The Perception of Space

Excerpt

When we look at an object with two eyes, we perceive it as singular, like we do other parts of the visual scene stimulating points on our retina that share a common visual direction. These points are termed "retinal corresponding points" and fall on an area called the "horopter". Points outside the horopter fall on slightly different retinal areas and so do not have the identical visual direction and lead to "retinal disparity", the basis of our depth discrimination. This retinal image disparity occurs due to the lateral displacement of the eyes. The region in visual space over which we perceive single vision is known as "Panum's fusional area", with objects in front and behind this area being in physiological diplopia (i.e., double vision). Our visual system suppresses this diplopia, and hence we do not perceive double vision under normal viewing conditions. To understand the discussion on the horopter and Panum's fusional space, the sense of direction will be introduced. Two terms describing direction sense are oculocentric and egocentric visual direction.