Why are dogs color blind?

Sometimes scientists are a bit like magicians. They can not only create a variety of fresh things, but also tell us a lot of unexpected things, such as dogs are color blind. To judge whether a person is a color-blind person, it is only necessary to let people recognize a few simple numbers or images from the colorful ones. So how do scientists know that dogs are color-blind?

Of course, if the dog is categorically said to be color blind, this statement is somewhat inaccurate. However, if "color blindness" here refers to comparison with humans. The dog can only see a part of the visible spectrum, so, yes, the dog is color blind. Scientists can determine this in two ways. But here is the first thing to let us see what our big world is like in the eyes of dogs.

There are two kinds of cones on the dog's retina, which can recognize light waves of short and medium wavelengths, that is, blue light (short wavelength light) and red yellow light (medium long wavelength light wave). Due to the small number of cones, the color of the world in the dog's eyes is very monotonous, not as colorful as the world in the eyes of human beings. However, humans have three types of cones that allow us to see light of all colors in the visible spectrum. Since the dog has only two kinds of cones, the color that the dog can distinguish is the same as that of the red-green blind patient. However, color blind patients can also see many other different colors, so can the dog see these colors as well? Scientists have taken two approaches to determine this.

One way is to illuminate the dog's eye with a beam of colored light, which results in an image that is reflected back from the dog's eye. The scientists studied the reflected image; then reflected it with the same light in human eyes to contrast image.

Another way is to train dogs to "tell" scientists about the world they see. In the experiment, the scientists showed the dog several sets of colors in succession, each with three colors, two of which were the same. In addition to giving a very small amount of training, the dog will use the nose to point the scientists to the light of the distinctive color in each group. Scientists only need to constantly change the color of the light and repeat the process, and can conclude that in the eyes of the dog, the world is black, white and dark gray, while the medium length red and yellow light and the short blue light wave are mixed, the world is just like the picture in black-and-white TV. Only the brightness of black enamel is different, and the change of color cannot be distinguished. The reason why guide dogs can distinguish between red and green signal lights is that they depend on the brightness of the two lights. The dog's discriminating power against gray shade is very subtle. By relying on this ability, the light and dark changes on the object can be distinguished, resulting in a stereoscopic visual image.