Contraction Patterns of Neck Muscles during Phonating by High-Density Surface Electromyography

Phonation is generated by sequentially closing and opening of vocal folds, which is controlled by the laryngeal musculature. Pitch that is the highest contributor to generate natural voice depends on the contraction of muscles over the neck. Proper evaluation of muscular activities from neck muscles would be helpful to understand the phonation functions. While surface electromyography (sEMG) technique has been chosen to investigate physiological characteristics of neck muscles for pitch estimation in previous studies, it remains unclear what are the contracting patterns on both left and right sides of the neck muscles. In this study, 80 channels of high-density (HD) sEMG electrodes were recorded from three healthy volunteers when they phonated vowel (/a/) during varying pitch from normal to high. The root mean square (RMS) of the HD sEMG signals was computed within a series of analysis windows. An averaged RMS was used to construct HD sEMG energy maps for offering average energy distribution of the neck muscles. Normalized RMS (NRMS) was calculated to quantitatively display the correlation of the neck muscles between the left and right sides. The results of sEMG waveforms and NRMS values showed obvious symmetry between the left and right sides of the front neck muscles. Additionally, the NRMS across all five rows revealed a left-right significant correlation (r=0.9432 ± 0.018, p<0.01). This pilot study suggests that HD sEMG would be a potential tool to assess contraction patterns of the neck muscles during phonation. Also, it might pave way for evaluating the muscle synergy during phonating.