Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, Massachusetts 02114, USA.
J Acoust Soc Am. 2013 Apr;133(4):2224-39. doi: 10.1121/1.4792129.
At low stimulus levels, basilar-membrane (BM) mechanical transfer functions in sensitive cochleae manifest a quasiperiodic rippling pattern in both amplitude and phase. Analysis of the responses of active cochlear models suggests that the rippling is a mechanical interference pattern created by multiple internal reflection within the cochlea. In models, the interference arises when reverse-traveling waves responsible for stimulus-frequency otoacoustic emissions (SFOAEs) reflect off the stapes on their way to the ear canal, launching a secondary forward-traveling wave that combines with the primary wave produced by the stimulus. Frequency-dependent phase differences between the two waves then create the rippling pattern measurable on the BM. Measurements of BM ripples and SFOAEs in individual chinchilla ears demonstrate that the ripples are strongly correlated with the acoustic interference pattern measured in ear-canal pressure, consistent with a common origin involving the generation of SFOAEs. In BM responses to clicks, the ripples appear as temporal fine structure in the response envelope (multiple lobes, waxing and waning). Analysis of the ripple spacing and response phase gradients provides a test for the role of fast- and slow-wave modes of reverse energy propagation within the cochlea. The data indicate that SFOAE delays are consistent with reverse slow-wave propagation but much too long to be explained by fast waves.
在低刺激水平下，敏感耳蜗的基底膜（BM）机械传递函数在幅度和相位上都表现出准周期性的波纹图案。对主动耳蜗模型响应的分析表明，这种波纹是由耳蜗内多次内部反射产生的机械干扰图案。在模型中，当负责刺激频率耳声发射（SFOAE）的逆行波在返回耳道的途中从镫骨上反射时，就会产生干扰，从而引发二次前向波，与刺激产生的初级波相结合。然后，这两个波之间的频率相关相位差会产生可在 BM 上测量到的波纹图案。对单个南美栗鼠耳朵的 BM 波纹和 SFOAE 的测量表明，波纹与耳道压力测量到的声干涉图案强烈相关，这与涉及 SFOAE 产生的共同起源一致。在对点击的 BM 响应中，波纹出现在响应包络的时间精细结构中（多个叶，增减）。波纹间距和响应相位梯度的分析为耳蜗内反向能量传播的快波和慢波模式的作用提供了一个测试。数据表明，SFOAE 的延迟与反向慢波传播一致，但太长而无法用快波解释。
