Research Group Experimental Oto-rhino-laryngology (ExpORL), Department of Neurosciences, KU Leuven - University of Leuven, Herestraat 49, bus 721, Leuven 3000, Belgium.
Research Group Experimental Oto-rhino-laryngology (ExpORL), Department of Neurosciences, KU Leuven - University of Leuven, Herestraat 49, bus 721, Leuven 3000, Belgium.
Hear Res. 2021 Apr;403:108175. doi: 10.1016/j.heares.2021.108175. Epub 2021 Jan 14.
Objectives In recent years, there has been significant interest in recovering the temporal envelope of a speech signal from the neural response to investigate neural speech processing. The research focus is now broadening from neural speech processing in normal-hearing listeners towards hearing-impaired listeners. When testing hearing-impaired listeners, speech has to be amplified to resemble the effect of a hearing aid and compensate for peripheral hearing loss. Today it is not known with certainty how or if neural speech tracking is influenced by sound amplification. As these higher intensities could influence the outcome, we investigated the influence of stimulus intensity on neural speech tracking. Design We recorded the electroencephalogram (EEG) of 20 normal-hearing participants while they listened to a narrated story. The story was presented at intensities from 10 to 80 dB A. To investigate the brain responses, we analyzed neural tracking of the speech envelope by reconstructing the envelope from the EEG using a linear decoder and by correlating the reconstructed with the actual envelope. We investigated the delta (0.5-4 Hz) and the theta (4-8 Hz) band for each intensity. We also investigated the latencies and amplitudes of the responses in more detail using temporal response functions, which are the estimated linear response functions between the stimulus envelope and the EEG. Results Neural envelope tracking is dependent on stimulus intensity in both the TRF and envelope reconstruction analysis. However, provided that the decoder is applied to the same stimulus intensity as it was trained on, envelope reconstruction is robust to stimulus intensity. Besides, neural envelope tracking in the delta (but not theta) band seems to relate to speech intelligibility. Similar to the linear decoder analysis, TRF amplitudes and latencies are dependent on stimulus intensity: The amplitude of peak 1 (30-50 ms) increases, and the latency of peak 2 (140-160 ms) decreases with increasing stimulus intensity. Conclusion Although brain responses are influenced by stimulus intensity, neural envelope tracking is robust to stimulus intensity when using the same intensity to test and train the decoder. Therefore we can assume that intensity will not be a confounder when testing hearing-impaired participants with amplified speech using the linear decoder approach. In addition, neural envelope tracking in the delta band appears to be correlated with speech intelligibility, showing the potential of neural envelope tracking as an objective measure of speech intelligibility.
目的 近年来，人们对从神经反应中恢复语音信号的时域包络以研究神经语音处理产生了浓厚的兴趣。研究重点现已从正常听力受试者的神经语音处理扩展到听力受损受试者。在测试听力受损的受试者时，语音必须放大以模拟助听器的效果并补偿外围听力损失。目前尚不清楚神经语音跟踪是否受到声音放大的影响，以及影响的方式。由于这些更高的强度可能会影响结果，因此我们研究了刺激强度对神经语音跟踪的影响。 设计 我们记录了 20 名正常听力受试者在听叙述故事时的脑电图（EEG）。故事以 10 到 80 分贝 A 的强度呈现。为了研究大脑反应，我们通过使用线性解码器从 EEG 重建语音包络并通过将重建的与实际包络相关联来分析语音包络的神经跟踪。我们研究了每个强度的 delta（0.5-4 Hz）和 theta（4-8 Hz）频段。我们还使用时间响应函数更详细地研究了响应的潜伏期和幅度，时间响应函数是刺激包络和 EEG 之间估计的线性响应函数。 结果 在 TRF 和包络重建分析中，神经包络跟踪都依赖于刺激强度。但是，只要解码器应用于与训练时相同的刺激强度，包络重建就对刺激强度具有鲁棒性。此外，delta 频段（而非 theta 频段）中的神经包络跟踪似乎与语音可懂度有关。与线性解码器分析类似，TRF 幅度和潜伏期都依赖于刺激强度：峰 1（30-50 ms）的幅度增加，而峰 2（140-160 ms）的潜伏期随着刺激强度的增加而减小。 结论 尽管大脑反应受到刺激强度的影响，但当使用相同的强度来测试和解码器时，神经包络跟踪对刺激强度具有鲁棒性。因此，我们可以假设，在使用线性解码器方法对使用放大语音的听力受损参与者进行测试时，强度不会成为混杂因素。此外，delta 频段中的神经包络跟踪似乎与语音可懂度相关，表明神经包络跟踪作为语音可懂度的客观测量具有潜力。
