Saturday, September 15, 2012

Not a Black and White Movie: What Our Pets See

Whenever movies portray the perspective of a dog or cat, they always use camera at knee level, looking up in black and white. In real life, a pet’s perspective is much different. These differences can be enlightening, and can give us a little glimpse into our four legged friends’ world.

Dogs can see basically two colors, a blue-violet and a yellow-green, with the other colors appearing as gray. Dogs also have a limited ability to differentiate the brightness of colors, with about half the ability that people have. This means for many dogs, different colors appear completely the same; a pattern on the wrapping paper of a birthday present could be literally invisible to them. Cats, who can see shades of gray better than dogs, can also see blue and yellow. While colors may not be obvious, a cat’s ability to detect differences in brightness levels may allow them to see the difference between colors that a dog may miss. 

Dani and I examine a kitty

Both dogs and cats have the ability to see in low levels of light much better than humans. This ability is partially related to the reflective surface in the rear of their eyes called the tapetum. People, who do not have a reflective tapetum, get “red eye” in a camera flash because the blood vessels in the back of the eye are visible. Dog’s and cat’s retinas are covered with a reflective surface, which often appears green, yellow or blue in a camera flash. This reflective surface allows the eye to acquire more light when in dim or dark areas. Additionally, dog’s and cat’s retinas have more rods, which detect dim light, then cones, which detect color. These changes allow dogs and cats to see five to seven times better in the dark than a person.

Nanu and Suszu demonstrate reflective tapetums and humping 
Gabby has a yellow tapetum
Eme and Nyah

The most interesting difference between pets and their owners is in the “processing center” of vision. While we think of our own eyes as simply recording whatever is in front of us exactly as it is, our eyes and brain add many small changes to make it easier for us to see important things, such as edges. This is how some optical illusions work, such as when a printed pattern appears to move as you stare at it; the “edge seeking” processors in our eye get confused by the pattern. This “edge seeking” allows us to be able read, since we can easily differentiate between letters.

"Processing Center" of the Human Eye

Dogs and cats visual “processing centers” don’t have the ability to find edges like ours do, which is why a dog or cat, no matter how intelligent, will likely never read. Their processors are tuned to finding movement, especially horizontally. This is why your pet may stare out the window, intense on watching something, when from our perspective there is nothing there. While our vision may see the detail and edges better, theirs is designed to detect that scurrying mouse or bug.

Dogs and cats truly live in a different world than us. They can see in the dark, and see movement that could be invisible to us. On the other hand, do not be offended is Fluffy seems less than excited about his wrapped birthday present; he may not even “see” the paper at all.

Michael Rumore, DVM

(Originally published in the Tampa Bay Weekly Newspapers in March, 2012)

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