Characterization of laryngealization as irregular vocal fold vibration and interaction with prosodic prominence

This paper introduces an original variant of recurrence analysis to quantify the degree of regularity of vocal fold vibration as captured by electroglottography during phonation. The proposed technique is applied to the analysis of laryngealized phonation as this phonation type typically shows irregular vibration cycles. The reliability of this approach is validated with synthetic vocal fold vibration signals, demonstrating that it permits measuring the regularity of vocal fold vibration, unaffected by changes in fundamental frequency. The method is also applied to real electroglottographic signals recorded at the onset of vowel-initial nonsense words produced in a speeded repetition task by five female German speakers. Results show that the degree of laryngealization during the production of word-initial vowels is modulated by the presence of stress (with stressed vowels being less laryngealized). Due to its robustness to changes of F0, the proposed technique proves to be a suitable tool for studying vocal fold regularity in concatenated speech. Its applications are not limited to the study of glottalization, since the degree of regularity of vocal fold vibration has paralinguistic functions and is a clinically relevant measure of voice pathologies.