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Deciphering the Human Visuomotor System

Deciphering the Human Visuomotor System. Cheryl Card March 13, 2001. Anatomy of the Brain. General terms: superior, inferior, ventral, dorsal Lobes: frontal, parietal, temporal, occipital. Anatomy of the Brain. Physiology of Visual System.

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Deciphering the Human Visuomotor System

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  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

  5. 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?

  6. 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

  7. DANGER! DANGER! The Action/Perception Theory • Milner and Goodale (1996) • Ventral = perception • Dorsal = action • Evidence from frog experiments…

  8. Evidence for Action/Perception • Dorsal lesion = optic ataxia • Patient can recognise objects but can’t pick them up • Ventral lesion = visual form agnosia • Patient can’t recognise objects, but can navigate using visual information

  9. 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!

  10. Organization of Motor Cortices • The homunculus • Overlapping, dynamic organization

  11. Transformations • Cell specificity • Synapses • Neurotransmitters • Other methods?

  12. 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

  13. A Third Possibility…

  14. 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

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