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Visual perception is the ability to interpret the surrounding
environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...
through
photopic vision Photopic vision is the vision of the human eye, eye under well-lit conditions (luminance level 10 to 108 Candela per square metre, cd/m2). In humans and many other animals, photopic vision allows color vision, color perception, mediated by cone cel ...
(daytime vision),
color vision Color vision, a feature of visual perception Visual perception is the ability to interpret the surrounding environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally ...

color vision
,
scotopic vision Scotopic vision is the vision of the eye under low-light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light is usual ...
(night vision), and
mesopic vision Mesopic vision is a combination of photopic vision Photopic vision is the vision of the human eye, eye under well-lit conditions (luminance level 10 to 108 Candela per square metre, cd/m2). In humans and many other animals, photopic vision allows c ...
(twilight vision), using light in the
visible spectrum The visible spectrum is the portion of the that is to the . in this range of s is called ' or simply . A typical will respond to wavelengths from about 380 to about 750 . In terms of frequency, this corresponds to a band in the vicinity of ...
reflected by objects in the environment. This is different from
visual acuity Visual acuity (VA) commonly refers to the clarity of vision Vision or The Vision may refer to: Perception Optical perception * Visual perception Visual perception is the ability to interpret the surrounding environment (biophysical), ...
, which refers to how clearly a person sees (for example "20/20 vision"). A person can have problems with visual perceptual processing even if they have 20/20 vision. The resulting
perception Perception (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the powe ...

perception
is also known as vision, sight, or eyesight (adjectives ''visual'', ''optical'', and ''ocular'', respectively). The various physiological components involved in vision are referred to collectively as the
visual system The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined b ...
, and are the focus of much research in
linguistics Linguistics is the scientific study of language, meaning that it is a comprehensive, systematic, objective, and precise study of language. Linguistics encompasses the analysis of every aspect of language, as well as the methods for studying ...

linguistics
,
psychology Psychology is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...

psychology
,
cognitive science Cognitive science is the interdisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of two or more academic discipline An academic discipline or academic field is a subdivision of knowledge that is Educ ...

cognitive science
,
neuroscience Neuroscience is the of the . It is a science that combines , , , , , and to understand the fundamental and emergent properties of s, and s. The understanding of the biological basis of , , , , and has been described by as the "epic chal ...

neuroscience
, and
molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modification, mechanisms, and interaction ...
, collectively referred to as
vision science Vision science is the scientific study of . Researchers in vision science can be called vision scientists, especially if their research spans some of the science's many disciplines. Vision science encompasses all studies of vision, such as how an ...
.


Visual system

In humans and a number of other mammals, light enters the eye through the
cornea The cornea is the transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * ...

cornea
and is focused by the
lens A lens is a transmissive optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, s ...
onto the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
, a light-sensitive membrane at the back of the eye. The retina serves as a
transducer A transducer is a device that energy from one form to another. Usually a transducer converts a in one form of energy to a signal in another. Transducers are often employed at the boundaries of , , and s, where electrical signals are converted t ...

transducer
for the conversion of light into
neuronal signals
neuronal signals
. This transduction is achieved by specialized photoreceptive cells of the retina, also known as the rods and cones, which detect the
photon The photon ( el, φῶς, phōs, light) is a type of elementary particle In , an elementary particle or fundamental particle is a that is not composed of other particles. Particles currently thought to be elementary include the fundamental s ...

photon
s of light and respond by producing
neural impulses
neural impulses
. These signals are transmitted by the
optic nerve The optic nerve, also known as cranial nerve II, or simply as CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the se ...

optic nerve
, from the retina upstream to central
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In Biology, biology, the nervous system is a Complex system, high ...

ganglia
in the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tiss ...

brain
. The
lateral geniculate nucleus The lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a relay center in the thalamus for the visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connec ...

lateral geniculate nucleus
, which transmits the information to the
visual cortex The visual cortex of the is the area of the that processes . It is located in the . Sensory input originating from the travels through the in the and then reaches the visual cortex. The area of the visual cortex that receives the sensory inpu ...

visual cortex
. Signals from the retina also travel directly from the retina to the
superior colliculus The superior colliculus (Latin for "upper hill") is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum, or optic lobe. The adjecti ...

superior colliculus
. The lateral geniculate nucleus sends signals to
primary visual cortex The visual cortex of the brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such a ...
, also called striate cortex.
Extrastriate cortex The extrastriate cortex is the region of the occipital The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on itself li ...
, also called
visual association cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual perception, visual information. It is located in the occipital lobe. Sensory input originating from the Eye, eyes travels through the lateral geniculate nucleus ...
is a set of cortical structures, that receive information from striate cortex, as well as each other. Recent descriptions of visual association cortex describe a division into two functional pathways, a
ventral Standard anatomical terms of location deal unambiguously with the of s, including s. Terms used generally derive from or roots and used to describe something in its . This position provides a definition of what is at the front ("anterior"), be ...
and a
dorsal Dorsal (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repu ...
pathway. This conjecture is known as the
two streams hypothesis The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct vis ...
. The human visual system is generally believed to be sensitive to
visible light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nano ...
in the range of wavelengths between 370 and 730 nanometers (0.00000037 to 0.00000073 meters) of the
electromagnetic spectrum The electromagnetic spectrum is the range of frequencies Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existe ...

electromagnetic spectrum
. However, some research suggests that humans can perceive light in wavelengths down to 340 nanometers (UV-A), especially the young. Under optimal conditions these limits of human perception can extend to 310 nm (
UV
UV
) to 1100 nm (
NIR
NIR
).


Study

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 Visual processing is a term that is used to refer to the brain's ability to use and interpret visual information from the world around us. The process of converting light Light or visible light is electromagnetic radiation within the portion ...
does to create what is actually seen.


Early studies

There were two major
ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
schools, providing a primitive explanation of how vision works. The first was the "
emission theory Emission theory, also called emitter theory or ballistic theory of light, was a competing theory for the special theory of relativity, explaining the results of the Michelson–Morley experiment of 1887. Emission theories obey the principle of relat ...
" of vision which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If an object was seen 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 who were followers of
Euclid Euclid (; grc-gre, Εὐκλείδης Euclid (; grc, Εὐκλείδης – ''Eukleídēs'', ; fl. 300 BC), sometimes called Euclid of Alexandria to distinguish him from Euclid of Megara, was a Greek mathematician, often referre ...

Euclid
's ''
Optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other wo ...
'' and
Ptolemy Claudius Ptolemy (; grc-koi, Κλαύδιος Πτολεμαῖος, , ; la, Claudius Ptolemaeus; AD) was a mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Greek: ) includes ...
's ''
Optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other wo ...
''. The second school advocated the so-called 'intromission' approach which sees vision as coming from something entering the eyes representative of the object. With its main propagators
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental quest ...

Aristotle
('' De Sensu''),
Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized Linguistic anglicisation (or anglicization, occasionally anglification, anglifying, or Englishing) is the practice of modify ...
('' De Usu Partium Corporis Humani'') and their followers, this theory seems to have some contact with modern theories of what vision really is, but it remained only a speculation lacking any experimental foundation. (In eighteenth-century England,
Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Greek: ) includes the study of such topics a ...

Isaac Newton
,
John Locke John Locke (; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Enlightenment Enlightenment, enlighten or enlightened may refer to: Age of Enlightenment * ...

John Locke
, and others, carried the intromission theory of vision forward by insisting that vision involved a process in which rays—composed of actual corporeal matter—emanated from seen objects and entered the seer's mind/sensorium through the eye's aperture.) Both schools of thought relied upon the principle that "like is only known by like", and thus upon the notion that the eye was composed of some "internal fire" which interacted with the "external fire" of visible light and made vision possible.
Plato Plato ( ; grc-gre, wikt:Πλάτων, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was an Classical Athens, Athenian philosopher during the Classical Greece, Classical period in Ancient Greece, founder of the Platonist school of thoug ...

Plato
makes this assertion in his dialogue '' Timaeus'' (45b and 46b), as does
Empedocles Empedocles (; grc-gre, Ἐμπεδοκλῆς Empedocles (; grc-gre, wikt:Ἐμπεδοκλῆς, Ἐμπεδοκλῆς; , 444–443 BC) was a Ancient Greece, Greek pre-Socratic philosopher and a native citizen of Akragas, a Greek city ...

Empedocles
(as reported by Aristotle in his ''De Sensu'', DK frag. B17).
Alhazen Ḥasan Ibn al-Haytham (Latinization of names, Latinized as Alhazen ; full name ; ) was a Muslim Arab Mathematics in medieval Islam, mathematician, Astronomy in the medieval Islamic world, astronomer, and Physics in the medieval Islamic world, ...
(965 – 1040) carried out many investigations and
experiment An experiment is a procedure carried out to support or refute a , or determine the or of something previously untried. Experiments provide insight into by demonstrating what outcome occurs when a particular factor is manipulated. Experime ...

experiment
s on visual perception, extended the work of Ptolemy on
binocular vision In , binocular vision is a type of in which an animal has two s capable of facing the same direction to perceive a single of its surroundings. Neurological researcher Manfred Fahle has stated six specific advantages of having two eyes rather t ...

binocular vision
, and commented on the anatomical works of Galen. He was the first person to explain that vision occurs when light bounces on an object and then is directed to one's eyes.
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian of the who was active as a painter, , engineer, scientist, theorist, sculptor and architect. While his fame initially rested on his achievements as a painter, he als ...

Leonardo da Vinci
(1452–1519) is believed to be 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 and
peripheral vision Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the ...

peripheral vision
.
Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Greek: ) includes the study of such topics a ...

Isaac Newton
(1642–1726/27) was the first to discover through experimentation, by isolating individual colors of the spectrum of light passing through a
prism A prism An optical prism is a transparent optics, optical element with flat, polished surfaces that refraction, refract light. At least one surface must be angled—elements with two parallel surfaces are not prisms. The traditional geometrical ...

prism
, that the visually perceived color of objects appeared due to the character of light the objects reflected, and that these divided colors could not be changed into any other color, which was contrary to scientific expectation of the day.


Unconscious inference

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branch ...

Hermann von Helmholtz
is often credited with the first modern study of visual perception. Helmholtz examined the human eye and concluded that it was incapable of producing a high quality image. Insufficient information seemed to make vision impossible. He therefore concluded that vision could only be the result of some form of "unconscious inference", coining that term in 1867. He proposed the brain was 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. * closer objects can block the view of more distant objects, but not vice versa * figures (i.e., foreground objects) tend to have convex borders 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 Thomas Bayes (/beɪz/; c. 1701 – 1761) was an English statistician, philosopher, and Presbyterian minister. Bayesian () refers to a range of concepts and approaches that are ultimately based on a degree-of-belief interpretation of probability, ...
studies of visual perception. Proponents of this approach consider that the visual system performs some form of
Bayesian inference Bayesian inference is a method of in which is used to update the probability for a hypothesis as more or becomes available. Bayesian inference is an important technique in , and especially in . Bayesian updating is particularly important in th ...
to derive a perception from sensory data. However, it is not clear how proponents of this view derive, in principle, the relevant probabilities required by the Bayesian equation. Models based on this idea have been used to describe various visual perceptual functions, such as the perception of motion, the perception of depth, and figure-ground perception. The " wholly empirical theory of perception" is a related and newer approach that rationalizes visual perception without explicitly invoking Bayesian formalisms.


Gestalt theory

Gestalt psychologists Gestalt psychology, gestaltism or configurationism is a List of psychological schools, school of psychology that emerged in the early twentieth century in Austria and Germany as a theory of perception that was a rejection to the basic principle ...
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 partially translates to "configuration or pattern" along with "whole or emergent structure". According to this theory, there are eight main factors that determine how the visual system automatically groups elements into patterns: Proximity, Similarity, Closure, Symmetry, Common Fate (i.e. common motion), Continuity as well as Good Gestalt (pattern that is regular, simple, and orderly) and Past Experience.


Analysis of eye movement

During the 1960s, technical development permitted the continuous registration of eye movement during reading, in picture viewing, and later, in visual problem solving, and when headset-cameras became available, also during driving. The picture to the right shows what may happen during the first two seconds of visual inspection. While the background is out of focus, representing the
peripheral vision Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in 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). Eye movements serve the function of , i.e., to select a fraction of all visual inputs for deeper processing by the brain. 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 The fovea centralis is a small, central pit composed of closely packed Cone cell, cones in the human eye, eye. It is located in the center of the macula lutea of the retina. The fovea is responsible for sharp central visual perception, vision (al ...
vision adds detailed information to the peripheral ''first impression''. It can also be noted that there are different types of eye movements: fixational eye movements (
microsaccade Microsaccades are a kind of fixational eye movement. They are small, jerk-like, involuntary Eye movement (sensory), eye movements, similar to miniature versions of voluntary saccades. They typically occur during prolonged visual fixation (visual) ...
s, ocular drift, and tremor), vergence movements, saccadic movements and pursuit movements. ''Fixations'' are comparably static points where the eye rests. However, the eye is never completely still, but gaze position will drift. These drifts are in turn corrected by microsaccades, very small fixational eye-movements. ''Vergence movements'' involve the cooperation of both eyes to allow for an image to fall on the same area of both retinas. This results in a single focused image. '' Saccadic movements'' is the type of eye movement that makes jumps from one position to another position and is used to rapidly scan a particular scene/image. Lastly, '' pursuit movement'' is smooth eye movement and is used to follow objects in motion.


Face and object recognition

There is considerable evidence that face and
object recognition The following outline is provided as an overview of and topical guide to object recognition: Object recognition – technology in the field of computer vision for finding and identifying objects in an image or video sequence. Humans recogn ...
are accomplished by distinct systems. For example, patients show deficits in face, but not object processing, while object agnosic patients (most notably, patient C.K.) show deficits in object processing with spared face processing. Behaviorally, it has been shown that faces, but not objects, are subject to inversion effects, leading to the claim that faces are "special". Further, face and object processing recruit distinct neural systems. Notably, some have argued that the apparent specialization of the human brain for face processing does not reflect true domain specificity, but rather a more general process of expert-level discrimination within a given class of stimulus, though this latter claim is the subject of substantial debate. Using fMRI and electrophysiology Doris Tsao and colleagues described brain regions and a mechanism for
face recognition A facial recognition system is a technology capable of matching a human face The face is the front of an animal's head that features three of the head's sense organs, the eyes, nose, and mouth, and through which animals express many of their ...
in macaque monkeys. The inferotemporal cortex has a key role in the task of recognition and differentiation of different objects. A study of the MIT shows that subset regions of the IT cortex are in charge of different objects. By selectively shutting off neural activity of many small areas of the cortex, the animal gets alternately unable to distinguish between certain particular pairments of objects. This shows that the IT cortex is divided into regions that respond to different and particular visual features. In a similar way, certain particular patches and regions of the cortex are more involved into face recognition than other objects recognition. Some studies tend to show that rather than the uniform global image, some particular features and regions of interest of the objects are key elements when the brain need to recognise an object in image. In this way, the human vision is vulnerable to small particular changes to the image, such as disrupting the edges of the object, modifying texture or any small change in a crucial region of the image. Studies of people whose sight has been restored after a long blindness reveal that they cannot necessarily recognize objects and faces (as opposed to color, motion, and simple geometric shapes). Some hypothesize that being blind during childhood prevents some part of the visual system necessary for these higher-level tasks from developing properly. The general belief that a
critical period In developmental psychology and developmental biology, a critical period is a maturational stage in the lifespan of an organism during which the nervous system is especially sensitive to certain environmental stimuli. If, for some reason, the orga ...
lasts until age 5 or 6 was challenged by a 2007 study that found that older patients could improve these abilities with years of exposure.


Cognitive and computational approaches

In the 1970s, David Marr developed a multi-level theory of vision, which analyzed the process of vision at different levels of abstraction. In order to focus on the understanding of specific problems in vision, he identified three levels of analysis: the ''computational'', ''algorithmic'' and ''implementational'' levels. Many vision scientists, including
Tomaso Poggio Tomaso Armando Poggio (born September 11, 1947 in Genoa Genoa ( ; it, Genova ; lij, Zêna ; English, historically, and la, Genua) is the capital of the Italian region of Liguria and the sixth-largest city in Italy. In 2015, 594,733 people ...

Tomaso Poggio
, have embraced these levels of analysis and employed them to further characterize vision from a computational perspective. 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 solutions to these problems are realized in neural circuitry. 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 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. Marr's 2D sketch assumes that a depth map is constructed, and that this map is the basis of 3D shape perception. However, both stereoscopic and pictorial perception, as well as monocular viewing, make clear that the perception of 3D shape precedes, and does not rely on, the perception of the depth of points. It is not clear how a preliminary depth map could, in principle, be constructed, nor how this would address the question of figure-ground organization, or grouping. The role of perceptual organizing constraints, overlooked by Marr, in the production of 3D shape percepts from binocularly-viewed 3D objects has been demonstrated empirically for the case of 3D wire objects, e.g. For a more detailed discussion, see Pizlo (2008). A more recent, alternative, framework proposes that vision is composed instead of the following three stages: encoding, selection, and decoding. Encoding is to sample and represent visual inputs (e.g., to represent visual inputs as neural activities in the retina). Selection, or , is to select a tiny fraction of input information for further processing, e.g., by shifting gaze to an object or visual location to better process the visual signals at that location. Decoding is to infer or recognize the selected input signals, e.g., to recognize the object at the center of gaze as somebody's face. In this framework, attentional selection starts at the
primary visual cortex The visual cortex of the brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such a ...

primary visual cortex
along the visual pathway, and the attentional constraints impose a dichotomy between the central and
peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of the computer. The term peripheral device refers to all hardware components that are attached to a computer and are controlled by the co ...

peripheral
visual fields for visual recognition or decoding.


Transduction

Transduction is the process through which energy from environmental stimuli is converted to neural activity. The
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
contains three different cell layers: photoreceptor layer, bipolar cell layer and ganglion cell layer. The photoreceptor layer where transduction occurs is farthest from the lens. It contains photoreceptors with different sensitivities called rods and cones. The cones are responsible for color perception and are of three distinct types labelled red, green and blue. Rods are responsible for the perception of objects in low light. Photoreceptors contain within them a special chemical called a photopigment, which is embedded in the membrane of the lamellae; a single human rod contains approximately 10 million of them. The photopigment molecules consist of two parts: an opsin (a protein) and retinal (a lipid). There are 3 specific photopigments (each with their own wavelength sensitivity) that respond across the spectrum of visible light. When the appropriate wavelengths (those that the specific photopigment is sensitive to) hit the photoreceptor, the photopigment splits into two, which sends a signal to the bipolar cell layer, which in turn sends a signal to the ganglion cells, the axons of which form the
optic nerve The optic nerve, also known as cranial nerve II, or simply as CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the se ...

optic nerve
and transmit the information to the brain. If a particular cone type is missing or abnormal, due to a genetic anomaly, a
color vision deficiency Color blindness (color vision deficiency) is the decreased ability to color vision, see color or differences in color. It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights. Color blindness may make so ...
, sometimes called color blindness will occur.


Opponent process

Transduction involves chemical messages sent from the photoreceptors to the bipolar cells to the ganglion cells. Several photoreceptors may send their information to one ganglion cell. There are two types of ganglion cells: red/green and yellow/blue. These neurons constantly fire—even when not stimulated. The brain interprets different colors (and with a lot of information, an image) when the rate of firing of these neurons alters. Red light stimulates the red cone, which in turn stimulates the red/green ganglion cell. Likewise, green light stimulates the green cone, which stimulates the green/red ganglion cell and blue light stimulates the blue cone which stimulates the blue/yellow ganglion cell. The rate of firing of the ganglion cells is increased when it is signaled by one cone and decreased (inhibited) when it is signaled by the other cone. The first color in the name of the ganglion cell is the color that excites it and the second is the color that inhibits it. i.e.: A red cone would excite the red/green ganglion cell and the green cone would inhibit the red/green ganglion cell. This is an
opponent process 360px, Diagram of the opponent process The opponent process is a color theory that states that the human visual system interprets information about color by processing signals from cone cells and rod cells in an antagonistic manner. There is so ...
. If the rate of firing of a red/green ganglion cell is increased, the brain would know that the light was red, if the rate was decreased, the brain would know that the color of the light was green.


Artificial visual perception

Theories and observations of visual perception have been the main source of inspiration for
computer vision Computer vision is an interdisciplinary scientific field that deals with how computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform ge ...
(also called
machine vision Machine vision (MV) is the technology and methods used to provide imaging-based automatic inspection and analysis for such applications as automatic inspection, process control, and robot guidance, usually in industry. Machine vision refers to ma ...

machine vision
, or computational vision). Special hardware structures and software algorithms provide machines with the capability to interpret the images coming from a camera or a sensor. For instance, the 2022
Toyota 86 The Toyota 86 and the Subaru BRZ are 2+2 (car body style), 2+2 sports cars jointly developed by Toyota and Subaru, manufactured at Subaru's Gunma assembly plant. The 2+2 fastback coupé is noted for its natural aspiration, naturally-aspirated bo ...

Toyota 86
uses the Subaru EyeSight system for driver-assist technology.


See also

*
Color vision Color vision, a feature of visual perception Visual perception is the ability to interpret the surrounding environment (biophysical), environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and ...

Color vision
*
Computer vision Computer vision is an interdisciplinary scientific field that deals with how computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform ge ...
*
Depth perception Depth perception is the ability to perceive the world in three s () and the distance of an object. Depth sensation is the corresponding term for non-human animals, since although it is known that they can sense the distance of an object (becaus ...
*
Entoptic phenomenon Entoptic phenomena (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following p ...
*
Gestalt psychology Gestalt psychology, gestaltism or configurationism is a school of psychology that emerged in the early twentieth century in Austria and Germany as a theory of perception Perception (from the Latin Latin (, or , ) is a classical ...
*
Lateral masking Lateral masking is a problem for the human visual perception of identical or similar entities in close proximity. This can be illustrated by the difficulty of counting the vertical bars of a barcode. In linguistics lateral masking refers to the int ...
*
Naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or micr ...
*
Machine vision Machine vision (MV) is the technology and methods used to provide imaging-based automatic inspection and analysis for such applications as automatic inspection, process control, and robot guidance, usually in industry. Machine vision refers to ma ...

Machine vision
*
Motion perception Motion perception is the process of inferring the speed and direction of elements in a scene based on visual The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which conn ...
*
Multisensory integration Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalitiesStimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus ...
*
Interpretation (philosophy) A philosophical interpretation is the assignment of meanings to various concepts, symbols, or objects under consideration. Two broad types of interpretation can be distinguished: interpretations of physical objects, and interpretations of concepts ...
*
Spatial frequency In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
* Visual illusion *
Visual processing Visual processing is a term that is used to refer to the brain's ability to use and interpret visual information from the world around us. The process of converting light Light or visible light is electromagnetic radiation within the portion ...
*
Visual system The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined b ...
*
SensationSensation refers to the processing of sense Sense relates to any of the systems and corresponding organs involved in sensation, i.e. the physical process of responding to Stimulus (physiology), stimuli and providing data for perception. During sensa ...
s


Vision deficiencies or disorders

*
Achromatopsia Achromatopsia, also known as total color blindness, is a medical syndrome that exhibits symptoms relating to at least five conditions. The term may refer to acquired conditions such as cerebral achromatopsia, but it typically refers to an autosom ...
*
Akinetopsia Akinetopsia (Greek: a for "without", kine for "to move" and opsia for "seeing"), also known as cerebral akinetopsia or motion blindness, is a neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being ...
*
Apperceptive agnosia Apperceptive agnosia is a failure in recognition that is due to a failure of perception. In contrast, associative agnosia is a type of agnosia where perception occurs but recognition still does not occur. When referring to apperceptive agnosia, vi ...
*
Associative visual agnosia Associative visual agnosia is a form of visual agnosia. It is an impairment in Recall (memory), recognition or assigning meaning to a Stimulus (physiology), stimulus that is accurately perception, perceived and not associated with a generalized def ...
*
Color blindness Color blindness (color vision deficiency) is the decreased ability to see color or differences in color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. Eng ...

Color blindness
*
Hallucinogen persisting perception disorder Hallucinogen persisting perception disorder (HPPD) is a chronic disorder in which a person has non-psychotic flashbacks of visual hallucinations or distortions experienced during a previous hallucinogen A hallucinogen is a psychoactive drug, p ...
* Illusory palinopsia *
Prosopagnosia Prosopagnosia (from Greek ''prósōpon'', meaning "face", and ''agnōsía'', meaning "non-knowledge"), also called face blindness, ("illILL may refer to: * '' I Love Lucy'', a landmark American television sitcom * Illorsuit Heliport (location ...

Prosopagnosia
*
Refractive error Refractive error, also known as refraction error, is a problem with focus FOCUS is a fourth-generation programming language (4GL) computer programming programming language, language and development environment that is used to build database quer ...

Refractive error
* Recovery from blindness * Scotopic sensitivity syndrome * Visual agnosia * Visual snow


Related disciplines

* Cognitive science * Neuroscience * Ophthalmology * Optometry * Psychophysics


References


Further reading

* Quotations are from the English translation produced by Optical Society of America (1924–25):
Treatise on Physiological Optics
'.


External links

*
The Organization of the Retina and Visual System

Effect of Detail on Visual Perception
by Jon McLoone, the Wolfram Demonstrations Project.
The Joy of Visual Perception
Resource on the eye's perception abilities.
VisionScience. Resource for Research in Human and Animal Vision
A collection of resources in vision science and perception.


Visibility in Social Theory and Social Research.
An inquiry into the cognitive and social meanings of visibility.
Vision
Scholarpedia Expert articles about Vision {{Authority control Visual perception, Vision, Perception Perception