Fiona Stritt

Nonlinear phenomenon common in extreme and traditional singing involves often coupled oscillations of glottal and supraglottic structures. Four such phonatory mechanisms—undertone, distortion, growl, and rattle—differ in supraglottic involvement and frequency ratio between glottal and supraglottic oscillators. However, the contribution of vocal tract (VT) configurations remains insufficiently understood. Using static three-dimensional magnetic resonance imaging and acoustic analysis, we investigated VT shaping in a professional singer. The VT was used to calculate volume–velocity transfer functions and was segmented into seven sub-volumes for geometric analysis. Acoustic recordings provided fundamental frequencies and pitches. Undertone and distortion showed the most speech-like configurations, with ventricular and epilaryngeal volumes largely unaffected by the laryngeal elevation. Growl involved laryngeal lowering and tongue retraction, facilitating epiglottic–arytenoid approximation. Rattle exhibited increased pharyngeal constriction. Growl showed clustering of resonance peaks around 2000–4000 Hz (singer's formant region), and high rattle showed alignment of twice the pitch with the first resonance frequency, suggesting an enhanced source–filter interaction. For this singer, the VT configuration differed systematically across the four phonatory mechanisms. These hypothesis-generating observations underline the potential role of VT configuration of nonlinearities in phonation and motivate larger studies relevant to voice pedagogy and clinical practice involving supraglottic sound production.

Conventional endoscopic imaging of vocal fold (VF) vibration provides only a two-dimensional superior view, missing essential vertical dynamics such as VF thickness and vertical displacement. Simulation studies have assigned these parameters important regulatory functions, underscoring the need for in vivo methods capturing the three-dimensional (3D) VF geometry and vibratory motion. In this in vivo case study, dynamic 3D VF MRI was applied in a professionally trained singer, achieving sub-millimeter spatial and sub-millisecond temporal resolution. Six phonation types were produced according to Estill Voice Training® terminology, each intended to elicit different VF thicknesses and supraglottic configurations. For each type, ten phase-binned 3D datasets of the larynx were reconstructed per oscillatory cycle. Segmentation yielded VF thickness, vertical and horizontal displacement, contact-area dynamics, glottal area waveforms, open quotient (OQ), and supraglottic/subglottic dimensions. These MRI-derived measures showed strong correspondence with those from high-speed imaging and electroglottography acquired from the same subject, indicating that dynamic VF MRI enables reliable in vivo quantification of vibratory and structural parameters. Each phonation type was characterized by distinct VF geometry, supraglottic shaping, and oscillatory behavior. Across types, OQ correlated closely with VF thickness, which systematically covaried with supraglottic adjustments. This suggests supraglottic posturing represents an additional dimension of control.

The human voice exhibits diverse expressions, primarily generated by the regular oscillatory movement of both vocal folds. However, further vocal tract structures can also oscillate, as observed in different singing styles, supraglottic voice substitutes and functional voice disorders. To describe the spectrum of irregular phonation types from a nonlinear systems perspective, we conducted in vivo investigations with a professional metal singer using transnasal high-speed digital imaging combined with electroglottography and acoustic data. Here, we analysed 10 distinct voice qualities. Some of these show oscillatory mechanisms characterized by nearly periodic patterns that differ in three key aspects: the ratio of glottal to supraglottic oscillations, their behaviour during the glissando and the oscillating structures primarily involved. Both reduced glottal adduction and increased glottal and supraglottic compression contribute to a greater degree of irregularity. The supraglottic oscillations can coexist with various glottal oscillation mechanisms. Based on the in vivo data, we identified various nonlinear phenomena of different categories that include synchronized oscillations with defined frequency ratios, bifurcations, biphonations and chaotic oscillations.

Voice disorders occur frequently in schoolteachers. The aim of the present cross-sectional study involving 124 German teachers was to investigate whether singing, voice training, and high self-efficacy are protective factors for vocal health. Furthermore, vocal self-concept was examined as a potential mediator explaining this relationship. Participants were assigned to the cases group if they had a clinically significant finding in voice examinations consisting of video laryngoscopy (VLS), auditory assessment (RBH), and the Voice Handicap Index (VHI) were assigned to the cases group. Psychosocial assessments comprised questions about singing activities and participation in voice training as well as validated questionnaires regarding self-efficacy (LSWS) and vocal self-concept (FESS). Group comparisons and mediation analyses were conducted. Analyses revealed a decreased risk of voice problems for teachers who sing regularly (OR: 0.442, p = 0.038). Furthermore, the absence of voice problems was associated significantly with higher self-efficacy ratings (t(113) = 1.71, p = 0.045). Both associations were mediated by vocal self-concept ratings (singing: ab = −0.422, 95%-CI [−1.102, −0.037]; self-efficacy: ab = −0.075, 95%-CI [−0.155, −0.022]). Participation in voice training in the past did not reduce the risk of voice problems significantly. The presented data suggest that regular singing and self-efficacy should be promoted in health care and prevention programs. Since no impact of sporadic participation in voice training activities on the occurrence of voice problems was found, efforts regarding the transfer of regular vocal exercises into daily life need to be intensified.