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Why are dogs the only animals that can see in black and white?
Question Date: 2006-01-20
Answer 1:

It has been thought for a long time that dogs are color blind or can only see black and white, but recent research suggests that a dog's world is not all black and white. In fact, it was here at UCSB that much of the research on dog sight was done, in the late 1980s. These experiments may well be the world's foremost research program on comparative color vision. For the study, a few pet dogs were volunteered to participate in an unharmful set of tests. All dogs were beloved family pets, both before and after the studies, and most belonged to the researchers themselves.

These experiments showed that dogs do see color, but in a more limited range than that seen by normal humans. Most animals don't see the world with the same vivid colors and definition as human beings, and most animals see fewer colors than we do (but some actually see more!)

Vision differs greatly among animal species largely as a direct result of the specifics of their visual equipment. We know this by looking at how many kinds of cone photoreceptors they have (which distinguish colors). Animals differ in eye shapes and structures and they do not possess all of the same structures.

Cone cells contain pigments that perceive specific wavelengths of color. Human vision is trichromatic, we have three types of cones that recognize different portions of the color spectrum. These cones allow us to see a range of colors that are a mix of red, blue, and green pigments. Dogs have only two types of cones -- their dichromatic color vision is similar to that of a human with red-green color-blindness. In addition, a dog's retina contains a much smaller ratio of cones to rods than ours does.

Human vision is optimized for seeing in bright light, because we are active during daylight hours. Dogs and cats, like many other predators, see best in dimmer light. They do not have the same need that we do to see bright intense colors. Although dogs may not have the color range and focus of humans, its night vision is far superior. This is due to a reflective structure behind their retina called the tapetum lucidum.

A good indication of what an animal can see is by looking at their own colors. The colors of their prey are also an indication of an animals ability to see color.

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