Speech control in children with Down syndrome
Two areas where speech fluency problems arise, the motor system and the speech-language interface, are described and their implications for characterising the dysfluencies made by children with Down syndrome are discussed. Research topics are identified and implications for the treatment of speech problems in children with Down syndrome are drawn.
Howell P. Speech control in children with Down syndrome. Down Syndrome Research and Practice. 2010;12(2);98-102.
Speech behaviours and their assessment in children with Down syndrome
Three types of problems with speech motor control
are typically experienced by children with Down
1) early articulation and phonological
2) fluency disorders such as stuttering and
3) developmental aphasia-type problems.
The first and second involve speech motor
processes and the second and third involve
interaction between the speech and language
processes. This contribution details how motor
factors affect speech and reports on the interface
between language and speech-motor processes. At the
end of each section, the fluency problems associated
with these processes are presented and evidence
whether children with Down syndrome are affected by
these problems is discussed. Research questions that
still need to be addressed are identified and the
final section, some potential clinical implications
The speech-motor system in early articulation
Sound production necessitates some air pressure
movement. The principal source of that energy is the
air in the lungs. This passes into the vocal
cavities above the larynx. The escape of air from
the lungs is controlled in different ways by
structures in the larynx and, in some circumstances,
in the vocal tract itself. The energy to produce
speech is referred to as the source of excitation.
One major type of excitation is voicing (e.g. in
vowels). In this mode, the vocal folds repeatedly
open and close, which chops up the flow of air from
the lungs. A
second type is voiceless energy, which can be
produced when the vocal folds are held close
together and a hissy stream of air escapes from the
lungs into the vocal tract, for example in the
consonants ‘p’, ‘t’ or ‘k’. Although children with
Down syndrome have breathing difficulties, which
affects lung pressure, and motor coordination
problems, which affects control of air escape from
the lungs and manoeuvres of cartilage and tissues in
the larynx, the impact these have on source
production has received little attention. Therefore,
related research questions are: how accurately can
children with Down syndrome change from voiced to
voiceless energy in connected speech, and is the
sound that enters the vocal tract well-structured so
that it leads to clear speech quality? Even
superficial listening to the speech of children with
Down syndrome suggests that the excitatory source is
poor. Examination of details of the energy source is
a major omission from the literature on children
with Down syndrome.
Data are lacking on children with Down syndrome,
but results on two adults with Down syndrome (one of
each gender) have been reported which examined
source characteristics. High jitter rates (pitch
perturbation) were reported, as were problems in
The articulators above
the larynx (commonly know as the vocal tract filter)
change in position as speech is produced and this
leads to the different sounds in languages. Thus, to
produce the vowel /i/, a speaker lifts the tongue
and pushes its tip forward in the vocal tract (close
to the gum ridge behind the teeth, but not quite in
contact). To produce the consonant /p/, the speaker
brings the lips into contact (stopping the flow of
air from the source) and then releases it. Monophthongal vowels involve little or no movement
of the articulators whereas consonants do. The
sustained shape of the vocal tract can be estimated
relatively easily for vowels, as vocal tract
resonances (formants) relate to the two coordinates
of movement (tongue height and its forward/backward
position). There have been no reports about how
children with Down syndrome compare to controls in
vowel production, although there has been a study on
MRI scans show clearly that children with
Down syndrome have different shaped vocal tracts
from controls and specify where in the tract these
differences occur. The main difference is that
the front part of the roof of the mouth is reduced
in children with Down syndrome. The amount of data
is limited at present and more exploration is
needed, hopefully in the form of longitudinal
scanning data for both genders. This should be used
to examine how the anatomical differences affect
vowel articulation. Currently MRI scans have only
been used for anatomical measurements, but it should
be possible to obtain scans while children with Down
syndrome and controls hold the vocal tract shape for
vowels. Coordination between the articulators in
consonant production can be measured using
physiological or acoustic techniques. Acoustic
measures are preferred as they are not invasive.
Howell, Anderson and Lucero describe techniques that
are appropriate for use with children with Down
The interface between language and the
There are two main views about how the
motor system receives language input from the
language system that can lead to fluency problems.
One considers that fluency problems are a result of
impaired (error-prone) language processing and that
the motor system responds passively to whatever
language input it receives. It has been proposed
that speakers become aware of these errors by
listening to their own speech (monitoring). If
errors occur, the speaker interrupts and repairs
them, which leads to aspects like whole or part-word
repetitions and pauses that are seen when there are
According to this view, if
children with Down syndrome have acute language
problems, they should make more linguistic errors of
all forms than typically-developing children. Such
groups have not been compared systematically for: a)
relative incidence of language errors, b) whether
there are specific components of language processing
that are particularly error prone in children with
Down syndrome. Children with Down syndrome have
hearing problems which would affect how well they
can monitor their overt speech output. There has
been no study which has assessed monitoring of
speech output in children with Down syndrome
compared to normal-hearing control children or
controls with similar hearing impairments to
children with Down syndrome.
The second alternative
argues that the dysfluency phenomena mentioned
earlier arise because the linguistic system has to
provide the output at a particular time for the
speech sequence to be produced fluently[7,8]. If the
language representation does not produce the output
to the speech motor system at the required time,
speakers hesitate or repeat words until the material
is ready and they can proceed, accounting for the
same dysfluencies as Levelt, in a different way.
This account does not assume there is monitoring.
Stuttering has been characterised as
involving fluent speech with interspersed dysfluencies. It can also have associated secondary
characteristics that occur while speech is taking
place (e.g. foot tapping or facial grimaces) and
affect wider aspects of behaviour. The overlap in
the type of dysfluencies seen in typically
developing and stuttering children makes diagnosis
difficult (see ref 9 for a review). However, it
appears that part-word repetitions, prolongations
and word blocks are features that are commonly seen
when stuttering persists. Although there is a wealth
of research evidence that indicates motor and
linguistic factors affect stuttering in
typically-developing children, the data on
stuttering in children with Down syndrome are sparse
and usually report prevalence rates of stuttering in
children with Down syndrome and some performance
differences between children with Down syndrome who
stutter and those who do not. Studies are needed
which look separately at linguistic and motor
influences on stuttering. Preus reported results on
47 speakers with Down syndrome out of 67 whose
speech was deemed intelligible to a panel of
judges. When whole-word and part-word
repetitions and prolongations were examined, 46.8%
were judged stuttering. If whole-word dysfluencies
were excluded, the frequency of stuttering reduced
to 34%. Preus considered that secondary symptoms
such as body movements, avoidance and postponement
are signs of awareness of stuttering and indicative
of a more advanced form. When only these signs
were included, 29.8% of the sample was still
considered to stutter, which suggests that
stuttering in its advanced form can occur in
children with Down syndrome. Some questions that
remain are how stuttering originates, how it
compares with typically-developing controls, how it
develops, whether it progresses at the same rate as
in typically-developing controls. Longitudinal work
on children with Down syndrome would be best to
answer these questions.
In a later examination of
the earlier data, Preus reported that 34% of the
group of children with Down syndrome had symptoms of
stuttering and 31% had symptoms of cluttering.
Cluttering is a pattern of speech closely allied to
stuttering. For instance, cluttering appears as the
same categorical disorder as stuttering in
DSM-IV. Other authors (most recently Ward)
argue that stuttering and cluttering are distinct.
Some of the defining characteristics that set
cluttering apart from stuttering are: 1) poorly
2) short attention span and poor
3) lack of complete awareness of
the problem and
4) high speech rate.
like 1) and 3) are difficult to measure. At a recent
conference, Howell and colleagues showed that nine
samples of clutterers from a longitudinal database
of clinical cases referred for fluency disorder
could not be distinguished from speakers who
stuttered but who later went on to recover. It would
therefore seem preferable to assess cluttering along
with stuttering in children with Down syndrome and
not as being distinct from it.
Telegraphic speech refers to loss of
function words. Speakers with Down syndrome have
been reported to have telegraphic speech[14,15].
Loss of function words is often associated with
dropping of morphologically-determined inflectional
endings. Eadie, Fey, Douglas and Parsons showed this
in a study they performed that compared children
with Down syndrome, controls (matched on mean length
of utterance) and children with specific language
impairment. Problems were reported for both the
children with Down syndrome and those with specific
language impairment for word-final inflections.
Related findings were reported by Vicari, Caselli
and Tonucci for 15 children with Down syndrome and
15 mental-age-matched controls. They reported no
difference in lexical development, but significantly
poorer ability by the children with Down syndrome in
terms of morphological processing.
It needs to be
established whether preventing problems at the early
stages of speech development prevents subsequent
speech and language problems, i.e. does remediation
dealing with early articulation problems reduce the
chances of the development of stuttering? In terms
of the two components of speech that need to be
controlled (source and filter), speech-language
therapists have vast experience in teaching
breathing control (source), although comparatively
little has been done with very young children, and
no reports could be found on children with Down
syndrome. Tongue shortening has been tried as a way
of dealing with vocal tract configuration issues in
people with Down syndrome (and also as a treatment
for stuttering). This seems a radical solution
and there are alternatives. For instance, speakers
learn to adapt to new articulatory configurations
(e.g. after trips to dentists) and procedures for
teaching compensatory strategies like these are a
less dramatic alternative that should be examined
first. More data are required on vowel and consonant
production and speech errors at these early stages
before clinical implications can be drawn.
Cooper suggested a behavioural
modification programme for treating people with Down
syndrome who stutter. Instead of modifying or
shaping feelings that may inhibit the development of
improved fluency, the focus should be on concepts
and explanations that are appropriate to the child’s
conceptual and linguistic skills. However, for these
methods to work the child needs to be aware that
he/she stutters, which may not always be the case
with children with Down syndrome. There are methods
that also work whether or not the child is aware of
stuttering: for example, operant conditioning
procedures, as verbal conditioning can occur without
awareness. One treatment that is widely used
with young children is the Lidcombe programme. If
the speech of children with Down syndrome who
stutter develops in the same way as in otherwise
typically-developing children who stutter, later
forms of treatment would need to be developed for
treating stutter in their speech (see
ref 21 for a
potentially suitable procedure that has been used in
Developmental aphasia type problems
terms of the symptoms that show some similarity with
aphasia, it is primarily necessary to establish
whether this supposed similarity actually obtains.
If it does, then the techniques which have been
successful with children with this disorder who do
not have Down syndrome could be employed with
children with Down syndrome. However, again more
data are required about the supposed similarity
before clinical implications can be drawn.
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This work was supported by grant 072639 from the Wellcome Trust to Peter
Howell. Peter Howell is at University College London. Correspondence to
Peter Howell, Department of Psychology, University College London, Gower
Street, London WC1E 6BT, UK • e-mail:
Paper prepared from presentations and discussions at the Down Syndrome
Research Directions Symposium 2007, Portsmouth, UK. The symposium was hosted
by Down Syndrome Education International in association with the Anna and
John J Sie Foundation, Denver. Major sponsors also included the Down
Syndrome Foundation of Orange County, California and the National Down
Syndrome Society of the USA.
First received: 31 July 2008; Revised version received 20 January 2009;
Accepted: 27 January 2009; Published online: January 2010