Three experiments examined the mechanisms by which downward shifts in reinforcer value influence learning in appetitive unblocking procedures. The downward shift was accomplished by omitting the 2nd of a 2-reinforcer sequence (food-food or food-sucrose). Performance of normal rats was compared with that of rats with lesions of the central nucleus of the amygdala, which are thought to interfere with surprise-induced enhancements of event processing. The results suggested that, in normal rats, omission of the 2nd reinforcer enhanced processing of the 1st reinforcer rather than processing of the conditioned stimuli and that lesions of the central nucleus eliminated this enhancement. The roles of reinforcement error signals in conditioning are discussed.