MadSci Network: Zoology
Query:

Re: How much better is my dog's night vision than mine?

Date: Tue Sep 7 11:23:00 1999
Posted By: Brenda Hefti, Grad student, Neuroscience Pgm/Physiology Dept
Area of science: Zoology
ID: 933719279.Zo
Message:


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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