Free energy and active inference - Karl Friston

Wednesday, 11 September, 2013 - 09:30 to 11:00

How much about our interaction 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 principle; such as hierarchical message passing in the brain and the perceptual inference that ensues. These perceptual abilities rest upon prior beliefs about the world – but where do these beliefs come from? We will consider recent proposals about the nature of prior beliefs and how they underwrite 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 visual searches and other forms of active inference. In short, if percepts correspond to hypotheses, then action could be construed as sampling data to test perceptual hypotheses – and accrue evidence for our very existence. I hope to illustrate these points using simulations of action observation and saccadic eye movements.

(all of which can be downloaded from

Friston K, Adams RA, Perrinet L and Breakspear M
Perceptions as hypotheses: saccades as experiments.
Front. Psychology (2012) 3:151.

Friston K, Mattout J, Kilner J.
Action understanding and active inference.
Biol Cybern. 2011 104:137–160

Friston K, Samothrakis S, Montague R.
Active inference and agency: optimal control without cost functions
Biol Cybern. 2012

Friston K.
The free-energy principle: a unified brain theory?
Nat Rev Neurosci. 2010 Feb;11(2):127-38