EEG-to-F0: Establishing artificial neuro-muscular pathway for kinematics-based fundamental frequency control
This work addresses the challenge of brain-computer interfaces for speech synthesis, though it is incremental as it simulates a simplified arm prototype rather than a full vocal tract.
The paper tackled the problem of controlling vocal fundamental frequency (F0) by establishing an artificial neuromuscular pathway using EEG signals and biomechanical modeling, achieving accurate F0 control as demonstrated through qualitative and quantitative comparisons.
The fundamental frequency (F0) of human voice is generally controlled by changing the vocal fold parameters (including tension, length and mass), which in turn is manipulated by the muscle exciters, activated by the neural synergies. In order to begin investigating the neuromuscular F0 control pathway, we simulate a simple biomechanical arm prototype (instead of an artificial vocal tract) that tends to control F0 of an artificial sound synthesiser based on the elbow movements. The intended arm movements are decoded from the EEG signal inputs (collected simultaneously with the kinematic hand data of the participant) through a combined machine learning and biomechanical modeling strategy. The machine learning model is employed to identify the muscle activation of a single-muscle arm model in ArtiSynth (from input brain signal), in order to match the actual kinematic (elbow joint angle) data . The biomechanical model utilises this estimated muscle excitation to produce corresponding changes in elbow angle, which is then linearly mapped to F0 of a vocal sound synthesiser. We use the F0 value mapped from the actual kinematic hand data (via same function) as the ground truth and compare the F0 estimated from brain signal. A detailed qualitative and quantitative performance comparison shows that the proposed neuromuscular pathway can indeed be utilised to accurately control the vocal fundamental frequency, thereby demonstrating the success of our closed loop neuro-biomechanical control scheme.