Are Dogs Really Color Blind?

https://www.thedailyresearch.com/?p=640

Dogs are peoples loved companions. They play with us, snuggled with us and are very loyal. Dogs can be more than just furry friends, they can be the eyes of the blind, aid in search and rescue missions and can sniff out illegal substances. It is commonly believed that dogs do all these things while viewing the world in monochrome tones.

But what if dogs have the ability to see in color? Could this mean that they can do tasks we thought were beyond their capacity? And could this mean that we can enrich their world with more colorful play toys and color based activities? Let’s take a closer look at the visual world of the dog and discover if these animals are, in fact, limited to black, white and tonal vision?

Color Vision: The function of cones

Cones are specialized light receptors found in the back of the eyes. Color vision is based in these cones. According to the Optics and Physiology of Vision the depth and intensity of the color vision depends on the number of color cones found in the eye and the degree to which these cones overlap. Humans have three types of cones, which means they are trichromatic. Humans are able to differentiate red from blue, green from yellow and the entire visual spectrum, that is known to us. But what about dogs? How many cones do they have and what if any colors can they see?

To answer these questions, it is necessary to take a look at some studies that have been done on the topic of color vision in dogs.

Studies

Color Vision in the dog

Clinical ophthalmologist Dr. Jay Neitz along with Timothy Geist and Gerald H. Jacobs conducted a famous experiment with canines at the University of California, Santa Barbara in 1989; the findings of this experiment were published in the paper Color Vision in The Dog.

Up until Neitz, Geist and Jacobs conducted their experiment it was generally accepted that dogs were color blind and thus that they saw the world in black, white and shades of grey.

Only once Neitz, Geist and Jacobs did their research into the color vision of domestic dogs did they find out the following facts. Firstly, Dogs have two different types of cones (color receptors) in their eyes making them dichromats. Secondly, that one of the cones in the dogs’ eyes peaks at the blue-violet range while the other peaks at the yellow-green range.

Thus it was concluded that while humans see the rainbow as violet, blue, blue-green, green, yellow, orange and red,

it was held that dog’s saw it as dark blue, light blue, gray, light yellow, darker yellow (almost brown), and very dark grey. Or put simply, dogs saw the world according to three basic colors: yellow blue and gray.

This results were support by later researches of Miller and Murphy in 1995.

Vision in Dogs Miller and Murphy

Veterinary ophthalmologist Dr. Christopher Murphy and Paul Miller, DVM wrote a paper title Vision in Dogs. Like Neitz Murphy and Miller found that the green, orange, red and yellow we see probably looks like different yellowish hues to the dog, while blue-green, blue and violet look like various shades of blue-gray.

Not all scientists agreed with the findings of Neitz and Miller and Murphy. Many scientists believed that the dogs were detecting changes in brightness and not actually discriminating between colors. Another, more recent Russian study, sort to put these claims to rest.

Read: Short Spine Syndrome: Rare Condition That Just 14 Dogs Suffer From

Colour cues proved to be more informative for dogs than brightness
Anna A. Kasparson, Jason Badridze, Vadim V. Maximov

Drawing on the knowledge gain from Neitz’s experiment namely, that dogs can distinguish blue and yellow, but not red and green, the Russian scientist printed four pieces of paper in different colors: dark yellow, dark blue, light yellow and light blue. They used dark and light hues so they could test the theory that dogs use brightness to distinguish between objects and things.

In the first test the dogs were trained to receive a food reward when shown four different colored pieces of paper, dark and light yellow, dark and light blue. To achieve this end, the researchers put one sheet of paper in front of food bowls that were placed inside locked boxes.

The researchers put a dark yellow piece of paper in front of a box containing a piece of raw meat (the box had been unlocked and remained so). Each test involved giving the dogs a chance to try and open one box. After three trials the dogs learnt that the dark yellow signified the box containing the raw meat.

The researchers wanted to check if the dogs were choosing the dark yellow paper based on its brightness or based on its color. To test this, the scientists put the light yellow paper in front of one box and the dark blue in front of another. If the dogs were to select the dark blue paper, then it would be concluded that their decision was based on brightness. Alternatively, if they chose the light yellow then it must be deduced that the dogs were making their decision based on color alone.

Each dog chose the light yellow paper more than 70 per cent of the time. Thus, the dogs were making their choses based on the color of the paper.

Anna A. Kasparson, Jason Badridze, Vadim V. Maximov write:

“Here, we show that for eight previously untrained dogs colour proved to be more informative than brightness when choosing between visual stimuli differing both in brightness and chromaticity. Although brightness could have been used by the dogs in our experiments (unlike previous studies), it was not. Our results demonstrate that under natural photopic lighting conditions colour information may be predominant even for animals that possess only two spectral types of cone photoreceptors.”

Is color vision necessary for dogs?

Dr Christin Fahrer DVM, MS, Diplomate ACVO said “Color vision for dogs is great for them, but is kind of a gift because I don’t know that they really need it to function,” she added that “Their retinas are built to focus on movement for survival; if they can focus on prey running, they don’t care if it’s brown or green of blue.” As we all know dogs also rely heavily on their sense of smell and this, says Fahere often supersedes any visual cues they might be receiving.

So although it may be nice to know that dogs can see the colors blue and yellow just as well as humans can, these findings may not make a great impact on how we relate to our furry companions. However, next time we choose a play toy for our dog we may choose the blue toy over the red.

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