Allen J B, Fahey P F
Acoustics Research Department, AT&T Bell Laboratories, Murray Hill, New Jersey 07974.
J Acoust Soc Am. 1993 Aug;94(2 Pt 1):809-16. doi: 10.1121/1.408182.
Acoustic intermodulation distortion products (DPs) are generated by the nonlinear motion of the basilar membrane (BM) in the cochlea, and propagate back to the ear canal where they may be measured. One common method of measuring these distortion products is to hold the higher-primary frequency f2 fixed while varying the lower-primary frequency f1. When doing this, it is well known that the ear canal distortion product is maximum for a particular value of f2/f1, usually between 1.1 and 1.4. In fact all odd order distortion products of the form fd(n) = f1 -n(f2-f1), n = 1,2,3,... are maximum at the same fd(n), independent of order n, but dependent on f2 which determines the place of DP generation. In this paper, it is argued that this maximum must result from filtering by micromechanical resonances within the cochlea. In fact the frequency where the neural tuning curve "tip" meets the "tail" is the same as the frequency where the distortion products are maximum. This suggests that each section of the basilar membrane must consist of two resonant impedances. The first is the usual series basilar membrane resonant impedance that gives rise to the characteristic frequency (CF). The second resonant impedance must be tuned to a frequency that is lower than the CF and must act as a shunt across the inner hair-cells, since it acts to reduce the forward transmission to the neuron, while, at the same time, it maximally couples all the distortion products back into the cochlear fluids, giving them a frequency dependent increase at its resonant frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
声学互调失真产物（DPs）由耳蜗中基底膜（BM）的非线性运动产生，并传播回耳道，在那里可以进行测量。测量这些失真产物的一种常见方法是在改变较低基频f1时保持较高基频f2不变。在这样做时，众所周知，耳道失真产物在f2/f1的特定值时最大，通常在1.1到1.4之间。实际上，所有形式为fd(n) = f1 - n(f2 - f1)，n = 1,2,3,...的奇数阶失真产物在相同的fd(n)处最大，与阶数n无关，但取决于决定DP产生位置的f2。在本文中，有人认为这种最大值必定是由耳蜗内的微机械共振滤波所致。事实上，神经调谐曲线“尖端”与“尾部”相交处的频率与失真产物最大处的频率相同。这表明基底膜的每个部分必定由两个共振阻抗组成。第一个是通常的串联基底膜共振阻抗，它产生特征频率（CF）。第二个共振阻抗必定调谐到低于CF的频率，并且必须作为跨内毛细胞的并联支路起作用，因为它起到减少向前传输到神经元的作用，同时，它将所有失真产物最大程度地耦合回耳蜗内的液体中，使其在共振频率处随频率增加。（摘要截于250字）
