Lee Donguk, Lewis James D, Harkrider Ashley, Hedrick Mark
Department of Audiology and Speech Pathology, University of North Texas, Denton.
Department of Communication Disorders and Sciences, Viterbo University, La Crosse, WI.
J Speech Lang Hear Res. 2025 Aug 12;68(8):4123-4138. doi: 10.1044/2025_JSLHR-24-00698. Epub 2025 Jul 17.
There is evidence from past animal work that the neural signal-to-noise ratio (SNR) is modulated through the action of the medial olivocochlear reflex (MOCR). This is commonly referred to as unmasking. However, evidence of unmasking in humans is limited, perhaps due to the traditional approach of measuring the MOCR using otoacoustic emissions-a preneural metric. The amplitudes and latencies of the late latency response (LLR) are sensitive to changes in SNR and may provide a means to noninvasively evaluate MOCR unmasking at the neural level. The purpose of this study was to investigate MOCR-mediated enhancement of ipsilateral noise in humans using the LLR.
Fifty normal-hearing adults were recruited. The LLR was measured for a 60 dB SPL, 1-kHz tone in both ipsilateral quiet and ipsilateral noise, with and without presentation of contralateral noise. For the ipsilateral noise conditions, the noise was presented at three different levels to achieve SNRs of +5 dB, +15 dB, and +25 dB. The contralateral noise was always 60 dB SPL white noise. LLR latencies (P1, N1, and P2) and interpeak amplitudes (P1-N1 and N1-P2) were measured for all conditions. In addition, otoacoustic emissions (OAEs) for a 1-kHz tone burst were measured in ipsilateral quiet both with and without contralateral noise. The same contralateral noise was used for both OAEs and LLRs.
For the ipsilateral noise conditions, SNR had a significant effect on LLR latencies and interpeak amplitudes: Latencies decreased, and amplitudes increased as SNR improved. The presentation of contralateral noise had a significant effect on P1 and N1 latencies, both of which decreased. LLR interpeak amplitudes significantly increased upon the presentation of contralateral noise. For the ipsilateral quiet condition, there were no significant effects of contralateral noise on LLR metrics. Though OAE magnitudes were significantly reduced upon presentation of contralateral noise, consistent significant relationships between OAE magnitude changes and changes in the LLR metrics were not found.
Findings suggest that the presentation of contralateral noise enhances the neural response to an ipsilateral noise, potentially through MOC efferent feedback.
过去的动物实验证据表明，神经信噪比（SNR）通过内侧橄榄耳蜗反射（MOCR）的作用进行调节。这通常被称为解掩蔽。然而，人类解掩蔽的证据有限，这可能是由于使用耳声发射（一种神经前指标）来测量MOCR的传统方法所致。晚潜伏期反应（LLR）的振幅和潜伏期对SNR的变化敏感，可能提供一种在神经水平上无创评估MOCR解掩蔽的方法。本研究的目的是使用LLR来研究人类中MOCR介导的同侧噪声增强。
招募了50名听力正常的成年人。在同侧安静和同侧噪声条件下，分别在有和没有对侧噪声呈现的情况下，测量60 dB SPL、1 kHz纯音的LLR。对于同侧噪声条件，以三种不同水平呈现噪声，以实现+5 dB、+15 dB和+25 dB的SNR。对侧噪声始终为60 dB SPL的白噪声。测量所有条件下的LLR潜伏期（P1、N1和P2）和峰间振幅（P1-N1和N1-P2）。此外，在同侧安静条件下，分别在有和没有对侧噪声的情况下，测量1 kHz短音的耳声发射（OAE）。OAE和LLR使用相同的对侧噪声。
对于同侧噪声条件，SNR对LLR潜伏期和峰间振幅有显著影响：随着SNR的改善，潜伏期缩短，振幅增加。对侧噪声的呈现对P1和N1潜伏期有显著影响，两者均缩短。对侧噪声呈现后，LLR峰间振幅显著增加。在同侧安静条件下，对侧噪声对LLR指标没有显著影响。尽管对侧噪声呈现后OAE幅度显著降低，但未发现OAE幅度变化与LLR指标变化之间存在一致的显著关系。
研究结果表明，对侧噪声的呈现可能通过MOC传出反馈增强了对同侧噪声的神经反应。
