Editing Visual system (section)

===Visual cortex===
{{Main|Visual cortex}}
[[File:Brodmann areas 17 18 19.png|thumb|200px|[[Visual cortex]]: <br />V1; V2; V3; V4; V5 (also called MT)]]
The visual cortex <!--is the largest system in the human brain{{citation needed|date=September 2024}} and--> is responsible for processing the visual image. It lies at the rear of the brain (highlighted in the image), above the [[cerebellum]]. The region that receives information directly from the LGN is called the [[Visual cortex#Primary visual cortex (V1)|primary visual cortex]] (also called V1 and striate cortex). It creates a bottom-up saliency map of the visual field to guide attention or eye gaze to salient visual locations.<ref name=":0">{{Cite journal|last=Li|first=Z|date=2002|title=A saliency map in primary visual cortex|url=https://www.sciencedirect.com/science/article/abs/pii/S1364661300018179|journal=Trends in Cognitive Sciences|volume=6|issue=1|pages=9–16|doi=10.1016/s1364-6613(00)01817-9|pmid=11849610|s2cid=13411369|url-access=subscription}}</ref>{{Clarify|date=September 2024|reason=The source says they are proposing something; can it be cited as consolidated knowledge?}} Hence selection of visual input information by attention starts at V1<ref>{{Cite journal|last=Zhaoping|first=L.|date=2019|title=A new framework for understanding vision from the perspective of the primary visual cortex|url=https://www.sciencedirect.com/science/article/abs/pii/S0959438819300042|journal=Current Opinion in Neurobiology|volume=58|pages=1–10|doi=10.1016/j.conb.2019.06.001|pmid=31271931|s2cid=195806018|url-access=subscription}}</ref> along the visual pathway.

Visual information then flows through a cortical hierarchy.  These areas include V2, V3, V4 and area V5/MT. (The exact connectivity depends on the species of the animal.) These secondary visual areas (collectively termed the extrastriate visual cortex) process a wide variety of visual primitives. Neurons in V1 and V2 respond selectively to bars of specific orientations, or combinations of bars.  These are believed to support edge and corner detection.  Similarly, basic information about color and motion is processed here.<ref>{{cite book |author1=Jessell, Thomas M. |author2=Kandel, Eric R. |author3=Schwartz, James H. |title=Principles of neural science |publisher=McGraw-Hill |chapter=27. Central visual pathways |location=New York |year=2000 |pages=[https://archive.org/details/isbn_9780838577011/page/533 533–540] |isbn=978-0-8385-7701-1 |oclc=42073108 |url-access=registration |url=https://archive.org/details/isbn_9780838577011/page/533 }}</ref>

Heider, et al. (2002) 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.<ref>[http://watarts.uwaterloo.ca/~cellard/teaching/PSYC771/heideretal%282002%29.pdf Heider, Barbara; Spillmann, Lothar; Peterhans, Esther (2002)  "Stereoscopic Illusory Contours— Cortical Neuron Responses and Human Perception" ''J. Cognitive Neuroscience'' '''14''':7 pp.1018-29] {{Webarchive|url=https://web.archive.org/web/20161011144931/http://watarts.uwaterloo.ca/~cellard/teaching/PSYC771/heideretal%282002%29.pdf |date=2016-10-11 }} accessdate=2014-05-18</ref>

[[File:restingStateModels.jpg|thumb|right|Visual cortex is active even during [[resting state fMRI]]. ]]