Shera Christopher A, Tubis Arnold, Talmadge Carrick L
Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, Massachusetts 02114, USA.
J Acoust Soc Am. 2008 Jul;124(1):381-95. doi: 10.1121/1.2917805.
Coherent-reflection theory explains the generation of stimulus-frequency and transient-evoked otoacoustic emissions by showing how they emerge from the coherent "backscattering" of forward-traveling waves by mechanical irregularities in the cochlear partition. Recent published measurements of stimulus-frequency otoacoustic emissions (SFOAEs) and estimates of near-threshold basilar-membrane (BM) responses derived from Wiener-kernel analysis of auditory-nerve responses allow for comprehensive tests of the theory in chinchilla. Model predictions are based on (1) an approximate analytic expression for the SFOAE signal in terms of the BM traveling wave and its complex wave number, (2) an inversion procedure that derives the wave number from BM traveling waves, and (3) estimates of BM traveling waves obtained from the Wiener-kernel data and local scaling assumptions. At frequencies above 4 kHz, predicted median SFOAE phase-gradient delays and the general shapes of SFOAE magnitude-versus-frequency curves are in excellent agreement with the measurements. At frequencies below 4 kHz, both the magnitude and the phase of chinchilla SFOAEs show strong evidence of interference between short- and long-latency components. Approximate unmixing of these components, and association of the long-latency component with the predicted SFOAE, yields close agreement throughout the cochlea. Possible candidates for the short-latency SFOAE component, including wave-fixed distortion, are considered. Both empirical and predicted delay ratios (long-latency SFOAE delay/BM delay) are significantly less than 2 but greater than 1. Although these delay ratios contradict models in which SFOAE generators couple primarily into cochlear compression waves, they are consistent with the notion that forward and reverse energy propagation in the cochlea occurs predominantly by means of traveling pressure-difference waves. The compelling overall agreement between measured and predicted delays suggests that the coherent-reflection model captures the dominant mechanisms responsible for the generation of reflection-source otoacoustic emissions.
相干反射理论通过展示刺激频率和瞬态诱发耳声发射如何从耳蜗隔中的机械不规则性对正向传播波的相干“反向散射”中产生，解释了它们的产生机制。最近发表的刺激频率耳声发射（SFOAE）测量结果以及从听觉神经反应的维纳核分析得出的近阈值基底膜（BM）反应估计值，使得能够在灰鼠身上对该理论进行全面测试。模型预测基于：（1）根据BM行波及其复波数对SFOAE信号的近似解析表达式；（2）从BM行波中推导波数的反演程序；（3）从维纳核数据和局部缩放假设获得的BM行波估计值。在4kHz以上的频率，预测的SFOAE相位梯度延迟中位数以及SFOAE幅度-频率曲线的总体形状与测量结果非常吻合。在4kHz以下的频率，灰鼠SFOAE的幅度和相位都显示出短潜伏期和长潜伏期成分之间存在强烈干扰的证据。对这些成分进行近似分解，并将长潜伏期成分与预测的SFOAE相关联，在整个耳蜗中都产生了密切的一致性。考虑了短潜伏期SFOAE成分的可能候选者，包括波固定失真。经验和预测的延迟比（长潜伏期SFOAE延迟/BM延迟）均显著小于2但大于1。尽管这些延迟比与SFOAE发生器主要耦合到耳蜗压缩波的模型相矛盾，但它们与耳蜗中正向和反向能量传播主要通过传播的压力差波发生的观点一致。测量和预测延迟之间令人信服的总体一致性表明，相干反射模型捕捉到了负责反射源耳声发射产生的主要机制。
