Body imitation in an enculturated orangutan (Pongo pygmaeus)

The mechanisms underlying the copying of others' actions in monkeys and apes are poorly understood. The author compared the ability of the 18-year-old, human-reared, language-trained orangutan Chantek to reproduce the same set of actions that Custance, Whiten, and Bard (1995) used with two chimpanzees. Previous studies (e.g., Miles, Mitchell, and Harper (1996)) had shown that Chantek was capable of imitating on command, but no direct comparison across studies had been attempted. The aim of this study was to investigate how he encoded observed behavior and what types of information he acquired from the experimenter. Chantek received the 48 test actions used by Custance et al. (1995). After the experimenter modeled the target action, Chantek was asked to do the same. Chantek's responses were scored for body part used, type of action performed, and general accuracy. In general, Chantek showed good accuracy in reproducing the experimenter's actions. Three types of errors were especially interesting. First, although he had a 90% matching accuracy between his own gross body areas (e.g., head, arms) and those of the experimenter, Chantek's accuracy decreased considerably for the body parts within those gross body areas. Second, Chantek performed better in those actions that involved some contact between his body parts. Finally, Chantek may have had some difficulty interpreting what he was expected to reproduce (e.g., when asked to raise his index finger, he raised his arm). The author argues that an attentional bias toward certain results or goals and a less differentiated ability to encode observed actions may be important factors contributing to the observed error patterns.