Delta/theta band EEG differentially tracks low and high frequency speech envelopes
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 overall speech envelope, which combines acoustic fluctuations across the spectral range. Using EEG recordings, we show that using this overall 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 reflects 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 overall speech envelope. HighlightsO_LIDelta/theta band EEG tracks band-limited speech-derived envelopes similar to real speech C_LIO_LILow and high frequency speech-derived envelopes are represented differentially C_LIO_LIHigh-frequency derived envelopes are more susceptible to attentional and contextual manipulations C_LIO_LIDelta band tracking shifts towards low frequency derived envelopes with more acoustic detail C_LI