Ku Emery M, Elliott Stephen J, Lineton Ben
Institute of Sound and Vibration Research, University of Southampton, Southampton, Hampshire, United Kingdom.
J Acoust Soc Am. 2009 Aug;126(2):739-50. doi: 10.1121/1.3158861.
It is somewhat surprising that linear analysis can account for so many features of the cochlea when it is inherently nonlinear. For example, the commonly detected spacing between adjacent spontaneous otoacoustic emissions (SOAEs) is often explained by a linear theory of "coherent reflection" [Zweig and Shera (1995). J. Acoust. Soc. Am. 98, 2018-2047]. The nonlinear saturation of the cochlear amplifier is, however, believed to be responsible for stabilizing the amplitude of a SOAE. In this investigation, a state space model is used to first predict the linear instabilities that arise, given distributions of cochlear inhomogeneities, and then subsequently to simulate the time-varying spectra of the nonlinear models. By comparing nonlinear simulation results to linear predictions, it is demonstrated that nonlinear effects can have a strong impact on the steady-state response of an unstable cochlear model. Sharply tuned components that decay away exponentially within 100 ms are shown to be due to linearly resonant modes of the model generated by the cochlear inhomogeneities. Some oscillations at linearly unstable frequencies are suppressed over a longer time scale, whereas those that persist are due to linear instabilities and their distortion products.
当耳蜗本质上是非线性的时候，线性分析却能解释耳蜗的如此多特征，这有点令人惊讶。例如，相邻自发性耳声发射（SOAE）之间常见的检测间隔通常由“相干反射”的线性理论来解释[茨威格和谢拉（1995年）。《美国声学学会杂志》98卷，2018 - 2047页]。然而，耳蜗放大器的非线性饱和被认为是稳定SOAE幅度的原因。在这项研究中，首先使用状态空间模型来预测给定耳蜗不均匀性分布时出现的线性不稳定性，然后模拟非线性模型的时变谱。通过将非线性模拟结果与线性预测进行比较，证明非线性效应会对不稳定耳蜗模型的稳态响应产生强烈影响。在100毫秒内呈指数衰减的尖锐调谐成分被证明是由耳蜗不均匀性产生的模型线性共振模式所致。一些处于线性不稳定频率的振荡在更长的时间尺度上受到抑制，而持续存在的振荡则是由于线性不稳定性及其失真产物。
