A dog's vision

[AngloScot]

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?

[BenDToy]

I don't know whether or not this is true, but the biology of a dog's eye would reveal this.

[j2buttonsw]

There are rods and cones in the retina of an eye. The rods "see" black and white and the cones "see" colour. Dogs only have rods in their retina.

[bernardo]

Also, one could do tests with dogs to see if they can tell the difference between two coloured cards or whatever.

[New Forester]

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...

[muggyjim]

That is fascinating! Its a question that sometimes comes to mind and I wanted to ask. I must try and think of something to ask now, but typically my mind has gone blank. :>0