Visual system

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This article is about the physiological components involved in vision. Visual system_sentence_0

For the ability to interpret the surrounding environment, see Visual perception. Visual system_sentence_1

"Visual sensor" redirects here. Visual system_sentence_2

For electronic visual sensors, see Visual sensor network. Visual system_sentence_3

Visual system_table_infobox_0

Visual systemVisual system_header_cell_0_0_0

The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the ability to detect and process visible light) as well as enabling the formation of several non-image photo response functions. Visual system_sentence_4

It detects and interprets information from the optical spectrum perceptible to that species to "build a representation" of the surrounding environment. Visual system_sentence_5

The visual system carries out a number of complex tasks, including the reception of light and the formation of monocular neural representations, colour vision, the neural mechanisms underlying stereopsis and assessment of distances to and between objects, the identification of particular object of interest, motion perception, the analysis and integration of visual information, pattern recognition, accurate motor coordination under visual guidance, and more. Visual system_sentence_6

The neuropsychological side of visual information processing is known as visual perception, an abnormality of which is called visual impairment, and a complete absence of which is called blindness. Visual system_sentence_7

Non-image forming visual functions, independent of visual perception, include (among others) the pupillary light reflex (PLR) and circadian photoentrainment. Visual system_sentence_8

This article mostly describes the visual system of mammals, humans in particular, although other animals have similar visual systems (see bird vision, vision in fish, mollusc eye, and reptile vision). Visual system_sentence_9

System overview Visual system_section_0

Mechanical Visual system_section_1

Together the cornea and lens refract light into a small image and shine it on the retina. Visual system_sentence_10

The retina transduces this image into electrical pulses using rods and cones. Visual system_sentence_11

The optic nerve then carries these pulses through the optic canal. Visual system_sentence_12

Upon reaching the optic chiasm the nerve fibers decussate (left becomes right). Visual system_sentence_13

The fibers then branch and terminate in three places. Visual system_sentence_14

Neural Visual system_section_2

Most of the optic nerve fibers end in the lateral geniculate nucleus (LGN). Visual system_sentence_15

Before the LGN forwards the pulses to V1 of the visual cortex (primary) it gauges the range of objects and tags every major object with a velocity tag. Visual system_sentence_16

These tags predict object movement. Visual system_sentence_17

The LGN also sends some fibers to V2 and V3. Visual system_sentence_18

V1 performs edge-detection to understand spatial organization (initially, 40 milliseconds in, focusing on even small spatial and color changes. Visual system_sentence_19

Then, 100 milliseconds in, upon receiving the translated LGN, V2, and V3 info, also begins focusing on global organization). Visual system_sentence_20

V1 also creates a bottom-up saliency map to guide attention or gaze shft. Visual system_sentence_21

V2 both forwards (direct and via pulvinar) pulses to V1 and receives them. Visual system_sentence_22

Pulvinar is responsible for saccade and visual attention. Visual system_sentence_23

V2 serves much the same function as V1, however, it also handles illusory contours, determining depth by comparing left and right pulses (2D images), and foreground distinguishment. Visual system_sentence_24

V2 connects to V1 - V5. Visual system_sentence_25

V3 helps process ‘global motion’ (direction and speed) of objects. Visual system_sentence_26

V3 connects to V1 (weak), V2, and the inferior temporal cortex. Visual system_sentence_27

V4 recognizes simple shapes, gets input from V1 (strong), V2, V3, LGN, and pulvinar. Visual system_sentence_28

V5’s outputs include V4 and its surrounding area, and eye-movement motor cortices (frontal eye-field and lateral intraparietal area). Visual system_sentence_29

V5’s functionality is similar to that of the other V’s, however, it integrates local object motion into global motion on a complex level. Visual system_sentence_30

V6 works in conjunction with V5 on motion analysis. Visual system_sentence_31

V5 analyzes self-motion, whereas V6 analyzes motion of objects relative to the background. Visual system_sentence_32

V6’s primary input is V1, with V5 additions. Visual system_sentence_33

V6 houses the topographical map for vision. Visual system_sentence_34

V6 outputs to the region directly around it (V6A). Visual system_sentence_35

V6A has direct connections to arm-moving cortices, including the premotor cortex. Visual system_sentence_36

The inferior temporal gyrus recognizes complex shapes, objects, and faces or, in conjunction with the hippocampus, creates new memories. Visual system_sentence_37

The pretectal area is seven unique nuclei. Visual system_sentence_38

Anterior, posterior and medial pretectal nuclei inhibit pain (indirectly), aid in REM, and aid the accommodation reflex, respectively. Visual system_sentence_39

The Edinger-Westphal nucleus moderates pupil dilation and aids (since it provides parasympathetic fibers) in convergence of the eyes and lens adjustment. Visual system_sentence_40

Nuclei of the optic tract are involved in smooth pursuit eye movement and the accommodation reflex, as well as REM. Visual system_sentence_41

The suprachiasmatic nucleus is the region of the hypothalamus that halts production of melatonin (indirectly) at first light. Visual system_sentence_42

Structure Visual system_section_3

Visual system_unordered_list_0

These are divided into anterior and posterior pathways. Visual system_sentence_43

The anterior visual pathway refers to structures involved in vision before the lateral geniculate nucleus. Visual system_sentence_44

The posterior visual pathway refers to structures after this point. Visual system_sentence_45

Eye Visual system_section_4

Main articles: Eye and Anterior segment of eyeball Visual system_sentence_46

Light entering the eye is refracted as it passes through the cornea. Visual system_sentence_47

It then passes through the pupil (controlled by the iris) and is further refracted by the lens. Visual system_sentence_48

The cornea and lens act together as a compound lens to project an inverted image onto the retina. Visual system_sentence_49

Retina Visual system_section_5

Main article: Retina Visual system_sentence_50

The retina consists of a large number of photoreceptor cells which contain particular protein molecules called opsins. Visual system_sentence_51

In humans, two types of opsins are involved in conscious vision: rod opsins and cone opsins. Visual system_sentence_52

(A third type, melanopsin in some of the retinal ganglion cells (RGC), part of the body clock mechanism, is probably not involved in conscious vision, as these RGC do not project to the lateral geniculate nucleus but to the pretectal olivary nucleus.) Visual system_sentence_53

An opsin absorbs a photon (a particle of light) and transmits a signal to the cell through a signal transduction pathway, resulting in hyper-polarization of the photoreceptor. Visual system_sentence_54

Rods and cones differ in function. Visual system_sentence_55

Rods are found primarily in the periphery of the retina and are used to see at low levels of light. Visual system_sentence_56

Cones are found primarily in the center (or fovea) of the retina. Visual system_sentence_57

There are three types of cones that differ in the wavelengths of light they absorb; they are usually called short or blue, middle or green, and long or red. Visual system_sentence_58

Cones are used primarily to distinguish color and other features of the visual world at normal levels of light. Visual system_sentence_59

In the retina, the photoreceptors synapse directly onto bipolar cells, which in turn synapse onto ganglion cells of the outermost layer, which will then conduct action potentials to the brain. Visual system_sentence_60

A significant amount of visual processing arises from the patterns of communication between neurons in the retina. Visual system_sentence_61

About 130 million photo-receptors absorb light, yet roughly 1.2 million axons of ganglion cells transmit information from the retina to the brain. Visual system_sentence_62

The processing in the retina includes the formation of center-surround receptive fields of bipolar and ganglion cells in the retina, as well as convergence and divergence from photoreceptor to bipolar cell. Visual system_sentence_63

In addition, other neurons in the retina, particularly horizontal and amacrine cells, transmit information laterally (from a neuron in one layer to an adjacent neuron in the same layer), resulting in more complex receptive fields that can be either indifferent to color and sensitive to motion or sensitive to color and indifferent to motion. Visual system_sentence_64

Mechanism of generating visual signals: The retina adapts to change in light through the use of the rods. Visual system_sentence_65

In the dark, the chromophore retinal has a bent shape called cis-retinal (referring to a cis conformation in one of the double bonds). Visual system_sentence_66

When light interacts with the retinal, it changes conformation to a straight form called trans-retinal and breaks away from the opsin. Visual system_sentence_67

This is called bleaching because the purified rhodopsin changes from violet to colorless in the light. Visual system_sentence_68

At baseline in the dark, the rhodopsin absorbs no light and releases glutamate which inhibits the bipolar cell. Visual system_sentence_69

This inhibits the release of neurotransmitters from the bipolar cells to the ganglion cell. Visual system_sentence_70

When there is light present, glutamate secretion ceases thus no longer inhibiting the bipolar cell from releasing neurotransmitters to the ganglion cell and therefore an image can be detected. Visual system_sentence_71

The final result of all this processing is five different populations of ganglion cells that send visual (image-forming and non-image-forming) information to the brain: Visual system_sentence_72

Visual system_ordered_list_1

  1. M cells, with large center-surround receptive fields that are sensitive to depth, indifferent to color, and rapidly adapt to a stimulus;Visual system_item_1_8
  2. P cells, with smaller center-surround receptive fields that are sensitive to color and shape;Visual system_item_1_9
  3. K cells, with very large center-only receptive fields that are sensitive to color and indifferent to shape or depth;Visual system_item_1_10
  4. another population that is intrinsically photosensitive; andVisual system_item_1_11
  5. a final population that is used for eye movements.Visual system_item_1_12

A 2006 University of Pennsylvania study calculated the approximate bandwidth of human retinas to be about 8960 kilobits per second, whereas guinea pig retinas transfer at about 875 kilobits. Visual system_sentence_73

In 2007 Zaidi and co-researchers on both sides of the Atlantic studying patients without rods and cones, discovered that the novel photoreceptive ganglion cell in humans also has a role in conscious and unconscious visual perception. Visual system_sentence_74

The peak spectral sensitivity was 481 nm. Visual system_sentence_75

This shows that there are two pathways for sight in the retina – one based on classic photoreceptors (rods and cones) and the other, newly discovered, based on photo-receptive ganglion cells which act as rudimentary visual brightness detectors. Visual system_sentence_76

Photochemistry Visual system_section_6

Main article: Visual cycle Visual system_sentence_77

The functioning of a camera is often compared with the workings of the eye, mostly since both focus light from external objects in the field of view onto a light-sensitive medium. Visual system_sentence_78

In the case of the camera, this medium is film or an electronic sensor; in the case of the eye, it is an array of visual receptors. Visual system_sentence_79

With this simple geometrical similarity, based on the laws of optics, the eye functions as a transducer, as does a CCD camera. Visual system_sentence_80

In the visual system, retinal, technically called retinene1 or "retinaldehyde", is a light-sensitive molecule found in the rods and cones of the retina. Visual system_sentence_81

Retinal is the fundamental structure involved in the transduction of light into visual signals, i.e. nerve impulses in the ocular system of the central nervous system. Visual system_sentence_82

In the presence of light, the retinal molecule changes configuration and as a result a nerve impulse is generated. Visual system_sentence_83

Optic nerve Visual system_section_7

Main article: Optic nerve Visual system_sentence_84

The information about the image via the eye is transmitted to the brain along the optic nerve. Visual system_sentence_85

Different populations of ganglion cells in the retina send information to the brain through the optic nerve. Visual system_sentence_86

About 90% of the axons in the optic nerve go to the lateral geniculate nucleus in the thalamus. Visual system_sentence_87

These axons originate from the M, P, and K ganglion cells in the retina, see above. Visual system_sentence_88

This parallel processing is important for reconstructing the visual world; each type of information will go through a different route to perception. Visual system_sentence_89

Another population sends information to the superior colliculus in the midbrain, which assists in controlling eye movements (saccades) as well as other motor responses. Visual system_sentence_90

A final population of photosensitive ganglion cells, containing melanopsin for photosensitivity, sends information via the retinohypothalamic tract (RHT) to the pretectum (pupillary reflex), to several structures involved in the control of circadian rhythms and sleep such as the suprachiasmatic nucleus (SCN, the biological clock), and to the ventrolateral preoptic nucleus (VLPO, a region involved in sleep regulation). Visual system_sentence_91

A recently discovered role for photoreceptive ganglion cells is that they mediate conscious and unconscious vision – acting as rudimentary visual brightness detectors as shown in rodless coneless eyes. Visual system_sentence_92

Optic chiasm Visual system_section_8

Main article: Optic chiasm Visual system_sentence_93

The optic nerves from both eyes meet and cross at the optic chiasm, at the base of the hypothalamus of the brain. Visual system_sentence_94

At this point the information coming from both eyes is combined and then splits according to the visual field. Visual system_sentence_95

The corresponding halves of the field of view (right and left) are sent to the left and right halves of the brain, respectively, to be processed. Visual system_sentence_96

That is, the right side of primary visual cortex deals with the left half of the field of view from both eyes, and similarly for the left brain. Visual system_sentence_97

A small region in the center of the field of view is processed redundantly by both halves of the brain. Visual system_sentence_98

Optic tract Visual system_section_9

Main article: Optic tract Visual system_sentence_99

Information from the right visual field (now on the left side of the brain) travels in the left optic tract. Visual system_sentence_100

Information from the left visual field travels in the right optic tract. Visual system_sentence_101

Each optic tract terminates in the lateral geniculate nucleus (LGN) in the thalamus. Visual system_sentence_102

Lateral geniculate nucleus Visual system_section_10

Visual system_description_list_2

  • Visual system_item_2_13

The lateral geniculate nucleus (LGN) is a sensory relay nucleus in the thalamus of the brain. Visual system_sentence_103

The LGN consists of six layers in humans and other primates starting from catarhinians, including cercopithecidae and apes. Visual system_sentence_104

Layers 1, 4, and 6 correspond to information from the contralateral (crossed) fibers of the nasal retina (temporal visual field); layers 2, 3, and 5 correspond to information from the ipsilateral (uncrossed) fibers of the temporal retina (nasal visual field). Visual system_sentence_105

Layer one (1) contains M cells which correspond to the M (magnocellular) cells of the optic nerve of the opposite eye and are concerned with depth or motion. Visual system_sentence_106

Layers four and six (4 & 6) of the LGN also connect to the opposite eye, but to the P cells (color and edges) of the optic nerve. Visual system_sentence_107

By contrast, layers two, three and five (2, 3, & 5) of the LGN connect to the M cells and P (parvocellular) cells of the optic nerve for the same side of the brain as its respective LGN. Visual system_sentence_108

Spread out, the six layers of the LGN are the area of a credit card and about three times its thickness. Visual system_sentence_109

The LGN is rolled up into two ellipsoids about the size and shape of two small birds' eggs. Visual system_sentence_110

In between the six layers are smaller cells that receive information from the K cells (color) in the retina. Visual system_sentence_111

The neurons of the LGN then relay the visual image to the primary visual cortex (V1) which is located at the back of the brain (posterior end) in the occipital lobe in and close to the calcarine sulcus. Visual system_sentence_112

The LGN is not just a simple relay station but it is also a center for processing; it receives reciprocal input from the cortical and subcortical layers and reciprocal innervation from the visual cortex. Visual system_sentence_113

Optic radiation Visual system_section_11

Main article: Optic radiation Visual system_sentence_114

The optic radiations, one on each side of the brain, carry information from the thalamic lateral geniculate nucleus to layer 4 of the visual cortex. Visual system_sentence_115

The P layer neurons of the LGN relay to V1 layer 4C β. Visual system_sentence_116

The M layer neurons relay to V1 layer 4C α. Visual system_sentence_117

The K layer neurons in the LGN relay to large neurons called blobs in layers 2 and 3 of V1. Visual system_sentence_118

There is a direct correspondence from an angular position in the visual field of the eye, all the way through the optic tract to a nerve position in V1 (up to V4, i.e. the primary visual areas. Visual system_sentence_119

After that, the visual pathway is roughly separated into a ventral and dorsal pathway). Visual system_sentence_120

Visual cortex Visual system_section_12

Main article: Visual cortex Visual system_sentence_121

The visual cortex is the largest system in the human brain and is responsible for processing the visual image. Visual system_sentence_122

It lies at the rear of the brain (highlighted in the image), above the cerebellum. Visual system_sentence_123

The region that receives information directly from the LGN is called the primary visual cortex, (also called V1 and striate cortex). Visual system_sentence_124

It creates a bottom-up saliency map of the visual field to guide attention or eye gaze to salient visual locations, hence selection of visual input information by attention starts at V1 along the visual pathway. Visual system_sentence_125

Visual information then flows through a cortical hierarchy. Visual system_sentence_126

These areas include V2, V3, V4 and area V5/MT (the exact connectivity depends on the species of the animal). Visual system_sentence_127

These secondary visual areas (collectively termed the extrastriate visual cortex) process a wide variety of visual primitives. Visual system_sentence_128

Neurons in V1 and V2 respond selectively to bars of specific orientations, or combinations of bars. Visual system_sentence_129

These are believed to support edge and corner detection. Visual system_sentence_130

Similarly, basic information about color and motion is processed here. Visual system_sentence_131

Heider, et al. Visual system_sentence_132

(2002) have found that neurons involving V1, V2, and V3 can detect stereoscopic illusory contours; they found that stereoscopic stimuli subtending up to 8° can activate these neurons. Visual system_sentence_133

Visual association cortex Visual system_section_13

Main article: Two Streams hypothesis Visual system_sentence_134

As visual information passes forward through the visual hierarchy, the complexity of the neural representations increases. Visual system_sentence_135

Whereas a V1 neuron may respond selectively to a line segment of a particular orientation in a particular retinotopic location, neurons in the lateral occipital complex respond selectively to complete object (e.g., a figure drawing), and neurons in visual association cortex may respond selectively to human faces, or to a particular object. Visual system_sentence_136

Along with this increasing complexity of neural representation may come a level of specialization of processing into two distinct pathways: the dorsal stream and the ventral stream (the Two Streams hypothesis, first proposed by Ungerleider and Mishkin in 1982). Visual system_sentence_137

The dorsal stream, commonly referred to as the "where" stream, is involved in spatial attention (covert and overt), and communicates with regions that control eye movements and hand movements. Visual system_sentence_138

More recently, this area has been called the "how" stream to emphasize its role in guiding behaviors to spatial locations. Visual system_sentence_139

The ventral stream, commonly referred as the "what" stream, is involved in the recognition, identification and categorization of visual stimuli. Visual system_sentence_140

However, there is still much debate about the degree of specialization within these two pathways, since they are in fact heavily interconnected. Visual system_sentence_141

Horace Barlow proposed the efficient coding hypothesis in 1961 as a theoretical model of sensory coding in the brain. Visual system_sentence_142

Limitations in the applicability of this theory in the motivated the V1 Saliency Hypothesis (V1SH) that V1 creates a bottom-up saliency map to guide attention exogenously. Visual system_sentence_143

With attentional selection as a center stage, vision is seem as composed of encoding, selection, and decoding stages. Visual system_sentence_144

The default mode network is a network of brain regions that are active when an individual is awake and at rest. Visual system_sentence_145

The visual system's default mode can be monitored during resting state fMRI: Fox, et al. Visual system_sentence_146

(2005) have found that ", in which the visual system switches from resting state to attention. Visual system_sentence_147

In the parietal lobe, the lateral and ventral intraparietal cortex are involved in visual attention and saccadic eye movements. Visual system_sentence_148

These regions are in the Intraparietal sulcus (marked in red in the adjacent image). Visual system_sentence_149

Development Visual system_section_14

Infancy Visual system_section_15

See also: Infant vision Visual system_sentence_150

Newborn infants have limited color perception. Visual system_sentence_151

One study found that 74% of newborns can distinguish red, 36% green, 25% yellow, and 14% blue. Visual system_sentence_152

After one month performance "improved somewhat." Visual system_sentence_153

Infant’s eyes don’t have the ability to accommodate. Visual system_sentence_154

The pediatricians are able to perform non-verbal testing to assess visual acuity of a newborn, detect nearsightedness and astigmatism, and evaluate the eye teaming and alignment. Visual system_sentence_155

Visual acuity improves from about 20/400 at birth to approximately 20/25 at 6 months of age. Visual system_sentence_156

All this is happening because the nerve cells in their retina and brain that control vision are not fully developed. Visual system_sentence_157

Childhood and adolescence Visual system_section_16

Depth perception, focus, tracking and other aspects of vision continue to develop throughout early and middle childhood. Visual system_sentence_158

From recent studies in the United States and Australia there is some evidence that the amount of time school aged children spend outdoors, in natural light, may have some impact on whether they develop myopia. Visual system_sentence_159

The condition tends to get somewhat worse through childhood and adolescence, but stabilizes in adulthood. Visual system_sentence_160

More prominent myopia (nearsightedness) and astigmatism are thought to be inherited. Visual system_sentence_161

Children with this condition may need to wear glasses. Visual system_sentence_162

Adulthood Visual system_section_17

Eyesight is often one of the first senses affected by aging. Visual system_sentence_163

A number of changes occur with aging: Visual system_sentence_164

Visual system_unordered_list_3

  • Over time the lens become yellowed and may eventually become brown, a condition known as brunescence or brunescent cataract. Although many factors contribute to yellowing, lifetime exposure to ultraviolet light and aging are two main causes.Visual system_item_3_14
  • The lens becomes less flexible, diminishing the ability to accommodate (presbyopia).Visual system_item_3_15
  • While a healthy adult pupil typically has a size range of 2–8 mm, with age the range gets smaller, trending towards a moderately small diameter.Visual system_item_3_16
  • On average tear production declines with age. However, there are a number of age-related conditions that can cause excessive tearing.Visual system_item_3_17

Other functions Visual system_section_18

Balance Visual system_section_19

Along with proprioception and vestibular function, the visual system plays an important role in the ability of an individual to control balance and maintain an upright posture. Visual system_sentence_165

When these three conditions are isolated and balance is tested, it has been found that vision is the most significant contributor to balance, playing a bigger role than either of the two other intrinsic mechanisms. Visual system_sentence_166

The clarity with which an individual can see his environment, as well as the size of the visual field, the susceptibility of the individual to light and glare, and poor depth perception play important roles in providing a feedback loop to the brain on the body's movement through the environment. Visual system_sentence_167

Anything that affects any of these variables can have a negative effect on balance and maintaining posture. Visual system_sentence_168

This effect has been seen in research involving elderly subjects when compared to young controls, in glaucoma patients compared to age matched controls, cataract patients pre and post surgery, and even something as simple as wearing safety goggles. Visual system_sentence_169

Monocular vision (one eyed vision) has also been shown to negatively impact balance, which was seen in the previously referenced cataract and glaucoma studies, as well as in healthy children and adults. Visual system_sentence_170

According to Pollock et al. Visual system_sentence_171

(2010) stroke is the main cause of specific visual impairment, most frequently visual field loss (homonymous hemianopia- a visual field defect). Visual system_sentence_172

Nevertheless, evidence for the efficacy of cost-effective interventions aimed at these visual field defects is still inconsistent. Visual system_sentence_173

Clinical significance Visual system_section_20

Proper function of the visual system is required for sensing, processing, and understanding the surrounding environment. Visual system_sentence_174

Difficulty in sensing, processing and understanding light input has the potential to adversely impact an individual's ability to communicate, learn and effectively complete routine tasks on a daily basis. Visual system_sentence_175

In children, early diagnosis and treatment of impaired visual system function is an important factor in ensuring that key social, academic and speech/language developmental milestones are met. Visual system_sentence_176

Cataract is clouding of the lens, which in turn affects vision. Visual system_sentence_177

Although it may be accompanied by yellowing, clouding and yellowing can occur separately. Visual system_sentence_178

This is typically a result of ageing, disease, or drug use. Visual system_sentence_179

Presbyopia is a visual condition that causes farsightedness. Visual system_sentence_180

The eye's lens becomes too inflexible to accommodate to normal reading distance, focus tending to remain fixed at long distance. Visual system_sentence_181

Glaucoma is a type of blindness that begins at the edge of the visual field and progresses inward. Visual system_sentence_182

It may result in tunnel vision. Visual system_sentence_183

This typically involves the outer layers of the optic nerve, sometimes as a result of buildup of fluid and excessive pressure in the eye. Visual system_sentence_184

Scotoma is a type of blindness that produces a small blind spot in the visual field typically caused by injury in the primary visual cortex. Visual system_sentence_185

Homonymous hemianopia is a type of blindness that destroys one entire side of the visual field typically caused by injury in the primary visual cortex. Visual system_sentence_186

Quadrantanopia is a type of blindness that destroys only a part of the visual field typically caused by partial injury in the primary visual cortex. Visual system_sentence_187

This is very similar to homonymous hemianopia, but to a lesser degree. Visual system_sentence_188

Prosopagnosia, or face blindness, is a brain disorder that produces an inability to recognize faces. Visual system_sentence_189

This disorder often arises after damage to the fusiform face area (FFA). Visual system_sentence_190

Visual agnosia, or visual-form agnosia, is a brain disorder that produces an inability to recognize objects. Visual system_sentence_191

This disorder often arises after damage to the ventral stream. Visual system_sentence_192

Other animals Visual system_section_21

See also: Eye, Vision in birds, Parietal eye, Vision in fishes, Arthropod visual system, and Cephalopod eye Visual system_sentence_193

Different species are able to see different parts of the light spectrum; for example, bees can see into the ultraviolet, while pit vipers can accurately target prey with their pit organs, which are sensitive to infrared radiation. Visual system_sentence_194

The mantis shrimp possesses arguably the most complex visual system in any species. Visual system_sentence_195

The eye of the mantis shrimp holds 16 color receptive cones, whereas humans only have three. Visual system_sentence_196

The variety of cones enables them to perceive an enhanced array of colors as a mechanism for mate selection, avoidance of predators, and detection of prey. Visual system_sentence_197

Swordfish also possess an impressive visual system. Visual system_sentence_198

The eye of a swordfish can generate heat to better cope with detecting their prey at depths of 2000 feet. Visual system_sentence_199

Certain one-celled micro-organisms, the warnowiid dinoflagellates have eye-like ocelloids, with analogous structures for the lens and retina of the multi-cellular eye. Visual system_sentence_200

The armored shell of the chiton Acanthopleura granulata is also covered with hundreds of aragonite crystalline eyes, named ocelli, which can form images. Visual system_sentence_201

Many fan worms, such as Acromegalomma interruptum which live in tubes on the sea floor of the Great Barrier Reef, have evolved compound eyes on their tentacles, which they use to detect encroaching movement. Visual system_sentence_202

If movement is detected the fan worms will rapidly withdraw their tentacles. Visual system_sentence_203

Bok, et al, have discovered opsins and G proteins in the fan worm's eyes, which were previously only seen in simple ciliary photoreceptors in the brains of some invertebrates, as opposed to the rhabdomeric receptors in the eyes of most invertebrates. Visual system_sentence_204

Only higher primate Old World (African) monkeys and apes (macaques, apes, orangutans) have the same kind of three-cone photoreceptor color vision humans have, while lower primate New World (South American) monkeys (spider monkeys, squirrel monkeys, cebus monkeys) have a two-cone photoreceptor kind of color vision. Visual system_sentence_205

History Visual system_section_22

In the second half of the 19th century, many motifs of the nervous system were identified such as the neuron doctrine and brain localization, which related to the neuron being the basic unit of the nervous system and functional localisation in the brain, respectively. Visual system_sentence_206

These would become tenets of the fledgling neuroscience and would support further understanding of the visual system. Visual system_sentence_207

The notion that the cerebral cortex is divided into functionally distinct cortices now known to be responsible for capacities such as touch (somatosensory cortex), movement (motor cortex), and vision (visual cortex), was first proposed by Franz Joseph Gall in 1810. Visual system_sentence_208

Evidence for functionally distinct areas of the brain (and, specifically, of the cerebral cortex) mounted throughout the 19th century with discoveries by Paul Broca of the language center (1861), and Gustav Fritsch and Edouard Hitzig of the motor cortex (1871). Visual system_sentence_209

Based on selective damage to parts of the brain and the functional effects of the resulting lesions, David Ferrier proposed that visual function was localized to the parietal lobe of the brain in 1876. Visual system_sentence_210

In 1881, Hermann Munk more accurately located vision in the occipital lobe, where the primary visual cortex is now known to be. Visual system_sentence_211

In 2014, a textbook "Understanding vision: theory, models, and data" illustrates how to link neurobiological data and visual behavior/psychological data through theoretical principles and computational models. Visual system_sentence_212

See also Visual system_section_23

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Visual system.