Visual perception

(Redirected from Vision (sense))
Jump to navigation Jump to search

WikiDoc Resources for Visual perception

Articles

Most recent articles on Visual perception

Most cited articles on Visual perception

Review articles on Visual perception

Articles on Visual perception in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Visual perception

Images of Visual perception

Photos of Visual perception

Podcasts & MP3s on Visual perception

Videos on Visual perception

Evidence Based Medicine

Cochrane Collaboration on Visual perception

Bandolier on Visual perception

TRIP on Visual perception

Clinical Trials

Ongoing Trials on Visual perception at Clinical Trials.gov

Trial results on Visual perception

Clinical Trials on Visual perception at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Visual perception

NICE Guidance on Visual perception

NHS PRODIGY Guidance

FDA on Visual perception

CDC on Visual perception

Books

Books on Visual perception

News

Visual perception in the news

Be alerted to news on Visual perception

News trends on Visual perception

Commentary

Blogs on Visual perception

Definitions

Definitions of Visual perception

Patient Resources / Community

Patient resources on Visual perception

Discussion groups on Visual perception

Patient Handouts on Visual perception

Directions to Hospitals Treating Visual perception

Risk calculators and risk factors for Visual perception

Healthcare Provider Resources

Symptoms of Visual perception

Causes & Risk Factors for Visual perception

Diagnostic studies for Visual perception

Treatment of Visual perception

Continuing Medical Education (CME)

CME Programs on Visual perception

International

Visual perception en Espanol

Visual perception en Francais

Business

Visual perception in the Marketplace

Patents on Visual perception

Experimental / Informatics

List of terms related to Visual perception

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Overview

In psychology, visual perception is the ability to interpret information from visible light reaching the eyes. The resulting perception is also known as eyesight, sight or vision. The various physiological components involved in vision are referred to collectively as the visual system.

Visual system

The visual system in humans allows individuals to assimilate information from the environment. The act of seeing starts when the lens of the eye focuses an image of its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of patterns of light into neuronal signals. The lens of the eye focuses light on the photoreceptive cells of the retina, which detect the photons of light and respond by producing neural impulses. These signals are processed in a hierarchical fashion by different parts of the brain, from the retina to the lateral geniculate nucleus, to the primary and secondary visual cortex of the brain.

Study of visual perception

The major problem in visual perception is that what people see is not simply a translation of retinal stimuli (i.e., the image on the retina). Thus people interested in perception have long struggled to explain what visual processing does to create what we actually see.

Early studies on visual perception

There were two major Grecian schools, providing a primitive explanation of how vision is carried out in the body.

The first was the "emission theory" which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If we saw an object directly it was by 'means of rays' coming out of the eyes and again falling on the object. A refracted image was, however, seen by 'means of rays' as well, which came out of the eyes, traversed through the air, and after refraction, fell on the visible object which was sighted as the result of the movement of the rays from the eye. Although this theory was championed by scholars like Euclid and Ptolemy and their followers, it was believed by Descartes.

The second school advocated the so called the 'intromission' approach which sees vision as coming from something entering the eyes representative of the object. With its main propagators Aristotle, Galen and their followers, this theory seems to have touched a little sense on what really vision is, but remained only a speculation lacking any experimental foundation.

Ibn al-Haytham (Alhacen), the "father of optics", pioneered the scientific study of the psychology of visual perception in his influential Book of Optics in the 1000s, being the first scientist to argue that vision occurs in the brain, rather than the eyes. He pointed out that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. He explained possible errors in vision in detail, and as an example, describes how a small child with less experience may have more difficulty interpreting what he/she sees. He also gives an example of an adult that can make mistakes in vision because of how one's experience suggests that he/she is seeing one thing, when he/she is really seeing something else.[1]

Ibn al-Haytham's investigations and experiments on visual perception also included sensation, variations in sensitivity, sensation of touch, perception of colours, perception of darkness, the psychological explanation of the moon illusion, and binocular vision.[2][3]

Unconscious inference

Hermann von Helmholtz is often credited with the first study of visual perception in modern times. Helmholtz held vision to be a form of unconscious inference: vision is a matter of deriving a probable interpretation for incomplete data.

Inference requires prior assumptions about the world: two well-known assumptions that we make in processing visual information are that light comes from above, and that objects are viewed from above and not below. The study of visual illusions (cases when the inference process goes wrong) has yielded much insight into what sort of assumptions the visual system makes.

The unconscious inference hypothesis has recently been revived in so-called Bayesian studies of visual perception. Proponents of this approach consider that the visual system performs some form of Bayesian inference to derive a perception from sensory data. Models based on this idea have been used to describe various visual subsystems, such as the perception of motion or the perception of depth.[4][5]

Gestalt theory

Gestalt psychologists working primarily in the 1930s and 1940s raised many of the research questions that are studied by vision scientists today.

The Gestalt Laws of Organization have guided the study of how people perceive visual components as organized patterns or wholes, instead of many different parts. Gestalt is a German word that translates to "configuration or pattern". According to this theory, there are six main factors that determine how we group things according to visual perception: Proximity, Similarity, Closure, Symmetry, Common fate and Continuity.

The cognitive and computational approaches

The major problem with the Gestalt laws (and the Gestalt school generally) is that they are descriptive not explanatory. For example, one cannot explain how humans see continuous contours by simply stating that the brain "prefers good continuity". Computational models of vision have had more success in explaining visual phenomena and have largely superseded Gestalt theory. Regarding Gestalt influence on the study of visual perception, Bruce, Green & Georgeson conclude:

"The physiological theory of the Gestaltists has fallen by the wayside, leaving us with a set of descriptive principles, but without a model of perceptual processing. Indeed, some of their "laws" of perceptual organisation today sound vague and inadequate. What is meant by a "good" or "simple" shape, for example?" [6]

In the 1980's David Marr developed a multi-level theory of vision, which analysed the process of vision at different levels of abstraction. In order to focus on the understanding of specific problems in vision, he identified (with Tomaso Poggio) three levels of analysis: the computational, algorithmic and implementational levels.

The computational level addresses, at a high level of abstraction, the problems that the visual system must overcome. The algorithmic level attempts to identify the strategy that may be used to solve these problems. Finally, the implementational levelattempts to explain how these problems are overcome in terms of the actual neural activity necessary.

Marr suggested that it is possible to investigate vision at any of these levels independently. Marr described vision as proceeding from a two-dimensional visual array (on the retina) to a three-dimensional description of the world as output. His stages of vision include:

  • a 2D or primal sketch of the scene, based on feature extraction of fundamental components of the scene, including edges, regions, etc. Note the similarity in concept to a pencil sketch drawn quickly by an artist as an impression.
  • a 2-1/2 D sketch of the scene, where textures are acknowledged, etc. Note the similarity in concept to the stage in drawing where an artist highlights or shades areas of a scene, to provide depth.
  • a 3 D model, where the scene is visualized in a continuous, 3-dimensional map.[7]

Marr unfortunately died of leukemia in Cambridge, Massachusetts at the age of 35, but his theory provides an important framework for the continued investigation of vision.

See also

Disorders/Dysfunctions

Related Disciplines

References

  1. Bradley Steffens (2006). Ibn al-Haytham: First Scientist, Chapter 5. Morgan Reynolds Publishing. ISBN 1599350246.
  2. Howard, I (1996). "Alhazen's neglected discoveries of visual phenomena". Perception. 25: 1203–1217.
  3. Omar Khaleefa (1999). "Who Is the Founder of Psychophysics and Experimental Psychology?". American Journal of Islamic Social Sciences. 16 (2).
  4. Mamassian, Landy & Maloney (2002)
  5. A Primer on Probabilistic Approaches to Visual Perception
  6. Bruce, V., Green, P. & Georgeson, M. (1996). Visual perception: Physiology, psychology and ecology (3rd ed.). LEA. p. 110.
  7. Marr, D (1982). Vision: A Computational Investigation into the Human Representation and Processing of Visual Information. MIT Press.

External links

Template:Sensory system Template:Psychology


Template:WH Template:WikiDoc Sources