Individual differences in supra-threshold sound encoding

描述（由申请人提供）：一个长期存在的困惑是，为什么听力阈值正常的听众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，例如当听众必须依赖选择性听觉注意时，“正常听力”听众之间的差异尤为明显。最近的动物实验表明，噪音暴露会损害听神经纤维的突触功能，但不会永久性地改变听力阈值，从而产生听神经病变。低自发率听觉神经纤维对编码超阈值声音的时间内容特别重要，可能优先受到影响。与动物实验结果一致，我们在正常阈值的听者身上的初步结果表明，选择性注意任务的主体间表现差异与旨在揭示超阈值水平下时间编码保真度的心理物理和生理测量相关。我们假设听神经病变可能比以前认识到的更常见：听力阈值正常的年轻听者的听觉神经纤维编码超阈值时间信息的保真度可能不同，从而影响他们在日常环境中的沟通能力。在没有阈值移位的动物中，声音暴露导致超阈值缺陷；因此，我们也假设听众

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.