The influence of thyroarytenoid and cricothyroid muscle activation on vocal fold stiffness and eigenfrequencies

Abstract

The influence of the thyroarytenoid (TA) and cricothyroid (CT) muscle activation on vocal fold stiffness and eigenmodes was investigated in a muscularly-controlled continuum model of the vocal folds. Unlike the general understanding that TA contraction reduces cover stiffness, this study showed that, with reference to the resting state of zero strain, vocal fold stiffness in both layers increased with either vocal fold elongation or shortening. As a result, whether vocal fold eigenfrequencies increased or decreased with CT/TA activation depended on whether the CT/TA interaction increased or decreased the degree of existing vocal fold deformation. For conditions of strong CT activation and thus an elongated vocal fold, increasing TA contraction reduced the degree of vocal fold elongation and thus reduced vocal fold eigenfrequencies. For conditions of no CT activation and thus a resting or slightly shortened vocal fold, increasing TA contraction increased the degree of vocal fold shortening and thus increased vocal fold eigenfrequencies. In the transition region of a slightly elongated vocal fold, increasing TA contraction first decrease and then increased vocal fold eigenfrequencies. These results indicated that vocal fold eigenfrequencies were determined primarily by vocal fold stiffness rather than vocal fold stress. © 2013 Acoustical Society of America.