Kirk D L, Yates G K
Department of Physiology, University of Western Australia, Nedlands, Australia.
J Acoust Soc Am. 1998 Sep;104(3 Pt 1):1544-54. doi: 10.1121/1.424365.
Electrically evoked oto-acoustic emissions (EEOAEs) are sounds present in the ear canal when ac current is passed into the cochlea. EEOAEs are attributed to the activation of fast electromotile responses in outer hair cells (OHCs). An interesting property of EEOAEs is the phenomenon of "acoustic enhancement," where the emission amplitude is increased by moderate-level sound [D. C. Mountain and A. E. Hubbard, Hear. Res. 42, 195-202 (1989)]. In this report a form of enhancement is described which occurs with displacements of the basilar membrane toward scala vestibuli, during amplitude modulation of the EEOAE waveform by low-frequency tones. This "SV-bias enhancement" possibly consists of two components: (i) a low-level component induced by sound at levels which produce nonlinear growth of the cochlear microphonic and which may be equivalent to the "acoustic enhancement" described previously, and (ii) a high-level component which occurs at sound levels well above those which cause saturation of the cochlear microphonic. The low-level component could be explained by either an increased access of the extrinsically applied current to a membrane-based source of OHC motility, perhaps coupled with a reduction in negative feedback, or an increase in electromotile output during scala vestibuli displacements, but the origin of the high-level component is obscure.
电诱发耳声发射（EEOAEs）是向耳蜗施加交流电时外耳道中出现的声音。EEOAEs归因于外毛细胞（OHCs）中快速电运动反应的激活。EEOAEs的一个有趣特性是“声学增强”现象，即中等强度的声音会增加发射幅度[D.C. 芒廷和A.E. 哈伯德，《听觉研究》42卷，第195 - 202页（1989年）]。在本报告中，描述了一种增强形式，它发生在低频音调对EEOAE波形进行幅度调制期间，基底膜朝着前庭阶位移时。这种“SV偏向增强”可能由两个成分组成：（i）由产生耳蜗微音器非线性增长的声音水平所诱发的低水平成分，它可能等同于先前描述的“声学增强”；（ii）在远高于使耳蜗微音器饱和的声音水平时出现的高水平成分。低水平成分可以通过以下两种方式之一来解释：要么是外部施加的电流增加了对基于膜的OHC运动源的接触，可能伴随着负反馈的减少；要么是在前庭阶位移期间电运动输出增加，但高水平成分的起源尚不清楚。
