Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees
Hallmark social activities of humans, such as cooperation and cultural learning, involve eye-gaze signaling through joint attentional interaction and ostensive communication. The gaze-signaling and related cooperative-eye hypotheses posit that humans evolved unique external eye morphologies, includi...
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| Format: | Article |
| Language: | English |
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eLife Sciences Publications Ltd
2022-03-01
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| Series: | eLife |
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| Online Access: | https://elifesciences.org/articles/74086 |
| _version_ | 1811228047527903232 |
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| author | Fumihiro Kano Yuri Kawaguchi Yeow Hanling |
| author_facet | Fumihiro Kano Yuri Kawaguchi Yeow Hanling |
| author_sort | Fumihiro Kano |
| collection | DOAJ |
| description | Hallmark social activities of humans, such as cooperation and cultural learning, involve eye-gaze signaling through joint attentional interaction and ostensive communication. The gaze-signaling and related cooperative-eye hypotheses posit that humans evolved unique external eye morphologies, including uniformly white sclera (the whites of the eye), to enhance the visibility of eye-gaze for conspecifics. However, experimental evidence is still lacking. This study tested the ability of human and chimpanzee participants to discriminate the eye-gaze directions of human and chimpanzee images in computerized tasks. We varied the level of brightness and size in the stimulus images to examine the robustness of the eye-gaze directional signal against simulated shading and distancing. We found that both humans and chimpanzees discriminated eye-gaze directions of humans better than those of chimpanzees, particularly in visually challenging conditions. Also, participants of both species discriminated the eye-gaze directions of chimpanzees better when the contrast polarity of the chimpanzee eye was reversed compared to when it was normal; namely, when the chimpanzee eye has human-like white sclera and a darker iris. Uniform whiteness in the sclera thus facilitates the visibility of eye-gaze direction even across species. Our findings thus support but also critically update the central premises of the gaze-signaling hypothesis. |
| first_indexed | 2024-04-12T09:51:55Z |
| format | Article |
| id | doaj.art-3b2d11ecac2d4cb5bafc82992053fbce |
| institution | Directory Open Access Journal |
| issn | 2050-084X |
| language | English |
| last_indexed | 2024-04-12T09:51:55Z |
| publishDate | 2022-03-01 |
| publisher | eLife Sciences Publications Ltd |
| record_format | Article |
| series | eLife |
| spelling | doaj.art-3b2d11ecac2d4cb5bafc82992053fbce2022-12-22T03:37:49ZengeLife Sciences Publications LtdeLife2050-084X2022-03-011110.7554/eLife.74086Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzeesFumihiro Kano0https://orcid.org/0000-0003-4534-6630Yuri Kawaguchi1Yeow Hanling2Centre for the Advanced Study of Collective Behaviour, University of Konstanz, Konstanz, Germany; Kumamoto Sanctuary, Kyoto University, Kumamoto, Japan; Max Planck Institute of Animal Behavior, Radolfzell, GermanyMesserli Research Institute, University of Veterinary Medicine Vienna, Vienna, Austria; Japan Society for the Promotion of Science (JSPS), Tokyo, Japan; Primate Research Institute, Kyoto University, Inuyama, JapanKumamoto Sanctuary, Kyoto University, Kumamoto, JapanHallmark social activities of humans, such as cooperation and cultural learning, involve eye-gaze signaling through joint attentional interaction and ostensive communication. The gaze-signaling and related cooperative-eye hypotheses posit that humans evolved unique external eye morphologies, including uniformly white sclera (the whites of the eye), to enhance the visibility of eye-gaze for conspecifics. However, experimental evidence is still lacking. This study tested the ability of human and chimpanzee participants to discriminate the eye-gaze directions of human and chimpanzee images in computerized tasks. We varied the level of brightness and size in the stimulus images to examine the robustness of the eye-gaze directional signal against simulated shading and distancing. We found that both humans and chimpanzees discriminated eye-gaze directions of humans better than those of chimpanzees, particularly in visually challenging conditions. Also, participants of both species discriminated the eye-gaze directions of chimpanzees better when the contrast polarity of the chimpanzee eye was reversed compared to when it was normal; namely, when the chimpanzee eye has human-like white sclera and a darker iris. Uniform whiteness in the sclera thus facilitates the visibility of eye-gaze direction even across species. Our findings thus support but also critically update the central premises of the gaze-signaling hypothesis.https://elifesciences.org/articles/74086eye coloreye-gazecomparative studycommunicationcooperationjoint attention |
| spellingShingle | Fumihiro Kano Yuri Kawaguchi Yeow Hanling Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees eLife eye color eye-gaze comparative study communication cooperation joint attention |
| title | Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees |
| title_full | Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees |
| title_fullStr | Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees |
| title_full_unstemmed | Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees |
| title_short | Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees |
| title_sort | experimental evidence that uniformly white sclera enhances the visibility of eye gaze direction in humans and chimpanzees |
| topic | eye color eye-gaze comparative study communication cooperation joint attention |
| url | https://elifesciences.org/articles/74086 |
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