Mark Megahan
Humans have always considered purple to be special. That’s because the shade doesn’t really exist as a true visible color. It’s really just your brain’s way of dealing with a visual “systems error.” Purple’s only a “pigment of our imagination.”
No color purple
Contrary to popular belief, purple isn’t a color. It’s more of a hallucination. As Science News Explores points out, “our brain makes it up.”
The wetware of our visual light sensor systems have evolved an interesting error handling routine which processes unexpected input in an incredibly efficient way.
The place to begin is by defining what light is. Any physicist will tell you that it’s simply “another term for electromagnetic radiation.” The light from our sun, for example, travels to earth in waves. Some we can see and others we can’t. Red is at the slow, long-wavelength end of the spectrum of what we can see. Above that is infrared which we perceive as heat.
At the other end is short, fast violet. We can’t see above that but it’s the ultraviolet stuff that would fry your eyes out to look at anyway. Like X-rays and gamma rays. Violet is not the same as purple.
Violet is a legitimate visible color of the “spectrum.” It’s essentially the bluest shade of blue that humans can perceive. Our eyes have special cells which react to light of red, green and blue.
“When light enters our eyes, the specific combination of cones it activates is like a code. Our brain deciphers that code and then translates it into a color.” In real life, red and blue are at opposite ends of a scale. Like the two ends of a two-by-four. When our eyes detect light from both ends of the scale at once, it bends the lumber into a loop to create purple out of thin air.
Confusing the brain
“Seeing something that’s purple, such as eggplants or lilacs, stimulates both short- and long-wavelength cones. This confuses the brain. If long-wavelength cones are excited, the color should be red or near to that. If short-wavelength cones are excited, the color should be near to blue.”
We’re hard-coded to deal with the confusion. “To cope, the brain improvises. It takes the visible spectrum — usually a straight line — and bends it into a circle. This puts blue and red next to each other.”
Our brains manage to apply the same subroutines which process blends of yellow with blue to make green or red to make orange. On the fly it creates an entire gradient pattern to correspond with blending red and blue. That’s what we all point to and call purple.
“Our brain now remodels the visible spectrum into a color wheel and pops in a palette of purples — which don’t exist — as a solution to why it’s receiving information from opposite ends of the visible spectrum.”
While physicists freak out over how that happens, over at the visual sciences lab they take it in stride. Anya Hurlbert at Newcastle University in England says “it’s a beautiful example of how our brains respond when faced with something out of the norm. But it’s not the only color that deserves our admiration.”
Purple isn’t that special to her. “All colors are made up by the brain. Full stop. They’re our brain’s way of interpreting signals from our eyes. And they add so much meaning to things we perceive.” It serves a solid purpose for survival. “The color of a bruise tells me how old it is. The color of a fruit tells me how ripe it is. The color of a piece of fabric tells me whether it’s been washed many times or it’s fresh off the factory line.“
