Performance enhancement of facial electromyogram-based facial-expression recognition for social virtual reality applications using linear discriminant analysis adaptation

Recent studies have indicated that facial electromyogram (fEMG)-based facial-expression recognition (FER) systems are promising alternatives to the conventional camera-based FER systems for virtual reality (VR) environments because they are economical, do not depend on the ambient lighting, and can be readily incorporated into existing VR headsets. In our previous study, we applied a Riemannian manifold-based feature extraction approach to fEMG signals recorded around the eyes and demonstrated that 11 facial expressions could be classified with a high accuracy of 85.01%, with only a single training session. However, the performance of the conventional fEMG-based FER system was not high enough to be applied in practical scenarios. In this study, we developed a new method for improving the FER performance by employing linear discriminant analysis (LDA) adaptation with labeled datasets of other users. Our results indicated that the mean classification accuracy could be increased to 89.40% by using the LDA adaptation method (p < .001, Wilcoxon signed-rank test). Additionally, we demonstrated the potential of a user-independent FER system that could classify 11 facial expressions with a classification accuracy of 82.02% without any training sessions. To the best of our knowledge, this was the first study in which the LDA adaptation approach was employed in a cross-subject manner. It is expected that the proposed LDA adaptation approach would be used as an important method to increase the usability of fEMG-based FER systems for social VR applications.