Neuro-physiological correlates of speech in stuttering

1. Presenter
V Amith Kishore
2 Msc(SLP)
Physiological basis of fluency and its disorders

2. The physiological basis of the fluency:
Coordination and timing
 Coordination of speech movements may be
thought of in two different ways, according to the
kinds of errors a failure of coordination can
produce.
 The first kind of coordination has to do with
spatial precision of movements. Discoordination
of this type results in movements that are
imprecise with regard to placement.

3.  This kind of discoordination by itself result in
articulation errors and seems of lesser interest in
a study of fluency than do other
discoordinations.
 Although spatial precision does not seem to be
an aspect of fluency itself, a number of facts
suggest a relation between articulation errors, at
least the functional kind, and stuttering.

4.  Furthermore, the child’s developing capacity for
spatially precise speech movements may affect the
development of speech fluency.
 The other kind of discoordination has to do with
precision of timing.
 To be temporally coordinated, the different
movements that comprise a speech gesture have
to be accurate not only in placement but also in
timing.

5.  Timing coordination refers to the ability to
produce different movements and have all of
them occur at the right time in relation to each
other or to a starting point.
 Temporal precision is just as important as
spatial precision.
 It will be helpful, in discussing coordination, to
understand the term coordinative structure
(Fowler and Turvey. 1980).

6.  A coordinative structure is a set of body parts,
muscles for moving them, and associated neural
mechanism that participate in the same act.
 It seems that the capacity to relax antagonistic
muscles has more to do with fluency than the
capacity to contract agonistic muscles.
 A coordinative structure is often said to operate
like a mass-spring system. Muscle tissue may
be stiff or springy depending on its current tonus,
and the body parts that muscle move around
differ in massiveness.

7.  These variations mean that a given coordinative
structure may be characterized according to its
springiness-its tendency to return to its original
length when stretched- as well as according to
its mass-which governs its tendency to continue
moving in a given direction.
 These two properties will have an important
influence on the way a specific speech
movement is performed.
 The more massive a coordinative is, the more
difficult it will be for the speaker to get it moving
and, once moving, to stop it or change the
direction of its movement.

8.  Thus movements of the jaw are slower to start
and stop than movements of the tongue tip
because the jaw is more massive.
 Stiffness in the coordinative structure will reduce
the peak velocity of the structure.
 In addition every mass-spring system has a
characteristic resonant frequency.
 Resonant frequency of a speech coordinative
structure is not fixed.

9.  Of course, the timing of movements does not
depend on massiveness and stiffness of the
peripheral mechanism.
 Certain neural mechanisms, both peripheral and
central, have an important influence in the timing
of movements.
 Different neurons transmit impulses at different
speeds, according to size of neuron, although
neural transmission is so rapid that it is unlikely
to influence the speed of structural movement.

10.  A coordinative structure may contain a number
of synapses, and each synapse requires
additional time.
 A coordinative structure involving more synaptic
junctures will be slower than one containing less.
 Although the time taken by signal to cross the
synaptic space may be a factor in speed of
neural mechanism.

11. Findings
Reaction time
 The reaction times of normal subjects vary with
structure, the subjects’ focus of attention, the
hemisphere stimulated, the age and sex of the
subjects, and a number of other variables
(Shadden, 1979).
 Although probably related to coordination and
motor control, the relation of reaction time
measures to speech in normal subjects is not
known.

12. Feedback
 DAF disrupts speech production (Black, 1951;
Lee, 1951, Wingate 1970)
 Auditory masking increases loudness, raises
fundamental frequency, and slows rate
(Wingate, 1970)
Gestural synchrony.
Interference
 Stuttering, and other discontinuities are both
likely to occur at syntactic locations where
language is being formulated (Starkweather and
Godor., 1983)

13. The relation of coordination to rhythm
 The rhythm depends on the speaker’s central
capacity to generate a temporal structure and
allocate peripheral speech movements to it.
 The speaker ability to use his or her sense of
rhythm, to adapt it to rhythmic needs of speech,
which may change from moment to moment, is
probably a more important capacity for fluency
than simple presence of a central rhythmic
“clock.”

14. Physiological characteristics of persons who
stutter

15. Physiological characteristics of persons who
stutter
 There has been a considerable research during the
past hundred years on the physiological functioning
of persons who stutter.
 Some findings that pertain to the following questions
are summarized here.

16.  What physiological process are investigated??
 How do persons who stutter, as a group, differ from
normal-speaking peers with regard to physiological
functioning???
 Are there subgroups of stutterers who function in
physiologically abnormal ways that may contribute
to the onset or maintenance of their stuttering????

17.  Many physiological processes have been investigated
in an attempt to identify the organic cause for stuttering.
 Those to which the most attention has been directed
during the past 100 years are discussed as follows.

18. The processes which we are going to discuss are
interrelated and have several implications.
1) when an investigator studies one process, he or
she is likely to be indirectly study others.
2) Investigator has to be cautious when
interpreting the results of his or her studies.

19.  Respiration
 Cardiovascular functioning
 Biochemical functioning
 Central nervous system functioning
 Autonomous nervous system functioning
 Sensori-perceptual functioning

20. Biochemical functioning
Three approaches have been used in research.
1) There have been studies in which the levels of specific
biochemicals in there bodies were compared to those in
stutterers (Hill, 1944a; Rastatter & Harr 1988)
2) There have been studies in which biochemicals
abnormalities were inferred by observing the effect of
certain drugs (such as Haloperidol) on their speech
fluency
3) There have been studies on the incidence of stuttering
among persons who have particular disturbance in
biochemical functioning, such as diabetes (van Riper,
1982)

21. Central nervous system functioning
 Among the investigated phenomena mediated by
this system are the following…
 Action potentials from the bilaterally paired
musculature of speech mechanism.
 Motor control
 Brain waves
 Hemispheric asymmetries for language processing

22.  Involuntary movements including tremors
 Manual motor performance
 Performance on neuropsychological tests
Autonomic nervous system functioning.
 It is well established that there is positive
relationship between the level of activity of the
sympathetic division and anxiety.

23.  It is also well established that there is a negative
relationship between its level of activity and
relaxation
 In addition it is generally accepted that anxiety level
can affect motor performance, including respiration,
phonation and articulation.

24. Sensori-perceptual functioning:
 Whether stutterers are different from their normal
speaking with regard to the functioning of their
auditory, tactile-kinesthetic, and visual systems
 Why study Sensori-perceptual functioning?

25.  Lets have a look how do they differ in functioning
Respiration
 Systematic research on the breathing movements of
persons who stutter started at the beginning of last
century (Beech & Fransella, 1968)
 The findings of most of this research support the
following conclusions:
 Various kinds of abnormalities in breathing
movements may occur during moments of stuttering.

26.  The same type of breathing abnormalities tend to
occur during both moments of stuttering and
expectancy of stuttering (van Riper 1936).
 Pattern of chest wall posturing for phonation are
qualitatively same.
 Abnormalities observed in the breathing movements
during moments of stuttering usually are not present
during silence (Bloodstein, 1987)

27. Cardiovascular functioning
 Systematic research on this topic has been ongoing
more than 90-years.
 Results show that pulse rate increases before and
during moments of stuttering (Fletcher, 1914)
 The following phenomenon are investigated…
 Heart rate, sinus arrhythmia, blood pressure, and
basal metabolic rate.

28. Biochemical functioning:
 The research on chemical make-up has been going
for more than 75 years.
 Among the biochemical phenomena that have been
studied indirectly or directly are alveolar Co2 level.
 Chemical composition of the blood, plasma levels of
adrenergic neurotransmitters and primary amino
acids.
 Some of the studies show indifferences.

29. Central nervous system functioning:
 Much of the recent physiological research is dealt
with CNS functioning.
 During 1930 s the studies suggest that stutterer are
less likely than normal speakers to have established
unilateral cerebral dominance.
 The studies have suggested that there is no
difference of brain waves during silence, auditory
and visual representation of the word anticipation of
speaking, and speaking.
 The prevalence of stuttering among persons with
known brain damage has been reported to be higher
than the general population.

30.  In this particular aspect the cerebral lateralization of
function has been more subjected to research.
 Aspects of sensory, motor and language functioning
have been studied that they are thought to be
mediated by either right or left side of their structure.
 One of the first strategies to investigate cerebral
lateralization of function and other manifestations
of cerebral sidedness, such as eyedness and
footedness (spanido, 1941) is handedness.

31.  Many studies have been carried by authors and they
hypothesized many things.
 Intrest on research of sidedness was lessened after
1940 s.
 The renewed interest in this topic was cerebral
lateralization of speech and language.

32.  The Wada test was one of the first methodologies used
during1960 s.
 Jones, 1966 reported that lack of lateralization
 Rosenfield & liljestrand, 1981 did not detect any lack of
lateralization.

33.  A second methodology that was used during this
period to study was dichotic listening
 Studies done by Curry and Gregory, 1969 are
consistent with this hypothesis.
 While Quinn, 1972; Cerf and Perkins, 1974 are not

34.  The third methodology that has been used to study
cerebral lateralization of speech and language is
Electroencephalography.
 Change in the brain waves that (usually alpha ones)
that usually occur in the right hemisphere are
compared to those that occur in the left while tasks
are being performed that involves linguistic
processing
 Normal speakers tend to evidence a larger change
in the left than in right hemisphere while performing
such tasks

35.  Some persons who stutters, on the other hand, have
reported to evidence large changes in right
hemisphere than in left hemispheres while doing so
(Moore, 1986).
 There are several other methodologies that have
been used to study cerebral lateralization for speech
and language include
 Auditory tracking
 Tachistoscopic viewing
 Finger tapping with right and left hands while
performing speech tasks
 The findings of studies which use this
methodologies are mixed

36.  Some findings of studies done by Johannsen and
victor, 1986; Rasatter and Dell, 1986b; Sussman
and MacNeilage, 1975) suggested that atleast
some persons who stutter use their right
hemisphere more than normal speakers do to
process speech and language.
 How ever these authors Brutten and Trotter, 1985;
Neilson, Quinn and Neilson 1976, did not indicate
any difference

37. Autonomic nervous system functioning.
 Seeman 1934, was the one of the first to look into
the possibility that abnormality in the functioning of
the autonomic nervous system could contribute the
etiology of stuttering.
 He hypothesized that stuttering may be due to
hyperactivity of sympathetic divison.

38.  His hypothesis received some support from the
findings of several studies of stutterers –sympathetic
reactivity during silence (Sedlacek 1947-48); Sovak
1935).
 However the presence of the abnormality is not a
necessary condition for the development of
stuttering.

39. Auditory functioning
 The prevalence of stuttering in hearing impaired
population appears to be lower than in the general
population (Andrews et al., 1983; Montgomery &
Fitch, 1988).
 The following aspects of the auditory functioning
have been investigated:
 Threshold for pure tones (St Louis & Hinzman,
1988)

40.  Relative phase angle of air- and bone conducted
sounds (Stromsta, 1957, 1972).
 Right ear versus left ear presentation of stimuls- as
in dichotic listening (Curry and Gregory, 1969;
Libertrau and Daly, 1981)
 Effect on delayed auditory feedback on oral cavity
not involving speech (Stark and Peirce 1970)

41.  The results of these studies were mixed
 Central auditory functioning at the level of the
brainstem (Anderson, Hood and Sellers, 1988;
Bonin, Ramig, & Prescott, 1985, Kent,1983; Stager,
1990)
 Horovitz et al., 1978 speculated, the reported
differences in auditory functioning resulted, in part,
from differences between them in anxiety level.

42. Tactile-kinesthetic functioning
 A disturbance in tactile-kinesthetic feedback can
have detrimental effect on performance of motor
acts.
 While such acts are occuring, information is
continuously being sent to the brain from receptors
in the muscles and the skin about the state of
contraction of the various muscles and the location
in space of the various structures involved in
performing the acts.

43.  Could a disturbance in tactile-kinesthetic feedback
disrupt the movement of articulators and vocalfolds
in a way that would cause a breakdown in fluency.
 The aspects they studied included threshold for
vibratory sensation (Fucci et al., 1985), intra-oral two
point discrimination (Jenson et al., 1975), and oral
recognition of forms (Jenson et al., 1975; Martin et
al., 1981; Stewart, Evans, & Fitch, 1985).
 The results of these studies were mixed

44.  The central component or experiential nature of
stuttering has for years been accepted to play a
large role in the pathology (Sheehan 1970, Van
Riper 1982).
 However, the origin of stuttering is thoight to be
a central involuntary block, though its true origin
and physiological nature remains unknown
(Kalinowski et al. 2000).

45.  Numerous neuroimaging studies have found
stuttering to be associated with increased
activity in motor regions such as the
supplementary motor area and superior lateral
premotor cortex with right lateralization (Fox et
al., 1996)
 Right frontal operculum (Preibisch et al. 2003)
 Fronto-motor areas, parietal, temporal, limbic
and insular areas of the right hemisphere
(Neumann et al, 2003)

46.  Further, suppression or deactivation relative to
normal speakers has been found in the primary
auditory association areas, left inferior frontal
cortex (Fox et al. 1996, Ingham et al, 2000).
 Posterior regions of the brain (Braun et al.
1997).
 Precentral gyrus (Preibisch et al. 2003).

47.  Though these data have been interpreted by
some to suggest factors causal to stuttering,
they are more likely to reflect a compensation or
neural effect of stuttering (Preibisch et al. 2003,
Neumann et al. 2003),especially since these
aberrant neural activity disappear under choral
speech conditions.
 Therefore these aberrant neural activities
probably reflect the highest level of
compensation or the neural effects of all covert
and overt stuttering behaviours.

48. Thank you…