Minimum variability of the vibratory patterns of the vocal folds during vowel production in adults with healthy vocal folds: An exploratory study

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Communication Sciences and Disorders


Mary Louise Edwards


Vocal folds, Vowel production, Glottal airflow

Subject Categories

Communication Sciences and Disorders | Medicine and Health Sciences


This study examined the minimum range of variability in vocal fold vibration during syllables as measured from glottal airflow. Repeated samples were taken from adults with healthy vocal folds four times within two weeks and four consecutive trials within one day. Sources of extraneous variability were minimized by (a) controlling subglottal pressure, (b) age-matching subjects, (c) controlling time of sampling, (d) taking menstrual cycle into account, and (e) low-pass filtering rather than inverse filtering oral airflow.

Eleven females and 11 age-matched males received medical exams to assess laryngeal health and vocal fold vibratory pattern. To elicit 3 different modes of vibration, subjects produced "bap" syllable strings at 5, 8, and 12 cm H 2 O subglottal pressure (P S ). FM tape recordings were made of oral airflow (collected with Rothenberg mask), subglottal pressure and electroglottograph signals. Data were digitized and low-pass filters extracted glottal airflow. Indices of variability were Coefficient of Variation (CV in %) and Median Absolute Deviation (MAD). Dependent measures were Fundamental Frequency (F 0 ), Amplitude Flow (A), Minimum Flow (L), Mean Flow (M), Open Quotient (Q O ), and Spectral Balance Ratio (SBR: ratio of the sum of harmonics above F 0 to that at F 0 ).

Ranked CV data across subjects and measures indicated that F0 had the smallest range of variability (0.6%), and L the largest (101%). F 0 most often had a small range of variability, while L most often had a large range. Females had larger MAD values than males for F 0 , Q O and SBR; males for A, L and M. Nonparametric statistical analyses revealed that magnitude of variability for L was not affected by sex of subject, subglottal pressure level, or time frame of testing, while the magnitude of variability for A was affected by sex, P S level, and time frame.

Conclusions include: (a) selected measures of glottal airflow do not vary in the same manner by sex, P S level, or time frame; (b) P S and time frame affect F 0 , L and Q O less than A, M, and SBR; and (c) control of P S decreases variability.


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