The Characteristics of Human Color Vision

Human color vision is complex and depends on the proper functioning of certain nerve cells and structures of the eyeball. Today's article will explain it to you.
The Characteristics of Human Color Vision

Last update: 01 August, 2021

Human color vision is one of our most complex processes. It’s based on a network of nerve cells that transform light stimuli into electrical impulses for the brain to process.

Are you ready to learn more about how the eyes perceive color?

If so, read on!

The human eye

The human eye has several structures that participate in the capture and perception of images. This is how a photographic camera works.

The crystalline lens is responsible for fixing the lens, while the iris regulates the amount of light that enters the eyeball. The retina acts as the photosensitive layer responsible for absorbing the light beams.

There are two types of cells in the retina that act as photoreceptors: rods and cones. The rods help to distinguish between shapes, forms, and contrasts, while the cones help sharpen and differentiate between the range of colors in the light spectrum.

Color and human vision

Color is the visual perception produced in the human eye as a result of its ability to discriminate between the various wavelengths that form part of the electromagnetic spectrum. In this sense, when an element or body is illuminated, it absorbs part of the light beams and reflects the rest.

All the light that is reflected is captured by the eye and processed by the occipital lobe of the brain, assigning it a specific tone. In fact, studies assert that the wavelength emitted by an object is responsible for its hue, this being the main physical component of the color.

In this sense, a banana or a lemon produces wavelengths between 570 and 580 nanometers, which are perceived as yellow by the human eye. However, the perception of color depends on the intensity of light rays incident on a given element.

The color of an object or body becomes more opaque until it is finally perceived as black in the absence of light. It is important to note that the black tone is the result of the absorption of all colors and not a specific wavelength.

A set of mood balls.
Humans perceive color based on wavelengths and it takes place between the retina and the brain.

Why are there different colors?

Color is an inherent factor in an object’s ability to absorb and reflect wavelengths. Human eyes perceive reflected beams of light. Then, the brain catalogs and assigns a color to each of them. The spectrum of light visible to humans is between 380 and 780 nanometers.

Therefore, the eyes perceive the reddish colors in blood or an apple as a result of their ability to capture part of the light and emit a wavelength of between 615 and 780 nanometers. Similarly, it captures light beams between 425 and 475 nanometers as blue.

Green, red, and blue are the primary colors of the visible spectrum. Thus, the variation in the quantity of these tones makes it possible to produce and perceive the rest of the colors. However, white is the result of the reflection of all wavelengths simultaneously.

Human color vision: How we differentiate between colors

Light is one of the most common forms of energy in the environment and the sun is its main source. It distributes via particles that allow it to strike objects. Light beams contain all the colors of the rainbow, which surfaces absorb and reflect according to their characteristics.

The retina is the neurosensory layer of the eye that captures the luminous stimuli projected in space. Cones are the cells responsible for receiving the wavelengths that describe color. Furthermore, studies identified three types of cones involved in the capture of the electromagnetic spectrum, according to wavelength: the L-, M- and S-cones.

Human eyes perceive colors by stimulation of photoreceptors that initiate an intrinsic molecular cascade involving substances such as opsin and retinol. Thus, the result is the transformation of light stimuli into electrical potentials that describe an inverted image.

The electrical stimuli forms and integrates into the optic nerve to then pass through the thalamus to reach the optic radiations. Finally, the stimuli reach the occipital lobe in Brodmann’s areas 17, 18, and 19. This is where the visual perception process completes and corrects the image.

Trichromatic theory versus opposing process theory

Currently, many theories try to explain the phenomena that give rise to color perception. However, the trichromatic and opposite process theories are the most widely accepted and studied in depth.

The trichromatic theory developed by Thomas Young in 1802 and modified by Herman Von Helmholtz in 1856 states that there are three types of cones in the retina. As per their design, these capture a specific range of wavelengths, corresponding to the colors blue, green, and red.

Young and Helmholtz emphasized that the perception of all colors is the result of the participation of these three receptors. These activate at different intensities. Thus, the human eye perceives the color red when the wavelength stimulates the red receptors with great intensity. In turn, it perceives the blue and green receptors weakly.

Moreover, physiologist Ewald Hering disagreed with the previous theory and described the theory of opposite processes at the end of the 19th century. According to Hering, human eyes perceive colors based on a system of opposing channels consisting of the colors red, yellow, blue, and green.

Thus, red is the opposite of green, yellow of blue, and white of black. Thus, the eyes perceive the hue of an object based on two colors that oppose each other. However, one of the colors suppresses the other according to the captured wavelength.

The theory of opposing processes explains why humans can visualize reddish yellow and yellowish-green tones but cannot visualize reddish-green or bluish-yellow tones.

Problems in human color vision

Alterations in color perception are usually the result of congenital or acquired conditions, according to several studies. Most of these alterations are hereditary and present in more than 8% of the male population.

They divide according to their form of presentation as:

  • Anomalous trichromatism
  • Monochromatism
  • Dichromatism
  • Anomalous trichromatism

The main characteristic of people with anomalous or defective trichromatism is having the three types of cones necessary for color perception, but with altered functioning. Therefore, these patients require a different intensity of the three basic colors than the average person to discriminate one tone from another.

This condition is responsible for the fact that these people can confuse the colors of objects or bodies around them. Thus, one could mistake it for color blindness.

Glasses for seeing black and white.
Anomalous trichromatism isn’t the same as color blindness. They’re similar but the intrinsic mechanism of the alteration isn’t the same.

Monochromatism

People with this condition usually have a lack of perception of colors in their environment. This is a result of the presence of only one type of cone in the retina or the total absence of them (achromatopsia). Similarly, people’s vision is often blurry and they have difficulty focusing in low light.

In general, monochromatism is responsible for the perception of all objects in black, white, and gray tones. This is why we know it as color blindness.

Dichromatism

This happens when the sufferer has an impairment in the functioning of a single group of cones. As a result, the retina retains two cone systems, allowing the person to have some color perception, even though it isn’t normal.

Color blindness is the most common form of dichromatism. This is a hereditary condition pertaining to the X chromosome. Thus, it’s more common in men. In addition, it has different degrees of affection.

Ways to identify disturbances in human color vision

Human eyes perceive the environment through a network of nerve cells known as cones and rods. Problems identifying colors in childhood are often a warning sign of a disturbance in these cells. Occasionally, people may feel their vision changes the color of objects.

Nowadays, early medical diagnosis greatly favors the long-term prognosis. Therefore, it’s always a good idea to consult an ophthalmologist regarding any visual symptoms.

Finally, while there’s no cure for inherited conditions, you can treat any acquired alterations to prevent a subsequent disability.

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