Question

Discuss how both the Trichromatic Theory and the Opponent Process Theory are necessary to understand color vision.

Answer 1

• 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.
• The theory began when Thomas Young proposed that color vision results from the actions of three different receptors. Young suggested that the eye contained different photoreceptor cells that were sensitive to different wavelengths of light in the visible spectrum.
• 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.
• The cone receptors differ in absorption amounts due to the amount of opsin amino acids in the receptor.
• The opponent process theory of color vision suggests that our ability to perceive color is controlled by three receptor complexes with opposing actions. These three receptors complexes are the red-green complex, the blue-yellow complex, and the black-white complex.
• According to the opponent process theory, these cells can only detect the presence of one color at a time because the two colors oppose one another. You do not see greenish-red because the opponent cells can only detect one of these colors at a time.
• While the trichromatic theory makes clear some of the processes involved in how we see color, it does not explain all aspects of color vision. The opponent process theory of color vision was developed by Ewald Hering, who noted that there are some color combinations that people simply never see.
• For example, while we often see greenish-blue or blueish-reds, we do not see reddish-green or yellowish-blue. Opponent process theory suggests that color perception is controlled by the activity of two opponent systems: a blue-yellow mechanism and a red-green mechanism.
• The opponent color process works through a process of excitatory and inhibitory responses, with the two components of each mechanism opposing each other.
• For example, red creates a positive (or excitatory) response, while green creates a negative (or inhibitory) response.
• These responses are controlled by opponent neurons, which are neurons that have an excitatory response to some wavelengths and an inhibitory response to wavelengths in the opponent part of the spectrum.
• The trichromatic theory explains how the three types of cones detect different light wavelengths, while opponent process theory explains how the cones connect to the ganglion cells. These ganglion cells are where the opposing elements inhibit each other to determine how color is perceived.
• 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.