Deciphering the Human Visuomotor System

1
Deciphering the Human Visuomotor System

• Cheryl Card
• March 13, 2001

2
Anatomy of the Brain

• General terms superior, inferior, ventral,
  dorsal
• Lobes frontal, parietal, temporal, occipital

3
Anatomy of the Brain
4
Physiology of Visual System

• Optic nerve projects to superior colliculus and
  to LGN
• SC mediates predator/prey reflexes
• LGN projects to primary visual cortex
• From primary visual cortex, the dorsal and
  ventral visual pathways diverge

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Retinotopic mapping

• Head-centred vs. retina-centred map of world?
• Henriques et al (1998) proved retinotopic mapping
  is used by brain
• Could this technique be used with robots?

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The What/Where Theory

• Mishkin and Ungerleider (1982)
• Ventral stream for what vision
• Dorsal stream for where vision
• Early anatomical evidence supported this theory
• More recently, theory has been challenged

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The Action/Perception Theory

• Milner and Goodale (1996)
• Ventral perception
• Dorsal action
• Evidence from frog experiments

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Evidence for Action/Perception

• Dorsal lesion optic ataxia
• Patient can recognise objects but cant pick them
  up
• Ventral lesion visual form agnosia
• Patient cant recognise objects, but can navigate
  using visual information

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Vision/Motor Connections

• Dorsal stream linked to premotor areas used for
  oculomotor control, reaching and grasping
• Ventral stream connected to areas for learning,
  memory, and social behaviour
• So for robotics, concentrate on dorsal stream
  research!

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Organization of Motor Cortices

1. The homunculus
2. Overlapping, dynamic organization

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Transformations

• Cell specificity
• Synapses
• Neurotransmitters
• Other methods?

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Synapses and Neurotransmitters

• Chemical synapses work by releasing
  neurotransmitters
• Electrical synapses have low resistance
  intercellular channels
• Neuromodulation involves multiple molecules,
  receptors, and channels
• Many reaction chains are 4th or 5th order

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A Third Possibility
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Conclusions for Robotics

• Use a dynamic, retinotopic map to (possibly) save
  processing time
• Concentrate on dorsal pathway research (action
  pathway)
• Motor organization must be flexible to emulate
  human brain
• Visuomotor transformations
• Massively interconnected neural network
• Multi-step chemical reactions in synapses