Is it true that dogs only see in black and white? If so, how is this proven?
No, dogs have some color vision, but more limited than that in humans. Dogs, like most mammals, have only two kinds of color receptors in their retinas (they are dichromats). These receptors differ in the wavelengths of light they are most sensitive to. Basically their color discrimination is equivalent to a human with red-green color blindness. There are a few mammals, such as whales, that have only one kind of color receptor and are thus entirely color blind, seeing the world in black and white.
Humans (along with the great apes and Old World Monkeys) have three kinds of color receptors (trichromats), most likely as an adaptation to finding and eating colorful fruit. Most other vertebrates, including birds, reptiles, and fish, have four kinds of color receptors, and have far better color discrimination than humans.
The earliest ancestors of mammals were probably nocturnal, and lost some of their ability to discriminate colors because they are more difficult to discriminate under low light conditions.
No, they actually do see in color, although they have what would be called color blindness in humans. Cecil has an old column on it.
To answer how they check, they perform the research on the animals by training them to respond to a pattern on a video screen, then alter the image until the animal can no longer pass the test. You can often see these sort of experiments on PBS shows, Nova, for example. Another test, giving a cat an award for a video response, a pattern of horizontal lines, then gradually making the lines finer and finer, until the cat can’t respond. They’ve determined that cat image resolution is very poor, they likely can’t tell one human face from another. Certainly not on a video screen.
If your cat can, it is likely using other clues, general size, shape, sound, smell, etc. The vid screen removes those clues.
Eyes have rods and cones in them. The cones see colors and details. The rods see black and white and are used for low light level and detecting movement.
Humans have three types of cones, dogs have only two. This is what effectively makes them red-green colorblind, as was already mentioned. Dogs also have a lot fewer cones in general than humans, which means that even though they can see some colors, they can’t see them as well as we can.
Dogs don’t have what is called a fovea (an area with 100 percent cones), which means they can’t see details as well as we can.
Dogs have a lot more rods than we do though. This means that they have much better night vision than we do, and it means that they can detect movement better than we can.
Dogs also have a structure called the Tapetum Lucidum which we don’t have. This is a reflective surface behind the retina that gives them even better night vision.
And makes them look possessed in any and all pictures.
You say that like they aren’t normally possessed anyway.
Oh, no wait. I’m thinking of cats.
This is by no means universally infallible, but my rule of thumb in remembering which animals have what kind of vision is as follows: the more colorful the animal, the more colors they’re likely able to perceive. My theory being that colors are often a means of communicating with other members of their species. Thus you have very colorful fish and birds, which as noted by Colibri above have greater color perception than mammals. And with whales being totally color blind, it’s interesting to note that the coloration of pretty much all whale species is along a spectrum from white to gray to black. (Yes, even the “Blue” whale.)
All I know is my dogs prefer orange balls to play with. They will chase different colors but if I throw an orange one and several other colors at once, only the Orange is brought back. Also they only carry the orange ones around all the time.
According to the book How Dogs Think
It’s worth learning what type of colours a dog has difficulty distinguishing between. Once I found out they are red green colour blind it made a lot sense that my dog had difficulty finding his bright red frisby in green grass when compared to his old blue frisby.
I don’t remember anything about testing, but in A Natural History of Seeing
Simon Ings discussed the different visual receptors of various species. ISTR that mantis shrimps had a huge number (more than 10?) different types of receptors, indicating that they could perceive light way into the ultraviolet spectrum. It has been a while since I read it, but I would imagine they based their conclusions on dissection and testing of tissues rather than the testing of shrimp - but I don’t know.