The NCS Model Of Stuttering
The following model reflects the current thinking of The National Center For Stuttering. It is the product of a careful analysis
of research findings from a number of scientific fields together with an
extensive number of clinical observations. It suggests that the vocal cords
are the core of the problem. (For a more concise, less technical description of the cause of stuttering, read A message to the person who stutters.)
We start by describing the sources of tension on the vocal cords. We have
learned, through empirical observation, that it is necessary to focus exclusively
on the tension which immediately PRECEDES the act of speaking. We show
how a heightened prespeech state of tension on the vocal cords can, under
certain circumstances and given a certain physiological predisposition,
lead directly to the onset (and maintenance) of stuttering.
There are five sources of immediate prespeech tension on the vocal cords.
Three relate to the act of speaking; two do not.
I. The first of the three speech related sources has to do with the tension
that must be developed to insure that speech starts with the right pitch
and intensity. The ability to tense the cords correctly in the absence
of sound is called "the prephonatory tuning" of the vocal cords.
II. The second speech related source affecting the prespeech tension on
the vocal cords is the speed of speech. More specifically, the faster the
start of speech, the greater the vocal cord tension required. Physiologists
understand that higher initial speeds require the activation of more muscle
fibers (that is, more tension) BEFORE the movement begins.
III. The third speech related source of prespeech tension on the vocal
cords comes from the anticipation of stuttering, more specifically, sound,
word, and speaking situation fears. These anticipatory stresses, associated
with the fear of impending struggle, increase muscle tension throughout
the body, including the vocal cords.
IV. The first of the nonspeech-related tensions comes from the "normal"
stresses associated with events at home, work or school. Added to these
are the stresses which can develop from unresolved subconscious conflicts,
as well as those arising from uncertainties regarding the correct course
of action to pursue in a given situation.
V. The second of the non speech related tensions is derived from systemic
sources. Some of these are: fatigue, nutritional deficiencies, allergies,
illnesses, drugs, alcohol, hormone fluctuations (both body and brain),
and atmospheric conditions(temperature, humidity, positive ions and pollutants).
The immediate prespeech tension on the vocal cords is the result of the
five just described sources. The combined strengths of the various sources,
at each moment in time, contribute to the overall level of the tension.
The sources can add to one another or cancel one another. THIS ACCOUNTS
FOR THE VARIABILITY IN THE SEVERITY OF THE DISORDER.
VI. There is occasionally a sixth source of tension. It is generally not
recognized, but recent research and clinical experience tends to support
its existence. WE PROPOSE IT AS THE PREDISPOSING FACTOR IN STUTTERING.
Before discussing it, some preliminary remarks are required. The vocal
cords are ancient structures. They have two original functions. The first
is to function as a tightly closing valve during swallowing to prevent
solids and liquids from entering the lungs. The second is also to close
tightly, trapping air in the chest making it rigid to use as a fulcrum
for the arms for strenuous activities such as lifting or fighting. In both
instances the vocal cords close tightly. These behaviors are automatic
responses of lower, more primitive centers of the brain.
The evolutionary onset of speech coincided with the development of higher
centers of the brain. As the Nobel Laureate, George Von Bekesy observed,
the study of higher centers is the study of greater levels of inhibitory
control, with higher centers serving to inhibit gross, less discriminating
responses from lower ones.
This is particularly true for the vocal cords. Speech requires extremely
precise, graded, time varying neural inputs to the vocal cords. A gross
tensing would be inappropriate and markedly interfere with the precise
prespeech tensions on the vocal cords.
In the condition known as Spasmodic Dysphonia we see clinical examples
of this loss of inhibitory control. Each time the person intends to speak
the vocal cords appear to close as in a swallow. The result is the effortful,
squeezed, or "choked" speech which characterizes the disorder.
WE SUBMIT THAT INDIVIDUALS DESTINED TO BECOME PEOPLE WHO STUTTER ARE BORN
WITH THE TENDENCY TO LOSE VARYING AMOUNTS OF INHIBITORY CONTROL OVER THEIR
VOCAL CORDS AND THAT THIS OCCURS ONLY WHEN THEY INTEND TO SPEAK UNDER CONDITIONS
OF SUFFICIENT VOCAL CORD TENSION.
Let us see how the six sources of prespeech vocal cord tension can be used
in a consideration of stuttering.
The vast majority of people who stutter report they are fluent when they
speak to themselves out loud alone. In that situation, they also report
they do not scan (look ahead for feared sounds or words). In such a situation,
sources III (the anticipation of stuttering) and VI (the loss of inhibitory
control) are absent while sources I (prephonatory tuning), II (speed stress),
IV (psychological stress), and V (systemic stress) can all be present.
If subtracting the contributions of sources III (the anticipation of stuttering)
and VI (the loss of inhibitory control) produces immediate fluency for
the vast majority of people who stutter, then there is clearly a threshold
for stuttering. When sources III and VI are absent, an individual's vocal
cord tensions are below the threshold and the person is fluent; when they
are present, the threshold level is exceeded and the individual either
stutters or engages in avoidance behaviors.
We shall now explain more fully the concept of threshold and how its attainment
"triggers" stuttering.
To do this, consider the following facts: The space between the vocal cords
represents the narrowest opening through which breathing occurs. It is
vitally important that this opening remain an opening, for its obliteration,
for even just a few minutes, would be life threatening. "Nature," recognizing
the importance of maintaining an airway, has provided the voice box with
a whole host of sensory receptors whose job it is to constantly inform
the brain about the position and tension on the vocal cords. This information
is used, along with information about the air pressure under the vocal
cords, to produce the appropriate muscular adjustments necessary to maintain
the airway.
Stuttering is largely a childhood onset disorder. Its early forms often
appear as seemingly effortless repetitions of sounds, syllables, or words
at the beginnings of phrases or sentences.
At the start of speech development, children often use single words to
denote entire linguistic concepts. As the brain matures, linguistic sophistication
occurs and one manifestation of this is increased sentence length. Where
once a single word stood to represent a thought, now stands a five word
sentence, replete with rules of grammar, syntax, and a whole host of other
sophisticated components.
Try this experiment. Using a paper and pencil, write the following two
items. First write the word: [The]. Then beneath it, write the sentence:
[The boys are walking]. Ask people to read both items. First, the word:
[The] by itself, followed by the sentence: [The boys are walking] by itself.
Listen carefully to the difference in speed between the two The's. [The]
spoken by itself is spoken leisurely but when it is in a sentence as the
first word it is dramatically speeded. If we had acoustic measuring equipment
we would see that AS THE SENTENCE LENGTH INCREASED, THE SPEED OF THE FIRST
WORD ALSO INCREASED.
What this means is that as the child's linguistic sophistication matures,
with its resultant increase in sentence length, there is also a progressive
increase in the speed of the first word. In terms of our model, source
II (speed stress) increases as the child's language sophistication develops.
Coinciding with the increase in source II is the development of internal
rules governing intonation and syllable stress. These rules are the prime
shapers of source I, the prephonatory tuning on the vocal cords.
So both sources I and II change dramatically during speech and language
maturation. Note that source III, the anticipatory stress, is absent, while
source IV, the psychological stress, and source V, the systemic stress,
are free to vary. The existence of source VI, the loss of inhibitory control,
is potentially present, but unelicited in the absence of sufficient vocal
cord tension.
Let us now imagine a particular child on a particular day. The child is
destined to become a person who stutters, and on this day, he is to begin.
The child is under external stress (starting school, for example). So source
IV is present. So, too, are sources I and II because the child is getting
ready to say a sentence in the classroom. Also imagine that several systemic
stresses are also present (the child has a cold and hasn't slept well).
So source V is present. Finally, with all these stresses simultaneously
present, a critical threshold level of tension is attained, and as the
child begins to speak, source VI, the loss of inhibitory control, occurs.
A very substantial tension suddenly descends upon the vocal cords, and
the smooth onset of vocal cord vibration is blocked. The child begins to
struggle to release the block. The struggle is usually of a certain type:
repetitions of sounds, syllables or words usually at the beginnings of
sentences.
The repetitions eventually lead to the child saying the desired first word,
and so become reinforced and learned. But learning implies a stimulus and
a response. The repetitions which characterize the beginning phase of stuttering
are the response; what is the stimulus?
To understand the stimulus, that is, the trigger for stuttering, we must
go back and consider the nerves present in and around the vocal cords.
These nerves provide information to the brain regarding the position and
tension on the cords. When a magnitude of tension is reached that prevents
the smooth initiation of vocal cord vibration, the child begins to struggle.
At the time the struggle occurs a characteristic pattern of sensory impulses
is being produced by these tension and position receptors. That is, a unique
pattern of sensory information is occurring, a pattern that only occurs
when the cords assume a particular position, and the tension levels within
and around the cords reach a critical level. Also, the pattern must be
bilateral,that is, the impulses must be coming from both sides of the voice
box, signaling both sides of the brain. IT IS THIS CHARACTERISTIC BILATERAL
SENSORY PATTERN WHICH IS THE TRIGGER FOR STUTTERING.
So stuttering is a set of learned responses to a unique pattern of nerve
impulses from the vocal cords. It follows, then, that to treat the problem,
one must prevent this pattern from reaching the brain.
This is best accomplished by reducing the tension developed on the vocal
cords PRIOR to the onset of speech. If this can be achieved, speech emerges
fluent and sounding normal.
For information about the multidimensional program for accomplishing
this goal, read the The
NCS Treatment Program or call The
National Stutterers' Hotline.
home page
|
|
