Logopedics Phoniatrics Vocology, 2014; Early Online: 1–7

ORIGINAL ARTICLE

Intraoral pressures produced by thirteen semi-occluded vocal tract

gestures

LYNN MAXFIELD1, INGO TITZE1,2, ERIC HUNTER1,3 & MARA KAPSNER-SMITH4

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1National Center for Voice and Speech, University of Utah, Salt Lake City, UT, USA, 2Department of Communication
Sciences and Disorders, University of Iowa, Iowa City, IA, USA, 3Department of Communication Sciences and Disorders,
Michigan State University, East Lansing, MI, USA, and 4Department of Speech and Hearing Sciences, University of
Washington, Seattle, WA, USA

Abstract
The use of semi-occluded vocal tract (SOVT) exercises as habilitative and rehabilitative tools has grown substantially in
the past two decades. As the use of these exercises has grown, so too has the number of variations of the phonatory gestures
used to create oral semi-occlusions. While much of the research on SOVT exercises to this point has been conducted using
straw phonation, there has been little discussion or investigation regarding how other phonatory gestures that are considered
For personal use only.

to be SOVT compare to one another. The current study sought to measure the intraoral pressure produced by 13 phona-
tory gestures generally thought of as oral semi-occlusions. Twenty subjects (10 male, 10 female) produced three tokens of
each gesture, and intraoral pressure was recorded via a thin, flexible-cannula pressure transducer. Pressures ranged between
0.1 and 1.0 kPa, but varied significantly between gestures and between subjects.

Key words: Manometry, oral pressures, semi-occlusion, vocal tract

Introduction
using a variety of SOVT gestures. Even those clini-
Vocal exercises that utilize a semi-occlusion of the cians who do not utilize these therapies in their
vocal tract (SOVT) have seen an increase in use in entirety still make use of SOVT exercises such as
voice clinics and singing studios over the past several phonating through straws, nasal continuants, or sim-
decades. Singing teachers frequently use nasal con- ilar phonatory gestures.
tinuants /m/, /n/, and /ŋ/ to elicit sympathetic vibra- Vocal tract semi-occlusions can be formed by oral
tions of facial tissues, which the singer can then articulators (lips, tongue, or both) without an assis-
associate with vocal tract shapes that are advanta- tive device, or with a straw or tube inserted between
geous to a more strongly resonant vocal tone (1,2). the lips. Regardless of the nature of the occlusion,
Additionally, the use of lip trills and ‘raspberries’ to SOVT exercises are primarily used for the same gen-
achieve similar ends has become common practice eral purposes of easing phonatory stresses exerted on
in singing studios of the Western classical music tra- the vocal folds and to encourage the development of
dition (1,3). Similarly, speech language pathologists a voice production that relies more heavily on source-
have adopted SOVT exercises into their clinical filter interaction than on adductory stress to give the
treatment of voice disorders. Indeed, entire therapy voice acoustic power. Several studies have been con-
protocols such as Lessac Madsen resonant voice ducted to determine precisely what benefits SOVT
therapy (4), vocal function exercises (5), accent exercises could be expected to have on vocal produc-
method (6), and resonance tubes (7) (later with soft- tion. Tube phonation has been shown theoretically to
walled tubes—Lax Vox (8)) have been developed result in an increased acoustic impedance of the

Correspondence: Lynn Maxfield, PhD, National Center for Voice and Speech, University of Utah, Salt Lake City, UT, USA. E-mail: lynn.maxfield@
utah.edu

(Received 12 November 2013 ; accepted 31 March 2014 )

ISSN 1401-5439 print/ISSN 1651-2022 online © 2014 Informa UK, Ltd.
DOI: 10.3109/14015439.2014.913074
 2 L. Maxfield et al.
vocal tract (9). In 2006, Titze further described the their participation in the study. Inclusion criteria
rationale and theoretical underpinnings for SOVT were healthy adults with normal voices and articula-
therapy (10). In this study, computer simulations tory facilities necessary to produce all the required
indicated that semi-occlusions increase the interac- phonatory gestures. The exclusion criterion was
tion between the sound source and the vocal tract by a history of voice problems that might have been
increasing the mean intraglottal air pressure along exacerbated by the study protocol. In the end,
with supraglottal pressures. Such an interaction, if in no subjects were excluded from the entire study.
the correct proportions, may create a situation in However, three subjects (2 female, 1 male) were
which the maximum flow declination rate (MFDR) unable to produce the raspberry (linguo-labial trill
within the glottis is increased (11). with the tongue extended between closed lips) and
In human subjects studies, SOVT exercises five subjects (3 female, 2 male) were unable to pro-
have been found to improve perceived voice quality duce the tongue trill even after multiple attempts and
(12–15) and acoustic output (11,13), though results coaching from the researcher. In these cases, aver-
relating to the underlying physiology of voice pro- ages were calculated using only data from those par-
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duction have been variable. Guzman et al. also ticipants who could successfully produce the gesture.
observed that SOVT exercises ‘produced a lower Table I represents the characteristics of each of the
[vertical laryngeal position], narrower aryepiglottic study participants, including a notation if a subject
opening, and a wider pharynx than resting position’ was unable to produce an exercise.
in 20 subjects with hyperfunctional dysphonia
(16), while Laukkanen et al. noted an increase in
thyroarytenoid activity relative to cricothryroid Equipment
activity during and following SOVT exercises (17). Subjects were fitted with a head-mounted micro-
While the theoretical and anecdotal evidence of phone (Countryman Isomax B3) and EGG collar
the usefulness of SOVT exercises in the voice clinic (Kay Elemetrics Model 6103). A Glottal Enterprises
and singing studio is abundant and relatively clear, PT-25 pressure transducer, connected to an MS-110
For personal use only.

questions remain regarding which phonatory ges- analog data and computer interface was used to mea-
tures are considered to be most effective as SOVT sure intraoral pressures via an 8-cm length of flexible
exercises. In particular, if the effectiveness of a vinyl tubing (1 mm internal diameter, 3 mm external
SOVT gesture to reduce adductory stresses on the diameter), which was inserted into the oral cavity and
vocal folds is related to the supraglottal pressures positioned behind the semi-occlusion (Figure 1). An
the gesture produces, can oral occlusions be ranked additional microphone was worn by the researcher
according to their corresponding intraoral pressure?
The current study sought to create such a rank
ordering by measuring the intraoral pressure created Table I. Participant characteristics.
by 13 semi-occlusions commonly used in SOVT Singer
exercises. Subject Gender Age (Y/N) Unable to produce

F01 Female No N Tongue trill

response
Methodology F02 Female 41 Y
F03 Female 29 N Raspberry,
Subjects tongue trill
F04 Female 29 N
A total of 20 volunteers were recruited to participate F05 Female 32 N
in this study, 10 male and 10 female, ranging in age F06 Female 37 Y
from 20 to 72 years old. Approval for this research F07 Female 21 Y
was granted by an institutional review board, and F08 Female 29 N Raspberry,
tongue trill
each subject was informed of the procedure before F09 Female 29 Y
consenting to participate in the study. It was antici- F10 Female 57 Y
pated that subjects who had previous singing train- M01 Male 23 Y
ing may be more skilled at regulating oral pressures. M02 Male 20 N Tongue trill
In order to track what effect singing training might M03 Male 26 N
M04 Male 55 Y
have on oral pressures, volunteers were divided into M05 Male 42 N
two groups, singers (n ⫽ 10; 5 male, 5 female) and M06 Male 35 Y
non-singers (n ⫽ 10; 5 male, 5 female), according to M07 Male 30 Y
their experience with previous singing training. The M08 Male 30 N Tongue trill
threshold for inclusion in the singer group was a his- M09 Male 71 Y
M10 Male 26 N Raspberry
tory of at least 1 year of singing instruction prior to
 SOVT oral pressures 3
During these phonation tasks, the researcher was
monitoring the subjects’ performance to ensure
proper compliance with the protocol. If necessary,
the subjects were given further guidance and tasks
were repeated. Once the researcher was reasonably
confident in the subjects’ ability to perform the vocal
tasks accurately, the entire protocol was repeated for
each of the following oral semi-occlusions: a thin
stirring straw between the lips (3.5 mm internal
diameter, 14.1 cm length; labeled ‘small straw’ in
results), a drinking straw between the lips (6 mm
internal diameter, 19.5 cm length; labeled ‘large
straw’ in results), a long curved straw immersed in
water (5 mm internal diameter, 1 cm external diam-
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eter, 36 cm length, 7 cm depth in water; labeled

‘straw in water’ in results), an /u/ vowel, voiced fric-
atives /β:/, /v/, /z/, and /Ʒ/, nasal consonants /m/ and
/n/, a lip trill, a raspberry (lingo-labial trill), and a
tongue trill. Care was taken throughout the record-
ing process to ensure that the pressure transducer
tubing was placed behind the semi-occlusion and
remained unoccluded by the tongue or cheeks.

Figure 1. Pressure transducer with tubing inserted behind

occlusion (shown here with small straw as occlusion). Analysis
For personal use only.

Following the data collection, LabChart7 was used

to extract mean intraoral pressures from the three
to record instructions given to the subject. All data
repeated comfortable pitch/comfortable loudness
input signals were processed through a 16-channel
phonations for each of the 13 occlusion gestures.
analog-digital data acquisition device capable of DC
Upon examination, it frequently appeared that
measurements (ADInstruments Powerlab 16/30).
intraoral pressures spiked just after onset of phona-
This device was then connected via USB cable to a
tion before stabilizing at a somewhat lower level
PC running ADInstruments LabChart7 software,
within 0.5 s. Since the aim of this study was to exam-
with which all data were recorded in a proprietary
ine the intraoral pressures required to maintain pho-
format and stored for analysis.
nation with semi-occlusions of the vocal tract, mean
intraoral pressures were recorded from a 3-second
Procedure section taken from the middle of the token.

Once consent was obtained and subjects were fitted

with the instrumentation described above, each sub-
Results
ject performed two to three pitch glides and was
instructed to stop at a ‘comfortable and repeatable’ The mean intraoral pressures for all subjects are
pitch. That pitch was noted for each subject and was shown in Figure 2, with error bars representing the
used for steady phonations throughout the protocol. standard error. As expected, females produced lower
Subjects were then asked to perform the following pressures overall than males. However, with few
tasks with the mouth in an open /a/ vowel shape: 1) exceptions, the average pressures were ranked in the
three pitch glide ‘sirens’ (gliding from the bottom of same order for both genders. These results also show
their pitch range to the top of their pitch range and a considerable range of pressures being created by
returning to the bottom) at a comfortable loudness, the different semi-occlusions. Male mean pressures
2) three sustained phonations held for 3–5 seconds ranged from 0.08 kPa (0.77 cmH2O) for the /m/ con-
on the comfortable pitch identified earlier and at a tinuant to 1.08 kPa (11.13 cm H2O) for the straw in
comfortable loudness, 3) one sustained phonation water. Mean female pressures ranged from 0.06 kPa
held for 3–5 seconds on the comfortable pitch and (0.61 cmH2O) for the /n/ continuant to 0.8 kPa
as softly as possible, and 4) one sustained phonation (8.23 cmH2O) for the straw in water. Individual
held for 3–5 seconds on the comfortable pitch and pressures varied to an even greater extent, from
as loudly as possible (without causing discomfort). 0.03 kPa (0.34 cmH2O) to 1.74 kPa (17.77 cmH2O)
 4 L. Maxfield et al.
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Figure 2. Mean intraoral pressure for all subjects (*indicates subjects had difficulty producing the semi-occlusion).

in males and from 0.03 kPa (0.35 cmH2O) to between singers and non-singers; however, the stan-
1.15 kPa (11.69 cmH2O) in females. Additionally, as dard errors would indicate that these differences may
For personal use only.

can be seen in Figure 2, relatively large standard not have been significant in these subjects.
errors resulted from the considerable differences in
individual performance of each task.
Discussion
Figures 3 and 4 represent the male and female
mean oral pressures, respectively, comparing singers Oral semi-occlusions designed for voice training
to non-singers. There does appear to be differences and therapy produced intraoral pressures within a

Figure 3. Male mean intraoral pressures, singers versus non-singers.

 SOVT oral pressures 5
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Figure 4. Female mean intraoral pressures, singers versus non-singers.

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magnitude range of about 10:1 at comfortable lung exercises to lower adductory stresses during phona-
pressures (Tables II and III). Nasal consonants (/m/ tion. Considering the standard errors, it is likely that
and /n/) produced only about half of the smallest a single semi-occlusion might well shift in the rank-
pressures produced with oral semi-occlusions (e.g. ing by one or two positions up or down with the
straws, fricatives, and trills). With such a large mag- addition of more subjects or more repetitions. It
nitude range, there may be varied training efficacy appears unlikely, however, that the ranking would
within this large inventory of exercises. change significantly from this order.
The likely root cause of the large standard errors The results also indicate that /m/, /n/, and /u/ pro-
in the pressures reported above is differences in lung duce quite low intraoral/supraglottal pressures. While
pressure between subjects. If lung pressure were singing teachers and clinicians may well find benefit
measured for each of these semi-occlusions, a ratio from exercises incorporating these semi-occlusions,
of intraoral pressure to lung pressure would be the current results seem to call into question whether
a more accurate measure of the ability of these or not those exercises fall into the same category as

Table II. Female mean pressures and standard errors.

All subjects Non-singers Singers

Females (kPa) Avg SD Avg SD Avg SD

/m/ 0.06882 0.018216 0.064843 0.015945 0.072797 0.019437

/n/ 0.062311 0.021496 0.059363 0.023394 0.065259 0.01896
/u/ 0.089218 0.042842 0.101841 0.037737 0.076595 0.043911
Large straw 0.192907 0.096332 0.226241 0.108673 0.159574 0.067288
/z/ 0.236588 0.103218 0.215216 0.060892 0.257959 0.129177
/ʒ/ 0.216041 0.078364 0.207951 0.069365 0.224131 0.085671
Tongue trill 0.339722 0.317297 0.23557 0.069448 0.416089 0.437781
Bilabial fricative 0.214548 0.22327 0.44572 0.366307 0.137626 0.123106
/v/ 0.344737 0.164682 0.28906 0.123946 0.400413 0.178676
Lip trill 0.339692 0.154148 0.389057 0.182664 0.3002 0.112111
Small straw 0.474503 0.216933 0.48272 0.231978 0.466285 0.200428
Raspberry 0.683618 0.294121 0.851734 0.335881 0.57748 0.215192
Straw in water 0.839575 0.267563 0.920262 0.310219 0.758888 0.184182
 6 L. Maxfield et al.
Table III. Male mean pressures and standard errors.

All subjects Non-singers Singers

Males (kPa) Avg SD Avg SD Avg SD

/m/ 0.079372 0.03061 0.089436 0.040298 0.069308 0.006887

/n/ 0.085105 0.057577 0.09073 0.07653 0.07948 0.026648
/u/ 0.99855 0.028144 0.104565 0.040726 0.096974 0.031859
Large straw 0.286015 0.159608 0.292158 0.1649 0.279872 0.153888
/z/ 0.322738 0.097256 0.2621 0.029898 0.383375 0.103295
/ʒ/ 0.337439 0.130202 0.243622 0.071525 0.431257 0.105763
Tongue trill 0.380012 0.167704 0.244698 0.130605 0.463165 0.14519
Bilabial fricative 0.422454 0.298852 0.379273 0.158474 0.465635 0.387017
/v/ 0.429702 0.235803 0.347575 0.122096 0.51183 0.287765
Lip trill 0.517554 0.18238 0.399124 0.131042 0.1732 0.051645
Small straw 0.596735 0.244192 0.599753 0.242704 0.593718 0.245633
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Raspberry 0.74522 0.230041 0.618764 0.164493 0.964312 0.225224

Straw in water 1.123089 0.364047 1.139582 0.322701 1.106596 0.400475

other SOVT exercises that produce higher intraoral diameters larger than 3.5 mm in air (i.e. not sub-
pressures. merged in water, which would provide more resis-
It also appears that singing training has some tance) may not produce the intraoral pressures
effect on intraoral pressures produced during SOVT desired for efficient and effective voice therapy.
phonation. Figures 3 (males) and 4 (females) show
significant differences in pressures produced by sing-
ers versus non-singers for several of the occlusions. If Conclusion
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it is desirable to find exercises that are effective for

This study provides data supporting a preliminary
most individuals, regardless of their history of vocal
rank-ordering of SOVT exercises according to the
training, finding exercises that produce pressures
intraoral pressures they produce during phonation.
consistently across subjects with varied experience
There is now evidence that, while many exercises can
levels and training backgrounds is important. The
be considered to fall into the category of SOVT exer-
results of this study seem to indicate that straw exer-
cises, intraoral pressures vary significantly between
cises do just that. Specifically, the 3.5 mm diameter
them and between individuals, bringing into question
straw between the lips (‘small straw’ in Figures) pro-
their equality in treatment efficacy. In particular, the
duced the most consistent pressures across subjects
nasal continuants /m/ and /n/ produce very low
for both males and females. It is likely that straw exer-
intraoral pressures, possibly calling into question their
cises owe their pressure stability to the fact that they
inclusion in the SOVT category of vocal exercises.
provide a semi-occlusion of fixed diameter and shape.
Phonation through thin tubes or straws that provide
All that the individual must do is ensure that the lips
resistance comparable to or greater than glottal resis-
form a tight seal around the straw. This is in contrast
tance may be one way to achieve adequate and some-
to an exercise such as the lip trill or bilabial fricative
what controlled intraoral pressures during SOVT
/β:/, which can be greatly affected by the tightness
exercises.
with which the subject performs the exercise (18).
Moving forward, a more accurate ordering may
Why, then, does it appear that the ‘large straw’
be created by taking into account the lung pressures
failed to provide the same stability among females
that individual subjects are using to produce SOVT
(Figure 4) that it provided among males (Figure 3)?
exercises. However, barring invasive measurements
This may be explained by the difference in dimen-
of lung pressure (e.g. tracheal puncture), the findings
sions of the glottis and vocal tract between males and
of this study provide a new lens through which clini-
females. In order to overcome the effects of vocal
cians may evaluate their own use of these exercises
training, it appears that the semi-occlusion must pro-
with their patients.
vide resistance to the airflow at a level similar to that
produced by the glottis itself. The large straw pro-
vided sufficient resistance in the males, whose mean Declaration of interest: The authors report no
glottal openings are larger and thus produce less conflicts of interest.
resistance, but it failed to do so in females, whose This work is partially supported by the National
mean glottal openings are smaller. Considering this Institutes of Health (NIDCD grant number
difference between males and females, straws with R01DC012045-01A). We are also happy to acknowl-
 SOVT oral pressures 7
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