INTRODUCTION: Semi-occluded vocal tract exercises (SOVTE) are often used in voice clinics. SOVTE change the acoustic vocal tract impedance in relation to the glottis impedance, improving voice quality. However, differences among SOVTE, such as the number of vibration sources into the vocal tract, are often disregarded by clinicians. Some SOVTE present single, whereas others double source. This study aims at investigating changes in voice production pattern for a series of SOVTE. A combined exercise (tongue-trill coupled with hand-over-mouth) was implemented to illustrate the effect of a secondary source of vibration in the vocal tract. METHOD: Twenty-three healthy volunteers performed a series of SOVTE: LaxVox, straw, lip-trill, tongue-trill, hand-over-mouth, humming, and tongue-trill combined with hand-over-mouth. Comfortable phonation served as control exercise. The dependent variables were electroglottography contact quotient (CQ), contact quotient range (CQr), fundamental frequency (F0), fundamental frequency range, and difference between the first formant frequency and F0 (F1 - F0). RESULTS: A significant difference for CQr scores compared with comfortable phonation was found for the combined tongue-trill with hand-over-mouth, lip-trill, LaxVox, and tongue-trill exercises. The F1 - F0 acoustic analysis showed significant differences in scores for exercises with one versus two sources of vibration. DISCUSSION AND CONCLUSION: The results indicate that SOVTE should be divided into two groups, as follows: (a) steady (single sourced) with lower CQr and F1 - F0 difference (hand-over-mouth, humming, and straw) and (b) fluctuating (dual source) with larger CQr and F1 - F0 difference (tongue-trill, lip-trill, and LaxVox). Because of these differences, also different therapeutic effects can be expected. Tongue-trill combined with hand-over-mouth exhibited mixed effects of both the exercise groups.

Department of Biophysics Faculty of Science Palacky University Olomouc Czech Republic

Department of Speech and Language Therapy The Royal National Throat Nose and Ear Hospital London United Kingdom

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