Phonation differentiation by non-contact laryngeal magnetomyography

Phonation is important for our daily communication and requires the activation of internal and external laryngeal muscles, which can be recorded by electromyography (EMG) using surface or needle electrodes. Here we present a new noncontact method, laryngeal magnetomyography. As a proof-of-concept, we investigated the feasibility of differentiating various vocalization conditions using laryngeal MMG in two healthy subjects using optically pumped magnetometers (OPM). We recorded magnetic muscle activity of the larynx and neighboring cervical muscles using a 3 × 5 array of OPMs. Subjects vocalized an /a/ in three different conditions: loud high pitch, loud low pitch, and soft high pitch, in 90 s blocks. After removing cardiac artifacts, MMG signals were in the range of 1.5 pT with significant amplitude differences between conditions. In both subjects, Linear Discriminant Analysis (LDA) was able to significantly classify vocalization conditions based on the spatial pattern of MMG activities. In sum, we show that laryngeal MMG allows contactless differentiation of phonations based on myomagnetic signals. Our results set the stage for future studies to explore this method for clinical diagnostics and therapy. Functional, contactless muscle recordings during vocalization enable new applications for miniaturized quantum sensors, e.g. in linguistic studies and speech rehabilitation.