Color vision: how do we see colors?

Color vision is a topic 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 you is blue for me?

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

The fundamental question, which many people have asked themselves on countless occasions, is what determines the color that we perceive of a visual stimulus; that is to say, Why do we see colors and how do we see them? Different theories have addressed color perception throughout history and in this article we will see the most notable ones.

Component and opponent processing

In 1802, Thomas Young proposed one of the first theories of color vision: the component or trichomatic 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. Furthermore, 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 opponent process in 1878.. Hering postulated the existence of two types of cells in the visual system to encode color and another type intended to encode 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).

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

Thus, for many years researchers leaned towards one theory or another, but Over time, it was shown that both coding mechanisms coexist in the visual system.. Let’s dig deeper.

Tests 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 for measuring the absorption spectrum of 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.

Regarding the theory of Hering, Chatterjee and Callaway (2003) verified the opponent processing of color at all levels of the retino-geniculo-striatal system. Thanks to this, they discovered that in each of them, there are cells that respond in one direction to one color and in the opposite direction to its complementary color.

Color Consistency and Retinex Theory

Previous theories are missing an explanation for a fundamental aspect of color perception: color constancy.. This concept refers to the fact that the color we perceive of an object is not simply a function of the wavelengths it reflects.

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

Thus, color constancy “is the tendency of an object to remain the same color despite large changes in the wavelength of the light it reflects (Pinel, 2012)”. In fact, it provides us with an adaptive function in our ability to distinguish some objects from others, since if this were not the case, the color would change every time the lighting changed.

Retinex Theory

Land’s Retinex theory (1977) maintains that “The color of an object is determined by its reflectance (the proportion of light of different wavelengths that is reflected by a surface)“.

Hurlbert and Wolf (2004), following this theory, state that “the visual system calculates the reflectance of surfaces. In this way, it perceives colors by comparing the light reflected by adjacent – ​​nearby – surfaces in at least three different wavelength bands (short, medium and long).”.

In other words, The visual system is capable of calculating the wavelengths reflected by a surface and still perceiving the same color, despite changes in lighting. It doesn’t matter if an object receives more or less light, its color will not change for us.

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

Science continues its path in color vision

As we see, despite the great scientific advances in terms of brain functioning, there is still much to find out. Color vision is a topic that is still relevant and, little by little, new discoveries are made. Theories evolve and this means that some may be discarded, others complemented and others completely new.

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