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Straight Dope Classic from Cecil's storehouse of human knowledge01-May-1987
Dear Cecil:
Are or are not cats and dogs really color-blind? How do they know? --Jim L., Chicago
Dear Jim:
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.
LATE NEWS!
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.
--CECIL ADAMS
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