What animals see, and how they see it
Special to the Tribune
Look straight ahead. If there is a wide vertical line down the center of your view. you are a horse. If your eyes are fixed in their sockets, you are an owl. If you have separate day and infrared night eyes, you are a reptile. If your view is out of focus and colors are blended, you are a cat. Measuring normal human vision as 20/20, studies show dog vision between 20/50 to 20/100, the horse 20/33, and the cat compares to 20/100. In dogs and cats the binocular field is 85 degrees, in horses it is around 65 degrees, and in people it is around 120 degrees. However, both dogs and cats have better perspective and depth perception due to the placement of their eyes. Cats detect light that is 6 times dimmer than normal humans can detect. Dogs also detect much lower levels of light than humans but not as low as cats.
When it comes to color vision, the birds have it. The pigeon is capable of detecting more subtle gradations of color than the most advanced computer program. Like people, cats have three types of cones, but cats live in a world of fuzzy pastels. Like 4 percent of humans who are color blind, dogs, who have just two types of cones, do not see red or green as separate colors. They only see the blues, yellows, and grays of a landscape. Some canine sports equipment, like the teeter toter used in agility trials, is painted dark blue with yellow contact areas because dogs appear to see blue and yellow best. Bulls see the bullfighter’s red cape in shades of gray.
Insects like bees have compound eyes. However, rather than multiple images they see a patchwork quilt or jigsaw puzzle. The range of vision for the bee and butterfly extends into the ultraviolet. The dragonfly’s brain works so rapidly it perceives most movement in slow motion. That’s why they are so elusive.
Birds living on seeds and fruits in the forest canopy need to differentiate between green and the colors of their chosen foods. Aquatic birds live in an environment where different colors predominate, and some control their focus underwater. Raptors have the most acute avian vision, able to spot and capture prey from on high. Most birds have laterally positioned eyes for a broader field of view, but raptors have frontally set eyes for increased binocular vision and depth perception.
Fish have well developed visual systems. Some have photoreceptors with peak sensitivities in the ultraviolet range. This may be because, like birds of the sky, they move about in a blue environment and need to contrast food sources or predators against a blue water background.
For the wild or domestic animal, basic visual capabilities provide raw information that is processed in the brain only after it’s compiled with other sensory information, especially scent and sound. This total vision is called the umwelt, explained in detail in the writings of Dr. Temple Grandin. The ground-breaking, autistic scientist sees the world in pictures just as the animals do.
The next time Fido can’t find the stick in the sand, consider that to him or her, both are the same color. The next time a pet photo features glaring devil eyes, remember that, unlike you, your pet has a tapetum, a night vision enhancer, that can reflect back the camera flash.
• Provided by the Lake Tahoe Humane Society and Society for the Prevention of Cruelty of Animals to help “Keep Tahoe Kind.” Dawn Armstrong is the executive director of the Lake Tahoe Humane Society and SPCA.