Phase asymmetries in normophonic speakers: visual judgments and objective findings

Abstract

Purpose: 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.

Method: 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.

Results: 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.

Conclusions: 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.

Figure 1

A medial position frame of a digital kymography (DKG) playback, which is a movie playing from posterior to anterior. The image on the left shows the line being scanned across the glottis. On the right, the corresponding kymographic image is shown.

Figure 2

A medial position frame of a mucosal wave kymography (MKG) playback. This type of display allows for the temporal representation of the dynamics of the vocal fold edges during glottal opening and closing in consecutive glottal cycles of sustained phonation. The MKG image brightness relates to the speed of motion, and the color shows the phase of motion (opening is green and closing is red). The mucosal wave extent appears as a double-edged or thicker curve during the closing phase.

Figure 3

Example of anterior-posterior symmetry visual-perceptual judgments of DKG playback made via the ALVIN program.

Figure 4

Left-right relative asymmetry A (%) measured as the ratio of the sum of phase asymmetry in pixels Δ₁, Δ₂ and Δ₃ in three consecutive glottal cycles and the sum T of the periods T₁, T₂ and T₃ of the same three cycles. Examples of (A) typical and (B) increased asymmetry levels are illustrated.

Figure 5

Histogram of the distribution of the left-right relative asymmetry values A (%) objectively measured from habitual and pressed phonations.