Food & Drink1 min ago
A dog's vision
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Is it true that all dogs can only see in shades of black and white? If so how can people be so sure without being able to look through the eyes of a dog themselves?
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For more on marking an answer as the "Best Answer", please visit our FAQ.J2buttons - if dogs only had rods, this would be true -- it is, for example, for microchiropteran bats, and like you I did think it was for dogs.
However, canids do have cones as well as rods. Apparently they have two types of cones instead of the usual human number of three (a few humans have four!). Dogs are therefore equivalent to a human with red-green colour-blindness:
http://www.uwsp.edu/psych/dog/LA/DrP4.htm
They do have fewer cones overall, and unlike us have many rods in the detailed focus area (fovea). This suggests that they ought to have better detailed vision in low-light conditions, but perhaps less vivid colours.
Whether they can actually use their theoretical colour-vision ability is another matter. Bernardo's idea would be the right approach, and it does seem to have been done (see particularly the last bit on this page):
http://www.straightdope.com/classics/a2_004.html
http://www.katiesbumpers.com/K9colorvision.htm
Cats seem to be similar.
I'll have to see if I can test our cattle...