Stereoscopic perception of depth between any two objects in space can be attributed only to the stimuli of the transverse (horizontal) disparity between the images of those objects in the two eyes. Experiment has shown,* however, that for a given retinal region of the two eyes the disparities that give rise to the stereoscopic experience are limited to a definite range; for disparities outside that range there is no patent stereopsis. In the same way that we account for the experimental fact of Panum's areas of fusion, we can also explain the range of disparities for stereopsis by the extent of overlapping of particular arborizations of neurons in the terminal regions of the cortex which arise from disparate retinal elements of the two eyes. This explanation would fit the concept that stereopsis rests on a neuroanatomic and physiologic basis.
We would expect these arborizations to overlap not only in a
OGLE KN. Stereopsis and Vertical Disparity. AMA Arch Ophthalmol. 1955;53(4):495-504. doi:10.1001/archopht.1955.00930010497006