Frequency and level dependence of the middle ear acoustic reflex and its decay measured in wideband absorbance with contralateral narrowband noise elicitors.

The acoustic reflex has potential as a diagnostic tool for identifying individuals with selective damage to cochlear sensory neurons (Bramhall et al., 2022; Feeney et al., 2023; Wojtczak et al., 2017). If damage to neurons is localized, then using broadband stimuli to elicit the reflex, as reported in the studies cited above, may not be most effective in revealing spatially restricted lesions. We have measured changes in absorbance with chirps delivered to one ear and contralateral narrowband noise to elicit the reflex. We aim to characterize the frequency and level dependence of changes in absorbance elicited by noise with different center frequencies as well as the decay of the reflex for prolonged elicitors as a baseline for comparison with similar measurements in individuals suspected of having neural damage. Our hypothesis is that elicitors that preferentially activate the damaged part of the reflex pathway will show the largest deviation from normal. We have identified a novel sensitization of the acoustic reflex following repeated exposure to moderate level elicitors such that absorbance changes more than double, regardless of the level of the elicitor, compared with the minimally stimulated contralateral ear. These changes recover slowly. We are measuring the growth of the reflex vs elicitor level and at constant elicitor level vs center frequency. We are also measuring the rate of reflex decay vs elicitor center frequency. Preliminary findings substantiate the measurement protocols in revealing differences between individuals and ears.