Effects of Velopharyngeal Opening on Vocal Fold Contacting
Channel: Filipa La
Date: 2020-05-15

Objectives: To test the hypothesis that the increased level of the highest spectrum peak in the 2-4kHz region with a slight VPO observed in a previous investigation is due to a change in the vibratory pattern of the vocal folds, e.g., an extension of the contact phase. Thus, we investigated how a wide, a narrow or the absence of a VPO affects the duration of the contact phase relative to the period, i.e., the contact quotient (CQEGG), and the speed of contacting (SCEGG). 
Methods: Four male and five female singers sang a sequence of five vowels at pitches covering one octave with a wide VPO, a narrow VPO and the velopharyngeal port closed. These conditions will be referred as ‘Much’, ‘Slight’ and ‘None’, respectively. Recordings of audio, electrolaryngograph, nasal and oral flows were made simultaneously using a hybrid system, a combination of a 110-MS computer interface and a Laryngograph microprocessor. The nasal and oral flows were captured by means of a flow mask that the singers held well sealed to their faces. A plastic divider plate at the level of the upper lip separated the oral and the nasal airflows. The VPO conditions were documented in terms of the amplitudes of the nasal and oral DC and AC airflows. The audio and the airflow signals were all digitized with a sampling frequency 48000 Hz and recorded in separate channels by the SpeechStudio software, providing also CQEGG. A Friedman test with a Bonferroni correction was used to test whether there were significant differences in CQEGG between the three VPO conditions.
Results: CQEGG was significantly higher for the ‘Much’ condition as compared to the ‘None’. No significant differences were found for the SQEGG, although the contacting was somewhat quicker  in ‘Slight’ than in ‘None’.
Conclusion: A wide VPO seems to significantly increase the CQEGG. This could be caused by a source filter-interaction but also by a change of glottal configuration due to a singers’ compensatory reaction. An effect on vocal fold vibration of a narrow VPO is probably too small, suggesting that The effect on the spectrum found in previous studies would be caused mainly by vocal tract resonance.