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Parallel streams of visual processing
RETINAL GANGLION CELL AXONS: OPTIC TRACT
Optic nerve
Optic tract
Optic chiasm
Hypothalamus: regulation of
i di h th
Lateral geniculate nucleus
circadian rhythms
Pretectum: reflex t l f il
Optic radiation
control of pupil and lens
radiation
Superior colliculus: orienting the movements of head and eyes
Striate cortex
of head and eyes
LATERAL GENICULATE NUCLEUS OF THE THALAMUS
LGN
The visual system thalamic nucleus
LGNMGN
LGN organized into 6 cell layersLGN organized into 6 cell layers2 Magnocellular layers4 Parvocellular layers
with thin layers of kinocellularwith thin layers of kinocellular(dust-like) neurons interposed
All LGN neurons • are monocular - respond to stimulation of one eye only
Type mLGN neurons in LGN magnocellular layers
• have concentric (ON/OFF or OFF/ON) receptive fields
• synapse with Type M retinal ganglion axons• have large concentric receptive fields• are insensitive to colorare insensitive to color• sensitive to small changes in brightness levels (scotopic vision)• are rapidly-adapting (motion sensitive)
Type pLGN neurons in LGN parvocellular layers • synapse with Type P retinal ganglion axons• ha e small concentric recepti e fields (high acuity)• have small concentric receptive fields (high acuity)• are sensitive to color (color sensitivity)• are not sensitive to small changes in brightness levels
Type kLGN neurons appear similar to Type pLGN neurons
• are slowly-adapting (indicate duration stimulus is “on”)
PRIMARY VISUAL CORTEX
Primary visual cortexcortex
Calcarine fissure
Cerebral cortex is differentiated into 6 horizontal layers
COLOR SELECTIVITY
SPECIALIZED PROCESSING
l i i f k
SPECIALIZED PROCESSING: CHARACTERISTICS OF V1 BLOB (COLOR ) CELLS
• color sensitive - target of kLGN axons• small concentric receptive fields• monocular - only one eye stimulates the blob cellsy y• indifferent to stimulus orientation• indifferent to stimulus movement (slowly-adapting)
RETINA
….
….
BLOBS
Striate cortex: V1
V1 BLOB CELL RESPONSES
Orientation selectivity
Li ht b ti l
Stimulusorientation
Stimuluspresented
Light bar stimulus projected on screen Recording from
visual cortexRecordRecord
0 1 2 3Time (sec)
ORIENTATION SELECTIVITY
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: COMMON CHARACTERISTICS OF INTERBLOB CELLS
l d i fi ld• elongated receptive fields• insensitive to color• binocular w/ ocular dominance
> one eye elicits a stronger response• most are sensitive to stimulus orientation
> strongest response to particular orientation> strongest response to particular orientation
….
….
Interblob cells
ORIENTATION SELECTIVITY
SPECIALIZED PROCESSINGSPECIALIZED PROCESSING: SHAPE/FORM & LOCATION V1 INTERBLOB CELLS
l d i fi ld• elongated receptive fields• insensitive to color• binocular w/ ocular dominance
> one eye elicits a stronger response• sensitive to stimulus orientation
> strongest response to particular orientation
•insensitive to movement - target of pLGN axons
> strongest response to particular orientation
> slowly-adapting response• location specific
> strongest response in field centerg p
Functional organization of the striate cortex
R
LRLR
LRLR
L
L
Optical imaging of functional domains im
ulus
ompu
ter
functional domains
Cortical vasculature
St co
Cam
era
ideo
dat
acq
uisi
tion
Amplifier
Vi
acLight guide
Single condition maps Orientation map
Neuronal circuits incircuits in striate cortex
Cells with i ilsimilar
function are linked through ghorizontal connections
What is the function of horizontal connections?
EXTRA-STRIATE AND ASSOCIATION AREAS
NON-HUMAN PRIMATES
HIGHER ORDER PROCESSINGV SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEXV1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX
EXTRASTRIATE CORTEX (V2, V3 & V4) SEND AXONS TOASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)
DORSAL STREAM: > SUPERIOR TEMPORAL & PARIETAL
NECESSARY FOR• spatial orientationp• binocular fusion• depth perception • spatial location
“THE WHERE”
• spatial location• movement detection
“THE WHERE”
HIGHER ORDER PROCESSINGV SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEXV1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX
EXTRASTRIATE CORTEX (V2, V3 & V4) SEND AXONS TOASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)
VENTRAL STREAM: > INFERIOR “TEMPORAL” GYRUS
ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS)
IMPORTANT FORSHAPE & COLOR
i• perception• discrimination• recognition g• memory• learning
“THE WHAT”
Motion processing
Shape processing in infero-temporal (IT) cortex