Looking around us, we can see so many things with a wide range of colors. These colors add to the beauty of the world. Even though we humans can’t detect all of the colors that exist in the world (shrimp are able to see in colors that don’t exist for us), we can still understand how enriching the world is.
Light hits an object and a certain wavelength is reflected back while all of the other wavelengths are absorbed. The wavelength that is reflected, enters our eyes. At the back of our eyes is the retina. The first layer of the retina is made up of ganglion cells, the second layer is bipolar cells, and the third is made up of cones and rods. Rods are more active when our eyes have detected a lower amount of light, meaning that the light levels are scotopic. Rods are at the periphery of the retina because they are more useful for detecting movement or images that aren’t directly in front of us.
They are also used for seeing during the night. Without rods, we would develop night blindness. Since rods are made up of Vitamin A, a deficiency of rods could be solved by eating foods that contain Vitamin A.
Cones are more active when our eyes have detected a higher amount of light, meaning the light levels are photopic. They are the photoreceptor cells that help us detect color. There are three types of cones: cones that detect red light, cones that detect green light, and cones that detect blue light. Shrimp have 16 cones, which is why they are able to detect more variation of light than us.
This is backed by the Young-Helmholtz trichromatic theory that says our eyes have to have three receptors that are sensitive to blue, green and red. This theory makes sense because color blind people usually don’t have cone receptor cells for one or more of these colors.
But there’s another theory called the opponent process theory. This theory says there are three oppositional pairs: red vs. green, blue vs. yellow, and black vs. white. When one of the colors in an oppositional pair is being detected, the cells for that color fire rapidly while the other color is below baseline (for example, when you’re looking at your green notebook, all of your “green” cells are firing rapidly, while all of the red cells are firing below baseline). We cannot see both of the colors in the same opposing channel at the same time. For example, you cannot see something that is reddish-green but you have seen something that is reddish-blue (purple).
The opponent process theory explains negative afterimages. When you stare at a colored object (for example, a blue circle) for about 20 seconds and then immediately look at a white surface, you will see its oppositional pair (a yellow negative afterimage) where the white surface is. This happens because after staring at the object of a color that’s part of an oppositional pair, the stimulated cells (i.e. the color of the object) will use up its resources and begin to get “tired.” Once you remove what you were looking at, the cells will fire below the baseline and at a higher rate.
The trichromatic theory explains color vision at a neural level and the opponent process theory explains color vision at a receptor level so both theories are correct.
VAAGEESHA DAS is a junior at Morgantown High School.
Information comes from:
- Baird, C. (2015, January 22). Why are red, yellow, and blue the primary colors in painting but computer screens use red, green, and blue? Science Questions with Surprising Answers.
- C, R. (2019, June 12). Difference Between Rods and Cones (with Comparison Chart and Similarities). Bio Differences.
- Cafasso, J. (2018, April 26). Opponent Process Theory. Healthline.
- Cherry, K. (2021, March 14). The Early Theory That Explains How We Perceive Color. Verywell Mind.
