Investigation of Vocal Bifurcations and Voice Patterns Induced by Asymmetry of Pathological Vocal Folds.

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Vocal fold asymmetry creates irregular entrainments and modulations in voice, which may lead to rough perceptual quality. The presence of asymmetry can also cause mid-phonation bifurcations where a small change in the phonatory system causes a drastic change in vibration pattern, resulting in transitions in and out of rough voice. This study surveys sustained phonation recordings of speakers with the diagnoses of vocal fold polyp or unilateral vocal fold paralysis to investigate the resulting voice patterns. This retrospective study observed 71 sustained phonation recordings from 48 patients. Segments with distinctive signal patterns were identified within each recording with narrowband spectrogram and computer-assisted analysis of spectral peaks. Phonation segmentation yielded 240 segments across all the recordings. Five voice patterns were recognized: (regularly or irregularly) entrained, modulated, uncoupled, unstable, and pulsed. Thirty-six patients (75%) exhibited irregular patterns. No single irregular pattern lasted for the entire phonation and was always accompanied by at least one mid-phonation bifurcation. Durations of the irregular segments (M = 0.4 s) were significantly shorter than the segments with the regular pattern (M = 1.4 s). The results suggest that vocal fold pathology frequently introduces dynamic vibratory patterns that affect both the acoustic signals and perceptions. Due to these abnormalities, it is important for clinical voice assessment protocols, both perceptual and acoustic, to account for these possible bifurcations, irregular signal patterns, and their tendencies.