Temporal Suppression of Clicked-Evoked Otoacoustic Emissions and Basilar-Membrane Motion in Gerbils.

Abstract

Otoacoustic emissions evoked by a click (CEOAEs) can be reduced if the evoking sound is preceded or followed by another ("suppressor") click. Studying the temporal suppression of CEOAEs can provide insights into the dynamics of cochlear nonlinearity. However, temporal suppression has never been measured in basilar-membrane (BM) motion. Thus, it remains unclear whether the characteristics of CEOAE temporal suppression are reflected in BM responses. Here we simultaneously measured ear-canal pressure and BM velocity (laser Doppler vibrometry) in response to clicks in gerbil. When the suppressor click preceded the evoking click, CEOAEs were maximally suppressed for interclick intervals (ICIs) equivalent to ~2 periods of the analyzed frequency (9-14 kHz). Maximal temporal suppression at nonzero ICIs has been previously observed in human CEOAEs. BM responses to clicks were maximally reduced when the suppressor click preceded the evoking one by ~1 period of the characteristic frequency (CF ~14 kHz). Thus, the "delayed" characteristics of CEOAE temporal suppression are reflected in BM motion, although on a different time scale. When the suppressor click followed the evoking click, CEOAEs were augmented rather than suppressed, while enhancement was not observed in BM motion at the CF. This result indicates that some aspects of CEOAE temporal suppression are intrinsic to CEOAE generation mechanisms and/or to places that are not reflected in a BM motion at a single-location.