Physiological Studies of the Palatopharyngeal Muscle as a Speech Muscle in the Adjustment of Velar Position during Speech Production

Background: We aimed to investigate the contribution of the palatopharyngeal muscle (PP) as a speech muscle in adjusting the velar position.

Methods: X-ray kinematic analysis of the position of the palatopharyngeal arch and an electromyographic study of the PP during speech were performed in two healthy volunteers.

Results: X-ray kinematic analysis revealed that the palatopharyngeal arch was positioned lower during the production of the low-back vowel /a/. However, no significant differences were observed between the vowels included in the nasal sounds during nasal sound productions. The electromyographic study showed higher PP activity during nasal sound productions. However, no significant differences were observed in muscle activity during the productions of five vowels or the same vowels included in the nasal sounds. During the production of two consecutive phonemes involving voiceless bilabial plosive consonants and nasal sounds, the PP activity demonstrated synchronous coordination with the levator veli palatini muscle activity. This activity was higher during the production of the low-back vowel /a/ included in the voiceless bilabial plosive consonant. It was also higher during the production of voiceless bilabial plosive sounds than during the production of voiced bilabial plosive sounds.

Conclusions: When the distance between the origin and arrest of the PP is achieved through the velar elevation, the tonic condition and muscle strength of the PP are enhanced. When the scaffold below the PP is stabilized by the contractions of the glossopharyngeal part of the superior pharyngeal constrictor muscle during the production of the low-back vowel, the PP likely contributes to regulation of the velar position.