LARYNGEAL DYNAMICS IN STUTTERING.pdf / KUNNAMPALLIL GEJO

7/27/2019 LARYNGEAL DYNAMICS IN STUTTERING.pdf / KUNNAMPALLIL GEJO

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LARYNGEAL DYNAMICS IN STUTTERING

LARYNGEALONSETANDREACTIONTIMEOFSTUTTERERS:

Historically, larynx has been considered to play a central role, if not exclusive role in

stuttering (Yates, 1800/1839), Hunt, 1861; Kenyon, 1943). With recent advances in

technology, new and more sophisticated measuring devices have been developed, the

purpose being, to investigate into the laryngeal behaviors of stutterers and and the role of

larynx in stuttering.

This area of research has, taken 3 distinct directions:

1. Studies of stutterers voice onset time (VOT), voice initiation time (VIT) andspeech initiation time (SIT).

2. Electromyographic investigation of stutterers laryngeal muscle activity.3. Fiberoptic studies.

1. Voice onset time (VOT):

VOT has been defined as the time that elapses from the release of the consonant burst

to the onset of periodic glottal vibration for the production of the vowel that follows

the production of the vowel that follows the consonant (Lisker and Abramson, 1964).

METHODOLOGIES AND INSTRUMENTATION

:VOT can thus be measured with any instrument that:

1. Reliably senses and records the end of consonantal implosion and the initiation ofglottal vibration for phonation.

2. And provides means of determining the time lapsed between these 2 events.

Three main methods have emerged, over the years, which are well suited for such

measurements:

1. Spectrography.2. Detecting the sizeable rise in intraoral air pressure that occurs during the

implosion phase of stop consonant production.


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3. X-ray motion picture and voice recorder. The former, we can see the start of theconsonantal release on the X-ray film and the latter tells us when phonation starts.

The difference between these 2 events, expressed in temporal units, is VOT.

Findings:

The measurements and comparisons of the VOTs of stutterers and normal speaking

control subjects mainly included investigation of fluent productions of simple, isolated

CV syllables, during the generation of longer syllable sequences, and during the

production of stop consonant plus vowel combinations in continuous oral reading. The

results of studies of stutterers and normal VOTs are given in the following table:

Authors Method Subjects Results

Angello and

Wingate (1972)

Pressure-sensor and

voice-recorder; CV

utterances.

Matched groups of

12 adult stutterers

and 12 normals.

Stutterers VOT

were longer.

Wendell (1973) Spectrographic

analysis of CVs.

Matched groups of

12 child stutterers

and 12 normals.

Stutterers VOTs

were longer.

Metz, Conture, and

Caruso (1979).

Spectrographic

analysis of 18

different soundclusters in words.

5-young adult

stutterers and 5-

normals.

Stutterers VOT

were longer on only

6 of the 18 clusters(p


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VOICE AND SPEECH INITIAION TIMES (VIT and SIT)

VIT is defined as the time lapse between the appearance of some experimenter-controlled

external stimulus (e.g., a pure tone of flash of light), and the subjects initiation of glottal

vibration for phonation. Thus, VIT represents the time lapse between the onset of non-

speech event and the starting of voicing.

In similar fashion, some investigators have required subjects to utter a response of one

word or longer, beginning with a voiced sound. These studies are viewed as measuring

speech initiation time (SIT).

METHODOLOGIES AND INSTRUMENTATION:

Though there have been some minor variations across experiments, most VIT/SIT

investigations have employed highly similar methods and designs. In a typical project, a

subject is presented with a warning signal, waits for the appearance of a cueing stimulus,

and then generates a desired response as soon as possible. The following table presents

the summary of both the VIT and SIT studies:

Authors Characteristics

of subjects

External

signal(s)used

Subjects

response

Findings

Adams and

Hayden (1976)

10 adult

stutterers and

10 age-andsex matched

normals.

1000Hz pure

tone.

Phonated

/a/.

Both groups shortened VIT

from the beginning to end of

the experiment. Stuttererswere slower on two of three

comparisons made.

Starkweather,

Hirschman and

Tannenbaum

(1976).

11 adult

stutterers and

11 age-and-sex

matched

normals.

Green light

presented on

the screen.

26 test

syllables

reflecting a

wide range

in place and

manner of

articulation.

Both groups shortened VIT

from the beginning to end of

the experiment. Stutterers

were slower acroos all test

trials and across all syllable

types investigated.

Reardon (1977) 5 adult

stutterers and 5

sex-matched

Auditory

stimulus.

Phonated /a/

and 6 other

test.

Stutterers had longer VITs

on every utterance. Stutterers

longestVITs occurred on the


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normals. syllables. six test syllables. Their

shortest VITs appeared on

the isolated vowel.

Cross, Shaden,

and Luper

(1979).

10 adult

stutterers and

10 age-and-sex

matched

normals.

4000 Hz

presented in

each ear in

separate

condition.

Phonated / /. No difference in stutterers

VIT when tested tone was

presented to left as compared

to the right ear. Overall,

stutterers were slower than

normals.

Cross and

Luper (1979).

9 stutterers

each, at ages 5

and 7 years+9

adults age-and

sex matched

with like

numbers of

normals.

1000 Hz pure

tone.

Phonated / /. In both groups, VIT

shortened as age inceased. At

all age levels studied,

stutterers were slower than

normals.

Lewis, Ingham,

and Gervens(1979)

10 adult

stutterers and alike number of

normals.

1000 Hz pure

tone and alight flash;

presented in

separate

condition.

Phonate an

isolatedvowel.

Stutterers were slower than

normals in both the auditoryand visual cueing.

Prosek,

Montgomery,

Walden

(1979).

10 adult

stutterers and

10 age-and-sex

matched

normals.

Light flash, a

1000 Hz pure,

and spoken

words;

presented in

separate

conditions.

16 VC

words (e.g,

ape).


normals in all cueing

conditios.

Cross, and 8 adult Visual Phonate /a/ Stutterers were slower than


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Cooke (1979) stutterers and 8

normal

speakers.

stimulus, and

an auditory

stimulus,

presented in

separate

conditions.

normals across all

experimental conditions. The

greatest difference between

groups appeared in the

auditory-vocal response

condition.

Adler and

Starweather

(1980)

A group of

stutterers and a

group of non-

stutterers.

A visual

stimulus.

A laryngeal

gesture.

The stutterers were slower

than the control subjects in

all experimental condition.

Cullinan and

Springer

(1980).

11 child

stutterers with

articulation and

language

problems; 9

pure

stutterers; and

20 age-and-sex

matched normalchildren.

1000 Hz pure

tone.

Phonate /a/. The two groups of stutterers

combined, had slower VITs

than did normals. However,

this difference was a function

of the extreme slowness of

the stutterers with the

associated articulation and

language problems. VIT did

not differ between the purestutterers and the normals.

Murphy and

Baumgartner

(1981)

6 child

stutterers and 7

normal

speaking

children.

1000 Hz pure

tone.

Phonated

/a/.

No differences were found

between the groups.

Reich, Till, and

Goldsmith

(1981)

13 adult

stutterers and

13 age-and-sex

matched

normals.

1000 Hz pure

tone.

Phonted /a/

and the

word

upper.


normals on the isolated

vowel production and on the

words production.

Watson, and 8 adult 1000 Hz pure Phonated No differences were found


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Alfonso (1982) stutterers and

13 age-and-sex

matched

normals.

tone, and a

light flash

presented in

separate

conditions.

/a/, and a

nonsense

syllable

phrase.

between groups in either

condition, either the vowel or

the nonsense syllable phrase

response.

Hayden,

Adams, and

Jordahl (1982)

10 adult

stutterers and

10 ex-matched

normal adults.

1000 Hz pure

tone.

Production

of 9

sentences,

all

beginning

with a

vowel (e.g.,

Almonds

are nuts)


the normals.

INTERPRETATION:

In four of the six VOT studies, stutterers had longer (slower) scores than normal speaking

control subjects. In the SIT/VIT investigations that were reviewed, significant slowness

among the stutterers was noted unequivocally in 11 of 17 projects. Mixed findings wereobtained in two studies. Non significant differences were observed between stutterers and

control subjects in just 4 of the 17 experiments. From these outcomes we may conclude

that stutterers as a group are likely to have slower VOTs and VIT/SITs than matched

normal subjects.s

Beyond the broad interpretation, these studies tell us even more.

1. Stutterers slowness in VOT cuts across productions of isolated CV syllables toprose material being read aloud (Hillman and Gilbert, 1977).

2. Stutterers slowness in producing isolated vowels (VIT) appears also to be presentin the production of single words (Reich, Till and Goldsmith, 1981), and sentence

length utterances that are initiated with vowels (SIT; Hayden, Adams, and

Jordahl, 1982).


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Shortly after the completion of the first several VOT and VIT experiments, there was

considerable conjecture that the slowness was caused by an individuals history of

stuttering. In other words, having spent years as a stutterer, a person would quite likely to

approach speech or speech-acts with an excess of muscular tension in the larynx. Such

muscular tension, a result of a history of stuttering, might then act to retard VOT and

VIT.

At two predictions can be drawn from this framework.

1. We could forecast that young stutterers, with relatively short histories ofstuttering, would be less likely to approach to speech and speech-like acts with

excess muscular tension.

2. it should also follow that young stutterers would have shorter VOT and VITvalues as compared to adult stutterers because the children had briefer histories of

stuttering, and hence had less time to develop higher levels of muscular tension in

the larynx.

The results of studies cited in the table, fail to bear out these predictions, both VOT and

VIT scores for younger stutterers were slower than those of control subjects (Wendell,

1973, and Cross and Luper, 1979). It was also shown that stutterers VIT improved with

age (Cross and Luper, 1979). Neither of these findings would be likely if stuttering were

the cause of the slowness. Rather, such slowness probably coincided with the onset of the

disorder. Indeed, it is even possible that difficulty in quickly initiating voicing is one of

the immediate causes of stutterers repetitions and prolongations of articulatory gestures

(Adams, 1974), viewed here and elsewhere as core characteristics of stuttering (Wingate,

1964).

The next explanation that was developed pertained only to VIT. I this account, stutterers

slowness is causally related to a specific defect in the auditory system that retards the

reception or processing of stimuli used to cue vocal responses. Needless to say, this

interpretation was abandoned when stutterers were found slower than normal VITs to

visual signals as well (Starkweather, Hirschman, and Tannenbaum, 1976).

Noting this slowness in both auditory and visual stimulation, thought was give to

attributing it to some central disturbance that would reduce the speed with which

stutterers organized and started transmitting neural signals to the periphery for voice


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production. Inherent to this formulation is the idea that stutterers neural organization and

transmission are both normal with the exception of the speech with which they take

place. Recently, some experimenters have measured stutterers reaction times for

nonspeech tasks, such as button pressing, by using lights and/or tones. Stutterers neural

reaction times have also been assessed (McFarlane and Prins, 1978). There are only a few

of these investigations and their findings are mixed. Therefore, it would be premature to

interpret them at this point.

Finally in review, Adams (1981) offered an elaboration on the position that stutterers may

be slow to organize and transmit normal neural commands to their musculature.

Specifically, it was suggested that in addition to integrating and sending commands more

slowly, stutterers may also send inappropriate commands to the periphery. This would

activate muscles in ways that could delay voicing. It is interesting to note that stutterers

VIT and SITs improve when voicing and speech are initiated in synchrony with a

rhythmic stimulus (Hayden, Adams, and Jordahl, 1982). This finding is procative because

we have known for years that rhythmic speech improves fluency. Perhaps rhythm

enhances fluency by helping a speaker with the timing of events that are integral to

speech production (Brayton and Conture, 1978; Hayden, Jordahl and Adams, 1982). Such

an event could be voice initiated.

Suchitra (1985) conducted a study to find the acoustic parameters VOT, SIT, STT, Foand rate of speech in stutterers in pre and post therapy condition and found:

1. Non stutterers values are smaller when compared to pre and post therapy VOTvalues of stutterers.

2. Speech initiation time less than that of Stutterer in pre and post therapy condition.3. Stutterer post therapy VOT value smaller than pre-therapy value.4. Reduced post therapy SIT value of Stutterer compared to pre-therapy.5. Both show no difference in Fo does not vary as compared to pre-therapy.

Sebastian (1997) studied the acoustic parameter in stutterers and non-stutterers

and came to the following conclusion.

1. The VOT values were less for non-stutterers compared to stutterers.2. No significant difference between the stutterers and non-stutterers in terms

of formant frequencies was found.

3. Significant differences were found between stutterers and non-stutterers inword duration and vowel duration.


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Then she came to the conclusion that the laryngeal mechanisms during speech

in different for stutterers to that of non-stutterers.

LARYNGEALMUSCLEACTIVITYOFSTUTTERERS

Electromyographic (EMG) studies of stuttering are important because they provideinformation about a different level of the speech production process. The

electromyography amplifies and records the minute electrical voltages generated each

time a motor unit fires in response to a neural impulse. As motor units fire more

rapidly or as many motor units fire in close succession, electrical activity in a muscle or

muscle group increases. EMG recordings reflect the level of contractile activity in

muscle tissue and the variations in this activity over time.

When EMG recordings are combined with other information, such as acoustic

analyses of the speech produced, and knowledge of the anatomy and physiology of the

muscles under study, some inferences may be made regarding movements and/or levels

of muscle tension.

Electromyography in Stuttering Research

Most of the early EMG studies conducted with stutterers were designed to

investigate basic neurophysiological difference between stutterers and nonstutterers

(Morley, 1937; Steer, 1937; Travis, 1934). More recent experiments have focused on

the moment of stuttering and compared EMG patterns during fluent utterances with

those generated during stuttering.

A number of studies of stuttering have attempted to use electromyography as an

index of psychological status, for example arousal, anxiety, vigilance, anticipation, or

expectancy.

One study, which did not directly measure intrinsic laryngeal muscle activity,

does offer valuable insight into general throat area muscle activity related to stuttering.

Shrum (1967) used silver disc surface electrodes to record from several sites including

two bilateral masseter (jaw) muscle sites, two bilateral platysma (neck) muscle sites, and

one leg muscle site. He measured the duration of muscle activity from moment A, when

muscle activity was elevated over the resting state, to moment B when initiation of

phonation was recorded. He found that the interval between moments A and B (duration


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of prephonatory muscle activity) was significantly longer for stutterers than for

nonstutterers. For stutterers, this interval was longest before words on which they

stuttered, shorter before words on which they expected to stutter (but did not), and

shortest before words spoken without anticipation or stuttering. Shrum interpreted these

findings as indicating that stutterers began to tense earlier than nonstutterers. An

alternate interpretation is that initiation of phonation was delayed in stutterers. This

second interpretation of Shrums findings is consistent with recent research

demonstrating longer VOTs and slower initiation of phonation.

OBSERVING LARYNGEAL MOVEMENTS OF STUTTERERS

Development of the flexible fiber optic endoscope (fiberscope) a flexible tube

containing bundles of glass or plastic fibers has had a great impact on otolaryngology,

speech science, and speech pathology. The fiberscope contains two bundles of optical

glass or plastic strands / fibers with one bundle carrying a cold, bright ligh t (e.g. xenon)

to illuminate the area under investigation and the other bundle returning a color image

back for visualization and / or recording (Boyd,1982).Because a fiberscope can be readily

passed through a bodily orifice, routine activities of heretofore inaccessible parts of the

body, such as the vocal folds, can be visualized. Its use in the study of laryngeal activity

associated with stuttering is the basis of this discussion (Conture, 1977, 1982a, 1983;

Conture, McCall & Brewer, 1977. 1979; Freeman, 1975.

Fiberscope Investigations of Stuttering

Ushijima et al. (1966) who filmed both inappropriate glottal openings as well as

tightly adducted true/false vocal folds during different instances of stuttering. Fujita

(1966), using posterior-anterior X-rays of the laryngeal area, also reported nonpredictable

openings and closings of the pharyngolaryngeal cavity associated with stuttering.

Shortly thereafter, Conture and associates in Syracuse and Freeman and associates

at Haskins Laboratories publicly presented their fiberscopic and electromyographic

observations of the larynx during stuttering. Conture and associates work focused on

fiberscope observations, while that of Freeman and colleagues involved

electromyographic studies of stuttering.


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Conture et als 1977 work indicated that the larynx is often (1) inappropriately,

nonpredictably open or (2) inappropriately closed during instances of stuttering. These

findings were consistent with those of Ushijima et al. (1966) and, coupled with Freeman

and Ushijimas (1978) EMG findings, clearly implicated laryngeal involvement in the

disrupted speech physiology that characterize stuttering.

Conture (1982a), shows that laryngeal behavior was more variable during sound /

syllable repetitions than sound prolongations. Moreover, sound/syllable repetitions also

contained the greatest number of nonviewable/nonmeasurable videoframes. Still, these

findings, which are consistent with previous reports, indicate that laryngeal behavior not

only differs between stuttering and fluent productions but also between different types of

stuttering as well.

In a time-course description of laryngeal behavior from beginning to end of an

adult stutterers sound / syllable repetition, it is apparent that during a sound/syllable

repetition, laryngeal behavior is highly variable; the vocal fold open and closes

throughout the repetition. The larynx is not static; it oscillates between abductory and

adductory postures. Preliminary data also suggest that the height of the larynx during

stuttering varies. In fact, videofluoroscopic observations of laryngeal height during

stuttering (Conture, Gould & Caruso, 1980) indicate that many repetitions are

characterized by a descending or lowering of the larynx compared to its height during

fluent productions of a vowel.

For some sound prolongations, the ventricular folds are also compressed medially,

above the adducted vocal folds, as the epiglottis is pulled posteriorly. Sound

prolongations with some stutterers show constriction of the pharyngeal area at the level

of the larynx. Stutterers, who point to their throat and say that the word got stuck here,

may not only be sensing excessive laryngeal adduction but aerodynamic back pressure.

Conversely, some sound prolongations, particularly those on /s/ and /f/, are

associated with widely opened vocal folds. Of course, the vocal folds should be abducted

during production of these sounds since they are voiceless; however, the degree of

abduction is excessive and lasts far too long. Furthermore, a Stutterer who senses these

extended laryngeal abductions may still describe them in much the same way as overly

adducted laryngeal behavior; that is, the Stutterermay say the word got stuck.


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Effect of binaural masking noise on stutteringa spectrographic

analysis (NANDU 1982)

Masking does reduce the frequency and severity of stuttering and also alters the

usual manner of initiating phonation. It makes the Stutterer to speak more slowly and

loudly (Cherry and Sayers, 1953; Hanley and Steer, 1949; Adams and Hutchinson 1974).

Auditory masking by noise brings about a reduction in secondary behavior,

mostly while using automatic feedback masking. Expressionless speech and reduction inspeech intelligibility observed. (Dewar et al 1976)

Masking helps the stutterers to learn to monitor their speech primarily by

proprioceptive, tactile and kinesthetic feed backs. It also distracts the subjects attentionfrom his speech and reduces anxiety and also changes the manner of speech (Van Riper,

1973).

The purpose of the study was to find out the effects of masking noise on rate ofspeech, fluency, fundamental frequency, voice onset time, vowel duration and vocal level

in stutterers and normals.

Subjects: Four stutters and four non stutters with age and sex matched

All speech recordings were done using unidirectional microphone

Subject read the passage in the presence and absence of masking noise. This reading was

recorded using tape recorder.

Results

Both stutterers and non stutterers showed an increase in vocal intensity levelunder binaural masking noise, how ever, stutterers showed greater increase in vocal

intensity than non stutterers.

No significant difference in voice onset time (VOT) was observed in stutterers

and non stutterers- both in the presence and absence of binaural masking noise.

An increase in vowel duration was found in both stutterers and non stutterers

under binaural masking.

In a study, Geetha (1979) has attempted to find out the linguistic characteristics ofstuttering, in Kannada language, of 15 stutterers by analyzing their spontaneous speech

and reading samples. She has concluded that, The content words are stuttered ore often than the function words. The consonants in general were stuttered more often than vowels. However,

stuttering was found on vowels also and in a minority of cases vowel stuttering

was more than the consonant stuttering.


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There is no difference between the adult and child stutterers in terms of theirrepetition characteristics of various linguistic units as syllable, word, part word,

phrases and sentences. With respect to syllable structure, maximum stuttering was observed on CV

syllables and the next in the order was vowel syllable.

Analysis of speech of stutters (dissertation)

This study was taken up to find out the relationship between frequency ofoccurrence of stuttering and various linguistic factors and to note the relationship

between voicing and stuttering in adult and children.

Subjects: 71 adult stutterers age ranging from 12- 35 yrs and 11 children who werediagnosed as stutterers age ranging from 6- 12 yrs were made to read 2 passages (one

passage consisted of both voiced and unvoiced sounds and another passage had only

voiced sounds. The readings were recorded using tape recorder

Most of the stutterers showed normal rate of speech. It is found that the initial syllable in the word is most frequently stuttered than

the syllable in any other position. Stuttering was found most frequently on vowels than on consonants, both in

the case of adults and children in the present study. The adult stutterers showed more stuttering while reading combined passage

than the voiced passage. However, children did not show any such difference.

Adams & Reis (1971, 1974) have found that there was greater frequency of

stuttering in passage which had both voiced and unvoiced sounds than in the

passage which had only voiced sounds. They also found that the adaptation rate

was faster in the latter. They have concluded that the frequency of stuttering wasrelated to the onset of phonation required. But Manning & Coufal (1976) found

that the difficulty in both stutterers and non stutterers was during voiced to voicedtransition than, during voiceless to voiced, voiced to voiceless and voiceless to

voiceless phonatory transitions.

Another investigation by manning and Coufal (1976) compared the speech of 11adult stutterers and a matched group pf 11 non stutterers. Four types of phoneme

to phoneme transitions were compared. The results indicated that both the groups

had a lower percentage of disfluencies during voiced to voiced transition than

during voiceless to voiced, voiced to voiceless and voiceless to voiceless

phonatory transitions.

Gayathri (1980) investigated some aspects of phonatory behavior in stutterers. Theaim of her study was 1) to test if different degrees of voicing during repeated reading

of a passage bring about difference in the amount of adaptation in stutterers. 2) to test

if there is any relationship between the frequency of stuttering and the onset ofphonation invaried contexts: syllables, word list and passages in stutterers. 3) to test if


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there is any relationship between the frequency of stuttering and the occurrence of

stressed syllables in stutterers.

It was concluded from the three experiments that:

1)

Varying degree of voicing during rehearsals bring about significant differences inthe amount of adaptation. Greatest amount of adaptation occurs when there isinvolvement of voicing during the rehearsals as in aloud rehearsals and whispered

rehearsals.

2) Stutterers have greater frequency of stuttering when transition from voiced tovoiceless or voiceless to voiced consonants is required. This is indicated by

greater frequency of stuttering in combined passage and combined word list when

compared with the frequency of stuttering in voiced passage and voiced word list.

The adaptation rate is also faster in a voiced passage. Therefore the stutterers haveless lesser difficulty when transition from voiced to voiceless consonants are not

required and vice versa.

3)

Stutterer stutters more often on the non-stressed syllables preceding the stressedsyllables. This may be because, the stutters have difficulty in moving on the

following stressed syllables and keep repeating or prolonging the preceding

syllable. Stuttering is rare during the transitions from the stressed syllables to the

following non stressed syllables. Stuttering is also less frequent during thetransition from non stressed syllables to non stressed syllables.

Stuttering as a learnt extricatory response to a laryngeal abductor reflex

(Schwartz):

This is core of stuttering block model by Schwartz (1974, 1975a, 1975b). It was

his discovery of that physical cause of the stuttering block that him enabled him to

develop a relatively simple treatment. He stated that the core of the stuttering block is the

tendency, under conditions of psychological stress, for the loss of supra medullar,

inhibition controls upon the PCA in the presence of sub glottal air pressure associated

with speech.

Schwartz (1976) lists several kinds of stress which contributes to

stuttering. Baseline stress consists of speakers amount of psychological and muscle

tension.

Physical stress (fatigue), external stress (bad news) and speed stress (need to talk

in hurry) may add to Stutterer psychological stress. Finally other factors such as

situations of communicative stress, sound and word fears and verbal uncertainty, trigger

anticipation of stuttering which adds to psychological stress. As the Stutterer acquires

large repertoire of struggle and coping behaviors, anticipation of stuttering alone becomes


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sufficient to evoke a laryngospasm or a set of distracting or avoidance behaviors to

prevent its occurrence.

Comments:

1. Schwartzs model of stuttering and his approach to therapy have beencontroversial. The question whether or not PCA is the strongest intrinsic

muscle of the larynx as raised by Freeman, Ushijima and Hirose (1975). To

support his statement, Schwartz conceded that it was at least one of the

strongest laryngeal muscles.

2. Freeman et al (1975) raised an important question as to whether the PCA isreflexively active in controlling glottal width during exhalation.

3. Zimmerman and Allen (1975) wondered how the model could account forstuttering on voiceless sounds. for this Schwartz explained that an increase in

subglottal air pressure associated with such sounds was responsible for

conditioned laryngospasms.

4. This model does not account for the linguistic findings of stuttering and it wasprobably not meant to do so

5. It does not predict any general motor coordination deficits in stutterers. Mostof the respiratory and articulatory errors are seen as learnt excitatory

behaviors.

M.F. Schwartz (1974) proposed that Agnello & Wingates (1972) finding

that stutterers had longer than normal voice onset times in stop consonant vowel syllables

was due to neural inhibition of the PCA.

In summary, whereas any kind of laryngeal irregularities during stuttering could

be explained by Schwartzs model, direct evidence of the reflexive contraction of the

PCA prior to speech is lacking. Since his model hinges on that presumption, unqualified

acceptance of the model must await further empirical verification.


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REFERENCES:

Analysis and Synthesis of Speech of stutterers. The Spectrographic analysis of Stutters Speech under delayed auditory feed back.

Analysis of Speech of stutterers. Voice Onset Time for Stutterers and non Stutterers.

Edward G.Conture, Stuttering Second Edition

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LARYNGEAL DYNAMICS IN STUTTERING.pdf / KUNNAMPALLIL GEJO