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Deciphering the Human Visuomotor System
Cheryl CardMarch 13, 2001
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Anatomy of the Brain General terms: superior, inferior,
ventral, dorsal Lobes: frontal, parietal, temporal,
occipital
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Anatomy of the Brain
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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…
DANGER!DANGER!
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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
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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 Cortices1. The homunculus2. 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