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Date of Graduation
5-15-2025
Semester of Graduation
Spring
Degree Name
Doctor of Audiology (AuD)
Department
Department of Communication Sciences and Disorders
First Advisor
Erin G. Piker
Second Advisor
Christopher G. Clinard
Abstract
Cervical vestibular evoked myogenic potentials (cVEMPs) are used in clinics and research to assess the function of primarily the saccule. cVEMPs are typically stimulated with transient clicks or tone bursts through air conduction and are recorded from the sternocleidomastoid (SCM) muscle. The SCM is contracted by turning the head either left or right. In this study, we used sustained sinusoidal bone conducted stimuli. Using this new stimulus method allowed us to look at the possibility of a sustained cVEMP response, compared to the typically recorded transient response, as well as analyze the amplitude and signal-to-noise ratio (SNR) of the responses. Obtaining sustained responses from otolith organs has not been examined so findings from sustained activity is under-researched, leaving the knowledge about the otolith organs and their non-linearity functions limited.
Six young adult females (ages 21-25) with no history of vestibular or auditory pathologies volunteered and participated in this study. Stimuli used were sinusoidal, bone-conducted tones at ten different frequencies ranging from 11 to 397 Hz with a time duration of 250 ms and were delivered via a hand-held minishaker. Participants maintained a muscle contraction of 50 µV by observing a real-time bar graph of EMG activation. EMG activation was obtained by the participants turning their head either right or left. The ten frequency conditions, plus two control conditions, were placed in a random order generator prior to each participant arriving. A 500 Hz air conduction toneburst cVEMP was recorded for all participants prior to the sinusoidal bone conduction responses, recording from the same SCM for all cVEMP testing. Participants took breaks as needed in between stimulus presentation to avoid straining their SCM as well as allowing to maintain consistent SCM activation. The analysis of the sinusoidal cVEMPs were used with an FFT-based approach. Amplitude and SNR of the responses were calculated based on the FFT. A present response was indicated by an SNR of greater than 6.13 dB SNR.
Preliminary results show sinusoidal cVEMPs are present and robust in young, healthy adult females. Sustained responses were the most robust in the low-to-mid-frequency range out of the ten different frequencies used. Large magnitude responses are present at the stimulus frequency and the response waveforms also contain onset and offset responses. Amplitude and SNR peak at approximately 80 Hz. Harmonic distortion products are also present in the FFT.
Sinusoidal cVEMPs show sustained responses with periodicity at the stimulus frequency. These cVEMPs are consistent with a vestibular origin but can provide new information about the human otolith system that cannot be obtained with conventional transient cVEMP recordings. Specially, the amplitude and SNR peaks are consistent with vestibular hair cells full-wave rectification in the saccule. The presence of harmonic distortion products are consistent with nonlinearities in the peripheral vestibular system. Further research can lead to a more in-depth understanding of the otoliths and their physiology.
