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 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!

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 Cortices 1. The homunculus 2. 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 4 th or 5 th 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