Electromyographic Studies of Facial Muscle Activity in Speech

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Abstract
The function of the lip muscles during coarticulation of different labial speech sounds has been studied electromyographically with concentric needle electrodes in a subject with phonetically and acoustioally normal speech. Polygraphic EMG recording made it possible to analyse in detail the participation of the various muscles in the articulatory movements of the lips for the labial speech sounds. The EMG pattern was characteristic of a particular speech sound in one and the slame context and highly reproducible in all the experiments undertaken. Two different types of EMG activity could be distinguished: 1) speech posture, i.e. background activity, which was most pronounced in M. lev. lab. and M. dep. lab. and appeared both before, during and between the different utterances, and 2) articulatory activity, which was associated with the rapid movements during utterances and occurred in all the muscles examined. On the basis of this latter activity it was possible to divide the labial musculature into two antagonistically active groups of muscles which appeared to receive reciprocal innervation: one for rounding or closing, the other for opening or spreading speech gestures. Motor unit activity in a particular muscle was not constant or a given speech sound but varied with both the intensity and the duration of the activity during the preceding sound.

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