BİOLOGİCAL(PSYCHOLOGY(CH.6((((VISION((1. Sensory(receptor(A!specialized!neuron!that!detects!a!particular!

category!of!physical!events.!!2. Sensory(transduction!The!process!by!which!sensory!stimuli!are!

transduced!into!slow,!graded!receptor!potential.!3. Receptor(potential(A!slow,!graded!electrical!potential!produced!by!

a!receptor!cell!in!response!to!a!physical!stimulus.!!!Extra!Notes:!!B!We!need!to!change!physical!energy!such!as!light!into!electrical!energy,!action!potential.!!B!Sensory!receptors!in!eyes!convert!light!into!electrical!energy.!This!process!is!called!sensory(transduction.!!!?We'receive'information'about'the'environment'from'sensory!receptors.'Stimuli'impinge'on'the'receptors'and'alter'their'membrane'potential.'This'process'is'known'as'sensory!transduction'because'sensory'events'are'transduced'(“transferred”)'into'changes'in'the'cells’'membrane'potential.'These'electrical'changes'are'called'receptor!potentials.'These'potentials'affect'the'release'of'neurotransmitters'and'hence'modify'the'pattern'of'firing'in'neurons'with'which'sensory'receptors'from'synapses.'Ultimately'the'information'reaches'the'brain.'''?Light'is'a'narrow'band'of'the'spectrum'of'electromagnetic'radiation.''?Electromagnetic'radiation'with'a'wavelength'of'between'380'and'760'nanomete'(one'billion'of'a'meter)'is'visible'to'us'?The'range'of'wavelengts,'we'call'light.''?The'perceived'color'of'light'is'determined'by'three'dimensions:'Hue,'Brightness,'Saturation.''4. Hue((renk!tonu)!One!of!the!perceptual!dimensions!of!color;!the!

dominant!wavelength.!!5. Brightness((parlaklık)!One!of!the!perceptual!dimensions!of!color;!

intensity.!!6. Saturation((doygunluk,!canlılık)!One!of!the!perceptual!dimensions!

of!color;!purity.!!!?Gözler'kafa'tasının'ön'kısmında'bulunan'kemik'boşluğu'(orbita)'içerisinde'asılı'bulunur.'Göz'akı'(sclera)'adı'verilen'en'dış'tabakası'sert'yapıdadır've'beyaz'renklidir.'Gözler'altı'adet'ekstraoküler'kas'aracılığı'ile'göz'akına'tutunur've'hareket'ederler.'Normalde'göz'küremizin'arka'kısmını've'bu'kasları'göremeyiz,'çünkü'bu'kasların'gözle'olan'bağlantıları'conjunctiva'ile'gizlenmektedir.'''?The'white'outer'layer'of'most'of'the'eye,'the'sclera,'is'opaque'and'does'not'permit'entry'of'light.'However,'the'cornea,'the'outer'layer'at'the'front'of'the'eye,'is'transparent'and'admits'light.'The'amount'of'light'that'enters'is'regulated'by'the'size'of'the'pupil,'which'is'an'opening'in'the'iris,'the'pigmented'ring'of'the'muscles'situated'behind'the'cornea.'(İris,'korneanın'arkasında'bulunan'pigmentli'kas'halkalarından'oluşur)'The'lens,'situated'immediately'behind'the'iris,'consists'of'a'series'of'transparent,'onion?like'layers.'Its'shape'can'be'altered'by'contraction'of'the'ciliary'muscles,'a'set'of'muscle'fibers'attached'to'the'outer'edge'of'the'lens.''Pupilla:'göz'bebeği/irisin'ortasındaki'açıklık''''

7. Saccadic(movement!The!rapid,!jerky!movement!of!the!eyes!used!in!scanning!a!visual!scene.!(Bir!görüntünün!taranması!sırasında,!gözlerin!kullandığı!hızlı!titreme!hareketi)!

8. Pursuit(movement(The!movement!that!the!eyes!make!to!maintain!an!image!of!a!moving!object!on!the!fovea.!(Foveada!hareket!eden!bir!objenin!görüntüsünü!korumak!üzere!gözlerin!yaptığı!hareket)!

9. Accommodation(Changes!in!the!thickness!of!the!lens!of!the!eye,!accomplished!by!the!ciliary!muscles,!that!focus!images!of!near!or!distant!objects!on!the!retina.!(Uzak!ya!da!yakındaki!cisim!görüntülerinin!ciliary!kaslarının!kasılarak!–böylece!lensin!şekli!değiştirilerekB!retina!üzerine!odaklanması)!

?Işık'lensi'geçtikten'sonra,'şeffaf've'jelatinsi'bir'madde'olan'vitreous'humor'(glassy'liquid=camsı'sıvı)'ile'dolu'olan'gözün'ana'kısmına'doğru'geçiş'yapar.'Light'then'falls'on'the'retina,'the'interior'lining'of'the'back'of'the'eye.'In'the'retina'are'located'the'receptor'cells,'the'rods'and'cones,'collectively'known'as'photoreceptors.''10. Retina!The!neural!tissue!and!photoreceptive!cells!located!on!the!

inner!surface!of!the!posterior!portion!of!the!eye.!(Gözün!arka!iç!kısmını!döşeyen!ışığa!duyarlı!hücrelerden!oluşan!sinir!tabakası).!

11. Rod(One!of!the!receptor!cells!of!the!retina;!sensitive!to!light!of!low!intensity.!!Although!rods!do!not!detect!different!colors!and!provide!vision!of!poor!activity,!they!are!more!sensitive!to!light.!In!a!very!dimly!lighted!environment,!we!use!our!rod!vision;!therefore,!in!dim!light!we!are!colorBblind!and!lack!of!foveal!vision.!!?The'human'retina'contains'approximately'120'million'rods'and'6'million'codes.'Although'they'are'greatly'outnumbered'by'rods,'cones'provide'us'with'most'of'the'information'about'our'environment.!!

12. Cone!One!of!the!receptor!cells!of!the!retina;!maximally!sensitive!to!one!of!three!different!wavelengths!of!light!and!hence!encodes!color!division.!!Cones!are!responsible!for!our!daytime!vision.!They!provide!us!with!information!about!small!features!in!the!environment!and!thus!are!the!source!of!vision!of!the!highest!sharpness,!or!acuity'(keskin!görmenin!kaynağıdır).!Cones!are!also!responsible!for!color!vision!–our!ability!to!discriminate!light!of!different!wavelengths.!!

!!13. Photoreceptor!A!specialized!structure!or!cell!that!is!sensitive!to!

light.!In!vertebrate!animals,!the!photoreceptors!are!the!rods!and!cones!of!the!eye's!retina.!Photoreceptor!is!a!nerve!ending,!cell,!or!group!of!cells!specialized!to!sense!or!receive!light.!It!transduces!photic!energy!into!electrical!potentials. !

14. Fovea!or!central!region!of!the!retina,!meditates!our!most!accurate!vision,!contains!only!cones.!!

Extra'Notes:'?Rons'and'Cones'exists'in'the'retina'and'rods'receive'light'and'dark,'and'cones'receive'colors.'?Fovea'is'the'specific'region'of'the'retina,'includes'amounts'of'cones.'That'allows'to'see'a'lot'of'detail.'Cones'give'a'lot'of'detail'vision.'15. Optic(disk!The!location!of!the!exit!point!from!the!retina!of!the!

fibers!of!the!ganglion!cells!that!form!the!optic!nerve;!responsible!for!the!blind'spot.!(Optik!disk!bölgesinde!fotoreseptör!olmadığı!için!kör!nokta!oluşur.)!!Optik!disk:!Ganglion!hücre!aksonlarının!birleşerek!optik!siniri!oluşturduğu!ve!gözü!terk!ettiği!bölge.!!

16. Bipolar(cell!A!bipolar!neuron!located!in!the!middle!layer!of!the!retina,!conveying!information!from!the!photoreceptors!to!the!ganglion!cells.!(Fotoreseptörlerden!aldığı!bilgiyi!ganglion!hücrelerine!iletir).!Bipolar!cells!are!neurons!whose!two!arms!connect!the!shallowest!and!deepest!layers!of!the!retina.!These!neurons!form!synapses!with!the!ganglion!cells!

17. Ganglion(cell!A!neuron!located!in!the!retina!that!receives!visual!information!from!bipolar!cells;!its!axons!give!rise!to!the!optic!nerve.!(Görsel!mesajı!bipolar!hücreden!alarak!beyne!ileten!sinir!hücresi;!aksonları!optic!siniri!oluşturur.)!

18. Horizontal(cell!A!neuron!in!the!retina!that!interconnects!adjacent!photoreceptors!and!the!outer!processes!of!the!bipolar!cells.!

19. Amacrine(cell(A!neuron!in!the!retina!that!interconnects!adjacent!ganglion!cells!and!the!inner!processes!of!the!bipolar!cells.!!

!20. Lamella(A!layer!of!membrane!containing!photopigments;!found!in!

rods!and!cones!of!the!retina.!!?The'nature'of'transduction'of'visual'information:'The'first'step'in'the'chain'of'events'that'leads'to'visual'perception'involves'a'special'chemical'called'a'photopigment.'Photopigments'are'special'molecules'embedded'in'the'membrane'of'the'lamellae.'A'single'of'human'rod'contains'approximately'tenmillionofthem'21. Photopigment(A!protein!dye!bonded!to!retinal,!a!substance!derived!

from!vitamin!A;!responsible!for!transduction!of!visual!information.!The!molecules!consist!of!two!parts:!an!opsin!(a!protein)!and!retinal!(lipid).!!

22. Opsin!A!class!of!protein!that,!together!with!retinal,!constitutes!the!photopigments.!(Bir!çeşit!proteindir,!retinal!ile!fotopigmentleri!oluşturur)!

23. Retinal(A!chemical!synthesized!from!vitamin!A;!joins!with!an!opsin!to!form!a!photopigment.!(Vitamin!A!ürünüdür,!opsinle!beraber!fotopigmentleri!oluşturur)!Retinal'is'synthesized'from'vitamin'A,'which'explains'why'carrots,'which'are'rich'in'this'vitamin,'are'said'to'be'good'for'your'eyesight.!!

24. Rhodopsin!There!are!several!forms!of!opsin;!for!example,!the!photopigment!of!human!rods,!rhodopsin!is!a!particular!opsin!found!in!rods!and!consists!of!rod'opsin!plus!retinal.!!

?Rodopsinin'bir'molekülü'ışığa'maruz'kaldığında,'iki'bileşenine'ayrılır:'rod'opsin've'retinal.'Bu'olay'meydana'geldiğinde'opsinin'gün'rengi'uçuk'sarıya'dönüşür;'bu'yüzden'ışığın'fotosigmenti'beyazlaşır.'The'splitting'of'the'photopigment'produces'the'receptor'potential:'a'change'in'the'membrane'potential'of'the'photoreceptor.'The'receptor'potential'affects'the'release'of'neurotransmitter'by'the'photoreceptor,'which'alters'the'firing'rate'of'the'bipolar'cells'with'which'the'photoreceptors'communicates(bu'da,'fotoreseptör'iletişiminde'bipolar'hücrelerin'tetiklenme'oranını'düzenler).'This'information'is'passed'on'to'the'ganglion'cells.'''25. Dorsal(lateral(geniculate(nucleus((LGN)!Retinal!ganglion!

hücrelerinin!aksonları,!bilgiyi!beynin!kalan!kısmına!getirirler.!Bunlar!optik!sinir!boyunca!ilerler!ve!talamusun!dorsal!lateral!geniculate!nucleusa!(LGN)!ulaşırlar.!!Dorsal!lateral!geniculate!nucleus!is!a!group!of!cell!bodies!within!the!lateral!geniculate!body!of!the!thalamus!and!receives!inputs!from!the!retina!and!projects!to!the!primary!visual!cortex.!

!

26. Magnocellular(layer!One!of!the!inner!two!layers!of!neurons!in!the!dorsal!lateral!geniculate!nucleus!and!transmits!information!necessary!for!the!perception!of!form,!movement,!depth,!and!small!differences!in!brightness!to!the!primary!cortex.!(primer!görme!korteksine!şekil,!hareket,!yoğunluk!ve!parlaklıkla!ilgili!küçük!değişiklilklerin!algılanması!için!gerekli!bilgiyi!aktarır)!

27. Parvocellular(layer!One!of!the!four!outer!layers!of!neurons!in!the!dorsal!lateral!geniculate!nucleus!and!transmits!information!necessary!for!the!perception!of!color!and!fine!details!to!the!primary!visual!cortex.!(primer!görme!korteksine!rengin!ve!en!ince!detayların!algılanması!için!gerekli!bilgiyi!aktarır)!

28. Konicellular(layer(One!of!the!sublayers!of!neurons!in!the!dorsal!lateral!geniculate!nucleus!found!ventral!to!each!of!the!magnocellular!and!parvocellular!layers;!transmits!information!from!shortBwavelength!(“blue”)!cones!to!the!primary!visual!cortex.!(primer!görme!korteksine!kısa!dalgaboyundaki!(mavi)!konlardan!bilgiyi!aktarır)!!Lateral!geniculate!nucleus!contains!six!layers!of!neurons,!each!of!which!receives!input!from!the!only!one!eye.!Layers!1,!4,!6!of!the!lateral!geniculate!nucleus!receive!input!from!the!contralateral!eye,!and!2,!3,!5!receive!input!from!the!ipsilateral!layer.!!Layers!1!and!2!are!the!Magnocellular!layers;!layers!3,!4,!5,!6!are!the!parvocellular!layers.!The!koniocellular!sublayers!are!found!ventral!to!each!of!the!parvocellular!and!Magnocellular!layers.!!!

?The'neurons'in'the'dorsal'lateral'geniculate'nucleus'send'their'axons'through'a'pathway'known'as'the'optic'radiations'to'the'primary'visual'cortex'–the'region'surrounding'the!calcarine!fissure.'29. Calcarine(fissure(A!horizontal!fissure!on!the!inner!surface!of!the!

posterior!cerebral!cortex;!the!location!of!the!primary!visual!cortex.!30. Striate(cortex!The!primary!visual!cortex!is!often!called!the!striate!

cortex!because!it!contains!a!darkstaining!layer!(striation)!of!cells.!!!

Anatomy(of(the(Visual(System(31. Optic(chiasm(A!crossBshaped!connection!between!the!optic!nerves!

(optic!sinirler!arasındaki!çapraz!yapılı!bir!baağlantıdır),!located!below!the!base!of!the!brain!(beyin!tabanının!altında),!just!anterior!to!the!pituitary!gland!(hipofizin!önündedir).!!

!!!!!!!

Coding(of(Visual(Information(32. Receptive(field!That!portion!of!the!visual!field!in!which!the!

presentation!of!visual!stimuli!will!produce!an!alternation!in!the!firing!rate!of!a!particular!neuron.!Receptive(field!as!an!"area!in!which!stimulation!leads!to!response!of!a!particular!sensory!neuron”.!The!receptive(field(of!a!neuron!in!the!visual!system!is!the!part!of!the!visual!field!that!neuron!"see"—that!is,!the!part!in!which!light!must!fall!for!the!neuron!to!be!stimulated.!

!

!

!?'Central'Versus'Peripheral'Acuity:'Ganglion'cells'in'the'fovea'receive'input'from'a'smaller'number'of'photoreceptors'than'in'the'periphery'and'hence'provide'more'acute'visual'information.'

Extra'Notes:'?Over'sixty'years'ago,'Hartline'(1938)'discovered'that'the'frog'retina'contained'three'types'of'ganglion'cells.'ON'cells'responded'with'an'excitatory'burst'when'the'retina'was'illuminated,'OFF'cells'responded'when'the'light'was'turned'off,'and'ON/OFF'cells'respond'briefly'when'the'light'went'on'and'again'when'it'went'off.'?'There'are'two'types'of'retinal'ganglion'cells:'"on?center"'and'"off?center".'An'on?center'cell'is'stimulated'when'the'center'of'its'receptive'field'is'exposed'to'light,'and'is'inhibited'when'the'surround'is'exposed'to'light.'Off?center'cells'have'just'the'opposite'reaction'?The'two'major'categories'of'ganglion'cells'(ON'and'OFF)'and'the'organization'of'their'receptive'fields'into'contrasting'center'and'surround'provide'useful'information'to'the'rest'of'the'visual'system.'

'(

Coding(of(Color(Objects!in!our!environment!selectively!absorb!some!wavelengths!of!light!and!reflect!others,!which,!to!our!eyes,!gives!them!different!colors.!

The!retinas!of!humans,!apes,!Old!World!monkeys,!and!one!species!of!New!World!monkey!contain!three!different!types!of!cones,!which!provides!them!(and!us)!with!the!most!elaborate!form!of!color!vision.!!!TRICHROMACY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!TETRACHROMACY!

!BTetrachromacy!birds!can!see!red,!green,!blue!and!an!ultraviolet!light.!!!?In'1802'Thomas'Young,'a'British'physicist'and'physician,'proposed'that'the'eye'detected'different'colors'because'it'contained'three'types'of'receptors,'each'sensitive'to'a'single'hue.'His'theory'was'referred'to'as'the'trichromatic'(three?color)'theory.'?Physiological'investigations'of'retinal'photoreceptors'in'higher'primates'have'found'that'Young'was'right:'Three'different'types'of'photoreceptors'(three'different'types'of'cones)'are'responsible'for'color'vision.'?Investigators'have'studied'the'absorption'characteristics'of'individual'photoreceptors,'determining'the'amount'of'light'of'different'wavelengths'that'is'absorbed'by'the'photopigments.'?These'characteristics'are'controlled'by'the'particular'opsin'a'photoreceptor'contains;'different'opsins'absorb'particular'wavelengths'more'readily.'!BTrichromatic!theory:!Trichromatic!vision:!Every!color!we!see!in!the!world!they!are!the!combination!of!these!3!colors.!.!3!types!of!cones!(receptors)!.!Cones!get!activated!depending!on!the!wavelength!.!"Color!mixing"!.!Blue/Green/Red!Red!cones!only!fire!if!there!is!red!light.!!Green!cones!only!fire!if!there!is!green!light.!Blue!cones!only!fire!if!there!is!blue!light.!Opponents!process!theory:!!.!Two!type!of!ganglion!cells:!YellowBblue!and!greenBred!.!As!one!cell!increases!its!firing!rate!to!yellow!light!in!the!center,!it!will!decrease!its!firing!rate!to!blue!light'''?'For'convenience,'the'short?,'medium?,'and'long?wavelength'cones'are'traditionally'called'"blue",'"green",'and'"red"'cones,'respectively.'?The'peak'sensitivities'of'the'three'types'of'cones'are'approximately'420'nm'(blue?violet),'530'nm'(green),'abd'560'nm'(yellow?green).''!?Genetic'defects'in'color'vision'appear'to'result'from'anomalies'in'one'or'more'of'the'three'types'of'cones.'33. Protanopia(An!inherited!form!of!defective!color!vision!in!which!red!

and!green!hues!are!confused;!“red”!cones!are!filled!“green”!cone!opsin.!People!with!protanopia!confuse(red!and!green.!They!see!the!world!in!shades!of!yellow!and!blue;!both.!

34. Deuteranopia(An!inherited!form!of!defective!color!vision!in!which!red!and!green!hues!are!confused;!“green”!cones!are!filled!“red”!cone!opsin.!People!with!deuteranopia(("secondBcolor!defect")!also!confuse!red!and!green!and!also!have!normal!visual!acuity.!Their!"green"!cones!appear!to!be!filled!with!"red"!con!opsin.!

35. Tritanopia(An!inherited!form!of!defective!color!vision!in!which!hues!with!short!wavelengths!are!confused.!“Blue”!cones!are!either!lacking!or!faulty.!("thirdBcolor!defect")!This!disorder!involves!a!faulty!gene!that!is!not!located!on!an!X!chromosome;!thus,!it!is!equally!prevalent!in!males!and!females.!People!with!tritanopia!have!difficulty!with!hues!of!short!wavelengths!and!see!the!world!in!greens!and!reds.!

?'At'the'level'of'the'retinal'ganglion'cell,'the'three?color'code'gets'translated'into'an'opponent?color'system.'Thus,'the'retina'contains'two'kinds'of'color?sensitive'ganglion'cells:'red?green'cells'and'yellow?blue'cells.'Some'color?sensitive'ganglion'cells'respond'in'a'center?surround'fashion.''

'BReceptive!Fields!of!ColorBSensitive!Ganglion!Cells:!When!a!portion!of!the!receptive!field!is!illuminated!with!the!color!shown,!the!cell’s!rate!of!firing!increases.!When!a!portion!is!illuminated!with!the!complementary!color,!the!cell’s!rate!of!firing!decreases.!

Color'='quality,'Wavelength'='quantity''quality'is'not'equal'to'quantity''Color'is'not'in'nature.'We'interpret'it'in'our'mind''?For'example,'red'light'excites'"red"'cones,'which'causes'the'excitation'of'red?green'ganglion'cells.''Green'light'excites'"green"'cones,'which'causes'the'inhibition'of'red?green'cells.'But'consider'the'effect'of'mediate'between'red'and'green,'it'will'stimulate'both'"red"'and'"green"'cones'about'equally.'Yellow?blue'ganglion'cells'are'excited'by'both'"red"'and'"green"'cones,'so'their'rate'of'firing'increases.'However,'red?green'ganglion'cells'are'excited'by'red'and'inhibited'by'green,'so'their'firing'rate'does'not'change.''

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Analysis(of(Visual(Information:(Role(of(the(Striate(Cortex((V1)(The'retinal'ganglion'cells'encode'information'about'the'relative'amounts'of'light'falling'on'the'center'and'surround'regions'of'their'receptive'field'and,'in'many'cases,'about'the'wavelength'of'that'light.'The'striate'cortex'performs'additional'processing'of'this'information,'which'it'then'transmits'to'the'visual'association'cortex.'The'striate'cortex'consists'of'six'principal'layers'(and'several'sublayers),'arranged'in'bands'parallel'to'the'surface.'These'layers'contain'the'nuclei'of'cell'bodies'and'dendritic'trees'that'show'up'as'bands'of'light'or'dark'in'sections'of'tissue'that'have'been'dyed'with'a'cell?body'stain.'?'Approximately'25'percent'of'the'striate'cortex'is'devoted'to'the'analysis'of'information'from'the'fovea,'which'represents'a'small'part'of'the'visual'field.'They'selectively'responded'to'specific'features'of'the'visual'world.'That'is,'the'neural'circuitry'within'the'visual'cortex'combines'information'from'several'sources.''?Orientation!and!Movement:'Most'neurons'in'the'striate'cortex'are'sensitive'to'orientation.'That'is,'if'a'line'or'an'edge'(the'border'of'a'light'and'a'dark'region)'is'positioned'in'the'cell’s'receptive'field'and'rotated'around'its'center,'the'cell'will'respond'only'when'the'line'is'in'a'particular'position?'a'particular'orientation.''Some'neurons'respond'best'to'a'vertical'line,'some'to'a'horizontal'line,'and'some'to'a'line'oriented'somewhere'in'between.'

?An'orientation?sensitive'neuron'in'the'striate'cortex'will'become'active'only'when'a'line'of'a'particular'orientation'appears'within'its'receptive'field.''!!!36. Simple(cell!An!orientationBsensitive!neuron!in!the!striate!cortex!

whose!receptive!field!is!organized!in!an!opponent!fashion.!(Zıt!biçimde!organize!olmuş!algısal!alanlara!sahip!olan,!striat!kortekste!oryantasyona!duyarlı!nöron)!

37. Complex(cell!A!neuron!in!the!visual!cortex!that!responds!to!the!presence!of!a!line!segment!with!a!particular!orientation!located!within!its!receptive!field,!especially!when!the!line!moves!perpendicularly!to!its!orientation.!(Belirli!bir!oryantasyon!hattında!en!iyi!cevapı!veren!görme!korteksindeki!nöron).!Complex!cell!responded!best!to!line!of!particular!orientation!but!did!not!show!an!inhibitory!surround;!that!is,!it!continued!to!respond!while!the!line!was!moved!within!the!receptive!field.!Thus,!these!neurons!also!served!as!movement!detectors.!In!addition,!complex!cells!responded!equally!well!to!white!lines!against!black!backgrounds!and!black!lines!against!white!backgrounds.!!

38. Hypercomplex(cell!responded!to!lines!of!a!particular!orientation!but!had!an!inhibitory!region!at!the!end!(or!ends)!of!the!lines,!which!meant!that!the!cells!detected!the!location!of!particular!ends!of!lines!of!a!particular!orientation.!!Ultimately,!hypercomplex!cells!can!provide!a!means!for!the!brain!to!visually!perceive!corners!and!curves!in!the!environment!by!identifying!the!ends!of!a!given!stimulus!

BCells!sensitive!to!orientation!of!a!stimulus!and!whose!receptive!field!is!organized!in!an!opponent!fashion:!Simple!cell!BCells!sensitive!to!orientation!and!movement!of!stimulus:!Complex!cell!BCells!sensitive!to!orientation!and!location!of!a!stimulus:!Hypercomplex!!

''?Certain'nerve'cells'are'only'sensitive'to'some'visual'field'only.'

?Neurons'in'the'primary'visual'cortex'detected'actually'responded'best'to'sine?wave'gratings.'39. Sine]wave(grating(A!series!of!straight!parallel!bands!varying!

continuously!in!brightness!according!to!a!sineBwave!function,!along!a!line!perpendicular!to!their!lengths.!SineBwave!grating,!bir!seri!bulanık!ve!odaksız!parallel!çubuklara!benzer.!A(square]wave(grating!parlaklıkta!değişken,!basit!bir!seri!dikdörtgen!şekilli!çubuklardan!oluşur;!bir!hat!boyunca!olna!parlaklık,!aşamalı!(kareBdalga)!bir!tarzda,!kendisine!dik!bir!şekilde!değişir.!!

!40. Spatial(frequency(The!relative!width!of!the!bands!in!a!sineBwave!

grating,!measured!in!cycles!per!degree!of!visual!angle.!(Görme!açısının!her!derecesindeki!döngülerle!ölçülen,!sineBwave!dalga!grating’indeki!bantların!göreceli!değişikliği.!BDifferent!spatial!frequencies!convey!different!information!about!the!appearance!of!a!stimulus.!High!spatial!frequencies!represent!abrupt!spatial!changes!in!the!image,!such!as!edges,!and!generally!correspond!to!configural!information!and!fine!detail.!Low!spatial!frequencies,!on!the!other!hand,!represent!global!information!about!the!shape,!such!as!general!orientation!and!proportions.!

!?We'perceive'depth'by'many'means,'most'of'which'involve'cues'that'can'be'detected'monocularly,'by'one'eye'alone.''?Binocular'vision'provides'a'vivid'perception'of'depth'through'the'process'of'stereoscopic'vision,'or'stereopsis.'Strereopsis,'el've'parmakların'ince'hareketlerinin'görsel'rehberliğinde'özellikle'önemlidir'(Bir'iğneye'iplik'geçirirken'stereopsis'süreci'etkili'olur.'''?Most'neurons'in'the'striate'cortex'are'binocular?'that'is'they'respond'to'visual'stimulation'of'either'eye.'Many'of'these'binocular'cells,'especially'those'found'in'a'layer'that'receives'information'from'the'magnocellular'system,'have'response'patterns'that'appear'to'contribute'to'the'perception'of'depth.'In'most'cases'the'cells'respond'most'vigorously'when'each'eye'sees'a'stimulus'a'slightly'different'location.'That'is,'the'neurons'respond'the'retinal!disparity,!a'stimulus'that'produces'images'on'slightly'different'parts'of'the'retina'of'each'eye.'This'is'exactly'the'information'that'is'needed'for'stereopsis;'each'eye'sees'a'three'dimensional'scene'slightly'differently,'and'the'presence'of'retinal'disparity'indicates'differences'in'the'distance'of'objects'from'the'observer.''41. Retinal(disparity(The!fact!that!points!on!objects!located!at!different!

distances!from!the!observer!will!fall!on!slightly!different!locations!on!the!two!retina;!provides!the!basis!for!stereopsis.!!

?The'parvocellular'system'receives'information'only'from'“red”'and'“green”'cones;'additional'information'from'“blue”'cones'is'transmitted'through'the'koniocellular'system.''?To'summarize,'neurons'in'the'striate'cortex'respond'to'several'different'features'of'a'visual'stimulus,'including'orientation,'movement,'spatial'frequency,'retinal'disparity,'and'color.'(Striat'korteksteki'nöronlar,'bir'görme'uyarısının'oryantasyon,'hareket,'boyutsal'frekans,'retinal'eşitsizlik've'renk'gibi'çeşitli'farklı'özelliklerine'cevap'verirler.)'(42. Cytochrome(oxidase((CO)(blob!In!the!striate!cortex,!information!

from!colorBsensitive!ganglion!cells!is!transmitted,!through!the!parvocellular!and!koniocellular!layers!of!the!LGN,!to!special!cells!grouped!together!in!cytochrome(oxidase((CO)(blob.!!Cytochrome(oxidase!is!the!central!region!of!a!module!of!the!primary!visual!cortex!revealed!by!a!stain!for!cytochrome!oxidase;!contains!waveBlength!sensitive!neurons,!part!of!the!parvocellular!layer.!!

!

43. CO(blobs(Most!of!them!are!sensitive!to!color!and!all!of!them!are!sensitive!to!low!spatial!frequencies!but!relatively!intensive!to!other!visual!features.!!Outside!the!Co!bulbs,!neurons!show!sensitivity!to!orientation,!movement,!spatial!frequency,!and!binocular!disparity,!but!most!do!not!respond!to!color.!!

!Modular(Organization(of(the(Striate(Cortex(Most!investigators!believe!that!the!brain!is!organized!in!modules,!which!probably!range!in!size!from!a!hundred!thousand!to!a!few!million!neurons.!Each!module!receives!information!from!other!modules,!performs!some!calculations,!and!then!passes!the!results!to!other!modules.!The!striate!cortex!is!divided!into!approximately!2500!modules,!each!approximately!0.5!×!0.7!mm!and!containing!approximately!150,000!neurons.!The!neurons!in!each!module!are!devoted!to!the!analysis!of!various!features!contained!in!one!very!small!portion!of!the!visual!field.!Collectively,!these!modules!receive!information!from!the!entire!visual!field,!the!individual!modules!serving!like!the!tiles!in!a!mosaic!mural.!The!modules!actually!consist!of!two!segments,!each!surrounding!a!CO!blob.!Neurons!located!within!the!blobs!have!a!special!function!'Role(of(the(Visual(Association(Cortex((?'Although'the'striate'cortex'is'necessary'for'visual'perception,'perception'of'objects'and'of'the'totality'of'the'visual'scene'does'not'take'place'there.'Each'module'of'the'striate'cortex'sees'only'what'is'happening'in'one'tiny'part'of'the'visual'field.''Thus,'for'us'to'perceive'objects'and'entire'visual'scenes,'the'information'from'these'individual'modules'must'be'combined.'That'combination'takes'place'in'the'visual'association'cortex.'44. Extrastriate(cortex(Visual!information!received!from!the!striate!

cortex!is!analyzed!in!the!visual!association!cortex.!Neurons!in!the!striate!cortex!send!axons!to!the!extrastriate(cortex.!Extrastriate!cortex!is!a!region!of!visual!association!cortex;!receives!fibers!from!the!striate!cortex!and!from!the!superior!colliculi!and!projects!to!the!inferior!temporal!cortex.!BThe!primate!extrastriate!cortex!consists!of!several!regions,!each!of!which!contains!one!or!more!independent!maps!of!the!visual!field.!!Each!region!is!specialized,!containing!neurons!that!respond!to!a!particular!feature!of!visual!information.!!

!Two!streams!of!visual!cortex:!!45. Dorsal(stream(or!pathway(A!system!of!interconnected!regions!of!

visual!cortex!involved!in!the!perception!of!spatial!location,!beginning!with!the!striate!cortex!and!ending!with!the!posterior!parietal!cortex.!(Where!an!object,!and!how!can!I!use!it)!

46. Ventral(stream!or!pathway(A!system!of!interconnected!regions!of!visual!cortex!involved!in!the!perception!of!form,!beginning!with!the!striate!cortex!and!ending!with!the!inferior!temporal!cortex.!!

The!dorsal!stream!receives!mostly!magnocellular!input,!but!the!ventral!stream!receives!approximately!equal!input!from!the!magnocellular!and!parvocellular/koniocellular.!!!BDorsal!stream!of!extrastriate!cortex:!"Where"!an!object!is!and!projects!to!posterior!part!of!parietal!lobe!BVentral!stream!of!extrastriate!cortex:!"What"!an!object!is!and!projects!to!inferior!part!of!temporal!lobe!!Extra!Notes:!!BThe!parvocellular,!koniocellular!and!magnocellular!system!provide!different!kinds!of!information.!!BThe!magnocellular!system!is!found!in!all!mammals,!whereas!the!parvocellular!and!koniocellular!system!are!found!only!in!some!species!of!primates.!BOnly!the!cells!in!the!parvocellular!and!koniocellular!system!analyze!information!concerning!color.!!BCells!in!the!parvocellular!system!also!show!high!spatial!resolution!and!low!temporal!resolution;!that!is,!they!are!able!to!detect!very!fine!details,!but!their!response!is!slow!and!prolonged.!!BThe!koniocellular!system!receives!information!only!from!“blue”!cones!and!does!not!provide!information!about!fine!detail.!!BNeurons!in!the!magnocellular!system!are!colorBblind!and!are!not!able!to!detect!fine!details,!but!can!detect!smaller!contrast!between!light!and!dark.!They!are!also!especially!sensitive!to!movement.!!

!

Perception(of(Color((As'we'saw'earlier,'neurons'within'the'CO'blobs'in'the'striate'cortex'respond'to'colors.'Like'the'ganglion'cells'in'the'retina'(and'the'parvocellular'and'koniocellular'neurons'in'the'LGN),'these'neurons'respond'in'opponent'fashion.''This'information'is'analyzed'by'the'regions'of'the'visual'association'cortex'that'constitute'the'ventral'stream.''47. Color(constancy(The!relatively!constant!appearance!of!the!colors!of!

objects!viewed!under!varying!lighting!conditions.!(Değişken!ışıklandırma!koşulları!altında!nesne!renklerinin!kısmen!sabit!görünümü.)!Damage!to!V4,!break!to!ability!the!color!constancy.!!

48. Cerebral(achromatopsia((vision!without!color)(Inability!to!discriminate!among!different!hues;!caused!by!damage!to!area!of!V8!of!the!visual!association!cortex.!Farklı!tonlar!arasında!ayırt!etme!yetersizliği;!visual!association!korteksinin!V8!alanındaki!hasar!bu!duruma!sebep!olmaktadır.!!The!patients!describe!their!vision!as!resembling!a!blackBwhite!film.!In!addition,!they!cannot!even!image!colors!or!remember!the!colors!of!objects!they!saw!before!their!brain!damage!occurred.!!Natural!and!Unnatural!Colors:!Neurons!in!color!sensitive!area!V8!responded!to!photographs!of!objects!in!their!natural!colors!(a)!but!not!to!those!of!objects!in!unnatural!colors!(b)!!

Perception(of(Form(?The'analysis'of'visual'information'that'leads'to'the'perception'of'form'begins'with'neurons'in'the'striate'cortex'that'are'sensitive'to'orientation'and'spatial'frequency.'?These'neurons'send'information'to'area'V2'that'is'then'relayed'to'the'subregions'of'the'visual'association'cortex'that'constitute'the'ventral'stream.'?In'primates'the'recognition'of'visual'patterns'and'identification'of'particular'objects'take'place'in'the'inferior'temporal'cortex,'located'on'the'ventral'part'of'the'temporal'lobe.'?This'region'of'the'visual'association'cortex'is'located'at'the'end'of'the'ventral'stream.'?It'is'here'that'analyses'of'form'and'color'are'put'together'and'perceptions'of'three?dimensional'objects'and'backgrounds'are'achieved.'''''''

49. Visual(agnosia(or!object(agnosia((failure!to!know)!Deficits!in!visual!form!perception!in!the!absence!of!blindness;!caused!by!brain!damage,!damage!to!the!human!visual!association!cortex.!Agnosia!refers!to!an!inability!to!perceive!or!identify!a!stimulus.!You!can!see!objects,!but!you!don’t!know!what!they!are.!However,!you!can!recognize!face.!!Visual!agnosia!is!caused!by!damage!of!those!parts!of!the!visual!association!cortex!that!contribute!to!the!ventral!stream.!Damage!to!Lateral!Occipital!Complex.!!

50. Lateral(occipital(complex((LOC)!A!region!of!extrastriate!cortex,!involved!in!perception!of!objects!other!than!people’s!bodies!and!faces.!!!

51. Prosopagnosia(Failure!to!recognize!particular!faces.!Patients!can!see!eyes,!ears,!etc.,!but!they!cannot!say!whose!face!it!is.!!

52. Fusiform(face(area((FFA)(A!region!of!the!visual!association!cortex!located!in!the!fusiform!gyrus!on!the!base!of!the!inferior!temporal!lobe;!involved!in!perception!of!faces.!!Also,!if!you!expert!on!sth,!such!as!birds,!dogs!etc,!this!area!become!active.!Fusiform!face!area!become!very!active!when!people!are!adult!rather!they!are!child.!!Right!part!of!fusiform!area!is!much!responsible!recognizing!face!rather!the!left!part.!!

!

!!53. Extrastriate(body(are((EBA)!A!region!of!the!visual!association!

cortex!located!in!the!lateral!occipitotemporal!cortex;!involved!in!perception!of!the!human!body!and!body!parts!other!than!face.!!

54. Parahippocampal(place(area((PPA)(A!region!of!the!medial!temporal!cortex;!involved!in!perception!of!particular!places!(“scenes”).!!Scene(recognition:!The!parahippocampal(place(area!(PPA)!is!a!subregion!of!the!parahippocampal!cortex!that!plays!an!important!role!in!the!encoding!and!recognition!of!scenes!(rather!than!faces!or!objects).!fMRI!studies!indicate!that!this!region!of!the!brain!becomes!highly!active!when!human!subjects!view!topographical!scene!stimuli!such!as!images!of!landscapes,!cityscapes,!or!rooms!(i.e.!images!of!"places").!Damage!to!the!PPA,!often!leads!to!a!syndrome!in!which!patients!cannot!visually!recognize!scenes!even!though!they!can!recognize!the!individual!objects!in!the!scenes!(such!as!people,!furniture,!etc.).!!

!Dorsal(Route((?We'need'to'know'not'only'what'things'are,'but'also'where'they'are'and'if'they'are'moving,'where'they'are'going.''?Without'the'ability'to'perceive'the'direction'and'velocity'of'movement'of'objects,'we'would'have'no'way'to'predict'where'they'will'be.'We'would'be'unable'to'catch'them'(or'avoid'letting'them'catch'us).!BOne!of!the!regions!of!the!extrastriate!cortex!–area(V5,!also!known!as!area!MT,!for!medial(temporalB!contains!neurons!respond!to!movement.!Damage!to!this!area!disrupts!ability!to!perceive!moving!stimuli.!

BA!region!adjacent!area!V5,!is!area(V5a!is!called!MST,!for!medial(superior(temporal,!receives!information!about!movement!from!V5!and!performs!a!further!analysis.!MTS!neurons!respond!to!complex!patterns!of!movement,!including!radial,!circular,!and!spiral!motion.!One!important!function!of!this!region!appears!to!be!analysis!of!optic(flow.!As!we!move!around!in!our!environment!or!as!objects!in!our!environment!move!in!relation!to!us,!the!sizes,!shapes,!and!locations!of!environmental!features!on!our!retinas!change.!!55. Optic(flow!The!complex!motion!of!points!in!the!visual!field!caused!

by!relative!movement!between!the!observer!and!environment;!provides!information!about!the!relative!distance!of!objects!from!the!observes!and!of!the!relative!direction!of!movement.!!Optik!akış!ismi!verilen!görsel!bilgi!akışı,!bir!nesnenin!hareketine!bakarak!mesafeleri!algılamamızı!sağlamaktadır.!

56. Akinetopsia(Inability!to!perceive!movement,!caused!by!damage!to!area!V5!(also!called!MTS)!of!the!visual!association!cortex.!!

57. Intraparietal(sulcus((IP)(The!end!of!the!dorsal!stream!of!the!visual!association!cortex;!involved!perception!of!location,!visual!attention,!and!control!of!eye!and!hand!movements.!Intraparietal!sulcus!have!5!regions:!AIP,!LIP,!VIP,!CIP,!MIP.!(anterior,!lateral,!ventral,!caudal,!medial)!!Anterior!intreparietal!region!says!that!how!to!grasp!objects.!!Ventral!intraparietal!region!is!responsible!to!point!things.!(Birşeyi!işaret!etmek)!Lateral!intraparietal!region!controls!saccadic!eye!movement.!!Caudal!intraparietal!region!is!responsible!for!seeing!depth!of!things.!Medial!intraparietal!region!is!responsible!to!reach!something.!!

!!Extra!Notes:!!BVisual!association!cortex!also!receives!information!from!superior!colliculi!in!brain!stem.!!BDorsal!route!analyze!information!faster,!and!dorsal!route!is!more!important!then!ventral!because!if!you!even!don’t!know!what!something!is,!if!you!know!where!it!is,!you!can!escape!from!it.!!BObjects’!bigness,!thickness!or!etc.,!are!analyzed!by!ventral!route.!Dorsal!route!say!how!can!you!use!it.!!(2.5!years!old!children!experiment!(scale!error)!!!BThe!importance!of!the!visual!system!is!shown!by!the!fact!that!approximately!25%!of!our!cerebral!cortex!is!devoted!to!this!sense!modality!and!by!the!many!discoveries!being!made!by!the!laboratories!that!are!busy!discovering!interesting!things!about!vision.!!BEyes,!Thalamus,!V1!and!Visual!Association!Cortex!all!play!an!important!role!in!analysis!of!visual!information.!!BDorsal!stream!in!Visual!Association!Cortex!specializes!in!analyzing!where!things!are!in!relation!to!us!or!how!to!react!to!them!while!the!ventral!stream!specializes!in!analyzing!what!things!are.!

!

(((((((

(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((

SUMMARY(! Light!consists!of!electromagnetic!radiation,!similar!to!radio!waves!but!of!a!different!frequency!and!wavelength.!Color!can!vary!in!three!perceptual!dimensions:!hue,!brightness,!and!saturation,!which!correspond!to!the!physical!dimensions!of!wavelength,!intensity,!and!purity.!(Renk,!üç!algısal!boyutta!değişkenlik!gösterebilir:!dalga!boyu,!yoğunluk!ve!saflığn!fiziksel!boyutlarına!karşılık!gelen!ton!parlaklık!ve!doygunluk.)!! The!photoreceptors!in!the!retina!–the!rods!and!the!conesB!detect!light.!Muscles!move!the!eyes,!so!that!images!of!particular!parts!of!the!environment!fall!on!the!retina.!Accommodation!is!accomplished!by!the!ciliary!muscles,!which!change!the!shape!of!the!lens.!!! Photoreceptors!communicate!with!bipolar!cells,!which!communicate!with!ganglion!cells!whose!axons!sends!visual!information!to!the!rest!of!the!brain.!In!addition,!horizontal!cells!and!Amacrine!cells!combine!messages!from!adjacent!photoreceptors.!!! When!light!strikes!a!molecule!of!photopigment!in!a!photoreceptor,!the!retinal!molecule!detaches!from!the!opsin!molecule,!a!process!known!as!bleaching!(beyazlatma).!(Işık,!bir!fotoreseptördeki!fotopigment!molekülüne!çarptığında,!ağarma!olarak!bilinen!bir!süreç!ile!retinal!molekül!opsin!molekülünden!ayrılır).!This!events!causes!a!receptor!potential,!which!changes!the!rate!of!firing!of!the!ganglion!cell,!signaling!the!detection!of!light.!!! Visual!information!from!the!retina!reaches!the!striate!cortex!surrounding!the!calcarine!fissure!after!being!relayed!through!the!magnocellular,!parvocellular,!and!koniocellular!layers!of!the!Lateral!Geniculate!Neurons.!Several!other!regions!of!the!brain,!including!the!hypothalamus!and!the!tectum,!also!receive!visual!information.!These!regions!help!to!regulate!activity!during!the!day–night!cycle,!coordinate!eye!and!head!movements,!regulate!the!size!of!the!pupils,!and!control!attention!to!visual!stimuli.!…………….!! ! Recordings!of!the!electrical!activity!of!single!neurons!in!the!retina!indicate!that!each!ganglion!cell!receives!information!from!photoreceptorsBjust!one!in!the!fovea!and!many!more!in!the!periphery.!The!receptive!field!of!most!retinal!ganglion!cell!consists!of!two!concentric!circles,!with!the!cells!becoming!excited!when!light!falls!in!one!region!and!becoming!inhibited!when!it!falls!in!the!other.!This!arrangement!enhances!the!ability!of!the!nervous!system!to!detect!contrasts!in!brightness.!ON!cells!are!excited!by!light!objects!against!dark!backgrounds;!OFF!cells!detect!dark!objects!against!light!backgrounds.!! Color!vision!occurs!as!a!result!of!information!provided!by!the!three!types!of!cones,!each!of!which!is!sensitive!to!light!of!a!certain!wavelength!:!long,!medium,!or!short.!The!absorption!characteristics!of!the!cones!are!determined!by!the!particular!opsin!that!their!photopigment!contains.!!! Most!forms!of!defective!color!vision!appear!to!be!caused!by!alterations!in!cone!opsins.!The!"red"!cones!of!people!with!protanopia!are!filled!with!"green"!cone!opsin,!and!the!"green"!cones!of!people!with!deuteranopia!are!filled!with!"red"!cone!opsin.!The!retinas!of!people!with!tritanopia!appear!to!lack!"blue"!cones.!

Most!colorBsensitive!ganglion!cells!respond!in!an!opposing!centerBsurround!fashion!to!the!pairs!of!primary!colors:!red!and!green,!and!blue!and!yellow.!The!responses!of!these!neurons!are!determined!by!the!retinal!circuitry!connecting!them!with!the!photoreceptors.!…………….!! ! The!striate!cortex!(area!V1)!consists!of!six!layers!and!several!sublayers.!Visual!information!is!received!from!the!magnocellular!and!parvocellular!layers!of!the!dorsal!lateral!geniculate!nucleus.!Information!from!V1!ia!sent!area!V2,!the!first!region!of!the!visual!association!cortex.!The!magnocellular!system!is!more!primitive,!phylogenetically!older,!colorBblind,!and!sensitive!to!movement,!depth,!and!small!differences!in!brightness.!The!parvocellular!system!and!koniocellular!system!is!evolved!more!recently.!The!parvocellular!system!is!colorBsensitive,!and!it!receives!information!from!“red”!and!“green”!cones!and!is!able!to!discriminate!finer!details.!The!koniocellular!system!provides!additional!information!about!color,!received!from!“blue”!cones.!!! ! The!striate!cortex!is!organized!into!modules,!each!surrounding!a!pair!of!CO!blobs,!which!are!revealed!by!a!stain!for!cytochrome!oxidase,!an!enzyme!found!in!mitochondria.!Each!half!of!a!module!receives!information!from!one!eye;!but!because!information!is!

shared,!most!of!the!neurons!respond!to!input!from!both!eyes.!The!neurons!in!the!CO!blobs!are!sensitive!to!color!and!to!lowBfrequency!sineBwave!gratings,!whereas!those!between!the!blobs!are!sensitive!to!sineBwave!gratings!of!higher!spatial!frequencies,!orientation,!retinal!disparity,!and!movement.!…………….!!! ! The!visual!cortex!consists!of!the!striate!cortex,!the!extrastriate!cortex!(also!called!the!prestriate!or!circumstriate!cortex),!and!the!visual!association!cortex!of!the!inferior!temporal!lobe!and!the!posterior!parietal!lobe.!The!visual!cortex!has!at!least!twentyBfive!different!subregions,!arranged!in!a!hierarchical!fashion.!The!extrastriate!cortex!receives!information!from!the!striate!cortex!and!from!the!superior!colliculus.!The!colorBsensitive!cells!in!the!CO!blobs!in!the!striate!cortex!send!information!to!area!V4!of!the!extrastriate!cortex.!Damage!to!the!area!V4!abolishes!color!constancy!(accurate!perception!of!color!under!different!lighting!conditions),!and!damage!to!area!V8!causes!cerebral!achromatospia,!a!loss!of!color!vision!but!not!form!of!perception.!!! ! The!visual!cortex!is!organized!into!two!streams.!The!ventral!stream,!which!ends!with!the!inferior!temporal!cortex,!is!involved!with!the!perception!of!objects.!Lesions!of!this!region!disrupt!visual!object!perception.!The!dorsal!stream,!which!ends!with!the!posterior!parietal!cortex,!is!involved!with!perception!of!location,!movement,!and!control!of!eye!and!hand!movements.!Damage!to!area!V5!or!to!the!posterior!parietal!cortex!disrupts!an!animal’s!ability!to!perceive!movement!or!the!spatial!location!of!objects.!! ! Functional!imaging!studies!indicate!that!specific!regions!of!the!cortex!are!involved!in!perception!of!form,!movement,!and!color,!and!these!studies!will!undoubtedly!enable!us!to!discover!to!correspondences!between!the!anatomy!of!the!human!visual!system!and!that!of!laboratory!animals.!Studies!with!humans!who!have!sustained!damage!to!the!ventral!stream!of!visual!association!cortex!sustain!a!perceptual!impairment!known!as!visual!agnosia.!! Prosopagnosia,!failure!to!recognize!faces,!is!caused!by!damage!to!the!fusiform!face!area,!a!region!on!the!medial!surface!of!the!extrastriate!cortex!on!the!base!of!the!brain.!The!fusiform!face!region!fails!to!develop!in!people!with!autism,!presumably!because!of!insufficient!motivation!to!become!expert!in!recognizing!other!people’s!faces.!Other!specialized!regions!of!the!visual!association!cortex!are!involved!in!the!recognition!of!body!parts!and!environmental!scenes.!!

Damage!to!the!area!V5!(also!called!area!MT/MTS)!disrupts!perception!of!movement.!Damage!to!the!posterior!parietal!cortex!disrupts!perception!of!the!spatial!location!of!objects.!Damage!to!the!human!visual!association!cortex!corresponding!to!area!V5!disrupts!perception!of!movement,!producing!a!disorder!known!as!akinetopsia.!!

In!addition,!transcranial!magnatic!stimulation!of!V5!causes!a!temporary!disrupts!of!perception!of!motion!and!functional!imaging!studies!show!that!perception!of!moving!stimuli!activate!this!region.!!

In!both!monkeys!and!humans,!area!MSTd,!a!region!of!extrastriate!cortex!adjacent!to!area!V5,!appears!to!be!specialized!for!perceiving!optic!flow,!one!of!the!cues!we!use!to!perceive!the!direction!in!which!we!are!heading.!!

The!ability!to!perceive!form!form!motionB!recognition!of!complex!movements!of!people!indicated!by!lights!attached!to!parts!of!their!bodyB!is!probably!related!to!the!ability!to!recognize!people!by!the!way!they!walk.!This!ability!apparently!depends!on!a!region!of!cerebral!cortex!on!the!ventral!bank!of!the!posterior!end!of!the!superior!temporal!sulcus.!!

Most!of!the!visual!association!cortex!at!the!end!of!the!dorsal!stream!is!located!in!the!intraparietal!sulcus:!LIP!and!VIP!are!involved!in!visual!attention!and!control!of!saccadic!eye!movements,!VIP!and!MIP!are!involved!in!visual!control!of!reaching!and!pointing,!AIP!is!involved!in!visual!control!of!grasping!and!manipulating,!and!CIP!is!involved!in!perception!of!depth!from!stereopsis.!!

Goodale!and!his!colleagues!suggest!that!the!primary!function!of!the!dorsal!stream!of!the!visual!association!cortex!is!better!characterized!as!“how”!rather!then!“what”;!the!role!of!the!posterior!parietal!cortex!in!control!of!reaching,!grasping,!and!manipulation!requires!visually!derived!information!of!movement,!depth,!and!location.!!BList!the!order!of!perception!through!the!brain:!Retina!>!Thalamus!>!Primary!visual!cortex!>!Visual!association!cortex!