Vision - How dogs see

  • 31/01/2010
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1) Dogs can see in much dimmer light than humans. This is because the central portion of a dog's retina is composed primarily of rod cells that "see" in shades of gray while human central retinas have primarily cone cells that perceive colour. The rods need much less light to function than cones do.

2) Dogs can detect motion better than humans can.

3) Dogs can see flickering light better than humans. The only significance to this appears to be that dogs may see television as a series of moving frames rather than as a continuous scene.

4) Dogs do not have the ability to focus as well on the shape of objects (their visual acuity is lower). An object a human can see clearly may appear to be blurred to a dog looking at it from the same distance.

A rough estimate is that dogs have about 20/75 vision. This means that they can see at 20 feet what a normal human could see clearly at 75 feet.

5) Dogs are said to have dichromatic vision -- they can see only part of the range of colours in the visual spectrum of light wavelengths. Humans have trichomatic vision, meaning that they can see the whole spectrum. Dogs probably lack the ability to see the range of colours from green to red. This means that they see in shades of yellow and blue primarily, if the theory is correct. Since it is impossible to ask them, it is not possible to say that they see these colours in the same hues that a human would. Whether or not the ability to see some colour is important to dogs or not is hard to say.

A dog with its eyes about 12 inches off the ground certainly sees the world a different way than a human with eyes about 48 inches off the ground like many 5th graders. As humans we tend to think of dog's visual capabilities as inferior to ours. It is different but it may suit their needs better than possessing accurate colour vision would.

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