The Ferrier Lecture, 1992. Seeing depth with two eyes: stereopsis

The primate's two eyes both point forward, and are a few centimetres apart. The task of extracting depth from two slightly dissimilar two-dimensional retinal images falls on the central nervous system. The mechanism is so effective that a good observer can detect, by stereopsis alone, depth differences of as small as 10 microns at a distance of 25 cm. Psychophysical and neurophysiological studies have begun to unravel the neural circuits in the brain which process the retinal signals to yield stereoscopic information.