Adaptive Algorithms for DPOAE Level-Map Acquisition

Distortion-product otoacoustic emissions (DPOAE) are intermodulation products stimulated by two tones and reflect the nonlinear mechanical processing within the inner ear by the so-called cochlear amplifier. Therefore, they are interpreted as a diagnostic measure of its functional state. Due to their small amplitudes and the correspondingly long averaging time, current clinical systems measure one DPOAE amplitude at approximately seven fixed frequencies, representing a one-dimensional (1D) scan. More advanced systems record input-output functions of the distortion-product amplitudes, where both tones are varied in a predefined ratio, resulting in a two-dimensional (2D) scan. A three-dimensional (3D) scan, where both stimulus tones are varied independently, yields more detailed information about the cochlea, but at the cost of longer measurement times. In this study, we introduce an adaptive measurement method, that autonomously collects more DPOAE data with sufficient signal-to-noise ratio (SNR) and leads more often to the identification of the so-called "individually optimal stimulus level path" than the previously used static method, which uses predefined fixed stimulus levels. In six ears of three subjects, the adaptive method detected 23% more valid DPOAE data. A bivariate histogram of area and density of DPOAE amplitudes for the optimal-path samples shows that the adaptive method balances these competing goals more effectively. This results in higher-quality DPOAE level maps. Thus, the adaptive method has proven to be a time-efficient approach to characterize cochlear function more comprehensively.