• Among the varied views regarding etiology of
stuttering, few of them consider stuttering as
an articulatory disorder.
• Evidence for this view comes from many
studies that have found many articulatory
abnormalities and errors in stutterers.
• Models have been proposed in this regard
which try to explain stuttering as an
Zimmerman’s model of Breakdown: the
Interaction of Information and Action
Zimmerman (1980) suggested that stuttering should
be regarded as a disorder of movement and that
the principles of motoric behavior be brought to
bear on the problem.
The focus on parameters such as velocity,
displacement and duration of movement and the
coordination and timing between articulatory
events was motivated by the possibility of relating
these events to underlying neurophysiologic
Disfluent events are associated with particular
patterns that preceded and followed them.
These findings led to the speculation about the
association between disfluent events and aberrant
activation of brainstem pathways that
physiologically link the articulators.
Specifically, it was suggested that lower velocities
and displacements and longer durations in the
movements of stutterers are associated with
processes that keep activation of BS pathways
below “threshold” level during perceptually fluent
Bernstein (1967) proposed that the onset of any
movement is preceded by preliminary tuning of
the excitability of all participating sensory and
Tuning or biasing facilitates or inhibits the
excitability of certain pools of motor neurons and
thereby alters the relationships among groups of
muscles and determines the kind of behavior
they will promote.
Inco-ordination may occur when either tuning or
triggering inputs are aberrant.
The excessive tension noted in some stutterers
prior to speech, the aberrant position of
articulators preceding oscillatory or tonic activity
of the articulators and the fact that most
stuttering occurs on initial gestures indicate that
the period before speech movements may be a
time in which aberrant inputs are likely to occur
The central commands for speech might exist
as spatially coded targets, auditory targets or
Whatever the representation of the code, the
commands must be executed to achieve the
critical spatial temporal relationship necessary
for intelligible speech. Temporal and spatial
relationships of the articulators must be
achieved through out a speech gesture and
that the fluent movement patterns are
dependent on such relationships.
These must be accomplished by the proper
neuromotor input via the cranial nerve nuclei and
motoneuron pools to proper muscles or muscle
system at the proper time.
The movements involved in achieving these goals,
the contacts made and the positions achieved
results in stimulation of many intraoral and perioral
It is posited that when a person speaks, he
usually operates the respiratory laryngeal and
supralaryngeal systems within certain ranges
of variability i.e. he usually stays within certain
limits in velocities, displacements,
accelerations and inter articulatory spatial and
For e.g. though the lower lip and jaw move
more or less simultaneously toward given
targets, (some normal variation occurs in lip
jaw synchrony). When these normal ranges
are exceeded the afferent nerve impulses
generated are presumed to increase the gains
at associated brainstem reflex pathways.
• If excitation reaches a “threshold level”, then
oscillation or tonic behaviors occurs.
• Such reflex connections have been shown to
disrupt the ongoing pattern behavior by altering
afferent input and changing muscle length and
tension which affect the gains and phases of these
If the velocity and displacement and the spatial
relationships remain below “threshold levels” of
variability so as not to increase reflex affects,
fluent production occurs, the stability and integrity
of the system is maintained, the visual feedback
mechanisms are employed and the speech
Stuttering as a defect in a coarticulatory
timing (Van Riper):
Van Riper (1971) defined a stuttering behavior
as a “word improperly patterned in time and the
speakers’ reaction thereto”.
Van Riper hypothesized that the stability of
motor patterns which maintain the integrity of
syllables is somehow lacking in stutterers due
in part to over-reliance on auditory feedback for
speech control instead of appropriate
monitoring via tactile kinesthetic proprioceptive
In addition, stutterers are thought to be deficient
in their ability to “time” or integrate long motor
sequences. Such “timing” is said to involve the
imposition of higher order integration to achieve
the proper serial order of a large number of
discrete motor sequences.
A dominant movement, such as stressed
syllable, is what typically “times” a speech
sequence up to phrase in length. Stutterers are
intermittently unable to achieve such “timing”
thereby producing sequences within
appropriate co articulation.
Van Riper also ruled out organic deficiencies in
this speech related functions (underlying
physiological difficulties). So, stuttering, he held
is the result of deficiencies in:
• The stability of motor patterns for syllables
• The ability to integrate a large number of
discrete events in correct temporal order and
• Speech related respirations, phonation and
The combined result of these short comings is
fractured syllables characterized by improper
coarticulatory transitions between sounds.
For e.g. early stuttered repetitions of CV
syllables often contain the schwa vowel instead
of the target vowel (e.g. /s∂-s∂- - sop/.)
In such repetitions, it appears that the stutterer
is searching for the appropriate coarticulatory
features for the sound(s) he is attempting to
When the correct features are achieved, the
stuttering is terminated
In other stuttering movements, precise timing
of transitional events between sound is often
lost due to breaks in airflow, excessive tension
and inappropriate postures.
Agnello also said that “the primary feature of
stuttering is essentially within the articulatory
transition from phone to phone.
Reason for these lacks of transitions lie
somewhere higher in the vocal tract resulting
in excessive supraglottal air pressure and
causes phonatory difficulties.
Van Riper’s model or stuttering as a defect of
co-articulatory timing is not concerned with
most of linguistic determinants.
Van Riper’s model i.e. a defect in timing may
explain some of the problems stutterers have
in maintaining rhythmic repetitions of various
speech and non-speech tasks.
It can be studied under 2 broad headings.
A. Temporal errors:
B. Spatial errors:
A. Temporal errors:
• Longer phoneme durations
• Shorter phoneme durations
• No significant difference
• Longer durations between articulatory events
• Inaccurate timing
B. Spatial errors:
• Spatially restricted movements
• Inappropriate articulatory placements
• Excessive articulatory movements
• Static positioning of articulators
• Forceful articulatory patterns
• Low velocities of articulators
• Reverse muscle movements
• Difficulty in stabilizing the articulatory movements
Longer Phoneme Duration:
Several studies have revealed increased phoneme
duration in stutterers.
• 6 stutterers with age Ranging from 18 to 39.
• Stutterers had significantly greater absolute vowel
and consonant durations than the non-stutterers
Montgomery and Cooke (1974)
• Studied part word repetitions in the speech of
adult stutterers using Spectrography
• Results indicate that longer consonant duration in
the initials segment of Stuttered word.
Prosek & Runyan (1982)
• Measured duration of stressed vowels;
extracted from connected speech using
• Results indicate that stuttering group spoke
with more pauses and with longer average
pause and vowel duration than Non-stutterers.
Stuttering Group total duration of stressed
vowel = 170.6 msec. Non-stuttering group
total duration of stressed vowel = 144.1 msec.
Kalveram & Jancke (1989)
Studied vowel duration under DAF condition
Longer vowel duration in stuttering group reported.
• 2 normally nonfluent and 2 stuttering children
using spectrographic analysis for vowel duration .
• Results indicate that stuttering group children had
significantly longer vowel duration than normal
Shorter phoneme duration:
A few authors have reported contradicting
results compared to the previously quoted
1.Reimann (1976) studied context dependence of
vowel duration in German words.
• Stuttering group had shorter vowels than
controls. Also stuttering group altered the
vowel duration depending on the consonant
that followed (similar to normals).
2. Production of vowels by stuttering children and
Howell, Williams & Young (1991)
• To analyze the acoustic properties of vowels in
children’s syllable repetition to establish whether
there are differences between children and adults
which might be indicative of the early
characteristic and progress of the disorder.
• 24 children and 8 teenage stutters
• Recorded 10 min duration sample
• From instances of syllable repetition – those which
started with voiced plosives and where final
repetition included a part of the vowel was chosen.
Acoustic analysis of speech waveforms for –
• Formant frequency
• Excitation source information
• No marked differences between the formant
frequency between 2 groups, indicating that both
groups position the supra glottal articulators in an
equivalent positioning order to produce the
intended vowel, whether spoken fluently or
• Duration of children’s stuttered vowels are
short in comparison with those of fluent vowels of
• No difference in intensities for fluent Vs.
dysfluent vowels in children, but in teenagers,
fluent vowels were higher in intensity than the
• Marked differences between excitation
applied to VT between dysfluent and fluent
vowels between both age groups.
• They suggest a thorough appreciation of
the properties of this component of
vocalization may be important in
understanding how stuttering develops.
No significant differences:
A few authors have reported no significant
differences between stuttering group and non-
stuttering group in phoneme duration.
1)Spectrographic Study of Vowels in Stutterers'
• Richard J. Klich Gaylene M. May; Journal of
Speech and Hearing Research Vol.25 364-370
• Measurements were made of the formant
frequencies and formanttransitions associated
with the vowels/i/,/æ/ and /u/ producedby seven
moderate-to-severe stutterers when they read
fluentlyin a control (normal) condition and under
four experimentalconditions: masking noise,
delayed auditory feedback, rhythmicpacing, and
• The first and second formant frequenciesin an
isolated/hVd/context were more centralized than
thosereported for nonstutterers. The formant
frequencies were centralizedeven more in
reading, but varied little across conditions despite
changes in fluency, speaking rates, and vowel
duration. Durationand rate of formant transitions
also were essentially the sameacross conditions.
• These findings indicate that stutterers' vowel
production is more restricted,spatially and
temporally, than nonstutterers'.
2) Acoustic Measures of Stutterers' and
Nonstutterers' Fluency in Two Speech
E. Charles Healey., Peter R. Ramig; Journal of
Speech and Hearing Research Vol.29 325-331
• The purpose of this study was to compare
stutterers' and nonstutterers'fluency during
multiple productions of two dissimilar speech
contexts. Twenty-two adult stutterers were
matched within 1year of age to 22 nonstutterers.
• Spectrographic analyses wereperformed on
subjects' five consecutively fluent productionsof a
simple isolated phrase and a phrase extracted
from an oralreading passage. Measures of fluent
voice onset time (VOT),and vowel, consonant,
and total phrase durations were calculatedfrom
the five repetitions of each phrase.
From the isolated phrase, there were a total
of five fluent durational measures (i.e., one
VOT, two vowel, one consonant, & one
phrase duration). For the phrase taken from
the oral reading passage, six fluentmeasures
were obtained (i.e., one VOT, three vowel,
one consonant,& one phrase duration).
• Results demonstrated that only oneof the five
measurements taken during the isolated phrase
conditionwas significantly different between the
groups. Three of thesix measures obtained from
the phrase taken from the oral readingcondition
revealed significant between-group differences.
Nogroup differences were associated with the
repetitions of eitherphrase for any of the
dependent measures for both groups.
• Thesefindings suggest that the length and
complexity of the speechtasks used to obtain
acoustic measures of stutterers' fluencyplay an
important role in the discovery of differences
betweenthe fluency of the two groups.
Longer duration between articulatory events:
• It is the period of inactivity between two
consecutive articulatory gestures. Adams et al.
• Healy et al. (1976) reports of longer duration
between articulatory events in stutterers.
Timing Control Accuracy in Normal Speakers
and Stutterers. Margaret H. Cooper; George D.
Allen., Journal of Speech and Hearing Research
Vol.20 55-71 March 1977.
• Cooper & Allen (1977) studied speech timing
control accuracy of S and NS group during speech
and non-speech activities.
• This study attempted to assess the abilities of
10 normal speakers,five stutterers in therapy,
and five stutterers no longer intherapy, to
control the time program of repeated
• The speech sample comprised of repeated
sentences, paragraphs,and nursery rhymes.
• Temporal accuracy was measured.
Results suggest that
• (1) there is a wide range of timing abilities, even
among thenormal speakers, with considerable
overlap between the differentgroups of speakers;
• (2) on most of the experimental tasks, normal
speakers are more accurate timers than are
• (3) stutterersreleased from therapy are more
accurate timers than are stutterersstill in therapy,
whenever these groups differ.
Spatially restricted movements:
It has been reported that the stutterer’s
articulatory movements are spatially restricted with
the velocity and the direction of movement altered.
• Used high speech cineradiography to describe
kinematics and spatial and temporal organization
of the perceptually fluent speech gestures for 6
stutterers and 7 non stutterers. He analyzed
movements of lower lip and jaw in CVC /mam/,
• Results revealed that Even in perceptually fluent
utterances, the organization of events necessary
for speech production differs between groups of
stutterers and nonstutterers.
Klich & May (1982)
• Studied formant frequency and rate of formant
transitions of vowels in adult stutterers
• Results revealed temporally and spatially
restricted vowel production.
Inappropriate articulatory placements:
• Studies done by the following authors reveal
that the articulatory movements in stuttering
groups are inappropriate.
• Used high speed cineradiography to describe
kinematics and spatial and temporal organization
of the perceptually fluent speech gestures for 6
stutterers and 7 non stutterers. He analyzed
movements of lower lip and jaw in CVC /mam/,
• He found stutterers having Asymmetry
between lip and jaw movements leading to
Van Riper (1982)
• Stuttering as a temporal disruption of the
simultaneous and successive programming of
muscular movements required to produce a
speech sound or its link to the next sound in a
• Based on spectrographic and cineflourographic
analysis, he suggested that during repetitions,
highly inappropriate articulatory postures may be
used; both in voiced and unvoiced sounds.
Mohan Murthy (1988)
• Studied acoustic aerodynamic and laryngeal
correlates of stuttering.
• Spectrographic analysis indicated articulatory
fixations followed by inspiratory frication.
Excessive articulatory movements:
Shapiro (1980) did an extensive study and
measured EMG activity of Orbicularis Oris,
superior longitudinal and intrinsic laryngeal
muscles of fluent and dysfluent speech of
• Excessive muscle activity during production of
fluent as well as non-fluent utterances.
• Inappropriate bursts of activity before and during
periods of silence in both fluent and dysfluent
• Lack of muscle coordination during periods of
blocks, whose normal function is reciprocal action.
These findings strongly suggest that stutterers
while speaking, experience many movements of
disruption of normal coordination.
Depending on number of factors including its
nature, intensity, duration and timing of disruption
its effect may or may not result in audible or
In some cases, disruption occurring at the onset of
a word may simply result in
• a slight delay in word initiation or
• a pause, too brief to be identified as dysfluency
In some other cases, the only result may be a
• shift in F0
• a voicing break
• fry phonation, or
• abnormally long onset time
Static Positioning of Articulators:
Zimmerman (1980) & Pindzola (1987)
• Stutterers articulator stay in static position during
the production of a phoneme.
• Used high speed cineflurographic technique to
record articulatory movements during fluent and
dysfluent speech from 4 stutterers and control
utterances from one normal speaker.
• Interarticulator positions occurring in both
perceptually fluent and dysfluent utterances of
stutterers were unlike those in fluent utterance of a
normal speaker. Aberrant interarticulator positions
preceded repetitive movements and static
• Reported that stutterers spend longer time
in static articulatory position. In other
words, the duration of steady state formant
was found to be longer in stutterers.
Forceful articulatory patterns:
• Webster (1974) suggested that stutterers use
articulatory patterns that are too forceful and
coarticulatory movements that are too rapid.
Lower velocities of articulators:
Studies done by various authors (Adams et al.
1975), Healy et al. (1976) & Zimmerman (1980)
have revealed lower velocities of articulators in
• Zimmerman (1980) used high speed
cineradiography to describe the kinematics and
spatial and temporal organization of perceptually
fluent utterances of 6 stutterers and 17 normal
• Results: Lower peak velocities of articulators in
Correlation of stuttering severity and
kinematics of lip closure
• Michael D., McClean., Kroll., Loffus, (1991)
Stutterers and nonstutterers differ in orofacial
movements associated with perceptually fluent
speech, however inconsistent results have
been obtained in this area.
Presence of some evidence that parameters of
stutterers fluent speech are associated with
stuttering severity, encourages one to use
correlation or regression analyses as approaches
to understanding anomalies in the movement
characteristics of stutterer’s fluent speech.
• To evaluate possible relationship between
stuttering severity and parameters of lip and jaw
movement associated with lip closure in fluent
• 17 adult stutterers (17-44 years); no speech
therapy since last 3 years of the time of testing.
Severity rating: By SLPs perceptually through
285 word passage and conversation. Also, %
words stuttered, and average duration of the 3
longest dysfluencies (reading and conversation
Movement recording and analysis:
• Head mounted strain system was used to
transduce upper lip (UL), lower lip (LL) and jaw
displacement. Word “Sapapple” ws stimulus
• Parameters analyzed: velocity, duration,
• Tendency for more severe stutterers to
– Longer movement durations
– Reduced movement velocities
Because the fluent utterances were judged,
interpretation is that the more severe stutterers
achieved their fluency by executing motor
compensations similar to those acquired during
speech therapy. This may have involved
adjustments in movement duration and/ or
Reverse muscle movements:
Study done by Guitar et al. (1988) details the muscle
activity of 2 muscles depressor anguli oris (DAO)
and depressor labii inferioris (DLI).
• Examined lip muscle activity during the speech
production of stutterers and normal fluent
• Action of the above muscles were recorded using
hooked were EMG.
• Word “peck”, “puck”, “puch”
• EMG records indicated nonstutterers activated
DAO prior to DLI for the production of initial /p/,
whereas, stutterers reversed the sequence of
onset, particularly when they stuttered.
• This onset reversal in stutterers supports the view
of stuttering as a disorder of timing. As these
reversed onsets are disruptions of the succession
of DAO and DLI. The release of the sound may
be delayed until the DAO activity is predominantly
over DLI activity and hence it depicts an error that
leads to a delay in the production of the sound.
Difficulty in stabilizing the articulatory movements:
Jansen et al. (1983) Investigated the difference
between stutterers and normal speakers in
phonatory and articulatory timing during the
initiation of fluent utterances of monosyllabic
words. EMG recordings of 4 articulatory muscles
– glottal vibration recordings.
Subjects: 155 S and 17 NS
• Average interval between voice onset and onset of
• Onset of EMG activity in each articulator
• Intrasubject variability of above measures
• No significant difference between S and NS in
average interval times and that stutterers in
general were significantly more variable in their
speech onset timing.
• Stutterers may have difficulty in stabilizing the
articulatory movements and the act of speaking
results in fluctuations in the speech of production
of sounds and sound sequences.
Rate and Rhythm of voluntary articulatory
• A number of early studies investigated stutterers’
abilities to produce rapid speech or speech muscle
movements (diadochokinesis) or rhythmic speech
Spriesterabach (1940) found no statistically
significant differences between stuttering and
nonstuttering subjects in maximum rate of jaw
opening, tongue protrusion, and lip closure.
Experimental subjects were slightly superior in jaw
and tongue movements but slightly inferior in lip
Strother & Kriegman (1943) also found
stutterers’ diadochokinetic rates slightly (but
insignificantly) higher for jaw openings, repeated /i/
productions (tongue tip to alveolar ridge), and lip
closures. By contrast, Rickenberg (1956) found
that stutterers were significantly slower than
controls in repeatedly uttering consonant vowel
(CV) syllables (/pa, ba, ma, ta, da, na, ka, ga, na/).
Rhythmic execution of jaw, tongue and lip
movements was investigated by Blackburn
(1931), and Seth (1934) (except tongue
movements). These three investigations showed
significant differences favoring nonstutterers.
Studies by Wolff (1935), Strother & Kriegman
(1944), however found no significant differences
between stutterers and nonstutterers on these
tasks. Uttering repetitive /pataka/ sequences.
Zaleski (1965) found stuttering children deviated
significantly more from a prior metronomic
stimulus than nonstuttering children.
Bloodstein (1944) & Johnson (1961) reported
slower than normal reading rates in adult
stutterers, an unsurprising result considering the
fact that it takes time to stutter.
Johnson & Rosen (1937) found that instructing
stutterers to read faster than normal resulted in
more stuttering and slower than usual in less
Fransella (1965) also found that stuttering was
reduced when subjects were asked to reduce their
Ingham, Martin & Kuhl (1974) assessed the
effects on stuttering in spontaneous speech
of speaking slower and faster than normal in
three adults stutterers. By means of a series
of lights, subjects were given feedback every
minute regarding how successful they were in
either speaking more slowly or more rapidly
than baseline rates. The procedures were
effective in reducing speech rate in all three
• Zinkin (1968) studied cineflurographic films of
the pharynx taken during stuttering and reported
considerable lack of coordination between
pharyngeal and other articulatory movements.
Instances were observed in which pharyngeal
movements were relatively fixed while other
articulators moved. The converse was also
observed, that is, examples of static articulatory
gestures were observed during periods of
• A number of studies have focused upon
coarticulatory characteristics of stuttered speech
co articulation refers to the normal phenomenon
during speech hereby the production of a given
sound is influenced by other sounds which occur
before and after the sound in an utterance.
Abnormal transitional movements first described
by Stromsta (1965).
• Various studied are:….
Abnormal formant transition:
• Presence of abnormal formant transitions
has been indicated in several studies.
• Stromsta (1965) demonstrated that the
spectrogram of stuttered speech revealed a
lack of usual falling or rising transitions seen in
the spectrograms of normal speakers. The
juncture formants were either absent or
• He also added that these children whose
dysfluencies showed anomalies in co articulation
failed to outgrow their stuttering, and those
children whose spectrograms showed normal
juncture formants had become fluent in the ten
years span since the original recordings were
Adams & Reis (1971)
• Investigated the difference in the frequency of
dysfluencies of voiced and voiceless phonemes in
• Stated that increased stuttering is more likely to
occur during voiceless voiced phonation transition
than voiced voiceless transitions. They
hypothesized that if the larynx was an important
site in the break down of fluency, then conditions
requiring increased laryngeal adjustment would
create an increased frequency of stuttering.
Angdlox et al. (1974)
• Analyzed spectrograms of the stutterer’s speech
• He concluded that stuttering dysfluencies did not
show the normal downward shift of the 2nd
formant associated with normal articulatory
• Compared stutterers and non stutterers
• Stutterers use rapid coarticulatory movements.
• Montgomery & Cooke (1976)
• Analyzed perceptually and acoustically carefully
selected set of part word repetitions from the speech
of adult stutterers.
• Spectrographic analysis revealed the abnormal or
formant transitions characterized the initial segment of
the stuttered word and the remainder of the word was
identical to its fluently produced counterpart. From
this they have concluded that if the articulatory
breakdown was confined to the initial consonant and it
was likely that abnormal formant transitions from initial
consonant to vowel, when present were due to deviant
formation of consonant rather than to faulty transition
Manning & Cautal (1987)
• Investigated the dysfluencies during voiced –
voiced, voiced-voiceless, voiceless-voiceless
phoneme to phoneme phonatory transitions.
Speech of 11 adult stutterers and a matched
group of non-stutterers were studied.
• Both stutterers and non stutterers group
demonstrated a lower percentage of dysfluencies
during voiced-voiced transitions than during
voiced-voiceless, voiceless-voiced and voiceless-
voiceless phonatory transitions.
• Studied acoustic temporal parameters in the
speech of two normally nonfluent and two
• Spectrographic analysis revealed that transition
duration of F2 and speed of transition of F1
showed a significant difference between stutterers
2 Extent of formant transition Suchithra (1985)
• Studied coarticulatory effects influent utterances of
stutterers and compared it with the normal
• Results indicated that though the rising and falling
trend of the formant frequency transition was the
same in the speech of stutterers, as it is in normal
speech. The extent is different in two groups i.e.
articulatory configuration for the production of a
phoneme in question was not fully achieved
(stutterers are slowest in completing the transition)
Other errors observed were: (by Raghunath,
a) Lack of formant transition
• The spectrogram of some dysfluent
utterances were characterized by absence of
formant transition. This indicates stutterers
are unable to transit or move from one
phoneme to another.
b) Longer transition duration
• The transition duration of F2 was longer for
dysfluent utterances than the corresponding
fluent utterances. This implies that the time
lapse between the movement of articulator
from one target to another is long (explains
c) Shorter transition durations
• I.e. shorter time lapse between movement
of articulators from one target to another
No Significant difference in VOT:
• Some studies have indicated no significant
difference between stutterers and non-stutterers
for VOT value.
• Brenner et al. (1972)
• Metz et al. (1979) spectrographic analysis
• Borden et al. (1985) EGG and acoustic analysis
• Zebrowski et al. (1985) acoustically analyzed
• Revathi (1989) acoustic temporal parameters in
the speech of 2 normally fluent and 2 stuttering
children. Spectrographic analysis revealed no
significant difference between stutterers and
normally nonfluent for VOT.
Acoustic analysis of young stutterers and
non-stutterer’s disfluencies (Healey &
• To identify and describe the acoustic features
of the disfluencies of preschool age children
that represent excessive tension of laryngeal
• To compare vocal FO patterns of similar
disfluencies (i.e. phrase, whole word and part
word repetitions) between preschool age
children who were diagnosed as ‘stutterers’ by
an SLP and those who were considered
normally fluent by parents and a clinician.
• Subjects – 2 groups
• 1 group 5 male stutterers (2.8 and 4.9 years)
• 2 group 4 male children (3 – 4.9 years)
• Tested and classified as normally nonfluent
• Sample recording “free play”
• Random sample of similar fluencies were
taken for analysis – PW, whole word and phrase
• Fed into computer for acoustic analysis
• Intonational plots as well as print out of the
individual F0 values were obtained. F0 mean, SD
and range in Hz and semitones were calculated.
• Reveal that there are no significant differences
between stutterers and non stutterers F0 mean
and F0 variability for disfluent segments within a
part word, while word or phrase repetition. The
same was found for perceptually fluent
• These findings support the notion that the
speech disfluencies of young stutterers and
normally fluent children are not categorically
different, at least, in terms of the vocal
frequencies and accessibility exhibited ruing a
• Moreover, the disfluent segments within the PW,
WW and PR did into alter the phonatory features
of the perceptually fluent words adjacent to those
• There are some studies which examines the
kinematic correlates in stuttering.
Zimmerman & Hanley (1983)
• Examined the effects of fluency enhancing
procedure, the adaptation effect produced by
repeated reading of a passage in three adults who
stutter using EMMA.
• They found no evidence to support the
hypothesis that reduced amplitude and velocities
of articulatory movement were characteristics of
fluent speech of adults who stutter.
Story Alphonso and Harris in 1996
• Assessed Articulatory dynamics using EMMA in
three adults who stutter pre and post treatment
with the Holliens precision fluency-shaping
• The fluent speech of these adults post treatment
was produced with lower displacements and
velocities compared to pre-treatment measures.
Caruso, Abbs & Gracco in 1988
• Sequencing of peak velocity of upper lip lowerlip
and jaw movement was reduced in adults who
stutter compared to normally fluent speakers.
But later studies by DeNeil, 1995; McClean,
Kroll & Loftus in 1990 failed to replicate this
McClean et al. 1990
• Fluent speech of stuttering and non stuttering
adults did not differ on any of 15 movement
parameters, though stuttering adults who had
been on an intensive treatment program did show
longer duration between events.
McClean, Levandow Ski & Cord in 1994.
• Also reported the absence of systematic
relationships between kinematics parameters and
Ward employed a phase portrait analysis
• Also failed to find differences between stuttering
adults on relative timing of articulatory peak
velocity sequences and further reported that even
at faster rates, adults who stutter did not show
unusual sequencing patterns and phase angle
variability was consistently greater in the stuttering
group and that the greatest phase angle variability
was observed at fast articulatory rates and when
altered stress patterns were required.
Formant Frequency Fluctuation In Stuttering
And Nonstuttering Adults
Michael Robb, Michael Blomgren, And Yang
Inferences were made regarding the vocal tract
stability of stutterers’ and nonstutterers’ fluent
speech through the examination of formant
frequency fluctuation (FFF).
Fifteen adult males served as subjects comprising
separate groups of untreated stutterers, stutterers
enrolled in a fluency-shaping treatment program,
and nonstuttering controls.
The steady-state portion of formant 2 (F2) was
examined in the production of various CVC
tokens and evaluated by examining the absolute
Hz difference in F2 across consecutive glottal
Results of the acoustic analysis indicated a
trend in FFF across the three groups.
The untreated stutterers displayed the greatest
FFF, followed by the control group, with the
treated stutterers displaying the most F2
• Data regarding formant transitions in the
dysfluent speech of children and adults
indicate that the pattern of second formant
(F2) transitions is variable.
• The F2 transitions are sometimes absent or
atypical (Howell & Vause, 1986;Stromsta,
1986; Yaruss & Conture, 1993), and when
they are appropriate they tend to be short in
duration (Yaruss & Conture, 1993).
Abnormal F2 transitions have also been
observed in the perceptually fluent speech of
stutterers (Howell & Vause, 1986; Robb &
Blomgren, 1997, Zimmermann, 1980).
Although past studies vary with regard to
analysis methods and speech samples,they
seem to confirm that individuals who stutter
experience difficulty transitioning from one
speech sound to the next.
In accord with these findings, treatment
approaches that address smooth, deliberate
articulatory transitions have shown improvements
in speech fluency (e.g., Webster, 1975).
The authors found clear differences between
groups for cycle-to-cycle variations in both
frequency (jitter) and amplitude (shimmer).
The differences in F0 perturbation were thought to
reflect difficulty by the stutterers in maintaining a
fixed laryngeal posture during vowel steady-state
The Newman et al. (1989) findings concerning
differences between stutterers and
nonstutterers in the laryngeal behavior (i.e., F0
perturbation) of their steady-state productions
would suggest that differences may also be
apparent in the supralaryngeal (e.g., formant
frequency) behavior characterizing vowel
• The purpose of this study was to use a
relatively unknown acoustic metric, formant
frequency fluctuation (FFF), to inferentially
evaluate vocal tract stability in the steady-state
vowel productions of normally fluent and
• The measure is based on the premise that a
change in vocal tract configuration can be
measured as a temporal change in formant
• It was hypothesized that persons who stutter
would differ from normally fluent speakers in the
F2 stability of their vowel steady-state productions
as a result of disordered motor steadiness within
the vocal tract.
• To the extent that FFF serves as a measure of
vocal tract stability, the present findings indicate
that disordered articulation is also manifest in the
steady-state portion of vowels.
Using refined methods of acoustic analysis
such as FFF, it is becoming increasingly clear
that the fluent speech of stutterers is more
different than similar to that of normally fluent
Some Spectral and Acoustic Correlates of
Stuttering: A pre- post Therapy Comparison
Santosh. M., AIISH., 2006.
This study investigated the efficacy of non-
programmed prolonged speech technique in
persons with stuttering. Subject’s reading,
spontaneous speech/ conversation were recorded
before and after and 6 months after non-
programmed prolonged speech therapy.
Percentage dysfluencies, type of dysfluencies,
rate of reading and mean naturalness score, and
temporal and spectral acoustic parameters were
measured. Aerodynamic, laryngeal, and
articulatory errors were also identified and
classified as visualized on wide band
Results showed a significant decrease in
percentage dysfluencies and rate of reading and
significant increase in mean naturalness score
from pre therapy to post therapy conditions in both
Speech Production Errors:
• Different types of errors were identified and
classified as visible on wide-band spectrograms as
respiratory errors, laryngeal errors articulatory
errors and multiple errors.
• Production of aspirated for unaspirated phoneme:
• Production of unaspirated for aspirated phoneme:
• Inspiratory intake (II): represented by the noise
energy as aperiodic vertical striations in all freqs
• Expiration: it was present between words starting
with retroflex stops and nasals depicted as noise
energy spread all over frequencies
• Production of unvoiced phonemes for voiced
• Production of voiced phoneme instead of partially
• Substitution of partially voiced phoneme for voiced
phoneme or addition of partially voiced phoneme:
• Cessation of voicing: characterized by complete
cessation of voicing depicted as absence of voice
bars on the baseline of the spectrogram and
indicates an open glottal gesture.
• Prolonged voicing:
• Substitution of voiced phoneme by voiced
murmured phoneme for voiced phoneme.
• Addition errors:
• Addition of /a/ , /i/ , and Click
• included substitution errors
• observed in initial syllable of dysfluent and fluent
utterances. Includes deletion of nasal, substitution
of nasals for nonnasals and others
• Absence of F2 transition: absence of transition
depicts inability to move smoothly from one
phoneme to other.
• Cluster reduction: by addition of vowels between
• Manner + voicing error:
• Substitution of unvoiced phoneme for voiced and
absence of F2 transition:
• Manner error and absence of F2 transition:
• Substitution of unvoiced phoneme for voiced
phoneme and cluster reduction:
• Inspiratory intake + /a/ + absence of F2 transition.
Some acoustical, aerodynamic and laryngeal
correlates of stuttering: pre-post therapy
Mohan.Murthy.G, AIISH (1988)
A single case study on a 17 year old male
stutterer. Speech dynamics during pre and post
therapy utterances were studied and compared.
Totally 29 dysfluent words were analyzed.
Perceptually dysfluencies were of 5 types.
• Intra word audible pause
• Intra word silent pause
• Whole word repetition
• Intra word repetition
• Phoneme repetition and prolongation.
Wide band bar type spectrograms with average
amplitude function were taken for the audio
recordings. Segment duration and formant
transitions were measured at the apparently
• Inhalation frication of varying duration(50-260ms)
and spectral characteristics were present
• Atypical CV and VC transitions of vocal fold cycles
• Some paradoxical observations where larynx
tracing & voice bars on spectrogram did not
• Inappropriate timing of voicing.
• A clear pattern of longer or shorter post therapy
segmental durations were not evident.
• Articulatory fixation during inhalatory frication
• Abnormal articulatory constrictions for fricatives
• Investigating speech motor practice and
learning in people who stutter.
• Namasivayam AK, van Lieshout P.
• Journal of Fluency Disorders. 2008
• In this exploratory study, authors investigated
whether or not people who stutter (PWS) show
motor practice and learning changes similar to
those of people who do not stutter (PNS).
• To this end, five PWS and five PNS repeated a set
of non-words at two different rates (normal and
fast) across three test sessions (T1, T2 on the
same day and T3 on a separate day, at least 1
The results indicated that PWS and PNS may
resemble each other on a number of performance
variables (such as movement amplitude and
duration), but they differ in terms of practice and
learning on variables that relate to movement
stability and strength of coordination patterns.
These findings are interpreted in support of recent
claims about speech motor skill limitations in
Bite-block perturbation in people who stutter:
immediate compensatory and delayed
Namasivayam AK, van Lieshout P, De Nil L.
Journal of Communication Disorders. 2008
• This exploratory study investigated sensory-motor
mechanisms in five people who stutter (PWS) and
five people who do not (PNS).
• Lip kinematic and coordination data were recorded
as they produced bi-syllabic nonwords at two rates
(normal and fast) in three conditions (jaw-free,
immediately after insertion of a bite-block, and
after a 10-min accommodation period).
At normal speech rates, effects of bite-blocks
on lip kinematics were similar for both PWS and
PNS speakers showing larger amplitudes, peak
velocities, shorter durations and more stable
movement cycle patterns. However, at fast
speech rates upper lip responses of PWS
exhibited larger amplitudes and peak velocities.
was found at normal speech rates.
At both speech rates, the presence of a bite-block
changed movement coordination patterns only for
However, at fast speech rates bite-blocks
decreased variability of coordination patterns for
No adaptive changes in movement stability were
found for either group, but a practice-related
increase in lower lip peak velocity
• These findings indicate that bite-block
perturbation did not exacerbate any
hypothesized limitation or difficulty in
controlling individual articulatory movements or
their coordination in PWS.
• The results also support the position that
specific motor control strategies are used by
PWS as compared to PNS to compensate for
bite-block perturbations under increased
speech rate demands.
Speech production in people who stutter: testing
the motor plan assembly hypothesis.
• van Lieshout PH, Hulstijn W, Peters HF.
• Journal of Speech and Hearing Research. 1996
The main purpose of the present study was to test
the hypothesis that persons who stutter, when
compared to persons who do not stutter, are less
able to assemble abstract motor plans for short
Subjects were adult males who stutter and
age- and sex-matched control speakers, who
were tested on naming pictures and words,
using a choice-reaction time paradigm for both
tasks. Words varied in the number of syllables
(1, 2, and 3 syllables) and, for the bisyllabic
words, also in the number of consonants (one
or more) at the onset of the second syllable.
Measurements consisted of speech reaction
times, word durations, and measures of relative
timing of specific motor events in the respiratory,
phonatory, and articulatory subsystems.
Results indicated that, in spite of longer
speech reaction times for persons who stutter
in comparison to control speakers, there was
no interaction with word size, a finding that
does not lend support to the abovementioned
hypothesis. Word durations were found to be
longer for persons who stutter, and, in
addition, there was an interaction of group
with word size. Both findings were associated
with longer delays for persons who stutter in
the onset of upper lip integrated
electromyographic (IEMG) activity and
thoracic compression, and a group effect on
the order of upper lip and lower lip IEMG
• Findings are taken to suggest the possibility
that persons who stutter may use different
motor control strategies to compensate for a
reduced verbal motor skill, and although the
nature of this reduced skill is unknown, it is
speculated that it relates to the processes
involved in the integration of sensory-motor
Gestural overlap in consonant clusters:
effects on the fluent speech of stuttering
and non-stuttering subjects.
• Huinck WJ, van Lieshout PH, Peters HF,
• Journal of Fluency Disorders. 2004
This study was designed to investigate if
persons who stutter differ from persons who do
not stutter in the coproduction of different types
of consonant clusters, as measured in the
number of dysfluencies and incorrect speech
productions, in speech reaction times and in
Based on the Gestural Phonology Model of
Browman and Goldstein, two types of
consonant clusters were formed: homorganic
and heterorganic clusters, both intra-syllabic
(CVCC) and inter-syllabic (CVC#CVC).
Overall, the results indicated that homorganic
clusters elicited more incorrect speech
productions and longer reaction times than the
heterorganic clusters, but there was no
difference between the homorganic and the
heterorganic clusters in the word duration
Persons who stutter showed a higher percentage
dysfluencies and a higher percentage incorrect
speech production than PWNS but there were no
main group effects in reaction times and word
However, there was a significant three-way
interaction effect between group, cluster type and
cluster place: homorganic clusters elicited longer
reaction times than heterorganic clusters, but only
in the inter-syllabic condition and only for persons
• results suggest that the production of two
consonants with the same place of articulation
across a syllable boundary puts higher demands
on motor planning and/or initiation than producing
the same cluster at the end of a syllable, in
particular for PWS.
Adaptation of stuttering frequency during
repeated readings: associated changes in
acoustic parameters of perceptually fluent
• Max L, Caruso AJ.
• Journal of Speech Language and Hearing
This study is part of a series investigating the
hypothesis that stuttering adaptation is a result of
motor learning. Previous investigations indicate
that nonspeech motor learning typically is
associated with an increase in speed of
performance. Previous investigations of
stuttering, on the other hand, indicate that
improvements in fluency during most fluency-
enhancing conditions or after stuttering treatment
tend to be associated with decreased speech
rate, increased duration of specific acoustic
segments, and decreased vowel duration
The present acoustic findings, obtained from 8
individuals who stutter, reveal that speech
adjustments occurring during adaptation differ
from those reported for other fluency-enhancing
conditions or stuttering treatment. Instead, the
observed changes are consistent with those
occurring during skill improvements for nonspeech
motor tasks and, thus, with a motor learning
hypothesis of stuttering adaptation.
• During the last of 6 repeated readings, a
statistically significant increase in articulation rate
was observed, together with a decrease in word
duration, vowel duration, and consonant-vowel
(CV) transition extent.
• Other adjustments showing relatively consistent
trends across individual subjects included
decreased CV transition rate and duration, and
increased variability of both CV transition extent
and vowel duration.
Speech motor correlates of treatment-related
changes in stuttering severity and speech
• Tasko SM, McClean MD, Runyan CM.
• Journal of Communication Disorders. 2007
Participants of stuttering treatment programs
provide an opportunity to evaluate persons who
stutter as they demonstrate varying levels of
fluency. Identifying physiologic correlates of
altered fluency levels may lead to insights about
mechanisms of speech disfluency.
This study examined respiratory, orofacial
kinematic and acoustic measures in 35 persons
who stutter prior to and as they were completing a
1-month intensive stuttering treatment program
Participants showed a marked reduction in
stuttering severity as they completed the treatment
program. Coincident with reduced stuttering
severity, participants increased the amplitude and
duration of speech breaths, reduced the rate of
lung volume change during inspiration, reduced
the amplitude and speed of lip movements early in
the test utterance, increased lip and jaw
movement durations, and reduced syllable rate. A
multiple regression model that included two
respiratory measures and one orofacial kinematic
measure accounted for 62% of the variance in
changes in stuttering severity.
Finally, there was a weak but significant tendency
for speech of participants with the largest
reductions in stuttering severity to be rated as
more unnatural as they completed the treatment
Influences of length and syntactic complexity on
the speech motor stability of the fluent speech
of adults who stutter.
• Kleinow J, Smith A.
• Journal of Speech Language and Hearing
The purpose of the present study was to
investigate the impact of utterance length and
syntactic complexity on the speech motor stability
of adults who stutter.
Lower lip movement was recorded from 8 adults
who stutter and 8 normally fluent controls.
They produced a target phrase in isolation
(baseline condition) and the same phrase
embedded in utterances of increased length
and/or increased syntactic complexity.
The spatiotemporal index (STI) was used to
quantify the stability of lower lip movements
across multiple repetitions of the target phrase.
Results indicated: (a) Adults who stutter
demonstrated higher overall STI values than
normally fluent adults across all experimental
conditions, indicating decreased speech motor
(b) the speech motor stability of normally fluent
adults was not affected by increasing syntactic
complexity, but the speech motor stability of adults
who stutter decreased when the stimuli were more
(c) increasing the length of the target utterance
(without increasing syntactic complexity) did not
affect the speech motor stability of either speaker
• These results indicate that language formulation
processes may affect speech production
processes and that the speech motor systems of
adults who stutter may be especially susceptible to
the linguistic demands required to produce a more
• The present findings, therefore, support the
hypothesis that linguistic complexity is one factor
that contributes to the disruptions of speech motor
stability characteristic of stuttering.
From planning to articulation in speech
production: what differentiates a person who
stutters from a person who does not stutter?
• van Lieshout PH, Hulstijn W, Peters HF.
• Journal of Speech and Hearing Research. 1996
The main purpose of the study was to differentiate
between people who stutter and control speakers
regarding their ability to assemble motor plans and
to prepare (and execute) muscle commands.
Adult males, who stutter, matched for age, gender,
and educational level with a group of control
speakers, were tested on naming words and
symbols. Group differences in muscle command
preparation were assessed from
electromyographic recordings of upper lip and
Results indicated that they were significantly
different in the timing of peak amplitudes in the
integrated electromyographic signals of upper lip
and lower lip (IEMG peak latency).
• Findings question the claim that people who
stutter have problems in creating abstract motor
plans for speech. In addition, it is argued that the
group differences in IEMG peak latency that were
found in the present study might be better
understood in terms of motor control strategies
than in terms of motor control deficits.
Jaw-phonatory coordination in chronic
• Loucks TM, De Nil LF, Sasisekaran J
• Journal of Communication Disorders. 2007
A deficiency in sensorimotor integration in a
person who stutters may be a factor in the
pathophysiology of developmental stuttering. To
test oral sensorimotor function in adults who
stutter, authors used a task that requires the
coordination of a jaw-opening movement with
phonation onset. The task was adapted from
previous limb coordination studies, which show
that movement coordination depends on intact
proprioception. They hypothesized that adult
stutterers would show deficient jaw-phonatory
coordination relative to control participants.
The task required initiation of phonation as a jaw-
opening movement passed through a narrow
spatial target. Target amplitude and jaw movement
speed were varied.
The stuttering group showed significantly higher
movement error and spatial variability in jaw-
phonatory coordination compared to the control
group, but group differences in movement velocity
or duration were not found.
The aberrant jaw-phonatory coordination of the
stuttering participants suggests that stuttering is
associated with an oral proprioceptive limitation,
although, the findings are also consistent with a
motor control deficit.
Variations in the relative speeds of orofacial
structures with stuttering severity.
• McClean MD, Runyan CM
• J Speech Lang Hear Res. 2000
Stuttering can be characterized in part as a
disorder in the coordination of different muscle
systems. In light of basic aspects of orofacial
physiology and development, the speeds of the
lips and tongue relative to the jaw may be an
important dimension for evaluating motor
coordination among persons who stutter (PWS).
To test this idea, an electromagnetic system
was used to obtain measures of lip, tongue, and
jaw speed in 38 adults (29 PWS and 9 normally
fluent speakers, NFS) as they repeated a simple
speech utterance at a normal rate.
Using categorical ratings of stuttering severity,
ratios of tongue speed to jaw speed were
significantly greater in PWS rated as severe,
compared to NFS and other PWS.
Significant increases in lower lip-to-jaw and
tongue-to-jaw speed ratios with stuttering
severity were also reflected in correlation
analyses relating speed ratios to a continuous
measure of stuttering severity.
These trends in speed ratio were related to
increases in lower lip and tongue speed and
decreases in jaw speed with stuttering severity.