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  • 2022-06-16 (xsd:date)
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  • Do Dogs See Only in Shades of Blue and Yellow? (en)
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  • Dogs may be human’s best friend, but canines have a very different view of the world around them. In particular, they see only in shades of blue and yellow — at least that's according to one online rumor. The dog blog Pets Reporter claimed: And we found that notion to be true, according to veterinary care experts at the VCA Animal Hospitals. While scientists can’t definitively describe how canine eyesight interprets the world — only a dog could say for sure — anatomical research of dog eyes suggests that our four-legged friends see only in shades of blues and yellows. Inside the back of the eye is a layer of cells that is sensitive to light known as the retina. Within the retina are millions of light-sensing cells known as photoreceptor cells. As light enters the eye, the photoreceptors interpret and transmit light information to the brain, allowing us to see our surroundings. There are two types of photoreceptors: rods and cones. Rods detect light levels and motion, as well as perceive black and white colors to help with seeing at night. Meanwhile, cones differentiate colors. Humans have three types of cones that allow us to identify combinations of red, blue, and green, according to the American Academy of Ophthalmology (AAO). Dogs, on the other hand, only have two types of cones that see blue and yellow hues. This limited color reception is known as dichromatic vision, noted VCA Animal Hospitals. This vision is comparable to humans with red-green color blindness, a condition that prevents them from distinguishing between the two colors. Just because dogs can’t see colors like we do doesn’t mean their vision isn’t any better or worse — it’s just different. While canines have less cones, they have more rods, allowing them to see in low-light conditions and to better identify moving objects. For the purpose of hunting in the dark, canine eyes have a larger lens and corneal surface and a reflective membrane, known as a tapetum, that enhances night vision, explained Jerry Klein, the American Kennel Club chief veterinary officer, in a blog post. They also have more rods, which improves low-light vision, in the retina. To compensate for their color blindness, dogs have a special trick up their snout, so to speak: their keen sense of smell. When playing a game of fetch, dogs cannot tell the difference between a red ball and a yellow ball. Luckily, they have a great sense of smell so they can usually identify their ball and avoid mix-ups when playing a game of fetch in the park, wrote the VCA Animal Hospital. [See also: Did Study Find Vegan Diet Could Be Better for Dogs' Health than Meat-Based Diets?] Tools like the Dog Vision Image Processing Tool, which we used below, provide comparisons of photographs, side-by-side, to show how dogs view things differently. Take a look at these dyed eggs, for example. The carton on the left shows red, orange, yellow, green, blue, and indigo eggs — like a human with healthy vision would see. The right shows those same eggs in muted yellow and blue tones. (en)
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