Top-down vs. Bottom-up

"Yu and Dayan describe a model of the role of acetylcholine and norepinephrine in balancing top-down expectation and bottom-up sensory input in guiding behavior. The model builds from data on physiological effects of modulators regulating the balance of cortical feedback and thalamic input." [Hasselmo 2005]

• Bayesian filtering estimates state given observations

• Uses conditional probabilities to infer from noisy data

• Anticipated versus perceived

• Seeing and hearing what you expect

• Schizophrenics who smoke regulating nicotinic ACh?