Abstract: We investigated the ability to perceive depth from shading, one of the pictorial depth cues, in three chimpanzee infants aged 4-10 months old, using a preferential reaching task commonly used to study pictorial depth perception in human infants. The chimpanzee infants reached significantly more to three-dimensional toys than to pictures thereof and more to the three-dimensional convex than to the concave. Furthermore, two of the three infants reached significantly more to the photographic convex than to the photographic concave. These infants also looked longer at the photographic convex than the concave. Our results suggest that chimpanzees perceive, at least as early as the latter half of the first year of life, pictorial depth defined by shading information. Photographic convexes contain richer information about pictorial depth (e.g., attached shadow, cast shadow, highlighted area, and global difference in brightness) than simple computer-graphic graded patterns. These cues together might facilitate the infants' perception of depth from shading.

Abstract: 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.

Abstract: The experiments investigated how two adult captive chimpanzees learned to navigate in an automated interception task. They had to capture a visual target that moved predictably on a touch monitor. The aim of the study was to determine the learning stages that led to an efficient strategy of intercepting the target. The chimpanzees had prior training in moving a finger on a touch monitor and were exposed to the interception task without any explicit training. With a finger the subject could move a small “ball” at any speed on the screen toward a visual target that moved at a fixed speed either back and forth in a linear path or around the edge of the screen in a rectangular pattern. Initial ball and target locations varied from trial to trial. The subjects received a small fruit reinforcement when they hit the target with the ball. The speed of target movement was increased across training stages up to 38 cm/s. Learning progressed from merely chasing the target to intercepting the target by moving the ball to a point on the screen that coincided with arrival of the target at that point. Performance improvement consisted of reduction in redundancy of the movement path and reduction in the time to target interception. Analysis of the finger's movement path showed that the subjects anticipated the target's movement even before it began to move. Thus, the subjects learned to use the target's initial resting location at trial onset as a predictive signal for where the target would later be when it began moving. During probe trials, where the target unpredictably remained stationary throughout the trial, the subjects first moved the ball in anticipation of expected target movement and then corrected the movement to steer the ball to the resting target. Anticipatory ball movement in probe trials with novel ball and target locations (tested for one subject) showed generalized interception beyond the trained ball and target locations. The experiments illustrate in a laboratory setting the development of a highly complex and adaptive motor performance that resembles navigational skills seen in natural settings where predators intercept the path of moving prey.

Abstract: Empathy is a necessary prerequisite for the occurrence of consolation. The term “consolation” contains a hypothesis about function, which is distress alleviation. The present study aims to confirm the occurrence of consolation in captive chimpanzees via the post-conflict/matched-control method (PC-MC) and to suggest its possible roles. We collected 273 PC-MC pairs in the group of Pan troglodytes housed in the ZooParc de Beauval (France). We confirmed the presence of consolatory contacts (mean level of consolation, 49.5% +/- 22.3% SEM) in the colony. Consolation rates were significantly higher than reconciliation levels (mean level of reconciliation, 28.9% +/- 16.8% SEM). The level of consolation was greater in the absence of reconciliation than in the presence of it, suggesting that consolation might be an alternative behavior. As friendship and relatedness did not influence the occurrence of consolation, they did not seem to be the best prerequisites for this behavioral mechanism, at least in this chimpanzee colony. Affinitive contacts with third parties were significantly more frequent when the victim called attention to itself during severe aggressions by screaming. These high-pitched sounds seem to be useful in eliciting aid from conspecifics, as occurs in young humans. The occurrence of consolation reduced the likelihood of further attacks among group-members. From this perspective, both victims and consolers most likely gain potential advantages by interacting with each other when aggression is particularly severe, reconciliation is not immediate, and consequently social stress reaches high levels.

Abstract: Reconciliation is a conflict resolution mechanism that is common to many gregarious species with individualized societies. Reconciliation repairs the damaged relationship between the opponents and decreases postconflict (PC) anxiety. The “integrated hypothesis” links the quality of the opponents' relationship to PC anxiety, since it proposes that conflicts among partners with high relationship quality will yield high levels of PC anxiety, which in turn will lead to an increased likelihood of reconciliation. We tested the integrated hypothesis in captive chimpanzees (Pan troglodytes) in the Arnhem Zoo, The Netherlands. We applied the standard PC/matched control (MC) method. Our results mostly support the integrated hypothesis, in that more valuable and compatible partners (i.e., males and frequent groomers) reconciled more often than less valuable and weakly compatible partners (i.e., females and infrequent groomers). In addition, PC anxiety was higher after conflicts among males than among females. Emotional arousal thus appears to be a mediator facilitating reconciliation. However, in contrast to the predictions derived from the integrated hypothesis, PC anxiety appeared only in aggressees, and not in aggressors, of conflicts. This suggests that while relationship quality determines PC anxiety, it is dependent on the role of the participants in the conflict.