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Color Vision: How Do We See Colors?

The vision of color is an important aspect of the human being. Distinguishing between different colors is, without a doubt, an adaptive operation. So, why and how do we perceive the colors?

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The vision of color is as interesting as it is complex. Many of us question whether, really, we all perceive color in the same way. Who has not ever asked a friend, what if what is red for me is blue?

The visual system perceives achromatic colors (white, black and gray) and chromatic colors. When speaking of color, reference is made to chromatic colors, and the correct term is nuance. Despite this, the most widespread and known concept is that of color.

The fundamental question, which many people have asked themselves innumerable times, is what determines the color that we perceive from a visual stimulus; that is, why do we see colors and how do we see them? Different theories have addressed the perception of color throughout history and in this article we will see the most outstanding.

Component and opponent processing

In 1802, Thomas Young proposed one of the first theories on the vision of color: the component or tricomatic theory. Later, it was polished by Hermann von Helmholtz in 1852. According to this theory, there are three different types of color receptors (cones) and each of them has a different spectral sensitivity. In addition, the color of a stimulus would be coded by the amount and proportion of activity of those receptors.

On the other hand, Ewald Hering proposed the theory of the opposing process, in 1878. Hering postulated the existence of two types of cells in the visual system to code the color and another type more destined to encode the luminosity. His hypothesis revolved around that each cell type encoded the perception of two complementary colors (pairs of colors that produce white or gray when combined to the same extent).

“Each person has their own color, a hue whose light filters just along the contours of the body. A kind of halo. As in the figures seen in backlight.”

-Haruki Murakami-

Now, on what did Hering base his theory? He observed that complementary colors do not occur together. In the words of the author, “there is no such thing as bluish yellow or reddish green.” Another argument that led him to elaborate his theory was that the postimage produced by staring at the color red is green and vice versa. As well as the postimage when looking at the yellow color is blue and vice versa.

Thus, for many years researchers were inclined towards one or another theory, but over time it was shown that both coding mechanisms coexist in the visual system. Let’s deepen.

Evidence of both theories

It was not until the early seventies of the last century, when Young’s theory was confirmed. Thanks to the microspectrophotometry (technique to measure the absorption spectrum of the photopigment containing a cone), the existence of three types of cones in the retina was observed in those living beings with good color vision.

At the same time, they discovered that each of these cones contains a different photopigment with its particular absorption spectrum. Thus, some cones are more sensitive to long wavelengths, others to medium waves and others to short waves.

With respect to Hering’s theory, Chatterjee and Callaway (2003) tested the opposing processing of color at all levels of the retino-geniculate-striated system. Thanks to this, they discovered that in each of them, there are cells that respond in one direction before a color and in the opposite direction before their complementary color.

The constancy of color and the Retinex theory

The previous theories are lacking in an explanation about a fundamental aspect in the perception of color: the constancy of color. This concept refers to the fact that the color we perceive of an object is not simply a function of the reflected wavelengths.

For example, when we see our room at dawn, the light is not the same as at noon. The wavelengths change, however, we perceive the same color. The wall of our room may seem more or less dark depending on the light, but we know that it is the same color.

Thus, the constancy of color “is the tendency of an object to remain the same color despite the large changes in the wavelength of the reflected light (Pinel, 2012)”. In fact, it provides us with an adaptive function in our ability to distinguish one object from another, since otherwise the color would change each time the object was made.

Retinex theory

The Land Retinex theory (1977) argues that “the color of an object is determined by its reflectance (the proportion of light of different wavelengths that reflects a surface)”.

Hurlbert and Wolf (2004), following this theory, affirm that “the visual system calculates the reflectance of the surfaces. In this way, he perceives the colors by comparing the light reflected by adjacent surfaces -primes- in at least three bands of different wavelengths (short, medium and long) “.

“There are things in the color that come up in me while I paint, big and intense things.”

-Vincent van Gogh-

In other words, the visual system is able to calculate the wavelengths that a surface reflects and still perceive the same color, despite changes in lighting. It does not matter that an object receives more or less light, its color will not change for us.

Shapely and Hawken (2002) state that Land’s theory is important because it implies the existence of a type of cortical neurons that are involved in chromatic vision, that is, in the vision of color.

Science follows its path in the vision of color

As we can see, despite the great scientific advances in terms of brain functioning, there is still much to be discovered. The vision of color is an ongoing theme and, little by little, new findings are made. Theories evolve and this means that some can be discarded, others complemented and others completely new.

“I try to apply colors as words that form poems, as notes that form music.”

-Joan Miro-

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