Characterizing Vocal Tract Dimensions in the Vocal Modes Using Magnetic Resonance Imaging

Objective The aim was to study vocal tract dimensions in four vocal modes – Neutral, Curbing, Overdrive and Edge – from Complete Vocal Technique (CVT) by means of magnetic resonance imaging (MRI). Furthermore, the purpose was to test the feasibility of MRI to assess CVT vocal modes. Methods Four nonclassical singers (two females, two males) trained in CVT were imaged with an MRI scanner while singing sustained vowels at same pitch (Bb4 for females, F4 for males) in all vocal modes. Audio signals were simultaneously recorded through a pipe for quality assurance purposes. Auditory evaluation was performed by three CVT teachers in the scanner control room via headphones, and by one CVT teacher inside the MRI room. Previously developed measurement models modified by the authors were used to measure vocal tract dimensions from sagittal MRI projections. Repeatability test was performed for all measurements. Results In all subjects, vocal tract dimensions displayed differences between the vocal modes. Edge stood out from other vocal modes by showing most laryngeal narrowing accompanied by shortest vocal tract and highest vertical laryngeal position. For Neutral, least mouth opening and shortest distance between tongue and palate were found. Curbing differed consistently from Edge and somewhat from Overdrive showing higher measured values for vocal fold length. Differences regarding vocal fold length were also detected between Neutral and Edge. As expected, differences in vocal tract dimensions were found between samples sung with different vowels. Conclusions Vocal tract adjustments play a key role in the production of the vocal modes. The model used to measure vocal tract dimensions succeeded in finding significant differences between the vocal modes, also detecting differences between different vowel productions. The method used to characterize vocal tract dimensions seem promising and would be worthwhile to apply to a larger material.