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The eye is a spherical, hollow structure composed of three tissue layers. The outer layer — the fibrous tunic, comprises the sclera — a white structure — and the cornea, which is transparent. The sclera encompasses some of the ocular surface, most of which is not visible. However, the 'white of the eye' is distinctively visible in humans compared to other species. The cornea, a clear covering at the front of the eye, enables light penetration. The eye's middle...
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Color perception begins in the retina, the light-sensitive layer at the back of the eye. Two main theories explain how colors are seen: the trichromatic theory and the opponent-process theory. The trichromatic theory, proposed by Thomas Young in 1802 and extended by Hermann von Helmholtz in 1852, suggests that color vision is based on three types of cone receptors in the retina. These cones are sensitive to different but overlapping ranges of wavelengths corresponding to red, blue, and green.
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At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category,...
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Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.
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Light rays enter the eye through the cornea, a transparent dome-shaped tissue that is the eye's outermost layer. The cornea bends or refracts, light rays traveling to the pupil. The shape of the cornea determines how much of the light is bent and whether the image will be focused correctly on the retina at the back of the eye. Once the light has passed through both refraction layers, it converges into a single focal point onto a small area. This is where photoreceptors start transforming...
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Optical perception, or vision, is an extraordinary sense dependent on converting light signals received via the ocular organs. These organs, known as eyes, are securely positioned within the bony cavities of the skull, called orbits. The orbits serve a dual purpose: a protective shield for the ocular globes and a stable attachment point for the soft ocular tissues. The eye's external protective mechanisms include the eyelids, which are edged with lashes that act as a barrier against foreign...
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Iris Fixation via External Pentagram Suturing
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Sclera and Iris Color Interact to Influence Gaze Perception.

Jessica L Yorzinski1, Christopher A Thorstenson2, Trezze P Nguyen3

  • 1Department of Ecology and Conservation Biology, Texas A&M University, College Station, TX, United States.

Frontiers in Psychology
|March 29, 2021
PubMed
Summary

White sclera significantly aids human gaze perception, especially with dark irises. Pigmented sclera impairs gaze evaluation, particularly in dark-eyed individuals, impacting social interaction.

Keywords:
depigmented scleragaze enhancement hypothesisgaze perceptionhuman eyeiris color

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Area of Science:

  • Human visual perception
  • Evolutionary biology
  • Social cognition

Background:

  • The white sclera enhances gaze perception in humans.
  • Iris color's influence on gaze perception is understudied.
  • The interplay between sclera and iris color in gaze perception requires investigation.

Purpose of the Study:

  • To investigate how the interaction between sclera and iris color affects human gaze perception.
  • To determine the role of scleral pigmentation in processing facial gaze cues.

Main Methods:

  • Recorded human participants' eye movements during a visual search task.
  • Utilized faces with directed or averted gaze, varying iris color (light/dark) and scleral pigmentation (depigmented/pigmented).

Main Results:

  • Participants accurately perceived gaze with depigmented sclera, irrespective of iris color.
  • Pigmented sclera slowed gaze evaluation, most significantly with dark irises.
  • Accuracy decreased with pigmented sclera, particularly for dark irises compared to light irises.

Conclusions:

  • Depigmented sclera are crucial for effective gaze perception, especially in individuals with dark irises.
  • The evolution of white sclera may have been vital for ancestral humans with dark irises to facilitate social communication.