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Title:

Duplex retina

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Optic nerve projects to lateral geniculate nucleus. ... Six layers in lateral geniculate. Two magnocellular layers and four parvocellular layers. ... – PowerPoint PPT presentation

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Title: Duplex retina


1
Duplex retina
  • First instance of vision as multiple
    specialized systems that operate in parallel
  • Partitions for sensitivity (rods) and resolution
    (cones).
  • Because of this division of labour (also called
    partitioning or parallel processing) we say we
    have a duplex retina

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Center surround receptive field
  • Bipolar and ganglion cells generate a retinotopic
    map of differences in illumination. They have
    on-centers/off- surrounds or off-centers/on-surrou
    nds. They ignore absolute light levels.
  • This is true both for cone pathways and rod
    pathways.

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Magnocellular and parvocellular pathways
  • Larger ganglion cells with more inputs project to
    magnocellular pathway (large cells in the lateral
    geniculate nucleus). Responses are more
    transient.
  • Smaller ganglion cells with few inputs project to
    parvocellular pathway (small cells in the lateral
    geniculate nucleus). Responses are more
    sustained.

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Magnocellular and parvocellular functions
  • Magnocellular pathway is specialized for motion
    detection and is more sensitive since it sums
    over a larger area. Good temporal, poor spatial
    resolution.
  • Parvocellular pathway is specialized for detail
    analysis, acuity, form, and color. Good spatial,
    poor temporal resolution.

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Geniculostriate pathway
  • Optic nerve projects to lateral geniculate
    nucleus. Other parallel pathways go to superior
    colliculus, pulvinar and hypothalamus.
  • Six layers in lateral geniculate. Two
    magnocellular layers and four parvocellular
    layers.
  • Ipsilateral eye goes to layers 2, 3, 5.
    Contralateral eye goes to layers 1, 4, 6.

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Ipsilateral eye goes to layers 2, 3,
5. Contralateral eye goes to layers 1, 4, 6.
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Where is the damage?
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Two important ideas
  • 1. Receptive fields that detect differences
  • 2. Magnocellular and parvocellular pathways
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