SCHOOL OF PHYSICS COLLOQUIUM and COSNet DISTINGUISHED VISITOR SEMINAR www.physics.usyd.edu.au/local/coll Monday 18th June, 2007 at 3:15 pm refreshments from 3pm Venue: Slade Lecture Theatre, Ground Floor, School of Physics Title: Towards a Theory of Learning and Levels for Biology Presenter: Prof. Tony Bell University of California at Berkeley Abstract: Learning, plasticity, adaptivity: these occur at the ecological, behavioural, neural and molecular levels amongst others. Yet each level is just a different description of the the same processes. Defined structural relations exist between the levels (networks within networks), and these define causal relations in time. I will describe how these causal relations are essentially inter-level in nature, consisting of downward ’boundary conditions’ and upward ’emergence’. Using them, information can travel from the top to the bottom of the reductionist hierarchy and vice-versa. This opens the possibility of defining new kinds of learning algorithm which exploit inter-level mappings for representational purposes. As examples, I will consider Spike Timing-Dependent synaptic Plasticity (STDP), and equations describing channel and enzyme kinetics. I will also present much review material on the nature of the biological material hierarchy and compare it to the scale-free systems successfully studied in physics by the renormalisation group theory.