Great apes' understanding of biomechanics: eye-tracking experiments using three-dimensional computer-generated animations.

Visual processing of the body movements of other animals is important for adaptive animal behaviors. It is widely known that animals can distinguish articulated animal movements even when they are just represented by points of light such that only information about biological motion is retained. However, the extent to which nonhuman great apes comprehend the underlying structural and physiological constraints affecting each moving body part, i.e., biomechanics, is still unclear. To address this, we examined the understanding of biomechanics in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), following a previous study on humans (Homo sapiens). Apes underwent eye tracking while viewing three-dimensional computer-generated (CG) animations of biomechanically possible or impossible elbow movements performed by a human, robot, or nonhuman ape. Overall, apes did not differentiate their gaze between possible and impossible movements of elbows. However, some apes looked at elbows for longer when viewing impossible vs. possible robot movements, which indicates that they may have had knowledge of biomechanics and that this knowledge could be extended to a novel agent. These mixed results make it difficult to draw a firm conclusion regarding the extent to which apes understand biomechanics. We discuss some methodological features that may be responsible for the results, as well as implications for future nonhuman animal studies involving the presentation of CG animations or measurement of gaze behaviors.

A new method of walking rehabilitation using cognitive tasks in an adult chimpanzee (Pan troglodytes) with a disability: a case study.

There are few studies of long-term care and rehabilitation of animals which acquired physical disabilities in captivity, despite their importance for welfare. An adult male chimpanzee named Reo at the Primate Research Institute of Kyoto University, developed acute myelitis, inflammation of the spinal cord, which resulted in impaired leg function. This report describes a walking rehabilitation system set up in a rehabilitation room where he lives. The rehabilitation apparatus consisted of a touch monitor presenting cognitive tasks and a feeder presenting food rewards at a distance of two meters from the monitor, to encourage him to walk between the monitor and the feeder repeatedly. Initially, Reo did not touch the monitor, therefore we needed adjustment of the apparatus and procedure. After the habituation to the monitor and cognitive tasks, he started to show behaviors of saving food rewards without walking, or stopping participation to the rehabilitation. Finally it took seven phases of the adjustment to determine the final setting; when the monitor automatically displayed trials in 4-h, AM (1000-1200 hours) and PM (1400-1600 hours) sessions through a day, Reo spontaneously walked from the monitor to the feeder to receive rewards, and returned to the monitor to perform the next trial. Comparison of Reo's locomotion in a no-task period and under the final setting revealed that the total travel distance increased from 136.7 to 506.3 m, movement patterns became multiple, and the percentage of walking increased from 1.2 to 27.2 % in PM session. The findings of this case study suggest that cognitive tasks may be a useful way to rehabilitate physically disabled chimpanzees, and thus improve their welfare in captivity.

Behavioral recovery from tetraparesis in a captive chimpanzee.

An adult male chimpanzee living in a captive social group at the Primate Research Institute of Kyoto University developed acute tetraparesis. He was paralyzed and received intensive care and veterinary treatment as previously reported in Miyabe-Nishiwaki et al. (J Med Primatol 39:336-346, 2010). The behavioral recovery of the chimpanzee was longitudinally monitored using an index of upright posture between 0 and 41 months after the onset of tetraparesis. Four phases were identified during the course of behavioral recovery. During Phase 0 (0-13 months), the chimpanzee remained lying on his back during the absence of human caretakers. An increase in upright posture occurred in Phase I (14-17 months), then remained at a stable level of around 50-70 % in Phase II (18-29 months). During Phases I and II, the subject's small treatment cage represented a spatial limitation. Thus, behavioral recovery was mainly mediated by arm muscle strengthening caused by raising the body trunk with the aid of materials attached to the cage walls as environmental enrichment. When the chimpanzee was moved to a larger rehabilitation room in Phase III (30-41 months), the percentage of upright posture constantly exceeded 80 %, except in the 40th month when he injured his ankle and was inactive for several days. The enlargement of the living space had a positive effect on behavioral recovery by increasing the types of locomotion exhibited by the subject, including the use of legs during walking. Rehabilitation works were applied in face-to-face situations which enabled the use of rehabilitation methods used in humans. The process of behavioral recovery reported in this study provides a basic data set for planning future rehabilitation programs and for comparisons with further cases of physical disability in non-human primates.