NCVS Blog and Forum

Studies have found that occupational voice users like teachers and call center workers are at nearly a two-fold increased risk for vocal injury than the average population.  To better understand this increased risk, small voice monitoring devices have been used (e.g. Voice Accumulators, Voice Dosimeters, Ambulatory Phonation Monitors).  However, it is unknown how these monitoring devices affect the behaviors of the user, which may in fact skew the very thing to be monitored.

Wordle art of the printed manuscript's words

A recent article in Logopedics, Phoniatrics, and Vocology discussed this question, written by Dr. Eric Hunter of the National Center for Voice (NCVS) and Speech at the University of Utah.  The report explored two questions: How do voice monitoring devices affect daily communication and how do participants feel about the physical design and function of these types of devices?

The study found that most of the subjects remained aware of the dosimeter while wearing it, which may impact the data collected. Furthermore, most subjects had difficulty with the device: first, skin irritation from attaching the accelerometer; and second, the size and inconvenience of the external pack used to process and store the data collected.

Dr. Hunter and colleagues at the NCVS have spent more than 10 years studying multi-day monitoring of voice use in a variety of settings, and archiving more than 10,000 hours of voice use. The vocal health of occupational voice users is a significant issue. Nearly one quarter of the U.S. workforce, or approximately 37 million individuals, depends on a healthy, versatile voice, as a tool for their profession. These are individuals who, in the event of the loss of vocal endurance and/or vocal quality, would be unable to perform their primary job responsibility.

 A printable version of this summary can be found here.

For additional information, see the full article by Dr. Eric J. Hunter, entitled “Teacher response to ambulatory monitoring of voice”, published in Logopedics, Phoniatrics, Vocology, 2012.

Studies Show Women at Higher Risk for Vocal Problems

Studies have found that approximately 10% more women than men, regardless of their occupation, have reported vocal issues that have lasted more than four weeks. They also make up the majority of several high-voice-use occupations (e.g., public school teachers, call center workers).

A recent in-depth review of gender physiological differences suggests potential reasons for this disparity.  This review was written by NCVS and affiliated researchers, and was published in Logopedics, Phoniatrics, and Vocology.  Differences between men and women that may be important factors in vocal health are discussed. Among these are differences in the laryngeal system, respiratory system (e.g., breathing mechanism, breath support) and endocrine system (e.g., general hormone differences, cyclic hormone variations), as well as perceptual differences (e.g., pain thresholds, general body awareness).

The authors conclude that more information is needed to better understand and treat women who currently suffer from vocal health issues.

Vocal health of occupational voice users is a significant issue. Nearly one quarter of the U.S. workforce, or approximately 37 million individuals, depends on a healthy, versatile voice as a tool for their profession. These are individuals who, in the event of the loss of vocal endurance and/or voice quality, would be unable to perform their primary job responsibility. These occupational voice users include, but are not limited to, teachers, counselors, emergency dispatchers, air traffic controllers, performers and telephone workers.

For additional information, see the full article by Eric J Hunter, Kristine Tanner, Marshall E Smith entitled “Gender differences affecting vocal health of women in vocally demandingcareers”, published in Logopedics, Phoniatrics, Vocology 2011 July.

Of humans and alligators

Our larynx (voice box) is a very complicated structure. The human voice is created when lung pressure increases and air is pushed through the larynx. An array of complicated movements inside the larynx moves vocal folds towards each other and stretches them. Almost like the string on a stringed instrument, human vocal cords (vocal folds) are elongated and shortened to achieve different tension and thereby distinctive oscillation frequencies, which result in the perceived pitch of our voice. However, larynges of different animals show different degrees of complexity. A study was conducted in which vocal production in American Alligators (Alligator mississippiensis) was examined.

Alligators possess a complex vocal repertoire yet Alligators don’t have the option to stretch their vocal folds the way humans do. So how does an alligator achieve their pitch modulation? This was the question asked by National Center for Voice and Speech researchers and their colleagues. Dr. Tobias Reide answered, “that leaves them with only two options: changing lung pressure and changing how pressed together their vocal folds are.”

The researchers investigated the relation between these variables (lung pressure and laryngeal resistance from vocal fold closure) and the voice pitch in live young alligators while they were calling. They also investigated the morphology of the alligator larynx by dissection and computer tomography.

Lung pressure variations alone did not explain fundamental frequency variations, the researchers found. Implementing physiological and morphological data in a computer model suggested that a fine-tuned interplay between lung pressure variations and vocal fold adduction is necessary to produce alligator sounds.

The alligator larynx represents an evolutionary early version of a larynx. Despite its limited flexibility, the evolved features allow it to produce a rather complex vocal repertoire. Future studies will have to identify specific adaptations which allow the alligators to make rather complex sounds with a larynx of limited flexibility. For example, ongoing investigations will look at the morphology and viscoelastic properties of alligator vocal folds to see if they help in facilitating the enormous frequency modulations.

To learn more about Alligators and their vocal folds read “Subglottal pressure and fundamental frequency control in contact calls of juvenile Alligator mississippiensis” by Tobias Riede, Isao T. Tokuda, and C. G. Farmer which can be found here. Or contact the National Center for Voice and Speech to talk to the researchers about their work.

New thoughts on Vocal Fundamental Frequency and Vocal Fold Mass: It’s not as we once thought.

Vocal pitch or fundamental frequency (F₀) during speech and song has often been described by the mass of the vocal cords (vocal folds.  However, mass (thicker and longer vocal folds) is an anatomical, not a functional concept.  Why should this concept, that has been used so often, no longer have credence?  The vocal fold is made up of a small amount of tissue that is attached to cartilages on three of its six sides.  As a unit, the attached tissue has little freedom to move.  Constraining the unattached tissue with boundaries creates vibrational displacements that are not uniform.  Thus, the amount of material in vibration is hard to quantify and to associate with a single mass, as often attempted in the scientific and medical literature.  It is better to consider two other variables that affect F₀ control: length and stress of a laminated (layered) “string”.  The formula for a vibrating string is used to prove this point where each layer should be considered a separate string.

Most would assume that if the thickness of the vibrating tissue is increased, and mass along with it, that F₀ would be lowered.  This is an incorrect assumption.  If there is a new mass then there will be a tissue to work to restore the moving mass, or a new spring.  Even if the mass increases an incredible amount one must consider the added stiffness to the vocal fold mass.  What if the vocal fold was longer?  This would result in a lower F₀, but this would occur despite the length or thickness of the string.  Hence, this would rule out mass as a variable.  The idea that mass or thickness of the vocal folds effects F₀ needs to be abandoned.  Although the focal fold dimensions affect F₀, the affects are explained only by elastic wave theory.

This new concept may change the way scientists study how the voice is created as well as give additional insights to surgeons when repairing damage vocal tissue or performing reconstructive surgery.

The above concept are discussed in more detail in a recently published article:
Ingo R. Titze. Vocal Fold Mass Is Not A Useful Quantity For Describing F₀ In Vocalization. Journal of Speech, Language, and Hearing Research 2011 April; 54 (2):520-2.