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The what vs. where account of the ventral/dorsal pathways was first described by [[Leslie Ungerleider|Ungerleider]] and [[Mortimer Mishkin|Mishkin]].<ref name="UngerleiderMishkin82">{{cite book|title=Analysis of Visual Behavior|chapter-url=https://archive.org/details/analysisofvisual00ingl|chapter-url-access=registration|vauthors=Ungerleider LG, Mishkin M|publisher=MIT Press|year=1982|veditors=Ingle DJ, Goodale MA, Mansfield RJ|location=Boston|pages=[https://archive.org/details/analysisofvisual00ingl/page/549 549–586]|chapter=Two Cortical Visual Systems|isbn=978-0-262-09022-3}}</ref>
More recently, [[Melvyn A. Goodale|Goodale]] and Milner extended these ideas and suggested that the ventral stream is critical for visual perception whereas the dorsal stream mediates the visual control of skilled actions.<ref name="GoodaleMilner">{{cite journal |year=1992 |title=Separate pathways for perception and action
Work such as the one from Franz et al.<ref name="Franz2005">{{cite journal |year=2005 |title=Illusion effects on grasping are temporally constant not dynamic
== Primary visual cortex (V1) ==
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The primary visual cortex is divided into six functionally distinct layers, labeled 1 to 6. Layer 4, which receives most visual input from the [[lateral geniculate nucleus]] (LGN), is further divided into 4 layers, labelled 4A, 4B, 4Cα, and 4Cβ. Sublamina 4Cα receives mostly [[Magnocellular cell|magnocellular]] input from the LGN, while layer 4Cβ receives input from [[Parvocellular cell|parvocellular]] pathways.<ref>Hubel, D.H., Wiesel, T.N.. ''Laminar and columnar distribution of geniculo-cortical fibers in the macaque monkey.'' Journal of Comparative Neurology, Issue 146, 421–450, 1972.</ref>
The average number of neurons in the adult human primary visual cortex in each hemisphere has been estimated at 140 million.<ref name="Leuba-Kraftsik-1994">{{cite journal |
=== Function ===
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The tuning properties of V1 neurons (what the neurons respond to) differ greatly over time. Early in time (40 ms and further) individual V1 neurons have strong tuning to a small set of stimuli. That is, the neuronal responses can discriminate small changes in visual [[Orientation (mental)|orientations]], [[spatial frequencies]] and [[color]]s (as in the optical system of a [[camera obscura]], but projected onto [[retina]]l cells of the eye, which are clustered in density and fineness).<ref name= kepler1604 /> Each V1 neuron propagates a signal from a retinal cell, in continuation. Furthermore, individual V1 neurons in humans and other animals with [[binocular vision]] have ocular dominance, namely tuning to one of the two eyes. In V1, and primary sensory cortex in general, neurons with similar tuning properties tend to cluster together as [[cortical column]]s. [[David Hubel]] and [[Torsten Wiesel]] proposed the classic ice-cube organization model of cortical columns for two tuning properties: [[ocular dominance columns|ocular dominance]] and orientation. However, this model cannot accommodate the color, spatial frequency and many other features to which neurons are tuned {{Citation needed|date=November 2011}}. The exact organization of all these cortical columns within V1 remains a hot topic of current research. The mathematical modeling of this function has been compared to [[Gabor transform]]s.{{Citation needed|date=May 2023}}
Later in time (after 100 ms), neurons in V1 are also sensitive to the more global organisation of the scene (Lamme & Roelfsema, 2000).<ref>{{cite book |last1=Barghout |first1=Lauren |title=Vision: How Global Perceptual Context Changes Local Contrast Processing (Ph.D. Dissertation). Updated to include computer vision techniques |date=2003 |publisher=Scholar's Press |isbn=978-3-639-70962-9 |url=https://www.morebooks.de/store/gb/book/vision/isbn/978-3-639-70962-9}}</ref> These response properties probably stem from recurrent [[feedback]] processing (the influence of higher-tier cortical areas on lower-tier cortical areas) and lateral connections from [[Pyramidal cell|pyramidal neurons]] (Hupe et al. 1998). While feedforward connections are mainly driving, feedback connections are mostly modulatory in their effects (Angelucci et al., 2003; Hupe et al., 2001). Evidence shows that feedback originating in higher-level areas such as V4, IT, or MT, with bigger and more complex receptive fields, can modify and shape V1 responses, accounting for contextual or extra-classical receptive field effects (Guo et al., 2007; Huang et al., 2007; Sillito et al., 2006).
The visual information relayed to V1 is not coded in terms of spatial (or optical) imagery{{citation needed|date=July 2020}} but rather are better described as [[edge detection]].<ref>{{cite journal |last1=Kesserwani |first1=Hassan |title=The Biophysics of Visual Edge Detection: A Review of Basic Principles |journal=Cureus |date=28 October 2020 |volume=12 |issue=10 |doi=
A theoretical explanation of the computational function of the simple cells in the primary visual cortex has been presented in.<ref name=Lin13BICY>{{cite journal |
{{anchor|saliencyMap}}
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According to the [[V1 Saliency Hypothesis]], V1 does this by transforming visual inputs to neural firing rates from millions of neurons, such that the visual location signaled by the highest firing neuron is the most salient location to attract gaze shift. V1's outputs are received by the [[superior colliculus]] (in the mid-brain), among other locations, which reads out the V1 activities to guide gaze shifts.
Differences in size of V1 also seem to have an effect on the [[Interindividual differences in perception|perception of illusions]].<ref name="surface_V1">{{cite journal |
== V2 == <!--Please keep this header, as it is a redirect -->
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'''Visual area V2''', or '''secondary visual cortex''', also called '''prestriate cortex''',<ref>Gazzaniga, Ivry & Mangun: ''Cognitive neuroscience,'' 2002</ref> is the second major area in the visual cortex, and the first region within the '''visual association area'''. It receives strong [[feedforward]] connections from V1 (direct and via the pulvinar) and sends strong connections to V3, V4, and V5. It also sends strong [[feedback]] connections to V1{{citation needed|date=February 2019}}.
In terms of anatomy, V2 is split into four quadrants, a [[Dorsum (biology)|dorsal]] and [[ventral]] representation in the left and the right [[cerebral hemisphere|hemispheres]]. Together, these four regions provide a complete map of the visual world. V2 has many properties in common with V1: Cells are tuned to simple properties such as orientation, spatial frequency, and color. The responses of many V2 neurons are also modulated by more complex properties, such as the orientation of [[illusory contours]],<ref name="illusory contours">{{cite journal |last1=von der Heydt |first1=R |last2=Peterhans |first2=E |last3=Baumgartner |first3=G |title=Illusory contours and cortical neuron responses |journal=Science |date=1984 |volume=224|issue=4654|pages=1260–62 |doi=10.1126/science.6539501 |pmid=6539501|bibcode=1984Sci...224.1260V}}</ref><ref name="A. Anzai, X. Peng 2007"/> [[binocular disparity]],<ref name="stereoscopic edges">{{cite journal|last1=von der Heydt |first1=R |last2=Zhou|first2=H|last3=Friedman|first3=H. S |title=Representation of stereoscopic edges in monkey visual cortex |journal=Vision Research |date=2000 |volume=40 |issue=15 |pages=1955–67 |doi=10.1016/s0042-6989(00)00044-4 |pmid=10828464 |s2cid=10269181 |doi-access=free}}</ref> and whether the stimulus is part of the figure or the ground.<ref>{{cite journal |last1=Qiu |first1=F. T |last2=von der Heydt |first2=R |title=Figure and ground in the visual cortex: V2 combines stereoscopic cues with Gestalt rules |journal=Neuron |date=2005 |volume=47 |issue=1 |pages=155–66 |pmid=15996555 |pmc=1564069 |doi=10.1016/j.neuron.2005.05.028
It is argued that the entire ventral visual-to-hippocampal stream is important for visual memory.<ref>{{cite journal|
In one study, the Layer 6 cells of the V2 cortex were found to play a very important role in the storage of Object Recognition Memory as well as the conversion of short-term object memories into long-term memories.<ref>{{cite journal|last1=López-Aranda
== Third visual cortex, including area V3 ==
[[File:Visual field maps.jpg|thumb|left|A visual field map of the primary visual cortex and the numerous extrastriate areas.
The term '''third visual complex''' refers to the region of cortex located immediately in front of V2, which includes the region named '''visual area V3''' in humans. The "complex" nomenclature is justified by the fact that some controversy still exists regarding the exact extent of area V3, with some researchers proposing that the cortex located in front of V2 may include two or three functional subdivisions. For example, David Van Essen and others (1986) have proposed the existence of a "dorsal V3" in the upper part of the cerebral hemisphere, which is distinct from the "ventral V3" (or ventral posterior area, VP) located in the lower part of the brain. Dorsal and ventral V3 have distinct connections with other parts of the brain, appear different in sections stained with a variety of methods, and contain neurons that respond to different combinations of visual stimulus (for example, colour-selective neurons are more common in the ventral V3). Additional subdivisions, including V3A and V3B have also been reported in humans. These subdivisions are located near dorsal V3, but do not adjoin V2.
Dorsal V3 is normally considered to be part of the dorsal stream, receiving inputs from V2 and from the primary visual area and projecting to the posterior [[parietal cortex]]. It may be anatomically located in [[Brodmann area 19]]. Braddick using fMRI has suggested that area V3/V3A may play a role in the processing of [[global motion]]<ref name="Braddick2001">{{cite journal |
Ventral V3 (VP), has much weaker connections from the primary visual area, and stronger connections with the [[inferior temporal cortex]]. While earlier studies proposed that VP contained a representation of only the upper part of the visual field (above the point of fixation), more recent work indicates that this area is more extensive than previously appreciated, and like other visual areas it may contain a complete visual representation. The revised, more extensive VP is referred to as the ventrolateral posterior area (VLP) by Rosa and Tweedale.<ref>{{cite journal |
== V4 ==
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[[File:Fusiform gyrus animation.gif|thumb|The fusiform gyrus is the hypothetical location of V4α, a secondary area for colour processing. More: [[Colour centre]]]]
'''Visual area V4''' is one of the visual areas in the [[extrastriate]] visual cortex. In [[Rhesus macaque|macaques]], it is located anterior to V2 and posterior to [[Inferior temporal gyrus|posterior inferotemporal area (PIT)]]. It comprises at least four regions (left and right V4d, left and right V4v), and some groups report that it contains rostral and caudal subdivisions as well. It is unknown whether the human V4 is as expansive as that of the macaque [[homology (biology)|homologue]] which is a subject of debate.<ref name="GoddardEtAl">{{cite journal |
V4 is the third cortical area in the [[Two-streams hypothesis#Ventral stream|ventral stream]], receiving strong feedforward input from V2 and sending strong connections to the [[Inferior temporal gyrus|PIT]]. It also receives direct input from V1, especially for central space. In addition, it has weaker connections to V5 and [[Angular gyrus|dorsal prelunate gyrus]] (DP).
V4 is the first area in the [[Two-streams hypothesis#Ventral stream|ventral stream]] to show strong attentional modulation. Most studies indicate that [[selective attention]] can change firing rates in V4 by about 20%. A seminal paper by Moran and Desimone characterizing these effects was the first paper to find attention effects anywhere in the visual cortex.<ref>{{cite journal|
Like V2, V4 is tuned for orientation, spatial frequency, and color.
The firing properties of V4 were first described by [[Semir Zeki]] in the late 1970s, who also named the area. Before that, V4 was known by its anatomical description, the [[prelunate gyrus]]. Originally, Zeki argued that the purpose of V4 was to process color information. Work in the early 1980s proved that V4 was as directly involved in form recognition as earlier cortical areas.{{citation needed|date=March 2016}} This research supported the [[two-streams hypothesis]], first presented by Ungerleider and Mishkin in 1982.
Recent work has shown that V4 exhibits long-term plasticity,<ref>{{cite journal|last1=Schmid|first1=M. C.|last2=Schmiedt|first2=J. T. |last3=Peters|first3=A. J. |last4=Saunders|first4=R. C.|last5=Maier|first5=A.|last6=Leopold|first6=D. A.|title=Motion-Sensitive Responses in Visual Area V4 in the Absence of Primary Visual Cortex|journal=Journal of Neuroscience|date=27 November 2013|volume=33|issue=48|pages=18740–18745|doi=10.1523/JNEUROSCI.3923-13.2013 |pmid=24285880 |pmc=3841445}}</ref> encodes stimulus salience, is gated by signals coming from the [[frontal eye fields]],<ref>{{Cite journal |last1=Moore |first1=Tirin |author-link1=Tirin Moore|last2=Armstrong|first2=Katherine M. |title=Selective gating of visual signals by microstimulation of frontal cortex |journal=Nature |volume=421|issue=6921|pages=370–373 |doi=10.1038/nature01341|pmid=12540901|bibcode=2003Natur.421..370M|year=2003|s2cid=4405385}}</ref> and shows changes in the spatial profile of its receptive fields with attention.{{citation needed|date=March 2016}} In addition, it has recently been shown that activation of area V4 in humans (area V4h) is observed during the perception and retention of the color of objects, but not their shape.<ref>{{Citation |last1=Kozlovskiy |first1=Stanislav |title=How Areas of Ventral Visual Stream Interact When We Memorize Color and Shape Information |date=2021 |url=https://link.springer.com/10.1007/978-3-030-71637-0_10 |work=Advances in Cognitive Research, Artificial Intelligence and Neuroinformatics |volume=1358 |pages=95–100 |editor-last=Velichkovsky |editor-first=Boris M. |access-date=2023-10-18 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-71637-0_10 |isbn=978-3-030-71636-3 |last2=Rogachev |first2=Anton |editor2-last=Balaban |editor2-first=Pavel M. |editor3-last=Ushakov |editor3-first=Vadim L.}}</ref><ref>{{Cite journal |last1=Stanislav |first1=Kozlovskiy |last2=Rogachev |first2=Anton |date=October 2021 |title=Ventral Visual Cortex Areas and Processing of Color and Shape in Visual Working Memory |url=https://linkinghub.elsevier.com/retrieve/pii/S0167876021006437 |journal=International Journal of Psychophysiology |language=en |volume=168 |pages=S155–S156 |doi=10.1016/j.ijpsycho.2021.07.437}}</ref>
== Middle temporal visual area (V5) ==<!-- This section is linked from [[V5]] -->
The '''middle temporal visual area''' ('''MT''' or '''V5''') is a region of extrastriate visual cortex. In several species of both [[New World monkey]]s and [[Old World monkey]]s the MT area contains a high concentration of direction-selective neurons.<ref name="BornBradley" /> The MT in primates is thought to play a major role in the [[motion perception|perception of motion]], the integration of local motion signals into global percepts, and the guidance of some [[Eye movement (sensory)|eye movements]].<ref name="BornBradley">{{cite journal |vauthors=Born R, Bradley D |
=== Connections ===
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MT is connected to a wide array of cortical and subcortical brain areas. Its input comes from visual cortical areas V1, V2 and dorsal V3 ([[dorsomedial area]]),<ref name="FellemanVanEssen">{{cite journal |vauthors=Felleman D, Van Essen D | title = Distributed hierarchical processing in the primate cerebral cortex | journal = [[Cerebral Cortex]] | volume = 1 | issue = 1 | pages = 1–47 | year = 1991| pmid = 1822724 | doi = 10.1093/cercor/1.1.1-a| doi-access = free }}</ref><ref name="UngerleiderDesimone">{{cite journal |vauthors=Ungerleider L, Desimone R | title = Cortical connections of visual area MT in the macaque | journal = Journal of Comparative Neurology | volume = 248 | issue = 2 | pages = 190–222 | year = 1986 | pmid = 3722458 | doi = 10.1002/cne.902480204| s2cid = 1876622 | url = https://zenodo.org/record/1229147 }}</ref> the [[koniocellular]] regions of the [[LGN]],<ref name="Sincich">{{cite journal |vauthors=Sincich L, Park K, Wohlgemuth M, Horton J | title = Bypassing V1: a direct geniculate input to area MT | journal = Nature Neuroscience | volume = 7 | issue = 10 | pages = 1123–8 | year = 2004 | pmid = 15378066 | doi = 10.1038/nn1318| s2cid = 13419990 }}</ref> and the [[pulvinar nuclei|inferior pulvinar]].<ref>{{cite journal |vauthors=Warner CE, Goldshmit Y, Bourne JA | title = Retinal afferents synapse with relay cells targeting the middle temporal area in the pulvinar and lateral geniculate nuclei | journal = Frontiers in Neuroanatomy | volume = 4 | page = 8 | year = 2010 | pmid = 20179789 | doi = 10.3389/neuro.05.008.2010 | pmc=2826187| doi-access = free }}</ref> The pattern of projections to MT changes somewhat between the representations of the foveal and peripheral visual fields, with the latter receiving inputs from areas located in the midline cortex and [[retrosplenial region]].<ref name="PalmerRosa2006">{{cite journal |vauthors=Palmer SM, Rosa MG | year=2006 | title=A distinct anatomical network of cortical areas for analysis of motion in far peripheral vision | journal=European Journal of Neuroscience | volume=24 |pages=2389–405 | doi=10.1111/j.1460-9568.2006.05113.x | pmid=17042793 | issue=8| s2cid=21562682 }}</ref>
A standard view is that V1 provides the "most important" input to MT.<ref name="BornBradley" /> Nonetheless, several studies have demonstrated that neurons in MT are capable of responding to visual information, often in a direction-selective manner, even after V1 has been destroyed or inactivated.<ref>{{cite journal |
MT sends its major output to areas located in the cortex immediately surrounding it, including areas FST, [[Medial superior temporal area|MST]], and V4t (middle temporal crescent). Other projections of MT target the eye movement-related areas of the frontal and parietal lobes (frontal eye field and lateral intraparietal area).
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The first studies of the [[electrophysiological]] properties of neurons in MT showed that a large portion of the cells are [[neuronal tuning|tuned]] to the speed and direction of moving visual stimuli.<ref name="DubnerZeki">{{cite journal |vauthors=Dubner R, Zeki S | title = Response properties and receptive fields of cells in an anatomically defined region of the superior temporal sulcus in the monkey | journal = Brain Research | volume = 35 | issue = 2 | pages = 528–32 | year = 1971 | pmid = 5002708 | doi = 10.1016/0006-8993(71)90494-X}}.</ref><ref name="MaunsellVanEssen">{{cite journal |vauthors=Maunsell J, Van Essen D | title = Functional properties of neurons in middle temporal visual area of the macaque monkey. I. Selectivity for stimulus direction, speed, and orientation | journal = Journal of Neurophysiology | volume = 49 | issue = 5 | pages = 1127–47 | year = 1983 | pmid = 6864242| doi = 10.1152/jn.1983.49.5.1127 | s2cid = 8708245 }}</ref>
[[Lesion]] studies have also supported the role of MT in motion perception and eye movements.<ref name=Dursteler1987>{{cite journal | title=Directional pursuit deficits following lesions of the foveal representation within the superior temporal sulcus of the macaque monkey |
However, since neurons in V1 are also tuned to the direction and speed of motion, these early results left open the question of precisely what MT could do that V1 could not. Much work has been carried out on this region, as it appears to integrate local visual motion signals into the global motion of complex objects.<ref name="Movshon">Movshon, J.A., Adelson, E.H., Gizzi, M.S., & Newsome, W.T. (1985). The analysis of moving visual patterns. In: C. Chagas, R. Gattass, & C. Gross (Eds.), Pattern recognition mechanisms (pp. 117–151), Rome: Vatican Press.</ref>
For example, ''lesion'' to the V5 leads to deficits in perceiving motion and processing of complex stimuli. It contains many neurons selective for the motion of complex visual features (line ends, corners). ''Microstimulation'' of a neuron located in the V5 affects the perception of motion. For example, if one finds a neuron with preference for upward motion in a monkey's V5 and stimulates it with an electrode, then the monkey becomes more likely to report 'upward' motion when presented with stimuli containing 'left' and 'right' as well as 'upward' components.<ref name="BrittenVanWezel">{{cite journal | title=Electrical microstimulation of cortical area MST biases heading perception in monkeys |
There is still much controversy over the exact form of the computations carried out in area MT<ref name="Wilson">{{cite journal | last1 = Wilson | first1 = H.R. | last2 = Ferrera | first2 = V.P. | last3 = Yo | first3 = C. | year = 1992 | title = A psychophysically motivated model for two-dimensional motion perception | journal = Visual Neuroscience | volume = 9 | issue = 1| pages = 79–97 | doi=10.1017/s0952523800006386| pmid = 1633129 | s2cid = 45196189 }}</ref> and some research suggests that feature motion is in fact already available at lower levels of the visual system such as V1.
<ref name="Tinsley">{{cite journal | title=The nature of V1 neural responses to 2D moving patterns depends on receptive-field structure in the marmoset monkey |
<ref name="PackBorn">{{cite journal | title=Two-dimensional substructure of stereo and motion interactions in macaque visual cortex |
=== Functional organization ===
MT was shown to be organized in direction columns.<ref name="Albright">{{cite journal |
==V6==
<!-- [[Dorsomedial area]] redirects to this section -->
The '''dorsomedial area''' (DM) also known as '''V6''', appears to respond to visual stimuli associated with self-motion<ref>{{cite journal |
There are similarities between the visual area V5 and V6 of the [[common marmoset]]. Both areas receive direct connections from the [[primary visual cortex]].<ref name= humanV6 />{{rp|7971}} And both have a high [[myelin]] content, a characteristic that is usually present in brain structures involved in fast transmission of information.<ref name="pitzalis2012">{{cite journal | pmc=3546310 | year=2013 | last1=Pitzalis | first1=S. | last2=Fattori | first2=P. | last3=Galletti | first3=C. | title=The functional role of the medial motion area V6 | journal=Frontiers in Behavioral Neuroscience | volume=6 | page=91 | doi=10.3389/fnbeh.2012.00091 | pmid=23335889 | doi-access=free }}</ref>
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Neurons in area DM/V6 of [[night monkey]]s and [[common marmoset]]s have unique response properties, including an extremely sharp selectivity for the orientation of visual contours, and preference for long, uninterrupted lines covering large parts of the visual field.<ref>{{cite journal |vauthors=Baker JF, etal | year = 1981 | title = Visual response properties of neurons in four extrastriate visual areas of the owl monkey (Aotus trivirgatus): a quantitative comparison of medial, dorsomedial, dorsolateral, and middle temporal areas | journal = Journal of Neurophysiology | volume = 45 | issue = 3| pages = 397–416 | doi = 10.1152/jn.1981.45.3.397 | pmid = 7218008 | s2cid = 9865958 }}</ref><ref>{{cite journal |vauthors=Lui LL, etal | year = 2006 | title = Functional response properties of neurons in the dorsomedial visual area of New World monkeys (Callithrix jacchus) | journal = Cerebral Cortex | volume = 16 | issue = 2| pages = 162–177 | doi=10.1093/cercor/bhi094| pmid = 15858163 | doi-access = free }}</ref>
However, in comparison with area MT, a much smaller proportion of DM cells shows selectivity for the direction of motion of visual patterns.<ref name="fmritools.com">{{Cite web |url=http://www.fmritools.com/kdb/grey-matter/occipital-lobe/calcarine-visual-cortex/index.html |url-status=unfit |title=Calcarine (Visual) Cortex
Recently, an area responsive to wide-angle flow fields has been identified in the human and is thought to be a homologue of macaque area V6.<ref>{{cite journal |
===Pathways===
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