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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
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]]. As an example, for an image comprising half side black and half side white, the dividing line between black and white has strongest local contrast (that is, edge detection) and is encoded, while few neurons code the brightness information (black or white per se). As information is further relayed to subsequent visual areas, it is coded as increasingly non-local frequency/phase signals. Note that, at these early stages of cortical visual processing, spatial location of visual information is well preserved amid the local contrast encoding (edge detection).
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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 | author=Braddick, OJ, O'Brien, JM| year=2001 | title=Brain areas sensitive to coherent visual motion | journal=Perception | volume=30 | pages=61–72 | doi = 10.1068/p3048 | pmid=11257978 | issue=1| s2cid=24081674 |display-authors=etal}}</ref> Other studies prefer to consider dorsal V3 as part of a larger area, named the [[dorsomedial area]] (DM), which contains a representation of the entire visual field. Neurons in area DM respond to
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 | doi = 10.1002/1096-9861(20000710)422:4<621::AID-CNE10>3.0.CO;2-E | last1 = Rosa | first1 = MG | last2 = Tweedale | first2 = R |name-list-style=vanc | year = 2000 | title = Visual areas in lateral and ventral extrastriate cortices of the marmoset monkey | journal = Journal of Comparative Neurology | volume = 422 | issue = 4| pages = 621–51 | pmid = 10861530 | s2cid = 25982910 }}</ref>
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* {{BrainInfo|ancil|699}} – Brodmann area 17 in guenon
* {{BrainMaps|visual%20cortex}}
* [http://topographica.org Simulator for computational modeling of visual cortex maps] at topographica.org<!-- Someone needs to create a page for Occipitotemportal sulcus, or at least fix the link. (Referring to the template below.) -->
{{Prosencephalon}}
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