Ingo R. Titze 1,2
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. One vital segment of these professional voice users are teachers. In
classrooms, teachers need to speak frequently, and often loudly, risking
occupational damage to their voices. However, unlike singers or actors, teachers
cannot cancel their performance (i.e., class) because of vocal fatigue; thus,
they must continue to use their voice in high demand situations. Further, two
studies suggest significant societal/individual impacts of these
voice problems may occur. First, while teachers comprise only 4.2% of the U.S. workforce,
a 2001 study calculated that their voice-related difficulties result in lost
workdays, payments to substitute teachers, voice therapy/rehabilitation costs,
and forced early retirement at an accumulated cost to the U.S. economy of an
estimated $2.5 billion annually (Verdolini and Ramig, Logopedics, Phoniatrics
and Vocology). Second, a 1991 study highlights what should be an expected
statistic: increased teacher absences led to decreased student attendance and
achievement (Ehrenbert et al. Journal of Human Resources, 1991).
(left) The NCVS Voice Dosimeter. (right) The accelerometer is attached to the sternal notch. The cabling runs underneath the clothing and the
dosimeter is worn at the hip to be as unobtrusive as possible.
Averages histograms for (left)
voice and silence occurrences per hour and (right) voice and silence accumulations in seconds per
hour.
Average (left) vocal
occurrences per hour and (right) voicing percentage per hour over a week.
References
Department of Speech Pathology and Audiology University of Iowa, Iowa City, IA
National Center for Voice and Speech,
The Denver Center for the Performing Arts, Denver, CO
Eric J. Hunter 2
National Center for Voice and Speech,
The Denver Center for the Performing Arts, Denver, CO
Jan G. vec 1,3
Groningen Voice Research Lab, Department of Biomedical Engineering, University of Groningen Medical Center, Groningen, the Netherlands
National Center for Voice and Speech,
The Denver Center for the Performing Arts, Denver, CO
Corresponding Author Address:
Eric J. Hunter , Ph.D.
The Denver Center for the Performing Arts
National Center for Voice and Speech
1101 13th Street
Denver, CO 80204
phone: 303-446-4839
fax: 303-893-6487
Popular version of paper 5aSC12
Presented Friday morning, June 8, 2007
153rd ASA Meeting, Salt Lake City, UT
As teaching is one of the most vocally demanding occupations, how can teachers
stay vocally healthy? What is enough vocal rest, or how long does it take for
the voice to recover (vocal recovery time)? The National Center for Voice and
Speech dosimetry data bank, currently consisting of more than 6600 hours of
voice recordings from 31 teachers, was used as the primary resource to answer
the following questions: How much do teachers actually speak in the course of a
school day? How much vocal rest do they get? How is this rest distributed
throughout the speech? How different is their voice use at work compared to when
they are not at work?
This data bank consists of voice recordings captured with the NCVS Voice
Dosimeter (Figure 1). The dosimeter can record up to 24 hours of voice data
before needing to be recharged, enough time for a normal day of speaking. The
dosimeter captures and records voice data 33 times a second. These data
determine whether the voice is being used (or the vocal cords are vibrating) and, if so,
the pitch and volume of the voice. Teachers involved in this ongoing study (the
data bank is still growing) wear the voice dosimeter all day for two weeks,
resulting in approximately 100,000 voice records per hour, 1.4 million records
per day, or 20 million records over an entire 14-day period. By capturing vocal
occurrences, occurrences of vocal silence were also known.
Figure 1.
Using these data, we were able to calculate how often teachers turned on their voices
(a vocal occurrence) and the duration of each occurrence; a short sentence may
have several vocal occurrences broken up by pauses or unvoiced consonants like
/k/. Analysis of these data captured vocal occurrences as short as 0.03 seconds
and as long as 100 seconds. On average, the teachers had 1,800 such occurrences per
hour at work, compared to 1,200 per hour during non-work periods (for as many as
20,000 per day). The high frequency of positioning the vocal folds for voicing may be a fatiguing factor
because voice muscles are used to move the vocal cords into position to vibrate,
potentially leading to repetitive motion fatigue (like pushing a button with
one finger 20,000 times a day). The data also showed that teachers vocal cords
were vibrating a cumulative average of 23% of their time at work (about 1 hour and 50 minutes of
voicing for 8 hours of work); this percentage diminished to 13% during off-work
hours and 12% on weekends (Figure 2).
Figure 2.
Figure 3.
According to Titze, Hunter and Švec (2007), this study helps pave the way for
understanding vocal fatigue in terms of repetitive motion (voice on/off) and
collision (vibration) of tissue, as well as how the voice can recover from
physical stress. Further, this study suggests that that many voice problems
stemming from vocal fatigue in teachers may come from the way teachers use their voices (e.g., teaching primarily in a monologue style, which allows
little vocal rest in a typical class period). Thus, the distribution of small
rest periods throughout a teachers speech (as a recovery time) may play an
important role to voice preservation; for example, eight hours of dialogue with
frequent turn-taking may preserve a teachers voice more than four hours of
near-monologue speech even if the overall amount of voicing is the same.
This study calls for further investigations on vocal health
of teachers and other professional voice users. What constitutes a minimum rest
period for tissues to experience any degree of recovery? Could hundreds of small
breaks (a few seconds to a few minutes) help renew blood circulation when the
vocal cords are not vibrating? What would be the ideal length and frequency of
larger voice breaks to heal a voice strained by use?
Acknowledgement
Funding for this work was provided by the
National Institute on Deafness and
Other Communication Disorders, grant number 1R01 DC04224. The authors would
like to thank the research team at the National Center for Voice and Speech with many
supporting roles in this work, particularly Albert Worley, Andrew Starr, and
Peter Popolo.
I. R. Titze, E. J. Hunter, and J. G. Švec. Voicing and silence periods in daily
and weekly vocalizations of teachers. Jounral of the Acoustical Society of
America 121 (1):469-478, 2007. (here) or (here)