Determining an optimal set of flesh points on tongue, lips, and jaw for continuous silent speech recognition

Articulatory data have gained increasing interest in speech recognition with or without acoustic data. Electromagnetic articulograph (EMA) is one of the affordable, currently used techniques for tracking the movement of flesh points on articulators (e.g., tongue) during speech. Determining an optimal set of sensors is important for optimizing the clinical applications of EMA data, due to the inconvenience of attaching sensors on tongue and other intraoral articulators, particularly for patients with neurological diseases. A recent study found an optimal set (tongue tip and body back, upper and lower lips) on tongue and lips for isolated phoneme, word, or short phrase classification from articulatory movement data. This four-sensor set, however, has not been verified in continuous silent speech recognition. In this paper, we investigated the use of data from sensor combinations in continuous speech recognition to verify the finding using a publicly available data set MOCHA-TIMIT. The long-standing speech recognition approach Gaussian mixture model (GMM)-hidden Markov model (HMM) and a recently available approach deep neural network (DNN)-HMM were used as the recognizers. Experimental results confirmed that the four-sensor set is optimal out of the full set of sensors on tongue, lips, and jaw. Adding upper incisor and/or velum data further improved the recognition performance slightly.