Vallejo Luis Angel, Hidalgo Antonio, Lobo Fernando, Tesorero María Antonia, Gil-Carcedo Elisa, Sánchez Elena, Gil-Carcedo Luis M
Hospital Universitario Del Río Hortega, Servicio de Otorrinolaringología, Universidad de Valladolid, Valladolid, España.
Acta Otorrinolaringol Esp. 2010 Mar-Apr;61(2):118-27. doi: 10.1016/j.otorri.2009.11.004. Epub 2010 Jan 29.
The cochlea has traditionally been considered as the first frequency selection filter in the auditory pathway due to the contraction of its external ciliated cells. Yet, much evidence has emerged from work carried out during experiments with animals, some of which is anatomical (connections between the auditory pathway and motor nuclei of the middle ear muscles) and other physiological, which indicates that the middle ear might be the first filter through which specific sounds from noisy environments may initially be isolated.
In cooperation with the Department of Mechanical Engineering of the Technical School of Industrial Engineering at the University of Valladolid (UVa) we have developed and refined a new admittance meter capable of evaluating changes in impedance that occur in the human middle ear depending on frequency. Using this device we have measured variation in impedance in 7 otologically healthy volunteers submitted to a varied range of sound environments.
We have found that hearing impedance is not constant but rather that the attention offered by the examined subjects when following a conversation in a noisy environment leads to variations in hearing impedance at high frequencies.
In the light of these findings we feel that the middle ear does not play a merely passive role in hearing but rather that the contraction of the endotympanic muscles makes possible variations in impedance such that the resonance frequency of the ear shifts towards higher frequencies, thus enhancing sound discrimination in noisy environments.
传统上，由于耳蜗外纤毛细胞的收缩，耳蜗被认为是听觉通路中的第一个频率选择滤波器。然而，在动物实验中已出现大量证据，其中一些是解剖学证据（听觉通路与中耳肌肉运动核之间的连接），另一些是生理学证据，这表明中耳可能是第一个滤波器，通过它可以初步分离嘈杂环境中的特定声音。
我们与巴利亚多利德大学（UVa）工业工程技术学院机械工程系合作，开发并改进了一种新型导纳仪，该导纳仪能够评估人中耳中随频率变化的阻抗变化。我们使用该设备测量了7名听力健康的志愿者在各种声音环境下的阻抗变化。
我们发现听力阻抗并非恒定不变，而是在嘈杂环境中进行对话时，被检查对象的注意力会导致高频听力阻抗发生变化。
基于这些发现，我们认为中耳在听力过程中并非仅仅起被动作用，而是鼓室内肌的收缩使得阻抗变化成为可能，从而使耳朵的共振频率向更高频率偏移，进而增强在嘈杂环境中的声音辨别能力。
