Sayles Mark, Stasiak Arkadiusz, Winter Ian M
Centre for the Neural Basis of Hearing, The Physiological Laboratory, Department of Physiology, Development and Neuroscience, University of Cambridge Cambridge, UK.
Front Syst Neurosci. 2015 Jan 12;8:248. doi: 10.3389/fnsys.2014.00248. eCollection 2014.
The auditory system typically processes information from concurrently active sound sources (e.g., two voices speaking at once), in the presence of multiple delayed, attenuated and distorted sound-wave reflections (reverberation). Brainstem circuits help segregate these complex acoustic mixtures into "auditory objects." Psychophysical studies demonstrate a strong interaction between reverberation and fundamental-frequency (F0) modulation, leading to impaired segregation of competing vowels when segregation is on the basis of F0 differences. Neurophysiological studies of complex-sound segregation have concentrated on sounds with steady F0s, in anechoic environments. However, F0 modulation and reverberation are quasi-ubiquitous. We examine the ability of 129 single units in the ventral cochlear nucleus (VCN) of the anesthetized guinea pig to segregate the concurrent synthetic vowel sounds /a/ and /i/, based on temporal discharge patterns under closed-field conditions. We address the effects of added real-room reverberation, F0 modulation, and the interaction of these two factors, on brainstem neural segregation of voiced speech sounds. A firing-rate representation of single-vowels' spectral envelopes is robust to the combination of F0 modulation and reverberation: local firing-rate maxima and minima across the tonotopic array code vowel-formant structure. However, single-vowel F0-related periodicity information in shuffled inter-spike interval distributions is significantly degraded in the combined presence of reverberation and F0 modulation. Hence, segregation of double-vowels' spectral energy into two streams (corresponding to the two vowels), on the basis of temporal discharge patterns, is impaired by reverberation; specifically when F0 is modulated. All unit types (primary-like, chopper, onset) are similarly affected. These results offer neurophysiological insights to perceptual organization of complex acoustic scenes under realistically challenging listening conditions.
听觉系统通常在存在多个延迟、衰减和失真的声波反射（混响）的情况下，处理来自同时活跃的声源（例如，同时说话的两个人的声音）的信息。脑干回路有助于将这些复杂的声学混合信号分离成“听觉对象”。心理物理学研究表明，混响与基频（F0）调制之间存在强烈的相互作用，当基于F0差异进行分离时，会导致竞争元音的分离受损。复杂声音分离的神经生理学研究集中在无回声环境中具有稳定F0的声音上。然而，F0调制和混响几乎无处不在。我们研究了麻醉豚鼠腹侧耳蜗核（VCN）中的129个单个神经元基于封闭场条件下的时间放电模式分离同时出现的合成元音/a/和/i/的能力。我们探讨了添加真实房间混响、F0调制以及这两个因素的相互作用对有声语音脑干神经分离的影响。单元音频谱包络的发放率表示对F0调制和混响的组合具有鲁棒性：在音调拓扑阵列上局部发放率的最大值和最小值编码元音共振峰结构。然而，在混响和F0调制同时存在的情况下，随机发放间隔分布中与单元音F0相关的周期性信息会显著退化。因此，基于时间放电模式将双元音的频谱能量分离成两个流（对应于两个元音）会受到混响的损害；特别是当F0被调制时。所有单元类型（初级样、斩波器、起始型）都受到类似的影响。这些结果为在现实挑战性听力条件下复杂声学场景的感知组织提供了神经生理学见解。
