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ARE DOGS COLORBLIND?

FROM "Ask Popular Science"
Edited by Cecilia Wessner
Research by Liz Cowley and Stacey Sutton

It is a mistaken notion that dogs see only in black and white. If, however, what you mean by colorblind is that dogs see only a portion of the visible spectrum as compared with what humans see, then yes, dogs are colorblind. And there are a couple of methods that scientists use to determine this. But first, it is important to understand how dogs see.

Dogs have two types of color photoreception, or cone cells, on their retinas that recognize short and medium-to-long wavelengths of light, corresponding to bluish hues (short wavelength) and red-yellow ones (long wavelengths). People, on the other hand, have three types of cone cells that enable us to see the full range of colors that make up the visible spectrum. Since dogs have only two types of cone cells, the colors they can distinguish are almost identical to the colors a human who has red-green color blindness would see. Of course, colorblind humans still see many different colors, and scientists think dogs see this range of colors as well.

How do scientists know? One way is to shine beams of colored lights into dogs' eyes and analyze the spectrum, or pattern, of light that is reflected back. The results are then compared with the pattern produced when the same lights are shined into human eyes.

Another way to study canine vision is to have the dogs "tell" scientists what they see. In one experiment, dogs are shown a series of three lights; in each case, two of the three lights are the same color. With a minimal amount of training, the dogs select with their noses the colored light that is different from the others. By varying the colors of the lights and repeating the process, scientists have determined that dogs see the world in black, white, and shades of gray, with long wavelength (red-yellow) and short wavelength (blue) colors thrown in.