Scientists have explained the human ability to see non-existent colors

A recent study explains why sometimes people see colors that aren't really there. This phenomenon is called "afterimages", when the eye recognizes false colors against the background of real colors when looking at an object for a long time. Through this process, the brain can be tricked into seeing color in a black-and-white image. This was reported on November 4 by Medical Xpress magazine.

The phenomenon of "afterimages" is associated with a mechanism that allows you to see colors the same way throughout the day, regardless of light conditions. Without it, the color of the world would change depending on whether a person is under yellow sunlight, in a green shadow or in blue light.

Scientists have been arguing about the causes of color afterimages for a long time. Associate professor of Psychology at the University of Southampton, Dr. Christoph Witzel discovered a missing link between illusory colors and the neural mechanisms that create them. The answer lies in the cones in the eyes.

"Color afterimages are a long—standing classic phenomenon, but the more we learn about it, the more it becomes a subject of confusion among experts and in textbooks," the expert noted.

There are different versions: this phenomenon is caused by reactions in the photosensitive cones in the eyes, it is associated with neural pathways that cause them to see opposite colors, or it is associated with a still unknown mechanism in the brain. Scientists have found that afterimages are not opposite, as previously thought. Instead, the illusory colors reflect what is happening in the photoreceptors.

To find out where the afterimages in the visual system come from, Dr. Witzel conducted a series of experiments. He developed special methods to measure the exact colors that people see in the afterimages, and tested three different predictions.

In one analysis, 50 participants were asked to look at a certain "initial" color, and immediately after, to try to match the color they saw. In another experiment, 10 participants adjusted the color of stable afterimages 360 times on a special display. The specialist compared the measurements with computational models of various stages of neural processing — photoreceptors, intermediate structures of the brain (thalamus) and visual cortex.

"During all the experiments, we found the same thing: afterimages are not caused by opposite colors, as many scientists believed. Instead, they correspond to what we would expect if they were caused by the cones of the eye adapting to light. Thus, we were able to say with certainty that afterimages arise from cones, and not from other parts of the visual system," Witzel emphasized.

Earlier, on October 29, Medical Xpress reported on the ability of blood vessels in the eyes to predict the risk of cardiovascular diseases and the process of biological aging of the body. According to the publication, people with simpler, less branched blood vessels are at increased risk of developing these diseases. It was noted that they have signs of aging such as increased inflammation and a shorter life expectancy.

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