He N, Schmiedt R A
Department of Otolaryngology and Communicative Sciences, Medical University of South Carolina, Charleston 29425-2242, USA.
J Acoust Soc Am. 1997 Jun;101(6):3554-65. doi: 10.1121/1.418316.
The fine structure of the 2 f1-f2 acoustic distortion product (ADP) was measured in humans with different primary level (L1/L2) and frequency (f2/f1, f2 > f1) ratios. The (L1/L2) ratio was varied under two conditions. In the first condition L1 was fixed at 50 dB SPL while L2 was varied from 30 to 75dB SPL in 5-dB steps. An upward frequency shift was observed in the ADP fine structure as L2 was increased. In the second condition, L2 was fixed at 50 dB SPL and L1 varied, and a downward frequency shift was observed. These opposing frequency shifts are predicted by a vector-sum model [Sun et al., J. Acoust., Soc. Am. 96, 2166-2174, 2175-2183 (1994)] and support the hypothesis that the ADP fine structure largely reflects place features of the area of overlap of the primary traveling waves. The mechanisms underlying the shifts in fine structure were further investigated by using three primary f2/f1 ratios: 1.11, 1.2, and 1.33. An orderly difference in the rate of fine-structure shift with level was observed as a function of f2/f1 ratio, with the largest rate of shift associated with the smallest frequency ratio. This observation, along with the fact that downward frequency shift (with L1 varied) is always at a larger rate than the upward shift (with L2 varied), suggests that ADP levels and fine structure are strongly influenced by the nonlinear compression present in the mechanics of the basilar membrane in the region of overlap between the primary traveling waves.
在人类受试者中，测量了具有不同基频水平（L1/L2）和频率比（f2/f1，f2 > f1）的2f1 - f2声畸变产物（ADP）的精细结构。在两种条件下改变（L1/L2）比值。在第一种条件下，L1固定在50 dB SPL，而L2以5 dB步长从30 dB SPL变化到75 dB SPL。随着L2增加，在ADP精细结构中观察到向上的频率偏移。在第二种条件下，L2固定在50 dB SPL，L1变化，观察到向下的频率偏移。这些相反的频率偏移由矢量和模型预测[Sun等人，《美国声学学会杂志》96，2166 - 2174，2175 - 2183（1994）]，并支持以下假设：ADP精细结构在很大程度上反映了初级行波重叠区域的位置特征。通过使用三种初级f2/f1比值：1.11、1.2和1.33，进一步研究了精细结构偏移的潜在机制。观察到精细结构随声压级变化的速率随f2/f1比值呈现有序差异，频率比最小的情况下，精细结构偏移速率最大。这一观察结果，以及向下频率偏移（L1变化时）总是比向上偏移（L2变化时）速率更大这一事实，表明ADP水平和精细结构受到初级行波重叠区域基底膜力学中存在的非线性压缩的强烈影响。
