Semantic context enhances neural envelope tracking

ABSTRACT

The speech envelope is known to be essential for speech understanding and can be reconstructed from the electroencephalography (EEG) signal in response to running speech. Today, the factors influencing this neural tracking of the speech envelope are still under debate. Is envelope tracking mainly related to the encoding of acoustic speech information or is it influenced by top-down processing of speech understanding and the availability of semantic context in the stimulus?

We recorded the EEG in 19 normal-hearing participants while they listened to two types of stimuli: concatenated Matrix sentences without contextual information and a coherent story. Each stimulus was presented with varying levels of background noise to vary speech understanding. The speech envelope was reconstructed from the EEG in both the delta (0.5-4 Hz) and the theta (4-8 Hz) band with the use of a linear decoder and then correlated with the real speech envelope in that band. We also conducted a spatiotemporal analysis using temporal response functions (TRFs).

For both stimulus types and filter bands the correlation between the speech envelope and the reconstructed envelope increased with increasing speech understanding. In addition, correlations were higher for the story compared to the Matrix sentences, indicating that neural envelope tracking may be enhanced by the availability of semantic context in the stimulus and speech understanding.