Peter Dayan, Angela J. Yu
Inference and adaptation in noisy and changing, rich sensory environ- ments are rife with a variety of speciﬁc sorts of variability. Experimental and theoretical studies suggest that these different forms of variability play different behavioral, neural and computational roles, and may be reported by different (notably neuromodulatory) systems. Here, we re- ﬁne our previous theory of acetylcholine’s role in cortical inference in the (oxymoronic) terms of expected uncertainty, and advocate a theory for norepinephrine in terms of unexpected uncertainty. We suggest that norepinephrine reports the radical divergence of bottom-up inputs from prevailing top-down interpretations, to inﬂuence inference and plasticity. We illustrate this proposal using an adaptive factor analysis model.