Title: Wideband and Time-series-based Middle Ear Muscle Reflex Estimation
Legend: We measured activation of the middle ear muscle reflex (MEMR) in 20 young clinically normal hearing human adults using wideband clicks in a novel time-series-based paradigm. The time-series allowed for statistical estimation of the reflex kinetics providing greater certainty in MEMR estimation over currently available methods. In panel A, exponential functions approximated group input/output characteristics of the MEMR across six 1/3rd octave band frequencies. In panel B, the frequency response of the MEMR is plotted for six input levels. Together, these data suggest that the MEMR is more potent in the low, compared to high, frequencies with a minimum at 2 kHz. This frequency response corroborates with average middle ear resonance. Logistic function approximated percent detection of the MEMR is plotted in panel C. These results suggest 95% of the sample had MEMR activation between 80 and 90 dB peak-to-peak (pp) SPL. MEMR thresholds obtained using wideband stimulus (clicks) are lower than that obtained in a clinical tympanometer. Unlike frequency differences in activation patterns, detection appears independent of reflex magnitude and frequency.
Citation: Boothalingam, S., and Goodman, S.S. (under review). Click-evoked Middle Ear Muscle Reflex: Implications for Medial Olivocochlear system Assays. Preprint DOI: https://doi.org/10.1101/2020.08.24.265462
Abstract: This study describes a time series-based method of middle ear muscle reflex (MEMR) detection using bilateral clicks, with implications for otoacoustic emission (OAE)-based medial olivocochlear reflex (MOCR) assays. Although current click-based methods can detect changes in the OAE evoking stimulus to monitor the MEMR, these methods do not discriminate between true MEMR-mediated vs. artifactual changes in the stimulus. We measured MEMR in 20 young clinically normal hearing individuals using a series of clicks presented at six levels (65 to 95 dB peak-to-peak SPL in 6 dB steps). Results were well-approximated by double-exponential functions. The change in ear canal pressure due to MEMR increased monotonically as a function of click level but non-monotonically with frequency. MEMR thresholds estimated using this method were lower than that obtained from a clinical tympanometer in ~94% of the participants. It is recommended that the OAE-evoking stimulus be monitored to determine the presence of MEMR across a wide band of frequencies in MOCR assays. A time series-based method, along with statistical tests, may provide additional confidence in detecting the MEMR. MEMR effects were smallest at 2 kHz which may provide avenues for minimizing the MEMR influence on the MOCR.
About the Lab: Sriram Boothalingam’s lab investigates how the brain controls the functioning of the ear and explores the implications of this control for human hearing. He uses otoacoustic emissions (sounds emanating from the ear), electroencephalography (electrical activity of the brain), and behavioral methods to study the ear-brain-behavior link. His research lies at the intersection of clinical and basic understanding of this link for hearing in children and adults.