Lateral geniculate lamination and the corticogeniculate projection: a potential role in binocular vision in the quadrants

Students of vision have long speculated about the functions of the distinct lamination of the lateral geniculate nucleus and the massive return projection from visual cortex to this thalamic structure. This paper proposes that these features of the visual system reflect, in part at least, its solution to a geometric problem inherent in binocular vision. Points in the visual quadrants are imaged on geometrically non-corresponding retinal points. Two such retinal loci, optically conjugate with a given visual point at one fixation distance or angle, will correspond to no single visual point at other fixation distances or angles. This raises potential problems for visual cortical neurons sensitive to a narrow range of binocular disparities. If these neurons are to function optimally at a variety of fixation distances and angles, their disparity tuning must be variable. It is suggested here that such dynamic disparity tuning is effected by the corticogeniculate projection acting on the segregated ocular representations in the geniculate laminae.