Slide 2 Abstract How much about our interactions with and
experience of our world can be deduced from basic principles? This
talk reviews recent attempts to understand the self-organised
behaviour of embodied agents, like ourselves, as satisfying basic
imperatives for sustained exchanges with the environment. In brief,
one simple driving force appears to explain many aspects of action
and perception. This driving force is the minimisation of surprise
or prediction error that in the context of perception corresponds
to Bayes-optimal predictive coding (that suppresses exteroceptive
prediction errors) and in the context of action reduces to
classical motor reflexes (that suppress proprioceptive prediction
errors). We will look at some of the phenomena that emerge from
this single principle; such as the perceptual encoding of sensory
trajectories (bird song and action perception). These perceptual
abilities rest upon prior beliefs about the world but where do
these beliefs come from? I will finish by discussing recent
proposals about the nature of prior beliefs and how they underwrite
the active sampling of the sensorium. Put simply, to minimise
surprising states of the world, it is necessary to sample inputs
that minimise uncertainty about the causes of sensory input. When
this minimisation is implemented via prior beliefs about how we
sample the world the resulting behaviour is remarkably reminiscent
of searches of the sort seen in exploration and visual searches.
Free energy and active inference Karl Friston University College
London The Statistical Physics of Inference and Control Theory
Granada, Spain September 12-16, 2012 Slide 3 Objects are always
imagined as being present in the field of vision as would have to
be there in order to produce the same impression on the nervous
mechanism - von Helmholtz Thomas Bayes Geoffrey Hinton Richard
Feynman From the Helmholtz machine to the Bayesian brain and
self-organization Hermann Haken Richard Gregory Hermann von
Helmholtz Slide 4 temperature What is the difference between a
snowflake and a bird? Phase-boundary a bird can act (to avoid
surprises) Slide 5 Hidden states in the worldInternal states of the
agent Sensations Action External states Fluctuations Posterior
expectations The basic ingredients Slide 6 Self organisation and
the principle of least action Maximum entropy principle The
principle of least free energy (minimising surprise) Minimum
entropy principle Ergodic theorem Slide 7 How can we minimize
surprise (prediction error)? Change sensations sensations
predictions Prediction error Change predictions Action Perception
action and perception minimise free energy Slide 8 Prior
distribution Posterior distribution Likelihood distribution
temperature Action as inference the Bayesian thermostat
20406080100120 Perception: Action: Slide 9 Hidden states in the
worldInternal states of the agent Sensations Action External states
Fluctuations Posterior expectations How might the brain minimise
free energy (prediction error)? By using predictive coding (and
reflexes) Slide 10 Free energy minimisationGenerative
modelPredictive coding with reflexes Slide 11 Expectations:
Predictions: Prediction errors: Generative model Model inversion
(inference) A simple hierarchy Outward prediction stream Inward
error stream From models to perception Slide 12 occipital cortex
geniculate visual cortex retinal input pons oculomotor signals
Prediction error (superficial pyramidal cells) Conditional
predictions (deep pyramidal cells) Top-down or backward predictions
Bottom-up or forward prediction error proprioceptive input reflex
arc David Mumford Predictive coding with reflexes Action Perception
Slide 13 Biological agents resist the second law of thermodynamics
They must minimize their average surprise (entropy) They minimize
surprise by suppressing prediction error (free-energy) Prediction
error can be reduced by changing predictions (perception)
Prediction error can be reduced by changing sensations (action)
Perception entails recurrent message passing in the brain to
optimize predictions Action makes predictions come true (and
minimizes surprise) Slide 14 Generating bird songs with attractors
Syrinx HVC time (sec) Frequency Sonogram 0.511.5 causal states
hidden states Slide 15 102030405060 -5 0 5 10 15 20 prediction and
error 102030405060 -5 0 5 10 15 20 hidden states Backward
predictions Forward prediction error 102030405060 -10 -5 0 5 10 15
20 causal states Predictive coding stimulus 0.20.40.60.8 2000 2500
3000 3500 4000 4500 5000 time (seconds) Slide 16 Perceptual
categorization Frequency (Hz) Song a time (seconds) Song bSong c
Slide 17 Prior distribution temperature Action as inference the
Bayesian thermostat 20406080100120 Perception: Action: Slide 18
visual input proprioceptive input Action with point attractors
Descending proprioceptive predictions Exteroceptive predictions
Slide 19 00.20.40.60.811.21.4 0.4 0.6 0.8 1 1.2 1.4 action position
(x) position (y) 00.20.40.60.811.21.4 observation position (x)
Heteroclinic cycle (central pattern generator) Descending
proprioceptive predictions Slide 20 Where do I expect to look?
Slide 21 saliencevisual inputstimulussampling Sampling the world to
minimise uncertainty Perception as hypothesis testing saccades as
experiments Free energy principleminimise uncertainty Slide 22
Hidden states in the worldInternal states of the agent Sensations
Action External states Fluctuations Posterior expectations Prior
expectations Slide 23 Frontal eye fields Pulvinar salience map
Fusiform (what) Superior colliculus Visual cortex oculomotor reflex
arc Parietal (where) Slide 24 Saccadic fixation and salience maps
Visual samples Conditional expectations about hidden (visual)
states And corresponding percept Saccadic eye movements Hidden
(oculomotor) states Slide 25 Thank you And thanks to collaborators:
Rick Adams Andre Bastos Sven Bestmann Jean Daunizeau Harriet Brown
Lee Harrison Stefan Kiebel James Kilner Jrmie Mattout Rosalyn Moran
Will Penny Klaas Stephan And colleagues: Andy Clark Peter Dayan Jrn
Diedrichsen Paul Fletcher Pascal Fries Geoffrey Hinton James
Hopkins Jakob Hohwy Henry Kennedy Paul Verschure Florentin Wrgtter
And many others Slide 26 Searching to test hypotheses life as an
efficient experiment Free energy principleminimise uncertainty
Slide 27 Perception and Action: The optimisation of neuronal and
neuromuscular activity to suppress prediction errors (or free-
energy) based on generative models of sensory data. Learning and
attention: The optimisation of synaptic gain and efficacy over
seconds to hours, to encode the precisions of prediction errors and
causal structure in the sensorium. This entails suppression of
free-energy over time. Neurodevelopment: Model optimisation through
activity- dependent pruning and maintenance of neuronal connections
that are specified epigenetically Evolution: Optimisation of the
average free-energy (free-fitness) over time and individuals of a
given class (e.g., conspecifics) by selective pressure on the
epigenetic specification of their generative models. Time-scale
Free-energy minimisation leading to