How Colors Enter the Brain
Although there are only three of them, it’s truly complicated!
As we have seen in my previous article on color vision:
there are still more misconceptions regarding colors and their processing. In this article, we will consider five myths and debunk (or confirm) them. Here we go:
(1) The Color Receptors Lie at the Outer Surface of the Retina.
Wrong!
Here is a cross-section of the retina, the tissue containing photo-receptors and other cells:
We would think that evolution (or the Creator of Everything) did something useful and constructed the retina so that the light-sensitive cells (in the picture: on top) are nearest to the source of light. And that is actually so — in the eyes of the octopus. But in human eyes, light is coming from below! The rods and cones, responsible for receiving light, lie in the back of the retina — as if someone were pulling a thick curtain in front of a mirror. What they get is a mere chaos of impulses. The brain has to laboriously eliminate random impressions, noise, diffused light-rays, superimposed signals etc., to get a (more or less) clear picture. Why did evolution build such an impractical structure? We don’t know. It’s probably because evolution doesn’t plan or think; it builds on what is there, stacks things upon each other, then looks for solutions for the troubles ensuing from this mindless engineering.
(2) Three Colors Enter the Brain
Wrong!
As you probably know (or read in my previous article), the color-sensitive cells in the retina, the cones, are sensible for three colors, red (more or less), green and blue. All colors may be derived through a mixture of them. But these colors are not sent to brain! Before they enter the appropriate regions, they are interconnected in a very complicated way. A simplified version looks like this:
Let’s try to explain. The three primary colors are first connected immediately behind the retina. This is quite complicated: first red and green are subtracted, and this difference is passed on together: this constitutes the red-green channel. But red and green are also added, which gives the sensation of yellow. These impulses are subtracted from blue, which constitutes the yellow-blue channel.
Finally, all three colors are weighed against each other and combined into one signal, the luminance or brightness, forwarded through the black-white channel. Because of these channels, complementary colors are possible. If you stare at a red surface for a long time and then at a white wall, a green afterimage appears (and vice versa; the same applies to yellow and blue and black and white). The reason: the brain compensates for the excess of nerve impulses, and that is why we think we see the complementary color. In reality, the brain recovers from an excess of potassium ions in the nerve cells.
The brain doesn’t process colors, it works with color differences. That’s why we always see a white sheet of paper as white. Its color intensity is first compared with the environment, then the reflected colors are offset against each other. And finally, experience comes into play. If this is lacking — as on the moon, for example — then people do not know how to judge the environment (see next item).
The further processing of colors via various intermediate stages is complicated and also not yet fully understood. At least five brain centers are currently known: the regions V1 to V4 and the actual visual center in the back of the head. In the sub-regions, the color channels (with the complementary colors) are connected and the shape and movement of a body are also mixed in, because these properties are perceived separately — how, we still have a rather incomplete idea.
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And there is a reason why we can recognize red and green shapes very well, but not blue ones: fruits and faces are red, yellow or green, and their shapes are important to us. Only the sky is blue, and it has no shape and does not need it.
(3) The Moon Is Made of Green Cheese
Yes indeed! At least that’s what astronauts saw as its color — among others.
Every Apollo mission had a different take on what the color of the surface of the Moon was. As we have seen, the brain works with color differences, not directly with colors. The moon was described by astronauts in a variety of colors, sometimes blue, sometimes green, sometimes brown, sometimes gray, even pink. In reality, moon rock is clearly colorless and dark. But the environment on the moon is completely different from that on Earth, and so the brain does not know how to classify and process color information.
(4) When There Are No Impressions, Our Nerve Cells Do Nothing
Wrong.
If a color receptor is stimulated, it does not send a current to the brain — on the contrary, it interrupts the so-called rest current. This always flows when the person cannot see anything — and when they see something, the current stops. Doing nothing is arduous!
(5) We Are Living in the Present
No, we don’t.
A simple experiment with colors provides amazing insights into the human brain. A vertical red line appears next to a green line. The combination of the two appears yellow, because red + green is known to add to yellow. There is nothing mysterious about this — so far!
Now the red line moves slowly across the screen, from left to right. When it reaches the middle of the screen, the green line appears again, in the same place as the red line. Result: For the viewer, the red line should briefly turn into a yellow one, then move back to a red line, while suddenly there is a green line in the middle of the screen. But that doesn’t happen! Instead, the red line always remains red. What happened?
When the scientists varied and analyzed the experiment, they recognized an important characteristic of human perception: we never see the world as it is at the moment we perceive it; rather, we see it as we unconsciously think it should be in the next moment (in the next half-tenth of a second). And only when the brain detects deviations between the predicted and actual reality is the prediction method corrected.
In our experiment, the brain thought that the red line was already a little further away. When the green line appeared, the two were clearly separated for human perception. They were not mixed in the perception centers, so their colors remained the same. And since the uniform and thus easily predictable movement of the red line did not change, the brain had no reason to correct its prediction method.
I programmed this simple experiment and tried it for myself. My experiences were different: When I watched the video several times, the red line became yellow before it met the green line! Which confirms the hypothesis: My brain knows what will happen and anticipates what’s to come. I’m still living in the future.
If you want to look for yourself, here is the experiment with different speeds:
Truly remarkable what colors tell us about the world and about us. We do not see the world as it is, but as it should be — and experiments with colors have shown us how the brain deceives us. But we live well with it!
