THE DISCOVERY OF THE PHYSICAL CAUSE
It was an accident. My discovery of the physical cause of stuttering was
one of those things I never expected to happen but that nonetheless succeeded
in changing the direction of my professional life. It was 1974, and I was
a Professor of Speech Science, helping design an operation to improve the
speech of patients born with cleft palate. I was using a machine called
a Sonagraph. The Sonagraph is an ultrasound device used by obstetricians
and applied to the abdomen to look at the fetus.
The portion of the Sonagraph touching the abdomen is called the transducer,
only in my instance I was applying the transducer to the side of the neck
to study throat-movement patterns in cleft-palate patients slated for surgery.
A consideration of these patterns was necessary to establish the donor
site - the place in the throat from which a piece of tissue would be taken
to close a hole in the roof of the mouth.
One of the patients stuttered, and with the Sonagraph it became clear
that the throat constricted forcefully before every stutter. First would
come the constriction, then the stutter. It was very regular, and I couldn't
help but pause and consider this curious event.
Failing to find a ready explanation, I called a Speech Pathologist to
ask if he knew anything of the relationship between throat constrictions
and stuttering I had observed. He knew of none, he said, since Speech Pathologists
had never been able to look at the throat during speech. My ultrasonic
scan represented something new.
Excited by the prospect of a new discovery, we arranged to have several
stutterers seen for ultrasonic examination. Within two weeks I had examined
five - and all displayed the same pattern of constrictions.
Having confirmed the non-uniqueness of my initial observation, I began
to systematically move the transducer along the side of the neck to see
if the throat constrictions varied in intensity along the vertical dimension.
The answer came quickly: the further down the throat, the more vigorous
The throat rests upon the larynx, or voice box, which contains the vocal
cords. The vocal cords are two small horizontal folds of tissue that lie
within, one on either side of the box. The larynx rests on top of the trachea
(or wind pipe) and its front cover is the Adam's apple. In order to speak,
the vocal cords are brought together by several pairs of muscles so that
they touch each other gently. The person then builds up an air pressure
beneath them by expelling air from the lungs. When the air pressure becomes
great enough, it blows the vocal cords apart, which sets them into vibration
and makes sound. This sound is the raw material for speech production;
it is converted into speech by moving the lips, tongue, jaw, teeth, palate
and other articulators.
When the transducer was applied to the side of the stutterer's larynx,
something happened which was not to be expected: just before every stutter,
the vocal cords would rise slightly and then suddenly slam together in
a constriction more violent still than any seen in the throat.
Here, I thought, was the center of the activity - the vocal cords -
pressed together forcefully. For some reason the stutterers were tensing
their vocal cords so powerfully that the air required for speaking couldn't
pass. It reminded me of a phenomenon in medicine known as a laryngeal
spasm, a forceful locking of the vocal cords which sometimes occurs
after an operation. From my ultrasonic examination, it appeared that stutterers
were exhibiting short-duration laryngeal spasms, but why, I didn't know.
I proposed an explanation which seemed outlandish at the time, but has
since been substantiated repeatedly by investigators - namely, that the
source of all stuttering is a locking of the vocal cords. But at that time
I did not understand what the relationship was between the struggles I
observed and the vocal cords.
I began to examine the struggles closely. For instance, some patients
would suck air in briefly through their mouths just before speaking - a
sort of inspiratory gasp. They reported that this facilitated fluency.
It soon became clear why. The more rapidly one inhales, the wider the vocal
cords open to allow a greater volume of air to pass. The patients were
using this rapid inspiratory movement to widely open locked vocal cords
so they could initiate speech before the cords locked again.
Similarly, other patients who spoke at the end of their breaths were
unknowingly making use of another strategy to open locked cords. There
are nerve endings in the lungs that detect air volume. When a person exhales
most of his air before speaking these receptors detect what they interpret
as the imminent collapse of the lungs, and signal the brain to initiate
inspiration. A single pair of muscles at the back of the voice box begins
to contract to force the vocal cords apart in preparation for the inflow
of air. A person cannot stutter when a pair of muscles is being powerfully
driven by the brain to open the vocal cords.
Other patients reported being able to speak after first swallowing.
During the swallow reflex the vocal cords close tightly to prevent liquids
or solid food from entering the lungs, and immediately after the swallow,
as part of the same reflex, the cords are opened forcefully so that respiration
may resume. The patients had unknowingly discovered that if they started
speech at the instant a swallow was completed, they could speak without
The non-speech behaviors of the stutterer now made sense. I was still
at a loss, however, to understand precisely how a locking of the vocal
cords could lead to the wide variety of speech struggles I observed.
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