Visual modularity: Difference between revisions

Revision as of 16:54, 19 October 2013

Revision as of 13:32, 23 April 2014

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==Motion processing==

[[Akinetopsia]] is an intriguing condition brought about by damage to the [[Extrastriate cortex]] MT+ that renders [[humans]] and [[monkeys]] unable to perceive motion, seeing the world in a series of static "frames" instead<ref name="zihl1">{{cite journal|last=Zihl|first=J.|coauthors=von Cramon, D.Y., Mai N., Schmid, C.|year=1991|title=Disturbance of movement vision after bilateral posterior brain damage|journal=Brain|issue=144|doi=10.1093/brain/114.5.2235|pages=2235–2252|volume=114|pmid=1933243}}</ref><ref name="zihl2">{{cite journal|last=Zihl|first=J.|coauthors=von Cramon, D.Y., Mai, N.|year=1983|title=Selective disturbances of movement vision after bilateral brain damage|journal=Brain|issue=106|doi=10.1093/brain/106.2.525-a|pages=313–340|volume=106}}</ref><ref name=Hess1989>{{cite journal | title=The" motion-blind" patient: low-level spatial and temporal filters | author=Hess, Baker, Zihl | journal=Journal of Neuroscience | year=1989 | volume=9 | issue=5 | pages=1628–1640 | pmid=2723744}}</ref><ref name=Baker1991>{{cite journal | title=Residual motion perception in a" motion-blind" patient, assessed with limited-lifetime random dot stimuli | author=Baker, Hess, Zihl | journal=Journal of Neuroscience | year=1991 | volume=11 | issue=2 | pages=454–461 | pmid=1992012}}</ref> and indicates that there might be a "motion centre" in the brain. Of course, such data can only indicate that this area is at least necessary to motion perception, not that it is sufficient; however, other evidence has shown the importance of this area to primate motion perception. Specifically, physiological, neuroimaging, perceptual, electrical- and [[transcranial magnetic stimulation]] evidence (Table 1) all come together on the area V5/hMT+. Converging evidence of this type is supportive of a module for motion processing. However, this view is likely to be incomplete: other areas are involved with [[motion perception]], including V1,<ref name="orban1">{{cite journal|last=Orban|first=G.A.|coauthors=Kennedy, H., Bullier, J.|year=1986|title=Velocity sensitivity and direction selectivity of neurons in areas V1 and V2 of the monkey: influence of eccentricity|journal=Journal of Neurophysiology|volume=56|issue=2|doi=10.1016/j.jphysparis.2004.03.004|pages=462–480|pmid=3760931}}</ref><ref name="mov1">{{cite journal|last=Movshon|first=J.A.|coauthors=Newsome, W.T.|year=1996|title=Visual response properties of striate cortical neurons projecting to area MT in macaque monkeys|journal=Journal of Neuroscience|volume=16|issue=23|pages=7733–7741|pmid=8922429}}</ref><ref>{{cite journal|last=Born|first=R.T.|coauthors=Bradley, D.C.|year=2005|title=Structure and function of visual area MT|journal=Annual Review of Neuroscience|volume=28|pages=157–189|pmid=16022593|doi=10.1146/annurev.neuro.26.041002.131052}}</ref> V2 and V3a <ref>{{cite journal|last=Grill-Spector|first=K.|coauthors=Malach, R.|year=2004|title=The Human Visual Cortex|journal=Annual Review of Neuroscience|volume=7|pages=649–677|doi=10.1146/annurev.neuro.27.070203.144220|pmid=15217346}}</ref> and areas surrounding V5/hMT+ (Table 2). A recent fMRI study put the number of motion areas at twenty-one.<ref name="stiers">{{cite journal|last=Stiers|first=P|coauthors=Peeters, R; Lagae, L; Van Hecke, P; Sunaert, S|title=Mapping multiple visual areas in the human brain with a short fMRI sequence|journal=NeuroImage|date=2006 Jan 1, 2006|year=2006|volume=29|issue=1|pages=74–89|doi=10.1016/j.neuroimage.2005.07.033|pmid=16154766|url=http://www.sciencedirect.com/science/article/pii/S1053811905005070|accessdate=28 April 2013}}</ref> Clearly, this constitutes a stream of diverse anatomical areas. The extent to which this is ‘pure’ is in question: with Akinetopsia come severe difficulties in obtaining structure from motion.<ref name=rizzo>{{cite journal|last=Rizzo|first=Matthew|coauthors=Nawrot, Mark; Zihl, Josef|title=Motion and shape perception in cerebral akinetopsia|journal=Brain|date=1 January 1995|volume=118|issue=5|pages=1105–1127|doi=10.1093/brain/118.5.1105|pmid=7496774}}</ref> [[V5/hMT+]] has since been implicated in this function<ref name=grunewald>{{cite journal|last=Grunewald|first=A|coauthors=Bradley, DC; Andersen, RA|title=Neural correlates of structure-from-motion perception in macaque V1 and MT|journal=The Journal of neuroscience : the official journal of the Society for Neuroscience|date=2002 Jul 15, 2002|volume=22|issue=14|pages=6195–207|pmid=12122078}}</ref> as well as determining depth.<ref name=angelis>{{cite journal|last=DeAngelis|first=GC|coauthors=Cumming, BG; Newsome, WT|title=Cortical area MT and the perception of stereoscopic depth|journal=Nature|date=1998 Aug 13, 1998|volume=394|issue=6694|pages=677–80|doi=10.1038/29299|pmid=9716130}}</ref> Thus the current evidence suggests that motion processing occurs in a modular stream, although with a role in form and depth perception at higher levels.

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| [[Physiology]] (single cell recording)

| Cells directionally and speed selective in MT/V5

| <ref name=zeki1>{{cite journal|last=Zeki|first=SM|title=Functional organization of a visual area in the posterior bank of the superior temporal sulcus of the rhesus monkey|journal=The Journal of physiology|date=1974 Feb 1974|volume=236|issue=3|pages=549–73|pmid=4207129|pmc=1350849}}</ref><ref name=vanessen1>{{cite journal|last=Van Essen|first=D. C.|coauthors=Maunsell, J. H. R.; Bixby, J. L.|title=The middle temporal visual area in the macaque: Myeloarchitecture, connections, functional properties and topographic organization|journal=The Journal of Comparative Neurology|date=1 July 1981|volume=199|issue=3|pages=293–326|doi=10.1002/cne.901990302|pmid=7263951}}</ref><ref name=maunsell>{{cite journal|last=Maunsell|first=JH|coauthors=Van Essen, DC|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|date=1983 May 1983|volume=49|issue=5|pages=1127–47|pmid=6864242}}</ref><ref name=felleman>{{cite journal|last=Felleman|first=DJ|coauthors=Kaas, JH|title=Receptive-field properties of neurons in middle temporal visual area (MT) of owl monkeys|journal=Journal of neurophysiology|date=1984 Sep 1984|volume=52|issue=3|pages=488–513|pmid=6481441}}</ref>

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| [[Neuroimaging]]

| Greater activation for motion information than static information in [[Visual_cortexVisual cortex#V5.2FMT|V5/MT]]

| <ref name="stiers"/><ref name=culham1>{{cite journal|last=Culham|first=JC|coauthors=Brandt, SA; Cavanagh, P; Kanwisher, NG; Dale, AM; Tootell, RB|title=Cortical fMRI activation produced by attentive tracking of moving targets|journal=Journal of neurophysiology|date=1998 Nov 1998|volume=80|issue=5|pages=2657–70|pmid=9819271}}</ref>

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| Electrical-stimulation & perceptual

| Following electrical stimulation of V5/MT cells perceptual decisions are biased towards the stimulated neuron’s direction preference

| <ref name=salzman>{{cite journal|last=Salzman|first=CD|coauthors=Murasugi, CM; Britten, KH; Newsome, WT|title=Microstimulation in visual area MT: effects on direction discrimination performance|journal=The Journal of neuroscience : the official journal of the Society for Neuroscience|date=1992 Jun 1992|volume=12|issue=6|pages=2331–55|pmid=1607944}}</ref>

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| [[Magnetic]]-stimulation

| Motion perception is also briefly impaired in humans by a strong magnetic pulse over the corresponding scalp region to hMT+

| <ref name=hotson>{{cite journal|last=Hotson|first=John|coauthors=Braun, Doris; Herzberg, William; Boman, Duane|title=Transcranial magnetic stimulation of extrastriate cortex degrades human motion direction discrimination|journal=Vision Research|year=1994|volume=34|issue=16|pages=2115–2123|doi=10.1016/0042-6989(94)90321-2|pmid=7941409}}</ref><ref name=beckers>{{cite journal|last=Beckers|first=G.|coauthors=Zeki, S.|title=The consequences of inactivating areas V1 and V5 on visual motion perception|journal=Brain|date=1 January 1995|volume=118|issue=1|pages=49–60|doi=10.1093/brain/118.1.49|pmid=7895014}}</ref><ref name=walsh>{{cite journal|last=Walsh|first=V|coauthors=Cowey, A|title=Magnetic stimulation studies of visual cognition|journal=Trends in cognitive sciences|date=1998 Mar 1, 1998|volume=2|issue=3|pages=103–10|doi=10.1016/S1364-6613(98)01134-6|pmid=21227086}}</ref>

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| [[Psychophysics]]

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| [[Physiology]] (single cell recording)

| Complex motion involving contraction/expansion and rotation found to activate neurons in medial superior temporal area (MST)

| <ref name=tanaka>{{cite journal|last=Tanaka|first=K|coauthors=Saito, H|title=Analysis of motion of the visual field by direction, expansion/contraction, and rotation cells clustered in the dorsal part of the medial superior temporal area of the macaque monkey|journal=Journal of neurophysiology|date=1989 Sep 1989|volume=62|issue=3|pages=626–41|pmid=2769351}}</ref>

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| [[Neuroimaging]]

| Biological motion activated superior temporal sulcus

| <ref name=grossman>{{cite journal|last=Grossman|first=E|coauthors=Donnelly, M; Price, R; Pickens, D; Morgan, V; Neighbor, G; Blake, R|title=Brain areas involved in perception of biological motion|journal=Journal of Cognitive Neuroscience|date=2000 Sep 2000|volume=12|issue=5|pages=711–20|doi=10.1162/089892900562417|pmid=11054914}}</ref>

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| [[Neuroimaging]]

| [[Tool]] use activated middle temporal gyrus and inferior temporal sulcus

| <ref name=beauchamp1>{{cite journal|last=Beauchamp|first=MS|coauthors=Lee, KE; Haxby, JV; Martin, A|title=FMRI responses to video and point-light displays of moving humans and manipulable objects|journal=Journal of Cognitive Neuroscience|date=2003 Oct 1, 2003|volume=15|issue=7|pages=991–1001|doi=10.1162/089892903770007380|pmid=14614810}}</ref>

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| [[Neuropsychology]]

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== Color processing ==

Similar converging evidence suggests modularity for color. Beginning with Gowers’ finding<ref name=gowers>{{cite book|last=Gowers|first=W.|title=A manual of diseases of the brain|year=1888|publisher=J & A Churchill}}</ref> that damage to the fusiform/lingual [[gyri]] in [[occipitotemporal cortex]] correlates with a loss in color perception ([[achromatopsia]]), the notion of a "color centre" in the primate brain has had growing support.<ref name=meadows>{{cite journal|last=Meadows|first=JC|title=Disturbed perception of colours associated with localized cerebral lesions|journal=Brain : a journal of neurology|date=1974 Dec 1974|volume=97|issue=4|pages=615–32|doi=10.1093/brain/97.1.615|pmid=4547992}}</ref><ref name=zeki2>{{cite journal|last=Zeki|first=S.|title=Parallelism and Functional Specialization in Human Visual Cortex|journal=Cold Spring Harbor Symposia on Quantitative Biology|date=1 January 1990|volume=55|issue=0|pages=651–661|doi=10.1101/SQB.1990.055.01.062}}</ref><ref name=grusser>{{cite book|last=Grüsser and Landis|title=Visual agnosias and other disturbances of visual perception and cognition|year=1991|publisher=MacMillan|pages=297–303}}</ref> Again, such clinical evidence only implies that this region is critical to color [[perception]], and nothing more. Other evidence, however, including [[neuroimaging]]<ref name="stiers"/><ref name=barzek2>{{Cite journal |author=Bartels, A. & Zeki, S. |title=Brain dynamics during natural viewing conditions - a new guide for mapping connectivity ''in vivo'' |journal=[[NeuroImage]] |volume=24 |issue=2 |pages=339–349 |year=2005 |doi=10.1016/j.neuroimage.2004.08.044 |quote=no |pmid=15627577}}</ref><ref name=barzek1>{{Cite journal |author=Bartels, A. & Zeki, S. |title=The architecture of the colour centre in the human visual brain: new results and a review |journal=[[European Journal of Neuroscience]] |volume=12 |issue=1 |pages=172–193 |year=2000 |doi=10.1046/j.1460-9568.2000.00905.x |quote=no |pmid=10651872}}</ref> and physiology<ref name=wachtler>{{cite journal|last=Wachtler|first=T|coauthors=Sejnowski, TJ; Albright, TD|title=Representation of color stimuli in awake macaque primary visual cortex|journal=Neuron|date=2003 Feb 20, 2003|volume=37|issue=4|pages=681–91|doi=10.1016/S0896-6273(03)00035-7|pmid=12597864|pmc=2948212}}</ref><ref name=kusunoki>{{cite journal|last=Kusunoki|first=M|coauthors=Moutoussis, K; Zeki, S|title=Effect of background colors on the tuning of color-selective cells in monkey area V4|journal=Journal of neurophysiology|date=2006 May 2006|volume=95|issue=5|pages=3047–59|doi=10.1152/jn.00597.2005|pmid=16617176}}</ref> converges on V4 as necessary to color perception. A recent [[meta-analysis]] has also shown a specific [[lesion]] common to achromats corresponding to V4.<ref name=bouvier>{{cite journal|last=Bouvier|first=S. E.|coauthors=Engel, SA|title=Behavioral Deficits and Cortical Damage Loci in Cerebral Achromatopsia|journal=Cerebral Cortex|date=27 April 2005|volume=16|issue=2|pages=183–191|doi=10.1093/cercor/bhi096|pmid=15858161}}</ref> From another direction altogether it has been found that when [[synesthesia|synaesthetes]] experience color by a non-visual stimulus, V4 is active.<ref name=rich>{{cite journal|last=Rich|first=AN|coauthors=Williams, MA; Puce, A; Syngeniotis, A; Howard, MA; McGlone, F; Mattingley, JB|title=Neural correlates of imagined and synaesthetic colours|journal=Neuropsychologia|year=2006|volume=44|issue=14|pages=2918–25|doi=10.1016/j.neuropsychologia.2006.06.024|pmid=16901521}}</ref><ref name=sperling>{{cite journal|last=Sperling|first=JM|coauthors=Prvulovic, D; Linden, DE; Singer, W; Stirn, A|title=Neuronal correlates of colour-graphemic synaesthesia: a fMRI study|journal=Cortex; a journal devoted to the study of the nervous system and behavior|date=2006 Feb 2006|volume=42|issue=2|pages=295–303|doi=10.1016/S0010-9452(08)70355-1|pmid=16683504}}</ref> On the basis of this evidence it would seem that color processing is modular. However, as with motion processing it is likely that this conclusion is inaccurate. Other evidence shown in Table 3 implies different areas’ involvement with color. It may thus be more instructive to consider a multistage color processing stream from the retina through to cortical areas including at least [[Visual_cortexVisual cortex#Primary_visual_cortex_Primary visual cortex .28V1.29|V1]], [[Visual_cortexVisual cortex#V2|V2]], [[Visual_cortexVisual cortex#V4|V4]], PITd and TEO. Consonant with motion perception, there appears to be a constellation of areas drawn upon for [[color perception]]. In addition, V4 may have a special, but not exclusive, role. For example, single cell recording has shown that only V4 cells respond to the color of a stimuli rather than its waveband, whereas other areas involved with color do not.<ref name=wachtler/><ref name=kusunoki/>

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| [[Wavelength]] sensitive cells in V1 and V2

| <ref name=livingstone>{{cite journal|last=Livingstone|first=MS|coauthors=Hubel, DH|title=Anatomy and physiology of a color system in the primate visual cortex|journal=The Journal of neuroscience : the official journal of the Society for Neuroscience|date=1984 Jan 1984|volume=4|issue=1|pages=309–56|pmid=6198495}}</ref><ref name=deyoe>{{cite journal|last=DeYoe|first=EA|coauthors=Van Essen, DC|title=Segregation of efferent connections and receptive field properties in visual area V2 of the macaque|journal=Nature|date=1985 Sep 5-11|volume=317|issue=6032|pages=58–61|doi=10.1038/317058a0|pmid=2412132}}</ref>

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| anterior parts of the inferior temporal cortex

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| Shape detection

| <ref name=pasupathy>{{cite journal|last=Pasupathy|first=A|title=Neural basis of shape representation in the primate brain|journal=Progress in brain research|year=2006|volume=154|pages=293–313|pmid=17010719|doi=10.1016/S0079-6123(06)54016-6|series=Progress in Brain Research|isbn=9780444529664}}</ref><ref name=david>{{cite journal|last=David|first=SV|coauthors=Hayden, BY; Gallant, JL|title=Spectral receptive field properties explain shape selectivity in area V4|journal=Journal of neurophysiology|date=2006 Dec 2006|volume=96|issue=6|pages=3492–505|pmid=16987926|doi=10.1152/jn.00575.2006}}</ref>

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| Link between [[Visual perception|vision]], [[attention]] and [[cognition]]

| <ref name=chelazzi>{{cite journal|last=Chelazzi|first=L|coauthors=Miller, EK; Duncan, J; Desimone, R|title=Responses of neurons in macaque area V4 during memory-guided visual search|journal=Cerebral cortex (New York, N.Y. : 1991)|date=2001 Aug 2001|volume=11|issue=8|pages=761–72|doi=10.1093/cercor/11.8.761|pmid=11459766}}</ref>

|}

== Form processing ==

Another clinical case that would a priori suggest a module for modularity in visual processing is visual [[agnosia]]. The well studied patient DF is unable to recognize or discriminate objects<ref name=mishkin>{{cite journal|last=Mishkin|first=Mortimer|coauthors=Ungerleider, Leslie G.; Macko, Kathleen A.|title=Object vision and spatial vision: two cortical pathways|journal=Trends in Neurosciences|year=1983|volume=6|pages=414–417|doi=10.1016/0166-2236(83)90190-X}}</ref> owing to damage in areas of the lateral occipital cortex although she can see scenes without problem – she can literally see the forest but not the trees.<ref name=steeves>{{cite journal|last=Steeves|first=Jennifer K.E.|coauthors=Culham, Jody C.; Duchaine, Bradley C.; Pratesi, Cristiana Cavina; Valyear, Kenneth F.; Schindler, Igor; Humphrey, G. Keith; Milner, A. David; Goodale, Melvyn A.|title=The fusiform face area is not sufficient for face recognition: Evidence from a patient with dense prosopagnosia and no occipital face area|journal=Neuropsychologia|year=2006|volume=44|issue=4|pages=594–609|doi=10.1016/j.neuropsychologia.2005.06.013|pmid=16125741}}</ref> [[Neuroimaging]] of intact individuals reveals strong occipito-temporal activation during object presentation and greater activation still for object recognition.<ref name=grillspector>{{cite journal|last=Grill-Spector|first=Kalanit|coauthors=Ungerleider, Leslie G.; Macko, Kathleen A.|title=The neural basis of object perception|journal=Current Opinion in Neurobiology|year=2003|volume=13|issue=3|pages=399|doi=10.1016/S0959-4388(03)00060-6}}</ref> Of course, such activation could be due to other processes, such as visual attention. However, other evidence that shows a tight coupling of [[perceptual]] and [[physiological]] changes<ref name=sheinberg>{{cite journal|last=Sheinberg|first=DL|coauthors=Logothetis, NK|title=Noticing familiar objects in real world scenes: the role of temporal cortical neurons in natural vision|journal=The Journal of neuroscience : the official journal of the Society for Neuroscience|date=2001 Feb 15, 2001|volume=21|issue=4|pages=1340–50|pmid=11160405}}</ref> suggests activation in this area does underpin object recognition. Within these regions are more specialized areas for face or fine grained analysis,<ref name=gauthier>{{cite journal|last=Gauthier|first=I|coauthors=Skudlarski, P; Gore, JC; Anderson, AW|title=Expertise for cars and birds recruits brain areas involved in face recognition|journal=Nature Neuroscience|date=2000 Feb 2000|volume=3|issue=2|pages=191–7|doi=10.1038/72140|pmid=10649576}}</ref> place perception<ref name=epstein>{{cite journal|last=Epstein|first=R|coauthors=Kanwisher, N|title=A cortical representation of the local visual environment|journal=Nature|date=1998 Apr 9, 1998|volume=392|issue=6676|pages=598–601|doi=10.1038/33402|pmid=9560155}}</ref> and human body perception.<ref name=downing>{{cite journal|last=Downing|first=PE|coauthors=Jiang, Y; Shuman, M; Kanwisher, N|title=A cortical area selective for visual processing of the human body|journal=Science|date=2001 Sep 28, 2001|volume=293|issue=5539|pages=2470–3|doi=10.1126/science.1063414|pmid=11577239}}</ref> Perhaps some of the strongest evidence for the modular nature of these processing systems is the [[double dissociation]] between object- and face (prosop-) agnosia. However, as with color and motion, early areas (see <ref name=pasupathy/> for a comprehensive review) are implicated too, lending support to the idea of a multistage stream terminating in the inferotemporal cortex rather than an isolated module.

== Functional modularity ==

One of the first uses of the term "module" or "modularity" occurs in the influential book "[[Modularity of Mind]]" by philosopher [[Jerry Fodor]].<ref name=fodor>{{cite book|last=Fodor|first=Jerry A.|title=The modularity of mind : an essay on faculty psychology|year=1989|publisher=MIT Press|___location=Cambridge, Mass. [ u.a.]|isbn=0-262-56025-9|edition=6. printing.}}</ref> A detailed application of this idea to the case of vision was published by Pylyshyn (1999), who argued that there is a significant part of vision that is not responsive to beliefs and is "cognitively impenetrable." <ref name=pylyshyn>{{cite journal|last=Pylyshyn|first=Z|title=Is vision continuous with cognition? The case for cognitive impenetrability of visual perception|journal=The Behavioral and brain sciences|date=1999 Jun 1999|volume=22|issue=3|pages=341–65; discussion 366–423|pmid=11301517}}</ref>

Much of the confusion concerning modularity exists in neuroscience because there is evidence for specific areas (e.g. V4 or V5/hMT+) and the concomitant behavioral deficits following brain insult (thus taken as evidence for modularity). In addition, evidence shows other areas are involved and that these areas subserve processing of multiple properties (e.g. V1<ref name=leventhal>{{cite journal|last=Leventhal|first=AG|coauthors=Thompson, KG; Liu, D; Zhou, Y; Ault, SJ|title=Concomitant sensitivity to orientation, direction, and color of cells in layers 2, 3, and 4 of monkey striate cortex|journal=The Journal of neuroscience : the official journal of the Society for Neuroscience|date=1995 Mar 1995|volume=15|issue=3 Pt 1|pages=1808–18|pmid=7891136}}</ref>) (thus taken as evidence against modularity). That these streams have the same implementation in early visual areas, like V1, is not inconsistent with a modular viewpoint: to adopt the canonical analogy in cognition, it is possible for different software to run on the same hardware. A consideration of [[psychophysics]] and neuropsychological data would suggest support for this. For example, psychophysics has shown that percepts for different properties are realized asynchronously.<ref name=moutoussis1/><ref name=viviani/> In addition, although achromats experience other cognitive defects<ref name=gegenfurtner>{{cite journal|last=Gegenfurtner|first=Karl R.|title=Sensory systems: Cortical mechanisms of colour vision|journal=Nature Reviews Neuroscience|year=2003|volume=4|issue=7|pages=563–572|doi=10.1038/nrn1138|pmid=12838331}}</ref> they do not have motion deficits when their lesion is restricted to V4, or total loss of form perception.<ref name=zeki2>{{cite journal|last=Zeki|first=S|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|date=2005 Jun 29, 2005|volume=360|issue=1458|pages=1145–83|doi=10.1098/rstb.2005.1666|pmid=16147515|pmc=1609195}}</ref> Relatedly, Zihl and colleagues’ [[Akinetopsia]] patient shows no deficit to color or object perception (although deriving depth and structure from motion is problematic, see above) and object agnostics do not have damaged motion or color perception, making the three disorders triply [[dissociable]].<ref name="zihl2"/> Taken together this evidence suggests that even though distinct properties may employ the same early visual areas they are functionally independent. Furthermore, that the intensity of subjective perceptual experience (e.g. color) correlates with activity in these specific areas (e.g. V4),<ref name="barzek2"/> the recent evidence that [[synesthesia|synaesthetes]] show V4 activation during the perceptual experience of color, as well as the fact that damage to these areas results in concomitant behavioral deficits (the processing may be occurring but perceivers do not have access to the information) are all evidence for visual modularity.

==See also==