Individual differences in supra-threshold sound encoding

描述(申请人提供)：一个长期存在的谜题是，为什么听力阈值正常的听者在其他听觉任务上表现出如此巨大的差异。当任务涉及分离多个声源时，“正常听力”听者之间的差异尤其明显，例如，当听者必须依赖选择性听觉注意时。最近的动物研究表明，噪声暴露可以损害听神经纤维的突触效能，而不会永久性地改变听力阈值，从而产生听神经病。低自发频率的听神经纤维对编码阈值以上声音的时间内容特别重要，可能优先受到影响。与动物研究一致，我们在正常阈值听者中的初步结果表明，在选择性注意任务上的被试之间的表现差异与旨在揭示高于阈值水平的时间编码保真度的心理物理和生理测量有关。我们假设，听神经病可能比之前认识到的要常见得多：听力正常的年轻听者可能在他们的听神经纤维编码超阈值时间信息的保真度方面有所不同，从而影响他们在日常环境中的沟通能力。在没有阈值偏移的动物中，声音暴露会导致超过阈值的缺陷；因此，我们还假设，具有 按传统定义，暴露在噪声中的听力损失可能还会遭受超过阈值的缺陷，这在很大程度上造成了沟通困难。这个项目的主要目标是对一群年轻的、听力正常的听众的听神经病进行量化。我们还将探索超阈值编码如何有助于由于噪声暴露而导致阈值升高的听者的表现差异。我们将：目标1)表征听觉通路皮质下部分阈值以上声音编码的个体差异；目标2)表征选择性参与能力的个体差异，并将它们与 编码保真度的差异；以及Aim 3)表征了超过阈值的声音编码保真度如何导致轻度至中度高频听力损失的听众的表现差异。我们将比较来自相同听众的生理指标(脑干反应、失真产物耳声发射和皮质反应)和行为指标，并使用计算模型来揭示这些指标之间的关系。我们的结果将量化阈值以上声音的外围编码在正常和升高阈值的听者之间的差异，并将确定阈值上的差异如何影响常见社交环境中的沟通能力。我们的结果可能会导致临床 超阈值听力保真度测试，量化了导致听力图相似的听者之间沟通能力差异的一个因素。

DESCRIPTION (provided by applicant): A long-standing puzzle is why listeners with normal hearing thresholds show such enormous variation in performance on other auditory tasks. Differences among "normal hearing" listeners are particularly pronounced when tasks involve separating multiple sound sources, such as when listeners must rely on selective auditory attention. Recent animal work shows that noise exposure can damage the synaptic efficacy of auditory nerve fibers without permanently altering hearing thresholds, producing auditory neuropathy. Low-spontaneous rate auditory nerve fibers, which are especially important for encoding the temporal content of supra-threshold sound, may be preferentially affected. Consistent with animal studies, our preliminary results in listeners with normal thresholds suggest that inter-subject performance differences on selective attention tasks correlate with psychophysical and physiological measures designed to reveal the fidelity of temporal coding at supra-threshold levels. We hypothesize that auditory neuropathy may be much more common than previously recognized: young listeners with normal hearing thresholds may differ in the fidelity with which their auditory nerve fibers encode supra-threshold temporal information, affecting their ability to communicate in everyday settings. Sound exposure leads to supra-threshold deficits in animals without threshold shifts; thus, we also postulate that listeners with conventionally defined hearing loss from noise exposure likely also suffer from supra-threshold deficits that contribute substantially to communication difficulties. The main objective of this project is to quantify auditory neuropathy in a cohort of young, "normal hearing" listeners. We will also explore how supra-threshold encoding contributes to performance differences in listeners with elevated thresholds due to noise exposure. We will: Aim 1) characterize individual differences in supra-threshold sound encoding in subcortical portions of the auditory pathway; Aim 2) characterize individual differences in the ability to selectively attend, and relate them to differences in coding fidelity; and Aim 3) characterize how supra-threshold sound encoding fidelity contributes to performance differences for listeners with mild to moderate high-frequency hearing loss. We will compare physiological (brainstem responses, distortion product otoacoustic emissions, and cortical responses) and behavioral measures from the same listeners and use computational models to unravel the relationships between these metrics. Our results will quantify how peripheral encoding of supra-threshold sound differs across listeners with both normal and elevated thresholds, and will establish how supra-threshold differences affect the ability to communication in common social settings. Our results could lead to a clinical test of supra-threshold hearing fidelity, quantifying one factor leading to differences in communication ability amongst listeners with similar audiograms.