stuttering and auditory functions..pdf/ kunnampallil gejo
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Stuttering and auditory
functions.
KUNNAMPALLIL GEJOJOHN,MASLP
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Content :
(1) Introduction.
(2) Auditory processing.
(3) Dichotic listening.
(4) Phase disparity.
(5) Acoustic reflex.
(6) Theoretical explanation of the auditory
effects.
(7) Types, tools, applications & effect of
auditory feedback.
(8) Tests results of auditory processing in
stuttering.
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INTRODUCTION :
Perkins, 1990
Stuttering is the involuntary disruption of a
continuing attempt to produce a spoken utterance.
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Auditory processing :
Term used to describe the recognition & interpretation of a
sound by the brain.
Ear acoustic to electrical interpreted by brain.
Learning to speak involves motor process.
sensory process.
Self hearing helps to -- monitor ones own speech.KUNNAMPALLIL GEJO
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Aspects
ofauditory functions
Relative phase
angle of air &
bone conductedsounds
Threshold for
pure tones
Effect of aud
fn on oral
activity notinvolving sp.
Central aud fng
at level of
brainstem.
Dichotic
listening.
Reflex
response of
ME msls to
sd.
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Auditory processing in stutters :
Stuttering may be the result of errors of stutterers self hearing
aspect.
In exploring this hypothesis , researchers have measured how
stutterers CNS process different sounds including speech.
The resulting hypothesis was that stuttering may have its origin
because of malfunctioning of the hearing mechanism in its role as
rural monitor.
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Findings of all aspects of physiological functioning in
stutterers :
(1) central auditory function in stutterers
Hall and Jerger assessed auditory function in 10 stutterers and 10
non-stutterers.
Performance for the 2 groups was compared for 7 audiometric
procedures including -- auditory reflex threshold, acoustic reflex
amplitude function, performance intensity, function for
monosyllabic phonetically balanced (PB word) performance
intensity for SSI, SSI-ICM, SSI-CCM and SSW.
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Acoustic reflex amplitude function, synthetic identification with
ICM and SSW test
As a group stutterers presented evidence of a central auditory
deficiency.
The pattern of the test result suggested in brainstem level.
The subjectivity of the deficiency is emphasized.
In 1959, Rousey, Goetzinger and Dirks observed that stutteringchildren perform less well than non stutterers in localizing sounds
in space.
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(2) Central processing in stuttering :
Hemispheric properties of stuttering --
Brain waves of stutterers have been examined & compared those
with non stutterers.
Manifestations of cortical dominance were studied .CNS
investigation suggested that stutters lack cerebral dominance for
speech.
Lindshy &Freestone (1942) suggested that stutters demonstrateright hemisphere dominance for language.
Wilkins EEG studies shown that final neural dysfunction rather
than hemispheric differences in stutterers.KUNNAMPALLIL GEJOJOHN,MASLP
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Right hemisphere activity --
Difficulty in
- Central auditory processing,
- Language development,
- Speech motor reaction time &
- Delay in tracing auditory stimuli
(may all be related to organization of speech, language & auditory
functions in brain).
People with stuttering may be using less effective part of brain for
processing speech functions.
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Fox (1996,2000) - decreased activity in auditory area during
increased stuttering ,so reduces the left brain communication of this
sensory information to frontal speech & language areas.
The abnormal right brain activity may be alternative pathology for
brain sensory information to travel to the front of the brain .
People who stutter use Right hemisphere which leads to
intermittent break down ,because Right hemisphere is not as adopt
as the left for processing rapid transmission that characterizesspoken language.
Right hemisphere is also associated with emotional expression.
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This suggestion has implication for the onset of stuttering in
childhood when many functions appear to have bilateral
representations.
Fluency may be vulnerable to emotional disturbances & caused by
excessive amounts of neurotransmitter dopamine in the left caudate
nucleus. (This is the area that translates speech into muscle
movements).
There is no conscious awareness of central auditory processing in
left caudate nucleus (This explains why stuttering that relay in
consciously controlling speech best only temporarily).
Inability to integrate what stutterers hear with the muscle
movements that he feels.
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Left auditory cortex activity in stuttering
Many brain imaging studies of stuttering have shown a lack
of activity in the left superior temporal lobe, including auditoryassociation areas & Wernickes area (FOX et al ,2000&DE NIL
et al,2003).
These findings suggest the possibility that when individual
stutter they are not using auditory feedback to monitor & control
their speech.
Another imaging study (SALMELIN et al ,1998) found that
stutters have a reversal of the normal pattern of activation ofthe left & right auditory cortices during stuttering .
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Stutters may have difficulty performing auditory processing tasks
(BARASCH et al ,2000) and that fluency can be induced by
changing the way stutters hear their own speech (BRAYTON &CONTURE ,1978;POWELL ,1987).
Auditory self monitoring may provide a stimulus to time or
integrate the sequence of activities that run in parallel when a
speaker decides what she will say, selects the linguistic elements for
it, and executes the utterance.
Thus the dyssynchrony or timing disturbance are the basis of
stuttering (Perkins,Kent,&Curlee,1991;Van Riper 1982) may becaused by a paucity of signals that synchronize the sequence for
speech output.
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Therapies that focus on the use of slow speech, gentle onset, and
light articulatory contacts may develop the clients auditory as well
as proprioceptive monitoring of speech.
Craver & Faber1982, Moore1986 found that stutterers have poor
recognition & recall of words on auditory presentations.
Carpenter & Sommers1987 found stutterers & nonstutterers have
equal auditory memory.
Dichotic listening :
In the dichotic listening paradigm, different sound are presented
simultaneously to the two ears.
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The listener must report everything he hears from both ears.
Since the sounds are simultaneous it is presumed that the listenermust alternate attention between the two ears, placing one percept
in short term memory while attending to the other and vise versa.
When normal adults are tested in the dichotic paradigm, there is a
slight advantage for certain sounds delivered to the right ear and for
other sounds delivers to the left ears.
Kimura was the first to demonstrate that verbal signals such as
words and digits are more accurately reported from the right ear (ie,left hemisphere) than from the left ear (ie, right hemisphere).
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After simultaneous dichotic presentation (Kimura, 1961,1967) the
reverse is true for melodies (Kimura 1967).
If stutterers are, indeed, lacking in suitable hemispheric dominance
for language, this fact should be readily revealed by a dichotic test.
Variables in dichotic testing. :
(1) It is important, for example, to ascertain the handedness of the
subjects being tested stating that subjects are right or left handed is
not as meaningful from laterality standpoint as the administration
of a detailed handedness questionnaire (Oldfield, 1971).
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(2) Another variable is the order in which subjects are instructed to
report sounds (ie, right ear first, left ear first, or either ear first).
Most investigators who have controlled this variable have notedthat there is a greater index of cerebral laterality when subjects
are instructed to report first from left ear and then from the right
ear.
(3) Another variables is the stability of the dichotic ear advantage
over time. Blumstein, Good glass and Tarter (1975), employing a
test retest experiment, contend that 85% of normal right handed
males have a right ear advantage in dichotic listening and that
any such test sample contains 15% misclassified subjects.
They observed that as many as 30% change ear dominance
when retested. Thus consistency between test and retest is an
important dimension in studies of cerebral laterality.
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Dichotic listening paradigms test a response to a sound input. The
test evaluates cerebral laterality in a steady state, it does not
evaluate laterality in the dynamic state of speech production.
This may be very important in the investigation of stuttering.
Suppose, for example that stutterers have a disturbance in cerebral
laterality that causes a compromise in their speech output.
This abnormality may not be static, that is, it may only appear
during speech or perhaps only at certain times during speech
production.
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Dichotic listening in stutterers :
Curry and Geogory (1969) used a dichotic listening paradigm with20 adult stutterers (19 males, 1 female) and 20 appropriate controls.
All were stated to be right handed.
The author employed several dichotic tasks, one of which was the
dichotic word test.
The test involves the recognition of pairs of consonant vowel
consonant (CVC) words of high familiarity presented in groups of 6
pairs with 0.5 sec separating each pair.
After each group of 6 word pairs had been presented, the subjects
attempted to recall the 12 different words, in any order and without
concern for which words had been presented to any particular ear.KUNNAMPALLIL GEJOJOHN,MASLP
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The anticipated right ear superiority was significantly less for
stutterers than for non stutterers.
75% of the non stutterers had right ear scores that were higher than
their left, this was true for only 45% of the stutterers.
Dorman and Porter (1975) evaluated 16 right handed adultstuttereres (12 males, 4 females) and compared them to 20 controls
(10 males, 10 females) subjects had to write down responses to
synthetically generated consonant vowel dichotic stimuli.
There was no significant difference between stutterers and non
stutterers.
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Pinsky and Mc Adam (1980) tested 5 adult stutterers and 5 fluent
speakers in a dichotic listening paradigm. All individuals were right
handed except one who was stated to be weakly right handed. Theauthors failed to find a significant difference between the stutterers
and non stutterers.
Rosenfield and Goodglass (1980) queried whether the above study
had failed to take into account a number of variables that might
affect the results. Children stutterers, for example, might be
different from adult stutterers.
In an effort to control all relevant variables. Rosenfield andGoodglass (1980) evaluated a group of adult male, strongly right
handed, stuttereres.
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They evaluated left cerebral dominance for language using
consonant vowel stimuli and tested right hemisphere laterality for
melodies by testing melody input.
Right ear advantages were obtained for consonant vowel stimuli
and left ear advantages were noted for melodies output significant
disturbance between the groups of stutterers and controls.
However, there were significantly greater number of stutterers than
controls who consistently failed to show the expected ear laterality
for either type of material.
As pointed out by Moore (1976) stutterers seem to differ fromnonstutterers when investigators employ meaningful verbal stimuli.
Of the dichotic studies that employs words or digits, rather than
meaningless consonant vowel or other stimuli, most find difference
between stutterers and non stutterers.KUNNAMPALLIL GEJOJOHN,MASLP
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Sussman and Mac Neilage (1975) employed a dichotic paradigm
and other paradigm, that of pursuit auditory traking.
They reasoned that dichotic listening tested elements of laterality
pertaining to speech perception, where as the tracking paradigm
test speech production.
Their experiment involved matching the frequency of the variable
tone in one ear to the to the frequency of the externally varied tone
in the other ear.
The former tone was altered by a transducer attached to the tongue
or jaw. KUNNAMPALLIL GEJOJOHN,MASLP
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The subject varied the frequency of this tone by approximately
moving tone or the jaw, subjects were required to match the
frequency of this transducer related tone to the frequency of theexternally varied tone.
The authors tested the right handed male and female stutterers andnonstutterers for laterality pertaining to speech perception (dichotic
listening) and speech production (tracking paradigm).
They noted a right ear advantage for both nonstutterers andstutterers on the dichotic studies, stutterers did not differ from
nonstutterers in laterality on the speech perception task.
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On the tracking paradigm, however normals had right ear advantage
whereas stutterers did not (i.e. nonstutterers best altered the
transducers tone when they heard it in the right ear and had to matchit against the externally varied tone in the left as opposed to having
a transducer tone in the left and the extremely varied tone in the
right).
This indicated left hemisphere dominance for nonverbal output.
Stutterers failed to demonstrate such laterality for non verbal output.
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Phase disparity :
In order to study intrinsic abnormality in the stutterers auditorymonitoring system, phase disparity between air and bone conducted
tones was studied.
In 1957, stromosta exploited the fact that two pure tones. 180degree out of phase but equal infrequency and amplitude, will
cancel each other out.
Stutterers and normal speakers listened to an air conducted tone
introduced to the ear and to a bone conducted tone of the samefrequency simultaneously introduced at the teeth.
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Subjects were asked to vary the phase and amplitude of air
conducted tone until a critical adjusted was achieved at which no
sound was audible to them.
There was a significant difference between stutterers and
nonstutterers in the relative phase angle of the air and bone
conducted sounds at 2000 Hz.
Using a similar method, Stromsta (1972) noted an unusual phase
disparity between stutterers left and right ears.
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The acoustic reflex :
One component of the total auditory monitoring system, theacoustic reflex has come under particular scrutiny because of its
intimate relation to vocalization.
The stapedius muscle contracts during vocalization, Brog andZakrisson (1975) visually and electromyographically evaluated
stapedius muscle activity that accompanied vocalization in fluent
speaker who had a perforated tympanic membrane.
EMG activity in the stapedius muscle accompanied speech, even atlow levels of phonation.
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Stapedius EMG activity occurred before the onset of vocalization
in 55% of their cases and after vocalization in 45 % (Borg and
Zakrisson, 1975) in the former instance the time difference betweenreflex onset and phonation onset was less than 75 msec.
The authors concluded that EMG activity in the spapedius muscleis not caused by feedback of the voice signal but, rather is centrally
mediated as a component of the vocalization process.
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Shearer and Simmons (1965) investigated stapedius muscle activity
in stutterers and non stutterers in ongoing speech.
They observed that stapedius muscle activity tended to parallel
vocalization in non stutterers.
In stutterers, however, parallelism was less consistent.
At time, the onset of stapedius activity seemed to be delayed
relative to the onset to the vocalization.
Hall and Jerger (1978) compared the acoustic reflex to external
sound in stutterers and controls. Reflex threshold was equivalent in
the two groups but reflex amplitude was smaller in the stuttering
group. KUNNAMPALLIL GEJOJOHN,MASLP
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Theoretical explanation of the auditory effects :
Feedback control theory has provided the main framework forexplaining the relation between stuttering and the processing of
auditory feedback.
Under feedback control theory,
(1)Feedback from sensory system plays a direct role in controlling
ongoing speech action.
(2)Delaying feedback results in speech control errors such asstuttering.
(3)Feedback control theory has never achieved a detailed
explanation of instances of stuttering (Garber and Seigel, 1982).KUNNAMPALLIL GEJOJOHN,MASLP
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Evidence supported by theory :
(1) Errors under DAF decrease with slower rates of speech sinceslower rates enable temporal summation to augment top down
priming of nodes for an intended output.
(2) Some subjects speak slower/ louder at the most disruptivefeedback delay despite instructions to speak always at maximum
rate. By speaking slower/ louder they can overcome the effects
of the returning feedback and gain better control over the output.
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Auditory feedback :
As we talk, the information is feedback to the brain by the way ofnumerous circuits.
These are called closed circuits or cycles ,which have all
components completely contained within speakers mechanism .
They provide the information to the speakers about what he said &
how he said it by the way of auditory, tactile & kinesthetic modes.
The return flow of information provided by these circuits helps tomonitor our own speech.
Errors are normally identified & corrected automatically .This
process is important for all learning behavioursKUNNAMPALLIL GEJOJOHN,MASLP
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Closed loop system
System organizes in closely connected special & temporal units.
There will not be any time normal course for the speaker topause & check the adequacy of the utterance after each word,
phrase or even after sentence uttered.
Hence, speech once learned become self regulatory withsatisfactory monitoring depends up on the proper functioning &
integration of the of the all feedback circuits .
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Types of auditory feedback :
(1) Altered Auditory Feedback --
Changing how stutterers hear their voices improves fluency. This
can be done in many ways:
Speaking in chorus with another person.
Hearing voice in headphones distorted.
Hearing a synthesized sound in headphones mimicking
phonation (masking auditory feedback, or MAF).
Hearing voice in headphones delayed a fraction of a second(delayed auditory feedback, or DAF).
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These phenomena are called altered auditory feedback.
No brain scans have looked at stutterers' auditory processing while
speaking with altered auditory feedback.
Hypothetically, introducing errors targeted at the area that integrates
auditory and somatic processing increases blood flow to that area,
increasing activity level to normal.
Nonstutterers can't tolerate altered auditory feedback.
Altered auditory feedback increases blood flow to non-stutterers'
auditory/somatic integration area, raising activity to an abnormally
high level.
Too much activity is as bad as not enough activity.
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Interestingly, the effects of too much activity in this area are
somewhat like stutteringrepeating words and unexpected silent
pauses.
Stuttering is reduced in many subjects by delayed, masked,
frequency altered feedback.
Even amplified feedback may have some of the same power.
The proportion of stuttering events prescribed telephone
conversations were significantly reduced in the AAF conditions
relative to the non-altered auditory feedback condition.
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(2) Delayed auditory feedback --
It refers to a delay in the return of the air conducted speech signalto the central auditory system.
As an electronic or mechanical phenomenon ,it was reported by
LEE(1950)who coined the term artificial stutter and commend onits fluency disruption effects.
The most disruptive interval was found to be in the 180-200 msec
(Fairbanks & Guttman 1958:Ham &Steer1967).
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The basic observation with which we are concerned is that when
normal speakers air conducted auditory feedback is retarded by a
time interval of the order of 0.2secs. amplified sufficiently tocomplete with their normal bone conducted feedback ,there tends
to be a disintegrative effect on their verbal output .
Delayed auditory feedback (DAF) apparently degrades the
individuals ability to self-monitor his or her ongoing speech.
In the normal speaker, the introduction of DAF via headphonesbreaks down the speakers fluency, often producing prolongation
of vowels and slurring of articulation.
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Under conditions of DAF, most normal speakers will show a
marked interruption of normal prosodic speaking patterns.
Conversely, in the stutterer, speech may become more fluent under
DAF, probably related to the prolongation of vowels which results
in a general slowing down of speaking rate.
Slowing down the stutterers rate of speech is often facilitative for
improving overall speech fluency.
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Procedures for DAF :
1. The selector mode on the Facilitator is set to DAF (the lettersDAF appear on the instrument window). The loudness level of
amplification-DAF is determined by the relative setting of the
VOLUME switch.
2. The relative time-delay on the Facilitator ranges from .05 to 0.5
secs, with the clinician able to control the delay-time by
increments of approximately 10 msecs (timing changes in msecs
are achieved by adjusting the delay time to the value appearing in
the instrument window).
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3. Explain to the patient something like this, "I want you to wear
these headphones as you read (or repeat) aloud. What you say will
be fed back to you on the phones a bit delayed. You wont be ableto hear yourself as you usually do when you speak. Just keep
speaking. I will record on another recorder how you sound.
4. After the initial testing on the effects of DAF on speech and
voice, play the recorded output back to the patient. Depending on
the effects of DAF, either go forward with more DAF practice or
stop using it.
5. For those patients who profit from using DAF, it isrecommended that the patient wear a portable Facilitator in the
provided waist-pack. The DAF mode should be used whenever it
appears to facilitate better speech or better oral reading.
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Tools used in auditory feedback --
Metronomic Pacing.
Delayed Auditory Feedback (DAF).
Looping.
Time-Warping.
Masking.
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(1) Pacer
The pacer provides metronomic pacing in the form of an
audible click to help assist patients with the timing/rhythm aspectsof speech production.
Among these are stutterers and patients with motor speech
disorders such as cerebellar ataxia and Parkinsons disease.
The pacer rate is adjustable from 50 to 150 beats per minute
adjustable in 5 beat increments.
(2)Delayed Auditory Feedback
The AFT program provides DAF, as a form of disruptivefeedback, which has proven to be effective in fluency therapy.
The DAF in AFT has a range of feedback from 150-500
milliseconds, adjustable in 10-millisecond increments.KUNNAMPALLIL GEJO
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(3)Looping Playback
Looping records the patients (or clinicians) speech and then playsthe digitally recorded speech back immediately.
This is used to develop critical self-listening skills.
Patients can hear their own speech just as an outside listener would
hear it.
The clinician or the patient can record the target production.
The absence of a visual display helps the patient focus strictly on
the auditory aspects of speech.
The duration of the recorded speech is from 5 to 30 seconds,
adjustable in one-second incrementsKUNNAMPALLIL GEJOJOHN,MASLP
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(4)Time-Warping
Time-warping provides the ability to record a patients speech
and immediately play the speech back at different rates withoutchanging the frequency content of the speech. This is very useful
for allowing patients to hear their articulation clearly by slowing, or
increasing, the rate of playback.
(5)Masking
In masking mode, a speech-band noise signal is played
through headphones so that patients cannot hear their own speech
production. This deliberately degraded feedback has been shown,
in some cases, to improve speech. In many patients, it can enhancethe proprioception of speech/voice behaviors (e.g., easy onset,
eliminating hard glottal attack, etc.).
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Applications of DAF :
The AFT program has a wide range of applications in speech-
language pathology including voice, articulation, motor speech
disorders, fluency, aphasia, professional voice, accent reduction,
and learning disabilities.
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(1) Planum Temporale Abnormality and DAF --
The planum temporale (PT) is an anatomical feature in the auditorytemporal brain region.
Typically people have a larger PT on the left side of their brains,
and smaller PT on the right side (leftward asymmetry).
A brain scan study found that stutterers have the opposite: their right
PT is larger than their left PT (rightward asymmetry).
A second study found that stutterers with this abnormal rightwardasymmetry had significantly improved fluency with DAF, but
stutterers with the normal leftward asymmetry didn't improve with
DAF.
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The study also found that stutterers with this abnormal rightward
asymmetry stuttered more severely than stutterers with the normal
leftward asymmetry.
In adults with persistent developmental stuttering and atypical PT
anatomy, fluency is improved with DAF.(Neurology 2004 Nov
9;63(9):1640-6.)
(2) Delayed Auditory Feedback Most Helpful for Those Who
Stutter with Atypical Auditory Anatomy --
(American Academy of Neurology-)
Researchers in New Orleans have identified a subset of stutterers
that may benefit most from delayed auditory feedback (a technique
by which the original acoustic speech signal is artificially modified
and then fed back via headphones).KUNNAMPALLIL GEJO
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Findings of their study were Delayed auditory feedback (DAF) has
been shown to induce fluency in many individuals who stutter,
though not all stutterers experience enhanced fluency by thistechnique.
The primary aim of this study was to learn if there is a relationship
between the anatomy of the auditory association cortex (planum
temporale) and fluency induced with DAF in adults with persistent
developmental stuttering.
The planum temporale is a brain structure important in processing
auditory information.
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A study group of 14 adults with this type of stuttering disorder and
14 control subjects read prose passages three times: at baseline, with
non-altered feedback, and with DAF.
Three measures of fluency were evaluated: stuttering event
frequency, severity, and reading time.
" a subgroup of adults with atypical rightward planum temporale
asymmetry, who were more disfluent at baseline and had fluency
induced with DAF," (Anne Foundas, MD,)
"However, deficits in auditory processing cannot account forstuttering in all people who stutter, because we identified another
subgroup of adults who had typical leftward planum temporale
asymmetry and who did not become more fluent with DAF."KUNNAMPALLIL GEJO
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Effect of auditory feedback on Non speech Oral activity :
Both stutterers and nonstutterers the delayed feedback conditionsproduced disturbances in the pattern such as errors ,prolonged lip
closures , and prolongation of the pattern.
However the effect of DAF was about the same for both group of
subjects.
It was only under DAF that any difference appearedstutterers
tend to have longer lip closures.
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Effect of DAF in normal speakers :
It is possible by means of magnetic tape recording &recording
device suitably designed to return a subjects vocal output via
earphones with a brief delay in transmission.
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Two explanations are given about the effects of DAF in normal
subjects :
(1) Normal speakers air conducted auditory feedback is by the
interval of the order 0.2sec& amplified sufficiently to complete
with their bone conduction feedback ,there tends to be a
disintegrative effect on their verbal output.
This disintegration takes the form of a slow speaking rate,
articulatory inaccuracy ,disturbances of fluency including blocks
&repetitions of the syllables like in stutters.
In addition there is an increase in loudness & pitch ,which
Fairbanks inferred to result from the subjects struggle to resist
the interference with their responseKUNNAMPALLIL GEJO
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(2) Following activation ,the nodes responsible for speech are self
inhibited & & then undergo a normal cycle of recovery .
This recovery cycle includes a period of hyper excitability during
which nodes have greater than normal sensitivity, with a peak
occurring approximately 200msec following onset of activation &
return to a resting level by 300msec following onset of activation.
This explains why the delay of 0.2 sec produces maximum
disruption of speech .
When feedback arrives 0.2sec after onset of activations ,it providesadditional priming of just activated nodes ,that produced it at
precise times
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When three sources of additional priming (amplification, hyper
excitability & normal bottom up priming) combine to exceed the top
down priming of appropriate nodes, these just activated nodes willbe reactivated under most primed principle, with an effect
resembling the repetition errors of stutterers.
Errors under DAF decrease with slower speech rates ,since lower
speech rates enables temporal summation to augment top downpriming of nodes for an intented output.
This may explain why some subjects speak slower at the most
disruptive feedback delay (0.2sec )despite instruction to speak
always at a maximum rate.
By speaking slower they can overcome the effects of returning
auditory feedback &gain better control over the output.
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Effect of DAF on stutterers :
Under the theory stuttering occurs whenever the just activatednodes receive greater priming than nodes to be activated next.
There are 2 hypothesis to account for this theory.
One hypothesis is that returning feedback is delayed by about 0.2
sec with in the sensory analysis nodes of stutterers & aquires
greater than normal amplitude due to mal functioning of the
stapedial reflex.
As a result the normal auditory feedback of these stutterers will
achieve the conditions, which disrupt the speech of normal
speakers receiving delayed & amplified auditory feedback .KUNNAMPALLIL GEJO
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Like wise shadowing & choral rehearsal prevents stuttering by
augmenting the priming of the appropriate or next to be activated
nodes.
The other hypothesis is that nodes of stutterers, evidence an
abnormal recovery cycle .
Both hypotheses predict that masking & returning auditory
feedback will reduce the probability of stuttering &lifying it
will have the opposite effect.
Both hypotheses predict release from auditory input guidesspeech production.
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Thus stuttering is overcome when others utter the words when
stutter is blocking since the input helps prime the appropriate
nodes to the level required for activation .
Finally both hypotheses predict that delay producing maximal
interference with speech will be shorter stutters than non stutterers
Brandt & Wilde (1977)found that like stuttering, the dysfluencies of
normal speakers under DAF was reduced when the subject read in
unison with another voice & they timed their speech to the beat of
a metronome.
Borden et al (1977) observed both similarities &differences
between normal speakers under DAF &stutterers in
electromyographic recordings from laryngeal & articulatory
muscles .KUNNAMPALLIL GEJO
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Venkatagiri(1982) found that like stutterers the DAF dysfluencies
of normal speakers showed a distinct adaptation , effect over
successive recordings occurred more often in content words
than on functional words , on long words than on short words .
Although the consistency effect was present,it was smaller when
compared to stutters .
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Practice & effect of DAF :
Practice with a sentence reduces the effect of DAF becausepractice strengths internal trace of the expected feedback
&successive movements are driven by discrepancy between
ongoing feedback &expected feedback or feedback trace.
This means practice should increase rather than decrease the
probability of errors for sentences produced under DAF.
These observations suggest that articulation is not under the direct
feedback control.(Adams1985).
Many more explanations are need to understand the relation
between stuttering &processing of auditory input.KUNNAMPALLIL GEJO
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(3) Frequency shifted Auditory Feedback (FAF) :
FAF downshift makes hear voice sounding like a gravel-voicedradio announcer saying his station's call letters.
A quarter-octave pitch shift reduces stuttering about 35%.
A half-octave pitch shift reduces stuttering about 65-70%.
A full-octave pitch shift reduces stuttering about 70-75%.
Combining DAF and FAF reduces stuttering about 80%.
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Shifting pitch up or down is equally effective in short-term studies.
But there may be long-term differences between up- anddownshifts.
FAF causes non-stutterers to speak at a higher or lower vocal pitch,
depending on whether the device is set for an up or down frequency
shift.
This higher or lower pitch vocal pitch results from changing vocal
fold tension.
In other words, FAF induces changes in vocal fold tension in non-
stutterers.
Speech clinics have reported that FAF devices induce vocal fold
relaxation in stutterers.KUNNAMPALLIL GEJO
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Usually, stutterers need a greater pitch shift, between one-half and
one octave down.
Also, the study used older headphones which lacked the bass
response of today's headphones.
FAF downshifts induce a slower speaking rate, similar to DAF.
If this effect is consistent, then a FAF downshift should produce
long-term carryover fluency.
Conversely, a FAF up shift (the Mickey Mouse voice) appears toinduce vocal fold tension. FAF up shifts induce faster speaking
rates.
If this effect is consistent, then a FAF up shift should result in poor
long-term performance (e.g., no carryover fluency, and possibly
"wearin off .KUNNAMPALLIL GEJO
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Tests results of auditory processing in stuttering :
(1) Auditory threshold :
Early report by Harms& Malone(1939)that each of 62 stutterers
examined by pure tone audiometry had a impairment of hearing,
but a succession of further studies failed to disclose any significant
lose.
Tomatis (cited by Van Riper,1982)stated that 90 % of his stutterers
had a hearing loss in one ear and related it to a theory involving
both auditory feedback and cerebral dominance.
Hugo,Aimard,Plantier & Wittling (1966) could find any difference
in sensitivity between the left & right ears of stutterers.
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MacCulloch & Eaton (1971) reported a lowered auditory pain
threshold for Puretones in a comparison of 44 stuttereres with a
group of controls .
Phase disparities
Stromsta (1957) in his study he used 2 pure tones of equal
frequency and amplitude and diametrically (180 degrees ) out ofphase cancel each other out.
Stutterers and normal speaker listened to an air conducted tone
and to bone conducted tone of same frequency simultaneouslyintroduced.
The subject then varied the phase and amplitude of air conducted
tone until a critical adjustment was at which no sound was audible
to them .KUNNAMPALLIL GEJO
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Using this procedure at frequencies of 500,1000,2000Hz,Stromsta
found that at 2000Hz there was differenc between stutterers and
nonstutterers in the average relative phase angle of air and boneconducted sounds as indicated by the amount of adjustment they
made.
Later by the same method, Stromsta found an unusual phasedisparity between stutterers left & right ears.
His subjects adjusted amplitude and phase of two air conductedtones heard at either ear until they cancelled an identical bone
conducted tone.
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At the point of cancellation the air conducted tones at the two ears
had a phase disparity at several frequencies about twice as wide ,
on the average, for the stutterers as for the nonstutterers.
Mangan (1982)replicated Stromastas earlier study and failed to
find a difference between stutterers and nonstutterers in phase
and amplitude adjustments of air and bone conducted sound .
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(2) Central auditory processing test :
Research has assessed how well individuals who stutter can processauditory signals in various parts of the brain.
Rouse ygoetzinger & Dirks (1959)reported that stuttering children
did not perform as well as non stutterers in making mediane plane
sound location response.
Sound localization findings by Kamiyama (1964)and Asp (1968)
were in agreement with those of Gregory ,although Asp observed
some differences on tests of loudness balance and Herndon(1967)found differences in the ability to discriminate between
different durations of the tone .
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A number of studies used the Synthetic sentence identification / Ipsi
lateral competing message test (SSI-ICM) to compare stutters
&non stutters.
This test requires participants to identify words in a nonsense
phrase (such as small boat with a picture has become ) when
competing noise is presented in the same ears.
Three studies using this test found that stutters performed worse
than normal participants (Hall &Jerger ,1978;Molt & Guilford,1979;Toscher & Rupp,1978).
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The more fluent normal speakers performed significantly better
than the less fluent normal speakers (Blood et al,1987).
Stuttering &normal dysfluencies may be associated with some
difficulty in central auditory processing.
In contrast to these studies Guitar (1987) found no differences
between stutters &non stutters on the SSI-ICM,but stutters in theirstudy had all recently completed a treatment program.
This finding intriguing in light of evidence from brain imaging
studies that individual who stutter who had demonstrated anabsence of activity before treatment in the left auditory cortex
showed normal levels of activity immediately after treatment (De
Neil et al &Ingham ,2003).
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In Staggered spondaic word test, the stimuli used are series of 2
bisyllabic words having equal stress on each syllable.
The syllables are then overlapped in time The overlapping
syllables a dichotic input to the listner.
Hall & Jerger(1962)stated that stutterers &nonstutterers
significantly differed in their total correct responses to thecompeting portion of the test.
Stutterers performed poorly on this test when compared to non
stutteres.
Another tool for assessing central auditory processing is the
masking level difference test(MLD) ,which requires listeners to
detect the onset &offset of a tone in the presence of masking noise.KUNNAMPALLIL GEJOJOHN,MASLP
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When masking noise is played in the same ear as the tone ,there
are fewer cues for listeners to use in filtering the tone from the
masking tone.
Listeners must use very subtle temporal cues to detect the tone ;
under these conditions ,persons who stutter perform more poorly
than groups of nonstutters(Guitar 1987).
These results may be interpreted to support to support the
outcome of the SSI studies because both tests require theparticipants to use temporal informationin one case (SSI),rapidly
changing formant frequencies in identifying words , and in the
other case (MLD), detection of the onset & offset of a tone in
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Two other studies of central auditory processing tested the
hypothesis that people who stutter have difficulty resolving
temporal differences.
Herndon (1966) found that stutters were poorer than nonstutters
at distinguishing Which of two brief tones was longer.
Barasch et al (2000) administered the duration pattern sequence
(DPS) test ,which involves judging the relative lengths of three
tones , and another measure in which subjects estimated durationsof tones & silent intervals .
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These tests failed to distinguish between the stuttering &
nonstuttering participants as groups, but they showed that less
fluent participants in each group scored worse on the DPS thanmore fluent participants.
In addition ,more disfluent subjects in both groups judged
temporal intervals to be longer than less disfluent subjects.
It has been suggested that fear &anxiety affect temporal processing
(Fraisse, 1963) and that anomalies in temporal processing may bean underlying cause of both stuttering (Kent 1984 ) and high levels
of normal disfluency(Wynne1982).
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Therefore, the researchers conclude that stutterers performance is
poor on all these central auditory function tests.
Stutterers as a group performed poorly than nonstutters on task
requiring fine discrimination of the small time difference in signals
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(3) Dichotic listening tests :
In the early studies, a procedure was developed to assesshemispheric dominance for speech &language by testing which ear
was more accurate at hearing speech sounds.
Kimura 1961 invented the dichotic listening test , which
simultaneously presented two different syllables dichotically.
Listeners reported which syllable they heard.
Auditory nerves connecting the ears to the cerebral hemispherecarry more information to the hemisphere on the opposite side
than to the hemisphere on the same side .
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Results with normal speakers indicated that syllables presented to
the R ear were most frequently reported as heard ,which was called
a R ear advantage for speech.
This procedure has been used to assess laterality differences
between stuttering &nonstuttering groups.
A number of experiments found that many persons who stutter donot show the typical R ear advantage that nonstutters do, which is
evidence that people who stutter do not have Lt hemisphere
dominance for language (Blood 1985;&Moore 1975).
Some dichotic studies found no difference between stutters
&nonstutters (Dorman 1975&Pinksy &McAdams ,1980).
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Other studies found no significant group differences but found that
fewer stutteres than nonstutters showed the expected Rear
advantage (Rosenfield &Goodglass 1980).
The more linguistically complex the stimulus ,the more likely that
the differences between stutters &nonstutters would be found .
Any auditory processing anomaly related to stuttering is likely tobe on a continuum rather than simply present or absent.
More severe or neurologically involved stutters may have more
abnormal auditory processing .
Researches view stuttering as disorder in the control of seqence &
timing .
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There are 5 observations which point the connection between
stuttering &processing of auditory input.
(1) Stuttering can be virtually eliminated in some with the flick of
switch introducing white noise with in the frequency range of
speech which is loud enough to mask the stutterers auditory
feedback (1955)
(2) Stapedial reflex of the middle ear appears to differ between
stutteres & nonstutterers.
The stapedial muscle normally contracts 100-165 msec prior tophonation ,there by reducing the amplitude of the ear drum
vibration & alternates the hearing of ones own speech .
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Webster &Lukes(`1968)found that stapedial reflex is less stable in
stutterers.
Dhonovitz & Johnson et al (1978) found that under conditions of
anxiety stutteres show less stapedial attenuation than nonstutters .
Hall & Jerger (1978) compared the acoustic reflexes to the external
sound in stutterers &controls.
Reflex threshold was equivalent was in 2groups, but reflex
amplitude was smaller in stuttering group.
Hannley and Dorman (1982) observed no difference in the latency
or amplitude of the reflex.
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March banks &El-Yaniv(1986) found no difference between
stutterers and normal speakers in middle ear muscle activity during
vocalization .
(3)Auditory processing of an about to be produced word
facilitates its correct production
Stutterers often release them from a block when someone elseword on which they have difficulty (Bar &Carmel 1970)
(4)stutterers become very fluent when their returning auditory
feedback is delayed by means of a recording &reproducing device(Hutchinson& Burk1973)
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(5) Reception errors like in stutterers can be obtained in normals
by amplifying as well as delaying their auditory feedback .
Researchers have tried to link the timing deficit to stuttering by
suggesting a single mechanism in brain may control both incoming
and outgoing signals.
Faulty timing of incoming signals would give rise to stutterers
poor performance on central auditory processing tests.
Faulty timing of outgoing signals would result in stuttering.
(4) Brain electrical potentials :
Studies of electrical brain activity in response to auditory
stimuli have provided further evidence that auditory processing is
abnormal in individuals who stutter.KUNNAMPALLIL GEJOJOHN,MASLP
M l d L (1983) f d h h d f k
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Molt and Luper(1983) found that stutterers had faster average peak
latency than normal speakers.
Studies by Hood (1987) & Parker (1995) reflecting both subcortical
&cortical activity have found group differences between stutters &
nonstutters.
However the first study found stutters responses to be slower than
nonstutters responses & the second study found them to be faster
than non stutters responses .
A study of Molt(1997) is more relevant to the question raised by the
brain imaging studies of whether person who stutter have a deficit
in the left auditory cortex.KUNNAMPALLIL GEJO
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Molt found that stutters have longer latencies & lower amplitudes
of brain waves in the in the cortex when they where asked to
make decisions about semantic incongruencies in sentences theylistened to
Early latency potential (ABR) --
Blood &Blood (1984) recorder longer wave III and wave V
latencies for stutterers and abnormal inter peak latency for five of
eight stutterers.
Smith,Blood and blood (1990) found no differences in latenciesbut greater amplitude of wave I for stutterers .
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Middle latency response in stutterers --
Studies have shown that auditory middle latency response Wave
Pb was prolonged in subjects who stutter as compared to normals .
Hood (1987)conducted an investigation of the MLR s of males
who stutter and found that the latency of the wave Pb was
significantly longer for those who stuttered than controls.
MLRs were recorded from 10 males who stutter &10 controls using
a variety of filter bands in response to clicks presented binaurally
at various rates.
The latency of Pb was found to be significantly shorter in the
group of subjects who stutter.
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Wave Pb of the MLR is generated by the thalamic portion of the
reticular activating system.
The thalamus is critical to speech and language production.
Other researchers suggest that the metabolism of the thalamus is
lower than normal(Rapoport1991)(JSHR,Vol.38,5-17,1995);
Significant difference in the delay of Wave Pb latencies in adultstutters as compare to the adult non stutters in both ears .
This indicate the differences in the thalamocortical pathways
&reticular formation as there are hypothesized to be the possiblegenerators for the MLR waves.
The difference may lead to poor temporal processing
&programming in stutterers .KUNNAMPALLIL GEJOJOHN,MASLP
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P300 event related potentials in stutterers --
Stutters exhibit different patterns of interhemispheric activity than
nonstutters with a tonal P300 task.
Insula and auditory cortical areas of the superior temporal lobe are
major sites of generation of the P300 response (Rogers et al 1991)
Blood (1991) tested stutterers using P300 and found no differencesbetween stutterers and nonstutterers in the latency of p300.
16 young adult males aged 17 to 36 years with Rt handed
compared with stutterers and found that stutterers exhibitedrelatively lower amplitude P300s in the right hemisphere.
This may be interpreted as possibility that altered cerebral
dominance plays an important role.KUNNAMPALLIL GEJOJOHN,MASLP
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