What is unique about the human eye? Comparative image analysis on the external eye morphology of human and nonhuman great apes
What is unique about the human eye? Comparative image analysis on the external eye morphology of human and nonhuman great apes
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DOI：
10.1016/j.evolhumbehav.2021.12.004
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发表时间：
2022-04-28
影响因子：
5.1
通讯作者：
Tajima, Tomoyuki
中科院分区：
文献类型：
--
作者：
Kano, Fumihiro;Furuichi, Takeshi;Tajima, Tomoyuki
凝视信号假说和与之相关的合作眼假说认为人类进化出特殊的外眼形态，包括暴露的白色巩膜（眼睛的白色），以增强眼睛注视方向的可见性，从而通过联合注意互动和明示交流促进同种交流。然而，最近的定量研究质疑了这些假设，因为新的发现表明，人类眼睛的某些特征在大型猿类物种中并不一定是独一无二的。因此，目前有一个激烈的辩论是否外部眼睛的特征，人类是不同于其他猿类，以及如何区分功能有助于眼睛注视方向的可见性。本研究利用最新的图像分析技术来测试人类眼睛特征在类人猿面部图像中的独特性。尽管人类和其他类人猿的眼睛特征有很多相似之处，但一个关键的区别是人类有均匀的白色巩膜，这使得眼睛轮廓和虹膜清晰可见，这两个基本特征有助于眼睛注视方向的可见性。然后，我们测试了这些特征对视觉噪声（如阴影和距离）的可见性的鲁棒性，并发现这两个眼睛特征在人眼中仍然是可检测的，而在这些视觉挑战条件下，其他物种的眼睛轮廓几乎无法检测到。总的来说，我们发现人类在其他类人猿中具有独特的外部眼睛形态，这确保了眼睛注视信号在各种视觉条件下的鲁棒性。我们的研究结果支持，也批判性地更新了注视信号假说的中心前提。
The gaze-signaling hypothesis and the related cooperative-eye hypothesis posit that humans have evolved special external eye morphology, including exposed white sclera (the white of the eye), to enhance the visibility of eye gaze direction and thereby facilitate conspecific communication through joint-attentional interaction and ostensive communication. However, recent quantitative studies questioned these hypotheses based on new findings that certain features of human eyes are not necessarily unique among great ape species. Accordingly, there is currently a heated debate over whether external eye features of humans are distinct from those of other apes and how such distinguishable features contribute to the visibility of eye-gaze direction. The present study leveraged updated image analysis techniques to test the uniqueness of human eye features in facial images of great apes. Although many eye features were similar between humans and other great apes, a key difference was that humans have uniformly white sclera which creates clear visibility of both the eye outline and iris-the two essential features contributing to the visibility of eye-gaze direction. We then tested the robustness of the visibility of these features against visual noise, such as shading and distancing, and found that both eye features remain detectable in the human eye, while eye outline becomes barely detectable in other species under these visually challenging conditions. Overall, we identified that humans have unique external eye morphology among other great apes, which ensures the robustness of eye-gaze signals in various visual conditions. Our results support and also critically update the central premises of the gaze-signaling hypothesis.