Duplex retina

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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