Editing Color (section)

=== Color in the brain<span class="anchor" id="Colour in the brain"></span> ===
{{main|Color vision#Color in the primate brain}}
<!--opponent process is not calculated in the brain, but still in neurons in the retina; this section needs to focus more on the visual cortex-->
While the mechanisms of [[color vision]] at the level of the [[retina]] are well-described in terms of tristimulus values, color processing after that point is organized differently. A dominant theory of color vision proposes that color information is transmitted out of the eye by three [[opponent process]]es, or opponent channels, each constructed from the raw output of the cones: a red–green channel, a blue–yellow channel, and a black–white "luminance" channel. This theory has been supported by neurobiology, and accounts for the structure of our subjective color experience. Specifically, it explains why humans cannot perceive a "reddish green" or "yellowish blue", and it predicts the [[color wheel]]: it is the collection of colors for which at least one of the two color channels measures a value at one of its extremes.

The exact nature of color perception beyond the processing already described, and indeed the status of color as a feature of the perceived world or rather as a feature of our ''perception'' of the world—a type of [[qualia]]—is a matter of complex and continuing philosophical dispute.{{citation needed|date=November 2022}}
[[File:Ventral-dorsal streams.svg|thumb|upright=1.25|The visual [[two-streams hypothesis#Dorsal stream|dorsal stream]] (green) and [[ventral stream]] (purple) are shown; the ventral stream is responsible for color perception]]
From the V1 blobs, color information is sent to cells in the second visual area, V2. The cells in V2 that are most strongly color tuned are clustered in the "thin stripes" that, like the blobs in V1, stain for the enzyme cytochrome oxidase (separating the thin stripes are interstripes and thick stripes, which seem to be concerned with other visual information like motion and high-resolution form). Neurons in V2 then synapse onto cells in the extended V4. This area includes not only V4, but two other areas in the posterior inferior temporal cortex, anterior to area V3, the dorsal posterior inferior temporal cortex, and posterior TEO.<ref name="Conway_2007">{{cite journal |vauthors=Conway BR, Moeller S, Tsao DY |date=November 2007 |title=Specialized color modules in macaque extrastriate cortex |url=https://authors.library.caltech.edu/100800/ |journal=Neuron |volume=56 |issue=3 |pages=560–73 |doi=10.1016/j.neuron.2007.10.008 |pmc=8162777 |pmid=17988638 |s2cid=11724926 |access-date=2023-12-08 |archive-date=2022-10-10 |archive-url=https://web.archive.org/web/20221010104403/https://authors.library.caltech.edu/100800/ |url-status=dead  |issn = 0896-6273}}</ref><ref name="Conway_2009">{{cite journal |vauthors=Conway BR, Tsao DY |date=October 2009 |title=Color-tuned neurons are spatially clustered according to color preference within alert macaque posterior inferior temporal cortex |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=42 |pages=18034–9 |bibcode=2009PNAS..10618034C |doi=10.1073/pnas.0810943106 |pmc=2764907 |pmid=19805195 |doi-access=free}}</ref> Area V4 was initially suggested by [[Semir Zeki]] to be exclusively dedicated to color,<ref>{{cite journal |vauthors=Zeki SM |date=April 1973 |title=Colour coding in rhesus monkey prestriate cortex |journal=Brain Research |volume=53 |issue=2 |pages=422–7 |doi=10.1016/0006-8993(73)90227-8 |pmid=4196224}}</ref> and he later showed that V4 can be subdivided into subregions with very high concentrations of color cells separated from each other by zones with lower concentration of such cells though even the latter cells respond better to some wavelengths than to others,<ref name="Zeki_1983">{{cite journal |vauthors=Zeki S |date=March 1983 |title=The distribution of wavelength and orientation selective cells in different areas of monkey visual cortex |journal=Proceedings of the Royal Society of London. Series B, Biological Sciences |volume=217 |issue=1209 |pages=449–70 |bibcode=1983RSPSB.217..449Z |doi=10.1098/rspb.1983.0020 |pmid=6134287 |s2cid=39700958}}</ref> a finding confirmed by subsequent studies.<ref name="Conway_2007" /><ref>{{cite journal |vauthors=Bushnell BN, Harding PJ, Kosai Y, Bair W, Pasupathy A |date=August 2011 |title=Equiluminance cells in visual cortical area v4 |journal=The Journal of Neuroscience |volume=31 |issue=35 |pages=12398–412 |doi=10.1523/JNEUROSCI.1890-11.2011 |pmc=3171995 |pmid=21880901}}</ref><ref>{{cite journal |vauthors=Tanigawa H, Lu HD, Roe AW |date=December 2010 |title=Functional organization for color and orientation in macaque V4 |journal=Nature Neuroscience |volume=13 |issue=12 |pages=1542–8 |doi=10.1038/nn.2676 |pmc=3005205 |pmid=21076422}}</ref> The presence in V4 of orientation-selective cells led to the view that V4 is involved in processing both color and form associated with color<ref name="Zeki_2005">{{cite journal |vauthors=Zeki S |date=June 2005 |title=The Ferrier Lecture 1995 behind the seen: the functional specialization of the brain in space and time |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=360 |issue=1458 |pages=1145–83 |doi=10.1098/rstb.2005.1666 |pmc=1609195 |pmid=16147515}}</ref> but it is worth noting that the orientation selective cells within V4 are more broadly tuned than their counterparts in V1, V2, and V3.<ref name="Zeki_1983" /> Color processing in the extended V4 occurs in millimeter-sized color modules called [[Glob (visual system)|globs]].<ref name="Conway_2007" /><ref name="Conway_2009" /> This is the part of the brain in which color is first processed into the full range of [[hue]]s found in [[color space]].<ref>{{Cite journal |last=Zeki |first=S. |date=1980 |title=The representation of colours in the cerebral cortex |url=https://www.nature.com/articles/284412a0 |journal=Nature |language=en |volume=284 |issue=5755 |pages=412–418 |bibcode=1980Natur.284..412Z |doi=10.1038/284412a0 |issn=1476-4687 |pmid=6767195 |s2cid=4310049}}</ref><ref name="Conway_2007" /><ref name="Conway_2009" />