The Visual Brain in Action

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The Visual Brain in Action

• A. David Milner and Melvyn A. Goodale

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• Vision evolves to provide distal sensory control
  of an organisms movements first.
• And thereafter to provide perception of the world
  per se.
• Independent input-output modules (pathways) from
  the visual receptors through to the motor nuclei
  vs. Representational systems

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Two visual systems

• Vision for action
• Vision for perception

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In the macaque monkey brainUngerleider and
Mishkin 1982

• A ventral stream projecting to the inferior
  temporal cortex (IT)
• A dorsal stream projecting to the posterior
  parietal cortex (PP)

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Ungerleider and Mishkin 1982

• Object vision vs. spatial vision
• What vs. where

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Milner and Goodale 1993

• Perception vs. guidance of action
• The dorsal stream guidance of actions
• The ventral stream perception, models of the
  world, contents, semantics,

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D.F. visual form agnosia (damage to the ventral
stream) Unable to make correct perceptual
reports But is able to make correct visualmotor
posting
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• RV optic ataxia (damage to the dorsal stream)

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• D.F. is able to govern her actions using visual
  information of which she has no awareness.
• In providing visual guidance for actions the
  dorsal stream acts in large part alone, purely in
  the here and now.
• The ventral stream both generates and is informed
  by stored abstract visual knowledge.

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Problems remains to be solved

• How the two streams interact both with each
  other, and
• With other brain regions in the production of
  purposive behavior.

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Ned Block

• Two visual system model proves that visual
  experience can occur with action.
• Hence, the sensorimotor model of visual
  perception is wrong.