The Sense of Sight
Thursday, January 18th, 2007 by Mike CronkIn researching the senses through various books and on-line articles, I have discovered such a wealth of information on each sense that it could comprise a book in and of itself. My aim with these articles is to deliver a summary and the bottom line, not necessarily the detailed physiology and testing which led to the final conclusion. For more detailed information, please see our reference materials listed in the library of our website: www.pantopspetsalon.com
Through educating ourselves about the five senses in dogs compared to our human capabilities, we develop a much greater understanding of the world our canine companions experience. Sight is our bag! It is our keenest sense and in most aspects, it is far superior to that of dogs. Our visual system has a greater portion of the brain devoted to it than to any of our other senses—not true for dogs. The amount of light taken in by the pupil and the amount of light interpreting structures within the eye (cones and rods) are markedly different between man and dog. Since dogs originally hunted and were usually very active during dawn and dusk, they are more sensitive to levels of brightness but their ability to perceive color falls by the wayside. When compared to other animals, though, the dog has relatively good vision. Based on current research, here is what we know:
Archived from “The Paw Report:” Issue #7, January
1. Dogs have larger pupils and more rods than humans, giving them superior night vision. It is estimated that dogs need ¼ the amount of light that humans do to see at night—cats, 1/7.
2. Humans focus—i.e. change from close vision to distant vision—better than dogs.
3. Dogs have better side to side vision enabling them to follow prey on the horizon. Horses and antelope have the same capability, allowing them to scan for predators better.
4. An object that can barely be seen by a dog at 20 feet can be seen by the person with normal vision (or corrective lenses) at 75 feet. While our visual acuity is 20/20, that of dogs is 20/75 –much worse. The standard driver’s license requires less than 20/40—meaning most of our dogs would have to wear glasses in order to drive legally!
5. Dogs have superior motion sensitivity. If an object 900 meters away is stationary, they can’t recognize it but once it moves they not only can see it, but identify it as well. Greyhounds can identify their owner when in motion, as much as a mile away! Yet, if the owner is standing still at 100 meters, they become invisible to the dog.
6. Because an average dog’s eyes are set more on the sides of the head, their field of vision is about 240 degrees compared to 200 in man (yes, Pekes and Pugs are the exception).
7. Dogs are not color blind, but the colors they see are not as rich or many as those seen by man. The latest research claims the following: “instead of seeing the rainbow as violet, blue, blue-green, green, yellow, orange, and red, dogs would see it as dark blue, light blue, grey, light yellow, brown, and very dark grey. In other words, dogs would see the colors of the world as basically yellow and blue. They see the colors green, yellow, and orange as yellowish and they see violet and blue as blue. Blue-green is then grey. Red is difficult for dogs to see and may register with them as dark grey or perhaps even black.” So much for the variety of color in dog food!
We have to be careful about generalizations with regard to the senses. Always keep in mind that the ancestor of the dog, the wolf, has evolved into a variety of breeds today through controlled breeding by man. Therefore, sight hounds are better adept at hunting and scent hounds are more adept at sniffing things out.