Olivocochlear activity and temporary threshold shift-susceptibility in humans

Area of Science:

• Auditory Neuroscience
• Otoacoustic Emissions
• Human Auditory Physiology

Background:

• Animal studies indicate medial olivocochlear efferent activity offers cochlear noise protection.
• The existence and role of these protective effects in humans remain unconfirmed.
• Contralateral suppression (CS) of otoacoustic emissions (OAE) serves as an indirect measure of olivocochlear activity.

Purpose of the Study:

• To investigate the human equivalent of noise-protective medial olivocochlear efferent effects.
• To assess the reliability of contralateral suppression (CS) of distortion product otoacoustic emissions (DPOAE) in humans.
• To determine if CS of DPOAE can predict individual susceptibility to temporary threshold shifts (TTS) from impulse noise.

Main Methods:

• Measured input/output functions of DPOAE with and without contralateral white noise stimulation in 94 normal-hearing males.
• Utilized a 'scissor paradigm' with varying sound pressure levels (L2) and frequencies (f2) for DPOAE measurement.
• Assessed TTS susceptibility in 83 subjects via pure tone audiometry before and after shooting exercises.

Main Results:

• CS of DPOAE demonstrated good test-retest repeatability, confirming its reliability as an audiological tool.
• CS was greatest at lower stimulus levels and varied across tested frequencies, with peaks at 2 kHz.
• No significant correlation was found between the degree of CS and individual susceptibility to TTS.

Conclusions:

• CS of DPOAE is a reliable audiological measure but does not predict susceptibility to mild noise-induced temporary threshold shifts in humans.
• Further longitudinal studies are needed to explore the link between medial olivocochlear bundle activity and permanent threshold shifts.
• The ultimate goal is to develop a diagnostic tool for predicting individual noise vulnerability and preventing noise-induced hearing loss.