Effects of laryngeal vibratory asymmetry on voice acoustics and perception

Abstract

Laryngeal vibratory asymmetry is commonly observed in many talkers, but its acoustic and perceptual consequences remain poorly understood. This study evaluates the relationships among vibratory symmetry, acoustic measures, and voice quality perception. We first test how the degree of left-right asymmetry in thyroarytenoid (TA) muscle activation relates to changes in voice quality as quantified by cepstral peak prominence (CPP). Using an in vivo canine phonation model, we stimulated each of the left and right TA muscles in a graded manner. Left-right asymmetry in vocal fold vibration was visually assessed, and CPP was measured from stable phonation. Results show that CPP is the highest at conditions of symmetric vibration and significantly decreases with increasing levels of asymmetry. In the subsequent audio rating experiment, 89 listeners ranked the phonation samples based on the quality (from worst to best). Overall, listeners prefer voices with higher CPP over those with lower CPP and voices with symmetric vibration over those with asymmetries. Results further reveal that listeners do not distinguish voices that fall within certain degrees of asymmetry. The relation between neuromuscular asymmetry and phonatory sound quality identified in this study has implications for clinical evaluation of the voice. [Work supported by NIH.]