Contralateral Stimulus Comparison of the Acoustic Reflex via Reflectance Measures

Abstract

The acoustic reflex (AR) occurs as the result of a contraction of the stapedius muscle in response to the presentation of a loud sound. When the stapedius muscle contracts, the ossicular chain and the tympanic membrane are stiffened. Generally, increased stiffness of the middle ear system causes low frequency sounds to be more readily reflected off the tympanic membrane, while high frequency sounds are more easily admitted into the middle ear. Wideband power reflectance (WPR) measures energy across a broad frequency range (200-6000Hz) as it is reflected off of the tympanic membrane. Use of WPR allows for measurement of stiffness effects across frequencies, in comparison to conventional immittance instruments, which measure admittance changes at a single probe tone frequency (226Hz). The purpose of this study was to identify whether reflectance measures could be used to differentiate reflectance patterns resulting from activation of the acoustic reflex as a function of contralateral stimulus type (broadband noise, 500, 1000, 2000 and 4000Hz). This study hypothesized that innervation distribution patterns of the basilar membrane would result in the AR producing different stiffness changes based on contralateral stimulus type. This study additionally demonstrates the potential of WPR to enhance understanding of the AR effects on the auditory system.