Abstract:

There is accumulating evidence that the fine structure of distortion product otoacoustic emissions (DPOAEs) in humans originates from an interference between two cochlear sources, one at the ``overlap'' site of the two primaries, and the other at the best frequency for the DPOAE. It is shown that the DPOAE onset behavior measured in humans, after the turn on of an external tone, is consistent with previous evidence for a ``two source'' origin of DPOAE fine structure [reviewed in Mills, J. Acoust. Soc. Am. 102, 413--429 (1997)]. A variation of Whitehead's methodology [J. Acoust. Soc. Am. 100, 1663--1679 (1996)] was used to measure the initial DPOAE buildup. The f1 primary was on continuously for a given measurement and the f2 primary was pulsed (square wave, 50% duty cycle) at a rate of 5 Hz. The DPOAE had an initial buildup, followed either by further growth of the DPOAE, when the DPOAE frequency was near a fine-structure maximum, or by decay of the DPOAE, when the DPOAE frequency was near a fine-structure minimum. This pattern of secondary growth/decay is shown to be further evidence favoring the two-source model of DPOAE fine structure.