Secretion Bubbling as the Sound Mechanism for Nasal Rustle: A Perceptual Study

Abstract

Purpose: Secretion bubbling on the superior aspect of the velopharyngeal (VP) valve typically occurs with a small VP opening during production of oral pressure consonants. The use of high-speed nasopharyngoscopy has shown correlation between the bubbling frequency and the acoustics captured with the nasal microphone of the nasometer. The purpose of this study was to investigate if the sound generated by the bubbling process is perceived as nasal rustle (also known as nasal turbulence). Method: Speech samples were extracted from the data of patients who were diagnosed with nasal rustle (five boys and five girls, ranging in age from 5 to 10 years old). A customized filter was used to remove the sound generated by the secretion bubbling. Six experienced listeners were asked to rate the perception of nasal rustle in each speech stimuli before and after the filtering process. Results: Rating values for the perception of nasal rustle were overall reduced in all cases after the filtering process. Furthermore, the perception of nasal rustle was eliminated in 40% of the cases. Rating reliability was excellent before the filtering process and moderate to good after filtering. Conclusion: Reducing the perception of nasal rustle using spectral filtering based on the bubbling frequencies supports the hypothesis that undesired sound in the nasal cavity is generated from the interaction of the turbulent airflow with the secretion bubbling. Supplemental Material: https://doi.org/10.23641/asha.19111544