Effect of Tongue Protrusion on Soft Palate Elevation: Validation Using Nasal Emission and Nasalance Score during Phonation

Abstract

　The oral cavity, nasal cavity, and pharynx play important roles for resonance during speech production. When the soft palate, which coordinates the presence or absence of nasal resonance, does not function adequately, clear production of speech sounds becomes difficult. The movement of the soft palate is an important element in speech production, but its relation with the tongue position is not fully understood. Therefore, in this study, we investigated how the position of the tongue affects the function of the soft palate while maintaining the mandibular position constant, by measuring the association between nasal resonance and actual nasal emission of air during vowel phonation. Data obtained from 13 young healthy adult females (21.7±0.9 years old) were analyzed. The subjects were asked to vocalize the vowel /a/ three times under two conditions: maximum mouth-opening only (open-mouth condition), and maximum mouth-opening plus maximum tongue protrusion (open-tongue condition). Four measures (i.e., mean, min, max, and start) of the nasal cavity resonance rates as a percentage (the nasalance score, or N-score), were determined using the Nasometer II 6450. The results showed that nasal resonance was significantly greater in the open-tongue condition than in the open-mouth condition for the start value (r＝0.562, p＜0.05), but no significant differences were found for the other conditions. Regarding the correlation between nasal emission and nasal resonance rate, significant correlations were found for mean and max in the open-mouth condition, but no significant correlations were found in the other conditions. It was suggested that the nasal resonance rate was affected when the tongue position was changed while the mandible position was kept constant.