What is color vision?
Color vision is one of the brain’s greatest inventions. The human vision system will tell you that a school bus is yellow and a stop sign is red. But the bus is not yellow, and the sign is not red.
The colors are actually all in your head — and, of course, in your eyes.
Color perception results from intricate interactions between light, the eyes and the brain. It’s not always a pretty picture. Some people have trouble perceiving color like everybody else does, which could indicate a disease or a deficiency in the visual system, such as so-called color blindness.
Learning more about how your eyes perceive color can give you a better understanding of this remarkable process.
How do light waves lead to color?
The sun, lasers and light bulbs all generate waves of light. These waves vibrate at a rate known as the wavelength, which exists along a spectrum. Animals perceive a small section of that spectrum called visible light. Other segments in the spectrum include infrared and ultraviolet light, which human eyes do not perceive.
Light rays travel from light sources to objects and surfaces in the environment. Some of this light gets absorbed, and some gets reflected.
When these reflected waves reach your eyes, your brain converts them into color perception.
First, your eyes take in light...
When you pull up to a school crosswalk and the crossing guard waves that red stop sign, the sun is beaming waves of visible light all around you.
Some of those waves bounce off the stop sign and hit the corneas of your eyes. From there, the light waves pass through the lens and the pupil and then activate millions of light-sensitive nerves in the retina.
The retina has three core components:
Rods – Rods are photoreceptor cells that are activated by dim light, shades of gray and the areas outside of your visual center (peripheral vision). A human retina has about 110 million rods.
Cones – Also photoreceptors, the cones are activated by colors and bright lights. (Memory tip: Cones and colors both start with the letter “c.”) Cones stand in the center of vision, where they help sharpen the images the brain translates into eyesight. Human retinas have around 6 million cones.
Ganglia – Retinal ganglion cells are output cells that communicate directly with the brain.
Rods and cones are at the back of the retina. They send their light information to the ganglia, which in turn transmit visual signals over the optic nerves to the brain.
Rods give people night vision, while cones work to colorize the world around you. When you pull up to a traffic light at night, your headlights trigger cones that reveal shadows in the distance — light waves from the traffic signal trigger the cones that perceive red, yellow or green.
...then your brain processes colors
While color perception gets its start in the rods and cones, the brain’s visual centers do most of the heavy processing work.
It’s believed that color processing happens primarily in the brain’s occipital lobe. However, this knowledge is evolving all the time as new technologies and greater understanding of genetics reveal more about the mechanics of translating light waves into color images.
It’s understandable that knowledge about the brain’s color capabilities keeps shifting. After all, the brain can do extremely subtle or complex things, such as hold color constant amid multiple light signals. It’s hard to nail down because scientists can’t look inside a living brain to see what it’s doing while processing colors. And there’s a lot going on.
Consider, for instance, the ruby slippers in “The Wizard of Oz.” They would probably still look shiny red to Dorothy under yellow or blue light. Why? Because your brain remembers how you see colors most of the time — meaning that if you see these colors in different lighting settings, the brain corrects things for you.
A 2020 article in Wired magazine explored some of the riddles of color perception in the brain. A recent study cited in the article noted that brain scans revealed that specific colors trigger neurons in specific areas of the brain. Studying these kinds of reactions will help scientists develop a fuller picture of the brain’s uncanny ability to process thousands of colors in real time.
Diseases and conditions that affect color vision
The term “color blindness” isn’t exactly accurate, as people with this condition still have eyesight. They also see some colors. Only a tiny fraction of those affected by color blindness have a complete lack of color perception.
That’s why medical science prefers “color vision deficiency.” People with this condition have a genetic abnormality that interferes with their ability to see certain shades or hues. They still perceive colors, but not the way that everybody else does. Color blindness tests can help establish the degree or variety of color blindness you may be experiencing.
Color vision deficiency tends to be more of an inconvenience than a hardship. But it can raise challenges for children in school if lesson plans have a lot of color-coded information. Graphic designers and electricians must be able to perceive colors correctly — these and other careers might not be a good choice for people with color vision deficiencies.
Several diseases have been associated with color vision deficiencies, including:
Photokeratitis – Snow blindness that happens when intense light inflames the cornea.
Retinitis pigmentosa – An inherited, degenerative disease of the retina.
Usher syndrome – A disorder that causes blindness and hearing loss. Retinitis pigmentosa is one of the top symptoms of Usher syndrome.
Loss of color vision might also result from Parkinson’s disease and the presence of cataracts.
What to do about color vision problems
If your color perception changes, you need an eye doctor to check things out. Depending on the nature of your color vision deficiency, you may be able to buy color blindness eyeglasses or contact lenses that help out.
Some eye color problems show up very early in life, so if you have kids, make sure they go to the eye doctor while they are young. That way you’ll have all the information you need for their schooling.
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Page published in February 2021
Page updated in September 2021