Neuromuscular Control of Vocal Loudness in Adults as a Function of Cue

• Author / Creator

  Tam, Andrea

• Background. Speech production in noisy environments is known to elicit the Lombard effect, which has been described as an involuntary increase to vocal loudness against background noise. Many studies have explored the auditory-perceptual mechanisms that contribute to the Lombard effect; however, the neuromuscular control mechanisms underlying the physiological adjustments for speech produced during the Lombard effect are not well understood. Together, data from animal, acoustic, and kinematic studies have suggested that control of vocal loudness adjustment during the Lombard effect is systematically distinct from loudness adjustment in response to explicit instruction. The present study examined the effects of different vocal loudness cues on respiratory control, as measured by vocal sound pressure level, lung volume, and chest wall intermuscular coherence during speech breathing tasks in healthy young adults. Methods & Analysis. Fifteen healthy young adults (20-32 yrs) were recorded during a wordless picture storytelling task, standardized sentence repetition task, and a maximum phonation task in three cue conditions: 1) At conversational loudness, which served as a baseline condition; 2) Verbal instruction to speak at perceived twice conversational loudness, and 3) In multi-talker noise (inducing Lombard changes). The following dependent variables were examined: acoustic recordings of vocal sound pressure level (dB SPL), lung volume events (lung volume initiations, terminations, excursions, and percent rib cage contribution to lung volume excursion), and intercostal-oblique intermuscular coherence. Exploratory analyses were conducted on fundamental frequency, as well as the relative activation of the intercostal and oblique muscles. Results. The main findings were that different cues for vocal loudness: i) Produced similar increases to vocal SPL; ii) Did not result in systematic changes to speech breathing parameters; iii) Produced comparable intermuscular coherence values within each task in the 15-59 Hz range, as well as in the 60-110 Hz range, with overall greater mean peak coherence observed in the 15-59 Hz bandwidth, regardless of cue or task. Exploratory analyses suggested that speakers modulated vocal loudness using systematic laryngeal adjustments, as measured by increased F0 in the loud speaking conditions. Conclusion. Different cues had no effect on the control of speech breathing, indicating that the respiratory control circuits involved in vocal loudness change are stable against perturbation in the healthy adult system when the targeted tracheal pressure is controlled for between different cues to increase loudness. The results add to a growing body of literature in which the application of surface EMG and coherence analyses are used as a noninvasive means for understanding speech motor control. Results from this study may provide a platform to further understand speech breathing in individuals with deficits that affect neuromuscular control of the respiratory system.

• Subjects / Keywords

  • Neuromuscular control
  • Vocal loudness
  • Intermuscular coherence
  • Lombard effect
  • Respiratory system
  • Speech breathing

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ZK5613P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.