Influence of 100Â Hz amplitude modulation on the human medial olivocochlear reflex

It is well known that medial olivocochlear system (MOC) activity causes inhibition of cochlear amplification that can be measured using otoacoustic emissions (OAEs). The temporal characteristics of this MOC inhibitory effect are still not well understood. Two experiments were performed to further explore a previously reported enhancement in MOC inhibition of OAEs by a broadband noise (BBN) elicitor modulated at 100 Hz (AM-BBN). In experiment I, MOC inhibition was measured for toneburst (1 and 2 kHz presented at 41.67 Hz) and stimulus-frequency (0.96-1.92 kHz) OAEs for two elicitor conditions, BBN and AM-BBN (100% modulation depth [MD]), in 27 young normal hearing adults. In experiment II, tonebursts were presented at 50 Hz instead of 41.67 Hz to test if the previously reported enhancement of the MOC response to 100 Hz AM-BBN is specific to a 50 Hz toneburst presentation rate. All elicitors caused significant reduction of both TB- and SF-OAE amplitude. AM-BBN evoked the same OAE inhibition compared to BBN in both experiments. This pattern was consistent across OAE types, and toneburst presentation rates. Results suggest that the MOC is not especially sensitive to 100 Hz AM-BBN; instead, AM dips in noise energy likely reduce its effectiveness in evoking MOC activity due to temporal energy integration.