英语听力文摘 English Digest 186、猫与色彩

（单词翻译）

　　Cats And Colors
人类能够很容易的分辨出不同的颜色。那么猫呢？虽然猫的视力很好，即使在非常昏暗的光线条件下也能看见，但它对于如何分辨不同的颜色似乎并不擅长。
"Cats and Colors" on this moment of science.
You can look at that quilt your cat is curled up on and see a patchwork¹ of greens, blues², and yellows. Your cat, however, cannot see color variation in the quilt.
Both humans and cats depend on the back layer of the eye, which is called the retina, to sense light and to distinguish between colors. The retina is made up, in part, of nerve cells that convert color and light into messages they send to the brain.
There are two types of cells: rods and cones³.

　　Rods are very sensitive to light, though they are not used in color vision. Cones on the other hand are not very sensitive to light but can be used in color vision.
Because cats have more rods than humans, they use these light-sensitive cells to see in even very dim light. Likewise, because cats have fewer cones than humans, they cannot distinguish between colors the way humans can.
But cat eyes do have some cones, and with work cats can learn how to distinguish between colors.
In experiments, scientists have taught cats to discriminate⁴ between two symbols when the only difference between them is their color.
Cats have learned how to make this discrimination, but only when the objects used were very large and the difference between the colors very pronounced. It’s not likely you’ll be able to teach your own cat how to tell the difference between two colors unless you are very patient.
Even under controlled laboratory conditions, cats do not learn how to differentiate⁵ between two colors until after making over 1,400 attempts.
These experiments showed researchers that though cats technically⁶ have the ability to tell the difference between two colors, they don’t use that ability in their daily lives.