1 Psy280: Perception Psy280: Perception Prof. Anderson Prof. Anderson Department of Psychology Department of Psychology Week 4 Week 4
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Psy280: PerceptionPsy280: Perception
Prof. AndersonProf. AndersonDepartment of PsychologyDepartment of Psychology
Week 4Week 4
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Lets enter the brain, shall we?Lets enter the brain, shall we?
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Visual maps: Multiple neuralVisual maps: Multiple neuralrepresentations of realityrepresentations of reality
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Neural convergence & divergence:Neural convergence & divergence:Complexity & parallel processingComplexity & parallel processing
Eye
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Eye to CNS�� Contralateral projectionsContralateral projections
�� RVFRVF——> left hemisphere> left hemisphere�� LVFLVF——>right hemisphere>right hemisphere
�� Multiple pathwaysMultiple pathways�� Retino-geniculate-striateRetino-geniculate-striate
pathwaypathway�� Conscious visionConscious vision
�� Retino-collicular-pulvinarRetino-collicular-pulvinarpathwaypathway�� Vision for actionVision for action�� Eye movementsEye movements�� UnconsciousUnconscious
�� Retino-SuprachiasmaticRetino-Suprachiasmaticnucleusnucleus
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Retino-geniculate-striate pathRetino-geniculate-striate path�� Vision for perceptionVision for perception
�� Conscious visionConscious vision
�� Cortical blindness: HemianopiaCortical blindness: Hemianopia�� Retina intact: Brain blindRetina intact: Brain blind
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Retino-collicular pathRetino-collicular path
�� ““BlindsightBlindsight””: Nonconscious sight: Nonconscious sight�� Visual cortical lesionVisual cortical lesion
�� Yet, above chance localizationYet, above chance localization�� Intact eye movementsIntact eye movements
�� Conclude:Conclude:�� Spared retino-collicular pathSpared retino-collicular path
�� Different Different ““kindkind”” of vision of vision
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Cortical blindness:Cortical blindness:Fear blindsightFear blindsight
XMorris et al., 2001
•Examine patient w/ cortical blindness
• Examine amygdala response to fear evoking events inthe absence of cortex/awareness
L R
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Intact/Seen Lesion/Blind
Cortical blindness:Cortical blindness:Fear blindsightFear blindsight
• Stimuli presented to intact and blind hemifield
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Intact Blind
Cortical blindness: FearCortical blindness: Fearblindsightblindsight
• Amygdala discrimination of fear in blind field
• Depends on retino-collicular pathway to amygdala
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RetinaRetina——>Suprachiasmatic>Suprachiasmaticnucleusnucleus
�� Other forms of nonconscious visionOther forms of nonconscious vision�� Non-rod, non-cone, melatonin basedNon-rod, non-cone, melatonin based
photoreceptorsphotoreceptors�� Regulation of circadian behaviorRegulation of circadian behavior
�� Humans lacking rods and conesHumans lacking rods and cones�� Sleep/wake cycles influence by lightSleep/wake cycles influence by light
�� Supported by connection between retina andSupported by connection between retina andbiological clock in the SCNbiological clock in the SCN
�� Conclude: Many types of Conclude: Many types of ““visionvision””
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Retino-geniculate pathway� Organization of LGN: Retinal origin
� Laminar structure
� Temporal/Nasal adjacent (Same VF)
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Retino-geniculate pathway:Parallel processing III
� Organization of LGN: Retinotopy� Adjacent regions in retina project
to adjacent regions of LGN
� 6 representations of retina in register
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Retino-geniculate pathway� LGN: Physiology
� Similar to retinal ganglion cells
� Center-surround
� LGN: Anatomy
� Not all retinal maps the same� Parvocellular (P-cells)
� Small cells
� Top 4 layers
� Largely Cone-based
� Magnocellular (M-cells)� Large cells
� Bottom 2 layers
� Largely rod-based
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Organization of visual cortices:Divide & Conquer!
�� BifurcationsBifurcations�� LGN LGN ——> V1> V1
�� 2 divisions2 divisions�� M & PM & P
�� V1 V1 ——> extrastriate> extrastriate�� Even greater divergenceEven greater divergence�� Maintain M & P originMaintain M & P origin
�� Differ in features (Parallel)Differ in features (Parallel)& complexity (Hierarchical)& complexity (Hierarchical)
Parvo
Magno
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M & P pathways:M & P pathways:Functional significanceFunctional significance
�� Do M & P pathways representDo M & P pathways representdifferent modes of perception?different modes of perception?
�� P-cells: colour and luminanceP-cells: colour and luminance�� Colour, form, textureColour, form, texture
�� M-cells: luminanceM-cells: luminance�� MotionMotion
�� Isoluminance studiesIsoluminance studies�� Robust motion when definedRobust motion when defined
by luminanceby luminance�� Decreased motion when defined byDecreased motion when defined by
color (isoluminant)color (isoluminant)
�� Lesions of M & PLesions of M & P
Motion
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Primary visual cortex:Striate cortex/V1/Area 17
� First cortical synapse in vision: Calcarine sulcus
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Striate cortex (V1): Retinotopy
�� 6 LGN maps 6 LGN maps ——>>1 striate map1 striate map
�� Up is downUp is down�� Right is leftRight is left�� Fovea is posteriorFovea is posterior
�� Map is distortedMap is distorted�� Cortical magnificationCortical magnification�� Like motor homunculusLike motor homunculus�� Fovea > peripheryFovea > periphery
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Neuropsychological evidence:Neuropsychological evidence:RetinotopyRetinotopy
�� Visual field deficits: ScotomasVisual field deficits: Scotomas�� Cortical blindnessCortical blindness
�� Hemianopia distinguishes between peripheral (retinal) andHemianopia distinguishes between peripheral (retinal) andcentral (cortical) blindnesscentral (cortical) blindness
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Striate cortex (V1):Eye and orientation selectivity
� Ocular dominance columns� Selective for each eye
� Orientation selectivity� Increase in complexity
relative to LGN
� “simple” cells
� Orientation detectors for
each region of retinal space
All from same portion of space
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10 min break!10 min break!
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How do we create orientationHow do we create orientationselectivity?selectivity?
�� Combine center surround cells to createCombine center surround cells to create““simplesimple”” cells cells
+-
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Does V1 have to representDoes V1 have to representevery orientation?every orientation?
�� NopeNope�� Distributed orDistributed or
coarse codingcoarse coding�� Orientation isOrientation is
coded bycoded bymagnitude ofmagnitude ofresponse acrossresponse acrossmultiple cellsmultiple cells
Orientation “tuning curve”
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Cortical magnification:Cortical magnification:The oblique effectThe oblique effect
�� Not just fovea versus peripheryNot just fovea versus periphery�� More cells/cortical space devoted to horizontalMore cells/cortical space devoted to horizontal
and vertical lines relative to obliqueand vertical lines relative to oblique
�� Physiology=Physiology=perceptionperception
Perception Brain signal: fMRI
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Orientation selectivity:Orientation selectivity:Nature or Nurture?Nature or Nurture?
�� Selective rearing during early developmentSelective rearing during early development�� Vertical or horizontal orientation blindnessVertical or horizontal orientation blindness
�� Reflects visual plasticity in V1Reflects visual plasticity in V1
Verticaldeprivation
Horizontaldeprivation
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Definitions: Visual angle andDefinitions: Visual angle andspatial frequencyspatial frequency
�� Angle of retinal projectionAngle of retinal projection�� Equal visual angle, same retinal sizeEqual visual angle, same retinal size
�� Spatial frequencySpatial frequency�� Number of light dark alternations (cycles) perNumber of light dark alternations (cycles) per
degree of visual angledegree of visual angle
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Spatial frequency channelsSpatial frequency channels
�� Visual system might decompose stimuli intoVisual system might decompose stimuli intodifferent scales (spatial frequencies)different scales (spatial frequencies)�� Small changes, big changes in fluctuation inSmall changes, big changes in fluctuation in
luminance over spaceluminance over space
Low f High f
Low High
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Fourier analysisFourier analysis
�� Can decompose eventsCan decompose eventsinto constituent spatialinto constituent spatialfrequency (SF)frequency (SF)componentscomponents
�� High SF captures edgesHigh SF captures edges
�� Descriptive or doesDescriptive or doesvisual system may usevisual system may usesimilar procedure ?similar procedure ?
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Simple cells and spatialSimple cells and spatialfrequencyfrequency
�� Tuning curves ofTuning curves ofsimple cellssimple cells
�� MaximallyMaximallyresponsive toresponsive todifferent SFdifferent SF
�� Suggests V1 doesSuggests V1 doesSF analysisSF analysis
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SF orientation coding andSF orientation coding andperceptionperception
�� Are these cells important for perception?Are these cells important for perception?�� Selective adaptationSelective adaptation
�� Exercise neurons until weak responseExercise neurons until weak response�� Like fatigued musclesLike fatigued muscles�� Examine contrast sensitivity at diff orientationsExamine contrast sensitivity at diff orientations
Dec
reas
e in
con
tras
tse
nsiti
vity
Orientation of grating40 20 0 20 40
test30°
Adapt0°
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Contrast sensitivity functionContrast sensitivity function
�� Adaptation results in selective fatigueAdaptation results in selective fatigue�� Reveals that CSF is the result of multiple SFReveals that CSF is the result of multiple SF
channelschannels
CSF
Con
tras
t sen
sitiv
ity
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SF adaptation and perceptionSF adaptation and perception�� Phenomenal and neural correlatesPhenomenal and neural correlates�� Perception determined by multiple SF channelsPerception determined by multiple SF channels�� Coarse coding across channelsCoarse coding across channels
�� Also: Perception differs for identical stimulusAlso: Perception differs for identical stimulus�� Perception parallels V1 response, not retinal imagePerception parallels V1 response, not retinal image
a
b
Neural response
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Beyond V1:Beyond V1:Higher order extra-striate corticesHigher order extra-striate cortices
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Higher order visual cortex:Higher order visual cortex:Extrastriate cortexExtrastriate cortex
�� CytoarchitectureCytoarchitecture�� Distinct from V1Distinct from V1
�� Functional correlatesFunctional correlates�� More complex features:More complex features:�� Motion, MT/V5Motion, MT/V5
�� Direction and speedDirection and speedSelectiveSelective
�� ColourColour�� DepthDepth�� FormForm
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EndEnd