Common hearing functions among mammals and birds

Abstract

Among many mammals and birds, frequency-place cochlear maps have a similar form and differ primarily with respect to the length of the cochlea or basilar papilla, and with respect to the frequency range of hearing. This is remarkable, especially given the differences in anatomical organization and evolutionary history between mammals and birds. This is a striking example of convergent or parallel evolution. With few exceptions, the cochleae of mammals and birds are indeed scale models of one another. One of the primary functions of the frequency-place map is in frequency analysis. Whether this function is defined by frequency discrimination thresholds, critical masking ratios, critical bands or auditory filters in general, frequency analytic performance, behaviorally-defined, can be laid out on the basilar membrane and a critical basilar membrane distance can be associated with a given performance criterion. In general, these critical distances differ according to the function (e.g., frequency delta Fs versus critical bandwidths), but are remarkably similar functions of frequency within and between species (they tend to be constant). It seems likely that evolution has selected the consequences of frequency analytic mechanisms for perception rather than the mechanisms themselves. [Work supported by NIH.]