Shera C A, Talmadge C L, Tubis A
Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston 02114, USA.
J Acoust Soc Am. 2000 Dec;108(6):2933-48. doi: 10.1121/1.1323234.
Distortion-product-otoacoustic-emission (DPOAE) phase-versus-frequency functions and corresponding phase-gradient delays have received considerable attention because of their potential for providing information about mechanisms of emission generation, cochlear wave latencies, and characteristics of cochlear tuning. The three measurement paradigms in common use (fixed-f1, fixed-f2, and fixed-f2/f1) yield significantly different delays, suggesting that they depend on qualitatively different aspects of cochlear mechanics. In this paper, theory and experiment are combined to demonstrate that simple phenomenological arguments, which make no detailed mechanistic assumptions concerning the underlying cochlear mechanics, predict relationships among the delays that are in good quantitative agreement with experimental data obtained in guinea pigs. To understand deviations between the simple theory and experiment, a general equation is found that relates the three delays for any deterministic model of DPOAE generation. Both model-independent and exact, the general relation provides a powerful consistency check on the measurements and a useful tool for organizing and understanding the structure in DPOAE phase data (e.g., for interpreting the relative magnitudes and intensity-dependencies of the three delays). Analysis of the general relation demonstrates that the success of the simple, phenomenological approach can be understood as a consequence of the mechanisms of emission generation and the approximate local scaling symmetry of cochlear mechanics. The general relation is used to quantify deviations from scaling manifest in the measured phase-gradient delays; the results indicate that deviations from scaling are typically small and that both linear and nonlinear mechanisms contribute significantly to these deviations. Intensity-dependent mechanisms contributing to deviations from scaling include cochlear-reflection and wave-interference effects associated with the mixing of distortion- and reflection-source emissions (as in DPOAE fine structure). Finally, the ratio of the fixed-f1 and fixed-f2 phase-gradient delays is shown to follow from the choice of experimental paradigm and, in the scaling limit, contains no information about cochlear physiology whatsoever. These results cast considerable doubt on the theoretical basis of recent attempts to use relative DPOAE phase-gradient delays to estimate the bandwidths of peripheral auditory filters.
畸变产物耳声发射（DPOAE）的相位与频率函数以及相应的相位梯度延迟因其能够提供有关发射产生机制、耳蜗波潜伏期和耳蜗调谐特性的信息而受到了广泛关注。常用的三种测量范式（固定f1、固定f2和固定f2/f1）产生的延迟显著不同，这表明它们依赖于耳蜗力学在性质上不同的方面。在本文中，理论与实验相结合，证明了简单的唯象学观点，即在不涉及耳蜗力学潜在详细机制假设的情况下，预测了延迟之间的关系，这些关系与豚鼠实验数据在定量上具有良好的一致性。为了理解简单理论与实验之间的偏差，找到了一个通用方程，该方程将DPOAE产生的任何确定性模型的三种延迟联系起来。这个通用关系既与模型无关又精确，它为测量提供了有力的一致性检验，也是组织和理解DPOAE相位数据结构的有用工具（例如，用于解释三种延迟的相对大小和强度依赖性）。对通用关系的分析表明，简单唯象学方法的成功可以理解为发射产生机制和耳蜗力学近似局部标度对称性的结果。通用关系用于量化测量的相位梯度延迟中与标度偏差的情况；结果表明，与标度的偏差通常较小，并且线性和非线性机制对这些偏差都有显著贡献。导致与标度偏差的强度依赖机制包括与畸变源发射和反射源发射混合相关的耳蜗反射和波干涉效应（如在DPOAE精细结构中）。最后，固定f1和固定f2相位梯度延迟的比值表明取决于实验范式的选择，并且在标度极限下，不包含任何关于耳蜗生理学的信息。这些结果对最近试图使用相对DPOAE相位梯度延迟来估计外周听觉滤波器带宽的理论基础提出了相当大的质疑。
