Phase asymmetries in normophonic speakers: visual judgments and objective findings

To ascertain the amount of phase asymmetry of the vocal fold vibration in normophonic speakers via visualization techniques and compare findings for habitual and pressed phonations.

Fifty-two normophonic speakers underwent stroboscopy and high-speed videoendoscopy (HSV). The HSV images were further processed into 4 visual displays: HSV playbacks, digital kymography (DKG) playbacks, mucosal wave kymography playbacks, and static kymographic images of the medial line from the DKG playback. Two types of phase asymmetries, left-right and anterior-posterior, were rated on a scale from 1 to 5. Objective measures of left-right phase asymmetry were obtained.

The majority of normophonic speakers (81%) were noted to display anterior-posterior asymmetry; however, 66% of those were characterized as mild. Seventy-nine percent of participants were noted to display left-right asymmetry; however, 72% of those were mild. A moderate relationship between the objective measures and subjective ratings was found.

Most normophonic speakers exhibit mild left-right and anterior-posterior asymmetries for both habitual and pressed phonations. Asymmetries were noted more often during habitual than pressed phonations, and when visualized by HSV and kymography than stroboscopy. Differences between objective measures and visual judgments support the need to quantify vocal fold vibratory features.