Articulatory changes in muscle tension dysphonia: Evidence of vowel space expansion following manual circumlaryngeal therapy

In a preliminary study, we documented significant changes in formant transitions associated with successful manual circumlaryngeal treatment (MCT) of muscle tension dysphonia (MTD), suggesting improvement in speech articulation. The present study explores further the effects of MTD on vowel articulation by means of additional vowel acoustic measures. Pre- and post-treatment audio recordings of 111 women with MTD were analyzed acoustically using two measures: vowel space area (VSA) and vowel articulation index (VAI), constructed using the first (F1) and second (F2) formants of 4 point vowels/ a{script}, i, æ, u/, extracted from eight words within a standard reading passage. Pairwise t-tests revealed significant increases in both VSA and VAI, confirming that successful treatment of MTD is associated with vowel space expansion. Although MTD is considered a voice disorder, its treatment with MCT appears to positively affect vocal tract dynamics. While the precise mechanism underlying vowel space expansion remains unknown, improvements may be related to lowering of the larynx, expanding oropharyngeal space, and improving articulatory movements. Learning outcomes: The reader will be able to: (1) describe possible articulatory changes associated with successful treatment of muscle tension dysphonia; (2) describe two acoustic methods to assess vowel centralization and decentralization, and; (3) understand the basis for viewing muscle tension dysphonia as a disorder not solely confined to the larynx.