Temchin A N, Rich N C, Ruggero M A
The Hugh Knowles Center, Audiology and Hearing Sciences, Northwestern University, Evanston, IL 60208-3550, USA.
Hear Res. 1997 Nov;113(1-2):29-56. doi: 10.1016/s0378-5955(97)00129-9.
The effects of low-frequency (50, 100, 200 and 400 Hz) 'suppressor' tones on responses to moderate-level characteristic frequency (CF) tones were measured in chinchilla auditory nerve fibers. Two-tone interactions were evident at suppressor intensities of 70-100 dB SPL. In this range, the average response rate decreased as a function of increasing suppressor level and the instantaneous response rate was modulated periodically. At suppression threshold, the phase of suppression typically coincided with basilar membrane displacement toward scala tympani, regardless of CF. At higher suppressor levels, two suppression maxima coexisted, synchronous with peak basilar membrane displacement toward scala tympani and scala vestibuli. Modulation and rate-suppression thresholds did not vary as a function of spontaneous activity and were only minimally correlated with fiber sensitivity. Except for fibers with CF < 1 kHz, modulation and rate-suppression thresholds were lower than rate and phase-locking thresholds for the suppressor tones presented alone. In the case of high-CF fibers with low spontaneous activity, excitation thresholds could exceed suppression thresholds by more than 30 dB. The strength of modulation decreased systematically with increasing suppressor frequency. For a given suppressor frequency, modulation was strongest in high-CF fibers and weakest in low-CF fibers. The present findings strongly support the notion that low-frequency suppression in auditory nerve fibers largely reflects an underlying basilar membrane phenomenon closely related to compressive non-linearity.
在灰鼠听觉神经纤维中，测量了低频（50、100、200和400赫兹）“抑制”音对中等强度特征频率（CF）音反应的影响。在70 - 100分贝声压级的抑制强度下，双音相互作用明显。在此范围内，平均反应率随抑制音强度增加而降低，瞬时反应率呈周期性调制。在抑制阈值时，无论CF如何，抑制相位通常与基底膜向鼓阶的位移一致。在较高的抑制音强度下，存在两个抑制最大值，与基底膜向鼓阶和前庭阶的峰值位移同步。调制和速率抑制阈值不随自发活动而变化，且与纤维敏感性仅有微弱关联。除了CF < 1千赫兹的纤维外，调制和速率抑制阈值低于单独呈现抑制音时的速率和锁相阈值。对于自发活动低的高CF纤维，兴奋阈值可能超过抑制阈值30分贝以上。调制强度随抑制音频率增加而系统地降低。对于给定的抑制音频率，调制在高CF纤维中最强，在低CF纤维中最弱。本研究结果有力地支持了这样一种观点，即听觉神经纤维中的低频抑制在很大程度上反映了一种与压缩非线性密切相关的潜在基底膜现象。
