Neural and Perceptual Mechanisms for Coding Frequency Modulation

频率和振幅的调制是自然声音的基本属性。频率调制 (FM)对于声音分离、说话者识别以及语音和音乐中的韵律跟踪至关重要。 FM灵敏度随着正常老化和听力损失而降低，从而限制了人的通信能力。 老年人和听力受损的人。重要的是，辅助听力设备，如助听器和 人工耳蜗植入物在恢复FM敏感性方面并不成功。这种限制部分是由于 对FM编码背后的神经和感知机制的不完全理解。人类调频 感知在低速率（fm < ~5-10 Hz）和载波频率（fc < 4-5 kHz）下最好，这也是最常见的。 与语音和音乐相关，灵敏度在更快的速率和/或更高的载波下恶化。这些比率和 人们普遍认为，与载波相关的趋势反映了FM编码的双重机制： 精确锁相时间精细结构（TFS;时间码），另一个基于保真度 跨音调定位轴的耳蜗滤波和幅度调制（AM）处理（包络/位置代码）。 至关重要的是，慢速率，低载波调频已被视为金标准的行为措施，单声道 TFS编码。拟议中的研究将使用心理声学，计算建模， 脑电图（EEG）测试的假设，神经和感知FM敏感性在正常- 听力收听者可以替代地由单一神经位置代码来解释。Aim 1将提供新的见解， 时间编码的必要性，在调频检测在年轻，听力正常的听众通过测试是否经典 时间编码的行为证据也被发现时，使用新的调幅刺激， 没有TFS提示。Aim 2使用严格的大规模方法来测试感知和神经退化是否 如目前所认为的，随着年龄的增长，在慢FM处理中，可以通过TFS编码来解释，或者这些 变化也可以在基于位置编码的统一框架内解释。这一目标具有重要意义 临床意义，因为它提供了第一个大规模的复制和扩展的一个新的脑电图措施， FM跟随响应（FMFR），其已被声称反映TFS编码对慢FM的个体保真度。 本研究结果将为今后的听障研究提供初步的数据和基础， 确定这些关键的声学线索如何受到不同类型和程度的听力损失的影响， 感知和神经反应都可以在统一的理论框架内解释， 为未来的感官干预提供了新的基础。

Modulations in frequency and amplitude are fundamental attributes of natural sounds. Frequency modulation (FM) is essential for sound segregation, talker recognition, and the tracking of prosody in speech and music. FM sensitivity degrades with normal aging and hearing loss, thereby restricting the communication abilities of older and hearing-impaired individuals. Importantly, assistive listening devices, such as hearing aids and cochlear implants, have not been successful in restoring FM sensitivity. This limitation is in part due to an incomplete understanding of the neural and perceptual mechanisms underlying FM coding. Human FM perception is best at the low rates (fm < ~5-10 Hz) and carrier frequencies (fc < 4-5 kHz) that are also most relevant for speech and music, with sensitivity worsening at faster rates and/or higher carriers. These rate and carrier-dependent trends are widely believed to reflect dual mechanisms for FM coding: one mechanism based on precise phase-locking to temporal fine structure (TFS; time code), and another based on the fidelity of cochlear filtering across the tonotopic axis and amplitude modulation (AM) processing (envelope/place code). Crucially, slow-rate, low-carrier FM has been treated as the gold standard behavioral measure for monaural TFS coding. The proposed research will use a combination of psychoacoustics, computational modeling, and electroencephalography (EEG) to test the hypothesis that neural and perceptual FM sensitivity in normal- hearing listeners can instead be explained by a unitary neural place code. Aim 1 will provide new insights into the necessity of time coding in FM detection in young, normal-hearing listeners by testing whether classic behavioral evidence for time coding is also found when using novel amplitude-modulated stimuli that provide no TFS cues. Aim 2 uses a rigorous, large-scale approach to test whether perceptual and neural degradations in slow FM processing with age can be accounted for by TFS coding, as currently believed, or whether these changes too can be explained within the unified framework based on place coding. This aim has important clinical implications, as it provides the first large-scale replication and extension of a new EEG measure, the FM following response (FMFR), which has been claimed to reflect individual fidelity of TFS coding to slow FM. The results will provide the preliminary data and foundation for future studies with hearing-impaired listeners to determine how these critical acoustic cues are affected by different types and degrees of hearing loss and how both perceptual and neural responses can be explained within a unifying theoretical framework in order to provide a novel basis for future sensory interventions.