ABSTRACT
The two eyes of the primate have extensively overlapping visual fields, but this would not require eye vergence changes if the visual apparatus did not exhibit the phenomenon of local signs. Stimulation of any small retinal region causes a sensation with a unique two-dimensional spatial signature. In order that a given external object have assigned to it identical spatial signatures in both eyes, it is necessary for the two eyes to assume a specific stance, namely the placing of the ocular images of the object on the retinal position of one eye which has an identical local sign as that on which the image is situated in the other eye. Such pairs of retinal positions in the two eyes are called corresponding points. In the normal subject, the two foveas are corresponding points.
