Esophageal and gastric pressures during singing are measured in four male professional singers performing singing tasks requiring rapid changes of subglottal pressure. Evidence for a consistent use of the diaphragm is found in all subjects. Some subjects punctually activate the diaphragm when there is a need for a rapid decrease of subglottal pressure, such as when singing a falling octave interval, when shifting from a loud to a soft note, to save air during a /p/ explosion, and in performing a trillo involving a repeated switching between glottal adduction and abduction. The first three cases were observed in the beginning of the phrase, presumably over the period that the pressure generated by the passive expiratory recoil forces of the breathing system was higher than the intended subglottal pressure. In addition to this, one subject exhibited a diaphragmatic tonus throughout the entire phrase. The phonatory relevance of a diaphragmatic activity was evaluated in a subsequent experiment. The transdiaphragmatic pressure was displayed on an oscilloscope screen as a visual feedback signal for singers and nonsingers, who performed various phonatory tasks with and without voluntary coactivation of the diaphragm. In most subjects this activity tended to increase the glottal closed/open ratio as well as the amplitude of the glottogram (i.e., the transglottal volume velocity wave-form as determined by inverse filtering). These changes suggest that diaphragmatic coactivation tends to affect phonation. Also, it tended to reduce the formant frequency variability under conditions of changing fundamental frequency suggesting a better stabilization of the vocal tract.
The articulatory EMG .activity of lip muscles was investigated in patients with Parkinsonism and dysarthria and compared with normal-speakers. Furthermore, the effect of L-Dopa treatment on the dysarthric EMG activity was evaluated. Although articulatory ability improved in the experimental situation, it was possible to recognize reproducible abnormalities of the EMG pattern common to all patients. The resting activity between utterances was markedly increased and often progressed to a sustained hypertonic background activity, particularly in M. lev. lab. and M. dep. lab., as a sign of an exaggerated speech posture during the utterance. The functional organization of the lip muscles into two antagonistic groups for contrasting speech gesture movements was impaired. There were no signs of reciprocal inhibition. There was an obvious relationship between this disturbed activity pattern and the misarticulation of labial stop consonants. Furthermore, a longer anticipation period and a lack of context dependence of the EMG activity were often observed. L-Dopa medication was followed by a reduction of background activity and a reestablishment of reciprocal activation. These findings are discussed in relation to available data on limb muscle function in Parkinsonism.
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