The term vision refers to the complex of eye and brain. It is this complex which guides a broad spectrum of human abilities.
The retina is a thin sheet of brain tissue in the eyes. It is the place where the brain first encounters light. Signals travel back-and-forth between the eyes and the rest of the brain. Visual processing involves several major sub-cortical centers plus a mosaic of dozens of distinct areas in the cerebral cortex. It is currently acknowledged that vision is the result of parallel, distributed processing in multiple areas and through multiple pathways. Fro example, information gathered by the retina about color is processed in a different area of the brain than information about movement.
As another example, ego centric direction describes the perceived location of an object compared to our body. This is derived from a combination of oculocentric direction (where our eyes are aimed), position of the eyes in the head, and the head's position relative to the body. The brain uses a reference point midway between the two eyes, known as the egocenter to compute egocentric direction. Enabling the brian to engage a whole body experience, bionocular vision is an intricate organization of biologic and psychologic components.
The majority of nerve cells from the retina project to the visual cortex. However, at least ten percent of the nerve cells take a different pathway stimulating areas of the brain stem dedicated to functions that seem remote to vision, when vision is narrowly defined. The existence of extensive sensory motor pathways supports a broader conceptualization of vision, integrating functions such as balance and visual-auditory localization.
Information from neuroimaging and insights from cognitive neuroscience demand a significant reformulation of the understanding of vision. Vision occurs neither in the eyes or the brian, but emerges from the collaboration of the eyes and the rest of the brain. Vision is a pervasive aspect of our existence which permeates all of our activities. Vision develops and, due to neural plasticity, can be enhanced. Developmental optometry is the discipline dedicated to the care of all aspects of the visual process.
As surely as the old system (for explaining vision) considered that the problem of knowledge and understanding could be separated from the problem of seeing, so the present one will find it increasingly difficult to draw a dividing line between the two.