Adaptive processing of electrosensory information occurs in the cerebellum-like structures of three distinct groups of fish. Associations within each of these structures result in the generation of negative images of predictable features of the sensory inflow. Addition of these negative images to the actual inflow removes the predictable features, allowing the unpredictable, information-rich sensory signals to stand out. Evidence from all three groups of fish indicates that the negative images are mediated by plasticity at parallel fiber synapses.