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Color perception is all in the mind, with the eye containing equipment that responds to light so the brain can process it. Humans have three different types of cones sensitized to short, medium, and long wavelengths. Researchers learned that people actually have a very uneven distribution of cones, which strongly suggests that key aspects of perception of color occur in the brain, not the eye.
Color perception is a fascinating series of physical and chemical reactions that allow some organisms to see in color. The process of perceiving color is literally all in the mind, with the eye containing the equipment that responds to light so the brain can process it. The number of colors an organism can distinguish can vary considerably, from animals that can see a very large range of millions of colors to animals that see in a much more limited range.
Two types of cells in the eye are responsible for vision: rods and cones. Both cells are found in the retina and respond to light as it enters the eye. Rods are highly sensitive to light, allowing for vision in a range of light levels, while cones are sensitized to colors of particular wavelength ranges. Humans have three different types of cones sensitized to short, medium and long wavelengths and are especially sensitive to yellow and green light. Organisms with three types of cones are known as trichromats, and other animals may have two types of cones (dichromats), while others have up to five (pentachromats).
Until 2005, researchers assumed that the number of cones in the eye was roughly the same for all people, and that all people had the same number of different types of cones. However, when imaging technology was developed that could be used to look into a living eye and distinguish between the different types of cones present, researchers learned that people actually have a very uneven distribution of cones. 40% of one person’s cones might be sensitive to medium wavelength light, while someone else might be only half as sensitive, but both people would perceive color the same way, which strongly suggests that key aspects of perception of color occur in the brain, not the eye.
When light enters the eye and strikes the cones, some cones light up in response to the wavelength to which they are sensitized. The response is sent along the optic nerve to the brain, and the brain processes the information, allowing the body to see in color. Color perception is important to many animals because it can be used to better distinguish the natural environment and because colors are often used as signals. Toadstools, for example, are sometimes colored as a warning.
The process of visual perception happens so quickly that people feel like it’s instantaneous, as they look at something and see it immediately. The eyes are also constantly feeding back new information, allowing people to detect changes such as movement. While the basic mechanisms of how vision and color perception work are understood, the processes are still a bit of a mystery to researchers. The underlying mechanisms of color blindness, for example, are not fully understood.
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