Editing Visual system (section)

== System overview ==
[[File:Comprehensive List of Relevant Pathways for the Visual System.png|thumb|This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for vision to their relevant endpoints in the human brain. Click to enlarge the image.]]
[[File:ERP - optic cabling.jpg|thumb|left|300px|Representation of optic pathways from each of the 4 quadrants of view for both eyes simultaneously]]

=== Optical ===
Together, the [[cornea]] and [[Lens (anatomy)|lens]] refract light into a small image and shine it on the [[retina]]. The retina [[Visual phototransduction|transduces]] this image into electrical pulses using [[Rods (eye)|rods]] and [[Cones (eye)|cones]]. The [[optic nerve]] then carries these pulses through the [[optic canal]]. Upon reaching the [[optic chiasm]] the nerve fibers decussate (left becomes right). The fibers then branch and terminate in three places.<ref>"How the Human Eye Sees." [[WebMD]]. Ed. Alan Kozarsky. WebMD, 3 October 2015. Web. 27 March 2016.</ref><ref>Than, Ker. "How the Human Eye Works." [[Live Science|LiveScience]]. [[TechMedia Network, Inc.|TechMedia Network]], 10 February 2010.   Web. 27 March 2016.</ref><ref>"How the Human Eye Works | Cornea Layers/Role | Light Rays." NKCF. The Gavin Herbert Eye Institute. Web. 27 March 2016.</ref><ref>Albertine, Kurt. Barron's Anatomy Flash Cards</ref><ref>Tillotson, Joanne. McCann, Stephanie. Kaplan's Medical Flashcards. April 2, 2013.</ref><ref>"Optic Chiasma." Optic Chiasm Function, Anatomy & Definition. Healthline Medical Team, 9 March 2015. Web. 27 March 2016.</ref><ref>Jefferey, G., and M. M. Neveu. "Chiasm Formation in Man Is Fundamentally Different from That in the Mouse." [[Nature (journal)|Nature.com]]. [[Nature Publishing Group]], 21 March 2007. Web. 27 March 2016.</ref>

=== Neural ===
Most of the optic nerve fibers end in the [[lateral geniculate nucleus]] (LGN). 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. These tags predict object movement.

The LGN also sends some fibers to V2 and V3.<ref>Card, J. Patrick, and Robert Y. Moore. "Organization of Lateral Geniculate-hypothalamic Connections in the Rat." [[Wiley Online Library]]. 1 June. 1989. Web. 27 March 2016.</ref><ref>{{Cite journal |last1=Murphy |first1=Penelope C. |last2=Duckett |first2=Simon G. |last3=Sillito |first3=Adam M. |date=1999-11-19 |title=Feedback Connections to the Lateral Geniculate Nucleus and Cortical Response Properties |url=http://dx.doi.org/10.1126/science.286.5444.1552 |journal=Science |volume=286 |issue=5444 |pages=1552–1554 |doi=10.1126/science.286.5444.1552 |pmid=10567260 |issn=0036-8075|url-access=subscription }}</ref><ref>{{Cite journal |last1=Schiller |first1=P. H. |last2=Malpeli |first2=J. G. |date=1978-05-01 |title=Functional specificity of lateral geniculate nucleus laminae of the rhesus monkey |url=https://www.physiology.org/doi/10.1152/jn.1978.41.3.788 |journal=Journal of Neurophysiology |language=en |volume=41 |issue=3 |pages=788–797 |doi=10.1152/jn.1978.41.3.788 |pmid=96227 |issn=0022-3077|url-access=subscription }}</ref><ref>{{Cite journal |last1=Schmielau |first1=F. |last2=Singer |first2=W. |date=1977 |title=The role of visual cortex for binocular interactions in the cat lateral geniculate nucleus |url=https://linkinghub.elsevier.com/retrieve/pii/0006899377909143 |journal=Brain Research |language=en |volume=120 |issue=2 |pages=354–361 |doi=10.1016/0006-8993(77)90914-3|pmid=832128 |s2cid=28796357 |url-access=subscription }}</ref><ref>{{Cite journal |last1=Clay Reid |first1=R. |last2=Alonso |first2=Jose-Manuel |date=1995-11-16 |title=Specificity of monosynaptic connections from thalamus to visual cortex |url=http://dx.doi.org/10.1038/378281a0 |journal=Nature |volume=378 |issue=6554 |pages=281–284 |doi=10.1038/378281a0 |pmid=7477347 |bibcode=1995Natur.378..281C |s2cid=4285683 |issn=0028-0836|url-access=subscription }}</ref>

V1 performs edge-detection to understand spatial organization (initially, 40 milliseconds in, focusing on even small spatial and color changes. Then, 100 milliseconds in, upon receiving the translated LGN, V2, and V3 info, also begins focusing on global organization). V1 also creates a bottom-up [[saliency map]] to guide attention or [[gaze shift]].<ref>{{Cite book |last=Zhaoping |first=Li |url=https://academic.oup.com/book/8719 |title=Understanding Vision: Theory, Models, and Data |date=2014-05-08 |publisher=Oxford University Press |isbn=978-0-19-956466-8 |edition=1st |language=en |chapter=The V1 hypothesis—creating a bottom-up saliency map for preattentive selection and segmentation |doi=10.1093/acprof:oso/9780199564668.001.0001}}</ref>

V2 both forwards (direct and via [[Pulvinar nuclei|pulvinar]]) pulses to V1 and receives them. Pulvinar is responsible for [[saccade]] and visual attention. 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. V2 connects to V1 - V5.

V3 helps process '[[global motion]]' (direction and speed) of objects. V3 connects to V1 (weak), V2, and the [[inferior temporal cortex]].<ref>{{Cite journal |last1=Heim |first1=Stefan |last2=Eickhoff |first2=Simon B. |last3=Ischebeck |first3=Anja K. |last4=Friederici |first4=Angela D. |last5=Stephan |first5=Klaas E. |last6=Amunts |first6=Katrin |date=2009 |title=Effective connectivity of the left BA 44, BA 45, and inferior temporal gyrus during lexical and phonological decisions identified with DCM |journal=Human Brain Mapping |language=en |volume=30 |issue=2 |pages=392–402 |doi=10.1002/hbm.20512 |issn=1065-9471 |pmc=6870893 |pmid=18095285}}</ref><ref>Catani, Marco, and Derek K. Jones. "Brain." Occipito‐temporal Connections in the Human Brain. 23 June 2003. Web. 27 March 2016.</ref>

V4 recognizes simple shapes, and gets input from V1 (strong), V2, V3, LGN, and pulvinar.<ref>{{Cite journal |last1=Benevento |first1=Louis A. |last2=Standage |first2=Gregg P. |date=1983-07-01 |title=The organization of projections of the retinorecipient and nonretinorecipient nuclei of the pretectal complex and layers of the superior colliculus to the lateral pulvinar and medial pulvinar in the macaque monkey |url=https://onlinelibrary.wiley.com/doi/10.1002/cne.902170307 |journal=Journal of Comparative Neurology |language=en |volume=217 |issue=3 |pages=307–336 |doi=10.1002/cne.902170307 |pmid=6886056 |s2cid=44794002 |issn=0021-9967|url-access=subscription }}</ref> V5's outputs include V4 and its surrounding area, and eye-movement motor cortices ([[Frontal eye fields|frontal eye-field]] and [[Lateral intraparietal cortex|lateral intraparietal area]]).

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. V6 works in conjunction with V5 on motion analysis. V5 analyzes self-motion, whereas V6 analyzes motion of objects relative to the background. V6's primary input is V1, with V5 additions. V6 houses the [[Topographic map|topographical map]] for vision. V6 outputs to the region directly around it (V6A). V6A has direct connections to arm-moving cortices, including the [[premotor cortex]].<ref>{{Cite journal |last1=Hirsch |first1=Ja |last2=Gilbert |first2=Cd |date=1991-06-01 |title=Synaptic physiology of horizontal connections in the cat's visual cortex |journal=The Journal of Neuroscience |language=en |volume=11 |issue=6 |pages=1800–1809 |doi=10.1523/JNEUROSCI.11-06-01800.1991 |issn=0270-6474 |pmc=6575415 |pmid=1675266}}</ref><ref>{{Cite journal |last1=Schall |first1=JD |last2=Morel |first2=A. |last3=King |first3=DJ |last4=Bullier |first4=J. |date=1995-06-01 |title=Topography of visual cortex connections with frontal eye field in macaque: convergence and segregation of processing streams |journal=The Journal of Neuroscience |language=en |volume=15 |issue=6 |pages=4464–4487 |doi=10.1523/JNEUROSCI.15-06-04464.1995 |issn=0270-6474 |pmc=6577698 |pmid=7540675}}</ref>

The [[inferior temporal gyrus]] recognizes complex shapes, objects, and faces or, in conjunction with the [[hippocampus]], creates new [[memories]].<ref>Moser, May-Britt, and Edvard I. Moser. "Functional Differentiation in the Hippocampus." Wiley Online Library. 1998. Web. 27 March 2016.</ref> The [[pretectal area]] is seven unique [[Nucleus (neuroanatomy)|nuclei]]. Anterior, posterior and medial pretectal nuclei inhibit pain (indirectly), aid in [[Rapid eye movement sleep|REM]], and aid the [[accommodation reflex]], respectively.<ref>{{Cite journal |last1=Kanaseki |first1=T. |last2=Sprague |first2=J. M. |date=1974-12-01 |title=Anatomical organization of pretectal nuclei and tectal laminae in the cat |url=https://onlinelibrary.wiley.com/doi/10.1002/cne.901580307 |journal=Journal of Comparative Neurology |language=en |volume=158 |issue=3 |pages=319–337 |doi=10.1002/cne.901580307 |pmid=4436458 |s2cid=38463227 |issn=0021-9967|url-access=subscription }}</ref> The [[Edinger–Westphal nucleus|Edinger-Westphal nucleus]] moderates [[pupil dilation]] and aids (since it provides parasympathetic fibers) in convergence of the eyes and lens adjustment.<ref>Reiner, Anton, and Harvey J. Karten. "Parasympathetic Ocular Control — Functional Subdivisions and Circuitry of the Avian Nucleus of Edinger-Westphal."Science Direct. 1983. Web. 27 March 2016.</ref> Nuclei of the optic tract are involved in smooth pursuit eye movement and the accommodation reflex, as well as REM.

The [[suprachiasmatic nucleus]] is the region of the [[hypothalamus]] that halts production of [[melatonin]] (indirectly) at first light.<ref>{{Cite journal |last1=Welsh |first1=David K |last2=Logothetis |first2=Diomedes E |last3=Meister |first3=Markus |last4=Reppert |first4=Steven M |date=April 1995 |title=Individual neurons dissociated from rat suprachiasmatic nucleus express independently phased circadian firing rhythms |journal=Neuron |language=en |volume=14 |issue=4 |pages=697–706 |doi=10.1016/0896-6273(95)90214-7|pmid=7718233 |doi-access=free }}</ref>