Extracting Different Levels of Speech Information from EEG Using an LSTM-Based Model
This work addresses the need to interpret EEG-speech decoding models for potential applications like hearing tests, but it is incremental as it builds on existing neural network methods.
The study tackled the problem of understanding what speech information EEG-based models use by analyzing an LSTM model's performance with different speech features, finding that it exploits silences, intensity, and phonetic classes, with mel spectrogram achieving the highest accuracy of 84%.
Decoding the speech signal that a person is listening to from the human brain via electroencephalography (EEG) can help us understand how our auditory system works. Linear models have been used to reconstruct the EEG from speech or vice versa. Recently, Artificial Neural Networks (ANNs) such as Convolutional Neural Network (CNN) and Long Short-Term Memory (LSTM) based architectures have outperformed linear models in modeling the relation between EEG and speech. Before attempting to use these models in real-world applications such as hearing tests or (second) language comprehension assessment we need to know what level of speech information is being utilized by these models. In this study, we aim to analyze the performance of an LSTM-based model using different levels of speech features. The task of the model is to determine which of two given speech segments is matched with the recorded EEG. We used low- and high-level speech features including: envelope, mel spectrogram, voice activity, phoneme identity, and word embedding. Our results suggest that the model exploits information about silences, intensity, and broad phonetic classes from the EEG. Furthermore, the mel spectrogram, which contains all this information, yields the highest accuracy (84%) among all the features.