Mills D M
Department of Otolaryngology, Head & Neck Surgery, Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle 98195-7923, USA.
J Acoust Soc Am. 1998 Jan;103(1):507-23. doi: 10.1121/1.421101.
The simple model introduced in Part I [J. Acoust. Soc. Am. 102, 413-429 (1997)] is used to simulate the response of the cochlea to three stimulus tones. The focus is on "emission suppression tuning curves" constructed using a third tone to suppress the cubic distortion tone emission (CDT, 2f1-f2) generated by two primary tones at frequencies f1 and f2 (intensities L1 and L2). A criterion decrease (here, 5 dB) of the CDT emission amplitude defines the 2f1-f2 emission suppression tuning curve. Applying traditional tuning curve measures to emission suppression tuning curves appears ineffective in determining the underlying cochlear amplifier characteristics. However, it is shown that there are three characteristics of emission suppression tuning curves which are particularly useful: (1) the "f2 threshold" which is the level of the third tone, L3, required for the criterion CDT amplitude decrease, under the condition that the third tone frequency, f3, is approximately equal to f2; (2) the "shoulder threshold" similarly defined for f3 << f2; and (3) the "tuning width," w40. The tuning width is defined to be the distance (in octaves) from the frequency f2 to the upper f3 frequency for which there is a criterion CDT decrease, in this case using the L3 level which is 40 dB above the f2 threshold. Model calculations appropriate to gerbils show that these measures are most accurately related to the underlying cochlear amplifier characteristics for parameters where the primary stimulus amplitudes satisfy L1/L2 > 20 dB and for which L1 is 25 dB or more below the sharp "notch" seen in the two tone input-output function. In this parameter region, the cochlear amplifier characteristics are related to measured quantities by the relationships wr approximately equal to w40 and Ga approximately equal to TE + w40gp. Here, Ga is the gain (dB) of the cochlear amplifier, defined as the total increase in cochlear response over the passive response, wr is the distance (octaves) over which the active cochlear response rises to a maximum, and gp is the passive increase (dB/octave) of the traveling wave along the basilar membrane. The measured quantities are TE, the difference (dB) between the shoulder threshold and the f2 threshold, and the tuning width, w40 (octaves), defined above. Model predictions are confirmed by measurements in adult gerbils.
第一部分[《美国声学学会杂志》102, 413 - 429 (1997)]中介绍的简单模型用于模拟耳蜗对三种刺激音的响应。重点在于使用第三种音来抑制由频率为f1和f2（强度为L1和L2）的两个主音产生的三次谐波失真音发射（CDT，2f1 - f2）构建的“发射抑制调谐曲线”。CDT发射幅度的标准降低（此处为5 dB）定义了2f1 - f2发射抑制调谐曲线。将传统调谐曲线测量方法应用于发射抑制调谐曲线，在确定潜在的耳蜗放大器特性方面似乎无效。然而，结果表明发射抑制调谐曲线有三个特别有用的特性：(1)“f2阈值”，即在第三种音频率f3近似等于f2的条件下，使CDT幅度达到标准降低所需的第三种音的电平L3；(2)类似地为f3 << f2定义的“肩部阈值”；(3)“调谐宽度”w40。调谐宽度定义为从频率f2到较高的f3频率的距离（以倍频程为单位），在此频率下CDT有标准降低，在这种情况下使用比f2阈值高40 dB的L3电平。适合沙鼠的模型计算表明，对于主刺激幅度满足L1/L2 > 20 dB且L1比在双音输入 - 输出函数中看到的尖锐“凹口”低25 dB或更多的参数，这些测量与潜在的耳蜗放大器特性最准确相关。在这个参数区域中，耳蜗放大器特性与测量量通过关系wr近似等于w40和Ga近似等于TE + w40gp相关。这里，Ga是耳蜗放大器的增益（dB），定义为耳蜗响应相对于被动响应的总增加量，wr是有源耳蜗响应上升到最大值的距离（倍频程），gp是沿基底膜的行波的被动增加量（dB/倍频程）。测量量是TE，即肩部阈值与f2阈值之间的差值（dB），以及上述定义的调谐宽度w40（倍频程）。模型预测通过对成年沙鼠的测量得到证实。
