ABSTRACT
In the last paragraphs of Chapter 5, I have explained how the evolution of the visual system has led to binocular vision ofdepth. In primitive organisms such as the pike and the chameleon it had become clear that convergence was the principal cue to depth in those animals. But in birds and mammals there came a new cue to depth: disparity (p. 51). In mammals the semidecussation of the optic nerves brought correspondingcortical points (representing identical directions in space at infinity) into close proximity, making non-corresponding, disparate, points (representing a nearby object in space) easily detectable.
