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SUMMARY:Variational free energy and the brain - Karl Friston\, UCL
DTSTART:20070412T120000Z
DTEND:20070412T130000Z
UID:TALK6667@talks.cam.ac.uk
CONTACT:Cordula Becker
DESCRIPTION:By formulating the original ideas of Helmholtz on perception\,
  in terms \nof modern-day theories\, one arrives at a model of perceptual 
 inference \nand learning that can explain a remarkable range of neurobiolo
 gical \nfacts.  Using constructs from statistical physics\, machine learni
 ng \nand probability theory the problems of inferring the causes of sensor
 y \ninput and learning the causal structure of their generation can be \nr
 esolved using exactly the same principles.  Furthermore\, inference \nand 
 learning can proceed in a biologically plausible fashion.  The \nensuing s
 cheme rests on Empirical Bayes and hierarchical models of how \nsensory in
 put is caused.  The use of hierarchical models enables the \nbrain to cons
 truct prior expectations in a dynamic and \ncontext-sensitive fashion.  Th
 is scheme provides a principled way to \nunderstand many aspects of cortic
 al organization and responses.\n\nIn terms of cortical architectures\, it 
 predicts that sensory \ncortices should be arranged hierarchically\, that 
 connections should be \nreciprocal\, and that forward and backward connect
 ions should show a \nfunctional asymmetry (backward connections are both m
 odulatory and \ndriving\, whereas forward connections need only be driving
 ).  In terms \nof synaptic physiology it predicts associative plasticity a
 nd\, for \ndynamic models\, spike–timing-dependent plasticity.  In terms
  of \nelectrophysiology it accounts for classical and extra-classical \nre
 ceptive field effects and long-latency or endogenous components of \nevoke
 d cortical responses.  It predicts the attenuation of responses \nencoding
  prediction error with perceptual learning and explains many \nphenomena l
 ike repetition suppression\, mismatch negativity (MMN) and \nthe P300 in e
 lectroencephalography.  In psychophysical terms\, it \naccounts for the be
 havioral correlates of these physiological \nphenomena\, e.g. priming\, an
 d global precedence.  The final focus of \nthis talk is on perceptual lear
 ning as measured with repetition \nsuppression and the implications for em
 pirical studies of coupling \namong cortical areas. 
LOCATION:Seminar Room (ground floor)\, Craik-Marshall Building
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