Burns E M, Keefe D H, Ling R
University of Washington, Seattle 98105, USA.
J Acoust Soc Am. 1998 Jan;103(1):462-74. doi: 10.1121/1.421122.
There is some controversy in the literature over whether the so-called "active mechanism" or "cochlear amplifier" is actually a power amplifier that can produce an output signal with more power than its input, or whether it simply minimizes dissipative losses within the cochlea without providing an actual power gain greater than unity. A corollary of this controversy is whether spontaneous otoacoustic emissions (SOAEs) represent the output of a nonlinear oscillator mechanism, i.e., a power amplifier which can produce an oscillatory output signal in the absence of an input oscillatory signal, or whether they represent the output of a noise-driven, passive, nonlinear system. This paper describes measurements of energy reflectance, and acoustic impedance in the ear canals of human subjects with strong SOAEs. The reflectance, and the resistive and reactive parts of the acoustic impedance, all show a frequency fine structure which correlates with SOAE frequencies, and which becomes more pronounced at low stimulus levels. In some ears at some SOAE frequencies, energy reflectance exceeds unity, and correspondingly, acoustic resistance is negative. This result demonstrates that there is a power gain at these frequencies: The power reflected from the cochlea to the ear canal exceeds the power incident. It is also consistent with the theory that these SOAEs are produced by a nonlinear oscillator mechanism in the cochlea.
关于所谓的“主动机制”或“耳蜗放大器”实际上是一个能够产生比其输入功率更大的输出信号的功率放大器，还是仅仅将耳蜗内的耗散损耗降至最低而不提供大于1的实际功率增益，文献中存在一些争议。这场争议的一个推论是，自发性耳声发射（SOAE）是代表非线性振荡器机制的输出，即一个在没有输入振荡信号的情况下能够产生振荡输出信号的功率放大器，还是代表一个由噪声驱动的、被动的、非线性系统的输出。本文描述了对具有强烈SOAE的人类受试者耳道内能量反射率和声阻抗的测量。反射率以及声阻抗的电阻和电抗部分，都呈现出与SOAE频率相关的频率精细结构，并且在低刺激水平时变得更加明显。在一些耳朵的某些SOAE频率处，能量反射率超过1，相应地，声阻为负。这一结果表明在这些频率处存在功率增益：从耳蜗反射到耳道的功率超过入射功率。这也与这些SOAE是由耳蜗中的非线性振荡器机制产生的理论相一致。
