Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA.
J Assoc Res Otolaryngol. 2012 Apr;13(2):219-35. doi: 10.1007/s10162-011-0310-3.
The medial olivocochlear reflex (MOCR) has been hypothesized to provide benefit for listening in noise. Strong physiological support for an anti-masking role for the MOCR has come from the observation that auditory nerve (AN) fibers exhibit reduced firing to sustained noise and increased sensitivity to tones when the MOCR is elicited. The present study extended a well-established computational model for normal-hearing and hearing-impaired AN responses to demonstrate that these anti-masking effects can be accounted for by reducing outer hair cell (OHC) gain, which is a primary effect of the MOCR. Tone responses in noise were examined systematically as a function of tone level, noise level, and OHC gain. Signal detection theory was used to predict detection and discrimination for different spontaneous rate fiber groups. Decreasing OHC gain decreased the sustained noise response and increased maximum discharge rate to the tone, thus modeling the ability of the MOCR to decompress AN fiber rate-level functions. Comparing the present modeling results with previous data from AN fibers in decerebrate cats suggests that the ipsilateral masking noise used in the physiological study may have elicited up to 20 dB of OHC gain reduction in addition to that inferred from the contralateral noise effects. Reducing OHC gain in the model also extended the dynamic range for discrimination over a wide range of background noise levels. For each masker level, an optimal OHC gain reduction was predicted (i.e., where maximum discrimination was achieved without increased detection threshold). These optimal gain reductions increased with masker level and were physiologically realistic. Thus, reducing OHC gain can improve tone-in-noise discrimination even though it may produce a “hearing loss” in quiet. Combining MOCR effects with the sensorineural hearing loss effects already captured by this computational AN model will be beneficial for exploring the implications of their interaction for the difficulties hearing-impaired listeners have in noisy situations.
中橄榄耳蜗反射（MOCR）被假设为在噪声环境中提供聆听的益处。MOCR 具有抗掩蔽作用的强有力的生理学支持来自于这样的观察，即听觉神经（AN）纤维对持续噪声的放电减少，并且对当 MOCR 被引发时的音调的敏感性增加。本研究扩展了一个用于正常听力和听力受损的 AN 反应的既定计算模型，以证明这些抗掩蔽效应可以通过降低外毛细胞（OHC）增益来解释，这是 MOCR 的主要作用。作为音调水平、噪声水平和 OHC 增益的函数，系统地检查了噪声中的音调响应。使用信号检测理论来预测不同自发率纤维组的检测和辨别。降低 OHC 增益会降低持续噪声的反应，并增加音调的最大放电率，从而模拟 MOCR 对 AN 纤维率级函数的解压能力。将本研究的建模结果与去大脑猫中的 AN 纤维的先前数据进行比较表明，在生理研究中使用的同侧掩蔽噪声除了从对侧噪声效应推断出的增益减少之外，可能还引发了多达 20 dB 的 OHC 增益减少。在模型中降低 OHC 增益还扩展了在广泛的背景噪声水平范围内的辨别动态范围。对于每个掩蔽器水平，预测了最佳的 OHC 增益减少（即，在不增加检测阈值的情况下实现最大辨别）。这些最佳增益减少随着掩蔽器水平的增加而增加，并且是生理现实的。因此，降低 OHC 增益可以改善噪声中的音调辨别能力，即使它可能在安静环境中产生“听力损失”。将 MOCR 效应与该计算 AN 模型已经捕获的感觉神经性听力损失效应结合起来，将有利于探索它们相互作用对听力受损者在嘈杂环境中遇到困难的影响。
