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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 REFERENCES Linked references are available on JSTOR for this article: https://www.jstor.org/stable/10.2307/24939336?seq=1&cid=pdfreference#references_tab_contents You may need to log in to JSTOR to access the linked references. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms

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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 of the voice by Robert T. Sataloff

T

These changes alter in turn the shape,

wenty years ago the human voice

Wilbur James Gould of New York City

was a mystery. Little was known

to promote such interactions, held its

position and tension of the suspended

about how it works or how to care

first symposium in 1972 and brought

vocal folds. The cricothyroid muscle,

for it, despite centuries of fascination

together laryngologists, voice scientists,

for example, participates in the control

with the voices of singers and actors

speech pathologists, singing and acting

of pitch by increasing the longitudinal

and the crudal importance of vocal com­

teachers and performers. The exchange

tension (stretching) of the vocal folds.

munication to society. Literature on voice medicine, and particularly on the

of ideas at that meeting led to new col­

The extrinsic muscles, also known as

laborations, new directions in research

the strap muscles of the neck, raise and

care of the professional voice, was

and many major advances.

lower the laryngeal skeleton. The re­

Today, 20 years later, it is possible

sulting accordion effect also changes

there was scant emphasis on how the

for a singer with a few "lost notes," a

the angles and distances between the

voice worked.

governor running for president, a sales­

cartilages and alters the resting lengths

The state of therapy was equally

person whose voice is weak, a smoker

of the intrinsic muscles. The larynx has

scarce. In the few papers that did exist,

weak. Nonsurgical treatments of benign

with a tumor or anyone else with a

a natural tendency to rise and fall as

vocal-fold problems were controversial,

voice complaint to get sophisticated

the pitch of the voice ascends and de­

and the surgery available involved vo­

medical attention. That care is a result

scends. Such large adjustments in posi­

cal-cord stripping. (Spedalists replaced

of the growing understanding of how

tion, however, interfere with the fine

the term "cord" about 10 years ago with

the voice works.

control over the vocal folds that is es­

the more descriptive term "fold.") This

The vocal mechanism involves the

sential for smooth vocal quality. For

procedure ripped away the superficial

coordinated action of many muscles,

that reason, classically trained singers

layers of the vocal fold under the as­

organs and other structures in the ab­

are generally taught to use their extrin­

sumption that healthy tissue would

domen, chest, throat and head. Indeed,

sic muscles to maintain the laryngeal

grow to replace the unhealthy tissue.

virtually the entire body influences the

skeleton at a fairly constant height re­

Unfortunately, many patients ended up

sound of the voice either directly or in­

gardless of pitch. This technique en­

permanently hoarse, although their vo­

directly. For grasping the vulnerabilities

hances a unified vocal quality through­

cal folds afterward looked normal.

of the vocal tract, a brief tour of this

out a singer's range.

Since that time, a new medical sub­

complex, delicate mechanism is neces­

specialty has emerged. Spurred by in­

sary. The first stop, and the best-known

terest in the problems of professional

part of the mechanism, is the larynx, or

singers and actors, scientific and tech­

voice box.

nological advances have raised the stan­

The larynx has four basic anatomic

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

dard of care for all voice patients. These

components: a cartilaginous skeleton,

folds that makes contact when they are

improvements were made possible by

intrinsic muscles, extrinsic muscles and

closed. The mucosa overlying the vocal folds is different from that lining the

interdisciplinary collaborations among

a mucosa, or soft lining. The most im­

professionals, who, at first, barely spoke

portant parts of the laryngeal skeleton

rest of the larynx and respiratory tract:

the same language. The VOice Founda­

are the thyroid cartilage, the cricoid car­

it is stratified squamous epithelium,

tion, which was established by physidan

tilage and the two arytenoid cartilages.

which is better suited to withstand the

The extrinsic muscles connect these car­

trauma of vocal-fold contact.

tilages to other throat structures; the in­ ROBERT T. SATALOFF is professor of otolaryngology at Jefferson Medical Col­ lege 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.

108

The vocal fold is not a simple muscle

between the carti­

covered with mucosa. In 1975 physician

One pair of intrinsic muscles extends

Minoru Hirano of Kurume, Japan, iden­ tified five distinct tissue layers in the

trinsic muscles

run

lages themselves. 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

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,

relative positions of the cartilages and

which surgeons successfully removed early in 1987. A year later he was able

pull them through a range of motions.

to resume giving concerts.

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109

CROSS SECTION OF VOCAL FOLD

{

EPITHELIUM

SUPERFICIAL LAMINA PROPRIA (MIDDLE LAYERS INTERMEDIATE OF VOCAL FOLD) DE

x z

ii:

« I c.. o

� z

x z

ii:

« I c.. o a: o

POSTERIOR CRICOARYTENOID MUSCLE TRANSVERSE AND OBLIQUE ARYTENOID MUSCLES

x z >­ a: « I c.. o (!) z

GLOT TIS

CRICOID CARTILAGE

ii: «

....J

VOCALIS MUSCLE THYROID CARTILAGE

structure. Beneath the thin, lubricated

quality. Singers and actors refer gen­

muscles of expiration are the abdomi­

epithelium on the surface lie the super­

erally to the entire power complex as

nal muscles, but internal intercostals

ficial, intermediate and deep layers of

their "support" or "diaphragm." Actu­

and other chest and back muscles also

tissue called the lamina propria. Under­

ally, the anatomy of the power com­

contribute.

lying the lamina propria is the thyro­

plex is complicated and not complete­

Trauma or surgery that alters the

arytenoid (or vocalis) muscle itself. The

ly understood, and performers who

structure or function of these muscles

five layers have different mechanical

use such terms do not always mean the

undermines the power source of the

properties that produce the smooth

same thing.

shearing motions essential to healthy vocal-fold vibrations. When the vocal folds vibrate, they pro­ duce only a buzzing sound. That sound

voice, as do asthma and other diseas­ es that impair expiration. People of­

T

he principal muscles of inspira­

ten compensate for deficiencies in their

tion, or inhalation, are the dia­

support mechanism by overworking

phragm (a dome-shaped muscle

their laryngeal muscles, which are not

resonates, however, throughout the su­

that extends along the bottom of the

designed to serve as a vocal power

praglottic vocal tract, which includes the

rib cage) and the external intercostal

source. Such behavior can result in de­

pharynx, the tongue, the palate, the oral

(rib) muscles. Expiration, or exhalation,

creased function, rapid fatigue, pain

cavity and the nose. That added reso­

is largely passive during quiet respira­

and even structural problems, such as

nance produces much of the perceived

tion: the mechanical properties of the

vocal-fold nodules.

character and timbre, or vocal quality,

lungs and rib cage typically force air

Like the muscular and skeletal sys­

of all sounds in speech and song.

out of the lungs effortlessly after a full

tems, the nervous system also contrib­ utes to voice production. The "idea" for

The power source for the voice is the

breath. Of course, active expiration is

infraglottic vocal tract-the lungs, rib

also pOSSible, and many of the muscles

a voice sound originates in the cerebral

cage and abdominal, back and chest

involved in this process are also used to

cortex and travels to motor nuclei in

muscles that generate and direct a con­

support voice production, or phonation.

the brain stem and spinal cord. These

trolled airstream between the vocal

During active expiration, muscles may

areas send out complicated messages

folds. As the glottis closes, opens and

raise the pressure within the abdomen

for coordinating the activities of the lar­

alters shape, its air resistance changes

and thereby force the diaphragm up­

ynx, the thoracic and abdominal mus­

almost continuously. The power source

ward. Alternatively, they may lower the

culature and the vocal-tract articulators.

must therefore make rapid, complex ad­

ribs and sternum to decrease the di­

Signals from certain divisions in the ner­

justments to maintain a steady vocal

mensions of the thorax. The primary

vous system, called the extrapyramidal

1 10

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REAR VIEW OF LARYNX

FRONT VIEW OF LARYNX

RIGHT VIEW OF LARYNX

HYOID BONE

EPIGLOTTIS

OBLIQUE ARYTENOID MUSCLE

OBLIQUE ARYTENOID MUSCLE

TRANSVERSE ARYTENOID MUSCLE

THYROID CARTILAGE

POSTERIOR CRICOARYTENOID MUSCLE

TRANSVERSE ARYTENOID MUSCLE CRICOTHYROID MUSCLE

TRACHEA

CRICOID CARTILAGE

POSTERIOR CRICOARYTENOID MUSCLE

Anatomy of the Voice ocal mechanism encompasses many muscles and or­

tom. The two vocalis muscles constitute the bodies of the

gans of the abdomen, chest, throat and head. The

vocal folds, which were formerly known as the vocal cords;

drawing at the far left portrays those in the throat and

a cross section of one of them appears above the represen­

V

(above)

head. Details of the larynx, or voice box, are shown to the

tation of the larynx. The remaining three drawings

right of that drawing in an orientation looking down on the

show the major muscles and cartilages of the larynx from

structure with the front-the Adam's apple-facing the bot-

the rear

(left),

the front and the right side.

tract and the autonomic nervous system,

structures and systems must work to­

have revealed how the larynx produces

also refine these activities.

gether. The physiology of voice produc­

a sound. Initially, the vocal folds are in

The nerves that control the muscles

tion is exceedingly complex, but the

contact, and the glottis is closed. As the

of the vocal tract are potential sources

voice can be likened to a trumpet. Power

lungs expel air, pressure below the glot­

of voice problems. For example, the

for the sound is generated by the chest,

tis builds, typically to a level of about

two recurrent laryngeal nerves control

abdomen and back musculature, which

seven centimeters of water for conver­

most of the intrinsic muscles in the lar­

produce a high-pressure airstream. A

sational speech. This pressure progres­

ynx. Because those nerves (especially

trumpeter's lips open and close against

sively pushes the vocal folds apart from

on the left) run through the neck, down

the mouthpiece to create a buzz simi­

the bottom up, until the glottis is open

into the chest and then back up to the

lar to that produced by the vocal folds.

and air begins to flow. Elastic and other

larynx, they are easily injured by trau­

This sound then resonates through the

forces resist the separation of the up­

ma or surgery on the neck and chest.

rest of the trumpet, which is analogous

per margin of the vocal folds, but the

to the supraglottic vocal tract.

airstream overpowers them.

M

uch of the progress during the

Bernoulli effect-that is, a reduction in

past 20 years has come from

the lateral air pressure caused by its

filling in the details of how vo­

forward motion. The effect tends to pull

Nerves also provide feedback to the

The flow of air, however, produces a

brain about voice production. Auditory feedback, which is transmitted from the ear through the brain stem to the cere­ bral cortex, allows a vocalist to match the sound produced with the sound in­

cal sounds originate and change. Part

the vocal folds shut, as do the elastic

tended. Tactile feedback from the throat

of this effort has involved modeling the

properties of the vocal-fold tissues. The

and muscles also may help with the

movements of the vocal folds. Although

pressure of the airstream below the

fine-tuning of vocal output, although

a vocal fold has a five-layer anatomy, it

glottis also diminishes as the glottis

that process is not fully understood.

behaves mechanically more like a three­

opens to let the air out.

Trained singers and speakers cultivate

layer structure, consisting of a cover

Because of these factors, the lower

their ability to use tactile feedback ef­

(epithelium and superficial layer of the

fectively because they expect that poor

lamina propria), a transition layer (in­

edges of the vocal folds begin to close almost immediately, even though the

room acoustics, loud musical instru­ ments or crowd noises will interfere with the auditory feedback. During phonation, all those anatomic

termediate and deep layers of the lami­

upper edges are still separating. That

na propria) and a body (thyroarytenoid muscle).

closure further diminishes the force of

Observations and modeling studies

vocal folds then snap back to the mid-

the airstream. The upper margins of the

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III

line and close the glottis. Subglottal pressure builds again, and the events

the driving forces involved in the mo­

tion in the mucosal layer. If the com­

tions of the vocal fold.)

plex vibration of that glottal wave is

repeat themselves. (It should be under­

An important aspect of this process is

stood that there is direct pressure and

that the lower part of the vocal folds be­

that the alternating variations rarely

gins to open and close before the upper

The vocal folds do not excite the air

drop the subglottal pressure to zero.

part. The rippling displacement of the

by vibrating like violin strings. Instead,

This fact is important in understanding

vocal-fold cover produces a wave mo-

impaired, hoarseness or other changes in voice quality may result.

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 vi­ bration. The mechanism is similar to

How the Voice Is Produced

T

that which causes the sound of hand

he production of speech or song, or even just a vocal sound, entails a complex orchestration of mental and physical actions. The idea for mak­

ing 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 en­ able the speaker or singer to achieve fine-tuning of the vocal output.

clapping. The sound from the larynx is a com­ plex tone containing a fundamental fre­ quency, or pitch, and many overtones, or higher harmonic partials. (Frequen­ cy is measured in hertz, the number of opening and closing cycles in the glbt­ tis 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

SPEECH AREA IN TEMPORAL CEREBRAL CORTEX

cavity and the nasal cavity act as a se­ ries of interconnected resonators for the voice signal. The system is more com­ plex than a trumpet because its walls, and hence its shape, are flexible. In any resonator, some frequencies are attenu­ ated while others are enhanced, or radi­

VOICE AREA IN MOTOR STRIP OF PRECENTRAL GYRUS

ated with higher amplitudes. Certain har­ monic partials therefore become rela­ tively softer while others grow louder. lohan Sundberg of the Royal Institute of Technology in Stockholm has shown for singers (and his colleague Gunnar Fant

NUCLEUS AMBIGUUS

for speakers) that the vocal tract has four or five important resonance fre­ quencies called formants. The intensity of the voice source diminishes uniformly

10TH CRANIAL (VAGUS) NERVE

SPINAL CORD

across its frequency spectrum except at the formant frequencies, where it peaks.

F

ormant

frequencies

are

estab­

lished 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 individ­

SUPERIOR LARYNGEAL NERVE

ually fixed and determined by age and sex: women and children have shorter vocal tracts than do men and conse­ quently have higher formant frequen­ cies. Nevertheless, the dimensions of

VAGUS NERVE

HYOID BONE

the vocal tract can be consciously ad­ justed to some degree, and mastering those adjustments is fundamental to voice training.

CRICOID CARTILAGE -------�

RECURRENT LARYNGEAL NERVE

One resonant frequency that has re­ ceived attention is known as the sing­ er's formant. It appears to be responsi­ ble for the "ring" in a singer's or speak­ er's voice. The ability to make oneself heard clearly even over an orchestra de­ pends primarily on the presence of the singer's formant: there is little or no

112

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significant difference in the maximum

amplitude of the voice's fundamental

vocal intensities of trained and untrained

frequency is low despite considerable

singers.

physical effort.

The singer's formant occurs at around

The amplitude of the voice source

hertz for all vowel

will also be low if the adductory forces

sounds. Aside from adding clarity and

are so weak that the vocal folds do not

2,300 to

3,200

projection to a voice, it also contributes

make contact and the glottis becomes

to differences in timbre. The singer's

inefficient. This condition results in

formant occurs in basses at about 2,400

breathy phonation. In contrast, a third

hertz, in baritones at 2,600 hertz, in ten­

and more desirable condition known as

ors at 2,800 hertz, in mezzo-sopranos

flow phonation is characterized by low

at 2,900 hertz and in high sopranos at

airstream pressure and low adductory

3,200 hertz. The singer's formant is of­

force, which increase the intensity of

ten much less pronounced in sopranos.

the fundamental frequency and make

Control over two vocal character­

the voice louder. To identify pressed,

istics-fundamental frequency and in­

breathy or flow phonation, voice spe­

tensity-is crucial. One way to raise the

cialists can plot changes in the flow of

fundamental frequency is to raise the

air through the glottis, thus producing

pressure

a graph called a flow glottogram.

of

the

airstream

moving

Sundberg has shown that a vocalist

sons, as the pressure rises, the vocal

can raise the amplitude of the funda­

folds tend to blow apart and to snap

mental frequency by 15 decibels or

shut more quickly and frequently. Sing­

more Simply by changing from pressed

ers learn to compensate for this ten­

phonation to flow phonation. Hence,

dency: otherwise, their pitch would rise

people who rely habitually on pressed

whenever they tried to sing louder.

phonation expend unnecessary effort

Generally, the most efficient tech­

to achieve a loud voice. The forces and

nique for altering the pitch is to change

patterns of muscle use recruited to

the mechanical properties of the vocal

compensate for this inefficiency may

folds. Contracting the cricothyroid mus­

damage the larynx.

cle makes the thyroid and cricoid carti­ This change exposes more surface area on the vocal folds to the airstream and

B

y understanding the vocal control mechanisms, physicians can de­ tect and correct the problems

thereby makes them more responsive

that abuse the voice and traumatize the

to air pressure. It also stretches the

vocal folds. Understanding the func­

elastic fibers of the vocal folds and in­

tion of each component of the vocal

creases their efficiency at snapping back

tract also aids the development of opti­

together. The pitch rises because the

mal strategies for rehabilitating dam­

cycles of opening and closing in the

aged voices.

glottis (phonatory cycles) shorten and

2

AIR IN TRACHEA 3

through the larynx. For mechanical rea­

lages pivot and stretches the vocal folds.

VOCAL FOLDS

4

SOUND

UPPER EDGE OF VOCAL FOLD

5

The development of new tools has been critical for the science of the

repeat more frequently. Vocal intensity, or loudness, depends

voice. Until the 1980s, the physician's

on how much the vocal-fold vibrations

ear was routinely the sole instrument

excite the air in the vocal tract. Raising

used to assess voice quality and func­

the air pressure increases the ampli­

tion. Practical techniques for observing

tude of the vibrations because the vo­

and quantifying voice functions were

cal folds move farther apart and snap

generally lacking.

together more briskly. Consequently,

In 1854, for instance, a singing teach­

during each phonatory cycle, the flow

er named Manuel Garcia devised the

of air through the larynx cuts off more

technique of indirect laryngoscopy. He

sharply, and the intensity of the pro­

used the sun as a light source and a

duced sound increases. A similar effect

dental mirror placed in a student's

increases the intensity of the sound of

mouth to look at the vocal folds. Indi­ rect laryngoscopy rapidly became a ba­

hand clapping. A useful biophysical indicator of the

6

LOWER EDGE OF VOCAL FOLD 7

sic tool for physicians, and it is still in

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

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

8

perspective is from the front of the lar­

ynx. Before the process starts

(1),

the

tract and the adductory (glottis-closing)

folds are together. They separate as air

forces of the vocal folds. Such a combi­ nation of forces results in a condition

is forced upward through the trachea

called pressed phonation, in which the

the sound ceases (8).

(2-7) and then come together again as

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113

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. Effec­ tive 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 stro­ bovideolaryngoscopy. It uses a micro­ phone placed near the larynx to trig­ ger a stroboscope that illuminates the vocal folds. If the frequency of the stroboscopic light is about two hertz

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

out of phase with the vibration, an ob­

about two seconds. The horizontal lines mark off frequencies in hertz from zero at

server can watch the vocal folds in sim­

the bottom to 7,000 at the top. The sonogram at the left is from a male speaker

ulated slow motion. A crude version of this technique was actually first devel­ oped in the 19th century. Only during

involves the insertion of thin electrodes

boosted the utility of such examina­

the past decade, however, have strobo­

into the laryngeal muscles. It is useful

tions. All these tools help physicians to

scopes become bright enough and vid­

in specialized circumstances for assess­

detect and record the information con­

eo cameras sufficiently sensitive for it

ing neuromuscular integrity and func­

tained in the sound of the voice more

to be useful routinely.

tion. For instance, measurements of

reliably and validly.

The stroboscopic effect permits de­

electrical activity in the laryngeal mus­

tailed evaluation of the vocal-fold edge.

cles may foretell a patient's recovery

Physicians can see small masses, vibra­

from vocal-fold paralysis. In that case,

A

technology has enhanced the di­

agnostic and therapeutic aspects of voice medicine, the need for

tory asymmetries, scars, early carcino­

before considering surgery, a physician

mas and other laryngeal abnormali­

might recommend waiting for a spon­

laryngeal surgery has diminished. Some

ties-many of which are not detectable

taneous recovery.

conditions require little more than the prescription of drugs. Medications must

under normal light. Digital analysis of

A skilled laryngologist or another

the images can also supplement visual

trained listener can glean much from

be used with caution, however, because

assessments, although poor image res­

the sound of a voice. Nevertheless, clin­

even many over-the-counter remedies

olution and some other problems have

icians and researchers need equipment

have side effects that adversely affect

limited the value of the technique so far.

capable of quantifying the vocal char­

voice function. Antihistamines, for ex­ ample, cause dryness in the vocal mu­

Another method for monitoring vo­

acteristics that are meaningful to the

cal-fold vibrations is electroglottogra­

ear. The available equipment is helpful,

cosa, which can lead to hoarseness and

phy. A weak high-frequency voltage be­

but it needs further improvement.

coughing. The anticoagulant properties

tween two electrodes placed on the neck

For example, acoustic spectrography

passes through the larynx. Changes in

displays the frequency and harmonic

the measured voltage generate a wave

spectrum of a voice and visually re­

Techniques have been developed to

on the electroglottograph that illus­

cords noise. The equipment depicts the

rehabilitate voices that have been dam­

trates vocal-fold contact. Information

acoustic signal and enables research­

aged through misuse. Voice therapy fa­

about the open glottis can be inferred

ers or physicians to make generaliza­

cilitates breathing and abdominal sup­

from photoglottography, which mea­

tions about the vocal quality, pitch and

port and helps to eliminate unnecessary

of aspirin can contribute to vocal-fold hemorrhages.

sures light passed from below the vocal

loudness. A variety of qualities can be

muscle strain in the larynx and neck. It

folds, or from flow glottography.

measured: the formant structure and

can even cure some structural problems

M

strength of the voice, the fundamental

of the vocal folds, most notably nod­

easurements of aerodynamic

frequency, breathiness, the harmonics­

ules (hard, callouslike growths). Ther­

function, which include com­

to-noise ratio (or clarity of the voice) and

apy helps patients to learn how to use

prehensive testing of pulmo­

perturbations of the cycle-to-cycle am­

each component of the vocal tract ap­

nary function and laryngeal airflow, are

plitude ( "shimmer" ) and of the cycle-to­

propriately so as to avoid straining and

especially valuable. Together they reveal

cycle frequency ( "jitter"). Subtle char­

abusing their voices, how to maintain

both the function of the vocal power

acteristics, however, still cannot be de­

the correct levels of moisture and mu­

source and the efficiency of the vocal

tected. For instance, in studies of voice

cus in their vocal tracts and how to mit­

folds for controlling airflow. Measure­

fatigue in trained singers, the difference

igate the effects of smoke and other hazards in the environment.

ments of phonatory ability-the abili­

between a rested and tired voice is usu­

ty to produce sounds-are Simple and

ally obvious to the ear, but significant

Good vocal hygiene and technique,

useful for quantifying vocal dysfunc­

changes cannot be detected consistently

however, are not always enough. Some

tions and evaluating the results of treat­

even with sophisticated equipment.

structural problems in the larynx must

ment. Such tests determine the frequen­

Psychological influences on the voice

be treated with surgery. These prob­

cy and intensity ranges of the voice,

are also critical, but the techniques for

lems include nodules that have not re­

how long a sound can be produced and

evaluating them are poorly standard­

sponded to voice therapy, polyps (soft­

other factors.

tissue growths), cysts (fluid-filled mass­

Laryngeal electromyography, another

ized. Nevertheless, well-developed ques­ tionnaires, tape recordings and assess­

technique for studying voice function,

ment of voice by several observers have

Most benign pathological conditions

114

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© 1992 SCIENTIFIC AMERICAN, INC

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es) and other growths.

that uses, instead of Teflon, a small amount of fat harvested from the pa­ tient'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 thy­ roid and cricoid cartilages and closing the space between them. These chang­ :t.'"'. �

.

....

• '

�

' .

•"

",00'

"" ....

_

_

�

......

� O-

•

:'

•

,

.0; . -.'

•

•

�

.

es lengthen and tense the vocal folds.

�

. .. ... ,. -.: :-�-/�=:--:--. --:--:. .��-.:--:.• �

.--::: --..:. ,: : -i-:'-:--.:' �::.:- :--:.-:-:-. .: .- .--.- ,-:' . :'. : .-.- . '.. .�

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--"--------�------"'--

with normal vocal folds; the one at the right is from a male speaker with growths

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

on his vocal folds. His voice makes additional noise in the range above 5,000 hertz

results of such surgery are not suffi­

and has disrupted and weakened harmonics between 2,000 and 4,000 hertz. The

ciently predictable for singers and oth­

result is that his voice sounds harsh and hoarse.

er professional voice users to elect them for purely aesthetic reasons. Nev­ ertheless, they are valuable for treating

are conveniently superficial. By a variety

is extremely useful for some lesions. It

certain voice abnormalities and for ad­

of delicate microsurgical techniques,

can seal off varicose blood vessels in

justing the vocal pitch of patients who

surgeons can now usually remove le­

the vocal folds that might hemorrhage,

have undergone sex-change surgery.

sions from the epithelium or the super­

and it can vaporize blood vessels that

B

ficial layer of the lamina propria without

nourish laryngeal polyps, papillomas

disrupting the intermediate or deep

and some cancers. Further research and

layers of the tissue, which form scars.

development in laser technology is like­

Such procedures are now commonly

ly to provide an instrument better suit­

described as phonosurgery. (That term

ed for microsurgery on the vocal fold

pathologists, teachers and singers, they

originally referred only to operations de­

in the near future.

have found their way into practical use

signed to alter vocal pitch and quality.) Most

voice surgery is

New surgical techniques for modify­

ecause most of the gains in treat­ ing the human voice have in­ volved collaborations among phy­

sicians, voice scientists, speech-language

in medical offices unusually quickly.

performed

ing the laryngeal skeleton have been pi­

Moreover, educating patients, singing

through the mouth while the surgeon

oneered by physician Nabuhiko Issiki

and acting students, voice teachers and the general public about the impor­

views the larynx through a metal tube

of Kyoto. These have become extreme­

called a rigid laryngoscope. An operat­

ly useful for treating vocal-fold paraly­

tance of the voice and its maladies has

ing microscope magnifies the larynx. A

sis, which is a common consequence of

had gratifying results. Education is of­

surgeon can then treat the laryngeal

viral infections, surgery or cancer. Tra­

ten the best preventive medicine, and it

abnormalities with microscopic scis­

ditionally, surgeons have treated vocal­

has already decreased the prevalence

sors, lasers and other instruments.

fold paralysis by injecting small vol­

of avoidable voice problems.

Nodules, polyps and cysts on the vi­

umes of Teflon into the affected vocal

For medical progress to continue, we

bratory margin of the vocal folds are

fold. The Teflon pushes the paralyzed

will need even more basic understand­ ing of voice science, better clinical evalu­

removed most safely with traditional

fold toward the midline of the glottis

surgical instruments. The operations

and allows the normal fold to meet it.

ation and quantification tools, and bet­

can be remarkably precise: in some cas­

The glottis can then close, and the pa­

ter surgical instruments, such as more

es, it is possible to raise the vocal-fold

tient's voice is often improved.

effective surgical lasers. We can antici­

mucosa, remove a cyst or other underly­

Yet although Teflon is relatively inert,

pate not only further clinical advances

ing mass and then replace the mucosa.

tissue reactions to it are not uncommon.

but also exciting applications in voice

Such minimally traumatic surgery does

The stiffness that the Teflon produces

training and development.

not even require postoperative voice

in the vocal-fold edge frequently impairs

rest, and rapid healing with good voice

the quality of the voice. Also, if the re­

quality usually follows.

sults of the Teflon injection are unsat­

Lasers are often celebrated as revolu­ tionary high-tech surgical instruments,

material from the tissues.

CLINICAL MEASUREMENT OF SPEECH AND

but they are not always the best choice

For these reasons, Teflon injections

for laryngeal surgery. At the power den­

have generally been replaced by thyro­

sities required for the surgical ablation

plasty. In this technique, a surgeon cuts

of tissue, the beam from a standard car­

a small window in the laryngeal skele­

bon dioxide laser would be surrounded

ton and pushes the thyroid cartilage

by a heat halo as much as 0.5 millimeter

and the laryngeal tissues inward. The

wide. If the beam were directed against

depressed cartilage is then held in place

a lesion on the edge of the vocal fold,

with an inserted Silastic block. Such an

the heat might provoke scarring in the

operation pushes the vocal fold toward

intermediate or deep layers of the lami­ na propria. Such a scar would create a

the midline without injecting a foreign body into the tissues, and it appears to

nonvibrating segment on the vocal fold;

be more reversible than Teflon injec­

hoarseness would result.

tion. My colleagues and I have also re­

Nevertheless, the carbon dioxide laser

FURTHER READING

isfactory, it is difficult to remove the

VOICE. R. J. Eaken. College Hill Press,

1987. THE SCIENCE OF THE SINGING VOICE.

J. Sundberg. Northern Illinois Universi­ ty Press,

1987.

PROFESSIONAL VOICE: THE SCIENCE AND ART OF CLINICAL CARE. R. T. Sataloff. Raven Press,

199 1.

THE SCIENCE OF MUSICAL SOUNDs. J. Sundberg. Academic Press,

199 1.

THE PRINCIPLES OF VOICE PRODUCTION. I. R. Titze. Prentice-Hall (in press). VOICE SURGERY.

W. J. Gould, R. T. Sata­

loff and J. R. Spiegel. C. V. Mosby Com­ pany (in press).

cently introduced an injection technique

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115