Panoramic versus stereo vision Binocular vision Visual scanning. Both eyes seeing the same scene reduces the field of view and allows other animals to sneak up undetected.
Prey animals prefer a panorama view of the world.
Tree apes swing from branch to branch and failure to instantly judge the world in 3D could lead to a nasty fall. Because our eyes are separated by about 65mm, the world seen by each retina is slightly different. The difference is great for objects nearby, but imperceptible for distant things, like mountains. Stereoscopic vision stops at about 200 meters away, because the difference between the two retinal images is then undetectable. A 3D perception of the world has to be built up in the brain, which computes the retinal differences and interprets them as 3D. People looking at a stereoscopic picture may find the third dimension only develops slowly.