Greenberg David, Monaghan Jessica J M, Dietz Mathias, Marquardt Torsten, McAlpine David
UCL Ear Institute, London, United Kingdom.
Department of Linguistics, Australian Hearing Hub, Macquarie University, Sydney, New South Wales, Australia; and
J Neurophysiol. 2017 Oct 1;118(4):2358-2370. doi: 10.1152/jn.01048.2015. Epub 2017 Jul 12.
Interaural time differences (ITDs) conveyed by the modulated envelopes of high-frequency sounds can serve as a cue for localizing a sound source. Klein-Hennig et al. ( 129: 3856, 2011) demonstrated the envelope attack (the rate at which stimulus energy in the envelope increases) and the duration of the pause (the interval between successive envelope pulses) as important factors affecting sensitivity to envelope ITDs in human listeners. Modulated sounds with rapid attacks and long pauses produce the lowest ITD discrimination thresholds. The duration of the envelope's sustained component (sustain) and the rate at which stimulus energy falls at the offset of the envelope (decay) are only minor factors. We assessed the responses of 71 single neurons, recorded from the midbrains of 15 urethane-anesthetized tri-colored guinea pigs, to envelope shapes in which the four envelope components, i.e., attack, sustain, decay, and pause, were systematically varied. We confirmed the importance of the attack and pause components in generating ITD-sensitive responses. Analysis of neural firing rates demonstrated more neurons (49/71) show ITD sensitivity in response to "damped" stimuli (fast attack and slow decay) compared with "ramped" stimuli (slow attack and fast decay) (14/71). Furthermore, the lowest threshold for the damped stimulus (91 μs) was lower by a factor of 4 than that for the temporally reversed ramped envelope shape (407 μs). The data confirm the importance of fast attacks and optimal pause durations in generating sensitivity to ITDs conveyed in the modulated envelopes of high-frequency sounds and are incompatible with models of ITD processing based on the integration of sound energy over time. Using single-neuron electrophysiology, we show that the precise shape of a sound's "energy envelope" is a critical factor in determining how well midbrain neurons are able to convey information about auditory spatial cues. Consistent with human behavioral performance, sounds with rapidly rising energy and relatively long intervals between energy bursts are best at conveying spatial information. The data suggest specific sound energy patterns that might best be applied to hearing devices to aid spatial listening.
高频声音调制包络所传达的耳间时间差（ITD）可作为声源定位的线索。克莱因 - 亨尼希等人（《神经科学杂志》129: 3856, 2011）证明，包络起始（包络中刺激能量增加的速率）和停顿持续时间（连续包络脉冲之间的间隔）是影响人类听众对包络ITD敏感度的重要因素。具有快速起始和长停顿的调制声音产生最低的ITD辨别阈值。包络持续成分（持续）的持续时间以及包络结束时刺激能量下降的速率（衰减）只是次要因素。我们评估了从15只经乌拉坦麻醉的三色豚鼠中脑记录的71个单神经元对包络形状的反应，其中包络的四个成分，即起始、持续、衰减和停顿，被系统地改变。我们证实了起始和停顿成分在产生ITD敏感反应中的重要性。对神经放电率的分析表明，与“斜坡形”刺激（缓慢起始和快速衰减）（14/71）相比，更多神经元（49/71）对“阻尼”刺激（快速起始和缓慢衰减）表现出ITD敏感性。此外，阻尼刺激的最低阈值（91微秒）比时间反转的斜坡形包络形状的阈值（407微秒）低4倍。数据证实了快速起始和最佳停顿持续时间在产生对高频声音调制包络中传达的ITD敏感度方面的重要性，并且与基于声音能量随时间积分来处理ITD的模型不相符。通过单神经元电生理学，我们表明声音“能量包络”的精确形状是决定中脑神经元能够多好地传达听觉空间线索信息时的关键因素。与人类行为表现一致，能量快速上升且能量爆发之间间隔相对较长的声音在传达空间信息方面表现最佳。数据表明了可能最适用于听力设备以辅助空间聆听的特定声音能量模式。
