Validating Spectral Moment Analysis as a Quantitative Measure of Speech Distortions in Speakers With Class III Malocclusions.

Purpose: This study examined the relationship between judged speech sound distortions and spectral moment metrics in speakers with Class III malocclusion. Methods: A quantitative online survey was distributed to 30 speech specialists (clinicians and/or students) and 100 lay listeners to judge the clarity of the sounds /s/, /ʃ/, /t/ and /k/ using a visual analog scale (VAS) from recordings of 11 Class III (underbite) Dentofacial Disharmony (DFD) patients and eight Class I controls. Patients and controls were grouped according to high, moderate, and low /s/-/ʃ/ first spectral moment differences. A linear mixed model was used to analyze the data. Results: VAS scale ratings increased as a function of decreasing spectral contrast for both groups of listeners. VAS ratings of speech specialists were more homogenous than lay listeners, and speech specialists rated distortions as less severe than lay listeners. Conclusions: Recordings of Class III DFD patients with low /s/-/ʃ/ first spectral moment differences were scored by listeners as having increased VAS scale ratings, indicative of more significant perceived speech-sound distortions. Spectral moment analysis appears to be a promising approach for characterizing speech of DFD patients and other craniofacial disorders.