Development of measurement system for basilar membrane vibrations using a laser Doppler vibrometer coupled to a microscope.

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Although amplitude of tympanic membranc vibrations is only a few nanometer when we talk in a low voice, we can understand clearly what they say. This is speculated to be caused by cochlear amplification. Otoacoustic Emissions (OAEs) are recognized as the byproduct of this cochlear amplication. However, mechanism of the amplification in the cochlea is obscure. Therefore, in this paper, cochlear basilar membrane vibrations of guinea pigs in live, dead, hypoxia conditions and when OAEs are generated using a laser Doppler vibrometer coupled to a compound microscope, and an attempt is made to clarify the mechanism of the cochlear amplification and its contribution toward the generation of OAEs. As the results of the measurements of basilar membrane vibrations in live, dead and hypoxia conditions, it is guessed that cochlear amplifier exists in the live guinea pigs and has nonlinearity and is influenced by the moderated hypoxia. Furthermore, simultaneous measurements of basilar membrane vibrations and OAEs suggest that cochlear nonlincar amplification contributes toward the origin of OAEs.