There is no doubt that dogs see the world differently than we do, but it is an urban legend that its view is only able to distinguish white, black and slight grayish shadows.
While most people are able to appreciate a full color spectrum ranging from red to violet, dogs’ eyes lack some of the light receptors that allow us to distinguish certain colors, especially red and green. But they are able to distinguish yellow and blue.
The different wavelengths of light translate into different colors in an animal’s visual system. The one above corresponds to the human view, and the one below to that of a dog.
Above: iStock/Getty Images Plus via Getty Images. Below: that same image processed by the Dog Vision Image Processing Tool, by András Péter.
What we see as red or orange, for a dog can be a shade of light brown. For my dog Sparky, a deep orange ball on the green lawn could be a light brown ball placed on an equally brownish grass. However, it is likely that your ball intense blue will appreciate it in a similar way. There is an online tool that allows us to check how our dog would see a certain image.
Animals can’t talk to explain how they see, but to measure their vision the researchers had no greater difficulty in training dogs to touch with the snout colored discs that lit up. They later trained the dogs to play the record that was a different color than the rest. When these well-trained dogs stopped knowing which discs they had to press, the scientists deduced that at that point they were no longer able to distinguish the differences between colors. These experiments also showed that dogs could only distinguish yellow and blue.
The retinas of humans, located at the back of our eyeballs, have three different types of cone-shaped cells that are responsible for us being able to distinguish the different colors we see. But when scientists used a technique called electroretinography to determine how dogs’ eyes reacted to light, they found that dogs have a smaller number of these conical receptors.
The light reaches the back of the eyeball, which is perceived by the sticks and cones. These send visual signals to the brain.
iStock/Getty Images Plus via Getty Images
But it’s not just that dogs see fewer colors than we do; they are also likely to see less sharply. The analyses show that both the structure and the functioning of your eye make objects located at a certain distance look more blurred. While for a person a perfect vision has a value of 20/20, the typical view of dogs hovers around 20/75. That means that what a person with normal vision can see sharply from 75 meters, to see the same the dog must be at 20. However, as dogs do not read the newspaper, this lower visual acuity does not affect your life.
There is probably a big difference between breeds in terms of the visual capacity of dogs. When it comes to hunting, for example, breeders have selected over the years dogs like English greyhounds for having better eyesight than other breeds like bulldogs.
But the issue becomes even more complicated. While people find it difficult to see clearly when there is little light, researchers believe that dogs can see just as well during dusk or dawn as during a bright morning. This is because, compared to humans, the retinas of dogs have a higher percentage and a greater variety of other types of visual receptor. These are the sticks, so called because of their shape, and that in low light conditions work better than conical cells.
On the other hand, dogs have a reflective layer of tissue on the back of the eyes that helps them see better when there is low light. This is the tapetum lucidum, which works as if it were a mirror and collects and concentrates the available light to help them see when it is dark. It is this tapetum lucidum that makes dogs and other mammals have that luminous reflection in their eyes when at night we point them in the face with a flashlight or try to take a photo with flash.
ItDogs have the same type of vision as many other animals, including cats and foxes. Researchers believe that for this type of predator it is important to detect the movements of their prey during the night, and for this reason their vision evolved in this way. Like many other mammals, dogs developed the ability to look for food and hunt during twilight or in low light conditions, which was to the detriment of their ability to distinguish a greater variety of colors. This is something most birds, reptiles and primates can do. Humans, on the other hand, do not evolve to be active at night, so we retain our ability to distinguish many colors as well as our clear vision.
Before we feel sorry for dogs because they are not able to distinguish all the colors of the rainbow, let us think that some of their other senses are much more developed than ours. They are able to perceive the high-pitched sounds from much farther away than we are, and their smell is much more powerful.
While Sparky may not be able to easily distinguish an orange toy on the lawn, you can certainly smell it and find it easily whenever you want.
This article is part of the Curious Kids series, which answers questions from children. In this case, the question “Is it true that dogs only see black and white?” was put by Oscar V., 9, who lives in Somerville, Massachusetts.
Nancy Dreschel, Associate Teaching Professor of Small Animal Science, Pennsylvania State University
This article was originally published in The Conversation. Read the original.
