Understanding the Trichromatic Theory of Color Vision

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According to the trichromatic theory of color vision, also known as the Young-Helmholtz theory of color vision, there are three receptors in the retina that are responsible for the perception of color. One receptor is sensitive to the color green, another to the color blue and a third to the color red. These three colors can then be combined to form any visible color in the spectrum.


How exactly do we perceive color? A number of theories have emerged to explain this phenomenon, and one of the earliest and best-known was the trichromatic theory.

Two renowned researchers, Thomas Young and Hermann von Helmholtz, contributed to the trichromatic theory of color vision. The theory began when Thomas Young proposed that color vision results from the actions of three different receptors. As early as 1802, Young suggested that the eye contained different photoreceptor cells that were sensitive to different wavelengths of light in the visible spectrum.

It was later in the mid-1800s that researcher Hermann von Helmholtz expanded upon Young's original theory and suggested that the cone receptors of the eye were either short-wavelength (blue), medium-wavelength (green), or long-wavelength (red). He also proposed that it was the strength of the signals detected by the receptor cells that determined how the brain interpreted color in the environment.

Helmholtz discovered that people with normal color vision need three wavelengths of light to create different colors through a series of experiments.

  • Helmholtz used color-matching experiments where participants would alter the amounts of three different wavelengths of light to match a test color.
  • Participants could not match the colors if they used only two wavelengths but could match any color in the spectrum if they used three.
  • The theory became known as the Young-Helmholtz theory of color vision.

Color Receptors

The identification of the three receptors responsible for color vision did not occur until more than 70 years after the proposal of the theory of thrichromatic vision. Researchers discovered that cone pigments have different levels of absorption. Cones are receptors located in the retina that are responsible for the vision of both color and detail.

The cone receptors differ in absorption amounts due to the amount of opsin amino acids in the receptor. The three different cone receptors are:

  • Short-wavelength cone receptors,
  • Middle-wavelength cone receptors, and
  • Long-wavelength cone receptors.

Trichromatic Theory and Opponent Process Theory

In the past, the trichromatic theory was often presented as competing with the opponent process theory for dominance in explaining color vision. Today, it is believed that both theories can be used to explain how the color vision system operates and that each theory applies to a different level of the visual process. The trichromatic theory explains how color vision works at the receptor level. Opponent process theory, on the other hand, offers an explanation for how it operates at the neural level.

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