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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...
Color Vision01:24

Color Vision

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.
UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in the...
Pigmentation01:19

Pigmentation

The color of the skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred to the keratinocytes via melanosomes.
Melanin occurs in two primary forms: eumelanin that provides black and brown pigment and pheomelanin that provides red color. Dark-skinned individuals produce more melanin than those with pale...
Perceptual Constancy01:12

Perceptual Constancy

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.
Size constancy is the recognition that an object remains the same size, even when its image on the retina changes. For instance, a bus is perceived to be large enough to carry people, even if it looks tiny from...
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Changes in Skin Color: Clinical Perspectives

The first thing a clinician sees is the skin, so the examination of the skin should be part of any thorough physical examination. Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the skin and its accessory organs.
Albinism
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Related Experiment Video

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Enabling High Grayscale Resolution Displays and Accurate Response Time Measurements on Conventional Computers
06:50

Enabling High Grayscale Resolution Displays and Accurate Response Time Measurements on Conventional Computers

Published on: February 29, 2012

The brightness of colour.

David Corney1, John-Dylan Haynes, Geraint Rees

  • 1UCL Institute of Ophthalmology, London, UK.

Plos One
|April 1, 2009
PubMed
Summary

The Helmholtz-Kohlrausch effect, where color saturation and hue influence perceived brightness, is explained by a Bayesian model of visual ecology. This suggests brightness perception is an adaptive response to the statistical relationship between retinal images and natural scenes.

Area of Science:

  • Visual perception science
  • Computational neuroscience
  • Psychophysics

Background:

  • Perceived brightness is influenced by spatial context and stimulus color.
  • The Helmholtz-Kohlrausch (HK) effect describes how color saturation and hue alter brightness perception.
  • This effect, known since the 19th century, lacks a clear explanation.

Purpose of the Study:

  • To explain the Helmholtz-Kohlrausch effect and contextual brightness perception.
  • To model human visual ecology using a Bayesian ideal observer approach.
  • To identify neural correlates of brightness perception using fMRI.

Main Methods:

  • Developed a Bayesian ideal observer model of human visual ecology.
  • Utilized fMRI to measure brain activity associated with brightness perception.

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Last Updated: Jun 24, 2026

Enabling High Grayscale Resolution Displays and Accurate Response Time Measurements on Conventional Computers
06:50

Enabling High Grayscale Resolution Displays and Accurate Response Time Measurements on Conventional Computers

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  • Analyzed the statistical relationship between retinal images and natural scenes.

    • Main Results:

    • The HK effect arises from encoding the non-linear statistical relationship between retinal images and natural scenes.
    • Cone photoreceptor response functions contribute to this complex relationship.
    • Activity in the primary visual cortex (V1) correlates with the perceived brightness of colors.

    Conclusions:

    • Brightness perception is an adaptive visual response to likely stimulus sources, based on statistical scene-image relationships.
    • Early visual system responses encode image statistics, while later stages relate images to scenes.
    • The visual cortex is adapted to process retinal signals based on past environmental interactions.