Peaks between peaks: Comparative intra-ear correlations in spontaneous otoacoustic emissions

Abstract

Spontaneous otoacoustic emissions (SOAEs) are a key facet of modern models of inner ear biomechanics, as the phenomenon provides crucial insight into the notion of the “active ear.” Manifesting as an idiosyncratic array of spectral peaks unique to a given ear, individual SOAE peaks have nonstationary properties (e.g., amplitude and frequency modulations). Further, it has been demonstrated that interpeak relations between these “AM” and “FM” properties can be correlated, indicative of coupling of the underlying generation mechanisms. This study takes a comparative approach to characterizing these correlations in a wide variety of species exhibiting SOAEs (humans, birds, lizards) despite relatively disparate inner ear morphologies. Initial results are consistent with previous reports (e.g., van Dijk and Wit, 1990, 1998) in that SOAE interpeak correlations for a given ear are themselves idiosyncratic: Sometimes peaks (adjacent or not) exhibit correlated (positive or negative) AM and/or FM fluctuations with delays up to the order of milliseconds (typically longer for humans, shorter for lizards), while sometimes no correlation is observed. We explore implications for how such may constrain models treating the inner ear as a spatially distributed tonotopic system (e.g., various biophysical roles for coupling).