Period and glottal width irregularities in vocally normal speakers.

Vocal fold vibratory irregularities can be caused by multiple factors. The underlying mechanism for irregularities is a difference in the mass or tension of the vibratory portion of the left versus the right vocal fold. The purpose of this study is to preliminarily investigate the prevalence of vocal fold vibratory irregularities in vocally normal speakers via high-speed videoendoscopy (HSV). Two aspects of irregularity, glottal width and period irregularity, were investigated in 52 vocally normal speakers undergoing videostroboscopy and HSV. The videostroboscopy and HSV recordings were processed and visually rated for glottal width and period irregularities. These ratings were also accomplished through the use of the novel digital kymography playback and from still kymographic images of the medial line of the vocal folds (mDKG). Objective measures of glottal width and period irregularities from the mDKG, and jitter and shimmer measures of the synchronously recorded acoustic waveforms, were also studied. The results suggest that period irregularities are less frequent in normophonic speakers than glottal width irregularities. However, more participants revealed acoustic jitter rather than acoustic shimmer above normal limits. Thus, speculation regarding the physiological source of these clinically used acoustic parameters continues. The lack of confidence in rating irregularity through stroboscopy and the discrepancies between visual ratings and objective measures requires future research efforts.