What is Stereopsis?

• Main Author: D Vishwanath
• Format: Article
• Language: English
• Published: SAGE Publishing 2012-07-01
• Series: i-Perception
• Online Access: http://ipe.sagepub.com/content/3/6/390.full.pdf

“Stereopsis” refers to the characteristically vivid qualitative impression of 3D structure that is observed when real (or simulated-3D) scenes are viewed binocularly. Stereopsis is associated with a compelling perception of solidity or 3-dimensionality, a clear sense of space between objects, and a phenomenal sense of realism. These visual characteristics are conventionally thought to be a result of the different views of an object afforded by binocular vision (disparity) or self-motion (motion parallax). However, such visual characteristics can also be obtained under controlled monocular viewing of pictures. One explanation for the impression of monocular stereopsis is based on the notion of cue-coherence/conflict (eg, Ames, 1925). When a picture is viewed with both eyes, binocular cues specify the flat picture surface and are in conflict with the 3-dimentionality implied by the pictorial cues. The elimination of these conflicting cues under monocular viewing putatively causes the enhancement of pictorial depth impression. The cue-coherence/conflict explanation also predicts a greater magnitude of perceived depth relief accompanying the greater impression of stereopsis. I will present an alternative theory that stereopsis is the conscious perception of the precision of the brains estimate of absolute (egocentrically scaled) depth. Both qualitative and quantitative empirical results are consistent with this theory. Specifically, they show that (i) the same qualitative characteristics of depth impression are reported under binocular viewing of real scenes, stereoscopic images, and controlled monocular viewing of pictures; (ii) the impression of stereopsis is measurable and its variation, under different viewing conditions is not consistent with a cue-conflict account; (iii) stereopsis can be elicited by manipulating egocentric distance cues when viewing pictures, without altering conflicting binocular cues; and (iv) under conditions that elicit stereopsis in pictures, perceived magnitude of depth is not greater than under normal binocular viewing of pictures.