Klinikum rechts der Isar, Technische Universität München Munich, Germany.
Medical Research Council Institute of Hearing Research, University Park Nottingham, UK.
Front Neurosci. 2014 May 27;8:112. doi: 10.3389/fnins.2014.00112. eCollection 2014.
The interaction of sound waves with the human pinna introduces high-frequency notches (5-10 kHz) in the stimulus spectrum that are thought to be useful for vertical sound localization. A common view is that these notches are encoded as rate profiles in the auditory nerve (AN). Here, we review previously published psychoacoustical evidence in humans and computer-model simulations of inner hair cell responses to noises with and without high-frequency spectral notches that dispute this view. We also present new recordings from guinea pig AN and "ideal observer" analyses of these recordings that suggest that discrimination between noises with and without high-frequency spectral notches is probably based on the information carried in the temporal pattern of AN discharges. The exact nature of the neural code involved remains nevertheless uncertain: computer model simulations suggest that high-frequency spectral notches are encoded in spike timing patterns that may be operant in the 4-7 kHz frequency regime, while "ideal observer" analysis of experimental neural responses suggest that an effective cue for high-frequency spectral discrimination may be based on sampling rates of spike arrivals of AN fibers using non-overlapping time binwidths of between 4 and 9 ms. Neural responses show that sensitivity to high-frequency notches is greatest for fibers with low and medium spontaneous rates than for fibers with high spontaneous rates. Based on this evidence, we conjecture that inter-subject variability at high-frequency spectral notch detection and, consequently, at vertical sound localization may partly reflect individual differences in the available number of functional medium- and low-spontaneous-rate fibers.
声波与人类耳廓的相互作用在刺激频谱中引入了高频（5-10 kHz）陷波，这些陷波被认为对垂直声音定位有用。一种常见的观点是，这些陷波被编码为听觉神经（AN）中的速率分布。在这里，我们回顾了以前在人类中发表的心理声学证据，以及对带有和不带有高频频谱陷波的噪声的内毛细胞反应的计算机模型模拟，这些模拟对这种观点提出了质疑。我们还展示了来自豚鼠 AN 的新记录以及对这些记录的“理想观察者”分析，这些记录表明，对带有和不带有高频频谱陷波的噪声的区分可能基于 AN 放电的时间模式所携带的信息。然而，所涉及的神经编码的确切性质仍然不确定：计算机模型模拟表明，高频频谱陷波被编码为可能在 4-7 kHz 频率范围内起作用的尖峰定时模式，而对实验神经反应的“理想观察者”分析表明，高频频谱区分的有效线索可能基于使用非重叠时间窗宽为 4 至 9 ms 的 AN 纤维的尖峰到达率进行采样。神经反应表明，对高频陷波的敏感性对于自发率低和中等的纤维比对自发率高的纤维最大。基于这一证据，我们推测，高频频谱陷波检测的个体间变异性，以及垂直声音定位的个体间变异性，可能部分反映了可用功能中、低自发率纤维数量的个体差异。
