotionally in several ways despite their general similarities. While bonobos show more affiliative behaviors towards conspecifics, chimpanzees display more overt and severe aggression against conspecifics. From a cognitive standpoint, bonobos perform better in social coordination, gaze-following and food-related cooperation, while chimpanzees excel in tasks requiring extractive foraging skills. We hypothesized that attention and motivation play an important role in shaping the species differences in behavior, cognition, and emotion. Thus, we predicted that bonobos would pay more attention to the other individuals’ face and eyes, as those are related to social affiliation and social coordination, while chimpanzees would pay more attention to the action target objects, as they are related to foraging. Using eye-tracking we examined the bonobos’ and chimpanzees’ spontaneous scanning of pictures that included eyes, mouth, face, genitals, and action target objects of conspecifics. Although bonobos and chimpanzees viewed those elements overall similarly, bonobos viewed the face and eyes longer than chimpanzees, whereas chimpanzees viewed the other elements, the mouth, action target objects and genitals, longer than bonobos. In a discriminant analysis, the individual variation in viewing patterns robustly predicted the species of individuals, thus clearly demonstrating species-specific viewing patterns. We suggest that such attentional and motivational differences between bonobos and chimpanzees could have partly contributed to shaping the species-specific behaviors, cognition, and emotion of these species, even in a relatively short period of evolutionary time.

Face and eye scanning in gorillas (Gorilla gorilla), orangutans (Pongo abelii), and humans (Homo sapiens): Unique eye-viewing patterns in humans among hominids

Because the faces and eyes of primates convey a rich array of social information, the way in which primates view faces and eyes reflects species-specific strategies for facial communication. How are humans and closely related species such as great apes similar and different in their viewing patterns for faces and eyes? Following previous studies comparing chimpanzees (Pan troglodytes) with humans (Homo sapiens), this study used the eye-tracking method to directly compare the patterns of face and eye scanning by humans, gorillas (Gorilla gorilla), and orangutans (Pongo abelii). Human and ape participants freely viewed pictures of whole bodies and full faces of conspecifics and allospecifics under the same experimental conditions. All species were strikingly similar in that they viewed predominantly faces and eyes. No particular difference was identified between gorillas and orangutans, and they also did not differ from the chimpanzees tested in previous studies. However, humans were somewhat different from apes, especially with respect to prolonged eye viewing. We also examined how species-specific facial morphologies, such as the male flange of orangutans and the black-white contrast of human eyes, affected viewing patterns. Whereas the male flange of orangutans affected viewing patterns, the color contrast of human eyes did not. Humans showed prolonged eye viewing independently of the eye color of presented faces, indicating that this pattern is internally driven rather than stimulus dependent. Overall, the results show general similarities among the species and also identify unique eye-viewing patterns in humans.

Enhanced recognition of emotional stimuli in the chimpanzee (Pan troglodytes)

Humans often have a better memory of emotional events than neutral events. From the comparative–cognitive perspective, we explored the enhancement of recognition memory by emotion in chimpanzees (Pan troglodytes) using a serial probe recognition task. In this task, we sequentially presented a list of pictures to subjects and then tested their recognition of specific pictures from within the list. We selected pictures of aggressive chimpanzees as emotional stimuli and less tensed, relaxed chimpanzees as neutral stimuli. In Experiment 1, we gave four-item lists to two young chimpanzees; one showed significantly greater recognition of pictures depicting aggressive chimpanzees than neutral ones. In Experiment 2, this chimpanzee was further tested using a recognition task with eight-item lists. The subject again showed better recognition of emotional stimuli than neutral. Furthermore, the presence of an emotional stimulus in the list also facilitated recognition of the neutral item immediately following it. Overall, although only one of the two chimpanzees showed enhanced recognition memory by emotional stimuli, this is the first demonstration of such a response in the chimpanzee. The findings are discussed in comparison with those of human studies.

Species difference in the timing of gaze movement between chimpanzees and humans

How do humans and their closest relatives, chimpanzees, differ in their fundamental abilities for seeing the visual world? In this study, we directly compared the gaze movements of humans and the closest species, chimpanzees, using an eye-tracking system. During free viewing of a naturalistic scene, chimpanzees made more fixations per second (up to four) than did humans (up to three). This species difference was independent of the semantic variability of the presented scenes. The gap–overlap paradigm revealed that, rather than resulting from the sensitivity to the peripherally presented stimuli per se, the species difference reflected the particular strategy each species employed to solve the rivalry between central (fixated) and peripheral stimuli in their visual fields. Finally, when presented with a movie in which small images successively appeared/disappeared at random positions at the chosen presentation rate, chimpanzees tracked those images at the point of fixation for a longer time than did humans, outperforming humans in their speed of scanning. Our results suggest that chimpanzees and humans differ quantitatively in their visual strategies involving the timing of gaze movement. We discuss the functional reasons for each species’ employing such specific strategies.

Perceptual mechanism underlying gaze guidance in chimpanzees and humans

Previous studies comparing eye movements between humans and their closest relatives, chimpanzees, have revealed similarities and differences between the species in terms of where individuals fixate their gaze during free viewing of a naturalistic scene, including social stimuli (e.g. body and face). However, those results were somewhat confounded by the fact that gaze behavior is influenced by low-level stimulus properties (e.g., color and form) and by high-level processes such as social sensitivity and knowledge about the scene. Given the known perceptual and cognitive similarities between chimpanzees and humans, it is expected that such low-level effects do not play a critical role in explaining the high-level similarities and differences between the species. However, there is no quantitative evidence to support this assumption. To estimate the effect of local stimulus saliency on such eye-movement patterns, this study used a well-established bottom-up saliency model. In addition, to elucidate the cues that the viewers use to guide their gaze, we presented scenes in which we had manipulated various stimulus properties. As expected, the saliency model did not fully predict the fixation patterns actually observed in chimpanzees and humans. In addition, both species used multiple cues to fixate socially significant areas such as the face. There was no evidence suggesting any differences between chimpanzees and humans in their responses to low-level saliency. Therefore, this study found a substantial amount of similarity in the perceptual mechanisms underlying gaze guidance in chimpanzees and humans and thereby offers a foundation for direct comparisons between them.

Nasal temperature drop in response to a playback of conspecific fights in chimpanzees: A thermo-imaging study.

Emotion is one of the central topics in animal studies and is likely to attract attention substantially in the coming years. Recent studies have developed a thermo-imaging technique to measure the facial skin temperature in the studies of emotion in humans and macaques. Here we established the procedures and techniques needed to apply the same technique to great apes. We conducted two experiments respectively in the two established research facilities in Germany and Japan. Total twelve chimpanzees were tested in three conditions in which they were presented respectively with the playback sounds (Exp. 1) or the videos (Exp. 2) of fighting conspecifics, control sounds/videos (allospecific display call: Exp. 1; resting conspecifics: Exp. 2), and no sound/image. Behavioral, hormonal (salivary cortisol) and heart-rate responses were simultaneously recorded. The nasal temperature of chimpanzees linearly dropped up to 1.5 °C in 2 min, and recovered to the baseline in 2 min, in the experimental but not control conditions. We found the related changes in excitement behavior and heart-rate variability, but not in salivary cortisol, indicating that overall responses were involved with the activities of sympathetic nervous system but not with the measureable activities of the hypothalamus-pituitary-adrenal (HPA) axis. The influence of general activity (walking, eating) was not negligible but controllable in experiments. We propose several techniques to control those confounding factors. Overall, thermo-imaging is a promising technique that should be added to the traditional physiological and behavioral measures in primatology and comparative psychology.