Deciphering the Human Visuomotor System

Cheryl CardMarch 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 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

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?

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

The Action/Perception Theory Milner and

Goodale (1996) Ventral =

perception Dorsal = action Evidence from

frog experiments…

DANGER!DANGER!

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

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!

Organization of Motor Cortices1. The homunculus2. Overlapping,

dynamic organization

Transformations Cell specificity Synapses Neurotransmitters Other methods?

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

A Third Possibility…

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