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Visual Pathways. visual hemifields project contralaterally exception: bilateral representation of fovea! Optic nerve splits at optic chiasm about 90 % of fibers project to cortex via LGN about 10 % project through superior colliculus and pulvinar but that’s still a lot of fibers! .

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visual pathways
Visual Pathways
  • visual hemifields project contralaterally
    • exception: bilateral representation of fovea!
  • Optic nerve splits at optic chiasm
  • about 90 % of fibers project to cortex via LGN
  • about 10 % project through superior colliculus and pulvinar
    • but that’s still a lot of fibers!

Note: this will be important when we talk about visuospatial attention

visual pathways1
Visual Pathways
  • Lateral Geniculate Nucleus maintains segregation:
    • of M and P cells (mango and parvo)
    • of left and right eyes

P cells project to layers 3 - 6

M cells project to layers 1 and 2

visual pathways2
Visual Pathways
  • Primary visual cortex receives input from LGN
    • also known as “striate” because it appears striped when labeled with some dyes
    • also known as V1
    • also known as Brodmann Area 17
visual pathways3
Visual Pathways
  • Primary cortex maintains distinct pathways – functional segregation
  • M and P pathways synapse in different layers

W. W. Norton

the role of extrastriate areas
The Role of “Extrastriate” Areas
  • Different visual cortex regions contain cells with different tuning properties
the role of extrastriate areas1
The Role of “Extrastriate” Areas
  • Consider two plausible models:
    • System is hierarchical:
      • each area performs some elaboration on the input it is given and then passes on that elaboration as input to the next “higher” area
    • System is analytic and parallel:
      • different areas elaborate on different features of the input
the role of extrastriate areas2
The Role of “Extrastriate” Areas
  • Functional imaging (PET) investigations of motion and colour selective visual cortical areas
  • Zeki et al.
  • Subtractive Logic
    • stimulus alternates between two scenes that differ only in the feature of interest (i.e. colour, motion, etc.)
the role of extrastriate areas3
The Role of “Extrastriate” Areas
  • Identifying colour sensitive regions

Subtract Voxel intensities during these scans…

…from voxel intensities during these scans

…etc.

Time ->

the role of extrastriate areas4
The Role of “Extrastriate” Areas
  • result
    • voxels are identified that are preferentially selective for colour
    • these tend to cluster in anterior/inferior occipital lobe
the role of extrastriate areas5
The Role of “Extrastriate” Areas
  • similar logic was used to find motion-selective areas

Subtract Voxel intensities during these scans…

…from voxel intensities during these scans

…etc.

STATIONARY

STATIONARY

MOVING

MOVING

Time ->

the role of extrastriate areas6
The Role of “Extrastriate” Areas
  • result
    • voxels are identified that are preferentially selective for motion
    • these tend to cluster in superior/dorsal occipital lobe near TemporoParietal Junction
    • Akin to Human V5
the role of extrastriate areas7
The Role of “Extrastriate” Areas
  • Thus PET studies doubly-dissociate colour and motion sensitive regions
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