Bachmann Florine L, MacDonald Ewen N, Hjortkjær Jens
Hearing Systems Section, Department of Health Technology, Technical University of Denmark, Lyngby, Denmark.
Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada.
Front Neurosci. 2021 Dec 21;15:738408. doi: 10.3389/fnins.2021.738408. eCollection 2021.
Linearized encoding models are increasingly employed to model cortical responses to running speech. Recent extensions to subcortical responses suggest clinical perspectives, potentially complementing auditory brainstem responses (ABRs) or frequency-following responses (FFRs) that are current clinical standards. However, while it is well-known that the auditory brainstem responds both to transient amplitude variations and the stimulus periodicity that gives rise to pitch, these features co-vary in running speech. Here, we discuss challenges in disentangling the features that drive the subcortical response to running speech. Cortical and subcortical electroencephalographic (EEG) responses to running speech from 19 normal-hearing listeners (12 female) were analyzed. Using forward regression models, we confirm that responses to the rectified broadband speech signal yield temporal response functions consistent with wave V of the ABR, as shown in previous work. Peak latency and amplitude of the speech-evoked brainstem response were correlated with standard click-evoked ABRs recorded at the vertex electrode (Cz). Similar responses could be obtained using the fundamental frequency (F0) of the speech signal as model predictor. However, simulations indicated that dissociating responses to temporal fine structure at the F0 from broadband amplitude variations is not possible given the high co-variance of the features and the poor signal-to-noise ratio (SNR) of subcortical EEG responses. In cortex, both simulations and data replicated previous findings indicating that envelope tracking on frontal electrodes can be dissociated from responses to slow variations in F0 (relative pitch). Yet, no association between subcortical F0-tracking and cortical responses to relative pitch could be detected. These results indicate that while subcortical speech responses are comparable to click-evoked ABRs, dissociating pitch-related processing in the auditory brainstem may be challenging with natural speech stimuli.
线性化编码模型越来越多地被用于对皮层对连续语音的反应进行建模。最近对皮层下反应的扩展研究提出了一些临床观点，可能会补充当前临床标准中的听觉脑干反应（ABR）或频率跟随反应（FFR）。然而，虽然众所周知听觉脑干对瞬态幅度变化和产生音高的刺激周期性都有反应，但这些特征在连续语音中是共同变化的。在这里，我们讨论了在区分驱动皮层下对连续语音反应的特征方面所面临的挑战。分析了19名听力正常的听众（12名女性）对连续语音的皮层和皮层下脑电图（EEG）反应。使用前向回归模型，我们证实，如先前研究所示，对整流后的宽带语音信号的反应产生了与ABR的V波一致的时间反应函数。语音诱发的脑干反应的峰值潜伏期和幅度与在头顶电极（Cz）记录的标准点击诱发ABR相关。使用语音信号的基频（F0）作为模型预测因子也可以获得类似的反应。然而，模拟表明，鉴于这些特征的高协方差以及皮层下EEG反应的低信噪比（SNR），不可能将对F0处时间精细结构的反应与宽带幅度变化区分开来。在皮层中，模拟和数据都重复了先前的研究结果，表明额叶电极上的包络跟踪可以与对F0缓慢变化（相对音高）的反应区分开来。然而，未检测到皮层下F0跟踪与皮层对相对音高的反应之间存在关联。这些结果表明，虽然皮层下语音反应与点击诱发的ABR相当，但在听觉脑干中区分与音高相关的处理可能对自然语音刺激具有挑战性。
