MadSci Network: Zoology |
Well, the best answer I can give you is: your dog's night vision is better than yours, but I don't know how much better. There are a few reasons for this, which I will explain: To get around communication barriers between animals and humans, scientists develop tests that rely on the animal's natural behaviors. Testing color vision is a good example. A good way to test color vision in an animal is to rely on their desire for food. So a scientist may not feed a dog one evening, so that in the morning it is hungry. Then, The scientist will place two sealed containers in front of the dog -- one is red, and the other is blue. The dog learns that the red one always contains food, and the blue one never does -- if he can tell the difference between the two colors. If not, the dog will never get it right more than half the time. Of course, I'm sure you see that there are problems with this experiment -- what if the dog can smell the food, and can tell that way? Or what if the red and blue look like two different shades of gray? The dog doesn't have to be able to see the colors to tell which container has the food. There is also a more difficult problem -- what if the dog is perfectly happy getting food half the time, and never really learns what he is supposed to do? (side note: it turns out that cats can probably see colors, and that many behavioral experiments with cats run into this last problem -- those who have cats will not find this very surprising!) These are problems that can be difficult to detect, and they can ruin the results of an experiment without anyone even realizing that the experiment is flawed. After that very long aside, I will tell you that it appears that dogs are worse than humans at: - color perception - binocular overlap (they see less of the world with both eyes) - accomodative range (how close up they can focus on objects) - visual acuity (they see about 40% as well as us, which probably translates to 20/60 or so on a vision chart) They seem to be better than humans at: - night vision - field of view (they see objects better in their peripheral vision) - gray scale differentiation (they see more shades of gray than us) - flicker fusion (they can see more images per second -- chances are they see movie frames individually, while we can't) - motion detection Unfortuanately, because of the general problems with animal experiments outlined above (and many others I haven't mentioned), it is difficult to know exactly how well dogs see in the dark. Dogs are known to hunt at night, so their night vision is good enough for that. All animals need some light to see -- it is impossible for any animal to see in complete darkness -- but dogs seem to need less light than humans. For a fairly readable review of the scientific literature, you can find the following article at your local university library or vetrinary school library: _Vision in Dogs_, by Miller and Murphy. Journal of the American Vetrinary Medical Association Vol. 207, Issue 12, pages 1623-1624. Published Dec. 15, 1995.
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