Temporal Resolution of Cochlear and Auditory Nerve Responses in Older Adults

描述(申请人提供)：衰老会削弱听者处理时间上复杂的声音刺激的能力，如语音。这种时间处理能力下降的原因包括与年龄相关的中枢听觉神经系统的变化。随着年龄的增长，周围听觉系统内的听觉神经纤维活动也变得更加不同步。此外，许多老年人患有耳蜗性听力损失，这可能通过减少耳蜗非线性而有效地限制时间处理能力。这项研究的长期目标是确定衰老造成的言语理解障碍的听觉基础。这项应用的目的是确定在多大程度上由听神经水平或听神经水平之前的年龄相关变化导致对时变语音线索的异常感知。中心假设是，衰老改变了耳蜗机能和听神经反应，从而干扰了理解语言的能力。这一假说的基础是有证据表明，时间语音特征的编码涉及非线性的耳蜗神经反应和同步的神经反应。评估老年人的外周(耳蜗、机械和听神经)时间加工是必要的，因为目前还不知道外周计时缺陷如何导致对时间语音线索的异常感知。该方法是测量生理反应，修改最近发表的用于评估时间分辨率和基底膜压迫的心理物理技术。然后，将这些测量结果与同一组听力正常或受损的老年人和年轻人在临时言语任务中的表现进行比较。具体目标1将基于使用前向掩蔽范式获得的听神经复合动作电位(CAPS)来测量时间分辨率。具体目标2将根据刺激频率耳声发射(SFOAEs)估计耳蜗机压和行程时间。对SFOAE和CAP反应的比较将确定老年人听觉系统中外毛细胞功能改变听神经反应的幅度和时间的程度。具体目标3将决定在临时言语任务中的表现是否取决于耳蜗机能反应和听神经反应。这项工作的基本原理是，一旦知道减少时间处理的来源，就可以设计出修复个别患者的时间处理问题的助听器配戴和康复训练策略。所提出的生理措施不会受到与年龄相关的认知或记忆变化的干扰。因此，这项研究具有额外的意义，因为它可能导致针对减少时间加工的来源的临床工具的开发。

DESCRIPTION (provided by applicant): Aging impairs the ability of listeners to process temporally complex acoustic stimuli, such as speech. Sources of this decline in temporal processing ability include age-related changes in the central auditory nervous system. Auditory nerve fiber activity within the peripheral auditory system also becomes more asynchronous with age. Furthermore, many older adults suffer from cochlear hearing loss, which may effectively limit temporal processing ability by reducing cochlear nonlinearity. The long-term goal of this research is to determine the auditory basis of speech understanding deficits imposed by aging. The objective of this application is to determine the extent to which abnormal perception of time-varying speech cues results from age-related changes at or before the level of the auditory nerve. The central hypothesis is that aging alters cochlear mechanical and auditory nerve responses, thereby interfering with the ability to understand speech. This hypothesis is based on evidence that nonlinear cochlear responses and synchronized neural responses are involved in the encoding of temporal speech features. Evaluation of peripheral (cochlear mechanical and auditory nerve) temporal processing in older adults is necessary because it is not known how peripheral timing deficits contribute to abnormal perception of temporal speech cues. The approach is to measure physiological responses, modifying recently-published psychophysical techniques used to assess temporal resolution and basilar membrane compression. These measures will then be compared to performance on temporal speech tasks in the same groups of elderly and young adults with normal or impaired hearing. Specific Aim 1 will measure temporal resolution based on auditory nerve compound action potentials (CAPs) obtained using a forward-masking paradigm. Specific Aim 2 will estimate cochlear mechanical compression and travel time from stimulus-frequency otoacoustic emissions (SFOAEs). Comparisons of SFOAE and CAP responses will determine the extent that the amplitude and timing of auditory nerve responses is altered by outer hair cell function in the auditory systems of older adults. Specific Aim 3 will determine whether performance on a temporal speech task depends on cochlear mechanical and auditory nerve responses. The rationale for this work is that once sources of reduced temporal processing are known, hearing aid fitting and rehabilitative training strategies can be devised that remediate the temporal processing problems of individual patients. Proposed physiological measures are free from confounding by age-related changes in cognition or memory. Therefore, this research has additional significance in that it may lead to development of clinical tools that will target sources of reduced temporal processing.