Figure 1.

Illustration of the steps used to extract speech and EEG features and to estimate the association between them. The speech signal is passed through a gammatone filter bank simulating cochlear processing, and the envelope at the output of each filter (i.e., the envelope of each speech band) is extracted as a speech feature. Similarly, different bands of the EEG and different sensor channels together form the different EEG features. For the lower-frequency bands (delta and theta), the EEG signals are used as is. For the alpha and beta bands, both the signals in those bands, and their envelopes are extracted as separate features. For the higher-frequency gamma bands, only the envelopes of the EEG signals in those bands are considered. These EEG features are then compared with the speech features using spectral coherence.