TY - JOUR T1 - The Known Unknowns: Neural Representation of Second-Order Uncertainty, and Ambiguity JF - The Journal of Neuroscience JO - J. Neurosci. SP - 4811 LP - 4820 DO - 10.1523/JNEUROSCI.1452-10.2011 VL - 31 IS - 13 AU - Dominik R. Bach AU - Oliver Hulme AU - William D. Penny AU - Raymond J. Dolan Y1 - 2011/03/30 UR - http://www.jneurosci.org/content/31/13/4811.abstract N2 - 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. ER -