Binocular Depth Cues
Binocular depth cues
Properties of the visual system that facilitate depth perception by the nature of messages that are sent to the brain.
Binocular depth cues are based on the simple fact that a person's eyes are located in different places. One cue, binocular disparity, refers to the fact that different optical images are produced on the retinas of both eyes when viewing an object. By processing information about the degree of disparity between the images it receives, the brain produces the impression of a single object that has depth in addition to height and width.
The second cue, called binocular convergence, is based on the fact that in order to project images on the retinas, the two eyes must rotate inward toward each other. The closer the perceived object is, the more they must rotate, so the brain uses the information it receives about the degree of rotation as a cue to interpret the distance of the perceived objects. Yet another cue to depth perception is called binocular accommodation, a term that refers to the fact that the lens of the eye changes shape when it brings an image into focus on the retina. The muscular activity necessary for this accommodation acts as a signal for the brain to generate perception of depth and distance.
BINOCULAR DISPARITY DEMONSTRATION
This simple experiment demonstrates binocular disparity. Hold a pencil about 12 inches (30 cm) from your face. With one eye closed, align the pencil with the edge of a doorway, window, or other vertical line in the room. Close the eye, open the other, and observe the position of the pencil: it will have jumped. Binocular disparity describes this phenomenon of different images of the pencil in each eye.
See also Vision
Bennett, Jill. Sight. Morristown, NJ: SilverBurdett, 1986.
Chalkley, Thomas. Your Eyes. 3rd ed. Springfield, IL: C.C. Thomas, 1995.
Elkins, James. The Object Stares Back: On the Nature of Seeing. New York: Simon & Schuster, 1996.