Vocal Fold Vertical Thickness in Human Voice Production and Control: A Review.

While current voice research often focuses on laryngeal adjustments in a two-dimensional plane from a superior endoscopic view, recent computational simulations showed that vocal control is three-dimensional and the medial surface vertical thickness plays an important role in regulating the glottal closure pattern and the spectral shape of the produced voice. In contrast, while a small glottal gap is required to initiate and sustain phonation, further changes in the glottal gap within this small range have only small effects on glottal closure and spectral shape. Vocal fold stiffness, particularly along the anterior-posterior direction, plays an important role in pitch control but has only a small effect on glottal closure and spectral shape. These results suggest that voice research should pay more attention to medial surface shape in the vertical dimension. Future studies in a large population of both normal speakers and patients are needed to better characterize the three-dimensional medial surface shape, its variability between speakers, changes throughout the life span, and how it is impacted by voice disorders and clinical interventions. The implications for voice pedagogy and clinical intervention are discussed.