Effects of noise-induced and metabolic hearing losses on temporal coding in noise

描述（由申请人提供）：听力损失的人在嘈杂的环境中理解言语通常有很大的困难，即使有助听器的帮助。知觉研究表明，快速变化的精细结构的时间处理缺陷是负责任的。然而，动物的神经生理学研究通常没有发现时间加工的缺陷。因此，言语可理解性差的基础仍不清楚。然而，现有的神经生理学研究是有限的，因为它们只测量了安静条件下的时间处理，并且主要检查了一种常见的听力损失形式（噪音诱发）。此外，这些研究没有检查宽频刺激的时间反应的频率调谐。本文提出的龙猫听觉神经纤维反应的神经生理学研究通过(1)量化背景噪音下的时间处理，(2)检查两种形式的听力损失，(3)量化时间反应的频率调谐，解决了这些局限性。Aim 1使用声学过度暴露来研究噪声性听力损失（NIHL），而Aim 2使用呋塞米注射来研究代谢性听力损失（MHL；呋塞米注射模拟这种常见的与年龄相关的听力损失，效果良好）。声刺激包括纯音和调幅音。时间处理将使用经典的矢量强度和从洗牌相关图计算的新相关指标进行量化。最后，Aim 3将采用时间响应对白噪声的维纳核分析来研究NIHL和MHL动物时间加工的频率调谐。提出的实验结果将用于检验三个假设。首先，听力损失会导致对背景噪声的时间处理能力下降。该假设基于信号处理模型，该模型预测随着听觉滤波器带宽的增加（即在处理任务期间更多的噪声能量进入滤波器，从而增加掩蔽），背景噪声对信号响应的影响更强。第二，根据听觉感知的相关研究，听力损失对颞叶精细结构加工的影响大于对振幅包络的影响。最后，对于一定程度的听力损失，与MHL相比，NIHL预计会导致更大的噪音时间处理缺陷。这一假设是基于先前在NIHL研究中观察到的带有超敏感尾的调谐曲线，而非MHL。在信号处理过程中，超敏感的尾部应该允许更多的噪声能量进入，从而在更大程度上降低时间编码。提出的研究将推进我们的知识在听觉处理的缺陷与两种常见形式的听力损失。本研究和其他研究确定的具体缺陷可用于指导新技术的开发（例如助听器和人工耳蜗设计），旨在恢复听力损失患者在真实听力条件下的语言感知。

DESCRIPTION (provided by applicant): People with hearing loss often have great difficulty understanding speech in noisy environments, even with assistance from a hearing aid. Perceptual studies suggest that a deficit in temporal processing of rapidly varying fine structure is responsible. However, neurophysiological studies in animals have generally not found a deficit in temporal processing. Hence, the basis for poor speech intelligibility remains unclear. The existing neurophysiological studies are limited, however, because they measured temporal processing under quiet conditions and primarily examined only one commonly occurring form of hearing loss (noise- induced). Furthermore, these studies did not examine the frequency tuning of temporal responses to broadband stimuli. The proposed neurophysiological study of auditory nerve fiber responses in chinchillas resolves these limitations by (1) quantifying temporal processing in background noise, where current hearing aids often fail, (2) examining two forms of hearing loss, and (3) quantifying the frequency tuning of temporal responses. Aim 1 uses acoustic overexposures to study noise-induced hearing loss (NIHL), while Aim 2 uses furosemide injections to study metabolic hearing loss (MHL; furosemide injections simulate this common form of age-related hearing loss with good results). Acoustic stimuli will include pure tones and amplitude modulated tones. Temporal processing will be quantified using classical vector strength and novel correlation indices computed from shuffled correlograms. Finally, Aim 3 will employ Wiener kernel analyses of temporal responses to white noise to study the frequency tuning of temporal processing in animals with NIHL an MHL. The results of the proposed experiments will be used to test three hypotheses. First, hearing loss is expected to result in a deficit in temporal processing in background noise. This hypothesis is based on models of signal processing, which predict a stronger effect of background noise on the response to a signal following an increase in auditory filter bandwidth (i.e. more noise energy enters the filter during the processing task, thereby increasing masking). Second, based on the related studies of auditory perception, hearing loss should degrade processing of temporal fine structure more than the amplitude envelope. Finally, for a given degree of hearing loss, NIHL is expected to result in a greater deficit in temporal processing in noise than MHL. This hypothesis is based on previous observations of tuning curves with hypersensitive tails in studies of NIHL, but not MHL. The hypersensitive tails should allow more noise energy to enter during signal processing, thereby degrading temporal coding to a greater degree. The proposed research will advance our knowledge of the deficits in auditory processing associated with two common forms of hearing loss. The specific deficits identified by this and other studies can be used to guide the development of new technologies (e.g. hearing-aid and cochlear-implant designs) aimed at restoring speech perception under real-world listening conditions in people with hearing loss. PUBLIC HEALTH RELEVANCE: Achieving the long term goal of greater speech intelligibility in people with hearing loss will require a detailed knowledge of the deficits in auditory processing associated with hearing loss. The proposed study of auditory nerve fiber responses in chinchillas advances this knowledge by quantifying the effects of two common forms of hearing loss on (1) temporal processing under noisy, real-world listening conditions and (2) temporal responses to broadband stimuli. The detailed knowledge provided by the proposed study and others will help guide the development of new technologies such as hearing-aid and cochlear implant designs aimed at restoring speech perception in people with hearing loss.