Beyond the retina: the visual pathways

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Beyond the retina the visual pathways

• PS2006/2005 Lecture 3

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Visual Pathways

• Geniculostriate System
• Tectopulvinar System

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Geniculostriate system
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Geniculostriate System
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Geniculostriate System

• Eye
• Lateral geniculate nucleus
• Visual cortex (V1, Primary visual cortex, Striate
  Cortex)

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Tectopulvinar System
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Tectopulvinar System

• Eye
• Superior colliculus (in the tectum)
• Pulvinar Nucleus (in the thalamus)
• Visual Cortex (V2, Secondary Visual Cortex,
  Extrastriate Visual Cortex)

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PrimaryVisual Cortex
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Blindsight

• Patient DB
• removal of striate cortex in right hemisphere
• area of blindness (Scotoma)
• could
• make eye movements to a brief light flash
• point to objects
• judge line orientations (X, O)

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Visual Agnosia

• Patient DF
• damage to ventrolateral regions of occipital lobe
• unable to recognise familiar faces, line
  drawings of objects or simple geometric shapes
• could reach out and grasp the objects in ways
  that reflect object properties

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Intact Recognition

• Patient RV
• could accurately identify line drawings (20/20
  compared to 2/20 for DF)
• unable to pick objects properly

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Two Visual Streams

• Double dissociation
• visual mechanisms mediating perception of objects
  distinct from those mediating actions directed at
  those objects

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Two Visual Streams