Components of the 2f(1)-f(2) distortion-product otoacoustic emission in a moth.

The noctuoid moth Empyreuma affinis has a simple tympanal organ with only two receptor cells attached to the eardrum. As in vertebrates, the growth of distortion-product otoacoustic emissions (DPOAE) with increasing stimulus level is characterized by two distinct components. An initial increase of DPOAE level for f(2) levels in the range of 30-65 dB SPL is followed by a second steep growth of the DPOAE at f(2) levels above 65 dB SPL. Both components increase at a slope of about 2 dB/dB and the difference between both components was used to assess a mechanical gain of the tympanal organ of 17 dB (n=23). At around 65 dB SPL, a notch in the level function coincides with an abrupt phase change of up to 180 degrees. The sensitive component induced by f(2) levels below 65 dB SPL is selectively affected by application of ethyl ether and disappears more quickly than the high-level component during ongoing deterioration of the moth preparation.