NONLINEAR CHARACTERISTICS OF ELECTRICALLY-EVOKED OTOACOUSTIC EMISSIONS

To further our knowledge of outer hair cell nonlinearities, we measure d the dependence of the electrically-evoked otoacoustic emissions (EEO Es) on current level for a wide range of electrical frequencies. Alter nating electrical current was delivered into the scala media of the ge rbil cochlea while the EEOE was measured with a probe-tube microphone. While the EEOE scaled linearly with current level for many frequencie s and current levers, notable exceptions occurred. For frequencies bel ow 300 Hz and currents above 20-30 mu A(peak), the gain (primary EEOE magnitude divided by the current level) increased abruptly. For higher frequencies, the gain often increased slightly with increasing curren t of up to 30-50 mu A(peak), but decreased at even higher current leve ls. We also investigated the enhancement of the EEOE due to simultaneo us acoustic stimulation. The enhancement of the EEOE was relatively in sensitive to current level with little change in enhancement for curre nt levels up to 20 mu A(peak). For current levels above approximately 10 mu A(peak) the enhancement decreased slightly. (C) 1998 Published b y Elsevier Science B.V. All rights reserved.