Parallel streams of visual processing
RETINAL GANGLION CELL AXONS: OPTIC TRACT Optic nerve Optic tract Optic chiasm Lateral geniculate nucleus Hypothalamus: regulation of circadian rhythms Pretectum: reflex control of pupil and lens Optic radiation Striate cortex Superior colliculus: orienting the movements of head and eyes
LATERAL GENICULATE NUCLEUS OF THE THALAMUS The visual system thalamic nucleus MGN LGN LGN organized into 6 cell layers 2 Magnocellular layers 4 Parvocellular layers with thin layers of kinocellular (dust-like) neurons interposed
All LGN neurons are monocular - respond to stimulation of one eye only have concentric (ON/OFF or OFF/ON) receptive fields Type mlgn neurons in LGN magnocellular layers synapse with Type M retinal ganglion axons have large concentric receptive fields are 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 have small concentric receptive e fields (high acuity) are sensitive to color (color sensitivity) are not sensitive to small changes in brightness levels are slowly-adapting (indicate duration stimulus is on ) Type klgn neurons appear similar to Type plgn neurons
PRIMARY VISUAL CORTEX Primary visual cortex Calcarine fissure
Cerebral cortex is differentiated into 6 horizontal layers
COLOR SELECTIVITY SPECIALIZED PROCESSING: CHARACTERISTICS OF V 1 BLOB (COLOR ) CELLS color sensitive i - target of fklgn axons small concentric receptive fields monocular - only one eye stimulates the blob cells indifferent to stimulus orientation indifferent to stimulus movement (slowly-adapting) BLOBS RETINA.. Striate cortex: V 1 V1 BLOB CELL RESPONSES
Orientation selectivity Stimulus orientation Stimulus presented Light bar stimulus projected on screen Recording from visual cortex Record 0 1 2 3 Time (sec)
ORIENTATION SELECTIVITY SPECIALIZED PROCESSING: COMMON CHARACTERISTICS OF INTERBLOB CELLS 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.. Interblob cells
ORIENTATION SELECTIVITY SPECIALIZED PROCESSING: SHAPE/FORM & LOCATION V 1 INTERBLOB CELLS 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 > slowly-adapting response location specific > strongest response in field center
Functional organization of the striate cortex R L R R L R L L
Optical imaging of functional domains imulus omputer St co Cortical vasculature Camera Light guide Amplifier Vi ideo data ac cquisition Single condition maps Orientation map
Neuronal circuits in striate cortex Cells with similar il function are linked through horizontal connections
What is the function of horizontal connections?
EXTRA-STRIATE AND ASSOCIATION AREAS NON-HUMAN PRIMATES
HIGHER ORDER PROCESSING V 1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX EXTRASTRIATE CORTEX (V 2, V 3 & V 4 ) SEND AXONS TO ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS) DORSAL STREAM: > SUPERIOR TEMPORAL & PARIETAL NECESSARY FOR spatial orientation binocular fusion depth perception spatial location movement detection THE WHERE
HIGHER ORDER PROCESSING V 1 SENDS MOST OF ITS AXONS TO EXTRASTRIATE CORTEX EXTRASTRIATE CORTEX (V 2, V 3 & V 4 ) SEND AXONS TO ASSOCIATION CORTEX (TEMPORAL & PARIETAL AREAS) VENTRAL STREAM: > INFERIOR TEMPORAL GYRUS IMPORTANT FOR SHAPE & COLOR perception discrimination recognition memory learning THE WHAT
Motion processing
Shape processing in infero-temporal (IT) cortex