title: Active inference and oculomotor pursuit: the dynamic causal modelling of eye movements.
abstract: BACKGROUND
  This paper introduces a new paradigm that allows one to quantify the Bayesian beliefs evidenced by subjects during oculomotor pursuit. Subjects' eye tracking responses to a partially occluded sinusoidal target were recorded non-invasively and averaged. These response averages were then analysed using dynamic causal modelling (DCM). In DCM, observed responses are modelled using biologically plausible generative or forward models - usually biophysical models of neuronal activity.
  
  
  METHODS
  Our key innovation is to use a generative model based on a normative (Bayes-optimal) model of active inference to model oculomotor pursuit in terms of subjects' beliefs about how visual targets move and how their oculomotor system responds. Our aim here is to establish the face validity of the approach, by manipulating the content and precision of sensory information - and examining the ensuing changes in the subjects' implicit beliefs. These beliefs are inferred from their eye movements using the normative model.
  
  
  RESULTS
  We show that on average, subjects respond to an increase in the 'noise' of target motion by increasing sensory precision in their models of the target trajectory. In other words, they attend more to the sensory attributes of a noisier stimulus. Conversely, subjects only change kinetic parameters in their model but not precision, in response to increased target speed.
  
  
  CONCLUSIONS
  Using this technique one can estimate the precisions of subjects' hierarchical Bayesian beliefs about target motion. We hope to apply this paradigm to subjects with schizophrenia, whose pursuit abnormalities may result from the abnormal encoding of precision.
authors.affiliation: The Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK. Electronic address: rick.adams@ucl.ac.uk.
authors.forename: Rick A
authors.initials: RA
authors.lastname: Adams
authors.affiliation: The Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK; Translational Neuromodeling Unit (TNU), Institute for Biomedical Engineering, University of Zurich & ETH Zurich, Wilfriedstr. 6, 8032 Zurich, Switzerland.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Aponte
authors.affiliation: The Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK; Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, 33 Queen Square, London WC1N 3BG, UK.
authors.forename: Louise
authors.initials: L
authors.lastname: Marshall
authors.affiliation: The Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK.
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Friston
mesh_terms: D000328:Adult; D001499:Bayes Theorem; D003198:Computer Simulation; D053483:Eye Movement Measurements; D005133:Eye Movements; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D017711:Nonlinear Dynamics; D010775:Photic Stimulation
keywords: Active inference; Dynamic causal modelling; Oculomotor control; Precision; Pursuit