Department for Cognitive Neuroscience, Faculty of Biology, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld, Germany.
Department for Cognitive Neuroscience, Faculty of Biology, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld, Germany.
Neuroimage. 2021 Jun;233:117958. doi: 10.1016/j.neuroimage.2021.117958. Epub 2021 Mar 17.
The representation of speech in the brain is often examined by measuring the alignment of rhythmic brain activity to the speech envelope. To conveniently quantify this alignment (termed 'speech tracking') many studies consider the broadband speech envelope, which combines acoustic fluctuations across the spectral range. Using EEG recordings, we show that using this broadband envelope can provide a distorted picture on speech encoding. We systematically investigated the encoding of spectrally-limited speech-derived envelopes presented by individual and multiple noise carriers in the human brain. Tracking in the 1 to 6 Hz EEG bands differentially reflected low (0.2 - 0.83 kHz) and high (2.66 - 8 kHz) frequency speech-derived envelopes. This was independent of the specific carrier frequency but sensitive to attentional manipulations, and may reflect the context-dependent emphasis of information from distinct spectral ranges of the speech envelope in low frequency brain activity. As low and high frequency speech envelopes relate to distinct phonemic features, our results suggest that functionally distinct processes contribute to speech tracking in the same EEG bands, and are easily confounded when considering the broadband speech envelope.
大脑中言语的表现通常通过测量节律性脑活动与言语包络的对齐程度来进行检查。为了方便地量化这种对齐（称为“言语跟踪”），许多研究考虑使用宽带言语包络，它结合了频谱范围内的声学波动。我们使用 EEG 记录表明，使用这种宽带包络可能会对言语编码产生扭曲的图像。我们系统地研究了人类大脑中单个和多个噪声载体呈现的受频谱限制的言语衍生包络的编码。在 1 到 6 Hz 的 EEG 频段中的跟踪差异地反映了低频（0.2-0.83 kHz）和高频（2.66-8 kHz）言语衍生包络。这与特定的载波频率无关，但对注意力操作敏感，并且可能反映了低频脑活动中来自言语包络不同频谱范围的信息的上下文相关强调。由于低频和高频言语包络与不同的音位特征相关，因此我们的结果表明，功能不同的过程有助于相同 EEG 频段中的言语跟踪，并且在考虑宽带言语包络时很容易混淆。
