title: The known unknowns: neural representation of second-order uncertainty, and ambiguity.
abstract: Predictions provided by action-outcome probabilities entail a degree of (first-order) uncertainty. However, these probabilities themselves can be imprecise and embody second-order uncertainty. Tracking second-order uncertainty is important for optimal decision making and reinforcement learning. Previous functional magnetic resonance imaging investigations of second-order uncertainty in humans have drawn on an economic concept of ambiguity, where action-outcome associations in a gamble are either known (unambiguous) or completely unknown (ambiguous). Here, we relaxed the constraints associated with a purely categorical concept of ambiguity and varied the second-order uncertainty of gambles continuously, quantified as entropy over second-order probabilities. We show that second-order uncertainty influences decisions in a pessimistic way by biasing second-order probabilities, and that second-order uncertainty is negatively correlated with posterior cingulate cortex activity. The category of ambiguous (compared with nonambiguous) gambles also biased choice in a similar direction, but was associated with distinct activation of a posterior parietal cortical area; an activation that we show reflects a different computational mechanism. Our findings indicate that behavioral and neural responses to second-order uncertainty are distinct from those associated with ambiguity and may call for a reappraisal of previous data.
authors: Wellcome Trust Centre for Neuroimaging, University College London, London WC1N 3BG, United Kingdom. d.bach@fil.ion.ucl.ac.uk
authors: Dominik R
authors: DR
authors: Bach
authors: Oliver
authors: O
authors: Hulme
authors: William D
authors: WD
authors: Penny
authors: Raymond J
authors: RJ
authors: Dolan
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D002755:Choice Behavior / Q000502:physiology; D003657:Decision Making / Q000502:physiology*; D005260:Female; D005715:Gambling / Q000523:psychology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D035501:Uncertainty; D055815:Young Adult