Human processing of faces is suggested to involve mechanisms specially devoted to this job. Even newborns, who have little experience with faces, show a visual preference for schematic faces. This suggests that some mechanisms for face processing may exist innately. In the present study, we examined how infants of nonhuman primates recognized schematic faces. We especially investigated whether infants of nonhuman primates would prefer facial stimuli, and, if they do, to compare developmental changes among primate species. In experiment 1, we used "face", "symmetrical scrambled face", and "asymmetrical scrambled face" as stimuli. Each "scrambled face" had the same facial parts as "face", but they were placed irregularly. Two of the three stimuli were presented simultaneously to infant macaque monkeys. We found that the monkeys preferred "face" to "symmetrical" or "asymmetrical scrambled face" from around 4 weeks of age. In experiment 2, we presented "face", "symmetrical scrambled face", and "facial configuration"(i.e. three black squares were placed in facial configuration). Infant macaques showed a preference for "facial configuration" before 4weeks of age, and subsequently looked "scrambled face" more than "face". However they switched to prefer "face" to "scrambled face" after eight weeks old. These results suggest that infant macaques distinguish "face" from "scrambled face" at 4 weeks of age, and the preference for schematic faces appear around 8weeks olds at the latest. In experiment 3, we presented the same stimuli as in experiment 2 to three chimpanzees. They preferred "face" to "symmetrical scrambled face" from around 8weeks after birth. They also preferred "facial configuration" to "scrambled face" in the same period. These three experiments revealed that a preference for schematic faces develops early in nonhuman primates as well as in humans. But it emerges at the different developmental stage among three species, possibly because their developmental speed differed. Moreover, we did not find evidence of facial preference in newborns. We suggest that some aspects of early recognition of schematic faces are shared by three primate species, but others may not.

KUWAHATA, Hiroko
Department of Psychology,
Faculty of Letters, Kyoto University
Yoshida Honmachi, Sakyo-ku, Kyoto
606-8501, Japan
kuwahata@psy.bun.kyoto-u.ac.jp