Nonlinear Processing and Temporal Encoding in the Utricular-Ocular Pathway: Insights from Amplitude-Modulated oVEMPs in Young Females

Purpose Ocular vestibular evoked myogenic potentials (oVEMPs) are widely used to assess utriculo-ocular function. However, oVEMPs have traditionally been elicited using transient stimuli, providing limited insight into temporal and nonlinear processing of the vestibular input. This study used amplitude-modulated stimuli to characterize temporal modulation transfer function (TMTF) and quantify nonlinear harmonic distortions in oVEMP responses. Methods Fourteen young adult females with normal hearing and no vestibular history were tested. Sinusoidally amplitude-modulated tones (500 Hz carrier, 100% modulation depth, 123 dB FL) were delivered via bone conduction across ten modulation frequencies (11 to 397 Hz). Responses were analyzed using fast Fourier transformation and quantified via amplitude, signal-to-noise ratio (SNR), phase coherence (PC), and harmonic components. Results Robust oVEMP responses were elicited across a broad range of modulation frequencies. Peak amplitude occurred at 79 Hz, while SNR and PC peaked between 79 and 113 Hz. Using a statistical SNR detection criterion of > 6.13 dB, the effective response range extended from 37 to 113 Hz. Harmonic distortion products were consistently detected up to the third harmonic, with peak response amplitudes and response rates converging near 110 Hz across harmonic components. Conclusions These findings provide the first characterization of the amplitude-modulated oVEMP TMTF and demonstrate temporal processing and nonlinear encoding within the utricular-ocular pathway. Extending this approach to vestibular disorders could help identify deficits not captured by transient measures, advance our understanding of vestibular pathophysiology, and improve clinical diagnosis. Optimal modulation frequencies for clinical and research applications of amplitude-modulated oVEMPs appear to lie between 37 and 113 Hz.