laryngeal dynamics in stuttering

LARYNGEAL DYNAMICS IN STUTTERINGLARYNGEAL ONSET AND REACTION TIME OF STUTTERERS:

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:

Studies of stutterers voice onset time (VOT), voice initiation time (VIT) and speech initiation time (SIT).

Electromyographic investigation of stutterers laryngeal muscle activity.

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 consonant (Lisker and Abramson, 1964).

Methodologies and instrumentation:

VOT can thus be measured with any instrument that:

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

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:

Spectrography.

Detecting the sizeable rise in intraoral air pressure that occurs during the implosion phase of stop consonant production.

X-ray motion picture and voice recorder. The former, we can see the start of the consonantal 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 Authors Method Method Subjects Subjects Results Results Angello and Angello and Wingate (1972) Wingate (1972)

Pressure-sensor Pressure-sensor and voice-and voice-recorder; CV recorder; CV utterances. utterances.

Matched groups Matched groups of 12 adult of 12 adult stutterers and 12 stutterers and 12 normals.normals.

Stutterers VOT Stutterers VOT were longer. were longer.

Wendell (1973) Wendell (1973) Spectrographic Spectrographic analysis of CVs analysis of CVs

Matched groups Matched groups of 12 child of 12 child stutterers and 12 stutterers and 12 normals. normals.

Stutterers VOTs Stutterers VOTs were longer. were longer.

Metz, Conture, Metz, Conture, and Caruso and Caruso (1979). (1979).

Spectrographic Spectrographic analysis of 18 analysis of 18 different sound different sound clusters in words clusters in words

5-young adult 5-young adult stutterers and 5- stutterers and 5- normals. normals.

Stutterers VOT Stutterers VOT were longer on were longer on only 6 of the 18 only 6 of the 18 clusters (p<0.05).clusters (p<0.05).

Authors Authors Method Method Subjects Subjects ResultsResultsZimmerman Zimmerman (1980) (1980)

X-ray motion X-ray motion picture and voice picture and voice recorder; 3 CVC recorder; 3 CVC words. words.

6-adults stutterers 6-adults stutterers and 7 normals and 7 normals

stutterers VOT stutterers VOT were longer. were longer.

Watson and Watson and Alfonso (1982) Alfonso (1982)

Spectrographic Spectrographic analysis of 3 analysis of 3 contiguous contiguous VCVC sequences. VCVC sequences.

8 adult stutterers, 8 adult stutterers, age-and-sex age-and-sex matched with 8 matched with 8 normals. normals.

No significant No significant between group between group difference in difference in VOT (p<0.05).VOT (p<0.05).

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

Authors Authors Characteristics Characteristics of subjects of subjects

External External signal(s)usesignal(s)used d

Subject’s Subject’s response response

Findings Findings

Adams Adams and and Hayden Hayden (1976) (1976)

10 adult 10 adult stutterers and stutterers and 10 age-and –10 age-and –sex matched sex matched normals. normals.

1000Hz 1000Hz pure tone.pure tone.

Phonated /a/. Phonated /a/. Both groups shortened Both groups shortened VIT from the beginning VIT from the beginning to end of the experiment. to end of the experiment. Stutterers were slower Stutterers were slower on two of three on two of three comparisons made. comparisons made.

StarkweatStarkweather, her, HirschmaHirschman and n and TannenbaTannenbaum um (1976). (1976).

11 adult 11 adult stutterers and stutterers and 11 age-and-sex 11 age-and-sex matched matched normals. normals.

Green light Green light presented presented on the on the screen. screen.

26 test 26 test syllables syllables reflecting a reflecting a wide range wide range in place and in place and manner of manner of articulation. articulation.

Both groups shortened Both groups shortened VIT from the beginning VIT from the beginning to end of the experiment. to end of the experiment. Stutterers were slower Stutterers were slower across all test trials and across all test trials and across all syllable types across all syllable types investigated. investigated.

Authors Authors CharacteristicCharacteristics of subjects s of subjects

External External signal(s)used signal(s)used


Findings Findings

Cross, Cross, Shaden, Shaden, and Luper and Luper (1979).(1979).

10 adult 10 adult stutterers and stutterers and 10 age-and-10 age-and-sex matched sex matched normals. normals.

4000 Hz 4000 Hz presented in presented in each ear in each ear in separate separate condition. condition.

Phonated Phonated /a/. /a/.

No difference in No difference in stutterers VIT when stutterers VIT when tested tone was tested tone was presented to left as presented to left as compared to the right compared to the right ear. Overall, stutterers ear. Overall, stutterers were slower than were slower than normals. normals.

Cross and Cross and Luper Luper (1979). (1979).

9 stutterers 9 stutterers each, at ages each, at ages 5 and 7 5 and 7 years+9 years+9 adults age-adults age-and –sex and –sex matched with matched with like numbers like numbers of normals.of normals.

1000 Hz pure 1000 Hz pure tone.tone.

Phonated Phonated / a/. / a/.

In both groups, VIT In both groups, VIT shortened as age shortened as age inceased. At all age inceased. At all age levels studied, levels studied, stutterers were slower stutterers were slower than normals. than normals.




Findings Findings

Lewis, Lewis, Ingham, and Ingham, and Gervens Gervens (1979) (1979)

10 adult 10 adult stutterers and a stutterers and a like number of like number of normals. normals.

1000 Hz pure 1000 Hz pure tone and a light tone and a light flash; flash; presented in presented in separate separate condition. condition.

Phonate an Phonate an isolated vowel. isolated vowel.

Stutterers were Stutterers were slower than slower than normals in normals in both the both the auditory and auditory and visual cueing. visual cueing.

Prosek, Prosek, Montgomery, Montgomery, Walden Walden (1979). (1979).

10 adult 10 adult stutterers and stutterers and 10 age-and-sex 10 age-and-sex matched matched normals normals

Light flash, a Light flash, a 1000 Hz pure, 1000 Hz pure, and spoken and spoken words; words; presented in presented in separate separate conditions. conditions.

16 VC words 16 VC words (e.g, ape). (e.g, ape).

Stutterers were Stutterers were slower than slower than normals in all normals in all cueing cueing conditios. conditios.




Findings Findings

Adler and Adler and Starweather (1980) Starweather (1980)

A group of A group of stutterers and stutterers and a group of a group of non-stutterers. non-stutterers.

A visual A visual stimulus. stimulus.

A laryngeal A laryngeal gesture.gesture.

The stutterers The stutterers were slower were slower than the than the control control subjects in all subjects in all experimental experimental condition condition

Cullinan and Cullinan and Springer (1980). Springer (1980).

11 child 11 child stutterers with stutterers with articulation articulation and language and language problems; 9 problems; 9 “pure” “pure” stutterers; and stutterers; and 20 age-and-20 age-and-sex matched sex matched normal normal children. children.

1000 Hz pure 1000 Hz pure tone. tone.

Phonate /a/. Phonate /a/. The two The two groups of groups of stutterers stutterers combined, combined, had slower had slower VITs than did VITs than did normals. normals. However, this However, this difference difference was a was a function of..function of..




Findings Findings

Murphy and Murphy and BaumgartneBaumgartner (1981) r (1981)

6 child 6 child stutterers stutterers and 7 and 7 normal normal speaking speaking children. children.

1000 Hz 1000 Hz pure tone. pure tone.

Phonated Phonated /a/./a/.

No No differences differences were found were found between the between the groups. groups.

Reich, Till, Reich, Till, and and Goldsmith Goldsmith (1981) (1981)

13 adult 13 adult stutterers stutterers and 13 age-and 13 age-and-sex and-sex matched matched normals.normals.

1000 Hz 1000 Hz pure tone. pure tone.

Phonted /a/ Phonted /a/ and the and the word word “upper”. “upper”.

Stutterers Stutterers were slower were slower than than normals on normals on the isolated the isolated vowel vowel production production and on the and on the word’s word’s production production




Findings Findings

Hayden, Hayden, Adams, and Adams, and Jordahl (1982) Jordahl (1982)

10 adult 10 adult stutterers and stutterers and 10 ex-matched 10 ex-matched normal adults. normal adults.

1000 Hz pure 1000 Hz pure tone. tone.

Production of Production of 9 sentences, all 9 sentences, all beginning with beginning with a vowel (e.g., a vowel (e.g., “Almonds are “Almonds are nuts”) nuts”)

Stutterers were Stutterers were slower than the slower than the normals. 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 sloweness among the stutterers was noted unequivocally in 11 of 17 projects. Mixed findings were obtained 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.

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

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

Stutterers’ slowness in producing isolated vowels (VIT) appears also to be present in 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).

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.

We could forecast that young stutterers, with relatively short histories of stuttering, would be less likely to approach to speech and speech-like acts with excess muscular tension.

It should also follow that young stutterers would have shorter VOT and VIT values 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. Is 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 production. Inherent to this formulation is the idea that stutterer’s 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 proactive 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.

LARYNGEAL MUSCLE ACTIVITY OF STUTTERERS

Electromyographic (EMG) studies of stuttering are important because they provide information 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 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 Shrum’s findings is consistent with recent research demonstrating longer VOTs and slower initiation of phonation.

Intrinsic laryngeal muscle activity in stuttering: Freeman and Shapiro each studied four stutterers.

Both used in-dwelling hooked-wire electrodes (except for some orbicularis oris recordings), and both attempted to record simultaneously from five intrinsic laryngeal muscles and from three to four articulator muscles. Most of what we presently know about intrinsic laryngeal muscle activity in stuttering is based on results from eight stutterers, with a total of 40 verifiable recordings (17 from articulator muscles, 22 from intrinsic laryngeal muscles, and 1 from an extrinsic laryngeal muscle).

However, recordings from the posterior cricoarytenoid muscle were obtained from only three subjects, and all statements regarding laryngeal abductor-adductory reciprocity in stuttering are based on data from threes three subjects.

Three significant findings have emerged from these studies and form the basis for the following discussion.

Levels of muscle activity: Stuttered speech (i.e. speech in which frequent perceived stutterings occurred) was accompanied by higher levels of muscle activity than was speech which contained little or no perceived stuttering. This finding was somewhat more pronounced for laryngeal than for articulator muscles.

The highest levels of muscle activity were associated with perceived stutterings and with disrupted coordination between agonist-antagonist laryngeal muscles. Patterns of muscle activity were similar to those reported by Sheehan & Voas (1954) in that the levels of muscle activity dropped dramatically at the moment a stuttered word was finally uttered (when the block terminated). It is impossible to say, however, if activity dropped because the block was terminated or if termination of the block was achieved because the level of muscle activity diminished.

Disruption of coordinated muscle activity: In those subjects (three in total) from whom recordings were obtained from the laryngeal abductor (posterior cricoarytenoid) and from at least one adductor muscle (lateral cricoarytenoid, vocalis, or interarytenoid), it was possible to study coordination of functional antagonists. In normal speakers, these muscles act with reciprocity. That is, when the abductor contracts, the adductors relax and vice versa. For the most part, perceived stutterings were accompanied by co contraction (disruption of reciprocity) of these muscles. However, Shapiro’s subject produced some disfluencies in which laryngeal cocontraction was not evident.

Freeman (1977) has agreed that disruption of reciprocity in laryngeal adductor and abductor muscles results is a temporary breakdown in the ongoing process of speech production (or, in other words, a physiological block). She hypothesized that the extent to which such disruption (physiological blocking) will fragment or interrupt speech output is dependent on (1) the duration and intensity of the cocontractions, (2) the locus in the speech sequence of its occurrence (between or within words); and (3) a speaker’s facility in developing and using strategies to cope with such disruption.

In evaluating laryngeal co contraction findings, studies of agonist-antagonist articulator muscles (Fibiger, 1977; Platt & Basili, 1973) also warrant consideration. These studies report co contraction of agonist-antagonist muscles in the lip and jaw, respectively, during moments of stuttering as well as the occurrence of observable, or measurable, tremor associated with such co contraction. The pattern of activity (including abductor-adductor co contraction) observed in one of Freeman’s subjects (DM, F1) could be interpreted as evidence of vocal tremor. Available evidence indicates that disruption of agonist-antagonist reciprocity (physiological blocking) of both laryngeal and articulator muscle is often associated with stuttered speech. When such co contraction is of sufficient duration and intensity, tremor may result.

Evidence of abnormal muscle activity during perceptually fluent utterances:

Both Freeman and Shapiro also found evidence of abnormal muscle activity during “perceptually fluent” utterances of stutterers. While most perceived stutterings (identified by listeners) were accompanied by disruptions in the normal coordination of muscle activity, similar disruptions also occurred in the speech sequence when listeners did not perceive stuttering. Freeman (1977) found that 7 of 26 perceptually fluent utterances of the word “syllable” showed positive, rather than expected negative, correlations between activity of laryngeal abductor (posterior cricoarytenoid) and adductor (Interarytenoid) muscles.

A post hoc examination revealed that a brief period of acoustic silence preceded each of these utterances, and that during these periods abductor-adductor co contraction occurred. Apparently, these pauses were too brief in duration to trigger listener perception of stuttering. Similarly, Shapiro (1980) published illustrations of (1) abnormal orbicularis oris activity during acoustic silences prior to perceptually fluent utterances, (2) abnormal activity of the cricothyroid muscle during a period of acoustic silence preceding an utterance, and (5) abnormal activity of the posterior cricoarytenoid during the utterance of an all-voiced, perceptually fluent word.

These findings strongly suggest that the stutterer, while speaking, experiences many moments of disruption of normal coordination (physiological blocks). Depending on a number of factors, including the nature, intensity, duration and timing of the disruption, its effects may or may not result in audible or perceptible stuttering. In some cases a disruption occurring at the onset of a word may simply result in a slight delay in the initiation of the word, a pause too brief to be identified as disfluency. In other cases, the only result may be a shift in fundamental frequency, a voicing break, fry phonation, or an abnormally long voice onset time.

In terms of muscle activity, “good coordination” occurs when muscles and muscle groups work together to produce the desired effects with a minimum of wasted effort. Exceptions to this principle of physiology occur in motor acts that may be described as inefficient or “poorly coordinated”. Specifically, co contraction of antagonist muscles has been found to occur (1) In physiological stress (created by imposition of high “loads” or resistance; Gelthorn, 1947); (2) in very rapid movements (Gosbel & Boulsset, 1966); (3) in the performance of a highly skilled task by untrained subjects (Bratanova, 1966); (4) in infants and young children (Fenges, Gergely, & Toth, 1960; Gater, 1967); (5) in neurological impairment (Kenny & Heabertin, 1962; Landan & Clare, 1959); and (6) in nonrhythmic performance (Kizmyan, 1965).

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 light (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 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.

Conture et al’s 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 Ushijima’s (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 stutterer’s sound / syllable repetition, it is apparent that during a sound/syllable repetition, laryngeal behavior is highly variable; the vocal folds open and close 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 stutterer may say “the word got stuck

Electroglottographic (EGG) observations of young stutterers’ fluency

Use of the fiberscope is a problem with children, particularly the very young child who is just beginning to stutter. With such small children, procedures that are noninvasive (ones that do not enter a bodily orifice or penetrate the outer skin) as well as nonintrusive (ones that do not restrict or interfere with natural speech production movements / gestures) are preferable. In terms of studying youngsters’ laryngeal behavior during speech, the electroglottograph (EGG) appears ideally suited.

EGG findings with a 4-year, 10-months-old male stutterer and a 4-year, 9-month-old male normally fluent speaker. Although the EGG traces of these children differ in a number of ways (for example, durations of sound segments) focus is non the shape of the individual glottal pulses of the EGG waveform in the perceptually fluent production of the word-medial vowel /e/ in “again”. Young stutterer’s EGG waveform is nearly triangular or saw tooth in shape, whereas the young normally fluent child’s EGG waveform is more rounded or arched and more nearly sinusoidal.

Using other analysis methodologies, we can determine that the stuttering youngster’s glottal vibratory cycle is open for approximately 30% and closed for about 70% of the glottal cycle, while the normally fluent youngster’s is approximately 50% closed per glottal cycle. For this one young stutterer, this suggests a greater degree of vocal fold tension than for the normally fluent youngster.

Some of our other preliminary EGG findings with young stutterers suggest that such excessive or inappropriate vocal fold adduction is most noticeable at the transitions between sounds. Thus, young stutterers may have a tendency to “tighten” or adduct their vocal folds when they move from consonant to vowel or vowel to consonant, regardless of the voicing characteristics of the consonant.

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 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.

Central to the model is an airway dilation reflex (ADR) which flares the nostrils, moves the body of the tongue forward, dilates the pharynx and abducts the glottis. According to Schwartz, ADR is mediated in the medulla and can be elicited by increased sub glottal pressures receptors in the trachea. During normal speech, subglottic pressure is elevated but ADR is not elicited because the higher central nervous system speech centers inhibit the medullary center which mediates the reflex. This supramedullary inhibition breaks down, under periods of psychological stress. As a result, ADR is elicited and causes PCA to contract and the glottis to abduct. Phonation is thus rendered impossible.

The speaker who finds himself unable to phonate typically overcomes the abduction by vigorous adductory effort of a “laryngospasm”. He may also attempt to do battle supraglottally by tensing the lips, tongue or jaw. Overt stuttering, then consists of learned extricatory behaviors to escape from laryngospasm or to avoid its occurrence altogether.

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 sufficient to evoke a laryngospasm or a set of distracting or avoidance behaviors to prevent its occurrence.

Comments:Schwartzs’ model of stuttering and his approach to therapy have been controversial. 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.Freeman et al (1975) raised an important question as to whether the PCA is reflexively active in controlling glottal width during exhalation. Zimmerman and Allen (1975) wondered how the model could account for stuttering on voiceless sounds. for this Schwartz explained that an increase in subglottal air pressure associated with such sounds was responsible for conditioned laryngospasms.

This model does not account for the linguistic findings of stuttering and it was probably not meant to do so it does not predict any general motor coordination deficits in stutterers. Most of the respiratory and articulatory errors are seen as learnt excitatory behaviors.

Since the PCA is hypothesized to contract prior to many stutterings, but abduction of the larynx has not been reported as consistent pattern prior to stutterings. Freeman & Ushijima (1974) recorded EMGs from a number of laryngeal and supraglottal muscles in a severe stutterer, did not observe activity either the PCA or genioglossus prior to stuttering. In other words, they found no evidence of ADR. On the contrary, Conture et al. (1977) reported glottal abduction as the primary laryngeal symptom during, not prior to part word repetitions.

In this case, it is difficult to imagine that the stutterers were struggling to free themselves from adductory laryngospasms. However, part word repetitions reflect a supra glottal response to ADR

M.F. Schwartz (1974) proposed that Agnello & Wingate’s (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, any kind of laryngeal irregularities during stuttering could be explained by Schwartz’s 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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laryngeal dynamics in stuttering

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