The Effectiveness of External and Middle Ears in Coupling Acoustic Power into the Cochlea

The aim of this paper is to evaluate measures of acoustic-power transfer for comparisons of the performance of the auditory peripheries of different species. To do so we will define three power transfer measures that can be computed from available data. The measures also separate the auditory periphery into functional subunits so as to enable estimations of the roles of different auditory specializations.The three measures of power transfer are: the Tower Utilization Ratio at the TM” (PUR), the “Effective Area of the External Ear” (EA), and the “Middle Ear Efficiency” (MEE). The three power measures serve different purposes: PUR is an index of the impedance-matching performance of the external and middle ear; EA and MEE quantify power flow through the external and middle ears. The EA and MEE can be combined to obtain a single measure of the power into the cochlea that we call the “Net Effective Area” (NEA).Our analysis suggests (1) the impedances of external and middle ears are poorly matched, (2) an appreciable fraction of the sound power which enters the middle ear is absorbed before it reaches the cochlea, (3) cochlear function at auditory threshold for pure tones can be roughly approximated by a power detector, and (4) the quantification of power transfer through the ears of different species is a useful comparative tool.