The Human Voice
Author(s): Robert T. Sataloff
Source: Scientific American , Vol. 267, No. 6 (DECEMBER 1992), pp. 108-115
Published by: Scientific American, a division of Nature America, Inc.
Stable URL: https://www.jstor.org/stable/10.2307/24939336
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The Human Voice
How the voice works was largely unknown until
modern technology became available. New instruments
are now improving the care and treatment ofthe voice
T
wenty years ago the human voice
was a mystery. Little was known
about how it works or how to care
for it, despite centuries of fascination
with the voices of singers and actors
and the crudal importance of vocal communication
to society. Literature on
voice medicine, and particularly on the
care of the professional voice, was
scarce. In the few papers that did exist,
there was scant emphasis on how the
voice worked.
The state of therapy was equally
weak. Nonsurgical treatments of benign
vocal-fold problems were controversial,
and the surgery available involved vocal-cord
stripping. (Spedalists replaced
the term "cord" about 10 years ago with
the more descriptive term "fold.") This
procedure ripped away the superficial
layers of the vocal fold under the assumption
that healthy tissue would
grow to replace the unhealthy tissue.
Unfortunately, many patients ended up
permanently hoarse, although their vocal
folds afterward looked normal.
Since that time, a new medical subspecialty
has emerged. Spurred by interest
in the problems of professional
singers and actors, scientific and technological
advances have raised the standard
of care for all voice patients. These
improvements were made possible by
interdisciplinary collaborations among
professionals, who, at first, barely spoke
the same language. The VOice Foundation,
which was established by physidan
ROBERT T. SATALOFF is professor of
otolaryngology at Jefferson Medical College
of Thomas Jefferson University in
Philadelphia and editor of The Journal
of Voice. He is also a professional singer
and singing teacher and serves on the
faculty of the Curtis Institute of Music
and of the Academy of Vocal Arts.
In addition, he is a university choir and
orchestra conductor. He has published
more than 150 scientific articles and 10
books, including Professional Voice: The
Science and Art of Clinical Care.
by Robert T. Sataloff
Wilbur James Gould of New York City
to promote such interactions, held its
first symposium in 1972 and brought
together laryngologists, voice scientists,
speech pathologists, singing and acting
teachers and performers. The exchange
of ideas at that meeting led to new collaborations,
new directions in research
and many major advances.
Today, 20 years later, it is possible
for a singer with a few "lost notes," a
governor running for president, a salesperson
whose voice is weak, a smoker
with a tumor or anyone else with a
voice complaint to get sophisticated
medical attention. That care is a result
of the growing understanding of how
the voice works.
The vocal mechanism involves the
coordinated action of many muscles,
organs and other structures in the abdomen,
chest, throat and head. Indeed,
virtually the entire body influences the
sound of the voice either directly or indirectly.
For grasping the vulnerabilities
of the vocal tract, a brief tour of this
complex, delicate mechanism is necessary.
The first stop, and the best-known
part of the mechanism, is the larynx, or
voice box.
The larynx has four basic anatomic
components: a cartilaginous skeleton,
intrinsic muscles, extrinsic muscles and
a mucosa, or soft lining. The most important
parts of the laryngeal skeleton
are the thyroid cartilage, the cricoid cartilage
and the two arytenoid cartilages.
The extrinsic muscles connect these cartilages
to other throat structures; the intrinsic
muscles run between the cartilages
themselves.
One pair of intrinsic muscles extends
from the arytenoid cartilages to a point
inside the thyroid cartilage, just below
and behind the Adam's apple. These
thyroarytenoid muscles form the bodies
of the vocal folds; the space between
them is the glottis. The vocal folds are
normally the source of the human voice.
The intrinsic muscles can change the
relative positions of the cartilages and
pull them through a range of motions.
108 SCIENTIFIC AMERICAN December 1992
These changes alter in turn the shape,
position and tension of the suspended
vocal folds. The cricothyroid muscle,
for example, participates in the control
of pitch by increasing the longitudinal
tension (stretching) of the vocal folds.
The extrinsic muscles, also known as
the strap muscles of the neck, raise and
lower the laryngeal skeleton. The resulting
accordion effect also changes
the angles and distances between the
cartilages and alters the resting lengths
of the intrinsic muscles. The larynx has
a natural tendency to rise and fall as
the pitch of the voice ascends and descends.
Such large adjustments in position,
however, interfere with the fine
control over the vocal folds that is essential
for smooth vocal quality. For
that reason, classically trained singers
are generally taught to use their extrinsic
muscles to maintain the laryngeal
skeleton at a fairly constant height regardless
of pitch. This technique enhances
a unified vocal quality throughout
a singer's range.
T
he soft tissues lining the larynx
are much more complex than had
been thought. The mucosa forms
the thin, lubricated surface of the vocal
folds that makes contact when they are
closed. The mucosa overlying the vocal
folds is different from that lining the
rest of the larynx and respiratory tract:
it is stratified squamous epithelium,
which is better suited to withstand the
trauma of vocal-fold contact.
The vocal fold is not a simple muscle
covered with mucosa. In 1975 physician
Minoru Hirano of Kurume, Japan, identified
five distinct tissue layers in the
VOCAL-FOLD SURGERY prolonged the
career of the popular singer Elton John.
He had trouble with his voice during a
tour of the U.S. in 1986. The problem
turned out to be a nonmalignant lesion,
which surgeons successfully removed
early in 1987. A year later he was able
to resume giving concerts.
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SCIENTIFIC AMERICAN December 1992 109
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x
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structure. Beneath the thin, lubricated
epithelium on the surface lie the superficial,
intermediate and deep layers of
tissue called the lamina propria. Underlying
the lamina propria is the thyroarytenoid
(or vocalis) muscle itself. The
five layers have different mechanical
properties that produce the smooth
shearing motions essential to healthy
vocal-fold vibrations.
When the vocal folds vibrate, they produce
only a buzzing sound. That sound
resonates, however, throughout the supraglottic
vocal tract, which includes the
pharynx, the tongue, the palate, the oral
cavity and the nose. That added resonance
produces much of the perceived
character and timbre, or vocal quality,
of all sounds in speech and song.
The power source for the voice is the
infraglottic vocal tract-the lungs, rib
cage and abdominal, back and chest
muscles that generate and direct a controlled
airstream between the vocal
folds. As the glottis closes, opens and
alters shape, its air resistance changes
almost continuously. The power source
must therefore make rapid, complex adjustments
to maintain a steady vocal
CROSS SECTION OF VOCAL FOLD
EPITHELIUM
LAMINA PROPRIA {SUPERFICIAL
(MIDDLE LAYERS INTERMEDIATE
OF VOCAL FOLD)
DE
POSTERIOR
CRICOARYTENOID
MUSCLE
TRANSVERSE AND
OBLIQUE ARYTENOID
MUSCLES
GLOTTIS
CRICOID CARTILAGE
VOCALIS MUSCLE
THYROID CARTILAGE
quality. Singers and actors refer generally
to the entire power complex as
their "support" or "diaphragm." Actually,
the anatomy of the power complex
is complicated and not completely
understood, and performers who
use such terms do not always mean the
same thing.
T
he principal muscles of inspiration,
or inhalation, are the diaphragm
(a dome-shaped muscle
that extends along the bottom of the
rib cage) and the external intercostal
(rib) muscles. Expiration, or exhalation,
is largely passive during quiet respiration:
the mechanical properties of the
lungs and rib cage typically force air
out of the lungs effortlessly after a full
breath. Of course, active expiration is
also pOSSible, and many of the muscles
involved in this process are also used to
support voice production, or phonation.
During active expiration, muscles may
raise the pressure within the abdomen
and thereby force the diaphragm upward.
Alternatively, they may lower the
ribs and sternum to decrease the dimensions
of the thorax. The primary
muscles of expiration are the abdominal
muscles, but internal intercostals
and other chest and back muscles also
contribute.
Trauma or surgery that alters the
structure or function of these muscles
undermines the power source of the
voice, as do asthma and other diseases
that impair expiration. People often
compensate for deficiencies in their
support mechanism by overworking
their laryngeal muscles, which are not
designed to serve as a vocal power
source. Such behavior can result in decreased
function, rapid fatigue, pain
and even structural problems, such as
vocal-fold nodules.
Like the muscular and skeletal systems,
the nervous system also contributes
to voice production. The "idea" for
a voice sound originates in the cerebral
cortex and travels to motor nuclei in
the brain stem and spinal cord. These
areas send out complicated messages
for coordinating the activities of the larynx,
the thoracic and abdominal musculature
and the vocal-tract articulators.
Signals from certain divisions in the nervous
system, called the extrapyramidal
1 10 SCIENTIFIC AMERICAN December 1992
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REAR VIEW OF LARYNX FRONT VIEW OF LARYNX RIGHT VIEW OF LARYNX
EPIGLOTTIS
OBLIQUE
ARYTENOID
MUSCLE
TRANSVERSE
ARYTENOID
MUSCLE
POSTERIOR
CRICOARYTENOID
MUSCLE
CRICOID
CARTILAGE
THYROID
CARTILAGE
TRACHEA
Anatomy of the Voice
HYOID BONE
OBLIQUE
ARYTENOID
MUSCLE
TRANSVERSE
ARYTENOID
MUSCLE
CRICOTHYROID
MUSCLE
POSTERIOR
CRICOARYTENOID
MUSCLE
V
ocal mechanism encompasses many muscles and organs
of the abdomen, chest, throat and head. The
drawing at the far left portrays those in the throat and
head. Details of the larynx, or voice box, are shown to the
right of that drawing in an orientation looking down on the
structure with the front-the Adam's apple-facing the bottom.
The two vocalis muscles constitute the bodies of the
vocal folds, which were formerly known as the vocal cords;
a cross section of one of them appears above the representation
of the larynx. The remaining three drawings (above)
show the major muscles and cartilages of the larynx from
the rear (left), the front and the right side.
tract and the autonomic nervous system,
also refine these activities.
The nerves that control the muscles
of the vocal tract are potential sources
of voice problems. For example, the
two recurrent laryngeal nerves control
most of the intrinsic muscles in the larynx.
Because those nerves (especially
on the left) run through the neck, down
into the chest and then back up to the
larynx, they are easily injured by trauma
or surgery on the neck and chest.
Nerves also provide feedback to the
brain about voice production. Auditory
feedback, which is transmitted from the
ear through the brain stem to the cerebral
cortex, allows a vocalist to match
the sound produced with the sound intended.
Tactile feedback from the throat
and muscles also may help with the
fine-tuning of vocal output, although
that process is not fully understood.
Trained singers and speakers cultivate
their ability to use tactile feedback effectively
because they expect that poor
room acoustics, loud musical instruments
or crowd noises will interfere
with the auditory feedback.
During phonation, all those anatomic
structures and systems must work together.
The physiology of voice production
is exceedingly complex, but the
voice can be likened to a trumpet. Power
for the sound is generated by the chest,
abdomen and back musculature, which
produce a high-pressure airstream. A
trumpeter's lips open and close against
the mouthpiece to create a buzz similar
to that produced by the vocal folds.
This sound then resonates through the
rest of the trumpet, which is analogous
to the supraglottic vocal tract.
M
uch of the progress during the
past 20 years has come from
filling in the details of how vocal
sounds originate and change. Part
of this effort has involved modeling the
movements of the vocal folds. Although
a vocal fold has a five-layer anatomy, it
behaves mechanically more like a threelayer
structure, consisting of a cover
(epithelium and superficial layer of the
lamina propria), a transition layer (intermediate
and deep layers of the lamina
propria) and a body (thyroarytenoid
muscle).
Observations and modeling studies
have revealed how the larynx produces
a sound. Initially, the vocal folds are in
contact, and the glottis is closed. As the
lungs expel air, pressure below the glottis
builds, typically to a level of about
seven centimeters of water for conversational
speech. This pressure progressively
pushes the vocal folds apart from
the bottom up, until the glottis is open
and air begins to flow. Elastic and other
forces resist the separation of the upper
margin of the vocal folds, but the
airstream overpowers them.
The flow of air, however, produces a
Bernoulli effect-that is, a reduction in
the lateral air pressure caused by its
forward motion. The effect tends to pull
the vocal folds shut, as do the elastic
properties of the vocal-fold tissues. The
pressure of the airstream below the
glottis also diminishes as the glottis
opens to let the air out.
Because of these factors, the lower
edges of the vocal folds begin to close
almost immediately, even though the
upper edges are still separating. That
closure further diminishes the force of
the airstream. The upper margins of the
vocal folds then snap back to the midSCIENTIFIC
AMERICAN December 1992 III
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line and close the glottis. Subglottal
pressure builds again, and the events
repeat themselves. (It should be understood
that there is direct pressure and
that the alternating variations rarely
drop the subglottal pressure to zero.
This fact is important in understanding
the driving forces involved in the motions
of the vocal fold.)
An important aspect of this process is
that the lower part of the vocal folds begins
to open and close before the upper
part. The rippling displacement of the
vocal-fold cover produces a wave moHow
the Voice Is Produced
T
he production of speech or song, or even just a vocal sound, entails a
complex orchestration of mental and physical actions. The idea for making
a sound originates in the cerebral cortex of the brain-for example, in the
speech area. The movement of the larynx is controlled from the voice area
and is transmitted to the larynx by various nerves. As a result, the vocal
folds vibrate, generating a buzzing sound. It is the resonation of that sound
throughout the area of the vocal tract above the glottis-an area that includes
the pharynx, tongue, palate, oral cavity and nose-that gives the sound the
qualities perceived by a listener. Auditory feedback and tactile feedback enable
the speaker or singer to achieve fine-tuning of the vocal output.
HYOID BONE
CRICOID CARTILAGE -------�
112 SCIENTIFIC AMERICAN December 1992
SPEECH
AREA IN
TEMPORAL
CEREBRAL
CORTEX
VOICE AREA
IN MOTOR
STRIP OF
PRECENTRAL
GYRUS
NUCLEUS
AMBIGUUS
10TH
CRANIAL
(VAGUS)
NERVE
SPINAL CORD
SUPERIOR
LARYNGEAL
NERVE
VAGUS
NERVE
RECURRENT
LARYNGEAL
NERVE
tion in the mucosal layer. If the complex
vibration of that glottal wave is
impaired, hoarseness or other changes
in voice quality may result.
The vocal folds do not excite the air
by vibrating like violin strings. Instead,
by opening and closing the glottis, they
create puffs of air in the vocal tract. The
sudden cessation of airflow at the end
of each puff produces an acoustic vibration.
The mechanism is similar to
that which causes the sound of hand
clapping.
The sound from the larynx is a complex
tone containing a fundamental frequency,
or pitch, and many overtones,
or higher harmonic partials. (Frequency
is measured in hertz, the number of
opening and closing cycles in the glbttis
each second.) Surprising as it may
seem, trained and untrained vocalists
produce about the same spectrums at
the vocal-fold level.
The pharynx (the throat area between
the mouth and the esophagus), the oral
cavity and the nasal cavity act as a series
of interconnected resonators for the
voice signal. The system is more complex
than a trumpet because its walls,
and hence its shape, are flexible. In any
resonator, some frequencies are attenuated
while others are enhanced, or radiated
with higher amplitudes. Certain harmonic
partials therefore become relatively
softer while others grow louder.
lohan Sundberg of the Royal Institute of
Technology in Stockholm has shown for
singers (and his colleague Gunnar Fant
for speakers) that the vocal tract has
four or five important resonance frequencies
called formants. The intensity
of the voice source diminishes uniformly
across its frequency spectrum except at
the formant frequencies, where it peaks.
F
ormant frequencies are established
by the shape of the vocal
tract, which can be altered by the
laryngeal, pharyngeal and oral cavity
musculature. Overall, the length and
shape of one's vocal tract are individually
fixed and determined by age and
sex: women and children have shorter
vocal tracts than do men and consequently
have higher formant frequencies.
Nevertheless, the dimensions of
the vocal tract can be consciously adjusted
to some degree, and mastering
those adjustments is fundamental to
voice training.
One resonant frequency that has received
attention is known as the singer's
formant. It appears to be responsible
for the "ring" in a singer's or speaker's
voice. The ability to make oneself
heard clearly even over an orchestra depends
primarily on the presence of the
singer's formant: there is little or no
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significant difference in the maximum
vocal intensities of trained and untrained
singers.
The singer's formant occurs at around
2,300 to 3,200 hertz for all vowel
sounds. Aside from adding clarity and
projection to a voice, it also contributes
to differences in timbre. The singer's
formant occurs in basses at about 2,400
hertz, in baritones at 2,600 hertz, in tenors
at 2,800 hertz, in mezzo-sopranos
at 2,900 hertz and in high sopranos at
3,200 hertz. The singer's formant is often
much less pronounced in sopranos.
Control over two vocal characteristics-fundamental
frequency and intensity-is
crucial. One way to raise the
fundamental frequency is to raise the
pressure of the airstream moving
through the larynx. For mechanical reasons,
as the pressure rises, the vocal
folds tend to blow apart and to snap
shut more quickly and frequently. Singers
learn to compensate for this tendency:
otherwise, their pitch would rise
whenever they tried to sing louder.
Generally, the most efficient technique
for altering the pitch is to change
the mechanical properties of the vocal
folds. Contracting the cricothyroid muscle
makes the thyroid and cricoid cartilages
pivot and stretches the vocal folds.
This change exposes more surface area
on the vocal folds to the airstream and
thereby makes them more responsive
to air pressure. It also stretches the
elastic fibers of the vocal folds and increases
their efficiency at snapping back
together. The pitch rises because the
cycles of opening and closing in the
glottis (phonatory cycles) shorten and
repeat more frequently.
Vocal intensity, or loudness, depends
on how much the vocal-fold vibrations
excite the air in the vocal tract. Raising
the air pressure increases the amplitude
of the vibrations because the vocal
folds move farther apart and snap
together more briskly. Consequently,
during each phonatory cycle, the flow
of air through the larynx cuts off more
sharply, and the intensity of the produced
sound increases. A similar effect
increases the intensity of the sound of
hand clapping.
A useful biophysical indicator of the
efficiency of vocal control strategies
can be seen in flow patterns during
each phonatory cycle. For example, a
vocalist may attempt to increase vocal
intensity by excessively raising both
the air pressure and the resistance
of the glottis to the flow of air, using
the muscles of the infraglottic vocal
tract and the adductory (glottis-closing)
forces of the vocal folds. Such a combination
of forces results in a condition
called pressed phonation, in which the
amplitude of the voice's fundamental
frequency is low despite considerable
physical effort.
The amplitude of the voice source
will also be low if the adductory forces
are so weak that the vocal folds do not
make contact and the glottis becomes
inefficient. This condition results in
breathy phonation. In contrast, a third
and more desirable condition known as
flow phonation is characterized by low
airstream pressure and low adductory
force, which increase the intensity of
the fundamental frequency and make
the voice louder. To identify pressed,
breathy or flow phonation, voice specialists
can plot changes in the flow of
air through the glottis, thus producing
a graph called a flow glottogram.
Sundberg has shown that a vocalist
can raise the amplitude of the fundamental
frequency by 15 decibels or
more Simply by changing from pressed
phonation to flow phonation. Hence,
people who rely habitually on pressed
phonation expend unnecessary effort
to achieve a loud voice. The forces and
patterns of muscle use recruited to
compensate for this inefficiency may
damage the larynx.
B
y understanding the vocal control
mechanisms, physicians can detect
and correct the problems
that abuse the voice and traumatize the
vocal folds. Understanding the function
of each component of the vocal
tract also aids the development of optimal
strategies for rehabilitating damaged
voices.
The development of new tools has
been critical for the science of the
voice. Until the 1980s, the physician's
ear was routinely the sole instrument
used to assess voice quality and function.
Practical techniques for observing
and quantifying voice functions were
generally lacking.
In 1854, for instance, a singing teacher
named Manuel Garcia devised the
technique of indirect laryngoscopy. He
used the sun as a light source and a
dental mirror placed in a student's
mouth to look at the vocal folds. Indirect
laryngoscopy rapidly became a basic
tool for physicians, and it is still in
VIBRATION OF VOCAL FOLDS is shown,
in a vertical cross section through the
middle part of the vocal folds, during
the production of a single sound. The
perspective is from the front of the larynx.
Before the process starts (1), the
folds are together. They separate as air
is forced upward through the trachea
(2-7) and then come together again as
the sound ceases (8).
2
AIR IN
TRACHEA
3
4
UPPER
EDGE OF
VOCAL
FOLD
5
6
LOWER
EDGE OF
VOCAL
FOLD
7
8
VOCAL FOLDS
SOUND
SCIENTIFIC AMERICAN December 1992 113
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daily use. (Today, of course, we use an
electric light instead of the sun.)
Yet as valuable as this technique has
been, it has many disadvantages. Effective
magnification of the vocal folds and
photographic documentation of their
condition are difficult. Also, standard
lighting does not permit physicians to
see the rapid, complex vibrations of
the vocal folds.
Currently the primary technique for
inspecting vocal-fold vibrations is strobovideolaryngoscopy.
It uses a microphone
placed near the larynx to trigger
a stroboscope that illuminates the
vocal folds. If the frequency of the
stroboscopic light is about two hertz
out of phase with the vibration, an observer
can watch the vocal folds in simulated
slow motion. A crude version of
this technique was actually first developed
in the 19th century. Only during
the past decade, however, have stroboscopes
become bright enough and video
cameras sufficiently sensitive for it
to be useful routinely.
The stroboscopic effect permits detailed
evaluation of the vocal-fold edge.
Physicians can see small masses, vibratory
asymmetries, scars, early carcinomas
and other laryngeal abnormalities-many
of which are not detectable
under normal light. Digital analysis of
the images can also supplement visual
assessments, although poor image resolution
and some other problems have
limited the value of the technique so far.
Another method for monitoring vocal-fold
vibrations is electroglottography.
A weak high-frequency voltage between
two electrodes placed on the neck
passes through the larynx. Changes in
the measured voltage generate a wave
on the electroglottograph that illustrates
vocal-fold contact. Information
about the open glottis can be inferred
from photoglottography, which measures
light passed from below the vocal
folds, or from flow glottography.
M
easurements of aerodynamic
function, which include comprehensive
testing of pulmonary
function and laryngeal airflow, are
especially valuable. Together they reveal
both the function of the vocal power
source and the efficiency of the vocal
folds for controlling airflow. Measurements
of phonatory ability-the ability
to produce sounds-are Simple and
useful for quantifying vocal dysfunctions
and evaluating the results of treatment.
Such tests determine the frequency
and intensity ranges of the voice,
how long a sound can be produced and
other factors.
Laryngeal electromyography, another
technique for studying voice function,
HEALTHY AND AIUNG VOICES are compared in these sonograms made as the
speakers produced the sound of "a" as in "father." Time runs from left to right for
about two seconds. The horizontal lines mark off frequencies in hertz from zero at
the bottom to 7,000 at the top. The sonogram at the left is from a male speaker
involves the insertion of thin electrodes
into the laryngeal muscles. It is useful
in specialized circumstances for assessing
neuromuscular integrity and function.
For instance, measurements of
electrical activity in the laryngeal muscles
may foretell a patient's recovery
from vocal-fold paralysis. In that case,
before considering surgery, a physician
might recommend waiting for a spontaneous
recovery.
A skilled laryngologist or another
trained listener can glean much from
the sound of a voice. Nevertheless, clinicians
and researchers need equipment
capable of quantifying the vocal characteristics
that are meaningful to the
ear. The available equipment is helpful,
but it needs further improvement.
For example, acoustic spectrography
displays the frequency and harmonic
spectrum of a voice and visually records
noise. The equipment depicts the
acoustic signal and enables researchers
or physicians to make generalizations
about the vocal quality, pitch and
loudness. A variety of qualities can be
measured: the formant structure and
strength of the voice, the fundamental
frequency, breathiness, the harmonicsto-noise
ratio (or clarity of the voice) and
perturbations of the cycle-to-cycle amplitude
("shimmer") and of the cycle-tocycle
frequency ( "jitter"). Subtle characteristics,
however, still cannot be detected.
For instance, in studies of voice
fatigue in trained singers, the difference
between a rested and tired voice is usually
obvious to the ear, but significant
changes cannot be detected consistently
even with sophisticated equipment.
Psychological influences on the voice
are also critical, but the techniques for
evaluating them are poorly standardized.
Nevertheless, well-developed questionnaires,
tape recordings and assessment
of voice by several observers have
boosted the utility of such examinations.
All these tools help physicians to
detect and record the information contained
in the sound of the voice more
reliably and validly.
A
technology has enhanced the diagnostic
and therapeutic aspects
of voice medicine, the need for
laryngeal surgery has diminished. Some
conditions require little more than the
prescription of drugs. Medications must
be used with caution, however, because
even many over-the-counter remedies
have side effects that adversely affect
voice function. Antihistamines, for example,
cause dryness in the vocal mucosa,
which can lead to hoarseness and
coughing. The anticoagulant properties
of aspirin can contribute to vocal-fold
hemorrhages.
Techniques have been developed to
rehabilitate voices that have been damaged
through misuse. Voice therapy facilitates
breathing and abdominal support
and helps to eliminate unnecessary
muscle strain in the larynx and neck. It
can even cure some structural problems
of the vocal folds, most notably nodules
(hard, callouslike growths). Therapy
helps patients to learn how to use
each component of the vocal tract appropriately
so as to avoid straining and
abusing their voices, how to maintain
the correct levels of moisture and mucus
in their vocal tracts and how to mitigate
the effects of smoke and other
hazards in the environment.
Good vocal hygiene and technique,
however, are not always enough. Some
structural problems in the larynx must
be treated with surgery. These problems
include nodules that have not responded
to voice therapy, polyps (softtissue
growths), cysts (fluid-filled masses)
and other growths.
Most benign pathological conditions
114 SCIENTIFIC AMERICAN December 1992
© 1992 SCIENTIFIC AMERICAN, INC
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• .... ",00' "" .... _ _ � ...... � O- • • :' .0; . -.' • • � . �
:t.'"'. � . ' � ' . •" , • �
.. - , ... .
.--:::.� --..:.,::-i-:'-:--.:' �::.:- :--:.-:-:-..: .- .--.-,-:' . :'. : .-.- . '.. : ., .. ,. -.::-�-/�=:--:--. --:--:..��-.:--:.---
--"--------�------"'--
with normal vocal folds; the one at the right is from a male speaker with growths
on his vocal folds. His voice makes additional noise in the range above 5,000 hertz
and has disrupted and weakened harmonics between 2,000 and 4,000 hertz. The
result is that his voice sounds harsh and hoarse.
are conveniently superficial. By a variety
of delicate microsurgical techniques,
surgeons can now usually remove lesions
from the epithelium or the superficial
layer of the lamina propria without
disrupting the intermediate or deep
layers of the tissue, which form scars.
Such procedures are now commonly
described as phonosurgery. (That term
originally referred only to operations designed
to alter vocal pitch and quality.)
Most voice surgery is performed
through the mouth while the surgeon
views the larynx through a metal tube
called a rigid laryngoscope. An operating
microscope magnifies the larynx. A
surgeon can then treat the laryngeal
abnormalities with microscopic scissors,
lasers and other instruments.
Nodules, polyps and cysts on the vibratory
margin of the vocal folds are
removed most safely with traditional
surgical instruments. The operations
can be remarkably precise: in some cases,
it is possible to raise the vocal-fold
mucosa, remove a cyst or other underlying
mass and then replace the mucosa.
Such minimally traumatic surgery does
not even require postoperative voice
rest, and rapid healing with good voice
quality usually follows.
Lasers are often celebrated as revolutionary
high-tech surgical instruments,
but they are not always the best choice
for laryngeal surgery. At the power densities
required for the surgical ablation
of tissue, the beam from a standard carbon
dioxide laser would be surrounded
by a heat halo as much as 0.5 millimeter
wide. If the beam were directed against
a lesion on the edge of the vocal fold,
the heat might provoke scarring in the
intermediate or deep layers of the lamina
propria. Such a scar would create a
nonvibrating segment on the vocal fold;
hoarseness would result.
Nevertheless, the carbon dioxide laser
is extremely useful for some lesions. It
can seal off varicose blood vessels in
the vocal folds that might hemorrhage,
and it can vaporize blood vessels that
nourish laryngeal polyps, papillomas
and some cancers. Further research and
development in laser technology is likely
to provide an instrument better suited
for microsurgery on the vocal fold
in the near future.
New surgical techniques for modifying
the laryngeal skeleton have been pioneered
by physician Nabuhiko Issiki
of Kyoto. These have become extremely
useful for treating vocal-fold paralysis,
which is a common consequence of
viral infections, surgery or cancer. Traditionally,
surgeons have treated vocalfold
paralysis by injecting small volumes
of Teflon into the affected vocal
fold. The Teflon pushes the paralyzed
fold toward the midline of the glottis
and allows the normal fold to meet it.
The glottis can then close, and the patient's
voice is often improved.
Yet although Teflon is relatively inert,
tissue reactions to it are not uncommon.
The stiffness that the Teflon produces
in the vocal-fold edge frequently impairs
the quality of the voice. Also, if the results
of the Teflon injection are unsatisfactory,
it is difficult to remove the
material from the tissues.
For these reasons, Teflon injections
have generally been replaced by thyroplasty.
In this technique, a surgeon cuts
a small window in the laryngeal skeleton
and pushes the thyroid cartilage
and the laryngeal tissues inward. The
depressed cartilage is then held in place
with an inserted Silastic block. Such an
operation pushes the vocal fold toward
the midline without injecting a foreign
body into the tissues, and it appears to
be more reversible than Teflon injection.
My colleagues and I have also recently
introduced an injection technique
that uses, instead of Teflon, a small
amount of fat harvested from the patient's
abdomen or arm. Like the Teflon
procedure, this one is relatively simple,
and it lacks the disadvantages of Teflon.
It requires further study.
Surgery on the laryngeal skeleton can
also modify a patient's pitch. A surgeon
can raise the pitch by pivoting the thyroid
and cricoid cartilages and closing
the space between them. These changes
lengthen and tense the vocal folds.
Alternatively, a surgeon can cut vertical
sections out of the thyroid cartilage to
shorten the vocal folds, decrease their
tension and thereby lower the pitch. The
results of such surgery are not sufficiently
predictable for singers and other
professional voice users to elect
them for purely aesthetic reasons. Nevertheless,
they are valuable for treating
certain voice abnormalities and for adjusting
the vocal pitch of patients who
have undergone sex-change surgery.
B
ecause most of the gains in treating
the human voice have involved
collaborations among physicians,
voice scientists, speech-language
pathologists, teachers and singers, they
have found their way into practical use
in medical offices unusually quickly.
Moreover, educating patients, singing
and acting students, voice teachers and
the general public about the importance
of the voice and its maladies has
had gratifying results. Education is often
the best preventive medicine, and it
has already decreased the prevalence
of avoidable voice problems.
For medical progress to continue, we
will need even more basic understanding
of voice science, better clinical evaluation
and quantification tools, and better
surgical instruments, such as more
effective surgical lasers. We can anticipate
not only further clinical advances
but also exciting applications in voice
training and development.
FURTHER READING
CLINICAL MEASUREMENT OF SPEECH AND
VOICE. R. J. Eaken. College Hill Press,
1987.
THE SCIENCE OF THE SINGING VOICE.
J. Sundberg. Northern Illinois University
Press, 1987.
PROFESSIONAL VOICE: THE SCIENCE AND
ART OF CLINICAL CARE. R. T. Sataloff.
Raven Press, 1991.
THE SCIENCE OF MUSICAL SOUNDs. J.
Sundberg. Academic Press, 1991.
THE PRINCIPLES OF VOICE PRODUCTION.
I. R. Titze. Prentice-Hall (in press).
VOICE SURGERY. W. J. Gould, R. T. Sataloff
and J. R. Spiegel. C. V. Mosby Company
(in press).
SCIENTIFIC AMERICAN December 1992 115
© 1992 SCIENTIFIC AMERICAN, INC
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