Burwood George W S, Ren Tianying, Nuttall Alfred L, Fridberger Anders
Oregon Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery, Oregon Health & Science University, Portland, OR 97239, USA.
Oregon Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery, Oregon Health & Science University, Portland, OR 97239, USA; Department of Biomedical and Clinical Sciences, Linköping University, SE-581 83 Linköping, Sweden.
Hear Res. 2024 Dec;454:109137. doi: 10.1016/j.heares.2024.109137. Epub 2024 Oct 28.
Low-frequency hearing is critically important for speech and music perception. However, technical and anatomical limitations previously made it difficult to study the mechanics of the low-frequency parts of the cochlea, but this changed with the introduction of optical coherence tomography vibrometry. With this technique, sound-evoked vibration can be measured from the apex of a fully intact cochlea. Results of such measurements generated controversy because conventional traveling waves, the hallmark of which is longer group delay closer to the helicotrema, were absent within the apical 20% of the guinea pig cochlea (Burwood et al, Science Advances 8:eabq2773, 2022). The validity of this result was questioned, primarily because group delays were calculated from phase values averaged across many points within the organ of Corti. Here we show that variations in phase across the organ of Corti are minor and does not affect the group delay significantly. We also assess the precision of phase measurements with optical coherence tomography. An artificial target with reflectivity similar to the organ of Corti was used. These measurements revealed that a commonly used commercial optical coherence tomography system produces half-cycle errors in 1-5 % of pixels, leading to a bimodal distribution of phase values. This problem can be easily addressed by using medians when computing averages, as was done by Burwood et al (2022). Hence, neither averaging across pixels nor technical factors can explain the apparent lack of conventional traveling waves at the apex of the guinea pig cochlea at low stimulus levels. The physiological mechanisms that operate at the apex apparently differ from other cochlear regions.
低频听力对于语音和音乐感知至关重要。然而，技术和解剖学上的限制使得以前很难研究耳蜗低频部分的力学原理，但随着光学相干断层扫描振动测量技术的引入，这种情况发生了变化。利用这项技术，可以从完全完整的耳蜗顶端测量声音诱发的振动。此类测量结果引发了争议，因为在豚鼠耳蜗顶端20%的区域内没有传统的行波（传统行波的标志是靠近蜗孔处的群延迟更长）（Burwood等人，《科学进展》8：eabq2773，2022）。这一结果的有效性受到质疑，主要是因为群延迟是根据柯蒂氏器内多个点的平均相位值计算得出的。在此我们表明，柯蒂氏器内相位的变化很小，对群延迟没有显著影响。我们还评估了光学相干断层扫描相位测量的精度。使用了一个反射率与柯蒂氏器相似的人工目标。这些测量结果表明，一个常用的商用光学相干断层扫描系统在1%至5%的像素中会产生半周期误差，导致相位值出现双峰分布。正如Burwood等人（2022年）所做的那样，在计算平均值时使用中位数可以轻松解决这个问题。因此，无论是像素平均还是技术因素都无法解释在低刺激水平下豚鼠耳蜗顶端明显缺乏传统行波的现象。耳蜗顶端运行的生理机制显然与其他耳蜗区域不同。
