Search

Gaze following is a fundamental component of triadic social interaction which includes events and an object shared with other individuals and is found in both human and nonhuman primates. Most previous work has focused only on the immediate reaction after following another’s gaze. In contrast, this study investigated whether gaze following is retained after the observation of the other’s gaze shift, whether this retainment differs between species and age groups, and whether the retainment depends on the nature of the preceding events. In the social condition, subjects (1- and 2-year-old human children and chimpanzees) witnessed an experimenter who looked and pointed in the direction of a target lamp. In the physical condition, the target lamp blinked but the experimenter did not provide any cues. After a brief delay, we presented the same stimulus again without any cues. All subjects looked again to the target location after experiencing the social condition and thus showed a carryover effect. However, only 2-year-olds showed a carryover effect in the physical condition; 1-year-olds and chimpanzees did not. Additionally, only human children showed spontaneous interactive actions such as pointing. Our results suggest that the difference between the two age groups and chimpanzees is conceptual and not only quantitative.

Finding hidden objects in space is a fundamental ability that has received considerable research attention from both a developmental and a comparative perspective. Tracking the rotational displacements of containers and hidden objects is a particularly challenging task. This study investigated the ability of 3-, 5-, 7-, and 9-year-old children and great apes (chimpanzees, bonobos, gorillas, and orangutans) to (a) visually track rotational displacements of a baited container on a platform and (b) infer its displacements by using the changes of position or orientation of 3 landmarks: an object on a container, the color of the containers, and the color of the platform on which the containers rested. Great apes and 5-year-old and older children successfully tracked visible rotations, but only children were able to infer the location of a correct cup (with the help of landmarks) after invisible rotations. The ability to use landmarks changed with age so that younger children solved this task only with the most explicit marker on the baited container, whereas older children, particularly 9-year-olds, were able to use landmark orientation to infer correct locations.

The prevalence of cooperation among humans is puzzling because cooperators can be exploited by free riders. Peer punishment has been suggested as a solution to this puzzle, but cumulating evidence questions its robustness in sustaining cooperation. Amongst others, punishment fails when it is not powerful enough, or when it elicits counter-punishment. Existing research, however, has ignored that the distribution of punishment power can be the result of social interactions. We introduce a novel experiment in which individuals can transfer punishment power to others. We find that while decentralised peer punishment fails to overcome free riding, the voluntary transfer of punishment power enables groups to sustain cooperation. This is achieved by non-punishing cooperators empowering those who are willing to punish in the interest of the group. Our results show how voluntary power centralisation can efficiently sustain cooperation, which could explain why hierarchical power structures are widespread among animals and humans.

Previous research has shown that many social animals follow the gaze of other individuals. However, knowledge about how this skill differs between species and whether it shows a relationship with genetic distance from humans is still fragmentary. In the present study of gaze following in great apes, we manipulated the nature of a visual obstruction and the presence/absence of a target. We found that bonobos, chimpanzees, and gorillas followed gaze significantly more often when the obstruction had a window than when it did not, just as human infants do. Additionally, bonobos and chimpanzees looked at the experimenter's side of a windowless obstruction more often than the other species. Moreover, bonobos produced more double looks when the barrier was opaque than when it had a window, indicating an understanding of what other individuals see. The most distant human relatives studied, orangutans, showed few signs of understanding what another individual saw. Instead, they were attracted to the target's location by the target's presence, but not by the experimenter's gaze. Great apes' perspective-taking skills seem to have increased in the evolutionary lineage leading to bonobos, chimpanzees, and humans.

The development of visual interaction between mother and infant has received much attention in developmental psychology, not only in humans, but also in non-human primates. Recently, comparative developmental approaches have investigated whether the mechanisms that underlie these behaviors are common in primates. In the present study, we focused on the question of whether chimpanzee mother and infant replace physical contact with visual contact. To test this hypothesis, we measured non-synchronous looking ('looking') between mother and infant. A unique setting, in which the mother chimpanzee stayed in one location and the infant chimpanzee moved freely, allowed us to analyze the relation between the visual interaction and the distance of a mother-infant pair during the first year of life. Our results showed that 'looking' increased when body contact decreased or when the distance between mother and infant increased. We also show a behavioral sequence of typical 'secure base' behavior, a behavior characterized by the infant regularly returning to its mother when exploring the environment. These findings imply that attachment between mother and infant chimpanzee appears to develop in a similar fashion as in humans.

An infant chimpanzee's joint visual attention to objects behind him was investigated. A recent study has shown that a 13-month-old infant chimpanzee can follow human social cues including glancing (Okamoto, Tomonaga, Ishii, Kawai, Tanaka, & Matsuzawa, 2002a). In humans, 12-month-olds do not follow gaze to objects behind them but 18-month-olds do (Butterworth & Jarrett, 1991). In the present study, from 13 months old, the infant chimpanzee had been tested to look at one of two identical objects, which an experimenter indicated by pointing or head turning. The objects were set in front of or behind the subject. In our series of experiments, we used moving or stationary objects as targets. Moreover, the experimenter manipulated a computer at the onset of each block of trials. The results show that by the age of 20 months, the infant reliably followed the experimenter's cues and looked back to the target behind him. Moving targets elicited more responses than stationary targets, and the subject showed more follow responses after having seen the experimenter manipulating the computer.

In this paper, we summarize a series of studies on the developmental changes in social cognition in mother-raised infant chimpanzees from birth to around 2 years old. The infants preferentially tracked a photograph of their mother's face at 1 month but showed indifferent preferences to faces at 2 months old. This change in facial recognition was correlated with a decrease in neonatal spontaneous smiling, increase in social smiling and a decline in neonatal imitation of facial expressions. Also at around 2 months, the infants began to show preferences for directed-gaze faces over averted gazes, and the amount of mutual gaze time between mother and infant chimpanzees increased. Thus, by 2 months of age, abilities required for dyadic interactions are already developed in chimpanzees as is the case in humans. The development of triadic interactions, however, is rather different between these two species. The infant chimpanzee can follow another's pointing or gaze at around 1 year, but even by 2 years old, does not “share” attention with the others.

We investigated the behavioural and cognitive development of a captive male infant chimpanzee, Ayumu, raised by his mother, Ai. Here we report Ayumu's achievements up to the age of 2 years and 3 months, in the context of complex computer-controlled tasks. From soon after birth, Ayumu had been present during an experiment performed by his mother. The task consisted of two phases, a matching-to-sample task in which she received token rewards, and the insertion of these tokens into a vending machine to obtain food rewards. Ayumu himself received no reward or encouragement from humans for any of the actions he exhibited during the experiment. At the age of 9 months and 3 weeks, Ayumu performed his first matching-to-sample trial. At around 1 year and 3 months, he began to perform them consistently. Also during this period, he frequently stole food rewards from his mother. At 2 years and 3 months, Ayumu succeeded for the first time in inserting a token into the vending machine. Once he had succeeded in using a token, he performed both phases of the task in sequence 20 times consecutively. The infant's behaviour was not shaped by food rewards but by a strong motivation to copy his mother's behaviour. Our observations of Ayumu thus mirror the learning processes shown by wild chimpanzees.

Gaze following is a fundamental component of triadic social interaction which includes events and an object shared with other individuals and is found in both human and nonhuman primates. Most previous work has focused only on the immediate reaction after following another’s gaze. In contrast, this study investigated whether gaze following is retained after the observation of the other’s gaze shift, whether this retainment differs between species and age groups, and whether the retainment depends on the nature of the preceding events. In the social condition, subjects (1- and 2-year-old human children and chimpanzees) witnessed an experimenter who looked and pointed in the direction of a target lamp. In the physical condition, the target lamp blinked but the experimenter did not provide any cues. After a brief delay, we presented the same stimulus again without any cues. All subjects looked again to the target location after experiencing the social condition and thus showed a carryover effect. However, only 2-year-olds showed a carryover effect in the physical condition; 1-year-olds and chimpanzees did not. Additionally, only human children showed spontaneous interactive actions such as pointing. Our results suggest that the difference between the two age groups and chimpanzees is conceptual and not only quantitative.

The use of gaze shifts as social cues has various evolutionary advantages. To investigate the developmental processes of this ability, we conducted an object-choice task by using longitudinal methods with infant chimpanzees tested from 8 months old until 3 years old. The experimenter used one of six gestures towards a cup concealing food; tapping, touching, whole-hand pointing, gazing plus close-pointing, distant-pointing, close-gazing, and distant-gazing. Unlike any other previous study, we analyzed the behavioral changes that occurred before and after choosing the cup. We assumed that pre-choice behavior indicates the development of an attentional and spatial connection between a pointing cue and an object (e.g. Woodward, 2005); and post-choice behavior indicates the emergence of object permanence (e.g. Piaget, 1954). Our study demonstrated that infant chimpanzees begin to use experimenter-given cues with age (after 11 months of age). Moreover, the results from the behavioral analysis showed that the infants gradually developed the spatial link between the pointing as an object-directed action and the object. Moreover, when they were 11 months old, the infants began to inspect the inside of the cup, suggesting the onset of object permanence. Overall, our results imply that the ability to use the cues is developing and mutually related with other cognitive developments. The present study also suggests what the standard object-choice task actually measures by breaking the task down into the developmental trajectories of its component parts, and describes for the first time the social-physical cognitive development during the task with a longitudinal method.

Can chimpanzees learn the reputation of strangers indirectly by observation? Or are such stable behavioral attributions made exclusively by first-person interactions? To address this question, we let seven chimpanzees observe unfamiliar humans either consistently give (generous donor) or refuse to give (selfish donor) food to a familiar human recipient (Experiments 1 and 2) and a conspecific (Experiment 3). While chimpanzees did not initially prefer to beg for food from the generous donor (Experiment 1), after continued opportunities to observe the same behavioral exchanges, four chimpanzees developed a preference for gesturing to the generous donor (Experiment 2), and transferred this preference to novel unfamiliar donor pairs, significantly preferring to beg from the novel generous donors on the first opportunity to do so. In Experiment 3, four chimpanzees observed novel selfish and generous acts directed toward other chimpanzees by human experimenters. During the first half of testing, three chimpanzees exhibited a preference for the novel generous donor on the first trial. These results demonstrate that chimpanzees can infer the reputation of strangers by eavesdropping on third-party interactions.

The present study investigated how anticipation of a target's appearance affects human attention to gaze cues provided by a schematic face. Subjects in a 'catch' group received a high number of 'catch' trials, in which no target stimulus appeared. Subjects in the control group did not receive any catch trials. As in previous studies, both groups showed a facilitation effect to the cued location during shorter stimulus onset asynchrony (SOA). In both groups, an analysis of eye movements confirmed that subjects' eyes remained on the fixation point, ruling out the possibility that the facilitation effect was due to shifting eye movements (saccades) as opposed to a shift in covert attention. But while the control group's response time (RT) decreased as SOA increased, the catch group's RT had a U-shaped pattern and the facilitation effect to the cued location was reversed at the longest SOA (1005 ms). These results suggest that subjects in the catch group disengaged their attention during long SOAs because they expected the trial to be a catch trial. This disengagement of attention during long SOAs results in a delay before attention could be re-focused to the previous location regardless of the cue validity ["IOR (inhibition of return)"-like-phenomenon]. Unlike the conventional IOR, we suggest that this "IOR"-like phenomenon caused by an unpredictive central gaze cue is likely to be mediated by an endogenous mechanism.

The ability of non-human primates to follow the gaze of other individuals has recently received much attention in comparative cognition. The aim of the present study was to investigate the emergence of this ability in a chimpanzee infant. The infant was trained to look at one of two objects, which an experimenter indicated by one of four different cue conditions: (1) tapping on the target object with a finger; (2) pointing to the target object with a finger; (3) gazing at the target object with head orientation; or (4) glancing at the target object without head orientation. The subject was given food rewards independently of its responses under the first three conditions, so that its responses to the objects were not influenced by the rewards. The glancing condition was tested occasionally, without any reinforcement. By the age of 13 months, the subject showed reliable following responses to the object that was indicated by the various cues, including glancing alone. Furthermore, additional tests clearly showed that the subject's performance was controlled by the "social" properties of the experimenter-given cues but not by the non-social, local-enhancing peripheral properties.

化学蒸着 (CVD) 法によるY型ゼオライトの細孔径制御について検討した。シラン化剤にテトラエトキシシランを用いエーテル共存下, 固定床流通型反応器中で CVD を行なった。このように調製した試料の細孔径を分子径の異なる炭化水素の吸着特性から評価した。1回処理した試料で 1,3,5- トリイソプロピルベンゼンが吸着しなくなった。3回処理で 1,3,5- トリメチルベンゼンが吸着しなくなり, また, 2,2,4- トリメチルペンタンの吸着速度も遅くなった。4回処理でキシレン類の競争吸着におけるパラ選択性が 50% を越えた。さらに, 5回処理ではヘキザンの吸着速度が遅くなった。このようにCVDをくり返すと細孔径は徐々に小さくなることが確認された。すなわち, 細孔径は 7.2Å (1回処理 ), 6.6Å (2回処理), 6.3～5.8Å (3回処理), 5.1Å (4回処理), 4.3Å (5回処理)。また, この細孔径制御はシリカバインダーには影響されなかった。