Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114, United States; Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, 243 Charles Street, Boston, MA 02114, United States; Graduate Program in Speech and Hearing Bioscience and Technology, Division of Medical Studies, Harvard University, Boston, MA 02115, United States.
Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114, United States.
Hear Res. 2021 Jun;405:108242. doi: 10.1016/j.heares.2021.108242. Epub 2021 Apr 9.
The human tympanic membrane (TM) and ossicles are generally considered to act as a linear system as they conduct low and moderate level environmental sounds to the cochlea. At intense stimulus levels (> 120 dB SPL) there is evidence that the TM and ossicles no longer act linearly. The anatomical structures that contribute to the nonlinear responses and their level and frequency dependences are not well defined. We used cadaveric human ears to characterize middle-ear responses to continuous tones between 200 and 20,000 Hz with levels between 60 and 150 dB SPL. The responses of the TM and ossicles are essentially sinusoidal, even at the highest stimulus level, but grow nonlinearly with increased stimulus level. The umbo and the stapes show different nonlinear behaviors: The umbo displacement grows faster than the stimulus level (expansive growth) at frequencies below 2000 Hz, while the stapes exhibits mostly compressive growth (grows slower than the stimulus level) over a wide frequency range. The sound pressure level where the nonlinearity first becomes obvious and the displacement at that level are lower at the stapes than at the umbo. These observations suggest the presence of multiple nonlinear processes within the middle ear. The existence of an expansive growth of umbo displacement that has limited effect on the stapes compressive growth suggests that the ossicular joints reduce the coupling between multiple nonlinear mechanisms within the middle ear. This study provides new data to test and refine middle-ear nonlinear models.
人耳鼓膜（TM）和听小骨通常被认为是一个线性系统，因为它们将低强度和中等强度的环境声音传导到耳蜗。在高强度刺激水平（>120dB SPL）下，有证据表明 TM 和听小骨不再呈线性。导致非线性响应的解剖结构及其水平和频率依赖性尚不清楚。我们使用尸体人耳来描述 TM 和听小骨对 200Hz 至 20000Hz 范围内、60dB SPL 至 150dB SPL 之间的连续音调的中耳响应。即使在最高刺激水平下，TM 和听小骨的响应基本上也是正弦波，但随着刺激水平的增加而呈非线性增长。鼓膜脐和镫骨表现出不同的非线性行为：在低于 2000Hz 的频率下，鼓膜脐的位移比刺激水平增长得更快（扩张性生长），而镫骨在较宽的频率范围内主要表现为压缩性生长（比刺激水平增长得更慢）。非线性首先变得明显的声压级和该级别的位移在镫骨处低于鼓膜脐。这些观察结果表明中耳内存在多种非线性过程。鼓膜脐位移的扩张性生长对镫骨压缩性生长的影响有限，这表明听小骨关节减少了中耳内多个非线性机制之间的耦合。本研究提供了新的数据来测试和完善中耳非线性模型。
