Evidence for nonlinearities of hydromechanical origin was first found in cochlear models (Békésy, 1928; Tonndorf, 1958). They were of two kinds: (1) amplitude-dependent events, i.e., eddies, leading to harmonic distortion, and (2) amplitude-dependent events, i.e., asymmetrical basilar-membrane displacements, leading to envelope detection, for instance of beats. The evidence on the type 1 event is still circumstantial (e.g., Dallos, 1973). However, the type 2 events appear to be compatible with the results of a number of physiological experiments on actual ears (e.g., Tonndorf, 1958; Goldstein and Kiang, 1968; Sellick et al., 1982; LePage, 1985).