Impact of syllable stress and phonetic context on the distribution of intermittent aphonia

The occurrence of intermittent aphonia, perceived as sudden interruptions of voicing in connected speech, often reflects high stiffness of the vocal fold mucosa as part of a voice disorder. This retrospective study aimed to investigate the overarching hypothesis that the aphonic instances in voices with intermittent aphonia are not totally randomly appearing, but related to syllable stress and phonetic context. Recordings of 31 dysphonic patients with intermittent aphonia reading a standard text were analyzed perceptually. All vowels of the text were labelled and categorized with regard to syllable stress and character of the phoneme preceding the vowel. The occurrence of aphonic instances within each syllable category was analyzed. Four different hypotheses were formulated and analyzed by the non-parametric Wilcoxon's signed-ranks test. The results showed a significantly higher occurrence of aphonic instances in unstressed syllables as opposed to stressed, in vowels following an unvoiced phoneme as opposed to a voiced, and in vowels following two or more unvoiced phonemes as opposed to one unvoiced phoneme. No significant difference was found between vowels following aspirated stops [p], [t], [k] as opposed to unaspirated stops [b], [d], [g]. The findings support the theory that both physiological and functional aspects may contribute to the phenomenon of intermittent aphonia.