Frank G, Kössl M
Zoologisches Institut der Universität München, Germany.
Hear Res. 1996 Sep 1;98(1-2):104-15. doi: 10.1016/0378-5955(96)00083-4.
Acoustic two-tone distortions are generated during non-linear mechanical amplification in the cochlea. Generation of the cubic distortion 2f1-f2 depends on asymmetric components of a non-linear transfer function whereas the difference tone f2-f1 relies on symmetric components. Therefore, a change of the operating point and hence the symmetry of the cochlear amplifier could be strongly reflected in the level of the f2-f1 distortion. To test this hypothesis, low-frequency tones (5 Hz) were used to bias the position of the cochlear partition in the gerbil. Phase-correlated changes of f2-f1 occurred at bias tone levels where there were almost no effects on 2f1-f2. Higher levels of the bias tone induced pronounced changes of both distortions. These results are qualitatively in good agreement with the results of a simulation in which the operating point of a Boltzman function was shifted. This function is similar to those used to describe outer hair cell (OHC) transduction. To influence OHC motility, salicylate was injected. It caused a decrease of the 2f1-f2 level and an increase in the level of f2-f1. Such reciprocal changes of both distortions, again, can be interpreted in terms of a shift of the operating point of the cochlear amplifier along a non-linear transfer characteristic. To directly influence the cochlear amplifier, DC current was injected into the scala media. Large negative currents (> -2 microA) caused a pronounced decrease of 2f1-f2 (> 15 dB) and positive currents had more complex effects with increasing and/or decreasing 2f1-f2 distortion level. The effects were time and primary level dependent. Changes of f2-f1 for DC currents > magnitude of mu 2A were in most cases larger compared to 2f1-f2 and reversed for certain primary levels. The current effects probably result from a combination of changing the endocochlear potential and shifting the operating point along a non-linear transfer function.
在耳蜗的非线性机械放大过程中会产生声学双音失真。三次失真2f1 - f2的产生取决于非线性传递函数的不对称分量，而差频f2 - f1则依赖于对称分量。因此，工作点的变化以及耳蜗放大器的对称性变化可能会在f2 - f1失真水平上得到强烈反映。为了验证这一假设，使用低频音调（5赫兹）来偏移沙鼠耳蜗隔板的位置。在对2f1 - f2几乎没有影响的偏置音调水平下，f2 - f1发生了相位相关的变化。更高水平的偏置音调会导致两种失真都发生明显变化。这些结果在定性上与玻尔兹曼函数工作点发生偏移的模拟结果高度一致。该函数类似于用于描述外毛细胞（OHC）转导的函数。为了影响OHC的能动性，注射了水杨酸盐。这导致2f1 - f2水平降低，f2 - f1水平升高。同样，这两种失真的这种相互变化可以根据耳蜗放大器工作点沿非线性传递特性的偏移来解释。为了直接影响耳蜗放大器，将直流电流注入中阶。大的负电流（> -2微安）会导致2f1 - f2明显降低（> 15分贝），而正电流会产生更复杂的影响，2f1 - f2失真水平会升高和/或降低。这些影响与时间和初级水平有关。对于直流电流> 2微安的情况，f2 - f1的变化在大多数情况下比2f1 - f2更大，并且在某些初级水平下会反转。电流效应可能是改变内淋巴电位和沿非线性传递函数移动工作点共同作用的结果。
