2012年4月18日水曜日

The Known Unknowns: Neural Representation of Second-Order Uncertainty, and Ambiguity


リスクと不確実性下の意思決定。不確実性は後部帯状皮質で保持されている。報酬確率(リスク)と不確実性(リスクについてのリスク)を独立に変動させられるタスクを開発したのがポイント。 http://www.jneurosci.org/content/31/13/4811

Dominik R Bach, Oliver Hulme, William D Penny, and Raymond J Dolan
Journal of Neuroscience
2011 vol. 31 (13) pp. 4811-4820

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.

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