Two-tone suppression and combination tone generation as computations performed by the Hopf cochlea.

Recent evidence suggests that the compressive nonlinearity responsible for the extreme dynamic range of the mammalian cochlea is implemented in the form of Hopf amplifiers. Whereas Helmholtz's original concept of the cochlea was that of a frequency analyzer, Hopf amplifiers can be stimulated not only by one, but also by neighboring frequencies. To reduce the resulting computational overhead, the mammalian cochlea is aided by two-tone suppression. We show that the laws governing two-tone suppression and the generation of combination tones naturally emerge from the Hopf-cochlea concept. Thus the Hopf concept of the cochlea reproduces not only local properties like the correct frequency response, but additionally accounts for more complex hearing phenomena that may be related to auditory signal computation.