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Related Concept Videos

Photoreceptors and Visual Pathways01:22

Photoreceptors and Visual Pathways

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, whereas...
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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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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 layer, the vascular tunic,...
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Perceptual constancy is the ability to recognize that objects remain consistent and unchanged even when their appearance varies due to changes in sensory input. There are four main types of perceptual constancy: size constancy, shape constancy, color constancy, and brightness constancy.
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Related Experiment Video

Updated: Jun 24, 2026

Visualizing Visual Adaptation
04:43

Visualizing Visual Adaptation

Published on: April 24, 2017

Knowledge alters visual contrast sensitivity.

Stephan de la Rosa1, Michael Gordon, Bruce A Schneider

  • 1University of Toronto, Mississauga, Ontario, Canada. delarosa@kyb.tuebingen.mpg.de

Attention, Perception & Psychophysics
|March 24, 2009
PubMed
Summary
This summary is machine-generated.

Knowledge and expectations, not just attention, influence visual contrast sensitivity. This top-down control helps the visual system adapt to upcoming contrast levels, optimizing perception and preventing overload.

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Investigating the Deployment of Visual Attention Before Accurate and Averaging Saccades via Eye Tracking and Assessment of Visual Sensitivity
06:46

Investigating the Deployment of Visual Attention Before Accurate and Averaging Saccades via Eye Tracking and Assessment of Visual Sensitivity

Published on: March 18, 2019

Area of Science:

  • Visual neuroscience
  • Perceptual psychology

Background:

  • Visual contrast sensitivity is influenced by surrounding luminance levels (bottom-up).
  • Attention (top-down) also modulates contrast sensitivity.
  • Existing models may not fully capture all top-down influences.

Purpose of the Study:

  • Investigate a novel form of top-down influence on contrast sensitivity.
  • Determine if knowledge or expectations, independent of attention, affect contrast sensitivity.
  • Explore the implications for visual system modeling.

Main Methods:

  • Experimental manipulation of expected visual contrast levels.
  • Measurement of observer sensitivity to contrast in target areas.
  • Comparison of contrast sensitivity under different knowledge/expectation conditions.

Main Results:

  • Knowledge and expectations about upcoming visual contrast significantly alter contrast sensitivity.
  • This effect appears independent of attentional modulation.
  • Demonstrated a new top-down control mechanism for visual sensitivity.

Conclusions:

  • Visual contrast sensitivity is subject to knowledge-driven, top-down control.
  • This mechanism may preset visual sensitivity for optimal performance and protection.
  • Suggests incorporating knowledge-based top-down influences into current models of contrast sensitivity.