Depth perception is the visual ability to perceive the world in three dimensions. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it Although any animal capable of moving around its environment must be able to sense the distance of objects in that environment, the term perception is reserved for humans, who are the only animals who can tell each other about their experiences of distances. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus " Qualia " (ˈkwɑːliə is "an unfamiliar term for something that could not be more familiar to each of us the ways things seem to us" ^[1]

Depth sensation is the ability to move accurately, or to respond consistently, based on the distances of objects in an environment. With this definition, every moving animal has some sensation of depth.

Depth perception arises from a variety of depth cues. These are typically classified into binocular cues that require input from both eyes and monocular cues that require the input from just one eye. Binocular vision is vision in which both Eyes are used together Monocular vision is vision in which each Eye is used separately ^[2] Binocular cues include stereopsis, yielding depth from binocular vision through exploitation of parallax. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Binocular vision is vision in which both Eyes are used together Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between Monocular cues include size: distant objects subtend smaller visual angles than near objects. The visual angle is the angle a viewed object subtends at the eye usually stated in degrees of arc ^[3]A third class of cues requires synthetic integration of binocular and monocular cues.

Contents 1 Monocular cues 2 Binocular and oculomotor cues 3 Inferred cues 4 Evolution 5 Depth perception in art 6 Disorders affecting depth perception 7 See also 8 References 9 Bibliography 10 External links 11 Notes

Monocular cues

• Motion parallax - When an observer moves, the apparent relative motion of several stationary objects against a background gives hints about their relative distance. Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between This effect can be seen clearly when driving in a car nearby things pass quickly, while far off objects appear stationary. Some animals that lack binocular vision due to wide placement of the eyes employ parallax more explicitly than humans for depth cueing (e. Binocular vision is vision in which both Eyes are used together g. some types of birds, which bob their heads to achieve motion parallax, and squirrels, which move in lines orthogonal to an object of interest to do the same). In Mathematics, two Vectors are orthogonal if they are Perpendicular, i ¹
• Depth from motion - A form of depth from motion, kinetic depth perception, is determined by dynamically changing object size. As objects in motion become smaller, they appear to recede into the distance or move farther away; objects in motion that appear to be getting larger seem to be coming closer. This a form of kinetic depth perception. Using kinetic depth perception enables the brain to calculate time to crash distance (TTC) at a particular velocity. When driving, we are constantly judging the dynamically changing headway (TTC) by kinetic depth perception.
• Color vision - Correct interpretation of color, and especially lighting cues, allows the beholder to determine the shape of objects, and thus their arrangement in space. Color vision is the capacity of an organism or machine to distinguish objects based on the Wavelengths (or frequencies) of the Light they reflect or emit The color of distant objects is also shifted towards the blue end of the spectrum. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. (e. g. distant mountains. ) Painters, notably Cezanne, employ "warm" pigments (red, yellow and orange) to bring features forward towards the viewer, and "cool" ones (blue, violet, and blue-green) to indicate the part of a form that curves away from the picture plane. A picture plane is the imaginary flat surface which is usually located between the Station point and the object being viewed and is ordinarily a vertical plane perpendicular
• Perspective - The property of parallel lines converging at infinity allows us to reconstruct the relative distance of two parts of an object, or of landscape features. Perspective, in context of vision and Visual perception, is the way in which objects appear to the Eye based on their spatial attributes or
• Relative size - An automobile that is close to us looks larger than one that is far away; our visual system exploits the relative size of similar (or familiar) objects to judge distance.
• Aerial perspective - Due to light scattering by the atmosphere, objects that are a great distance away have lower luminance contrast and lower color saturation. Aerial perspective or atmospheric perspective is the effect on the appearance of an object by the Atmosphere between it and a viewer (or the technique of depicting Contrast is the difference in visual properties that makes an object (or its representation in an image distinguishable from other objects and the background In Colorimetry and Color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity In computer graphics, this is called "distance fog". Computer graphics are Graphics created by Computers and more generally the Representation and Manipulation of Pictorial Data Distance fog is a technique used in 3D computer graphics to enhance the perception of distance by simulating Fog. The foreground has high contrast; the background has low contrast. Objects differing only in their contrast with a background appear to be at different depths. ^[4]
• Depth from Focus - The lens of the eye can change its shape to bring objects at different distances into focus. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Knowing at what distance the lens is focused when viewing an object means knowing the approximate distance to that object.
• Occlusion (also referred to as interposition) - Occlusion (blocking the sight) of objects by others is also a clue which provides information about relative distance. However, this information only allows the observer to create a "ranking" of relative nearness.
• Peripheral vision - At the outer extremes of the visual field, parallel lines become curved, as in a photo taken through a fish-eye lens. Peripheral vision is a part of vision that occurs outside the very center of gaze The term visual field is sometimes used as a Synonym to Field of view, though they do not designate the same thing In Photography, a fisheye lens is a Wide-angle lens that takes in an extremely wide hemispherical image This effect, although it's usually eliminated from both art and photos by the cropping or framing of a picture, greatly enhances the viewer's sense of being positioned within a real, three dimensional space. (Classical perspective has no use for this so-called "distortion", although in fact the "distortions" strictly obey optical laws and provide perfectly valid visual information, just as classical perspective does for the part of the field of vision that falls within its frame. )
• Texture gradient - Suppose you are standing on a gravel road. The gravel near you can be clearly seen in terms of shape, size and colour. As your vision shifts towards the distant road the texture cannot be clearly differentiated.

Binocular and oculomotor cues

• Stereopsis or Retinal disparity - Animals that have their eyes placed frontally can also use information derived from the different projection of objects onto each retina to judge depth. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain The vertebrate retina is a light sensitive part inside the inner layer of the Eye. By using two images of the same scene obtained from slightly different angles, it is possible to triangulate the distance to an object with a high degree of accuracy. In Trigonometry and Geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either If an object is far away, the disparity of that image falling on both retinas will be small. If the object is close or near, the disparity will be large. It is stereopsis that tricks people into thinking they perceive depth when viewing Magic Eyes, Autostereograms, 3D movies and stereoscopic photos. Magic Eye is a series of books published by NE Thing Enterprises (Renamed in 1996 to Magic Eye Inc An autostereogram is a single-image Stereogram (SIS designed to create the visual illusion of a three- Dimensional (3D scene from a two-dimensional Stereoscopy, stereoscopic imaging or 3-D (three-dimensional imaging is any technique capable of recording three-dimensional visual
• Accommodation - This is an oculomotor cue for depth perception. Accommodation is the process by which the:eye increases Optical power to maintain a clear image ( focus) on an object as it draws near the eye When we try to focus on far away objects, the ciliary muscles stretches the eye lens, making it thinner. The Ciliary Muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances The kinesthetic sensations of the contracting and relaxing ciliary muscles (intraocular muscles) is sent to the visual cortex where it is used for interpreting distance/depth.
• Convergence - This is also an oculomotor cue for distance/depth perception. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain By virtue of stereopsis the two eye balls focus on the same object. In doing so they converge. The convergence will stretch the extraocular muscles. The extraocular muscles are the six Muscles that control the movements of the (human eye. Kinesthetic sensations from these extraocular muscles also help in depth/distance perception. The angle of convergence is larger when the eye is fixating on far away objects.

Of these various cues, only convergence, focus and familiar size provide absolute distance information. All other cues are relative (ie, they can only be used to tell which objects are closer relative to others). Stereopsis is merely relative because a greater or lesser disparity for nearby objects could either mean that those objects differ more or less substantially in relative depth or that the foveated object is nearer or further away (the further away a scene is, the smaller is the retinal disparity indicating the same depth difference).

Binocular cues can be directly perceived far more easily and eloquently than they can be described in words. Binocular vision is vision in which both Eyes are used together Try looking around at the room you're in with just one eye open. Then look with just the other eye; the difference you notice will probably be negligible. After that, open both eyes, and see what happens.

Inferred cues

It would be over-simplification to ignore the mental processes at work as a person sees with two normal eyes. The fact that binocular stereopsis is occurring, enables the brain to infer and perceive certain additional depth in the form of a mental construct. Closing one eye shuts down this stereo construct. Recent work toward improving digital display of stereoscopic images has re-vitalized the field, as practical applications often do. Those working in the field have identified several processes of interpolation, previously ignored or considered irrelevant. These provide a linkage in the mental construct of objects visible to only one eye, while viewing with both eyes in a forward direction. Recent literature has addressed the relationship between the stereo viewing area and the periphery. Recent analysis has demonstrated that objects just outside the angle of double visual coverage, are, in fact, integrated by the mind into the stereo construct by a process of inference. Briefly stated, " all objects, in even moderate focus, within the central viewing field of a single eye, are, an important part of the stereo construct". Their physical position is noted, and SEEN very accurately in the mental stereo visualization process, though visible to only one of the 2 eyes in use.

Evolution

Most open-plains herbivores, especially hoofed grazers, lack binocular vision because they have their eyes on the sides of the head, providing a panoramic, almost 360º, view of the horizon - enabling them to notice the approach of predators from almost any direction. Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell However most predators have both eyes looking forwards, allowing binocular depth perception and helping them to judge distances when they pounce or swoop down onto their prey. Animals that spend a lot of time in trees take advantage of binocular vision in order to accurately judge distances when rapidly moving from branch to branch.

Matt Cartmill, a physical anthropologist & anatomist at Duke University Medical Center, has criticized this theory, citing other arboreal species which lack stereoscopic vision, such as squirrels and certain birds. Duke University is a private Research University located in Durham, North Carolina, United States. A squirrel is one of the many small or medium-sized Rodents in the family Sciuridae. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Instead, he proposes a "Visual Predation Hypothesis," which argues that ancestral primates were insectivorous predators resembling tarsiers, subject to the same selection pressure for frontal vision as other predatory species. Tarsiers are Prosimian Primates of the genus Tarsius, a Monotypic genus in the family Tarsiidae, which is itself the He also uses this hypothesis to account for the specialization of primate hands, which he suggests became adapted for grasping prey, somewhat like the way raptors employ their talons. Birds of prey are Birds that hunt for food primarily on the wing using their keen senses especially vision A claw is a curved pointed appendage found at the end of a toe or finger in most Mammals, Birds, and some Reptiles. link to PDF

Depth perception in art

Photographs capturing perspective are two-dimensional images that often illustrate the illusion of depth. A photograph (often shortened to photo) is an Image created by Light falling on a light-sensitive surface usually Photographic film or an electronic (This differs from a painting, which may use the physical matter of the paint to create a real presence of convex forms and spacial depth. Painting (pān'tīng in Art, is the practice of applying Color to a Surface (support base such as e ) Stereoscopes and Viewmasters, as well as 3-D movies, employ binocular vision by forcing the viewer to see two images created from slightly different positions (points of view). Stereoscopy, stereoscopic imaging or 3-D (three-dimensional imaging is any technique capable of recording three-dimensional visual View-Master ® is a trademark for a device for viewing seven 3-D images (also known as stereo images on a paper disk Three-dimensional space is a geometric model of the physical Universe in which we live By contrast, a telephoto lens — used in televised sports, for example, to zero in on members of a stadium audience — has the opposite effect. The viewer sees the size and detail of the scene as if it were close enough to touch, but the camera's perspective is still derived from its actual position a hundred meters away, so background faces and objects appear about the same size as those in the foreground.

Trained artists are keenly aware of the various methods for indicating spacial depth (color shading, distance fog, perspective and relative size), and take advantage of them to make their works appear "real". Distance fog is a technique used in 3D computer graphics to enhance the perception of distance by simulating Fog. Perspective, in context of vision and Visual perception, is the way in which objects appear to the Eye based on their spatial attributes or The viewer feels it would be possible to reach in and grab the nose of a Rembrandt portrait or an apple in a Cezanne still life — or step inside a landscape and walk around among its trees and rocks. Rembrandt Harmenszoon van Rijn (July 15 1606 &ndash October 4 1669 was a Dutch painter and etcher.

Cubism was based on the idea of incorporating multiple points of view in a painted image, as if to simulate the visual experience of being physically in the presence of the subject, and seeing it from different angles. Cubism was a 20th century Avant-garde Art movement, pioneered by Pablo Picasso and Georges Braque, that revolutionized European The radical "High Cubist" experiments of Braque and Picasso circa 1909 are interesting but more bizarre than convincing in visual terms. Georges Braque ( May 13, 1882 &ndash August 31, 1963) was a major 20th century French painter and sculptor Pablo Diego José Francisco de Paula Juan Nepomuceno María de los Remedios Cipriano de la Santísima Trinidad Martyr Patricio Clito Ruíz y Picasso (October 25 1881 &ndash April 8 1973 Year 1909 ( MCMIX) was a Common year starting on Friday (link will display full calendar of the Gregorian calendar (or a Common year starting Slightly later paintings by their followers, such as Robert Delaunay's views of the Eiffel Tower, or John Marin's Manhattan cityscapes, borrow the explosive angularity of Cubism to exaggerate the traditional illusion of three-dimensional space. Robert Delaunay ( April 12 1885 — October 25 1941) was a French artist who used orphism, similar to abstraction The Eiffel Tower (Tour Eiffel /tuʀ ɛfɛl/ is an Iron Tower built John Marin ( December 23, 1870 - October 2, 1953) born in Rutherford New Jersey, was an early American modernist artist A century after the Cubist adventure, the verdict of art history is that the most subtle and successful use of multiple points of view can be found in the pioneering late work of Cezanne, which both anticipated and inspired the first actual Cubists. Cezanne's landscapes and still lifes powerfully suggest the artist's own highly-developed depth perception. At the same time, like the other Post-Impressionists, Cezanne had learned from Japanese prints the significance of respecting the flat (two-dimensional) rectangle of the picture itself; Hokusai and Hiroshige ignored or even reversed linear perspective and thereby remind the viewer that a the picture can only be "true" when it acknowledges the truth of its own flat surface. Post-Impressionism is the term coined by the British artist and Art critic Roger Fry in 1910 to describe the development of French art since Manet. was a Japanese Artist, Ukiyo-e painter and Printmaker of the Edo period. was a Japanese Ukiyo-e artist and one of the last great artists in that tradition By contrast, European "academic" painting was devoted to a sort of Big Lie that the surface of the canvas is only an enchanted doorway to a "real" scene unfolding beyond, and that the artist's main task is to distract the viewer from any disenchanting awareness of the presence of the painted canvas. The Big Lie is a Propaganda technique It was defined by Adolf Hitler in his 1925 autobiography Mein Kampf as a lie so "colossal" that Cubism, and indeed most of modern art is a struggle to confront, if not resolve, the paradox of suggesting spacial depth on a flat surface, and explore that inherent contradiction through innovative ways of seeing, as well as new methods of drawing and painting. Cubism was a 20th century Avant-garde Art movement, pioneered by Pablo Picasso and Georges Braque, that revolutionized European History of Modern art Roots in the 19th century Although modern Sculpture and Architecture are reckoned to have emerged at the end of the nineteenth

Disorders affecting depth perception

• Ocular conditions such as amblyopia, optic nerve hypoplasia, and strabismus may reduce the perception of depth. Amblyopia, otherwise known as lazy eye, is a disorder of the Visual system that is characterized by poor or indistinct vision in an eye that Optic nerve hypoplasia is a medical condition that results in underdevelopment of the Optic nerves Development of the optic nerve During the second month of Strabismus (from Greek: στραβισμός strabismos, from στραβίζειν strabizein "to squint" from στραβός strabos
• Since (by definition), binocular depth perception requires two functioning eyes, a person with only one functioning eye has none.

It is typically felt that Depth perception must be learned in infancy using an unconscious inference. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also

See also

• Space perception (Spatial perception)
• Visual perception
• Senses
• Optical illusion
• Retina
• Perception
• Eye

References

Bibliography

• Palmer, S. E. (1999) Vision science: Photons to phenomenology. Cambridge, MA: Bradford Books/MIT Press.
• Pinker, S. (1997). Steven Arthur Pinker (born September 18 1954 is a prominent Canadian - American experimental psychologist, cognitive scientist, and author Year 1997 ( MCMXCVII) was a Common year starting on Wednesday (link will display full 1997 Gregorian calendar The Mind’s Eye. In How the Mind Works (pp. How the Mind Works (ISBN 0-393-31848-6 is a book by American cognitive scientist Steven Pinker, published in 1997. 211–233) ISBN 0-393-31848-6
• Purves D, Lotto B (2003) Why We See What We Do: An Empirical Theory of Vision. Sunderland, MA: Sinauer Associates.
• Scott B. Steinman, Barbara A. Steinman and Ralph Philip Garzia. (2000). Foundations of Binocular Vision: A Clinical perspective. McGraw-Hill Medical. ISBN 0-8385-2670-5

External links

• VisualFunHouse Optical Illusions Optical Illusions based on perception
• A fascinating experiment in depth perception

• Adults and Children Gain Depth Perception

• What is Binocular (Two-eyed) Depth Perception?

• Why Some People Can't See in Depth

• Dale Purves Lab [1]

• Depth perception and sensory substitution |[2]

Notes

¹ The term 'parallax vision' is often used as a synonym for binocular vision, and should not be confused with motion parallax. The former allows far more accurate gauging of depth than the latter.

---

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic