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Uchikoshi, M., Yu, L., & Hattori, Y. (2026). Gibbons (Hylobates spp.) show increased attention to eyes when viewing conspecific faces: An eye-tracking study. Animal Behavior and Cognition, 13(3), 228-238. https://doi.org/10.26451/abc.13.03.02.2026

For humans, the face is a socially important visual stimulus, and the evolution of face perception has received considerable attention in research on non-human primates. However, little is known about face perception in gibbons, a key phylogenetic group among apes and humans. To address this gap, we used an eye-tracking device to examine how gibbons view face photographs, with the participation of three male adult gibbons. A total of 48 stimuli, consisting of gibbon and human faces showing neutral expressions were presented, and the gibbons were allowed to view them freely. Areas of interest (AOI) were defined for the eyes, nose, mouth, face periphery, and background in each image. We tested the effects of the AOIs and presented face species on viewing time. In analyses pooling data across individuals, gibbons spent significantly more time viewing the eyes than any other area and viewed gibbon eyes longer than human eyes. In separate analyses for each individual, two gibbons viewed the eyes significantly longer than the nose or mouth. Longer viewing times for gibbon eyes than human eyes were observed in all individuals. These results indicate that eyes are a highly salient facial feature for gibbons, albeit variably among individuals, and that gibbons’ viewing patterns differ when looking at a conspecific or an allospecific face. These findings are consistent with face-scanning studies in macaques and great apes. Further studies are needed to confirm the generality of these results and to uncover other characteristics of gibbon face perception.

Gibbons, Small apes, Eye-tracking, Face perception, Own-species bias