THE INFLUENCE OF CONTRALATERAL WHITE-NOIS E ON HUMAN DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS

The influence of contralateral white noise with levels of 50 and 60 dB nHL on the amplitude of distortion-product otoacoustic emissions (DPOA E) was measured. Thirty ears of normally hearing adults (17 women, 13 men, mean age 26,5 +/- 5,3 years) were examined. Two representative DP OAE frequencies 2f(1)-f(2) = 1342 Hz and 6341 Hz were compared. The lo wer DPOAE frequency was placed in the frequency region where middle-ea r pressure has a strong influence on DPOAE amplitudes, the higher DPOA E frequency respectively in the region where lesser influence is exert ed by middle-ear pressure. During the application of contralateral whi te noise a statistically significant total of 85% of DPOAE amplitudes was reduced, although there was some variation in the individual behav iour of DPOAE amplitudes. In general the higher DPOAE frequency (6341 Hz) was reduced distinctly less than the lower DPOAE frequency (1342 H z). The reaction of DPOAE amplitude depended closely on the time cours e of the contralateral stimulus and amplitude reductions were present over 10 minutes without adaptation or fatigue. It is not possible to d ifferentiate between middle-ear or inner-ear mediate effects but the m iddle ear is at least involved. Based on the presence of those DPOAE a mplitude reductions over ten minutes without adaptation or fatigue and the fact that lower frequencies are influenced much more than higher frequencies a synergistic effect - middle-ear and efferent mediated - is suggested.