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20-September-2008 09:29:05 - Visual perception Redirected from Eyesight Psychology Greek letter 'psi' Portal History Areas RESEARCH Abnormal Biological Cognitive Developmental Emotion Experimental Evolutionary Mathematical Neuropsychology Personality Positive Psychophysics Social Transpersonal APPLIED Clinical Educational Forensic Health Industrial Organizational School Sport LISTS Publications Topics Therapies view talk 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. Contents 1 Visual system 2 Study of visual perception 2.1 Early studies on visual perception 2.2 Unconscious inference 2.3 Gestalt theory 2.4 Analysis of Eye-Movements 3 The cognitive and computational approaches 4 See also 4.1 Disorders/Dysfunctions 4.2 Related Disciplines 5 References 6 External links Visual system Main article: 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 The visual dorsal stream green and ventral stream purple are shown. Much of the human cerebral cortex is involved in vision. The visual dorsal stream green and ventral stream purple are shown. Much of the human cerebral cortex is involved in vision. There were two major ancient Greek 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. This theory was championed by scholars like Euclid and Ptolemy and their followers. 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 light did not play any role in this theory and it remained only a speculation lacking any experimental foundation. Leonardo DaVinci: The eye has a central line and everything that reaches the eye through this central line can be seen distinctly. Leonardo DaVinci: The eye has a central line and everything that reaches the eye through this central line can be seen distinctly. Ibn al-Haytham also known as Alhacen or Alhazen, the father of optics, was the first to reconcile both schools of thought in his influential Book of Optics 1021. He argued that vision is due to light from objects entering the eye, and he developed an early scientific method emphasizing extensive experimentation in order to prove this. He pioneered the scientific study of the psychology of visual perception, 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. For a little child however ugly a mother is , it does not matter to it as the definition of beauty is not that well defined for the little child as it is with any other adult . 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.This can be easily related to the famous saying Beauty lies in the eye of the beholder. That is a flower which may appear beautiful for one adult, may not appeal that much to the other.1 Al-Haytham carried out many investigations and experiments on visual perception, extended the work of Ptolemy on binocular vision, and commented on the anatomical works of Galen.23 Leonardo DaVinci,1452-1519, was the first to recognize the special optical qualities of the eye. He wrote The function of the human eye, ... was described by a large number of authors in a certain way. But I found it to be completely different. His main experimental finding was that there is only a distinct and clear vision at the line of sight, the optical line that ends at the fovea. Although he did not use these words literally he actually is the father of the modern distinction between foveal vision and peripheral vision. Unconscious inference Hermann von Helmholtz is often cred with the first study of visual perception in modern times. Helmholtz examined the human eye and concluded that it was, optically, rather poor. The poor quality information gathered via the eye seemed to him to make vision impossible. He therefore concluded that vision could only be the result of some form of unconscious inferences: a matter of making assumptions and conclusions from incomplete data, based on previous experiences. Inference requires prior experience of the world: examples of well-known assumptions - based on visual experience - are: light comes from above objects are normally not viewed from below faces are seen and recognized upright 4 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. Another type of the unconscious inference hypothesis based on probabilities 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.56 Gestalt theory Main article: Gestalt psychology 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. One of the reasons why Gestalt laws have often been disregarded by cognitive psychologists is a lack of understanding the nature of peripheral vision. It is true that visual perception only takes place during fixations. But during fixations not only the high definition foveal vision at the fixation point, but also the peripheral vision is functioning. Due to its lack of acuity and relative independence of eye position due to its extreme wide angle it is an image compressing system. While foveal vision is very slow only 3 to 4 high quality telescopic images per second, peripheral vision is very inaccurate but also very fast up to 90 images per second - permitting to see the flicker of the European 50Hz TV images. Elements of the visual field are thus grouped automatically according to laws like Proximity, Similarity, Closure, Symmetry, Common fate and Continuity. Analysis of Eye-Movements see text see text During the 1960s the technical development permitted the continuous registration of eye movements during reading7 in picture viewing 8 and later in visual problem solving 9 and when headset-cameras became available, also during driving.10 The picture to the left shows what may happen during the first two seconds of visual inspection. While the background is out of focus, representing the peripheral vision, the first eye movement goes to the boots of the man just because they are very near the starting fixation and have a reasonable contrast. The following fixations jump from face to face. They might even permit comparisons between faces. It may be concluded that the icon face is a very attractive search icon within the peripheral field of vision. The foveal vision adds detailed information to the peripheral first impression. 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. More recently, the computational models of visual perception have been developed for Virtual Reality systems - these are closer to real life situation as they account for motion and activities which populate the real world.11 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? 12 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 level attempts 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.13 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 Color vision Motion perception Depth perception Visual illusion Disorders/Dysfunctions Achromatopsia Color blindness Scotopic Sensitivity Syndrome Related Disciplines Psychophysics Neuroscience Cognitive Science Optometry Ophthalmology References ^ Bradley Steffens 2006. Ibn al-Haytham: First Scientist, Chapter 5. Morgan Reynolds Publishing. ISBN 1599350246. ^ Howard, I 1996. Alhazen's neglected discoveries of visual phenomena. Perception 25: 1203-1217. doi:10.1068/p251203. ^ Omar Khaleefa 1999. Who Is the Founder of Psychophysics and Experimental Psychology?. American Journal of Islamic Social Sciences 16 2. ^ Hans-Werner Hunziker, 2006 Im Auge des Lesers: foveale und periphere Wahrnehmung - vom Buchstabieren zur Lesefreude In the eye of the reader: foveal and peripheral perception - from letter recognition to the joy of reading Transmedia Stäubli Verlag Zürich 2006 ISBN 978-3-7266-0068-6 ^ Mamassian, Landy Maloney 2002 ^ A Primer on Probabilistic Approaches to Visual Perception ^ TAYLOR, ST.: Eye Movements in Reading: Facts and Fallacies. American Educational Research Association, 2 4, 1965, 187-202. ^ Yarbus, A. L. 1967. Eye movements and vision, Plenum Press, New York ^ Hunziker, H. W. 1970. Visuelle Informationsaufnahme und Intelligenz: Eine Untersuchung über die Augenfixationen beim Problemlösen. Schweizerische Zeitschrift für Psychologie und ihre Anwendungen, 1970, 29, Nr 1/2 ^ Cohen, A. S. 1983. Informationsaufnahme beim Befahren von Kurven, Psychologie für die Praxis 2/83, Bulletin der Schweizerischen Stiftung für Angewandte Psychologie ^ A.K.Beeharee - http://www.cs.ucl.ac.uk/staff/A.Beeharee/research.htm ^ Bruce, V., Green, P. Georgeson, M. 1996. Visual perception: Physiology, psychology and ecology, 3rd, LEA, 110. ^ Marr, D 1982. Vision: A Computational Investigation into the Human Representation and Processing of Visual Information. MIT Press. External links Empiristic theory of visual gestalt perception Visual Perception 3 - Cultural and Environmental Factors Gestalt Laws Summary of Kosslyn et al.'s theory of high-level vision The Organization of the Retina and Visual System Dr Trippy's Sensorium A website dedicated to the study of the human sensorium and organisational behaviour Effect of Detail on Visual Perception by Jon McLoone, The Wolfram Demonstrations Project. v d e Nervous system: Sensory systems / senses Special senses Visual system - sight Auditory system - hearing Chemoreception Olfactory system - smell Gustatory system - taste Touch Pain Heat Balance Mechanoreception Pressure, vibration, proprioception Other Sensory receptor v d e Visualization Fields of visualization Creative visualization Chemical imaging Crime mapping Data visualization Educational visualization Flow visualization Geovisualization Information visualization Medical imaging Music visualization Product visualization Scientific visualization Software visualization Volume visualization Image types Chart Computer graphics Diagram Graph of a function Ideogram Illustration Information graphics Interactive visualization Map Photograph Pictogram Statistical graphics Table Technical drawing Experts Jacques Bertin Stuart Card Thomas A. DeFanti Michael Friendly Nigel Holmes Jock D. Mackinlay Michael Maltz Bruce H. McCormick Charles Joseph Minard Otto Neurath William Playfair Clifford A. Pickover Lawrence J. Rosenblum Adolphe Quetelet George G. Robertson Ben Shneiderman Edward Tufte Related fields Cartography Computer graphics Graph drawing Graphic design Imaging science Information science Mental visualisation Neuroimaging Spatial analysis Visual analytics Visual communication Visual perception Retrieved from http://en..org/wiki/Visual_perception Categories: Neuroscience | Visual perception | Vision | Perception Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages БългарÑ?ки Català Česky Dansk Deutsch Español Euskara Français í•œêµì–´ Hrvatski മലയാളം Nederlands 日本語 Polski Português РуÑ?Ñ?кий SlovenÄ?ina SlovenÅ¡Ä?ina Suomi УкраїнÑ?ька ייִדיש ä¸æ–‡ This page was last modified on 11 August 2008, at 19:25
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