Binocular depth cues are properties of the visual system used by both eyes in order to determine depth perception and distance.
Binocular depth cues help an individual judge distance from objects while processing information received by both eyes and converting it into a single image. Because there is a physical distance between the eyes, each eye receives a slightly different image of an object. Ten different depth cues have been identified, but only three of them—convergence, binocular parallax, and binocular accommodation—require the use of both eyes. The set of depth cues are accommodation, convergence, binocular parallax, monocular movement parallax, retinal image size, linear perspective, texture gradient, overlapping, aerial perspective, and shades and shadows.
Convergence is what occurs when the eyes move inward together as an object approaches and comes into close proximity. The closer the object to the observer, the greater the degree of inward rotation of the eyes. The brain uses the information regarding rotation degree to judge distance from the observer. This cue is useable only at short distances from the observer (less than about 35 feet).
Binocular parallax functions at medium distances. It is the process by which the slightly disparate images seen by each eye are combined into one and distance away from the observer is estimated. By processing information about the degree of disparity between the two images it receives, the brain produces a combined image of a single object that has depth in addition to height and width.
The third cue for binocular depth perception is binocular accommodation, which refers to the manner in which the lenses in both eyes simultaneously adjust to focus on objects that are in the far distance.
See also Ames room ; Figure-ground perception ; Visual angle.
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