Figure 3. Generalization gradients and origins of receiver bias.

(A) Receiver biases exert directional selection on a signal trait (e.g., tail length in birds) and may create heightened responsiveness to supernormal stimuli. The blue curve depicts responsiveness by an unbiased receiver. Peak shift (orange line), area shift (green line), and open-ended (red line) ‘generalization gradients’ (see Table 1: Glossary) are generated by discrimination learning, which here is illustrated by a negative (S −) and a positive (S +) training stimulus. (B) Other receiver biases can also derive directly from a peripheral sensory bias (e.g., in the retina), or from the higher level ‘Perceptual’ processing of the sensory input (e.g., visual cortex). The general increase in phenotypic plasticity from peripheral to higher level neural processing is indicated.