Slama Michaël C C, Delgutte Bertrand
Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts 02114, Speech and Hearing Bioscience and Technology Program, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts 02114, Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts 02114, and Speech and Hearing Bioscience and Technology Program, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
J Neurosci. 2015 Mar 11;35(10):4452-68. doi: 10.1523/JNEUROSCI.3615-14.2015.
Speech reception depends critically on temporal modulations in the amplitude envelope of the speech signal. Reverberation encountered in everyday environments can substantially attenuate these modulations. To assess the effect of reverberation on the neural coding of amplitude envelope, we recorded from single units in the inferior colliculus (IC) of unanesthetized rabbit using sinusoidally amplitude modulated (AM) broadband noise stimuli presented in simulated anechoic and reverberant environments. Although reverberation degraded both rate and temporal coding of AM in IC neurons, in most neurons, the degradation in temporal coding was smaller than the AM attenuation in the stimulus. This compensation could largely be accounted for by the compressive shape of the modulation input-output function (MIOF), which describes the nonlinear transformation of modulation depth from acoustic stimuli into neural responses. Additionally, in a subset of neurons, the temporal coding of AM was better for reverberant stimuli than for anechoic stimuli having the same modulation depth at the ear. Using hybrid anechoic stimuli that selectively possess certain properties of reverberant sounds, we show that this reverberant advantage is not caused by envelope distortion, static interaural decorrelation, or spectral coloration. Overall, our results suggest that the auditory system may possess dual mechanisms that make the coding of amplitude envelope relatively robust in reverberation: one general mechanism operating for all stimuli with small modulation depths, and another mechanism dependent on very specific properties of reverberant stimuli, possibly the periodic fluctuations in interaural correlation at the modulation frequency.
言语接收严重依赖于言语信号幅度包络中的时间调制。在日常环境中遇到的混响会大幅削弱这些调制。为了评估混响对幅度包络神经编码的影响，我们在未麻醉兔子的下丘（IC）中记录单个神经元的活动，使用在模拟消声和混响环境中呈现的正弦幅度调制（AM）宽带噪声刺激。尽管混响降低了IC神经元中AM的速率编码和时间编码，但在大多数神经元中，时间编码的降解小于刺激中AM的衰减。这种补偿很大程度上可以由调制输入 - 输出函数（MIOF）的压缩形状来解释，该函数描述了从声刺激到神经反应的调制深度的非线性转换。此外，在一部分神经元中，对于混响刺激，AM的时间编码比在耳朵处具有相同调制深度的消声刺激更好。使用选择性地具有混响声某些特性的混合消声刺激，我们表明这种混响优势不是由包络失真、静态双耳解相关或频谱染色引起的。总体而言，我们的结果表明，听觉系统可能具有双重机制，使幅度包络的编码在混响中相对稳健：一种是对所有调制深度较小的刺激起作用的一般机制，另一种是依赖于混响刺激非常特定特性的机制，可能是调制频率处双耳相关性的周期性波动。
