COGS 17 Lecture Notes - Lecture 7: Lateral Geniculate Nucleus, Optic Chiasm, Inferior Temporal Gyrus
Lec 4B - Vision
● Visual crossover
○ Path that information takes from outside world through visual system
○ Divide left and right visual field
■ Right visual field to left eye connects to ipsi-lateral brain
■ Right visual field to right eye connects to contralateral brain
■ Left visual field to right eye connects to ipsi-lateral brain
■ Left visual field to left eye connects to contralateral brain
■ Only after reaches cortex, is visual field info combined via
corpus callosum
● Magnification
○ Visual cortex (v1)
○ Topological - preserves spatial relationships
■ Map of input in v1
■ But absolute size is not maintained
■ Fovea is greatly (80x) magnified
● Visual Imagery
○ Activates some of the same areas as actual visual perception
○ Seeing an elephant far away vs imagining an elephant far away
● Visual pathways
○ Dorsal pathway
■ where/how (motion and depth)
■ Parietal pathway
■ Magnocellular pathway - named after cells in retina
● Large ganglions in rods and cones of periphery
● From high convergence rods (many:1)
○ Ventral pathway
■ who/what (color and detail)
■ Temporal pathway
■ Parvocellular pathway - named after cells in retina
● Small ganglions in cones of fovea
● From low convergence cones (1:1)
○ optic nerve (axons of ganglions) to LGN (lateral geniculate nucleus) of
thalamus
■ Optic chiasm is where “cross-over” of optic nerves occur
■ Each LGN has 6 layers
● Divisions within LGN
○ Magnocellular pathways are layers 1 and 2
○ Parvocellular pathways are layers 3-6
● Layers also organized by which EYE (L or R) is
dominant in layer
○ Some axons along the magnocellular pathway go first to the superior
colliculus (not straight to the LGN) in the tectum of the midbrain
■ Used in coliculu to map location of visually moving stimuli
■ Implicated in “blindsight”
● Allowed by inferior colliculus???
■ From there, this sub-pathway goes on to the LGN
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Document Summary
Path that information takes from outside world through visual system. Right visual field to left eye connects to ipsi-lateral brain. Right visual field to right eye connects to contralateral brain. Left visual field to right eye connects to ipsi-lateral brain. Left visual field to left eye connects to contralateral brain. Only after reaches cortex, is visual field info combined via. Activates some of the same areas as actual visual perception. Seeing an elephant far away vs imagining an elephant far away. Magnocellular pathway - named after cells in retina. Large ganglions in rods and cones of periphery. Parvocellular pathway - named after cells in retina. Optic nerve (axons of ganglions) to lgn (lateral geniculate nucleus) of thalamus. Optic chiasm is where cross-over of optic nerves occur. Magnocellular pathways are layers 1 and 2. Layers also organized by which eye (l or r) is.