Face contains various types of information for the social life of human and nonhuman primates. In this presentation, we report the two experiments for the recognition of faces and gaze in infant chimpanzees (Pan troglodytes).
EXPERIMENT 1: Development of recognition of mother's face.
In Experiment 1, we tested the developmental changes in the preference of mother's face in infant chimpanzees using tracking response as a measure. Subjects were the three infant chimpanzees born in 2000. Experiment began before the 1 month of age. We prepared the photographs of the mother of each baby and "average" chimpanzee face using the computer-graphic technology. We set these photographs onto the CCD camera and move it from the front of the subject's face to either left or right side slowly. Before 4weeks of age, the infants showed little number of tracking responses and did not show any preferences. During 4 to 8 weeks old, they showed strong preference for mother's face. From 8 weeks old, they showed again no preferences, but exhibited frequent tracking responses. Until 4 weeks of age, the subject spent most of time only with their mother, and during 4 to 8 weeks, they experienced the increased exposures to the other chimpanzees. These trends in visual experience may be one of the factors for the developmental changes in the preference for mother's face.
EXPERIMENT 2: Gaze following in an infant chimpanzee.
The second experiment examined how an infant chimpanzee followed the human gaze. We tested the ability of gaze following using tapping, pointing, head turning, and glancing cues from 7 months of age. The subject successfully followed the tapping and pointing cues in 9 months old, and the head turning cue in 11 months old. Furthermore, nonreinforcement probe tests revealed that the subject reliably followed the glancing cue (eye movement only) in 13 months old. Additional tests verified that the subject's behavior was not controlled by the nonsocial properties of the cues (such like spatial proximity of the cue to the target object and peripheral presentations of the cue). These results clearly demonstrated that the chimpanzees use other's social cue to orient their attention to the specific object in their early infancy.

TOMONAGA, Masaki
Section of Language & Intelligence,
Primate Research Institute,
Kyoto University
Inuyma, Aichi, 484-8506, Japan
tomonaga@pri.kyto-u.ac.jp