Carole T. Ferrand

Harmonics-to-Noise Ratio: An Index of Vocal Aging

Distinguishing between vocal changes that occur with normal aging and those that are associated with disease is an important goal of research in voice. Several acoustic measures have been used in an attempt to illuminate the integrity of the vocal mechanism, including harmonics-to-noise ratio (HNR), jitter, and fundamental frequency (F0). HNR is a measure that quantifies the amount of additive noise in the voice signal; jitter reflects the periodicity of vocal fold vibration. In this study, measures of HNR, jitter and F0 were used to compare vocal function in three groups of normally speaking women: young adults, middle-aged adults, and elderly adults. Significant differences in HNR emerged between the elderly women and the other two groups. F0 differences were also apparent between the elderly group and the two younger groups; there were no significant differences in jitter between the three groups. HNRwas found to be a more sensitive index of vocal function than jitter. The significant lowering of HNR evident in t he elderly speakers may be attributable in part to medications taken by the majority of these elderly subjects.

Effects of practice with and without knowledge of results on jitter and shimmer levels in normally speaking women

The effects of practice on jitter and shimmer were assessed in two groups of normally speaking women. Subjects in both groups sustained trials of /a/ as steadily as possible during a baseline session, two practice sessions, and a transfer session. Subjects in one group received visual and verbal feedback during the practice sessions. Subjects in the other group received no feedback. Shimmer means remained essentially stable over the four sessions for both groups, and no differences were apparent between the groups. Jitter values were significantly different between sessions for both groups, and between the two groups for the practice sessions. These results are consistent with findings from manual performance and retention tasks. The present findings also support a recently developed neurologic model of jitter.

Selected aspects of central processing and vocal motor function in stutterers and nonstutterers: P300, laryngeal shift, and vibratory onset

Abstract The present study was designed to evaluate aspects of central processing and simultaneous laryngeal function in stutterers and nonstutterers using a recently developed continous flow model of phonatory reaction time. Simultaneous measurements were made of P300 brain potentials, laryngeal positioning movements prior to vocal fold closure, and onset of vocal fold vibration in 10 stutterers and 10 nonstutterers. The temporal ordering of these three events was evaluated and differences between the two groups examined. No significant differences were found in the vocal motor or P300 responses. Stutterers and nonstutterers appeared to be using a similar temporal patterning. This patterning may indicate an overlap between sensory and motor processing in phonatory reaction time tasks. Use of the present model with its quantifiable components of laryngeal shift, P300, and onset of vocal fold vibration, can yield valuable information regarding temporal aspects of central processing and laryngeal function.

Harmonics-to-noise ratios in normally speaking prepubescent girls and boys

This study examined harmonics-to-noise ratios (HNR) in 4 groups of normally speaking children. HNRs were calculated for the vowels /ai/ and /inverted v/, selected from conversational speech samples of 80 children aged 4, 6, 8, and 10 years (10 boys and 10 girls at each age level). HNR values for /inverted v/ were significantly higher than those for /ai/. Significant age differences emerged for /ai/ between ages 4 and 8, and ages 8 and 10. Girls obtained significantly higher HNRs than boys for the /ai/ vowel. Overall, the HNR values for these normally speaking children were lower than those reported for normally speaking adults. These findings suggest that acoustic values for children cannot be validly compared to those for adults, and that the childs gender and age should be taken into account when applying spectral analyses to research and/or clinical situations.