Tech & Science

Your Very Good Dog Isn't Colorblind After All

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A dog plays with a ball in a field of wheat in Godewaersvelde, northern France on July 31, 2013. PHILIPPE HUGUEN/AFP/Getty Images

You might have known your dog is colorblind—but to which colors? People often think their dogs see just in black and white, but new research finally confirms the spectrum dogs struggle with the most is from red to green.

Red-green colorblindness is called deuteranopia. In humans of Northern European ancestry, it shows up in about 8 percent of men and .5 percent of women. But researchers in Italy found it shows up in probably 100 percent of dogs.

“[I]f you are planning to train your dog to fetch a ball that fell on the green grass of your garden, think of using a blue, and not red, ball," study lead researcher Marcello Siniscalchi, a professor in the Department of Veterinary Medicine at Italy’s University of Bari, told LiveScience.

The photoreceptor cells in our eyes that determine what colors we can see are called cones. Humans have three kinds: one sensitive to red wavelengths, another to green, and another to blue. Dogs, though, only have two: yellow and blue. The researchers said this means dogs can probably see both yellow and blue, plus shades that combine them. A study detailing the findings was published online last week in the journal Royal Society Open Science.

Previous research had led scientists to suspect that what dogs were colorblind to specifically was red and green, but Siniscalchi put that to the test by having 16 very good dogs look at a modified version of the Ishihara Color Vision Test. Normally, the test consists of looking at colored circles on top of which is a number written in a different color—so a person with deuteranopia, who can’t distinguish between red and green, wouldn’t be able to read a red number on a green circle. But since Siniscalchi was working with dogs, not people, and thus needed to keep their attention, he swapped out the numbers for animations of running cats. Animal science is fun sometimes.

Dogs could still see the cats when they were bright red and on a mottled green background. But when the color contrast was more mild, the dogs no longer noticed the cats.

"The present work showed, for the first time directly, canine red-green blindness by using a modified test of color vision in humans," Siniscalchi told LiveScience.

In terms of being news you can use beyond playing fetch, if you need to mark a fence or other obstacle on the grass for your dog to see, stay away from reds as well as greens. To the dog, it’s all kind of the same.

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