A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Are cats and dogs really color-blind? How do they know?

May 1, 1987

Dear Cecil:

Are or are not cats and dogs really color-blind? How do they know?

Cecil replies:

You ever see a cat who could pick out a tie? Believe me, cats'll wear things you wouldn't put on a dog. Scientists, however, are not content with anecdotal evidence. They often test animal color sensitivity by trying to link color with food. One such experiment was conducted in 1915 by two scientists at the University of Colorado, J.C. DeVoss and Rose Ganson. They put fish in two jelly jars and then lined both with paper, one gray and one colored. If a cat picked the colored jar, it got to eat the fish. Nine cats, 18 months, and 100,000 tries later, the researchers established that cats picked the right jar only half the time--the level of pure chance. On the other hand, cats could readily distinguish between different shades of gray. Ergo, cats are color-blind.

Doubts about this conclusion arose some years later, however. Cats have cones as well as rod-type vision receptors in their retinas, and cones have long been associated with color vision in humans. Neurologists who wired up feline brains with electrodes discovered that, on laboratory instruments at least, cats responded to light of different wavelengths--which is to say, color. So researchers went back for another round of fish experiments. Finally, in the 1960s, they managed to teach the cats to discriminate between colors. But it took some doing--one group found it took their cats between 1,350 and 1,750 tries before they got the hang of it.

From this one might deduce one of two things: either cats are exceptionally dense, a proposition Cecil has no trouble buying, or else they just don't give a hoot about color. Most cat scholars have opted for choice #2, saying that the ability to distinguish colors is obviously of no importance to cats and hence not something they learn readily.

Less work has been done on dogs than on cats, but what there is suggests canine color sensitivity isn't very good either. Much the same can be said for mammals in general, with the exception of primates. In contrast, some of your supposedly lower order creatures, such as fish, turtles, and especially birds, can distinguish color with ease. The fact that these primitive beasts should have more advanced visual abilities than their mammalian betters has always struck observers as a little odd; clearly the evolutionary progress of color vision has been more erratic than one might expect.


To the Teeming Millions:

OK, so we know cats can see in color. Now comes new research indicating that dogs can see in color, too.

Three scientists at the University of California at Santa Barbara adopted the traditional strategy of trying to tempt the dogs with food. The menu, frankly, could have stood some improvement: would YOU cooperate with people whose idea of a reward was a cheese-and-beef-flavored pellet? Nonetheless, the researchers found three mutts who were sufficiently desperate to play along. They showed the dogs three screens lit up from behind with colored lights--two of one color, the third of a different color. The mutts got the pellet if they poked the odd-colored screen with their noses.

The dogs had no difficulty distinguishing colors at the opposite ends of the visible spectrum, such as red and blue, and they proved to be demons with blues in general, quickly learning to differentiate blue from violet. But they bombed at other colors, confusing greenish-yellow, orange, and red.

The researchers concluded that dogs suffer from a type of colorblindness that in humans is called deuteranopia. Normal humans have three types of color receptors for red, green, and blue. Deuteranopes lack the green receptor, and thus (apparently) can't tell a lemon from a lime--or, for that matter, a red traffic light from a green one. One more reason to put your foot down next time the pooch says he wants to drive.

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