Created by the human brain, the color magenta does not exist – 04/03/2023 – Science

Observe the image below: it illustrates the variety of colors present in the spectrum of visible light, which our eyes can perceive.

Maybe you haven’t noticed, but there’s one in particular that doesn’t show up: magenta.

It is not there and not in the visible light spectrum in nature. Why, then, do we see it?

Our brains are spongy information processors that convert the billions of events happening around us into signals we can understand.

There are sounds, aromas, flavors, sensations… one of those elements that surround us are the electromagnetic fields, formed by waves that, depending on the frequency, can produce a series of effects.

Some serve, for example, to heat food in the microwave, others show us the bones of the body in x-ray exams, and there are those that make radio programs travel from transmission stations to listeners’ devices.

The human body is capable of perceiving with the senses only a small fraction of these wavelengths – much of it through the eyes, by means of what is called visible light.

Why we detect only a restricted range of the electromagnetic wave spectrum is still being studied.

What we do know, for example, is that waves between 400 and 700 nanometers in length, or the spectrum of visible light, are the only wavelengths that travel easily through water. This range is also the portion of the spectrum of electromagnetic waves that the Sun emits the most.

Since our earliest ancestors lived in the sea and were exposed to the Sun, it makes sense that we evolved to detect the most common and useful wavelengths in the spectrum.

From waves to colors

Our eyes detect colors through cones, specialized cells that are concentrated in the macula, the center of the retina.

There are three types of cones in the human eye:

– Type L: sensitive to long wavelengths

– Type M: sensitive to medium wavelengths

– Type S: sensitive to short wavelengths

S cones detect blue ones; the M’s, the green ones; the Ls, the red ones. But we see more than just red, green and blue. That’s because the eye cone cells overlap at the wavelengths they detect, as the following graph illustrates:

Looking at the image, you can see that when a ray of light with a wavelength of 570 nanometers enters the eye, it stimulates the L and M cones.

The responses are combined and turned into an electrical message that is sent along the optic nerve to the brain as a single signal. And it is this signal that we interpret as yellow light.

A strange quirk of this system is that when two beams of light whose wavelengths add up to the same thing – in this case, 570 nanometers – enter the eye at the same time, the signal that is sent to the brain is the same.

These two rays of light combined also make us see yellow.

The screen of the device through which you are viewing the images also works according to the way our brain perceives colors. If you look closely, you’ll see that the screens are made up of small groups of red, green and blue lights – but they can reproduce the full spectrum.

Every color we perceive can be generated through this dual pathway: a single wavelength of light or a combination of wavelengths that stimulate our cones in the same way.

Except one.

the magenta

Officially, magenta does not exist.

There is no wavelength of light for magenta, which means that it is the human brain that creates this color. But how?

We perceive it only when the S and L cones pick up a pure red and blue light signal.

We don’t yet know why the brain creates it. The mechanism may, however, have been very useful to our primate ancestors who lived in evergreen forests.

Magenta fruits and flowers would have the greatest contrast against a green background, and seeing them made it easier for our ancestors to find food.

Our brains make all these kinds of weird cognitive leaps all the time. You might be surprised at how much of the world around you isn’t quite what it seems.

Text originally published here.

*This text was adapted from the BBC Reel video “Magenta: The color that doesn’t exist”. If you want to see the original content, in English, here.