Color and Acuity Differences between Dogs and Humans

by Jennifer Davis
Copyright © 1998

Most humans have the ability to see all the different colors of the electromagnetic spectrum, and consequently perceive all its' colors. [The color that is perceived is a result of the visual system, and not the spectrum itself.] Animals, such as the dog, are often thought of as being at a disadvantage by not being able to see all the hues of the spectrum. Evolutionarily however, the dog and the human each developed the visual system that worked best for them. Humans have depended on their diurnal ability and a sense of color throughout time to help them find food. Dogs on the other hand, were not originally diurnal animals, until humans domesticated them. Consequently, the ability to see at night was originally more important to the dog than color. After all, their prey is often camouflaged with the surroundings, so they are unable to rely on color vision cues as heavily as humans do to find food.

The retina of the eye is lined with both rods and cones in humans and dogs. The rods are much more prevalent in both species, but even more so in the dog than the human. The rods are adapted to work best in low light and are used for motion detection. The central retina of the canine eye contains about 20% cones, while humans have an area of 100% cones called the fovea. The cones work best in mid to high levels of light and have the ability to detect color.

Humans are believed to have three different cone types, a trichromat, while dogs have two, a dichromat. Each cone contains a photopigment that is maximally sensitive to a separate wavelength of light. These photopigments are what makes color vision possible. A human's three cone types are maximally sensitive at 445 nm, 535 nm, and 570 nm respectively. The canine cones are maximally sensitive at 429 nm and 555 nm.

The fact that dogs have two different types of cones does not mean that their brains have the ability to interpret the information that the rods and cones send. To determine what colors a dog can see, behavioral studies can be done. One such study conducted by Neitz, Geist and Jacobs involves three colored squares being placed in front of a dog. By training the dog to pick the odd colored square of the three, the researcher is able to guess what colors the dog can see. The question that then arose was if the dog was choosing the panel for it's color or due to it's brightness. It was found by use of different brightnesses for the squares that the dog was indeed choosing the square for the color and not brightness cues. Through these studies it has been suggested that an average dog sees similar to a human deuteranope, a person that is red-green colorblind. Consequently, the dog's world consists of yellows, blues, and grays. When a human perceives a red object it appears as yellow to the dog, while a green object appears as white, a shade of gray. This white region, also called the neutral point, occurs around 480 nm in visual spectrum. According to the electromagnetic spectrum, 480 nm would appear as a greenish-blue hue. All wavelengths longer than the neutral point are indistinguishable from one another to the dog and would all appear as yellow.

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