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Seeing in color

“After sleeping through a hundred million centuries we have finally opened our eyes on a sumptuous planet, sparkling with color, bountiful with life.” ~ Richard Dawkins.

As the colorful spectacle of a long desert spring wanes, I am captivated by the remaining sparse splashes of yellow and purple that make me stop and stare. Have you ever wondered, what is color? Well, studies show that color is all in the head. It is our brain’s perception of light that creates the illusion of a world filled with colors.

Light is electromagnetic radiation. White light, the spectrum visible to us, is made of many wavelengths. Objects and surfaces absorb some wavelengths and reflect others.

It is the reflected wavelengths that we detect as colors. A white surface reflects all the light, whereas a dark surface absorbs it all. Our retinas have different receptors that are sensitive to light including cells called cones. There are a billion cones in each eye. The human eye has three types of cones, each for different ranges (shorter, medium, or longer) of wavelengths of light (between 400 and 700 nm). Each type of cone is responsive most robustly to the wavelengths we label as red (longer), green (medium) and blue (shorter). However, the ranges overlap, so any wavelength stimulates more than one type of cone. Cones transmit signals corresponding to the wavelengths to the visual cortex which, based on the different combinations of wavelengths, reports “colors” to our consciousness.

Thus, the real world is colorless, and every hue is some combination of red, green, and blue generated by our brains. Each cone type can register 100 different color shades, amounting to a million different colors that healthy human eyes can see. We could have even better color vision if, like the mantis shrimp, we had 12 different types of cones or the bluebottle butterfly, which has 15! Some birds and bees even have receptors that respond to the shorter wavelengths of ultraviolet radiation, and some boa constrictors and pythons can detect the long wavelength infrared range. Sadly, we have no way of knowing what any of these creatures ‘see’ in terms of color. In fact, we can’t even know another human’s experience of a color such as red, because our neurons do not respond to light in some standard or pre-programmed way.

Research suggests that color perception develops in response to experiences of incoming light information in the world. One study looked at male squirrel monkeys whose eyes have only two types of cone cells corresponding to wavelengths of light we call "blue" and "green;" To them, "red" wavelengths appear neutral, and they cannot find red dots in a gray background. Scientists inserted a gene into the DNA of some of the green-sensitive cells and converted them into red cones. Even though neurons in the monkeys' brains were wired to receive signals from green cones, they adapted to receiving signals from red sensitive cones instead, enabling the monkeys to use the information to identify red dots in a gray image. So, it appears that the brain takes in whatever information it has and confers some sort of perception. When we are born, our brains most likely do the same thing, giving us each our own unique circuitry of color.

Given that, isn’t it fascinating that people all over the world agree on how they label different wavelengths of light as color, and associate many of the same colors with the same emotional responses? For example, throughout the world, yellow evokes joy and red is the only color that is strongly associated with both a positive feeling (love) and a negative feeling (anger). After all, humans do share a history of evolution and development on this planet and have the same brains and perceptual systems, leading us to see the world in similar ways. If only we acknowledged that more often!

Post by: Nadia Fike

Read more:1. Macuso, K., et al. Gene therapy for red-green colour blindness in adult primates. Nature. 2009. 461: 784-7. PMID 19759534 DOI: 10.1038/Nature08401 2. Jonauskaite, D., et al. Universal patterns in color-emotion associations are further shaped by linguistic and geographic proximity. Psychological Science. 2020.31(10), 1245-1260. DOI:10.1177/0956797620948810


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