Stereopsis

Stereopsis (from Ancient Greek στερεός (stereós) 'solid' and ὄψις (ópsis) 'appearance, sight') is the component of depth perception retrieved through binocular vision.

[1] The perception of depth and three-dimensional structure is, however, possible with information visible from one eye alone, such as differences in object size and motion parallax (differences in the image of an object over time with observer movement),[2] though the impression of depth in these cases is often not as vivid as that obtained from binocular disparities.

In particular, patients who have comparatively lower visual acuity tend to need relatively larger spatial frequencies to be present in the input images, else they cannot achieve stereopsis.

[16] The coarse stereoscopic system seems to be able to provide residual binocular depth information in some individuals who lack fine stereopsis.

[17] Individuals have been found to integrate the various stimuli, for example stereoscopic cues and motion occlusion, in different ways.

[23] Stereopsis has a positive impact on exercising practical tasks such as needle-threading, ball-catching (especially in fast ball games[24]), pouring liquids, and others.

While some of these tasks may profit from compensation of the visual system by means of other depth cues, there are some roles for which stereopsis is imperative.

As to car driving, a study found a positive impact of stereopsis in specific situations at intermediate distances only;[27] furthermore, a study on elderly persons found that glare, visual field loss, and useful field of view were significant predictors of crash involvement, whereas the elderly persons' values of visual acuity, contrast sensitivity, and stereoacuity were not associated with crashes.

[29][30] It has long been recognized that full binocular vision, including stereopsis, is an important factor in the stabilization of post-surgical outcome of strabismus corrections.

Many persons lacking stereopsis have (or have had) visible strabismus, which is known to have a potential socioeconomic impact on children and adults.

In particular, both large-angle and small-angle strabismus can negatively affect self-esteem, as it interferes with normal eye contact, often causing embarrassment, anger, and feelings of awkwardness.

It has been noted that with the growing introduction of 3D display technology in entertainment and in medical and scientific imaging, high quality binocular vision including stereopsis may become a key capability for success in modern society.

[32] Nonetheless, there are indications that the lack of stereo vision may lead persons to compensate by other means: in particular, stereo blindness may give people an advantage when depicting a scene using monocular depth cues of all kinds, and among artists there appear to be a disproportionately high number of persons lacking stereopsis.

Stereopsis was first explained by Charles Wheatstone in 1838: "… the mind perceives an object of three dimensions by means of the two dissimilar pictures projected by it on the two retinæ …".

Leonardo da Vinci had also realized that objects at different distances from the eyes project images in the two eyes that differ in their horizontal positions, but had concluded only that this made it impossible for a painter to portray a realistic depiction of the depth in a scene from a single canvas.

Researchers included Peter Ludvig Panum, Ewald Hering, Adelbert Ames Jr., and Kenneth N. Ogle.

Nevertheless, when the two half images were viewed one to each eye, the square area was almost immediately visible by being closer or farther than the background.

Our visual systems clearly solve the correspondence problem, in that we see the intended depth instead of a fog of false matches.

Also in the 1960s, Horace Barlow, Colin Blakemore, and Jack Pettigrew found neurons in the cat visual cortex that had their receptive fields in different horizontal positions in the two eyes.

Their findings were disputed by David Hubel and Torsten Wiesel, although they eventually conceded when they found similar neurons in the monkey visual cortex.

[39] In the 1980s, Gian Poggio and others found neurons in V2 of the monkey brain that responded to the depth of random-dot stereograms.

In 1939 the concept of the prism stereoscope was reworked into the technologically more complex View-Master, which remains in production today.

Stereopsis appears to be processed in the visual cortex of mammals in binocular cells having receptive fields in different horizontal positions in the two eyes.

This effect, first demonstrated on a random dot stereogram, was initially interpreted as an extension of Panum's fusional area.

[45] Later it was shown that the hysteresis effect reaches far beyond Panum's fusional area,[46] and that stereoscopic depth can be perceived in random-line stereograms despite the presence of cyclodisparities of about 15 deg, and this has been interpreted as stereopsis with diplopia.

attempts have been made to reproduce human stereo vision on rapidly changing computer displays, and toward this end numerous patents relating to 3D television and cinema have been filed in the USPTO.

tends to employ Fresnel lenses or plates over the liquid crystal displays, freeing the user from the need to put on special glasses or goggles.

Random-dot stereopsis tests use pictures of stereo figures that are embedded in a background of random dots.

[49] The ability of stereopsis can be tested by, for example, the Lang-Stereotest, which consists of a random-dot stereogram upon which a series of parallel strips of cylindrical lenses are imprinted in certain shapes, which separate the views seen by each eye in these areas,[50] similarly to a hologram.