Childhood Apraxia of Speech
Ad Hoc Committee on Apraxia of Speech in
About this Document
This technical report was developed by the American Speech-Language-Hearing
Association (ASHA) Ad Hoc Committee on Apraxia of Speech in Children. The report
reviews the research background that supports the ASHA position statement on
Childhood Apraxia of Speech (2007). Members of the Committee were Lawrence
Shriberg (chair), Christina Gildersleeve-Neumann, David Hammer, Rebecca
McCauley, Shelley Velleman, and Roseanne Clausen (ex officio). Celia Hooper,
ASHA vice president for professional practices in speech-language pathology
(2003–2005), and Brian Shulman, ASHA vice president for professional
practices in speech-language pathology (2006–2008), served as the
monitoring officers. The Committee thanks Sharon Gretz, Heather Lohmeier, Rob
Mullen, and Alison Scheer-Cohen, as well as the many select and widespread peer
reviewers who provided insightful comments on drafts of this report.
The goal of this technical report on childhood apraxia of speech (CAS) was to
assemble information about this challenging disorder that would be useful for
caregivers, speech-language pathologists, and a variety of other health care
professionals. Information on CAS has often been the most frequent clinical topic
downloaded by visitors to ASHA's Web site. This report addresses four
questions most often asked about CAS: (a) Is it a recognized clinical disorder? (b)
What are its core characteristics? (c) How should it be assessed? and (d) How should
it be treated?
To address these four questions, the Committee undertook a review of the scientific
foundations of CAS and trends in professional practice. A preliminary survey of the
literature indicated that it would not be feasible to complete a systematic review
consistent with evidence-based practice. The primary barriers to such a review were
unresolved controversies about the quality rankings for commonly used research
designs, as proposed in several evidence-based practice systems. The Committee
therefore elected to complete narrative reviews restricted to peer-reviewed
literature published since 1995, with additional sources consulted as needed for
coverage of certain topics. We developed a template to summarize each study and
consensus procedures to evaluate the strength and quality of evidence for research
findings in relation to the four questions posed above. Findings from reviews and
the consensus evaluation procedures were synthesized to form the bases for the
information provided in this document, including recommendations on several key
professional issues. The final document incorporated extremely useful information
from select and widespread reviewers who responded to invitations to review
preliminary drafts of this document, including a draft posted on ASHA's Web
In this initial section of the report, we introduce terms and concepts, consider
issues associated with the definition of CAS, and discuss scientific and
professional information related to the reported increased prevalence of CAS.
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The Committee recommends childhood apraxia of speech (CAS)
as the classification term for this distinct type of childhood (pediatric)
speech sound disorder. Beginning with the first word in this term, two
considerations motivate replacing the widely used
developmental with the word childhood. One
consideration is that CAS support groups in the United States, the United
Kingdom, and elsewhere have requested that developmental
not be used in a classification term for this disorder. Inclusion of this
word is reportedly interpreted by service delivery administrators as
indicating that apraxia is a disorder that children “grow out
of” and/or that can be serviced solely in an educational
environment (see relevant discussion on the Apraxia-Kids listserv:
www.apraxia-kids.org/talk/subscribe.html). A second rationale for the use of
CAS as a cover term for this disorder, rather than alternative terms such as
developmental apraxia of speech (DAS) or
developmental verbal dyspraxia (DVD), is that our
literature review indicated that apraxia of speech occurs in children in
three clinical contexts. First, apraxia of speech has been associated
causally with known neurological etiologies (e.g.,
intrauterine stroke, infections, trauma). Second, apraxia of speech occurs
as a primary or secondary sign in children with complex
neurobehavioral disorders (e.g., genetic, metabolic). Third,
apraxia of speech not associated with any known neurological or complex
neurobehavioral disorder occurs as an idiopathic neurogenic speech
sound disorder. Use of the term apraxia of
speech implies a shared core of speech and prosody features,
regardless of time of onset, whether congenital or acquired, or specific
etiology. Therefore, childhood apraxia of speech (CAS) is
proposed as a unifying cover term for the study, assessment, and treatment
of all presentations of apraxia of speech in childhood. As above,
CAS is preferred over alternative terms for this
disorder, including developmental apraxia of speech and
developmental verbal dyspraxia, which have typically
been used to refer only to the idiopathic presentation.
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Rationales for the second and third words in the classification term CAS
reflect empirical findings for children suspected to have this disorder. The
alternative terms—apraxia of speech versus
(verbal) dyspraxia—each have established
traditions in international literatures. Apraxia of speech
is more widely used in the United States following the Mayo Clinic
traditions (Duffy, 2005), whereas
verbal dyspraxia is the preferred term in many other
English-speaking countries. Differentiating between these alternatives based
solely on etymological distinction (i.e., total [a] vs.
partial [dys] absence or lack of function) is problematic
when applied to CAS. Clinical experience indicates that although a child
suspected to have CAS may have very limited speech, seldom is a child
completely without mastery of some speech sounds. Notwithstanding this
difference, and to parallel usage for the possible acquired form of this
disorder in adults (i.e., AOS), the Committee recommends use of the affix a
for this classification term.
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Several other types of apraxia and several types of dysarthria play prominent
roles in the scientific foundations of CAS. Physicians and researchers
recognize ideomotor and limb kinetic praxis problems that
may or may not be present in persons with apraxia of speech. As discussed in
this report, orofacial and limb apraxias are of particular interest as the
presence of one or both in a child suspected to have CAS may provide support
for the diagnosis, particularly in prelingual children. Apraxia in other
systems may also play important roles in treatment. For example, the
presence of limb apraxia may preclude using manual signs for functional
communication. Moreover, the presence of orofacial apraxia may support the
need for either more aggressive or alternative approaches to the use of
phonetic placement cues in speech treatment.
Concerning dysarthria, a neuromotor disorder presumed not to involve the
planning or programming deficit in apraxia (see below), some forms of these
two disorders may share common speech characteristics. As discussed in later
sections, a significant research challenge is to determine the diagnostic
boundaries between CAS and some types of dysarthria with which it may share
several speech, prosody, and voice features.
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Although the core feature of CAS, by definition, is proposed to be similar to
the core feature of AOS in adults, this relationship does not preclude the
possibility of important differences in associated features. For example,
Maassen (2002) noted that
“a fundamental difference between [adult] AOS and
[CAS]…is that in [CAS] a specific underlying speech motor
impairment has an impact on the development of higher phonological and
linguistic processing levels” (p. 263). Despite a much larger and
well-developed literature in AOS, including many chapter-length discussions
of alternative theoretical frameworks, the Committee elected not to include
reviews of theory and research on acquired apraxia of speech in this report.
This decision was motivated by the view that the scientific foundations of
CAS should be based on research directly concerned with this and related
childhood speech sound disorders. However, as discussed in several places in
this document, the Committee has attempted to anticipate likely parallels
between acquired apraxia of speech in adults and CAS, a task made more
difficult by differences in terminology used to describe them. Treatment
guidelines for acquired apraxia of speech have recently been proposed by the
Academy of Neurological Communicative Disorders and Sciences (Wambaugh, Duffy, McNeil, Robin, &
Rogers, 2006a, 2006b).
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The Committee compiled a table of more than 50 definitions of CAS that have
appeared in the research and clinical literature, primarily within the past 10
years. A few of the more widely cited definitions dating back to the early 1970s
are provided in the table to sample the variety of perspectives on the nature of
CAS among researchers, including some definitions found in secondary sources
such as Web sites and professional organizations consulted by caregivers and
health care professionals. We are keenly aware of the limitations of any
definition of CAS until the behavioral correlates and neural substrates of this
disorder have been identified and extensively cross-validated. Considering its
value for children, caregivers, clinicians, researchers, and stakeholders,
however, we viewed the scope of our task as including a working definition of
CAS. Recognizing an almost certain need for revision based on emerging research
findings, the Committee proposes the following definition:
Childhood apraxia of speech (CAS) is a neurological
childhood (pediatric) speech sound disorder in which the precision and
consistency of movements underlying speech are impaired in the absence
of neuromuscular deficits (e.g., abnormal reflexes, abnormal tone). CAS
may occur as a result of known neurological impairment, in association
with complex neurobehavioral disorders of known or unknown origin, or as
an idiopathic neurogenic speech sound disorder. The core impairment in
planning and/or programming spatiotemporal parameters of movement
sequences results in errors in speech sound production and prosody.
Review of the research literature indicates that, at present, there is no
validated list of diagnostic features of CAS that differentiates this symptom
complex from other types of childhood speech sound disorders, including those
primarily due to phonological-level delay or neuromuscular disorder
(dysarthria). Three segmental and suprasegmental features that are consistent
with a deficit in the planning and programming of movements for speech have
gained some consensus among investigators in apraxia of speech in children: (a)
inconsistent errors on consonants and vowels in repeated productions of
syllables or words, (b) lengthened and disrupted coarticulatory transitions
between sounds and syllables, and (c) inappropriate prosody, especially in the
realization of lexical or phrasal stress. Importantly, these features are not
proposed to be the necessary and sufficient signs of CAS. These and other
reported signs change in their relative frequencies of occurrence with task
complexity, severity of involvement, and age. The complex of behavioral features
reportedly associated with CAS places a child at increased risk for early and
persistent problems in speech, expressive language, and the phonological
foundations of literacy as well as the possible need for augmentative and
alternative communication and assistive technology. It is useful to comment
briefly on the core elements of this definition.
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As required of any proposed disorder classification, definitions of CAS have
three elements that may be given in any order: description of the core
problem, attribution of its cause or etiology, and listing of one or more
diagnostic signs or markers. Definitions of CAS, such as the one above,
invariably include the proposed core problem, whereas the other two elements
may or may not be addressed. One of the major differences among alternative
definitions of CAS is whether the core problem is proposed to include input
processing as well as production, and if so, whether auditory, sensory, and
prosodic aspects of perception may prefigure in the deficit. An example of a
framework that might implicate the latter is the speech motor control model
in development by Guenther and colleagues (e.g., Guenther, 2006; Guenther
& Perkell, 2004). Whereas some of the definitions of CAS
reviewed by the Committee view the core problem as one of planning and
programming the spatiotemporal properties of movement sequences underlying
speech sound production, others propose that the deficit extends to
representational-level segmental and/or suprasegmental units in both input
processing and production.
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Definitions of CAS have universally ascribed its origin to neurologic
deficits, with alternative viewpoints differing with respect to specific
neuroanatomic sites and circuits. There is also clear agreement that
whatever the neural substrates of CAS, they differ from those underlying the
several types of dysarthria. The definition of CAS proposed for this report
is also clearly consistent with this neurogenic perspective.
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In addition to the core problem and etiology, the third element in the
proposed definition of CAS and those reviewed by the Committee is the
inclusion of the key diagnostic features of the disorder. Three such
features are included in the present definition, with discussion of other
candidate features reviewed in subsequent sections of this report. The three
features in the present definition of CAS represent a consensus conclusion
based on our evaluations of the clinical research and our evaluation of
comments from reviewers of preliminary drafts of this report. A major
conclusion of this report is that there presently is no one validated list
of diagnostic features of CAS that differentiates this disorder from other
types of childhood speech sound disorders, including those apparently due to
phonological-level deficits or neuromuscular disorder (dysarthria).
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As with several other complex neurobehavioral disorders (e.g., autism, attention
deficit hyperactivity disorder), the prevalence of CAS has reportedly increased
substantially during the past decade. For example, in a study of 12,000 to
15,000 estimated diagnostic outcomes for children referred with speech delay of
unknown origin from 1998 to 2004, a staff of 15 speech-language pathologists in
a large metropolitan hospital diagnosed 516 (3.4%–4.3%) of these
children as having suspected CAS (Delaney
& Kent, 2004). Much needed population prevalence data are not
available, including information by race and ethnicity. One preliminary
population estimate, based solely on clinical referral data, is that CAS may
occur in one to two children per thousand (Shriberg, Aram, & Kwiatkowski, 1997a), a population rate
that is much lower than the rate at which this classification currently appears
to be assigned. Although currently there are no epidemiologically sound
estimates of the prevalence of CAS in the United States or elsewhere, several
interacting factors likely contribute to clinical diagnostic figures as high as
those reported by Delaney and Kent (2004).
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One potential source of the apparent increased diagnostic prevalence of CAS
in the past one to two decades is the impact of legislative changes during
this period. Since the passage of early intervention statutes, particularly
the Individuals with Disabilities Education Improvement Act of 2004 (IDEA
'04, Part C), speech-language pathologists are asked to evaluate
and identify communicative disorders as early as possible in infants and
toddlers. A major problem in classifying young prelingual children (i.e.,
children with severe delays in the onset of speech) is that a diagnosis of
CAS must be based on variables other than speech itself. As discussed later
in this report, findings claiming that behaviors such as difficulty in
feeding or excessive drooling are pathognomonic (positive signs) of CAS are
tentative at best. For children suspected to have CAS who do have at least a
moderate inventory of speech sounds, their communication profiles can be
similar to those of children with other speech-language disorders or
neurobehavioral disorders (Davis, Jakielski,
& Marquardt, 1998; Davis
& Velleman, 2000). Thus, although we use the term
CAS for children who are the focus of the research
reviewed in this document, it should be understood that the lack of a gold
standard for differential diagnosis requires that all such classificatory
labels be considered provisional.
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Increased information on a disorder may both reflect and contribute to
increased prevalence. For CAS, the past decade has seen dramatic increases
in both. Interest in CAS is readily apparent when reviewing the increased
number of research symposia (e.g., Shriberg
& Campbell, 2003), clinical workshops, and parent support
groups on CAS. Although there have been no formal accounts describing the
history of this clear trend, it appears to parallel similar development in
other disorders. From an academic perspective, information about CAS has
traditionally been embedded within undergraduate and graduate courses in
speech disorders in children or, more typically, in motor speech disorders
in children and adults. However, for many speech-language pathologists,
applied information on this topic is typically learned in workshops
presented by persons with varying research and clinical backgrounds and/or
experience with children suspected to have CAS. The Committee's
anecdotal observations are that such workshops are currently among the most
widely advertised opportunities for continuing education credits.
The major source of readily available information on CAS is the Internet,
including its numerous Web sites and electronic discussion forums that
include information on this topic. As with other unregulated medical and
health-related information sources, the accuracy and usefulness of
information presented on the Internet varies substantially. Some sites
available internationally provide excellent information, including detailed
guidelines for caregivers seeking service delivery options.
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Speech-language pathologists must be knowledgeable about reimbursement
alternatives and insurance guidelines. Because insurance companies
frequently require that a child have a medical diagnosis to approve
coverage, there may be increased use of CAS as a diagnostic classification
for a severe childhood speech sound disorder. However, insurance claims for
children with this diagnosis may sometimes be denied due to the continuing
controversial status of CAS as a clinical entity and its increased
prevalence in diagnostic coding.
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Clearly the major source of overdiagnosis of CAS is the inconsistent and
conflicting behavioral features purported to be diagnostic signs of CAS
(Shriberg, Campbell, et al.,
2003; Shriberg & McSweeny,
2002). In addition to children who may be misdiagnosed as false
positives (persons said to have a disorder who do not), diagnostic
guidelines also may result in false negatives (persons said not to have a
disorder who do). Later discussion addresses this fundamental issue.
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On the first of four questions motivating this technical report—Is CAS
a clinical entity?—the Committee concludes that the weight of
literature findings support the research utility of this type of speech sound
disorder. A primary research source for this position is the findings on apraxia
of speech that occur as sequelae to a neurological disorder and within a number
of complex neurobehavioral disorders, as noted later in this document. On the
second question of the core features and behavioral markers of CAS, the
Committee proposes a definition of CAS that classifies it as a neurological
disorder affecting the planning/programming of movement sequences for speech.
However, there currently are no lists of behavioral features that are validated
as necessary and sufficient for the diagnosis of CAS, although three general
characteristics are proposed as possible candidates based on our narrative
review and consultation with peer evaluators. On the third and fourth questions,
this report does not include specific guidelines for the assessment and
treatment of CAS, primarily due to the lack of research support to date for such
guidelines. In a section titled Professional Issues, we review general
recommendations by experienced clinical practitioners, but specific guidelines
for clinical practice are deferred to future ASHA policy documents. Finally, we
have noted some issues that may be associated with the recent increase in the
diagnosis of suspected CAS, including birth-to-three legislation, increased
availability and accessibility of information on CAS, reimbursement issues, and
the lack of diagnostic guidelines.
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We begin a review of the scientific foundations of CAS with an overview of typical
and atypical speech acquisition, highlighting those segmental and suprasegmental
behaviors that are frequently studied in CAS research. For example, we include
prelinguistic speech development in each section because children suspected to have
CAS are often reported to not babble at all, to babble less frequently than their
typically developing peers, or to produce less mature, complex babble. Thus, a
review of these foundational prelinguistic behaviors and their implications for
later speech-language development seems warranted. In addition to delays in reaching
developmental milestones, children suspected to have CAS may follow idiosyncratic
developmental paths. For this reason, reference to typical milestones may be useful
for diagnosis (i.e., atypical profiles may be suggestive of CAS).
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In any discussion of speech motor control, or speech production generally,
the terms variable and inconsistent are
likely to arise. They are often used interchangeably and without precise
definitions. This is of particular concern with respect to CAS, as some
clinical investigators use inconsistency as a key
classification criterion for the disorder. Some common uses of
variable and inconsistent include the
differential use of a certain phoneme or sound class in different
word positions (e.g., the child produces /k/ accurately in final
position but substitutes [t] for /k/ in prevocalic
differential use of a certain phoneme or sound class in different
word targets, even in the same word position (e.g., the child
produces /m/ accurately in certain well-rehearsed words such as
“mommy,” but does not produce it
accurately in similar or even seemingly easier words such as
differential use of a certain phoneme or sound class in multiple
repetitions of the same word (e.g., the child produces
“fish” once as
“pish”, once as
“pit”, once as
“fit”, and another time as
“shiff”). This may include measures of the
number of different errors the child made in the word (e.g., in
the example above, errors consisted of stopping of /f/, stopping
of /∫/, and metathesis) or measures of the frequency
at which a given error type is used (e.g., in the example above,
stopping was the most consistent error type because stopping was
used four times, and metathesis only once). This type of
inconsistency is sometimes referred to as
“token-to-token variability” (Seddoh et al., 1996).
Except where specified otherwise within in this document,
inconsistency refers to differences in multiple
productions of the same target word or syllable (i.e., token-to-token
variability). Variability is used elsewhere, when meaning 1
or meaning 2, or more than one of the above meanings, is included within the
findings being reported or when parameters other than speech production
(e.g., pitch) are being discussed.
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Beginning this review with research on typical oral-motor development,
studies indicate that jaw control is established by about 15 months, before
control is established for the upper and lower lips (Green, Moore, Higashikawa, & Steeve, 2000;
Green, Moore, & Reilly,
2002). Motor development is slower for structures, such as the lips,
that have more degrees of freedom of movement (Green et al., 2002). Tongue development is also
gradual, with extrinsic tongue movements necessary for swallowing and
sucking developed prior to the intrinsic tongue movements required for fine
motor control (S. G. Fletcher, 1973;
Kahane, 1988). Such findings are
hypothesized to account for the high frequency of occurrence of
infants' production of syllables that can be articulated without
changes in lip or tongue configuration—including labial
consonants with low and neutral vowels, coronal (alveolar and dental)
consonants with high front vowels, and dorsal (velar) consonants with high
back vowels (Davis & MacNeilage,
1995; MacNeilage & Davis,
1990). The high prevalence of such syllables is claimed to be
associated with infants' early ability to open and close the jaw,
creating the consonant-vowel alternation necessary for the syllable, with
the lower lip (for labials) or the tongue (for alveolars and velars)
essentially “going along for the ride.” Some clinical
reports indicate that these immature patterns may persist in children
suspected to have CAS (Velleman,
Through processes of differentiation and refinement, the slightly older child
acquires independent control over individual articulators (lips, different
portions of the tongue) and learns to produce more specialized
configurations to grade movements, eventually sequencing these articulatory
postures without extraneous movements (Davis
& MacNeilage, 2000; Green
et al., 2000). Thus, automaticity and flexibility develop over
time. Both neuromotor maturation and practice are believed to underlie this
developmental process, with vocal experience leading to the formation of
specific neuronal pathways for finer levels of control (Green et al., 2000). Coarticulation that reflects poor
temporal control or poor differentiation of structures decreases, whereas
coarticulation that reflects language-specific efficiency increases, as the
child becomes more adept (Nijland et al.,
2002; Nijland, Maassen, van der
Meulen, et al., 2003). One model of the role of perception in
this process was provided by Guenther and colleagues (e.g., Guenther, 2006; Guenther & Perkell, 2004). In a following
section, we will see that these developmental changes may not occur
spontaneously in children suspected to have CAS.
In the present context it is especially relevant to note that mastication and
deglutition (swallowing) skills are not direct precursors to speech. Motor
control of feeding functions is separate from motor control for vocalization
early in infancy (Moore & Ruark,
1996), as is motor control for speech breathing versus breathing
at rest (Moore, Caulfield, & Green,
2001). Although “the labiomandibular movement patterns
established for feeding may influence initial attempts to coordinate these
structures for speech” (Green et
al., 2000, p. 252), this influence is more likely to be negative
than positive, as feeding patterns involve tight linking of lips with jaw in
a highly rhythmic stereotyped pattern. To produce a variety of syllables
within varied prosodic patterns requires the child to overcome the
interdependent inflexible patterns associated with sucking. Speech requires
finer levels of coordination (Green et al.,
2000) but lower levels of strength than are available for other
oral-motor activities (Forrest, 2002).
Thus, a consensus opinion among investigators is that nonspeech oromotor
therapy is not necessary or sufficient for improved speech production (see
also Professional Issues: Treatment).
When children reach middle school age and even beyond, their speech
production continues to be more variable, less flexible, and less accurate
than adult speech. Variability is especially noted during the initial
portion of speech or speech-like movements, with more feedback required for
unfamiliar speech tasks (Clark, Robin,
McCullagh, & Schmidt, 2001). Furthermore, as discussed in
Clark et al., children's speech may be constrained by resource
allocation needs, such as the need to scale back the extent of a movement in
order to complete it more quickly. For example, children between the ages of
5 and 6 years are able to partially compensate for the presence of a bite
block between their teeth without an increase in variability or a change in
coarticulation patterns, although vowel accuracy is decreased somewhat and
segment durations are increased (Nijland,
Maassen, & van der Meulen, 2003). Maximum performance
rates have been shown to increase with age, with changes from 3.7 same
syllable repetitions of /pΛ/ per second and only 1.3 repetitions
of “patty-cake” at age 2;6–2;11
[years;months] to 5.5 same syllable repetitions and 1.6 repetitions of
“patty-cake” at age 6;6–6;11 (Robbins & Klee, 1987). Maximum
performance rates continue to increase with maturity, with young adult same
syllable repetitions typically reported at average rates between 6 and 7 per
second and 5.8 to 6.9 repetitions per second of
/pΛtΛkΛ/ (Baken & Orlikoff, 2000). However, Williams and
Stackhouse (1998, 2000) reported that rate of speech may
be a less reliable measure of motor control in preschool children than
accuracy and consistency of response. Again, many of the core questions
about CAS address the possibility that children suspected to have CAS have
different developmental trajectories on these and other motor control
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Speech development begins long before the first word is spoken. Development
of this system occurs as a child gains motor control of the speech mechanism
and learns the phonological rules for production of the ambient language or
languages. Prelinguistic perceptual and vocal experiences lay the groundwork
for later speech and language. For example, the frequency of a
child's vocalizations at 3–6 months is correlated with
several later developmental milestones, including performance on the Bayley
Verbal Scale at 11–15 months and expressive vocabulary size at 27
months (Stoel-Gammon, 1992).
One of the most important motor precursors to first oral words is canonical
babbling, the rhythmic production of repetitive consonant-vowel (CV)
sequences with complete consonant closures and fully resonant vowels (Ejiri, 1998; Oller, 1986). The frequency of occurrence of
“true” supraglottal nonglide consonants in babble is
positively correlated with phonological development and even with language
skills (Stoel-Gammon, 1992). Children
who demonstrate consistent vocal motor schemes, or favorite babbles, tend to
develop words earlier (McCune &
Vihman, 1987). Children suspected to have CAS who are reported by
their parents to have babbled very little or with very little phonetic
diversity (Davis & Velleman,
2000) are at a linguistic disadvantage long before word production
begins. The frequency and characteristics of early vocalizations also can be
affected by perceptual factors such as early otitis media with effusion
(Petinou, Schwartz, Mody, &
Gravel, 1999; Rvachew, Slawinski,
Williams, & Green, 1999), as well as by physiological and
other factors (see Kent, 2000).
Research suggests that the earliest stages of speech development in
monolingual and bilingual speakers are highly similar regardless of language
environment (Buhr, 1980; Davis & MacNeilage, 1995; Gonzalez, 1983; Kent, 1992; Locke
& Pearson, 1992; MacNeilage & Davis, 1990; Oller & Eilers, 1982; Poulin-Dubois & Goodz, 2001; Thevenin, Eilers, Oller, & Lavoie,
1985; Zlatic, MacNeilage,
Matyear, & Davis, 1997). Babbling includes stops, nasals,
and glides at the labial and coronal places of articulation (Davis & MacNeilage, 1995; Kent & Bauer, 1985; Locke, 1983; Oller, Eilers, Urbano, & Cobo-Lewis, 1997),
nonrounded vowels (Davis &
MacNeilage, 1990; Kent &
Bauer, 1985; Levitt &
Aydelott-Utman, 1992), and simple CV and CVCV syllable shapes
(Boysson-Bardies, Sagart, &
Bacri, 1981; Buhr, 1980;
Oller & Eilers, 1982;
Vihman, Ferguson, & Elbert,
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In the first linguistic stage, from 12 to 18 months, babbling decreases and
word production increases. While slight differences in frequencies of sounds
and word shapes are reported cross-linguistically (Boysson-Bardies & Vihman, 1991; Maneva & Genesee, 2002), the
considerable cross-linguistic similarities observed in babbling also exist
in first words. Children from various language environments mainly produce
coronal and labial stops, nasals, and glides, and simple CV syllable shapes
in their first words (Boysson-Bardies
& Vihman, 1991; Eilers,
Oller, & Benito-García, 1984; Gildersleeve-Neumann, 2001; Goldstein & Cintrón,
2001; Oller, Wieman, Doyle, &
Ross, 1976; Teixeira &
Davis, 2002; Vihman et al.,
1986). In addition, limited research on English-learning infants and
infants in other monolingual language environments suggests that low front,
non-rounded vowels are most frequent in first words (Davis & MacNeilage, 1990; Gildersleeve-Neumann, 2001; Levitt & Aydelott-Utman, 1992; So & Dodd, 1995; Stoel-Gammon & Dunn, 1985;
Teixeira & Davis, 2002).
Research on sounds in the first words of simultaneous bilinguals is
extremely limited; however, it appears that similar consonants (Keshavarz & Ingram, 2002) and
word shapes (Kehoe & Lleo,
2003) predominate. Information is not currently available on possible
Children's early speech patterns include phonotactic errors such as
reduplication (e.g., “wawa” for
“water”), consonant harmony (e.g.,
“goggie” for “doggie”), and
final consonant deletion (e.g., “da” for
“dog”) during their first 12–18 months of
word production; these error patterns typically are markedly diminished by 3
years of age in children who are typically developing, although not, as
reviewed later, in children suspected to have CAS. Apparent regression, in
which the child produces a word less accurately but also with less
variability than before, may also occur during the first year of word
production as children systematize their phonologies (Vihman & Velleman, 1989). Individual sounds
may be produced variably, even within the same word, although speech
production patterns (i.e., frequent phonological processes) are consistent
(Demuth, 2001; Ferguson & Farwell, 1975; Taelman & Gillis, 2002; Velleman & Vihman, 2002).
Between the ages of 2 and 3 years, the speech sound system of typically
developing children expands in complexity, resulting in productions of a
greater variety of consonants, vowels/diphthongs, and word shapes. By this
age, children in English-learning environments begin to produce the more
complex sounds—velars, fricatives, affricates, and
liquids—generally mastering the majority of sounds with these
features by approximately 5 years of age (Stoel-Gammon & Dunn, 1985). The few studies that have
examined vowel and diphthong development suggest that accurate production of
all vowels and most diphthongs (but not rhotic vowels) is achieved by age 3
(Bassi, 1983; Larkins, 1983; Pollock
& Berni, 2003). In Pollock and Berni's study,
the average percentage of vowels correct for children between 18 and 23
months was 82%, increasing to 92% for 24- to 29-month-olds, 94% for 30- to
35-month-olds, and 97% by 36 months of age. As subsequently discussed, the
picture is very different for children suspected to have CAS. For typically
developing children, more complex word shapes become frequent during this
early period, with many consonant clusters, final consonants, and unstressed
syllables correctly produced, resulting in a large increase in accuracy and
intelligibility (Stoel-Gammon &
Dunn, 1985). Consonant clusters emerge by the first third of the
fourth year (36–40 months), usually appearing first in final
position in speakers of Mainstream American English (Kirk & Demuth, 2003). Typically developing
children are reportedly 26%–50% intelligible by 2 years,
71%–80% intelligible by 3 years, and 100% intelligible by 4 years
(Coplan & Gleason, 1988;
Weiss, 1982). It is also after
age 2 that the diverse effects of a child's ambient language become
most apparent (see below; Goldstein &
Washington, 2001; Johnson
& Wilson, 2002; Walters,
In typical and most atypical, nonapraxic speech during this age period,
earlier developing sounds tend to be substituted for later developing sounds
that the child may not be able to produce as easily (e.g., stops substitute
for fricatives and glides substitute for liquids). Children with nonapraxic
speech sound disorders appear to be most successful at producing the correct
voicing features of a segment and least successful at maintaining the
correct place of articulation (Forrest
& Morrisette, 1999). Although perceptual and articulatory
constraints are the primary posited source of English-learning
children's difficulty with affricates, fricatives, and liquids, the
frequency of sounds in a particular environment also plays an important role
in the age and order of phoneme mastery. Children from language environments
with a greater frequency of occurrence of certain less universally common
sounds (e.g., liquids, fricatives) tend to produce these sounds earlier and
better, suggesting the early influence of the ambient language. For example,
Russian children who are exposed to many palatalized consonants as well as
non-palatalized consonants typically master the palatalized ones first
(Zharkova, 2004). Other research
in non-English monolingual language environments has shown ambient language
effects on the greater earlier accuracy of fricatives and affricates (Pye, Ingram, & List, 1987) as
well as dorsal sounds and multisyllabic words (Gildersleeve-Neumann, 2001; Teixeira & Davis, 2002). In addition, children
in other language environments may produce words with different error
patterns. For instance, it is common for young Finnish children to have
initial consonant deletions, an atypical phonological process in
English-speech acquisition (Vihman &
Ambient language effects on speech sound acquisition are also observed in
bilingual children. Bilingual children may show an effect of each language
on their productions within that language, such as reported for a
Hindi-English simultaneous bilingual child who used predominantly
monosyllables in English and predominantly disyllables in Hindi (Bhaya Nair, 1991; Vihman & Croft, in press).
Simultaneously bilingual children produce different segments and word shapes
depending on which of their two language environments they are in (Holm & Dodd, 1999; Holm, Dodd, Stow, & Pert, 1999;
Johnson & Lancaster,
1998; Kehoe & Lleo,
2003; Keshavarz & Ingram,
2002). Mixing of errors has been observed in the carryover of the
phonetic and phonological properties of one language to the other, resulting
in greater rates of error when compared to monolingual peers (Goldstein & Cintrón,
2001). Although bilingual children may follow the general
developmental path, their speech patterns might still be expected to be
influenced by the phonology/ies of their native language(s). Clearly, the
large, cross-linguistic literature on typical and atypical speech sound
acquisition provides a rich database for comparative research on speech
development in children suspected to have CAS.
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Infants' early discrimination of prosody (see Speech Perception) is
followed by production of language-specific prosodic patterns. By
6–12 months, their vocalization patterns reflect the dominant
prosodic contours (e.g., falling vs. rising pitch; Whalen, Levitt, & Wang, 1991) of the ambient
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English-speaking children use falling intonation contours first, then rising
contours, to mark phrase and utterance boundaries (Tonkava-Yampolskaya, 1973). Typical English-learning
children have been shown to use frequency, amplitude, and duration
appropriately to mark sentential emphasis (Skinder, Strand, & Mignerey, 1999), as do children with
speech delays (Shriberg, Aram, &
Kwiatkowski, 1997b, 1997c). The primary period for the development of prosody occurs
from approximately 5 to 8 years of age (Local, 1980; Wells, Peppe,
& Goulandris, 2004). However, even typically developing
children may not have adultlike comprehension and production of prosody
until 10 or 12 years of age (Allen &
Hawkins, 1980; Morton &
Trehub, 2001). In English, later-developing prosodic functions
include the production of compound words, rise-fall or fall-rise prosody on
a single word to convey emotion, high rising pitch to request clarification,
accent on a nonfinal word to convey emphasis (e.g., “I want a
black bus”), and the comprehension of
another person's use of accent to emphasize a certain part of an
utterance (Wells et al., 2004).
Children's stress patterns parallel the dominant stress patterns of
their languages in late babbling and early words (e.g., predominantly
trochaic stress-first patterns in English; iambic stress-last patterns in
French; Vihman, DePaolis, & Davis,
1998). By 2½ years of age, English learners'
vowel durations differ appropriately in stressed versus unstressed syllables
(Smith, 1978), and they are able
to produce weak syllables in initial position (e.g., the first syllable of
“giraffe”) and between two stressed syllables (e.g.,
the second syllable of “telephone”; Gerken, 1994; Kehoe & Stoel-Gammon, 1997). Children with
speech delay but not apraxia cease to delete such weak syllables by age 6
(Velleman & Shriberg,
1999); as reviewed later, children suspected to have CAS may persist
in such patterns. By age 6, typically developing children have different
coarticulatory and temporal patterns depending on the syllable structure of
a word. For example, Dutch-learning children have coarticulation and
duration patterns that differ with the metrical structure of the word (Maassen, Nijland, & van der Meulen,
2001; Nijland, Maassen, van der
Meulen, et al., 2003).
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Between birth and 2 months of age, human beings are already able to
discriminate among languages with different rhythmic patterns (Mehler et al., 1988), among words that
differ by number of syllables (Bijelac-Babic,
Bertoncini, & Mehler, 1993), and among different vowels
(Kuhl & Miller, 1975) and
different consonants (Eilers, 1977;
Eilers & Minifie, 1975;
Jusczyk, Murray, & Bayly,
1979; Levitt, Jusczyk, Murray,
& Carden, 1988). Some of these capacities may be innate,
but others are learned through perceptual experience. For example, the
neonate attends longer to her own mother's voice (DeCasper & Fifer, 1980) and to
her own language prosody in conversational speech (Mehler et al., 1988). Speech perception skills become
more and more language-specific as the child approaches 1 year of age. By 10
months, infants display preferences for stress patterns (Jusczyk, Cutler, & Redanz,
1993; Morgan, 1996; Weissenborn, Hohle, Bartels, Herold, &
Hofmann, 2002), consonants, and sequences of consonants and
vowels from their own language (Gerken
& Zamuner, 2004; Jusczyk,
Friederici, Wessels, Svenkerud, & Jusczyk, 1993; Jusczyk, Luce, & Charles-Luce,
1994). Furthermore, at 10–12 months, babies are less able
than at earlier ages to discriminate segmental contrasts that are not
relevant to their own languages (Werker
& Tees, 1984).
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At 4 years of age, children with nonapraxic speech disorders are
significantly worse than their typically speaking peers at discriminating
commonly misarticulated sounds from sounds that are generally substituted
for them. There is a significant difference between the two groups'
ability to identify whether a sound was produced correctly versus
incorrectly within a word (e.g., [tæt] vs. [kæt] for
Ohberg, Grawberg, & Heyding, 2003).
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Children with speech delay often also have language delays, especially in
expressive morphology (Paul & Shriberg,
1982; Rvachew, Gaines, Cloutier,
& Blanchet, 2005). Their morphological errors cannot be
attributed to speech difficulty. For example, Rvachew et al. reported that
children with speech delay omitted /s/ and /z/ in final position more often in
grammatical morphemes (plural, third person singular) than in uninflected words
even though the phonetic complexity was the same in both contexts. Furthermore,
frequency of omission of morphemes was correlated with mean length of utterance
([MLU] in words), not with articulatory skills.
A few studies have investigated profiles of children with speech delay only
versus those who also have language delay. In a study of 15 children with speech
delay only and 14 children with both speech and language delay, Lewis,
Freebairn, Hansen, Iyengar, and Taylor (2004) reported that the speech patterns of the two groups were similar
at school age (ages 8–10 years), with frequent liquid simplifications
and distortion errors. The speech delay only group persisted in immature
consonant harmony/assimilation errors, whereas the speech and language delay
group produced frequent final consonant deletions, which, although not described
in this study, may have been associated with morphological deficits. As part of
a larger study, Nathan, Stackhouse, Goulandris, and Snowling (2004) followed 19 children with speech
delay only and 19 children with both speech and language delay from preschool
(age 4;6) through kindergarten (age 5;8) to school age (age 6;9). In preschool,
the speech delayed only group performed better overall on articulation
assessments as well as on language measures. At the two later ages, the children
with speech delay only seemed to have normalized (caught up to typically
developing peers), whereas the deficits of the speech and language delay group
persisted. To date, there are no studies that have systematically compared
specific language patterns (e.g., morphological vs. syntactic errors) in
children with language delay only to those of children with both speech and
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Studies indicate that at age 4, children with speech delay are at higher risk for
impaired phonological awareness skills (e.g., rhyme matching, onset
segmentation, onset matching) compared to children who are typically developing,
although in one such study significant differences between the two
groups' early literacy skills were not detected (Rvachew et al., 2003). Between the ages of 6 and 8 years
of age, children without speech sound or language disorders develop the
metalinguistic ability to explicitly identify the number of syllables in a word
and the placement of individual sounds or clusters within words (Marquardt, Sussman, Snow, & Jacks,
2002). Children with a familial history of speech delay/disorder
(including those with CAS, as discussed in the following section) are at higher
risk for literacy difficulties, especially if they also demonstrate language
delay (Bird, Bishop, & Freeman,
1995; Larrivee & Catts,
1999; Lewis et al., 2004; Nathan et al., 2004; Webster & Plante, 1992). In a study of 47 children
with speech deficits only (reportedly including CAS), speech and language
deficits, or no speech or language deficits, Nathan et al. reported that
preschool language ability, especially for expressive language, is a strong
predictor of later phonemic awareness skills. These investigators also found
that persistent speech difficulties (beyond age 6;9) are strongly predicted by
concurrent deficits in phonemic awareness. An ASHA document (ASHA, 2001) includes useful information about
phonological awareness development and disorders.
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The large literature on typically developing speech has been reviewed from the
perspective of the key areas of possible developmental differences between
children who are typically developing, children with nonapraxic speech sound
disorders, and children diagnosed with CAS. The goal was to provide a reference
basis for the review of CAS literature to follow. Notable areas of difference
were found in the early and seemingly effortless development of vowels and
prosody in children who do not have CAS. Important areas of overlap in the
speech of typical learners and children suspected to have CAS include the
gradual development of consonant repertoires and phonotactic structures
(syllable and word shapes) and gradual decreases in both variability and
inconsistency. Research indicates that children with any type of speech sound
disorder are at increased risk for language and literacy difficulties, although
the literature reviewed in the next section indicates that children suspected to
have CAS may be at considerably greater risk.
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Studies of the developmental neurobiology of CAS are expected to provide an
understanding of the relevant neural substrates and identify useful early diagnostic
biomarkers. Even when such information becomes available, speech-language
pathologists will still need to use behavioral tools (e.g., standardized tests,
informal assessment measures, parental observations, reports from other
professionals) to provide the individualized profiles needed to differentiate
children suspected to have CAS from children with other types of speech-language
disorders. To date, as previewed in the Introduction and Overview, no one test score
or behavioral characteristic has been validated to differentially diagnose CAS
(i.e., there are no necessary and sufficient markers). The present section provides
an extended review of behavioral research in CAS.
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In both research and clinical settings, the diagnostic challenge is to
differentiate CAS from speech delay, dysarthria, and other speech sound
disorders. Many of the speech and other behaviors (i.e., signs)
thought to be associated with CAS are also found in children with more broadly
defined speech sound disorders (McCabe,
Rosenthal, & McLeod, 1998). The differentiation between
apraxia and dysfluency (stuttering, cluttering) is a less common clinical need,
although there are some behavioral overlaps and children suspected to have CAS
may go through periods of dysfluency (Byrd
& Cooper, 1989). The question of differentiating language
behaviors occurring in CAS from those in specific language impairment (SLI) is
also highly challenging, a question that has only recently begun to be addressed
in the clinical literature (Lewis et al.,
Behavioral variables that have been studied in association with CAS can be
divided into six major domains: nonspeech motor, speech production, prosody,
speech perception, language, and metalinguistic/literacy. Within each of these
domains, reference is made to core deficits in timing, programming, and
sensorimotor coordination. However, due to the lack of a definitive diagnostic
marker for CAS, conclusions from studies seeking to identify such markers are
limited by issues of participant selection and circularity. When study
participants are selected based solely on clinician referrals, it is difficult
to determine which diagnostic criteria were used by individual clinicians, how
clinicians differentially weighted their criteria, and the amount of agreement
within and between clinicians. In fact, clinical agreement has not been
demonstrated in recent studies. Davis et al. (1998) and Forrest (2003)
reported high degrees of clinical disagreement among practicing speech-language
pathologists in their criteria for diagnosing CAS. There are similar problems in
research contexts. In a recent CAS study, two research teams were able to reach
only 55% agreement on the assignment of 35 speech sound disordered study
participants to CAS or non-CAS groups (Shriberg,
Campbell, et al., 2003). This diagnostic uncertainty among both
clinicians and researchers is the primary barrier to research on the underlying
nature of CAS. As suggested by Strand (2001), another significant research constraint is the heterogeneity of
children with CAS due to the co-occurrence of other disorders with CAS, as well
as individual differences in compensatory behaviors that may be secondary to the
Definitional circularity is most evident when study participants are selected
based on the presence of certain signs and those signs or derivatives of them
are part of the study's descriptive findings. Because of the presumed
low prevalence of CAS, it is difficult to conduct large scale studies of
children with etiologically undifferentiated speech sound disorders hoping to
identify speech and other characteristics unique to CAS. Moreover, there is
increasing evidence that the signs of CAS not only vary among children with the
disorder, but also change as children mature (Lewis et al., 2004; Shriberg,
Campbell, et al., 2003). Thus, although there may be neural
phenotypes that persist beyond the developmental period, it is likely that
behavioral markers will need to be developed for several developmental epochs.
CAS may be a complex of signs, with varying neurologic, motor, and behavioral
characteristics that can be identified only by its unique profile over time
(Ekelman & Aram, 1983). It is
vital not to confuse descriptions with explanations; the varying behavioral
consequences of a disorder can obscure as well as clarify its fundamental
nature. Within each of the six behavioral domains listed above, we report
findings supporting associations with CAS, followed by some perspectives on
theories of CAS.
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Nonspeech motor behaviors are primarily used to differentiate children
suspected to have CAS from children with various types of dysarthria,
although there is some overlap between the two motor speech disorders.
Nonspeech motor signs of CAS that are most commonly proposed in the
literature (some of which are also cited as signs of dysarthria) include the
following: general awkwardness or clumsiness, impaired volitional oral
movements, mild delays in motor development, mildly low muscle tone,
abnormal orosensory perception (hyper- or hyposensitivity in the oral area),
and oral apraxia (e.g., Davis et al.,
1998; McCabe et al., 1998;
Shriberg et al., 1997a). The
nonspeech motor features typically listed for oral apraxia are impaired
volitional oral movements (imitated or elicited postures or sequences such
as “smile-kiss”) and groping (e.g., Davis et al., 1998; McCabe et al., 1998; Shriberg et al., 1997a). Murdoch, Attard, Ozanne, and Stokes
(1995) documented weaker lingual
muscles and reduced tongue endurance in children who demonstrated oral
apraxia than in typically developing children; a nonapraxic, phonologically
disordered control group was not included in the study. Dewey, Roy,
Square-Storer, and Hayden (1988) found
that limb, oral, and verbal apraxia tend to co-occur in children. They
highlighted the transition difficulties (moving from one action in a
sequence to the next) exhibited by children “with a specific
deficit in verbal sequences of consonantvowel syllables” (p. 743)
and noted that repetition of the same action was far less of a problem. They
also stressed the volitional aspect of the disorder, as did Maassen,
Groenen, and Crul (2003) and D.
Nelson (1995). Specifically, Dewey et
al. (1988) found that demonstrating
the action of an object was a problem for their participants with CAS only
when the children were miming the action without the object in hand. Crary
and Anderson (1991) also noted that
compared to children without a diagnosis of CAS, children with this
diagnosis had slower rates and less accurate performance on sequences of
hand and facial movements.
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Motoric aspects of speech, especially repetitions of
syllables (maximum repetition rate [MRR]) and productions
of alternating syllables (diadochokinesis [DDK] or alternating
motion rate [AMR]), are commonly used to diagnose CAS both clinically and
for research participant selection. The utility of these measures has been
verified in several research studies, including Davis et al. (1998), McCabe et al. (1998), Nijland et al. (2002), Thoonen, Maassen,
Gabreëls, and Schreuder (1999), and Thoonen, Maassen, Wit, Gabreëls, and Schreuder
(1996). Thoonen et al. (1996), for example, reported that
maximum sound prolongation of vowels (e.g., producing /a/ for as long as
possible) and MRRs for single syllables (e.g.,
/pΛtΛkΛ/ etc.) differentiated children with
a diagnosis of spastic dysarthria from both children with a CAS diagnosis
and those who were typically developing. Maximum sound prolongation of
fricatives and maximum repetition rate of trisyllabic sequences
(/pΛtΛkΛ/) differentiated children with
apraxia from those who were typically developing. Thus, the differences
between children with CAS and those who were typically developing were only
significant for the more complex tasks (prolongations of more difficult
consonant sounds; sequences of different syllables). Control groups of
children with other speech sound disorders of unknown origin were not
tested. Lewis et al. (2004) found
significant differences between preschool and school-age children with CAS
and matched children with non-CAS speech delay in their ability to repeat
nonwords and multisyllabic words, with the CAS group performing more poorly.
Children with CAS also had significantly lower Total Function scores on the
Robbins and Klee (1987) oral-motor
assessment, which includes DDK. Moreover, children with CAS had more
difficulty on the Fletcher Time-by-Count test of DDK (S. G. Fletcher, 1978) at school age.
Lists of the speech behaviors proposed to characterize CAS abound in the
research and clinical literatures. Frequent characteristics include some
features that clearly are shared with other speech sound disorders (McCabe et al., 1998), including slow
development of speech, reduced phonetic or phonemic inventories, multiple
speech sound errors, reduced percentage of consonants correct, and
unintelligibility. Commonly proposed characteristics (Davis et al., 1998; McCabe et al., 1998; Shriberg et
al., 1997a) that are less likely to be found in children with
nonapraxic speech sound disorders include reduced vowel inventory, vowel
errors, inconsistency of errors, increased errors in longer or more complex
syllable and word shapes (especially omissions, particularly in word-initial
position), groping, unusual errors that “defy process
analysis,” persistent or frequent regression (e.g., loss of words
or sounds that were previously mastered), differences in performance of
automatic (overlearned) versus volitional (spontaneous or elicited)
activities, with volitional activities more affected, and errors in the
ordering of sounds (migration and metathesis), syllables, morphemes, or even
words. However, many of these features are found in children who do not fit
the overall pattern of CAS (McCabe et al.,
1998), leading some reviewers to question their diagnostic
specificity for CAS (e.g., Macaluso-Haynes,
1978). Moreover, as discussed later, many of these posited
features are not consistent with a deficit in praxis. For example, motor
speech theories typically assign selection and sequencing of sounds,
syllables, and words to a processing stage that precedes
the planning and programming of movements needed to realize these units as
manifest speech. Error patterns that are not consistent with a praxis
deficit but are especially common in children suspected to have CAS need to
be studied to understand whether or not they are causally related and, if
they are, to identify the explanatory mechanisms.
Detailed studies of differences between children suspected to have CAS
compared to those with typical development or with other subtypes of speech
delay have sought to identify the diagnostic characteristics of CAS. As
noted previously, all such studies have research design limitations due to
the lack of certainty that the children suspected to have CAS indeed have
this disorder. As just one of many examples, Maassen et al. (2001) reported that children with CAS
have less predictable speech errors than children who are typically
developing. These authors provided useful acoustic data documenting a lack
of systematic effects of given phonetic contexts on certain sounds in the
speech production of children with CAS. However, because of the absence of a
control group of children with other speech sound disorders and because the
only inclusionary criterion information provided was that “Clear
cases of [CAS] were selected according to clinical criteria described by
Hall, Jordan, and Robin (1993) and
Thoonen et al. (1996)”
(Maassen et al., 2001, p. 146),
it is difficult to evaluate claims that variability of this type may be a
unique feature of CAS.
Speech sampling methods may also be crucial to interpretation of findings.
Shriberg et al. (1997b) reported that
a group of children, chosen by five individual researchers as exemplars of
these researchers' diagnosis of CAS, did not have any speech
production errors in conversational speech that could be used to
differentiate them from control children with speech delay of unknown
origin. A potential constraint on these findings, as discussed more recently
in Shriberg, Campbell, et al. (2003),
is that these findings were based on conversational speech samples, rather
than on children's responses to challenging speech production tasks
designed to evoke more discriminative error patterns.
In a widely cited study of speech motor behaviors, McCabe et al. (1998) attempted to identify potential
features of apraxia retrospectively (from clinic files) in a mixed group of
50 children with speech disorders, 9 of whom had been identified as having
apraxia of speech by their speech-language pathologists. They described
characteristics of CAS in some of the 50 children who had been classified as
speech disordered (non-CAS). The characteristics most often identified in
the total group were “changed level of awareness of own speech
errors, problems with imitation of speech, breathing
difficulties/asthma/allergies, decreased performance on DDK tasks, and
presence of ‘soft’ neurological signs or minimal brain
damage” (McCabe et al.,
1998, p. 113). These were also the most commonly reported symptoms in
the subset of children who previously had been identified by their
speech-language pathologists as having apraxia. However, McCabe et al.
reported “inconsistent speech performance,” vowel
errors, and incorrect production of “lingual phonemes”
(/l/, /r/) as best differentiating this CAS group from their other
participants. Other differences that distinguished the two groups
quantitatively included slow development of speech, idiosyncratic sound
substitutions, and syllable omissions.
Lewis et al. (2004) compared a group
of children suspected to have CAS to two other groups of children
longitudinally: one group with non-CAS speech sound disorders only and one
group with both speech and language disorders. The CAS group was selected
based on both a diagnosis of CAS by the child's speech-language
pathologist and on the child meeting at least four out of eight criteria for
CAS. The CAS group differed from the speech disorder group, especially at
school age, on syllable structures, sound sequencing, vowel and voicing
errors, unusual types of errors, and the persistence of their error
patterns. At school age, the children with CAS had more speech errors
overall, more unusual errors, and more syllable sequencing errors in
conversational speech than the children with both speech and language
disorders (but see McNeil, Robin, &
Schmidt, 1997, for an alternative interpretation of phoneme-level
sequencing errors in AOS).
Ball, Bernthal, and Beukelman (2002)
used a very careful procedure to identify participants with CAS, including
diagnosis by a speech-language pathologist and administration of the
Screening Test for Developmental Apraxia of Speech (Blakeley, 1980) and the Tasks for Assessing Motor
Speech Programming Capacity (Wertz,
LaPointe, & Rosenbeck, 1984). A panel of three
speech-language pathologists then rated each child on a scale of 1
(not CAS) to 5 (definitely CAS) based
on a list of 17 characteristics of CAS. The 36 children included in the
study each had an average rating of at least 3. They also had other
co-occurring language, social, and behavioral impairments. The purpose of
the study was to attempt to identify more inclusive communication profiles
of children with CAS. Following this identification procedure, an assessment
battery of tests and measures was administered to the participants, and test
results were subjected to cluster analysis to identify groups of
participants who shared particular patterns of communication performance.
Twelve of the participants who had been rated as having a high
likelihood/severity of CAS had notable deficits in the following areas
compared to participants in the other clusters: receptive language,
vocabulary, MLU, percentage of consonants correct, intelligibility, and
Acoustic analyses have been used by several authors to characterize more
precisely the speech production differences of children with CAS.
Participants with CAS in these studies have demonstrated decreased
differentiation of stop place of articulation (Sussman, Marquardt, & Doyle, 2000), decreased
differentiation of vowels (Nijland et al.,
2002), higher degrees of anticipatory coarticulation within
syllables (Maassen et al., 2001;
Nijland, Maassen, van der Meulen, et
al., 2003), lack of impact of syllable boundaries or syllable
shape on coarticulation (Maassen et al.,
2001; Nijland, Maassen, van der
Meulen, et al., 2003), lack of intersyllabic coarticulation, and
variable idiosyncratic patterns (Nijland et
al., 2002) that were less predictable acoustically in any given
phonetic context (Maassen et al.,
2001). Nijland, Maassen, van der Meulen, et al. (2003) further noted that children with CAS had higher
scores than typically developing children on measures of coarticulation and
vowel accuracy when a bite block was placed between their teeth. As noted
previously, additional studies using control groups of children with other
forms of speech delay would strengthen the claims of this carefully executed
With respect to severity, McCabe et al. (1998) found that severity of speech impairment, as defined by the
percentage of consonants correct, is correlated with the number of features
of CAS that a child exhibits even among children without this diagnosis and
that CAS may be quantified on a continuum of severity as measured in this
way. Relative to prognosis, Lewis et al. (2004) reported that, at school age, participants with CAS had
more persistent difficulties in repeating nonsense words and sequencing
syllables than participants who had previously been diagnosed with a non-CAS
speech sound disorder.
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A consistent finding in the literature is that individuals suspected to have
CAS have atypical prosody, including a variety of types of prosodic deficits
(Davis et al., 1998; McCabe et al., 1998; Shriberg et al., 1997a). Also often
noted are variations in rate, including both prolonged sounds and prolonged
pauses between sounds, syllables, or words, which gives the listener the
impression of staccato speech (syllable segregation), with
sounds, syllables, or words produced as independent entities lacking smooth
transitions to other structural units (Shriberg, Green, Campbell, McSweeny, & Scheer, 2003). As
in other motor speech disorders, reduced range of or variable pitch, as well
as reduced range of or variable loudness, gives the listener the impression
of monotone, monoloud speech, respectively. Variable nasal resonance
(sometimes hyponasal, sometimes hypernasal) has also been noted in the
clinical research literature. Duration, pitch, and loudness combine to form
the percept of stress in English; this, too, is commonly reported to be
atypical in children suspected to have CAS. In a series of studies, Shriberg
et al. (1997a, 1997b, 1997c)
documented excessive-equal stress (all or most syllables in a word or
sentence receiving prominent stress) in approximately 50% of each of three
different samples of children suspected to have CAS. They noted that younger
children with CAS were also rated as more involved than children with speech
delay on perceptual measures of rate and resonance. However, excessive-equal
stress was the only feature that reliably distinguished any of several CAS
subgroups from control groups of children with speech delay of unknown
etiology. Those children who exhibited excessive-equal stress also produced
more distortions of early consonant sounds than the other children, but
their error types (relative proportions of substitutions vs. omissions vs.
distortions) and their severity and variability levels did not differ from
those of the children with speech delay. The authors speculated that the
children with a diagnosis of CAS who did not demonstrate excessive-equal
stress may either have been incorrectly diagnosed or were possibly
exhibiting another type of CAS. In a later article, Shriberg, Campbell, et
al. (2003) suggested that the
presence of stress errors may change over time within an individual with
CAS. Odell and Shriberg (2001)
further noted that prosodic disturbances may be different in adults with
acquired apraxia of speech versus children with CAS. Children with CAS in
their sample had excessive-equal stress, but, in contrast to the sample of
adults with acquired apraxia of speech, did not have inappropriate phrasing
Velleman and Shriberg (1999) completed
metrical analyses of the lexical stress patterns of children with CAS who
had inappropriate stress, children with CAS who did not have inappropriate
stress, and children with speech delays of unknown origin. They found that
the pattern of stress errors of the children with CAS did not differ
substantially from the error pattern of younger, typically developing
children, suggesting that either the children with CAS were misdiagnosed or
that such errors reflect prosodic delay rather than disorder. That is,
participants with CAS who had inappropriate stress tended to either omit or
overstress weak (unstressed) syllables, especially in the initial position
of words, as do typically developing 2-year-old children. However, whereas
the children with speech delay ceased to make such errors after the age of
6, lexical stress errors of this type had persisted into adolescence in the
participants suspected to have CAS with inappropriate stress.
Stress differences in CAS have also been examined using acoustic analyses.
Munson, Bjorum, and Windsor (2003)
reported that the vowel durations, fundamental frequencies, vowel
intensities and f0 peak timing of stressed syllables produced by children
with CAS were appropriate despite the fact that the children were perceived
as producing inappropriate stress patterns. Skinder et al. (1999) also found that children with CAS
marked stress in the same ways as children who were typically developing,
although there was more variability within the CAS group. Again, listeners
had judged the children with CAS as less accurate in their stress production
than the typically developing children, but the acoustic measures used did
not identify the source of these perceptions. Skinder et al. suggested that
listeners were confused or distracted from attending to prosodic details by
the higher number of segmental errors produced by the children with CAS.
Shriberg, Campbell, et al. (2003), in
contrast, reported that ratios based on acoustic measures of stressed versus
unstressed syllables differed in children with CAS who perceptually were
noted to produce excessive-equal stress compared to control children with
speech delay. The acoustic differences were quantitative rather than
qualitative. Thus, it may not be that children with CAS have uniquely
different stress patterns. Rather, it may be their inability to fully
contrast stressed versus unstressed syllables that leads to the impression
of inappropriate stress patterns. Note that these and associated stress
findings are consistent with findings reviewed earlier indicating that the
phonetic distinctiveness of vowels/diphthongs and consonants is reduced in
the speech of children suspected to have CAS.
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A few studies have addressed the hypothesis that children suspected to have
CAS have deficits in auditory perception, auditory discrimination, and/or
auditory memory. Bridgeman and Snowling (1988) reported that compared to control children, children with CAS
have more difficulty discriminating sound sequences in nonsense words.
Groenen and Maassen (1996) found that
children with CAS did not have difficulty identifying the place of
articulation of a consonant but did have difficulty discriminating
consonants with subtle acoustic differences associated with place of
articulation. Furthermore, deficits in place discrimination were found to be
correlated with deficits in accurate production of place. Maassen et al.
(2003) also reported that
compared to children with typically developing speech, children with CAS had
poorer identification as well as poorer discrimination of vowels. Given the
likelihood of phoneme-specific relationships between production and
perception in children with other speech sound disorders (Rvachew, Rafaat, & Martin,
1999), an important research goal for theories of CAS is to determine
if the speech perception deficits described above are replicable and whether
they are unique to children with CAS.
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There is general agreement in reviews of the literature that children
suspected to have CAS typically also have significant language deficits
(e.g., Crary 1984, 1993; Ozanne, 1995; Velleman &
Strand, 1994). As with the perceptual findings reviewed in the
previous section, a research challenge is to determine how such constraints
are associated with the praxis deficit in planning and programming that
defines CAS. One possibility is that language impairments are a consequence
of having any type of disorder affecting neurological development (Robin, 1992). In response to another
possiblity—that all expressive language deficits in children with
CAS are due to their speech involvements—Ekelman and Aram (1983) documented language errors in a
group of children with CAS that were clearly not due to the
children's phonological deficits. Their participants made incorrect
choices of pronouns and verbs. They also failed to invert auxiliary
(helping) and copula (be) verbs in questions. More
recently, Lewis et al. (2004) found
that language impairments were more significant and persistent in children
with CAS than in children with non-CAS speech sound disorders. The authors
concluded that language symptoms are “a key aspect of the
disorder” (p. 131) based on the following observations: (1) gains
in articulation did not eliminate language deficits (e.g., morphological
omissions of plural, possessive, third person singular, and past tense
markers are not simply due to an inability to produce final consonant
clusters); (2) receptive as well as expressive language deficits were noted,
although expressive language consistently lagged behind receptive language;
and (3) there was a strong family history of language impairment in the
families of the children with CAS (Lewis et
Language symptoms that might differentiate children suspected to have CAS
from children with SLI have been implied in the literature. For example,
Velleman and Strand (1994) modeled
CAS as a disorder of hierarchical organization, which suggests that language
errors should take the form of part-whole and sequencing difficulties. Lewis
et al. (2004) failed to find language
differences between children with CAS and children with a combined language
and non-CAS speech sound disorder on standardized tests at the preschool
level. As indicated above, they did identify more persistent receptive and
expressive language difficulties among the children in the CAS group at
school age; analyses of the children's spontaneous spoken and/or
written language would have strengthened this claim. Overall, the literature
remains inconclusive on whether there are differences in the language
profiles of children with CAS versus children with SLI or with combined
language and nonapraxic speech sound disorder.
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Children with any sort of speech production deficit are at higher risk for
difficulty with phonological awareness, which itself is a
“critical element of literacy development” (Justice & Schuele, 2004, p.
378). Although CAS researchers frequently cite literacy and other academic
difficulties as a characteristic of the disorder, few studies have explored
this topic and some have been limited by the lack of a speech delayed
comparison group. For example, Marion, Sussman, and Marquardt (1993) demonstrated that children with
CAS have more difficulty perceiving and producing rhymes than do children
with typically developing speech. Marquardt et al. (2002) similarly showed that children with CAS score
lower than typically developing children on metaphonological (phonological
awareness) tasks, such as tapping to count the syllables in a word and using
blocks to represent the structure of a word (e.g., using black blocks to
represent the consonants and white blocks to represent the vowels in the
word blue [i.e., black black white]). Given that a history
of speech delay puts a child at increased risk for phonological awareness
deficits, it will be important to cross-validate such interesting findings
with control groups who have speech sound disorders other than CAS.
Lewis et al. (2004), as cited
previously, found that children with CAS had deficits in word attack, word
identification, and spelling in comparison to children with speech disorders
only. Their participants with CAS also scored significantly lower on tasks
requiring them to spell unpredictable words, compared to scores from
children with a combination of language and nonapraxic speech disorders.
Finally, it is useful to note that children suspected to have CAS have
sometimes been described as having increased self-awareness of their own
speech production limitations (McCabe et
al., 1998; Velleman &
Strand, 1994). This is a special type of metalinguistic awareness
(the ability to reflect consciously about or comment on linguistic elements,
structures, or processes) that, to date, has not been addressed in
CAS research to date has almost exclusively focused on English-speaking
participants in several countries, with the exception of several cohorts of
Dutch children with CAS studied by Maassen and colleagues (Maassen et al., 2001, 2003; Nijland, Maassen, & van der Meulen, 2003; Thoonen et al., 1999). Although not
exploring cross-linguistic similarities or differences between individuals
with CAS who speak Dutch or English, these investigators have used CAS
criteria from studies of English-speaking participants. Dutch and English
are similar in phonetic and phonotactic properties and it appears that
features of CAS may be similar in the two language environments. The
Committee did not identify any studies that have compared aspects of CAS in
individuals speaking different dialects of English or speaking languages
that differ markedly from English in phonetic, phonemic, and phonotactic
properties. Cross-linguistic studies of CAS could provide greater
understanding of the effects of language and culture on its short- and
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Theories about the nature of CAS are based on a limited number of observations
that seem to be shared among most researchers. There appears to be general
agreement that (a) the behaviors associated with CAS may vary from child to
child and from time to time within the same child, (b) severity of expression
may range from mild to severe, and (c) CAS is a symptom complex, rather than a
unitary disorder (Dewey, 1995; Hall, 1989; Le-Normand, Vaivre-Douret, Payan, & Cohen, 2000; Lewis et al., 2004; Maassen, 2002; McCabe et
al., 1998; Shriberg, Campbell, et al.
2003; Strand, 2001; Velleman & Shriberg, 1999). Beyond
such observations, theories of the nature of CAS can be divided into the
following two general categories: frameworks that focus on suprasegmental
perspectives and those that emphasize sensorimotor perspectives.
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There appears to be widespread agreement that syllables and prosody are
affected in more profound, distinctive ways in CAS than are other aspects of
speech or phonology. Some researchers have hypothesized that deficits in the
syllabic framework of speech result in prosodic symptoms (Davis et al., 1998; Maassen, 2002; Marquardt et al., 2002; Nijland,
Maassen, van der Meulen, et al., 2003). Others have proposed the
reverse: that fundamental prosodic deficits affect syllable and segment
production (Boutsen & Christman,
2002; Odell & Shriberg,
2001). Other researchers have emphasized the critical roles of timing
(e.g., Shriberg, Green, et al., 2003)
and sequencing deficits (e.g., Thoonen et
al., 1996) as core features underlying many of the other
segmental and suprasegmental characteristics of CAS.
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Several theoretical frameworks for CAS posit that core deficits are in the
relationship between perception or sensory processing and some aspect of
motor processing. Maassen (2002), for
example, proposed that deficient sensorimotor learning leads to weak
prelinguistic articulatory-auditory mappings, which in turn fail to support
full phoneme-specific mappings. He noted that “higher-level
knowledge…must be acquired by the child via the problematic
speech production and perception skills” (p. 265). Maassen
suggested that unlike typically developing children, children with CAS seem
to process real words more similarly to the way they process nonsense words.
Maassen speculated that such processing renders their linguistic systems
(e.g., lexical representations) less able to support online language
processing tasks. Barry (1995a),
Boutsen and Christman (2002), and
Odell and Shriberg (2001) focused on
the related issue of online self-monitoring and feedback systems. These
investigators proposed that children with CAS may have weak sensorimotor
feedback loops or decreased ability to respond to such feedback. Thus,
children with CAS may be unable to either benefit immediately from feedback
in order to self-correct or to appropriately grade actions, or may be unable
to use this feedback to alter incomplete representations or motor plans for
future retrieval. Such a sensorimotor deficit could also underlie proposed
difficulties in automating motor programs, such that each word production
must be planned anew (Barry, 1995a;
Nijland et al., 2002; Nijland, Maassen, van der Meulen, et al.,
Deficits in the preprogramming, programming, and execution of speech motor
events (Klapp, 1995, 2003) have each been proposed as a core
deficit in CAS. Unfortunately, explicit definitions for each of these
processes are, themselves, a source of debate in associated literatures.
Most theoretical proposals place the source of the speech production
difficulties in CAS further “upstream” than the actual
execution of the motor plan. Marquardt, Jacks, and Davis (2004), for example, attributed high
inconsistency levels in children with CAS to “lack of neural
instantiation of phonemic representations” (p. 142) and unstable
motor programs for word targets. They noted that increases in accuracy are
associated with increases in stability (i.e., decreases in inconsistency),
presumably reflecting more specific, stable motor plans for words. A further
common theme in all such discussions is a deficit in integration or
coordination across different levels proposed to be relevant to speech
production (and, in some cases, speech perception as well). Such levels
include syllabic, phonemic, or motor representations; motor plans and/or
programs; and neuromotor group networks. Thus, multiple levels of speech
motor processing, and the relationships among them, have been implicated in
processing perspectives on CAS.
In prior decades, discussion of the core deficit(s) in CAS was often framed
as a debate between linguistic/psycholinguistic perspectives versus motor
perspectives. Currently, this opposition is more appropriately described as
a debate between motor + linguistic versus motor-only views. As discussed
previously, the primary question is how to reconcile the linguistic
behaviors that have been associated with CAS in the research
literature—differences in speech perception, phonological
awareness, phonological patterns, and expressive language—with
the core problem of praxis from which this disorder takes its name. In
widely cited papers on AOS, McNeil and colleagues have argued on formal
grounds that such deficits cannot be accommodated as core features of AOS
(McNeil, 1997; McNeil et al., 1997). Rather, if
present, they likely reflect secondary consequences of apraxia of speech.
Thus, from a theoretical perspective, the lines are drawn fairly sharply.
Following McNeil's rationale, if research validates deficits in
speech processes that precede planning/programming of movement sequences for
speech, reconsideration would have to be given to the appropriateness of the
term apraxia for this clinical entity.
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Studies of the behavioral features of CAS have been limited by methodological
constraints and circularity in subject ascertainment criteria and by incomplete
controls (e.g., comparing children with CAS only to children who are typically
developing, rather than to children with other speech sound disorders). These
limitations notwithstanding, there appears to be a research consensus that
children suspected to have CAS often have deficits in any or all of the
following domains: nonspeech motor behaviors, motor speech behaviors, speech
sounds and structures (i.e., word and syllable shapes), prosody, language,
metalinguistic/phonemic awareness, and literacy. Thus, at present, CAS presents
as a complex of signs that varies across children and within the same child over
time. An important corollary concept, however, is that many of these behavioral
characteristics are also observed in children with other forms of speech sound
disorders. Notably, although we restricted our search to literature published in
English, we found few studies of children with CAS who speak languages other
than English. Finally, theories of the nature of CAS continue to reflect
difficulty in explaining the relationship of a core deficit in motor planning
and/or programming to deficits in other domains observed as part of the symptom
complex seen in children with CAS.
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One research approach that meets some of the needs discussed in the previous section
is studies of children suspected to have CAS who share some common biological
difference or disorder. This section reviews findings from two examples of this
approach. One approach is to study families of children with
idiopathic (i.e., a disorder of unknown origin) CAS to determine if
affected family members share one or more genetic differences not found in
unaffected family members. The second type of design is studies of children reported
to have CAS as a secondary feature in a well-characterized complex neurobehavioral
disorder, such as fragile X syndrome. In each of these two
designs—studying children with idiopathic CAS and studying children with
CAS as secondary signs within complex neurobehavioral
disorders—information on the molecular genetics and developmental biology
of the disorder can be used to develop an eventual explanatory account of CAS.
Specifically, controlled investigations can be designed to study associations
between the genotypic (genetic) characteristics of children suspected to have CAS
and phenotypic (biobehavioral) manifestations of the disorder. Genotype/phenotype
studies are widely reported in complex neurobehavioral disorders but have only
recently begun to appear in the genetics literature on speech sound disorders.
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A striking example of the productivity of studying genetic antecedents of CAS is
the programmatic study series of a four-generation London family referred to as
the KE family. Extensive research on this family, approximately
50% of whom have an orofacial apraxia, apraxia of speech, and
cognitive-linguistic involvements, has had wide-ranging scientific impact in a
number of disciplines in the life sciences. At the time this report was
prepared, however, two constraints associated with the findings reviewed here
have been perceived to limit the clinical impact of this study series on
research and practice in CAS. First, due to the array of cognitive, language,
motor, psychosocial, and possible craniofacial involvements in affected KE
family members, researchers have questioned the value of generalizations from
these findings to children with CAS. That is, the affected individuals in this
family appear to have significantly more involved clinical profiles than
reported for children suspected to have idiopathic CAS, as described in the
previous section. Such differences may be more quantitative than qualitative,
given that, as noted previously, most views of CAS characterize it as a
symptom complex, which, by definition, suggests concomitant
involvements in multiple domains. A second perceived limitation on
generalization of findings from the KE studies to CAS is that the mutations in
the gene identified in this family have not been found in many children
suspected to have CAS or in children with other verbal trait disorders. Several
published and unpublished molecular genetic studies of speech and language
disorders have reported negative findings, although recent studies have
implicated FOXP2 deficits in some other families with speech
problems apparently consistent with CAS: For reviews, see citations at the end
of this introduction. Thus, in genetic epidemiology terms, the gene responsible
for CAS in the affected KE family members appears to have low attributable risk
in the general population.
As reviewed next, the Committee views studies of the KE family as a model of the
type of programmatic research that may lead to an eventual understanding of one
class of etiological origins of CAS—CAS due to familial or new
(sporadic) genetic differences. The following chronologically sequenced sections
summarize findings for the KE family at four overlapping levels of
methodological observation: descriptive-linguistic, genetic, neuropsychological,
and neuroimaging. Table 1 provides
additional technical details on findings in each of the latter three topics,
including text relevant to the present focus on CAS excerpted from these primary
sources. Extended syntheses of this large body of studies authored by the
principal investigators are available in several excellent sources: Fisher, Lai,
and Monaco (2003), Marcus and Fisher
(2003), Newbury and Monaco (2002a, 2002b), and Vargha-Khadem, Gadian, Copp, and Mishkin (2005). The Online Mendelian Inheritance in
Man (OMIM; 2007) database will continue
to provide up-to-date reviews and bibliographies of associated genetic research.
Table 1. Studies of the KE family sequenced by area of study. All entries (research
questions, findings, interpretations, conclusions) are quoted directly from
the articles, with light editing (indicated by ellipses and brackets) used
for brevity and clarity.
|Area of study
||Fisher, Vargha-Khadem, Watkins, Monaco, & Pembrey (1998, pp. 168, 170)
||Chromosome 7 region identified that cosegregates with the speech and
language disorder [in affected members of KE family], confirming
autosomal dominant inheritance with full penetrance. Further
analysis of microsatellites from within the region enabled us to
fine map the locus responsible (designated SPCH1) to a 5.6-cM
interval in 7q31. [These findings provide]…the first
formal evidence for a single autosomal gene involved in speech and
language disorder, and represent a major step towards its
identification. … This gene is unlikely to be one
specifically involved in grammar; nevertheless, it is clearly
crucial for the normal acquisition of language
||Lai et al. (2000) Lai,
Fisher, Hurst, Vargha-Khadem, & Monaco (2001, p. 519)
||Our previous work mapped the locus responsible, SPCH1, to a 5.6-cM
interval of region 7q31 on chromosome 7 [Fisher et al., 1998]. We also identified an
unrelated individual, CS, in whom speech and language impairment is
associated with a chromosomal translocation involving the SPCH1
interval [Lai et al., 2000].
Here [Lai et al., 2001] we
show that the gene FOXP2, which encodes a putative transcription
factor containing a polyglutamine tract and a forkhead DNA-binding
domain, is directly disrupted by the translocation breakpoint in
||Vargha-Khadem, Watkins, Alcock, Fletcher, & Passingham
(1995, pp. 932, 933)
||…the affected members were significantly more impaired on
the simultaneous and successive movements than on the single
movements. Thus, the praxic deficits of the affected members are not
confined to articulation but also involve nonlinguistic oral and
Knowledge of neural and genetic correlates
of this phenotype could provide important clues to underpinnings of
the primary human faculties of speech and language as well as of the
many other functions in which the affected members are also
||Alcock, Passingham, Watkins, & Vargha-Khadem (2000a, pp. 17, 29)
||Affected KE family members made errors on tasks requiring oral
movements involving more than one group of muscles—marked
impairment on tasks requiring either simultaneous or sequential
movements. It is concluded that affected members of the KE family
resemble patients with acquired dysphasia in having difficulties
with oral praxis and that speech and language problems of affected
family members arise from a lower level disorder.
||Alcock, Passingham, Watkins, & Vargha-Khadem (2000b, pp. 42, 44, 45)
||Affected family members were not impaired on any tasks involving
musical intonation, but they were impaired on tasks involving the
perception and production of rhythm. Because the tapping tests did
not require oromotor coordination, impairment cannot be explained by
either a language deficit or an oral praxis deficit.
are consistent with neural findings in this family, including
abnormalities bilaterally in the head of the caudate nucleus and
many motor-related areas of the left hemisphere, including an area
of functional underactivity in the supplementary motor area (SMA),
the same area in which Halsband et al. (1993) found that lesions
disrupted the production of rhythms.
[The authors propose
that] a timing and a sequencing deficit could account for deficits
in both oral movements and tapping—these deficits could
affect language, particularly difficulties in perceiving and
producing morphemes of low phonetic substance (Leonard, 1989). [The
authors consider a]…common underlying deficit
explanation, versus possibility of several primary coexisting
deficits, each related to a different structural or functional
abnormality among the several that have now been identified in these
When taken together with the impaired discrimination of rhythms,
[the present findings are] best explained by a central deficit in
the processing of timing.
||Watkins, Dronkers, & Vargha-Khadem (2002, pp. 452, 454)
||It is likely that both developmental disorders and acquired
disorders of language have advantages and disadvantages for
cognition; advantages of a developmental disorder over an acquired
one are that there is presumably maximal brain plasticity and
capacity for reorganization and compensation; [in contrast,] an
acquired disorder could have advantages over a developmental one
because of the pre-morbid period of normal development and normal
use of language and other cognitive functions…
||We suggest that, in the affected family members, the verbal and
nonverbal deficits arise from a common impairment in the ability to
sequence movement or in procedural learning. Alternatively, the
articulation deficit, which itself might give rise to a host of
other language deficits, is separate from a more general verbal and
non-verbal developmental delay.
||Vargha-Khadem et al. (1998,
pp. 12695, 12697, 12699)
||Investigation of the three-generation KE family, half of whose
members are affected by a pronounced verbal dyspraxia, has led to
identification of their core deficit as one involving sequential
articulation and orofacial praxis. A positron emission tomography
activation study revealed functional abnormalities in both cortical
and subcortical motor-related areas of the frontal lobe, while
quantitative analyses of magnetic resonance imaging scans revealed
structural abnormalities in several of these same areas,
particularly the caudate nucleus, which was found to be abnormally
||Although the mean scores of the affected members taken as a group
fall significantly below those of the group of unaffected members on
nearly every test used thus far to assess an aspect of their speech
and language function and orofacial praxis, every one of the
affected members is impaired individually on just three tests,
namely, word repetition, nonword repetition, and simultaneous and
sequential orofacial movements… On none of these three
tests do the individudal scores of the affected members overlap with
those of the comparison groups…
||[The data in this paper] confirm a major prediction derived from the
affected members' phenopytpic profile and its persistence
into adult life, namely, the presence of bilateral pathology in at
least one and possibly other components of the motor system. Thus,
the bilateral reduction in the volume of the caudate nucleas
provides a plausible explanation for their orofacial dyspraxia which
has persisted into maturity largely unchanged despite an origin in
early development. Importantly, this same brain abnormality might
also explain their verbal dyspraxia.
||Watkins, Vargha-Khadem, et al. (2002, p. 465)
||[The methods used] revealed a number of mainly motor- and
speech-related brain regions in which the affected family members
had significantly different amounts of grey matter compared with the
unaffected and control groups, who did not differ from each other.
Several of these regions were abnormal bilaterally.
||Affected family members had significantly more grey matter than
controls [in some neuroanatomic areas] and significantly less grey
matter than the unaffected members in others [see Liégeois, 2003,
below, for summary].
||The volume of the caudate nucleus was significantly correlated with
the performance of affected family members on a test of oral praxis,
a test of nonword repetition and the coding subtest of the Wechsler
||Belton, Salmond, Watkins, Vargha-Khadem, & Gadian (2003, pp. 194, 198, 199)
||These results confirm that a point mutation in FOXP2 is associated
with several bilateral grey matter abnormalities in both motor and
language related regions… The association of the caudate
nucleus with motor planning and seqencing, and with cognitive
function…is suggestive of the role that this structural
abnormlity may play in the phenotype of the affected
members… In the case of bilateral abnormalities in these
regions, reorganization would be compromised.
||Liégeois, Baldeweg, Connelly, Gadian, &
Vargha-Khadem (2003, pp.
||Abnormally low levels of gray matter density have been found [in
affected KE family members] in the inferior frontal gyrus, the head
of the caudate nucleus, the precentral gyrus, the temporal pole, and
the cerebellum, whereas abnormally high levels of gray matter
density have been found in the posterior superior temporal gyrus
(Wernicke's area), the angular gyrus, and the putamen. How
these structural abnormalities affect brain function during language
processing remains unclear. … The aim of the present
study was to determine the pattern of brain activation associated
with the FOXP2 mutation in the KE family using functional magnetic
resonance imaging (fMRI). We predicted that the regions that are
morphologically abnormal bilaterally in the affected members would
also be functionally abnormal, as evidenced by performance on
||The unaffected family members showed a typical left-dominant
distribution of activation involving Broca's area in the
generation tasks and a more bilateral distribution in the repetition
task, whereas the affected members showed a more posterior and more
extensively bilateral pattern of activation in all tasks.
||Liégeois et al. (2003, p. 1234)
||Consistent with previously reported bilateral morphological
abnormalities, the affected members showed significant
underactivation relative to the unaffected members in
Broca's area and its right homolog, as well as in other
cortical language-related regions and in the putamen.
||The present findings demonstrate that the affected members of the KE
family display highly atypical fMRI brain activation when performing
both covert and overt verb generation tasks, as well as when
repeating words… The FOXP2 gene may therefore have an
important role in the development of a putative frontostriatal
network involved in the learning and/or planning and execution of
speech motor sequences, similar to that involved in other types of
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Despite the wide-ranging, cross-disciplinary impact of research on the KE
family, there are few published descriptions of the segmental and
supra-segmental error profiles of affected individuals. Hurst, Baraitser,
Auger, Graham, and Norell (1990), the
first paper by the U.K. (London and Oxford) researchers, included brief case
summary paragraphs for 6 family members. These reports primarily described
the speakers' apparent impairment in the organization of manual
movements for signing and speech movements, with the clinical speech profile
of affected family members interpreted by the researchers as consistent with
CAS (“developmental verbal dyspraxia”; p. 352).
The Hurst et al. (1990) report was
followed by a series of papers by Canadian researchers (primarily at McGill
University) providing descriptive-linguistic analyses of selected affected
KE family members. Using a variety of corpora, they interpreted their
findings to suggest that the core deficit in these individuals was in their
grammatical morphology (Gopnik, 1990a,
1990b; Gopnik & Crago, 1991; Matthews, 1994). More relevant for the present focus,
Fee (1995) provided a perceptually
based comprehensive description of the consonant errors of 8 affected family
members sampled at two points in time. She reported that, even as adults,
these speakers had deletion and substitution errors, especially on final
consonants and consonant clusters. Goad (1998) provided a thorough analysis of the grammatical impairment in
plurals in 5 affected adult family members, focusing on alternative
theoretical explanations in prosodic versus morphological domains. Also, in
a study assessing knowledge of lexical stress rules, Piggott and Kessler
Robb (1999) reported that affected
family members had considerably more incorrect and variable judgments of
what constitutes appropriate lexical stress than unaffected family members.
Although the investigators in this group did not use the term
apraxia or dyspraxia, they reported
that affected family members produced polysyllabic words that had
“prominent pauses separating them” and that were
“evenly stressed” (p. 61). Thus, prosodic impairment
has been described as a key feature shared among affected family
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As indicated in Table 1, the molecular
genetic findings for the KE family began with the report by Fisher,
Vargha-Khadem, Watkins, Monaco, and Pembrey (1998), which identified a region on chromosome 7 in affected
family members that was subsequently narrowed to a susceptibility locus
(i.e., a region of increased risk) on 7q31 termed SPCH1. This finding was
the bridge between the earlier descriptive-linguistic characteristics
summarized above and later identification of the FOXP2 gene
within the SPCH1 region. Two studies from the London/Oxford research group
(Lai et al., 2000; Lai, Fisher, Hurst, Vargha-Khadem, &
Monaco, 2001) provided information on this transcription gene,
FOXP2 (see Table
1). As a transcription gene, the protein products of
FOXP2 influence the function of other genes, which in turn
reportedly may affect both linguistic and sensorimotor aspects of speech and
language acquisition. The U.K. group is conducting two large-scale projects
to identify all genes “downstream” of
FOXP2 to determine how products of these genes may
contribute to speech-language acquisition and disorder (cf. Marcus & Fisher, 2003).
A number of studies (e.g., Liégeois et al., 2001; MacDermot et al., 2005; Tyson, McGillivary, Chijiwa, & Rajcan-Separovic,
2004; Zeesman et al., 2006)
have supported the association of FOXP2 with apraxia of
speech, as well as with a variety of other deficits first observed in
affected members of the KE family. In addition, more recent research related
to FOXP2 and the KE family has also suggested possible
mechanisms by which CAS and dysarthria may co-occur. Morgan,
Liégeois, Vogel, Connelly, and Vargha-Khadem (2005) used FMRI and electropalatography
(EPG) to study 5 affected members of the KE family and 5 sex-, age-, and
handedness-matched controls. In addition to brain abnormalities reported
previously in the motor cortex, the EPG data were reportedly consistent with
speech sound distortions, with excessive variability in lingual-palatal
contacts. Morgan and colleagues suggested that the FOXP2
mutation in the KE family has disrupted the development and function of the
brain regions involved in both planning and execution of speech movements
(i.e., the latter process consistent with dysarthria). Finally, Shriberg et
al. (2006) described a mother and a
19-year-old daughter who from early ages were treated for apraxia of speech
associated with a balanced 7;13 translocation affecting
FOXP2. Detailed speech and prosody analyses indicated that
the mother's and daughter's speech profiles are consistent
with both apraxia of speech and spastic dysarthria.
As indicated in the introduction to this section, findings from the KE family
have prompted widespread interdisciplinary interest in the
FOX family of genes. Examples at the time this report was
in preparation include studies tracing the evolutionary history of
FOXP2 (e.g., Enard et
al., 2002) and studies describing transcription processes and
other molecular features of FOXP2 and the larger family of
FOX genes (e.g., Bruce
& Margolis, 2002; Ferland,
Cherry, Preware, Morrisey, & Walsh, 2003; Takahashi, Liu, Hirokawa, & Takahasi,
2003; Tamura, Morikawa, Iwanishi,
Hisaoka, & Senba, 2003; B. Wang, Lin, Li, & Tucker, 2003; Zhang, Webb, & Podlaha, 2002). A major finding
for definitional issues in CAS is that, as described in the studies cited
immediately above, both FOXP1 and FOXP2
genes are expressed (switched on) widely in the brain. Importantly, these
locations include many of the primary neuroanatomic sites that subserve
speech-language development and processing. Additional work focusing on
these genes and their counterparts in animals has suggested the potential to
develop animal models for speech-language disorders; for example, Teramtizu,
Kudo, London, Geschwind, and White (2004) in songbirds and Shu et al. (2005) in mice.
A number of studies in the emerging discipline of linguistic genetics
(genetic studies of verbal traits and disorders) have sought to determine
whether deficits in FOXP2 are linked to other
neurobehavioral disorders, including language impairment, dyslexia, and
autism. As indicated previously, with the exception of a finding in autism
(Gong et al., 2004),
FOXP2 deficits have not been found in children with other
neurobehavioral disorders (see OMIM for current findings).
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Following their initial rejoinders to the Canadian group's
interpretation of the communicative deficit in affected KE members (P. Fletcher, 1990; Vargha-Khadem & Passingham, 1990), the U.K.
research group (i.e., Hurst et al.,
1990) published four descriptive papers. The papers described
findings from an extensive battery of neuropsychological and other measures
given to family members and a number of control groups, including
information on affected individuals' articulatory and prosodic
involvements. As shown in Table 1,
Vargha-Khadem, Watkins, Alcock, Fletcher, and Passingham (1995) reported that the orofacial
apraxia used as the phenotype for affected family members was accompanied by
an array of deficits in other verbal and nonverbal domains, involving both
comprehension and production. In particular, they summarized their
alternative descriptive-explanatory perspective on the KE family as
suggesting “a broad phenotype which transcends impaired
generation of syntactical rules and includes a striking articulatory
impairment as well as defects in intellectual, linguistic, and orofacial
praxic functions generally” (Vargha-Khadem et al., 1995, p. 930).
Among other findings in two subsequent papers, Alcock and colleagues (Alcock, Passingham, Watkins, &
Vargha-Khadem, 2000a, 2000b)
reported that affected family members' deficits involve both
comprehension and production of rhythms, as assessed using verbal and
nonverbal (i.e., tapping) modalities. These authors speculated that a core
problem in timing may underlie the performance deficits of affected family
members on the diverse comprehension and production tasks included in the
The fourth paper (Watkins, Dronkers,
& Vargha-Khadem, 2002) provided extensive
neuropsychological information on cognitive-linguistic involvements in
affected family members, who were compared to a sample of adults with
aphasia. These findings are of particular interest for issues addressing
similarities and differences in acquired adult AOS and CAS, as well as
suggesting neostriatal (basal ganglion) involvement in praxic deficits in
movement sequencing and procedural learning. If such findings are replicated
in studies of other individuals with FOXP2 or other genetic
deficiencies, they will have important implications for assessment and
treatment of CAS.
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As sampled in Table 1, a series of
neuroimaging findings in affected members of the KE family has provided
unprecedented information on neuroanatomic structures and circuits
associated with this subtype of orofacial apraxia and apraxia of speech.
Findings have possible implications for the developmental neurobiology of
CAS symptoms and, more generally, speech-language acquisition.
In the first neuroimaging study of the KE family, Vargha-Khadem et al. (1998) reported that affected KE family
members have diverse, bilateral neuroanatomic differences from unaffected
members, primarily involving the neostriatum and associated neural circuits.
Although the FOXP2 gene was identified 2 years later as the
gene deficit transmitted to affected family members, the authors'
speculations about alternative genetic origins of these findings (e.g., see
the following excerpts) remain relevant:
Our data suggest that development of the neural mechanisms mediating
the acquisition of fine oromotor coordination (both vocal and
nonvocal) and of speech and language are interdependent, such that
abnormality in the one will be associated with abnormality in the
…a central abnormality affecting speech production could
have a cascading effect resulting in intellectual
At this stage, we cannot discount the alternative possibility that
the different components of the phenotypic profile are the
consequence of abnormalities in several different neural networks
resulting from disruption of either a single gene or even several
contiguous genes (Vargha-Khadem et
al., 1998, p. 12700)
As summarized in Table 1, the study by
Watkins, Vargha-Khadem, et al. (2002)
reported significant differences in white matter volumes bilaterally in
affected compared to nonaffected KE family members and controls, with
affected family members having both larger and smaller volumes at different
neuroanatomic sites. These morphometric data underscore the complexity of
the pathophysiology of CAS in these family members. Using different
neuroimaging methods, Belton, Salmond, Watkins, Vargha-Khadem, and Gadian
(2003) provided additional
neuroanatomic findings, again supporting bilateral involvements and
morphological differences in areas that subserve both motor and language
processing. Finally, Liégeois, Baldeweg, Connelly, Gadian, and
Vargha-Khadem (2003) used both
functional neural imaging methods and verbal processing measures to attempt
to relate structural findings to behavioral findings in the affected
individuals. The extended discussion of neural and neurocognitive findings
in this paper provides a promising research agenda for studies in process on
the genetic substrates of speech-language challenges.
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The many research reports indicating that CAS occurs in children with diverse
neurologic disorders (e.g., as a sequela of neuronal migration disorders,
infection, or trauma) were not reviewed in this document. The Committee did
attempt to review a representative sample of studies reporting CAS in complex
neurobehavioral disorders. Although both contexts for CAS provide promising
avenues for research in all forms of CAS, most of the latter had disappointingly
little technical information on the speech and prosody characteristics of the
children reported to have CAS. However, these studies typically are rich in
information on the neurophysiological pathways for each disorder, with
implications for alternative descriptive-explanatory levels for an eventual
understanding of CAS (e.g., genetic, biochemical, neuromotor). Table 2 includes brief descriptions of
findings from a sample of such studies.
Table 2. Sample findings from studies of children with complex neurobehavioral
disorders and reported apraxia of speech. All table entries are paraphrased
summaries or quoted directly from the abstract or text of the articles, with
light editing (indicated by brackets) used for brevity and clarity.
||Boyar et al. (2001)
||Of 5 siblings with pervasive developmental disorder associated with
an interstitial duplication of 15q11–q13 inherited from
their mother, 4 had limb apraxia and apraxia of speech.
||Scheffer et al. (1995)
||Of 5 family members with benign rolandic epilepsy (BRE), all
experienced oral and speech dyspraxia without prominent dysarthria;
simple tasks (e.g., poking out the tongue) were difficult; they
experienced difficulty with organization and coordination of high
speed movements, impairing their ability to produce fluent and
intelligent speech; receptive processing impairment affected the
children more significantly than adults.
||[Authors suggest that] the findings of subtle speech disturbances in
typical BRE is the key; autosomal dominant rolandic epilepsy
(ADRESD) may represent a more severe manifestation of the same
relationship; speech dyspraxia is intrinsically related to rolandic
discharges; it is more difficult to explain why family members with
BRE have longstanding difficulties of speech and language function;
perhaps the impact of the epileptiform activity at a developmentally
vulnerable stage results in damage.
||Spinelli, Rocha, Giacheti, & Ricbieri-Costa (1995)
||Of 10 participants with fragile X, 5 had word-finding difficulties,
1 had verbal paraphasias, and 4 had clearly dyspraxic speech.
Participants with each disorder did not overlap; neither of the 2
females had clearly dyspraxic speech.
||Webb, Singh, Kennedy, & Elsas (2003)
||Of 24 galactosemia patients consenting to formal speech evaluations,
15 (63%) had verbal dyspraxia.
||Bashina, Simashkova, Grachev, & Gorbachevskaya (2002)
||The results of comparing clinical data and EEG traces supported the
stepwise involvement of frontal and parietal-temporal cortical
structures in the pathological process. The ability to organize
speech and motor activity is affected first, with subsequent
development of lesions to gnostic functions, which are in turn
followed by derangement of subcortical structures and the cerebellum
and later by damage to structures in the spinal cord. A clear
correlation was found between the severity of lesions to motor and
speech functions and neurophysiological data: the higher the level
of preservation of elements of speech and motor functions, the
smaller were the contributions of theta activity and the greater the
contributions of alpha and beta activities to the EEG.
||Weistuch & Schiff-Meyers (1996)
||[A case study is presented of a 5-year-old boy in whom] chromosomal
studies revealed a de novo balanced translocation between first and
second chromosomes. Results of the neurological, speech/language,
cognitive, and play evaluations revealed a child with a severe
expressive speech-language deficit but good nonverbal cognitive and
communicative skills. Oral-mechanism examination appeared to be
normal, but [the child] had difficulty performing oral motor tasks.
The neurologist reported that the child could not smile or
lateralize, elevate, or rapidly protrude tongue on command.
Volitional nonverbal apraxia and apraxia of speech were well
documented in this child.
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Limb apraxias, oral apraxia, and apraxia of speech have been frequently
reported for children with autism or a pervasive developmental disorder
(e.g., Boyar et al., 2001; Page & Boucher, 1998; Rogers, Bennetto, McEvoy, &
Pennington, 1996; Seal &
Bonvillian, 1997). Well-controlled studies are needed to test the
hypothesis that apraxia of speech is more prevalent in autism than as occurs
idiopathically in the general population. At the time this report was in
preparation, several studies in process were studying this question using
contemporary inclusionary/exclusionary criteria for both autism and CAS.
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CAS has been noted as comorbid with or a sequela of several forms of
epilepsy, including benign rolandic epilepsy and autosomal dominant rolandic
epilepsy, the latter of which is a rare form associated with more severe and
long-term communicative disorders. Scheffer et al. (1995; see Table
2) provided interesting research hypotheses on the diagnostic
significance of comorbid epilepsy and apraxia, again underscoring the value
of studying apraxia in the context of well-characterized neurological and
complex neurobehavioral disorders.
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Fragile X syndrome is a genetically transmitted complex neurobehavioral
disorder in which speech and prosody deficits are associated with reduced
intelligibility (Roberts, Hennon, &
Anderson, 2003). Reports indicate that some of these deficits
overlap with diagnostic criteria for CAS, but the measures used to assess
the nature of speech and prosody involvement have typically not been well
developed. At the time this report was in preparation at least one research
study in process was attempting to replicate the Spinelli, Rocha, Giacheti,
and Ricbieri-Costa (1995) findings
(see Table 2) of apraxia of speech in
40% of a small sample of children with fragile X syndrome.
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Some form of CAS reportedly also occurs in 40%–60% of children
with one of the several genetic forms of the metabolic disorder,
galactosemia (Elsas, Langley, Paulk, Hjelm,
& Dembure, 1995; Hansen et
al., 1996; C. D. Nelson,
Waggoner, Donnell, Tuerck, & Buist, 1991; D. Nelson, 1995; Robertson, Singh, Guerrero, Hundley, & Elsas,
2000; Webb, Singh, Kennedy, &
Elsas, 2003). At the time this report was in preparation, a study
of CAS in galactosemia was in process using a relatively large sample of
children with this disorder.
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Limb and speech apraxia are reportedly part of the sequence of neurological
dysfunctions that characterize the degenerative course of expression of Rett
syndrome. Because the apraxic disorder is so profound that children at this
stage essentially do not speak (Bashina,
Simashkova, Grachev, & Gorbachevskaya, 2002; Schanen et al., 2004), it is difficult
to study speech apraxia in individuals with this neurobehavioral disorder.
Genetic studies indicate that the molecular regions involved in Rett
syndrome include susceptibility genes for a number of disorders reported to
involve speech-language deficits (N. J.
Wang, Liu, Parokonny, & Schanen, 2004).
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One of the most active and productive areas of genetic research in complex
neurobehavioral disorders involves the identification of persons with
translocations that affect speech processing. The case study reported in
Weistuch and Schiff-Meyers (1996)
(see Table 2) illustrates the
potential for CAS research in chromosomal translocations. Recall that it was
a child with a translocation involving a breakpoint in chromosome 7 that
helped the U.K. investigators identify the SPCH1 susceptibility region for
the apraxic disorder found in the KE family. Somerville et al. (2005) reported a child with chromosome
duplications affecting genes at 7q11.23 (the Williams-Beuren syndrome
microdeletion locus) who has “severe delay in expressive
speech.” Kriek et al. (2006) also described a child with a duplication in the same region
who reportedly also has significant speech delay (cf. Tassabehji & Donnai, 2006). These two papers
have prompted a large-scale study now in process seeking to determine if
duplications of this locus are present in children who reportedly have CAS.
Lichtenbelt et al. (2005) described a
child and 4 other reported cases with a rare supernumerary ring chromosome
on 7q. All 5 cases have severely delayed expressive speech. Finally,
Shriberg, Jakielski, Patel, and El Shanti (Shriberg, 2006) described 3 siblings with an unbalanced 4q;16q
translocation whose speech and prosody profiles also are consistent with CAS
and with dysarthria.
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Research on the genetic bases of CAS is emerging in genetic studies of families
in which CAS appears to be inherited and in genetic studies of individuals with
chromosomal disorders that include CAS in a symptom complex. Although the
complex of cognitive, linguistic, sensorimotor, and craniofacial involvements
reported for some members of the KE family is not routinely observed in other
children suspected to have idiopathic CAS, the extensive neuropsychological and
neuroimaging findings from family members with deficits in the
FOXP2 gene have motivated widespread research efforts to
understand the role of this gene in phylogenetic (in a species) and ontogenetic
(in an individual) development of communication. Recent case studies are
beginning to report other genomic regions of interest on chromosome 7 and on
other chromosomes that appear to be associated with severe speech delay
consistent with CAS. At the time this report was in preparation, a total of 35
cases (including 15 affected members of the KE family) had been reported in
which severe speech sound disorder suspected to be CAS has been associated with
genetic differences (Shriberg, 2006).
There are only sparse research literatures, to date, on CAS in the context of
neurological and complex neurobehavioral disorders. Such studies have the
potential to contribute significant information to our understanding of the
origins of this disorder and its pathophysiology.
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Assessment is a broad construct encompassing many clinical decisions, including
those related to diagnosis, severity of impairment, prognosis, and treatment
focus. Diagnostic aspects of assessment serve as the focus of this section
because diagnosis has a central role in clinical practice and in research, where
it is fundamental to participant selection and description. Although of obvious
importance for comprehensive treatment planning, the co-occurring problems that
have been identified in persons with CAS (e.g., in expressive language and
literacy) are not discussed here.
Several books published during the past decade have described diagnostic methods
for CAS (e.g., Caruso & Strand,
1999; Hall et al., 1993; Velleman, 2003). Such resources and, in
fact, every publication related to assessment identified for inclusion in this
report have taken the position that the diagnosis of CAS falls within the
professional responsibility of the discipline of speech-language pathology.
Inspection of the more widely cited sources indicates that they typically
address many of the issues and variables in assessment noted in the present
discussion. However, because standardized tests for diagnostic assessment of CAS
do not have the quality of evidence associated with peer reviewed research,
review of these sources is outside of the scope of this report. The Buros
Mental Measurements Yearbook series (e.g., Plake & Impara, 2001; Plake, Impara, & Spies, 2003)
provides detailed reviews of several instruments developed primarily for
diagnostic assessment of CAS.
The assessment literature was divided into three categories of peer reviewed
articles: those using expert opinion for recommendations about assessment, those
examining the methods currently used by clinicians and researchers, and those
studying variables that may prove to be biobehavioral markers of the disorder,
and thus potentially key indicators to diagnosis. The last of these categories
is the most extensively studied; it also includes much that is controversial. As
a group, peer reviewed articles consisting entirely of expert commentaries on
CAS diagnosis are addressed briefly, but readers are cautioned to consider the
potential subjectivity and the lack of transparency that is associated with
expert opinion (ASHA, 2004).
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Two articles since 1995—Crary (1995) and Davis and Velleman (2000)—included diagnosis as a major focus. Although each
article offered lists of areas to examine, neither described specific decision
rules linking observed behaviors with the final diagnosis or even highly
specified protocols. This is a frequent pattern in pedagogically oriented
discussions of clinical methods. Notwithstanding the potential applied value of
such discussions, they typically lead to considerable ambiguity when applied
within a research context, where a premium needs to be placed on methodological
replicability. They may also be subject to wide variability in clinical
Crary (1995) outlined a protocol intended
to help clinicians identify dysarthria, oral apraxia, limb apraxia, and CAS. The
protocol addresses five major areas: motor, motor speech,
articulation/phonological skills, language, and an “other”
category that included several additional areas. Discussion of some aspects of
the protocol is relatively detailed. For example, specific suggestions are given
for examining reflexes, sampling spontaneous language, and evoking and
interpreting responses to diadochokinetic tasks. Specific guidelines for the
identification of CAS are not provided. Rather, the assumption is that examining
a child's performance on the array of recommended tasks will provide
the speech-language pathologist with adequate information to arrive at a
diagnosis and engage in treatment planning.
Davis and Velleman (2000) discussed
differential diagnosis within the context of a broader examination of many
topics concerning CAS in infants and toddlers. Although there is considerable
interest in this age group, Davis and Velleman was the only article the
Committee identified that addressed the nature of signs in very young children
suspected to have CAS. Their list of exclusionary and inclusionary
characteristics is based on features they described as typical of older children
diagnosed with CAS, but with the list modified to accommodate the more
restricted language development and assessment data expected for very young
children. Davis and Velleman's list of speech characteristics includes
limitations in sound inventories (consonants and vowels), suprasegmental
abnormalities, and variability in or lack of consistent speech patterning. They
also listed six co-occurring characteristics related to the role of gestures in
communication, gross and fine motor delays, clumsiness, volitional oral motor
skills, diadochokinetic rates, and syntax. These recommendations
notwithstanding, the authors urged extreme caution in reaching a diagnosis in
very young children and suggested a period of trial intervention prior to
diagnosis. As in the Crary (1995) article,
these authors did not specify how the list of characteristics leads to a
diagnosis, such as the number of characteristics required for diagnosis or a
relative ranking of the importance of each characteristic in reaching the
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Two studies since 1995 have examined speech-language pathologists'
perspectives on assessment of CAS, either as a primary (Forrest, 2003) or secondary (Davis et al., 1998) focus. Such studies provide insights into
commonly held perspectives, developed from experiences in academic training
programs, attendance at workshops and other postgraduate presentations on CAS,
and from personal assessment and treatment experiences. These reports emphasize
that as knowledge about the assessment of CAS accumulates from a scientific
perspective, it will be important to disseminate it in ways that maximize
effective clinical practice.
The Committee viewed it important to review the information from these two
reports in some detail, beginning with the earlier study by Davis and colleagues
(1998). Davis et al. proposed eight
speech and three nonspeech characteristics for use in the diagnosis of CAS, a
list that they developed from the existing research literature. The eight speech
characteristics are limited consonant and vowel repertoire, frequent omission
errors, high proportion of vowel errors, inconsistent articulation errors,
altered supra-segmental characteristics, increased errors on longer units of
speech output, significant difficulty imitating words and phrases, and
predominant use of simple syllable shapes. Of these characteristics, the authors
noted that several of these and other candidate features are also consistent
with other types of severe speech sound disorders (i.e., “incomplete
consonant repertoire, multiple speech errors, restricted production of word
shapes, and poor performance on diadochokinesis”; Davis et al., 1998, p. 41).
To recruit participants for their descriptive study, Davis and colleagues (1998) described the eight characteristics
listed above to practicing speech-language pathologists at conferences, asking
clinicians to refer children diagnosed with this condition for possible
participation in a longitudinal study. Although characteristics were described
(possibly at some length) to the referring clinicians, it is unclear whether
specific measures to quantify the characteristics were recommended. Further, it
was not clear whether the referring speech-language pathologists were given
guidance about referring children who had some, but not all, of the listed
Twenty-two children were subsequently referred with a firm or tentative diagnosis
of CAS. Of those, only 4 (18%) were also identified as having CAS by the
researchers. Findings for 5 children—4 for whom CAS was considered
incorrectly diagnosed and 1 for whom CAS was considered correctly
diagnosed—were described in detail to illustrate the ways in which
misdiagnosed children failed to demonstrate the studied characteristics. The
authors concluded that their study demonstrates the need for increased
quantification of diagnostic indicators, with a focus on characteristics
specific to CAS, rather than those found frequently among children with severe
speech sound disorders. Three characteristics mentioned as potential candidates
based on this kind of specificity are vowel misarticulations, variability of
repeated productions, and suprasegmental differences, although the basis on
which these three diagnostically relevant characteristics were selected was
unclear. In addition, the authors warned consumers of the research literature to
exercise caution when interpreting findings of previous studies in which
clinician referral served as a primary basis for CAS diagnosis.
Forrest (2003) recruited as participants
for her study 75 speech-language pathologists attending a workshop on CAS who
indicated that they had had at least some experience with this disorder.
Methodological constraints acknowledged by the author included a lack of
detailed information about participant expertise and the nonrandom
representativeness of the sample. Participants were asked to list three
characteristics that they considered “necessary” for a
diagnosis of CAS. This process produced a list of 50 characteristics, 6 of which
accounted for about 51% of the responses. The 6 most frequently cited
characteristics were inconsistent productions (14.1%), general oral-motor
difficulties (9.3%), groping (7.9%), inability to imitate sounds (7.5%),
increased errors with increased utterance length (6.6%), and poor sequencing of
sounds (6.2%); the remaining 44 characteristics generated by the group were each
cited by fewer than 4% of the participants. Forrest concluded that practicing
clinicians may use widely varying and potentially contradictory criteria in the
diagnosis of CAS. Although she did not address the extent to which clinicians
may overdiagnose CAS in the course of their practice, as had Davis and
colleagues (1998), Forrest's
study documented likely inconsistencies in the clinical criteria used to
diagnose CAS and underscored the need for research on this topic.
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The 16 studies reviewed next have yielded findings that may be informative for an
eventual understanding of the behavioral characteristics suspected to define the
disorder. As noted in Davis et al. (1998),
not all proposed characteristics of CAS may be observed in every child suspected
to have CAS, and some may be considerably more important for differential
diagnosis. Perhaps that is why it has been difficult for proposed markers to
meet standard statistical criteria, including high sensitivity (the proportion
of true positives, or individuals with the target disorder for which the marker
is positive) and high specificity (the proportion of true negatives, or
individuals without the target disorder for which the marker is negative; see
Sackett, Straus, Richardson, Rosenberg,
& Haynes, 2000). By definition, an ideal diagnostic marker
for CAS would be one that was perfectly sensitive and perfectly specific, a goal
seldom met for any complex disorder. Few of the studies we identified have
provided sensitivity and specificity estimates, and many have not provided
inferential statistical tests to examine the likelihood that observed
differences in groups were greater than chance. Other challenges posed in the
search for diagnostic markers of CAS have been raised in several places in this
report, including the likelihood that effective diagnostic markers may change
over time (e.g., Lewis et al., 2004;
Shriberg, Campbell, et al., 2003;
Skinder, Connaghan, Strand, & Betz,
Table 3 is a summary of findings for 16
studies that compared the performance of a group of children suspected to have
CAS to the performance of at least one other group of children. This
inclusionary criterion in our review was used because only those variables that
can differentiate children suspected to have CAS from children with other
closely related disorders are likely candidates for sensitive and specific
diagnostic markers. Thus, although studies without comparison groups (e.g.,
Marquardt et al., 2002, 2004) have provided potentially valuable
information about CAS—including variables that may turn out to be
important diagnostic markers—they have been omitted from the present
discussion. Moreover, Table 3 also does
not include findings from otherwise informative studies that did not use
inferential statistics to examine group differences (e.g., Barry, 1995a, 1995b;
Betz & Stoel-Gammon, 2005;
Peter & Stoel-Gammon, 2005)
or that addressed comparisons between children and adults with developmental
versus acquired forms of motor speech disorder (e.g., Barry, 1995a; Odell
& Shriberg, 2001). The focus of Table 3 is on between-group differences even where these
findings were not the major focus of the study. Note that findings from several
of these studies were discussed from the perspective of the earlier reviews of
behavioral correlates of CAS. The present emphasis is on the applied value of
findings for assessment. Essentially, Table
3 provides a tabular summary of recent findings meeting the
Committee's inclusionary criteria for a potential diagnostic marker of
Table 3. Findings for 16 studies of children with CAS compared with children in four
types of comparison groups: typical speech (TS), speech delay (SD),
dysarthria (DYS), and speech and language impairment (S/L). Findings that
included diagnostic accuracy statistics are indicated by an asterisk; the
remaining included only conventional inferential statistics. Within each
major assessment domain, articles are arranged alphabetically by first
||Nijland, Maassen, & van der Meulen (2003)
|CAS (n = 5) vs. TS (n = 5)
CAS > TS in improvement in coarticulation and vowel
quality in response to bite block condition, as measured using F2
values CAS < TS in compensation in response to bite block
condition CAS > TS in within-subject variability of F2
|Nijland, Maassen, van der Meulen, Gabreëls,
Kraaimaat, & Schreuder (2002)
|CAS (n = 9) vs. TS (n = 6)
CAS > TS in frequency of idiosyncratic coarticulation
patterns, as measured using F2
CAS > TS in within-speaker variability of F2 frequencies
in nonsense words
CAS < TS in distinctiveness between midvowel F2 ratios,
indicating less distinctiveness between vowels
|Nijland, Maassen, van der Meulen, Gabreëls,
Kraaimaat, & Schreuder (2003)
|CAS (n = 6) vs. TS (n = 6)
CAS > TS in degree of coarticulation effects, as measured
using F2 values
CAS < TS in change of durations related to syllable
|Shriberg, Green, Campbell, McSweeny, & Scheer
|CAS (n = 15) vs. TS (n = 30) vs.
SD (n = 30)
CAS > TS and SD groups in the coefficient of variation
ratio (i.e., the ratio of the variation of pause durations relative
to the variation of speech segment durations)*
|Sussman, Marquardt, & Doyle (2000)
|CAS (n = 5) vs. TS (n = 5)
CAS < TS in coarticulation effects (as measured using
Locus equations of CV syllables for the consonants /b, d, g/
produced with 10 vowel contexts)
|Thoonen, Maassen, Gabreëls, &
|CAS (n = 10) vs. TS (n = 11) vs.
SD (n = 11) vs. DYS (n = 9)
CAS < TS, SD, DYS in maximum rate of alternating
sequences combined with maximum fricative prolongation*
|Thoonen, Maassen, Gabreëls, Schreuder,
& de Swart (1997)
|CAS (n = 11) vs. TS (n = 11)
CAS > TS in rate of singleton consonant errors and
CAS < TS in benefit to accuracy from real-word versus
nonsense word status
|Thoonen, Maassen, Wit, Gabreëls, &
|CAS (n = 11) vs. TS (n = 11) vs.
DYS (n = 9)
CAS < TS in fricative prolongation, trisyllabic
repetition rate, and 2 measures related to trisyllabic repetition
(number of sequencing errors and number of attempts)*
DYS < TS, CAS in monosyllabic repetition rate and vowel
||Munson, Bjorum, & Windsor (2003)
|CAS (n = 5) vs. SD (n = 5)
CAS < SD in matching of target stress contours during
nonword repetitions, as judged by listeners despite no group
differences in acoustic variables associated with stress
|Shriberg, Aram, & Kwiatkowski (1997a)
|Study 1: CAS (n = 14 [7 younger and 7 older]) vs.
SD (n = 73)
CAS > SD in use of inappropriate stress for a younger
subgroup of participants
Study 2: CAS (n = 20) vs. SD (n =
CAS > SD in frequency of inappropriate stress, including
older as well as younger participants*
|Shriberg, Aram, & Kwiatkoski (1997b)
|CAS (n = 19) vs. SD (n = 73)
CAS > SD in frequency of inappropriate stress
|Shriberg, Campbell, Karlsson, Brown, Mcsweeny,
& Nadler (2003)
|CAS (n = 11) vs. SD (n = 24)
CAS > SD in frequency of abnormally high or low lexical
stress ratio scores (composites of values obtained for 3 acoustic
variables [amplitude area, frequency area, duration] for the strong
syllable divided by values of those variables for the weak syllable
||Groenen & Maassen (1996)
|CAS (n = 17) vs. TS (n = 16)
CAS < TS in discrimination of place of production in stop
|Maassen, Groenen, & Crul (2003)
|CAS (n = 11) vs. TS (n = 12)
CAS > TS in response variability in identification of
stimuli from two vowel continua
CAS > TS in size of just noticeable difference
(jnd) in discrimination of stimuli from the
same two continua
CAS > TS in variability in jnd in
discrimination of stimuli from the same two continua
CAS > TS in measure derived from identification and
|Speech, oral and written language, and Performance IQ
||Lewis, Freebairn, Hansen, Iyengar, & Taylor
||Mean age at
|CAS (n = 10) vs. SD (n = 10) vs.
S/L (n = 10)
CAS < SD at preschool testing on
Goldman-Fristoe Test of Articulation (GFTA), Khan-Lewis Phonological
Analysis, multisyllabic word repetition (MWR) accuracy of phoneme
production, nonsense word repetition (NWR) accuracy of phoneme
production, oral and speech motor control protocol total functional
score (TFS), Test of Language Development—Primary
|Lewis, Freebairn, Hansen, Iyengar, & Taylor
||Mean age at
|CAS < SD at school age follow-up on GFTA,
NWR, MWR, Fletcher Time-by-Count Test of Diadochokinetic Syllable
Rate, CELF-R (including Total, Receptive, and Expressive subscores),
Test of Written Spelling-3, Woodcock Reading Mastery
Tests—Revised, Wechsler IndividualAchievement Test,
selected WISC-III Performance subtests
CAS < S/L at school-age follow-up on NWR; Fletcher
Time-By-Count Test; Performance IQ; CELF-R Total Language, Receptive
Language, and Expressive Language scores; and TWS-3 total score and
unpredictable word score
CAS < S/L and SD in change scores adjusted for preschool
performance (residualized change) for CELF-R Expressive Language
score, suggesting less change or later emerging weaknesses
CAS < SD in change scores adjusted for preschool
performance (residualized change) for CELF-R Total Language measure
and NWR, suggesting less change or later emerging weaknesses
CAS < S/L and SD groups at follow-up for the WISC-III
Performance subtests: Coding, Block Design, and Block Assembly
CAS < S/L and SD in change scores adjusted for preschool
performance (residualized change) for CELF-R Expressive Language
score, suggesting less change or later emerging weaknesses
CAS < SD in change scores adjusted for preschool
performance (residualized change) for CELF-R Total Language measure
and NWR, suggesting less change or later emerging weaknesses
CAS < S/L and SD groups at follow-up for the WISC-III
Performance subtests: Coding, Block Design, and Block Assembly CAS
< SD at follow up on WISC-III Performance subtests:
Picture Completion and Picture Arrangements
|Nonspeech oral-motor skills
||Murdoch, Attard, Ozanne, & Stokes (1995)
||CAS: 8;8 (M)
TS: 8;2 (M)
|CAS (n = 6) vs. TS (n = 6)
CAS < TS in maximum tongue strength, as measured by
CAS < TS in ability to sustain maximum tongue pressures,
as measured by pressure at onset, pressure at offset, area under the
CAS < TS in repetition of maximum tongue movements, as
measured by pressure at first repetition and pressure at tenth
repetition, and across all 10 repetitions
CAS < TS in pressure at last repetition and across all
maximum force repetitions produced in 10 s
] Children with CAS were rediagnosed as showing some dysarthrias.
Twelve of the 16 studies in Table 3
involve comparisons of children suspected to have CAS to participants in one
other group of children. Among those 12 studies, the comparison group was
children with typical speech development (8 studies) or children with speech
delay (4 studies). The remaining 4 studies included two or three comparison
groups. Three of these included a group of children with speech delay (Lewis et al., 2004; Shriberg, Campbell, et al., 2003; Thoonen et al., 1999), 3 included a group of children with
typical speech development (Shriberg, Green, et
al., 2003; Thoonen et al.,
1996, 1999), 2 included a group of
children with dysarthria (Thoonen et al.,
1996, 1999), and only 1 included a
group of children with speech and language disorders (Lewis et al., 2004). For purposes of differential
diagnosis, studies that include children from other closely related disordered
groups, as well as typically developing children, are obviously likely to be
most helpful. In contrast, studies in which comparisons are made only to
children with typical speech sound development may identify variables that
distinguish between children with and without speech sound disorders of any kind
(i.e., are sensitive for speech sound disorder), but are not specific for CAS.
The breadth of variables examined in these 16 studies mirrors the history of
proposed underlying deficits, symptoms, and comorbid disorders in this
controversial disorder (e.g., Crary, 1995;
Yoss & Darley, 1974).
Specifically, the major assessment domains in Table 3 include potential diagnostic markers in speech production (8
studies), prosody (4 studies), speech perception (2 studies), nonspeech
oral-motor skills (1 study), and language and literacy skills (including both
oral and written language; 1 study). Notice also that although half of these
studies included non-English speakers, they were all children who speak Dutch,
which, as noted previously, is linguistically very similar to English. A
critical need exists for studies identifying biobehavioral markers in children
who are bilingual or monolingual in non-Germanic languages.
Although few specific findings were replicated within and across investigator
groups, we note the frequency of the following two diagnostic findings for CAS
in Table 3: lowered performance on tasks
involving production of multiple syllables (e.g., diadochokinetic, nonsense word
production, multisyllabic word production tasks) and differences or disorders on
tasks involving a variety of related prosodic variables. On the first type of
potential marker of CAS, the study by Thoonen et al. (1996) is unique for its findings indicating that
multisyllabic word tasks differentiated CAS from dysarthria. On the second class
of potential markers summarized in Table
3, differences in the stress patterns of children with CAS were
identified by Shriberg and colleagues in three studies (Shriberg et al., 1997a, 1997b; Shriberg, Campbell, et al.,
2003) and in a fourth study by Munson et al. (2003). Each of these studies compared the performance of
children with CAS to that of children with other speech sound disorders. Two of
the studies (Shriberg et al., 1997b;
Shriberg, Campbell, et al., 2003)
included information on diagnostic accuracy (sensitivity, specificity) of the
proposed stress markers.
Although no well-validated behavioral markers have emerged, the studies in Table 3 are interpreted as support for the
perspective that children suspected to have CAS present unique patterns of
difficulties in speech production, as well as in wider skill areas (e.g., areas
related to nonverbal intelligence and literacy). In the present context,
findings from these controlled studies suggest that many of the variables that
have been proposed on the basis of clinical experience may eventually meet
criteria for valid diagnostic markers. Note that these potential markers include
variants of those reviewed previously in this section that are currently in use
by practicing clinicians. Importantly, some of the CAS findings may reflect
sequelae of underlying markers (e.g., literacy differences may reflect poor
phonological foundations) rather than behavioral markers that tap core
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The literature reviewed on diagnostic assessment included recommendations cited
in peer-reviewed literature, descriptions of current patterns of clinical
practice, and findings from comparative studies in which between-group
statistical differences suggest potential markers with high diagnostic accuracy.
Currently, it appears that many of the features of CAS proposed by investigators
and used by practicing clinicians overlap those of other severe speech and
language disorders. Domains and measures that may have the greatest promise for
sensitive and specific identification of CAS are maximal performance for
multisyllabic productions and prosody. However, Williams and Stackhouse (1998) reported that rate changes far less
between the ages of 3 and 5 in typically developing children than do accuracy
and consistency. Such findings underscore the challenge of evaluating children
in the toddler age range, at which time even in typically developing children,
features such as multisyllabic productions and wide-ranging prosodic contexts
are not as likely to occur.
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Although CAS is thought to require specialized and relatively intensive treatment
(e.g., Davis & Velleman, 2000; Hall, 2000b; Strand, 1995; see later discussion), there are few recent articles that
have addressed this topic and even fewer that have reported treatment efficacy
findings. Methodological challenges include those described in preceding sections of
this report—the lack of a standard definition for CAS, difficulties in
differential diagnosis, likely significant heterogeneity in symptomatology, and
changing symptomatology over time (cf. Le-Normand et
al., 2000; Lewis et al., 2004).
Some of the potential treatment domains that follow from the literature reviewed in
the previous section include the areas of speech perception, speech production,
nonspeech motor skills, prosody, language (including narrative and pragmatic
skills), and metalinguistic/literacy skills. Notably, however, the few articles
reviewed below, which comprise the recent treatment literature as well as selected
older articles, have focused primarily on the overall communication skills of these
children and on improvement in speech production. Most of the studies have been
conducted within a clinical rather than school setting, making their
generalizability to school practice as yet hard to gauge. Treatment involving
oral-motor exercises as a means of addressing speech-motor production was included
as a small component of a multicomponent treatment approach in only one of the
reviewed studies (Bahr, Velleman, & Ziegler,
1999; see Forrest, 2002, for a
critique). To date, there is no treatment study in CAS that has focused on
culturally and linguistically diverse populations.
As indicated in the Introduction and Overview, contemporary reviews of treatment have
been heavily influenced by the emerging standards of evidence associated with
evidence-based practice (ASHA, 2004; Reilly, Douglas, & Oates, 2004; Yorkston et al., 2001). Table 4 is an adaptation of the Scottish Intercollegiate
Guidelines Network (SIGN) used in ASHA's 2004 technical report,
Evidence-Based Practice in Communication Disorders: An
Introduction. This system illustrates one of several currently used to
classify levels of evidence for treatment studies. As this report was finalized, an
amended version of the Oxford Centre for Evidence-Based Medicine system seems more
likely to be adopted by ASHA.
Table 4. Levels of evidence for studies of treatment efficacy, ranked according to the
quality and credibility from highest/most credible (Ia) to lowest/least
credible (IV). Reprinted from ASHA (2004, p. 2); adapted from SIGN.
||Well-designed meta-analysis of >1 randomized controlled
||Well-designed randomized controlled study
||Well-designed controlled study without randomization
||Well-designed quasi-experimental study
||Well-designed nonexperimental studies (i.e., correlational and case
||Expert committee report, consensus conference, clinical experience
of respected authorities
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Reduced intelligibility and comprehensibility (i.e., the ability to convey
intended messages within communicative contexts; Yorkston, Strand, & Kennedy, 1996) are viewed as especially
debilitating for many children with CAS (e.g., Hall, 2000a, 2000b). Treatment
goals for such children have sometimes focused on facilitation of overall
communication, with some studies using AAC. From the perspective of the World
Health Organization's (WHO) International Classification of
Impairments, Disabilities, and Handicaps (WHO, 1980) and International Classification of
Functioning, Disability, and Health (WHO, 2001), interventions designed to directly improve
overall communicative functioning may indirectly improve a child's
ability to function within relevant social and educational contexts. This
immediate focus on communicative effects differentiates AAC interventions from
studies focused on behavioral deficits (e.g., speech production deficits). In a
case study, Harlan (1984) described an
intervention that simultaneously used manual signing to support a
child's communication, while visual and tactile cueing were used to
foster speech production goals. A similar case study was reported in Culp (1989).
Two relatively recent investigations (Bornman,
Alant, & Meiring, 2001; Cumley
& Swanson, 1999) have used case study methodologies to
examine AAC interventions in a total of 4 children with CAS. Bornman and
colleagues, who focused on a 6-year-old child, described use of an alternative
digital voice output device. Cumley and Swanson, who studied 3 children of
differing ages (preschool, elementary, and junior-high school age), used
multimodal AAC that incorporated both a high-technology device and
low-technology communication aids (e.g., context-specific communication board,
remnant board, symbol dictionary) along with speech, gestures, and manual signs.
Findings from both reports provide detailed descriptions of the implementation
of AAC interventions for this population, suggesting the range of outcome
behaviors that might be affected using these approaches (e.g., language, success
in repairs of communication breakdown, level of communicative initiations). Both
studies emphasized interdisciplinary and family involvement as important to
successful implementation. Despite their descriptive value, however, these
studies provide only a low level of support for the efficacy of AAC with
children having CAS, due to the limited experimental control in case studies and
the limited information on all measures (note the positioning of case studies at
Level III in the SIGN evidence hierarchy; see Table 4).
Two additional recent studies (Binger &
Light, in press; Harris, Doyle
& Haaf, 1996) used the more rigorous methodology of single
subject experimental designs to address the language and communication needs of
participants, but studied children with significant concomitant language
disorders, developmental delay, or both. In the study by Harris et al., a
5-year-old boy with a “provisional diagnosis of developmental apraxia
of speech” (p. 232) who also exhibited receptive language delays,
served as the focus of a multiple baselines across communicative contexts (i.e.,
book reading and structured discourse) single subject design. The goal of the
intervention was to teach the segmentation and combination of syntactic
constituents to the child who primarily used messages consisting of a single
symbol in his augmented communications. Although the child was described
initially as using “multiple modalities of vocalization, gesture,
facial expression and PCS [Picture Communication Symbols] to
communicate” (p. 232), outcome data were limited to attainment of
augmented communication goals. Over twenty-two 45-minute treatment sessions,
positive effects of treatment on the use of multiple symbol communications were
observed after baselining for both communicative contexts, with a greater effect
observed in book reading than in structured discourse.
Binger and Light (in press) examined the effects of aided AAC modeling on the
development of multisymbol messages in 5 preschoolers—2 of whom had
diagnoses that included developmental delay and CAS. One of the latter 2
children had severe CAS. Both children used communication boards rather than
devices with voice output, the mode used by the other 3 children in the study. A
single subject multiple probe design was used. Symbol use was coded as having
taken place whether the child used a graphic symbol on the AAC device, a manual
sign, a consistently produced spoken “word,” or a
conventional head gesture (to indicate “yes” or
“no,” respectively). Other outcome measures examined were
the number of different semantic-syntactic categories used as well as social
validation measures. Both children with CAS showed positive gains across outcome
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Most treatment research has focused directly on improving speech production,
using several approaches that are consistent with the prevalent views, reviewed
previously, of CAS as a motor speech disorder. Writing in a professional
journal, but aiming primarily at a nonprofessional audience, Hall (2000b) usefully classified CAS treatment
approaches into four categories: linguistic approaches, motor-programming
approaches, combinations of linguistic and motor-programming approaches, and
approaches using specific sensory and gestural cueing techniques. Not included
in Hall's classification, but of historical interest, are early and
influential rhythmic approaches such as melodic intonation therapy (Helfrich-Miller, 1984, 1994), which was discussed in earlier treatment reviews
appearing as a book chapter (e.g., Jaffe,
1984), as well as in more recent such reviews (e.g., Square, 1999).
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Powell (1996) described a case study
of a child who had been diagnosed with CAS and oral apraxia. Previous
treatment at two different facilities, in which the child was typically seen
for two 30-minute sessions per week, had yielded little progress. Treatment
had reportedly appeared to focus on production of early developing sounds
and those that were emerging in the child's phonetic inventory, as
well as on the use of AAC. Powell initiated intensive treatment (four 1-hour
sessions per week for a 3-month period in the summer) that included a
significant focus on increasing the child's stimulability for
sounds not appearing in his speech. The rationale for increasing
stimulability, characterized as a phonologic approach, was based on findings
from research (Powell, 1993)
indicating that for children with speech sound disorders,
“stimulable sounds are likely to be added to the
speaker's phonetic inventory whereas non-stimulable sounds will
continue to be excluded” (Powell,
1996, p. 319). This goal was supplemented by other components
more typical of a traditional articulation approach (Bernthal & Bankson, 2004), including
stabilization of inconsistently used sounds in words and generalizations of
known sounds to the conversational level. Over the 3-month period, the
child's productive repertoire went from 11 to 17 phones, a 55%
increase. The author suggested that these findings indicate the potential
value of targeting stimulability in children with CAS. However, the overall
lack of control, characteristic of a case study (see Table 4, Level III), provides only a low level of
evidence for the findings. For example, the multiple components included in
the rich intervention protocol prohibit clear assignment of the source of
the findings to the stimulability activities.
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Motor programming approaches, which may also be termed
articulatory or phonetic approaches,
include integral stimulation (Strand
& Debertine, 2000; Strand
& Skinder, 1999) as well as a number of commercially
available intervention programs (e.g., Dauer,
Irwin, & Schippits, 1996; Kaufman, 1995; Kirkpatrick,
Stohr, & Kimbrough, 1990; Strode & Chamberlain, 1993; Williams & Stephens, 2004). Of these examples,
efficacy research has been reported only for the integral stimulation
approach (Strand & Debertine,
2000; Strand & Skinder,
1999). Integral stimulation is a modification of a treatment approach
developed for adults with apraxia by Rosenbek, Lemme, Ahern, Harris, and
Wertz (1973). It incorporates
principles of motor learning described by earlier authors in the field
(e.g., Rosenbek, Hansen, Baughman, &
Lemme, 1974) and also by researchers from outside of the field of
speech-language pathology. Notable in the latter category is the research by
Schmidt and colleagues (e.g., Schmidt,
1991; Schmidt & Bjork,
1992). Manipulation of parameters that affect motor learning, such as
frequency and nature of practice opportunities and knowledge of results and
performance, are fundamental elements of the integral stimulation approach.
Strand and Debertine completed a multiple-baseline-across-behaviors single
subject design to examine the efficacy of integral stimulation over 33
sessions (30 minutes, four times per week) for a girl (age 5;9) with low
comprehensibility (10%–20%) and CAS. Speech production gains for
a small number of functional one- and two-word phrases (e.g.,
“Hi, Dad”, “Not now!”,
“No!”) were observed when probe data for these treated
items were compared against baseline and control measures.
The generalizability of Strand and Debertine's (2000) findings is limited by a lack of replication
across subjects and because single subject experimental designs are not
recognized within the SIGN hierarchy shown in Table 4. Nonetheless, such designs are thought to
demonstrate a high degree of experimental control, especially for
heterogeneous and rare participant populations for which randomized control
trials may prove unfeasible or even ill-advised (Ylvisaker et al., 2002).
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For the time period reported at publication of this review, approximately the
past 12 years, the only published treatment study that can be readily
classified using Hall's (2000b) category of combined linguistic-motor programming treatment
is the research described in Bahr et al. (1999). This exploratory study described an inclusion classroom
staffed by a speech-language pathologist and elementary school teacher as
the context for treatment of 4 children diagnosed with suspected CAS
(referred to as “oral motor impairments”; Bahr et al., 1999, p. 25), as well as 5
children with speech sound disorders. It may be described as a combined
linguistic-motor programming approach because it was based on the work of
Velleman and Strand (1994), who, as
described in Bahr et al., proposed that CAS represents “an
underlying impairment of the ability to generate hierarchical plans or
sequences of behaviors—whether they be motor or linguistic or
both” (p. 21). Speech production served as a focus within a
regular kindergarten curriculum in which 5 children with typically
developing speech also participated. Classroom activities ranged from those
focusing on oral-motor and oral sensory experiences (e.g., light touch and
brushing of the face and articulators) to more phonological aspects of
speech production focusing on phoneme practice. The latter activities made
use of tactile cues as well as descriptive phrases to define important sound
characteristics, such as those used in Metaphon (Dean & Howell, 1986). Sounds were practiced in
varying phonetic contexts and, over time, in longer and more complex
syllabic structures. Prosody also served as a treatment focus. If children
were unable to complete activities within the group context, they received
individual treatment on an as-needed basis. The authors' impression
was that children made positive progress in speech production and
intelligibility, but no data were provided to support those
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As with the class of approaches above, there have been no treatment methods
during the review period that have focused on specific sensory and gestural
cueing techniques, although this approach has been described as a component
of intervention in many less recent papers (e.g., Bashir, Graham-Jones, & Bostwick, 1984; Chappell, 1974; Chumpelik, 1984; Hayden
& Square, 1994; Klick,
1985). However, one recent paper that described what may be
considered a sensory and gestural cueing approach consists of a literature
review and case description concerned with the use of instrumentation to
support children's speech production treatment (Gibbon, Stewart, Hardcastle, & Crampin,
1999). The authors introduced the use of electropalatography for
children described as having persistent speech sound disorders, a category
that can include children suspected to have CAS (although CAS was not
considered as a diagnosis for the child described). Electropalatography is
used to obtain detailed assessment of tongue movement and provides visual
feedback regarding tongue contact with an artificial palate.
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There have been few treatment studies of CAS since approximately 1995. Four
treatment studies were identified, none of which met the highest level of
evidence within both the hierarchy described in Table 4 and others that have been proposed (e.g., Robey, 2004). Examination of the earlier
treatment literature (i.e., before 1995) failed to reveal a stronger evidence
base. For example, Rosenbek et al. (1974)
and Yoss and Darley (1974) reported on
treatment studies falling virtually at the same level of evidence as the
majority of more recent studies described above, due to their use of single- and
multiple-case study methods. Earlier reported treatment studies shared current
emphasis on the importance of practice, use of visual cues (ranging from mirror
work to gestural cues to written words), early introduction of self-monitoring,
and attention to stress production. These themes were noted in a review of this
literature completed by Pannbacker (1988). Clearly, the limited evidence on treatment efficacy is one of the
most clinically pressing needs in CAS research identified in this report.
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Earlier sections of this report have reviewed the scientific foundations for viewing
CAS as a clinical entity. The Committee views the aggregate literature findings as
support for the position that CAS should be included as a diagnostic entity within
the class of childhood speech sound disorders. Findings also support viewing CAS as
a symptom complex, with specific features varying in type and severity from child to
child and over time. The available information indicates that unlike speech delay,
the speech and prosody characteristics of CAS are likely to persist past the
developmental period (Lewis et al., 2004).
Moreover, language and metalinguistic/literacy deficits appear to often accompany
the motor speech constraints that are the core deficit in CAS. Although research to
date has not provided sufficient information to support specific assessment and
treatment guidelines, the following discussion includes general interim
recommendations for assessment and treatment of this challenging neurobehavioral
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The Committee concludes that CAS is a communication disorder for which there is,
at present, no certain genetic, neurobiologic, or behavioral marker. A
well-trained speech-language pathologist with specific experience in pediatric
speech sound disorders, including motor speech disorders, is the appropriate
professional to assess and diagnose CAS. Referral to an occupational therapist
for nonspeech, sensory-motor, or fine motor issues is often appropriate.
Referral to a physical therapist is also warranted if gross motor skills or
overall muscle tone are of concern, as is referral to a pediatric neurologist if
neurological indicators (e.g., potential seizure activity) are present. As CAS
may be a secondary diagnosis for children with autism, Down syndrome, and other
widely recognized disorders with genetic and/or neurobehavioral bases, the
speech-language pathologist may not be the first professional to assess the
client. Whatever the history of identification or differential diagnosis, the
evaluation and treatment of the child's speech sound disorder falls
within the realm of clinical speech pathology. Thus, it is a speech-language
pathologist who diagnoses CAS, not a neurologist or other medical practitioner.
Speech-language pathologists who lack training or experience with this disorder
should refer such cases to others or carry out assessments and interventions
under the supervision of a speech-language pathologist with the appropriate
background. Moreover, if an examiner lacks knowledge or experience in an allied
area that is relevant for a particular child, such as AAC for the child with
severe CAS, the examiner should make a referral to another speech-language
pathologist with expertise in that area.
Overdiagnosis of CAS has become a widely discussed professional issue. As
reviewed previously, speech-language pathologists appear to lack information
about the key diagnostic characteristics of the disorder (Davis et al., 1998; Forrest,
2003) and research indicates that many of its features overlap with
those of other speech sound disorders (McCabe et
al., 1998). In view of the many diagnostic constraints reviewed in
this document, it may be more appropriate in some diagnostic reports to use
classification terms such as CAS cannot be ruled out, signs are
consistent with CAS, or suspected to have CAS,
rather than an unequivocal CAS. These cautions in
classification apply especially to the challenges associated with diagnosis of
younger children. Research has not addressed the question of the youngest age at
which a diagnosis of CAS can be valid and reliable. Clinical guidelines on the
appropriate minimum age for the diagnosis of CAS appear to range from under 2
years of age to under 4 years of age, including both children with idiopathic
CAS and with CAS as a secondary symptom in neurological and complex
Assessment of children for whom the diagnosis of childhood apraxia of speech is
in question should include measures of all the domains described in this report:
nonspeech oral-motor, speech production, prosody, voice, speech perception,
language, and, for older children, metalinguistic/literacy skills. Of these
domains, there is some consensus on the validity of the following three
segmental and suprasegmental features of CAS: (a) inconsistent errors on
consonants and vowels in repeated productions of syllables or words, (b)
lengthened and disrupted coarticulatory transitions between sounds and
syllables, and (c) inappropriate prosody, especially in the realization of
lexical or phrasal stress. A thorough case history is vital. The cultural and
linguistic background of each child must be fully understood and provisions made
in assessment to address relevant sociolinguistic needs.
Although research support for specific assessment procedures is limited by
methodological variables discussed previously, clinically experienced
researchers stress the diagnostic importance of certain key contrasts (Caruso & Strand, 1999; Davis & Velleman, 2000; Davis et al., 1998; Hall et al., 1993; Hodge,
1994; Skinder-Meredith, 2001;
Thoonen et al., 1999; Velleman, 2003). Throughout an evaluation,
emphasis should be on differentiating children's performance on
functional/automatic versus volitional actions, single postures versus sequences
of postures, simple contexts versus more complex or novel contexts, repetitions
of the same stimuli versus repetitions of varying stimuli (e.g., sequential
motion rates vs. alternating motion rates), and tasks for which auditory versus
visual versus tactile versus combinations of cues are provided. Fluidity
(smoothness) and rate as well as accuracy should be monitored, as there may be
trade-offs among these variables (e.g., the child's productions are
very smooth if slow compared to arrhythmic if rapid). Assessment should include
performance in multiple contexts (e.g., spontaneous, elicited, imitation;
syllable, single-word, phrase, sentence, discourse). At present, no standardized
test incorporates all of these features and those that have been formally
critiqued (e.g., Apraxia Profile [Hickman,
1997], Guyette, 2001; Screening
Test of Developmental Apraxia of Speech-2 [Blakely, 2001], McCauley,
2003; Verbal Motor Production Assessment for Children [Hayden & Square, 1999], Snyder, 2005) have been found lacking in
terms of important psychometric standards. Few of these recommendations have
been studied in well-controlled designs, but some findings support their
importance in differentiating children suspected to have CAS from those with
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Assessment and diagnosis of CAS are the responsibility of the speech-language
pathologist with specialized knowledge, training, and skills in this area.
The symptoms of CAS change over time and may be influenced by development in
other behavioral domains. Although no single differential diagnostic marker
with high sensitivity and specificity has been documented to date, there is
some consensus among clinical researchers on three segmental and
supra-segmental features observed in children suspected to have CAS.
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Given the need for repetitive planning, programming, and production practice
in motor speech disorders, clinical sources stress the need for intensive
and individualized treatment of apraxia, especially for children with very
little functional communication. There is emerging research support for the
need to provide three to five individual sessions per week for children with
apraxia as compared to the traditional, less intensive, one to two sessions
per week (Hall et al., 1993; Skinder-Meredith, 2001; Strand & Skinder, 1999).
Ideally, this should be done in as naturalistic an environment as possible
to facilitate carry-over and generalization of skills. Although home
practice is critical for optimal progress, it cannot take the place of
individual treatment provided by a speech-language pathologist who has
expertise in motor speech skill facilitation. For the diverse backgrounds of
children seen for early intervention, including their stages of
psychological/emotional development, the Committee sees value in endorsing a
treatment plan for optimum progress based on provision of intensive therapy.
Individual differences among children will also underlie rationale for
changing the form, content, and intensity of treatment throughout the course
of intervention. If toddler and preschool-age children are seen for early
intervention that targets their speechmotor deficits, the frequency of
treatment may be able to be reduced over time. As long as the primary goal
is to improve the motoric aspects of the child's speech production
(i.e., more time for motor practice), individual therapy should be the
preferred approach regardless of age. For children whose severity of
involvement has decreased and whose treatment goals have begun to move
toward language and pragmatic skills enhancement, a combination of both
individual and small group therapy may also be optimal for some children,
providing that a treatment focus is maintained on speech production.
For children with apraxia who also require other therapeutic services (e.g.,
occupational therapy, physical therapy), care must be taken to vary therapy
activities to avoid fatigue. Collaborative decision-making is critical in
such cases, where creative use of alternatives, such as co-treatment, should
be considered (Davis & Velleman,
2000; Velleman & Strand,
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In view of the Committee's information indicating that children are
being enrolled for treatment of CAS at increasingly younger ages, careful
consideration should be given to the length of the therapy session. If
repetitive practice of speech-motor patterns is targeted in a therapy
session, many children in the younger age ranges can remain engaged for only
a maximum of 30 minutes per session. There are certainly those children for
whom “adjustment” time is necessary prior to the
introduction of more intensive treatment activities. Some service providers
are allotted a certain number of minutes or hours per week of therapy time
per child. Given the option between two 1-hour sessions and four 30-minute
sessions, many clinical researchers strongly recommend the latter (e.g.,
“more sessions—less time per session”;
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The treatment literature in CAS indicates that the operating principles and
strategies overlap those recommended for children with other speech sound
disorders. Overall, the principles of motor learning theory and intensity of
speech-motor practice appear to be the most often emphasized in an optimal
treatment program. These recommendations include the need for distributed
practice, in which speech-motor practice is carried out across a variety of
activities, settings, and situations, and includes several exemplars per
pattern (e.g., Strand & Skinder,
1999). Recall from the discussion above that speech requires more
flexibility, less stereotyped rhythmicity, finer levels of coordination, and
lower levels of strength than other nonspeech oral motor activities such as
chewing, blowing, and the like. A systematic review addressing this topic is
currently underway by an ASHA committee through its National Center for
Evidence-Based Practice. Until the committee report is available, the
consensus opinion is nonspeech oro-motor therapy is neither necessary nor
sufficient for improved speech production. Another often-cited
recommendation is to take advantage of other areas of strength for children
with CAS by utilizing a multisensory approach to treatment. The use of sign
language, pictures, AAC systems, visual prompts, and touch cues have been
described as being extremely effective for children with CAS, providing
functional communication while at the same time supporting and enhancing
verbal speech production. Another important element for optimal progress and
carry-over is to involve as many important people in the child's
life as possible, in a culturally appropriate manner, in understanding and
completing therapy goals outside the treatment setting.
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Although reimbursement and funding issues are a concern for all childhood
speech sound disorders, insurance funding issues in CAS have become a topic
of considerable interest. As reviewed, children with CAS are likely to
require intensive services over a long period of time. In a study on
treatment outcomes from one large facility, Campbell (1999) reported that children with the diagnosis of CAS
needed 81% more individual therapy sessions than children described as
having a phonological disorder in order to achieve the same functional
outcome. Of even more interest to funders are Campbell's findings
indicating that the average cost of achieving the same functional outcome
for a child with CAS was $11,325, compared to $2,000 for a child with a
phonological disorder. This study reported that in addition to time needed
for treatment of children with CAS, professionals needed additional time to
identify the appropriate diagnostic codes for CAS, write reports, educate
funders, and assist caregivers with advocacy needs in order to pursue
reimbursement. Web sites such as that of the Childhood Apraxia of Speech
Association of North America (http://www.apraxia-kids.org) have developed
useful materials to help caregivers and others with the complex of resources
to aid families and therapists in securing insurance funding.
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Recent research has continued to validate co-morbid deficits that accompany
the severe speech production constraints that characterize children with
CAS. As reviewed, Lewis and her colleagues in a follow-up study reported
that children with CAS are likely to have deficits in both expressive and
receptive language as well as in academic areas such as reading, spelling,
and written expression (Lewis et al.,
2004). Lewis et al. proposed that speech-language pathologists should
consider offering phonological awareness and preliteracy training as part of
intervention for children with CAS at risk for language learning challenges.
For some children with CAS, therapy approaches that focus exclusively on oral
output are inadequate, requiring augmentative and alternative modes of
communication (Cumley & Swanson,
1999). AAC systems, of all types, require time for speech-language
pathologists, other school personnel, and the child to learn and use in
order to expand communication opportunities. Thus, in addition to their
needs for intensive, individual speech and/or AAC treatment to maximize
effective communication, children with CAS will also require therapeutic
time to address a number of other issues—all of which contribute
to these children becoming functional communicators who can be comfortable
with and learn in the school environment. This level of need places demands
on the speech-language pathologist, regardless of practice setting. It also
requires that both private speech therapy providers and school-based
clinicians work closely with one another and with families. Collaboration is
required in order to optimally integrate the child's needs into the
intervention time available and to assemble the best possible program of
services for affected children.
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Although the specific forms of treatment may change over time, the Committee
recommends that children with CAS receive intensive services, especially in
the earlier stages of intervention. The rationale for this recommendation is
based on the assumption that the child's potential for
normalization of speech and prosody may be substantially reduced if not
addressed during early periods of growth and development. There are
treatment constraints (e.g., limited funding, limited staff availability) in
certain settings that make it challenging to secure intensive, individual
therapy. Resources need to be made available to insurance companies, school
districts, and specialized programs to provide children with CAS the best
opportunity to develop functional communication. Sociodemographic issues
should be addressed to ensure that all children with CAS receive the type
and intensity of services needed to treat this complex motor speech
The Committee also underscores the responsibility of ASHA and its membership
to educate allied health care professionals on current perspectives in CAS
so that timely referrals are made and appropriate therapeutic services are
supported. This requires education at both local and national levels. More
generally, speech-language pathologists must be adequately trained in areas
such as differential diagnosis of childhood motor speech disorders, motor
learning theory, cueing strategy usage, and other intervention techniques
that clinical researchers have reported as effective. Such knowledge and
skills training is the responsibility of academic training programs. New
forms of partnerships must emerge among clinicians and across therapeutic
settings to create intervention programs that maximize resources and address
the multifaceted deficits presented by this clinical population. Finally,
trends in the treatment literature indicate that professional education and
collaboration are needed to enhance the resources and opportunities for
children with apraxia of speech.
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The Committee has attempted to provide a broad-based review of contemporary issues,
findings, and directions in CAS research and practice. The summaries at the end of
each section were designed to provide a digest of the key issues, findings, and
directions that emerged from our review of the literature. We conclude this report
with a consolidated list of research needs and the Committee's primary
recommendations, the latter of which are also available in the companion position
statement on this topic.
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The Committee's primary conclusion is that, as with many other complex
neurobehavioral disorders, research in CAS has not provided clear answers to the
following five interdependent questions: (1) What are the biobehavioral origins
of CAS? (2) What methods to diagnose CAS are valid and reliable for children of
different ages and with co-occurring problems? (3) What is the prognosis for
children with CAS? (4) What are the most effective ways to treat CAS? and (5)
What might be done to prevent CAS and/or mitigate its impact on other areas of
development? The Committee's most compelling single finding is the lack
of consensus among investigators on the core diagnostic features of this
disorder, thus limiting the utility of all research on optimum assessment and
treatment. That is, lack of one or more necessary and sufficient diagnostic
markers of CAS limits studies of the origins and neural substrates of CAS, and
in turn, the scope and depth of our guidelines and recommendations for service
The Committee's second conclusion is that there is a need for
large-scale, collaborative interdisciplinary research in CAS. CAS research
clearly needs to expand to different, broader types of research models. Most of
the CAS findings reviewed in this report reflect the research of individuals or
relatively small groups of investigators using small numbers of participants
suspected to have CAS. In comparison, emerging findings from research on such
widely studied complex neurobehavioral disorders as autism, dyslexia, and
language impairment reflect the research of many international,
multidisciplinary collaborations. The only such research of this scope on CAS to
date is the programmatic studies of the KE family.
The following list of six basic and applied needs is a brief outline of the
Committee's recommendations for a CAS research agenda.
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Speech motor control and neurolinguistic studies using contemporary
methods in such disciplines as neurophysiology, neurochemistry,
neural imaging, kinematics, and acoustics to describe the
pathophysiology of CAS.
Molecular genetic studies using contemporary genomic and
bioinformatic resources to provide an eventual account of the
developmental neurobiology of CAS.
Epidemiological studies of CAS to delineate the gender-specific risk
for this disorder in children reared in different countries,
languages, races, ethnicities, and cultures.
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Cross-linguistic longitudinal studies to identify the core behavioral
features of CAS and to develop clinically efficient diagnostic
protocols for valid and reliable assessment of children at
prelinguistic and later stages of CAS.
Studies to develop treatment programs that are appropriate for
children of all ages and backgrounds with idiopathic CAS, as well as
multidisciplinary studies to develop treatment programs for children
with apraxia of speech occurring as the sequela of neurological
deficits and within complex neurobehavioral disorders.
Randomized control trials and smaller-scale studies to test the
efficacy of alternative treatment programs for children of all ages,
types, and severities of expression of CAS, with findings enabling
the development of guidelines for best practices.
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The Committee recommends that childhood apraxia of speech be recognized
as a type of childhood (pediatric) speech sound disorder that warrants
research and clinical attention.
The Committee recommends that childhood apraxia of speech
(CAS) be recognized as the classification term for children
with this disorder.
The Committee recommends the following definition for CAS:
Childhood apraxia of speech (CAS) is a
neurological childhood (pediatric) speech sound disorder in
which the precision and consistency of movements underlying
speech are impaired in the absence of neuromuscular deficits
(e.g., abnormal reflexes, abnormal tone). CAS may occur as a
result of known neurological impairment, in association with
complex neurobehavioral disorders of known or unknown origin, or
as an idiopathic neurogenic speech sound disorder. The core
impairment in planning and/or programming spatiotemporal
parameters of movement sequences results in errors in speech
sound production and prosody.
Review of the research literature indicates that, at present, there is no
one validated list of diagnostic features of CAS that differentiates
this disorder from other types of childhood speech sound disorders,
including those due to phonological-level delay or neuromuscular
disorder (dysarthria). Three segmental and suprasegmental features of
CAS that are consistent with a deficit in the planning and programming
of movements for speech have gained some consensus among investigators
in apraxia of speech in adults and children: (a) inconsistent errors on
consonants and vowels in repeated productions of syllables or words, (b)
lengthened and disrupted coarticulatory transitions between sounds and
syllables, and (c) inappropriate prosody, especially in the realization
of lexical or phrasal stress. These features are not proposed to be the
necessary and sufficient signs of CAS. As with other reported signs,
they change in relative frequency of occurrence with task complexity,
severity of involvement, and age. The complex of behavioral features
reportedly associated with CAS places a child at increased risk for
early and persistent problems in speech, expressive language, the
phonological foundations for literacy, and the possible need for
augmentative and alternative communication and assistive technology.
The Committee recommends that the American Speech-Language-Hearing
Association (ASHA) adopt the position that although referrals to other
professionals, including neurologists, occupational therapists, and
physical therapists, may often be appropriate for associated, nonspeech
issues, it is the speech-language pathologist who is responsible for
making the primary diagnosis of childhood apraxia of speech and for
designing, implementing, and monitoring the appropriate individualized
speech-language treatment program and/or augmentative and alternative
systems and assistive technology.
The Committee recommends that careful consideration be given to the form
and frequency of treatment for children suspected to have CAS, due to
its potential to persist and to be associated with other verbal trait
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