The eyes transmit information to the brain about what kind of light is falling on them. If the eyes are tightly closed, no light enters the retina and we should not see anything.
Why, when we close our eyes, do we sometimes still see colored spots and even patterns?
This is a side effect of the brain's ability to recognize the colors and brightness of points in the visual field. The lighting conditions around are constantly changing, but we must correctly determine the colors when it's daytime outside, and when it's night, and when we walk through a green forest, and when we swim underwater, and even if we get to a disco and everything around is illuminated by multi-colored spotlights … If you take photographs of the same item under such different conditions, all photos will show that item in different colors. And yet, we will always correctly determine the color of an object in a variety of circumstances, unless there are color blind people among us. How do we do it?
Different cells of the retina - cones - react to light of different colors. Some of them react most strongly to red light, others to blue, and still others to green. The cones send information to the brain about the color of each point in the visual field, and the brain figures out how to interpret it. If the brain interpreted information from the cones in a straightforward manner, we would often misidentify colors. For example, if we were in a room lit with red light, then all objects in it would appear red to us, because the cones responsible for the red color would send the most powerful signals to the brain. But in fact, after a few minutes in such a room, our eyes will adjust, and we will begin to correctly determine the colors of objects.
This will happen because the brain will change its idea of what "zero red" is. In a room with red lighting, it is definitely taller than in the more familiar white or yellow light. After a few minutes in a room lit with red light, the brain will begin to "subtract" this excess redness from the colors of all objects, and we will begin to perceive their colors correctly (although most of the red signals will still come from the cones).
How does the brain know exactly how much red to subtract? This happens by itself, because the cells that normally detect redness will work too actively in the red room and begin to get tired. Their activity will quickly return to normal levels, but it will already correspond to a greater redness than before.
In fact, this adjustment of the neurons that recognize colors occurs even under the most ordinary lighting. In the same way, we adjust to the brightness of the light. If a color is too bright or something is illuminated very strongly, the brain automatically subtracts the excess brightness or excess color. The areas in which the adjustment took place, we sometimes see, closing our eyes. It turns out something like a negative, which we “see” for a while, even when we close our eyes. And we can see patterns due to the fact that we tend to look for order even where there is none. Including, in spots that can be seen when we close our eyes.
(In addition to the negative effect arising from the adjustment of the visual system, spots and lines in front of the eyes may appear due to violations of its work. Most often, such violations occur due to spasms of the vessels of the retina or brain. The spots that appear have nothing to do with the fact what we are looking at, and can be seen with both open and closed eyes. Vascular spasms occur due to overwork, lack of sleep or nervous tension. So if you see spots and patterns that are unlike anything else, this is not a very good sign.)
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Also, false visual sensations can occur due to mechanical action on the eyes - for example, if you rub a closed eye. In addition, they can be induced artificially - by acting on the areas of the brain that are responsible for vision. False visual sensations that occur without the influence of light are called phosphenes.
To make sure that the brain adjusts our sense of color, you can use these pictures:
Focus on the cross in the middle of one of the circles on the left for 20 seconds, and then move your gaze to the cross in the middle of the gray square on the left. You will see a circle of the opposite color (for example, if you initially looked at a red circle, and then move your gaze to a gray background, you will see a green circle). Gray is neutral, so against its background you see a color that is the opposite of what your eyes have become accustomed to.
It is interesting that with the help of such tricks one can learn to see even "impossible" colors - objects of the real world cannot have such colors, but thanks to the properties of our visual system, one can see them. To do this, you need to get used to a certain bright color, and then turn your gaze to the background of the opposite color. For example, get used to red and shift your gaze to a green background. As the brain gets used to the color red, it will subtract redness from everything that the eyes see. But green is already the opposite of red, and if you subtract red from it, you get something like "super green". You won't be able to print a picture of this color, so experiment with your color vision yourself.