Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees

Experimental evidence that uniformly white sclera enhances the visibility of eye-gaze direction in humans and chimpanzees

Blog Article

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 Mountaineering - Femme - Skis 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 Aluminum Ornament 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.