Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa.
Department of Communication Sciences and Disorders, Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin.
J Neurophysiol. 2021 May 1;125(5):1938-1953. doi: 10.1152/jn.00410.2020. Epub 2021 Feb 24.
Functional outcomes of medial olivocochlear reflex (MOCR) activation, such as improved hearing in background noise and protection from noise damage, involve moderate to high sound levels. Previous noninvasive measurements of MOCR in humans focused primarily on otoacoustic emissions (OAEs) evoked at low sound levels. Interpreting MOCR effects on OAEs at higher levels is complicated by the possibility of the middle-ear muscle reflex and by components of OAEs arising from different locations along the length of the cochlear spiral. We overcame these issues by presenting click stimuli at a very slow rate and by time-frequency windowing the resulting click-evoked (CE)OAEs into short-latency (SL) and long-latency (LL) components. We characterized the effects of MOCR on CEOAE components using multiple measures to more comprehensively assess these effects throughout much of the dynamic range of hearing. These measures included CEOAE amplitude attenuation, equivalent input attenuation, phase, and slope of growth functions. Results show that MOCR effects are smaller on SL components than LL components, consistent with SL components being generated slightly basal of the characteristic frequency region. Amplitude attenuation measures showed the largest effects at the lowest stimulus levels, but slope change and equivalent input attenuation measures did not decrease at higher stimulus levels. These latter measures are less commonly reported and may provide insight into the variability in listening performance and noise susceptibility seen across individuals. The auditory efferent system, operating at moderate to high sound levels, may improve hearing in background noise and provide protection from noise damage. We used otoacoustic emissions to measure these efferent effects across a wide range of sound levels and identified level-dependent and independent effects. Previous reports have focused on level-dependent measures. The level-independent effects identified here may provide new insights into the functional relevance of auditory efferent activity in humans.
中橄榄耳蜗反射（MOCR）激活的功能结果，如在背景噪声中改善听力和防止噪声损伤，涉及中等至高强度的声音。以前对人类 MOCR 的非侵入性测量主要集中在低强度声音下诱发的耳声发射（OAE）。在较高水平上解释 MOCR 对 OAE 的影响很复杂，因为可能存在中耳肌肉反射，并且 OAE 的成分可能来自耳蜗螺旋长度的不同位置。我们通过以非常缓慢的速率呈现点击刺激并通过时频窗口将产生的点击诱发（CE）OAE 分成短潜伏期（SL）和长潜伏期（LL）分量来克服这些问题。我们使用多种措施来描述 MOCR 对 CEOAE 分量的影响，以更全面地评估这些影响在听力的大部分动态范围内。这些措施包括 CEOAE 幅度衰减、等效输入衰减、相位和生长函数斜率。结果表明，MOCR 对 SL 分量的影响小于 LL 分量，这与 SL 分量在特征频率区域稍下方产生一致。幅度衰减测量在最低刺激水平下显示出最大的影响，但斜率变化和等效输入衰减测量在较高刺激水平下并未降低。这些后一种措施不太常见，可能为个体之间听力表现和噪声敏感性的可变性提供了一些见解。在中等至高强度声音下运行的听觉传出系统可能会改善背景噪声中的听力并提供噪声保护。我们使用耳声发射来测量这些传出效应在广泛的声音水平范围内，并确定了与水平相关和独立的效应。以前的报告主要集中在与水平相关的措施上。这里确定的与水平无关的效应可能为人类听觉传出活动的功能相关性提供新的见解。
