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Binocular vision has further advantages aside from stereopsis, in particular the enhancement of vision quality through binocular summation; persons with strabismus (even those who have no double vision) have lower scores of binocular summation, and this appears to incite persons with strabismus to close one eye in visually demanding situations.
Stereoscopy creates the impression of three-dimensional depth from a pair of two-dimensional images. [5] Human vision, including the perception of depth, is a complex process, which only begins with the acquisition of visual information taken in through the eyes; much processing ensues within the brain, as it strives to make sense of the raw information.
Stereoblindness (also stereo blindness) is the inability to see in 3D using stereopsis, or stereo vision, resulting in an inability to perceive stereoscopic depth by combining and comparing images from the two eyes. Individuals with only one functioning eye have this condition by definition since the visual input of the second eye does not exist.
Disadvantages of stereo cards, slides or any other hard copy or print are that the two images are likely to receive differing wear, scratches and other decay. This results in stereo artifacts when the images are viewed. These artifacts compete in the mind resulting in a distraction from the 3D effect, eye strain and headaches.
Wiggle stereoscopy offers the advantages that no glasses or special hardware is required; most people can perceive the effect more quickly than when using cross-eyed and parallel viewing techniques. Furthermore, it offers stereo-like depth to people with limited or no vision in one eye.
In 1833, an English scientist Charles Wheatstone discovered stereopsis, the component of depth perception that arises due to binocular disparity.Binocular disparity comes from the human eyes having a distance between them: A 3D scene viewed through the left eye creates a slightly different image than the same scene viewed with the right eye, with the head kept in the same position.
Thus, each eye has a slightly different view of the world around. This can be easily seen when alternately closing one eye while looking at a vertical edge. The binocular disparity can be observed from apparent horizontal shift of the vertical edge between both views. At any given moment, the line of sight of the two eyes meet at a point in space.
The random dot stereogram provided insight on how stereo vision is processed by the human brain. According to Ralph Siegel, Julesz had "unambiguously demonstrated that stereoscopic depth could be computed in the absence of any identifiable objects, in the absence of any perspective, in the absence of any cues available to either eye alone." [1]