It’s the same reason “the dress” was so baffling.
What do you see in this photo?
Just a regular plate of red strawberries, with some weird blue tinting going on? Well, here’s a shocker: there are actually no red pixels in this image—at all! It’s an optical illusion (just like the blurry ham from the beginning of the year, or the shiny legs from October.) Don’t believe me? If you have Photoshop, you can see for yourself: Just use the eyedropper tool to isolate the “red” parts. You’ll see, no matter where you click, that the colors are all blue or gray.
This optical illusion was first shared on Twitter by Kitaoka Akiyoshi, a professor of psychology at Ritsumeikan University in Japan, specializing in visual perception and optical illusions. According to Akyoshi, what is making these gray/blue strawberries look red is “color constancy.” It’s a trick our brain plays where it resist the effects of alternative coloring, illumination, or filtering. Basically, if we perceive the coloring of something to be just a little off, our brains will compensate to make us see what we think we should see. Color constancy is the same reason why “the dress” was so controversial in 2015: those who saw the dress as gold and cream had registered the blue in the image as a filter that they needed to compensate for. The people who saw blue and black just saw the image for what it was: blue and black.
Though it makes for great viral content, color constancy doesn’t only happen in still photos—our brains do this every day. “The physical components of your face, for example, may differ between the morning and noon, but we are not aware of it thanks to color constancy,” Akiyoshi told RealSimple.com in an email.
Can’t see the red in the strawberries at all? That doesn’t mean that your brain isn’t affected by color constancy. According to Akiyoshi, this image is an extreme demonstration of the phenomenon. The overall blue tint might be so strong that your brain can tell it’s being tricked and therefore doesn’t compensate.