Binocular vision comprises three principal processes, namely (1) the coordination of the extraocular muscles and the intrinsic adjustment of the ciliary and other internal muscle fibers in order to bring the two images on the fovea, (2) the fusion of the two monocular images or sensations into a single perception and (3) the projection of this composite image into space.
Fusion is an association of the images received by the two retinas so that one composite picture is formed. Exactly how this takes place is still a controversial subject. Some investigators believe that the process is a diffuse cortical one, while others assume that a fusion center exists in the cortex although its anatomic location has not been found. According to the latter view the fusion center would receive fibers from the occipital cortex of both sides and also proprioceptive fibers from the extraocular muscles. The images must be fused