Sinusoidal amplitude modulation alters contralateral noise suppression of evoked otoacoustic emissions in humans

It is well established that low-level broad band noise can elicit an amplit ude decrease in evoked otoacoustic emissions recorded in the opposite ear. However, the influence of the temporal characteristics of the contralateral stimulus on this effect remains largely unknown. In the present study, oto acoustic emissions evoked by 60 dB SPL clicks were recorded in 19 normal-he aring subjects using the Otodynamics ILO88, successively in absence and pre sence of a contralateral noise that was either steady or modulated sinusoid ally in amplitude at different depths (from 25% to 100% in 25 point steps) and rates (from 50 Hz to 800 Hz in half-octave steps). The energy was kept constant whatever the modulation depth. The results showed that the evoked otoacoustic-emission attenuation effect induced by contralateral stimulation varied depending on the modulation dep th and frequency of the contralateral amplitude-modulated noise. The larges t suppression effect was observed at the 100 Hz modulation frequency and th e 100% modulation depth. The 50 Hz modulation resulted in less suppression than with unmodulated noise. An interpretation of these results in terms of the influence of temporal amplitude fluctuations falling within a certain range on medial olivocochlear bundle activity is discussed. (C) 1999 IBRO. Published by Elsevier Science Ltd.