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Journal of Communication Disorders 55 (2015) 44–62
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Journal of Communication Disorders
Volubility, consonant, and syllable characteristics in infants
and toddlers later diagnosed with childhood apraxia of
speech: A pilot study
Megan Overby a,*, Susan S. Caspari b
a Duquesne University, 600 Forbes Avenue, Department of Speech-Language Pathology, Fisher Hall 421, Pittsburgh, PA 15282, United States
b Private Practice, 222 Cornell Avenue, Swarthmore, PA 19081, United States
A R T I C L E I N F O
Article history:
Received 29 August 2014
Received in revised form 26 February 2015
Accepted 6 April 2015
Available online 20 April 2015
Keywords:
Childhood apraxia of speech
Early intervention
Infants
Toddlers
A B S T R A C T
Purpose: This pilot study explored the volubility, consonant singleton acquisition, and
syllable structure development between infants and toddlers (birth–24 months) with
typical speech sound production (TYP) and those later diagnosed with childhood apraxia
of speech (CAS).
Method: A retrospective longitudinal between- and within-subjects research design was
utilized (TYP N = 2; CAS N = 4). Vocalizations from participants were analyzed between
birth–24 months from home videotapes, volunteered by the children’s parents, according
to type (nonresonant vs. resonant), volubility, place and manner of consonant singletons,
and syllable shape (V, CV, VC, CVC, VCV, CVCV, VCVC, and ‘‘Other’’).
Results: Volubility between groups was not significant but statistically significant
differences were found in the number of: resonant and non-resonant productions;
different consonant singletons; different place features; different manner classes; and
proportional use of fricative, glottal, and voiceless phones. Infants and toddlers in the CAS
group also demonstrated difficulty with CVCs, had limited syllable shapes, and possible
regression of vowel syllable structure.
Conclusions: Data corroborate parent reports that infants and toddlers later diagnosed
with CAS present differently than do those with typical speech sound skills. Additional
study with infants and toddlers later diagnosed with non-CAS speech sound disorder is
needed.
Learning outcomes: Readers will: (1) describe current perspectives on volubility of
infants and toddlers later diagnosed with CAS; (2) describe current perspectives of the
consonant singleton and syllable shape inventories of infants and toddlers later diagnosed
with CAS; and (3) discuss the potential differences between the speech sound
development of infants and toddlers later diagnosed with CAS and those with typical
speech sound skill.
� 2015 Elsevier Inc. All rights reserved.
* Corresponding author at: Duquesne University, 600 Forbes Avenue, Department of Speech-Language Pathology, Fisher Hall 421, Pittsburgh, PA 15282,
United States. Tel.: +1 412 396 2524.
E-mail addresses: overbym@duq.edu (M. Overby), casparisue@gmail.com (S.S. Caspari).
http://dx.doi.org/10.1016/j.jcomdis.2015.04.001
0021-9924/� 2015 Elsevier Inc. All rights reserved.
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mailto:overbym@duq.edu
mailto:casparisue@gmail.com
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M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–62 45
1. Introduction
In the study of childhood communication disorders, small-scale investigations of infant and toddler vocalizations have
played an important role in the development of effective early assessment and intervention practices. These preliminary studies,
typically limited to examining consonant and syllable profiles within specific populations or subgroups, have aided our
understanding of children with typical speech sound development, at high risk for speech-language disorder (Oller, Eilers, Neal,
& Schwartz, 1999), Down’s syndrome (Smith & Oller, 1981), and hearing impairment (Ertmer et al., 2002; Ertmer & Mellon, 2001;
Ertmer, Kloiber, Jung, Kirleis, & Bradford, 2012). Although initially descriptive in nature, small-scale single subgroup studies
provide important direction for larger comparative studies within heterogeneous populations (Receveur et al., 2005).
A proposed subgroup of particular interest to speech-language pathologists (SLPs) is childhood apraxia of speech (CAS), a
disorder in which sensory and speech praxis motor deficits result in inconsistent errors on consonants and vowels, difficulty
with segmental and syllable transitions, and/or inappropriate lexical or phrasal prosody (American Speech-Language-
Hearing Association ASHA, 2007). Studies of CAS have concentrated on children older than 3 years and are rarely
longitudinal, though one notable exception is a longitudinal study reported in three related articles (exploring consonant
and syllable structure patterns, vowel production, and phonetic variability) of three children with CAS between the ages of
4.6 and 7.7 years (Davis, Jacks, & Marquardt, 2005; Jacks, Marquardt, & Davis, 2006; Marquardt, Jacks, & Davis, 2004).
While studies of older children with CAS are important, a growing body of evidence points to genetic underpinnings of the
disorder, suggesting the impairment should be manifested prelinguistically in early vocal development (Fisher, Lai, &
Monaco, 2003; Highman, Hennessey, Sherwood, & Leitão, 2008; Highman, Hennessey, Leitão, & Piek, 2013; Lewis, Freebairn,
Hansen, Taylor, et al., 2004; Worthey et al., 2013). However, most of what is hypothesized about the early course of CAS has
come from parents’ anecdotal recall of their child’s speech development (Highman et al., 2008, 2013; Le Normand, Vaivre-
Douret, Payan, & Cohen, 2000; Teverovsky, Bickel, & Feldman, 2009), and although longitudinal studies of the early speech
sound behaviors of children who later present with CAS would be helpful in further understanding the disorder, there are
currently no such studies. To address this gap, this is the first in an anticipated series of longitudinal studies exploring the
speech sound skills between birth and 24 months for a small opportunistic sample of infants who later presented with
suspected childhood apraxia of speech (CAS).
1.1. Suspected early descriptors of childhood apraxia of speech (CAS)
As reported by Marquardt et al. (2004), children with CAS may demonstrate high levels of token and error token
variability, low levels of word target stability, and variability across and within children. Though little is known about the
speech sound development of infants and toddlers later diagnosed with CAS, they are reported by their parents and by
investigators to be different from children with typical speech sound development across several parameters.
1.1.1. Low volubility
Volubility, the amount of vocalization produced regardless of the type of vocalization, has not been studied in infants and
toddlers later diagnosed with CAS. Parents of children with CAS have reported their children were ‘‘quiet’’ as infants (Aziz,
Shohdi, Osman, & Habib, 2010; Velleman & Strand, 1994) and reduced overall vocal output has been speculated to be
descriptive of children with CAS (Davis & Velleman, 2000). In a retrospective study of 192 parents of children with CAS, 71%
of parents reported their child had minimal speech at the time of diagnosis, 52% had poor intelligibility, and 42% struggled to
speak (Teverovsky et al., 2009). However, children were identified with the disorder based solely on parent report.
Aziz et al. (2010) explored the language, speech, and non-speech oral skills of 30 children (aged 4–6 years): 10 with
multiple phonological disorders (MPD); 10 with suspected CAS (CAS); and 10 with typical speech-language development. A
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http://www.jneurodevdisorders.com/content/5/1/29
http://refhub.elsevier.com/S0021-9924(15)00024-6/sbref0345
	Volubility, consonant, and syllable characteristics in infants and toddlers later diagnosed with childhood apraxia of speech: A pilot study
	1 Introduction
	1.1 Suspected early descriptors of childhood apraxia of speech (CAS)
	1.1.1 Low volubility
	1.1.2 Emergence of consonant inventories
	1.1.3 Limited syllable structures
	1.1.4 Summary
	2 The current study
	2.1 Method
	2.1.1 Participants
	2.1.2 Assessments
	2.1.2.1 Speech motor control
	2.1.2.2 Speech sound production
	2.1.2.3 Language skills
	2.1.3 Data collection from videotapes
	2.1.4 Reliability
	3 Results
	3.1 Volubility
	3.2 Consonant singleton inventories
	3.3 Consonant singleton use by types of place feature
	3.4 Consonant singleton use by type of manner class
	3.5 Consonant singleton use by voicing feature
	3.6 Development of syllable structures
	3.7 Individual profiles of infants and toddlers later diagnosed with CAS
	4 Discussion
	5 Limitations and future research needs
	6 Conclusion
	Acknowledgements
	Appendix A Appendix A
	Appendix B Appendix B
	Appendix C Continuing Education Questions
	Referenceslittle (or had little phonetic
diversity) compared to 50% of the MPD group and 30% of the control group.
Highman et al. (2008) compared parental recall of early babbling and vocalizations among parents of children with
suspected CAS (CAS) (n = 20), Specific Language Impairment (SLI) (n = 20), and typically developing (TD) speech-language
skills (n = 20). Multiple measures of volubility were determined by asking parents if they heard their child ‘‘make many
sounds,’’ ‘‘make vowel noises,’’ or produce different types of babbling. Overall volubility was significant between the CAS and
TD groups (phave been limited to simple consonant (C) or vowel (V)
structures (such as CV) with little diversity when compared to typically developing peers.
The aim of the current study was to ascertain whether parental report and common perceptions among professionals of
differences in the speech sound development (volubility, consonant use, and syllable shapes) of infants and toddlers later
diagnosed with CAS could be quantified between birth and 24 months.
M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–62 47
2. The current study
This investigation was a retrospective longitudinal between- and within-subjects design comparing the experimental
group to the comparison group. Participants’ speech-language skills were assessed between ages 36 months–76 months, and
then home videotapes between birth and 24 months, provided by the parents, were analyzed. Our directional hypotheses
were that infants and toddlers later diagnosed with CAS would: (a) have less volubility than the comparison group as well as
produce fewer resonant productions than the comparison group; (b) use fewer and less diverse consonants than the
comparison group; (c) use fewer and less diverse syllable shapes than the comparison group.
2.1. Method
2.1.1. Participants
Participants were four monolingual English-speaking children with CAS (3 males, 1 female; age: M = 41.75 months,
SD = 8.50, range = 36–54 months) (CASF1, CASM1, CASM2, CASM3) selected from the caseloads of the authors and two
children with typical speech sound skills (1 male, 1 female; age: M = 64 months, SD = 17.0, range, 76–52 months) (TYPF1,
TYPM1). All children had to have been regularly videotaped by their parents between birth and 24 months, with at least 2 h of
video available for analysis by the researchers.
All participants were identified by their parents as White (Non-Hispanic). Socioeconomic status was considered via
coding of parent education level (2 years college or technical school = 0, 4 years college = 1, post-graduate = 2) and current
employment (unskilled employment such as grocery clerk or stay-at-home parent = 0 and skilled employment such as
banking or education = 1). Mann–Whitney U analysis of the means revealed no statistically significant difference between
the groups (CAS M = .88, SD = .25; TYP M = 1.13, SD = .18).
Exclusionary criteria included structural deficits (e.g. cleft lip and/or palate), documented or suspected hearing loss
(participants with more than three acute episodes of otitis media from birth to 24 months were excluded), receptive
language delay, autism, syndromes, developmental delay, and dysarthria. Participants in the TYP group were required to
have a standard score of 85–115 on a standardized measure of articulation.
2.1.2. Assessments
Participants were identified by the authors (both of whom have training in the differential diagnosis of CAS) based upon
clinical examination of the child’s speech motor control, speech sound production, and language (Table 1). Assessments for
participants with CAS varied slightly according to the initial reason for referral to the authors’ caseloads.
2.1.2.1. Speech motor control. Assessment of speech motor control included differentiation of the child’s performance
relative to skills described by ASHA (2007): functional/automatic vs. volitional movement; single articulatory postures vs.
sequences of articulatory postures; simple contexts vs. more complex or novel contexts; repetitions of the same stimuli vs.
repetitions of varying stimuli; tasks incorporating auditory vs. visual vs. tactile vs. combinations of cues; fluidity
(smoothness), rate, and accuracy of production; and performance in multiple contexts (e.g., spontaneous, elicited, imitation
levels of syllables, single-word, phrases, sentences, and discourse). Both standardized (Kaufman Speech Praxis for Children)
(Kaufman, 1995) and unstandardized measures (diadochokinetic rate (Robbins & Klee, 1987); the Dynamic Evaluation of
Motor Speech Skill (DEMSS) (Strand, McCauley, Weigand, Stoeckel, & Baas, 2013)) were administered. As a measure of oral,
non-verbal motor planning and programming skills, the second author administered the Examination for Non-Verbal Oral
Apraxia (NVOA) (Strand, 2005) to some participants.
Diagnosis of CAS was confirmed using a version of the pediatric adaptation of the Mayo Clinic assessment for motor
speech disorders (‘‘Mayo 10’’) (Shriberg and Strand, 2014; Shriberg, Potter, & Strand, 2011; Shriberg, Lohmeier, Strand, &
Jakielski, 2012). In the pediatric ‘‘Mayo 10,’’ CAS is identified if the child demonstrates at least four Mayo Clinic signs of CAS
over a range of three or more speech tasks. For example, a child demonstrating four different signs (e.g., vowel distortions,
prosody/stress errors, voicing errors, and groping) in only a single speech task (e.g., conversational speech) would not meet
criteria for diagnosis of CAS. On the other hand, criteria would be met if those same signs were identified across at least three
different speech tasks, as in the following example: (a) vowel distortions in connected speech and in repetition of words with
three or more syllables; (b) voicing errors in connected speech and in repetition of 1-syllable words; and (c) groping when
repeating one syllable words and in DDK tasks (see Appendix A, Table A1). To be counted as a sign in a speech task, there must
have been at least two exemplars within that task.
2.1.2.2. Speech sound production. Speech sound production was assessed with either the Diagnostic Evaluation of
Articulation and Phonology (DEAP) (Dodd, Hua, Crosbie, Holm & Ozanne, 2002) or Goldman-Fristoe Test of Articulation – 2
(GTFA – 2) (Goldman & Fristoe, 2000). Percent of consonants correct – revised (PCC – R) and percent of vowels correct –
revised (PVC – R) (Shriberg et al., 1997) was calculated and intelligibility considered following procedures described by
Shipley and McAfee (2009).
2.1.2.3. Language skills. Standardized language measures included the Peabody Picture Vocabulary Test – 3 (Dunn & Dunn,
1997), Peabody Picture Vocabulary Test – 4 (Dunn & Dunn, 2007), Clinical Evaluation of Language Fundamentals – 4
Table 1
Descriptive data for participants at time of diagnosis.
Participant Gender Age
(months)
Speech and nonverbal motor control Speech sound production Language
Mayo
10 signsa
Speech
tasksb
Test Score Intelligibility PCC-Rc PVC-Rd Articulation
test
Standard
score
Test Standard
score
MLUe
Word Utterance
CASF1 F 54 VW R1S KSPCf 80% 74% 79% 90% DEAPg CELF-4h 3.0
DS R2S Oral movements 28 Articulation 4 Core Language 90
AT RMS Basic movements 77 Phonology 5 Receptive Language 77
IS ART Complex movements 47 Expressive Language 93
VE CSS Language Structure 89
SR DDK DDKi 0 CTOPPj (Composites)
ID /p^t^k^/ Phonological awareness 100
Rapid Naming 88
Phonological Memory 82
CASM1 M 41 VW R1S DEMSSk 62% 38% 77% 73% GFTA-2l 107 PPVT-4m 113 4.1
DS R2S Vowels 108/120
SE RMS Accuracy 226/240 OWLSn
VE ART Prosody 23/24 Oral Composite 118
ID CSS Consistency 36/42 Listening Comprehension 113
Oral Expression 120
CASM2 M 36 VW R1S DEMSS 36% 34% 58% 62% n/a n/a PPVT-3o 111 1.9
SE R2S Vowels 102/120
VE RMS Accuracy 164/240 CELF-P2q
ID CSS Prosody 22/24 Receptive Language 77
Consistency 21/42 Expressive Language 85
Language Structure 71
NVOAp 10/20 Language Content 91
CASM3 M 36 VW R1S DEMSS 14% 1% 72% 79% n/a n/a PPVT-3 109 CNDr
DS R2S Vowels 106/120
AT RMS Accuracy 162/240 CELF-P2
IS CSS Prosody 23/24 Receptive Language 86
VE Consistency 22/42 Expressive Language 79
Language Structure 73
NVOA 8/20 Language Content 93
TYPF1 F 76 None None 99% 94% 91% 99% GTFA-2f 103 PLS-5g 4.5
Auditory Comprehension 112
Expressive Communication 128
Total Language 122
TYPM1 M 52 None None 97% 85% 91% 99% GTFA-2 110 PLS-5 5.1
Auditory Comprehension 122
Expressive Communication 133
Total Language 129
Note. a Mayo Clinic System Signs acronyms in Appendix A; b Speech tasks affected by one or more signs(acronyms in Appendix A); c Percent of Consonants Correct-Revised (based on intelligible utterances) (Shriberg
et al., 1997); d Percent of Vowels Correct-Revised (based on intelligible utterances) (Shriberg et al., 1997); e Mean Length of Utterance; f Kaufman Speech Praxis for Children (Kaufman, 1995); g Diagnostic Evaluation
of Articulation and Phonology (Dodd et al., 2002); h Clinical Evaluation of Language Fundamentals – 4 (Semel et al., 2003); i Diadochokinetic rate (Robbins & Klee, 1987); j Comprehensive test of phonological
processing (Wagner et al., 1999); k Dynamic evaluation of motor speech skill (Strand et al., 2013); l Goldman–Fristoe Test of Articulation – 2 (Goldman & Fristoe, 2000); m Peabody Picture Vocabulary Test – 4 (Dunn
& Dunn, 2007); n Oral and Written Language Scales (Carrow-Woolfolk, 1996); o Peabody Picture Vocabulary Test – 3 (Dunn & Dunn, 1997); p Nonverbal Oral Apraxia; q Clinical Evaluation of Language Fundamentals
Preschool – 2 (Semel et al., 2004); rCould not determine; sPreschool Language Scale – 5 (Zimmerman, Steiner, & Pond, 2011).
M
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 C
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M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–62 49
(Semel, Wiig, & Secord, 2003), Clinical Evaluation of Language Fundamentals – Preschool –2 (Semel, Wiig, & Secord, 2004),
and the Oral Written Language Scale (Carrow-Woolfolk, 1996). The Comprehensive Test of Phonological Processing
(Wagner, Torgesen, & Rashotte, 1999) was administered only to CASF1 due to her age, school-readiness, and parental
referral question. Mean length of utterance was obtained for all participants except CASM3 because neither the examiner
nor the child’s mother could determine his word boundaries with a reasonable degree of certainty.
2.1.3. Data collection from videotapes
Home videotapes from birth to age 2 (CASF1 = 4.97 h; CASM1 = 3.66 h; CASM2 = 3.19 h; CASM3 = 3.28 h; TYPF1 = 3.73 h;
TYPM1 = 2.50 h) were obtained from the parents of the participants. Video footage across both groups typically consisted of
clips 5 s to several minutes in duration, recording events parents wished to preserve and not for the specific purpose of
recording their child’s vocal levels. Footage represented a cross-section of every-day events in the life of the participant (bath
time, meal time, sibling play, etc.) as well as special events such as holidays and birthdays. To ascertain whether the context
of the videos was similar across the two groups, 10% of the video clips were randomly selected by graduate students in
speech-language pathology blind to the participant’s diagnostic status and, after training by the first author, were coded
following procedures similar to those described in the literature (Patten et al., 2014; Watson, Crais, Baranek, Dykstra, and
Wilson, 2013). Each clip was coded according to number of persons in the video, the level of social interaction, the amount of
physical restriction of the child, and the level of social intrusion and/or verbal encouragement used by adults or other
children to engage a verbal or nonverbal response from the child; equal sample sizes were randomly selected among the 10%
for analysis. There was a significant effect for the number of people in the video (t(48) = 3.06, p = .004), with more people
(M = 3.28, SD = 1.72) being in the CAS videos than in the TYP videos (M = 2.00, SD = 1.19), but not for any other condition. All
the children in the CAS group had siblings whereas only 1 of the 2 TYP participants did.
Videos were then played through VLC Media Player on a ThinkCentre desktop computer, and then listened to with
Beyerdynamic DT 770 PRO professional headphones. Vocalizations were coded as either nonresonant or resonant following
breathgroupprocedure(asinglevocalizationoccurredonasingleegressivebreath)asdescribedintheliterature(Nathani&Oller,
2001; Vihman, Macken, Miller, Simmons, & Miller, 1985). Nonresonant sounds included vegetative sounds (burps, coughs, loud
breaths, reflexive grunting, etc.), fixed signals (laughter, crying, sighing, etc.), and protophones (quasi-resonant nuclei, marginal
syllables, and quasi-resonant canonical syllables). Resonant utterances included vowels, consonant (C) and vowel (V) sequences,
canonical babbling, and words, which could be transcribed using the International Phonetic Alphabet (IPA). Vocalizations
produced with competing noise or vocalizations from other individuals were disregarded, but the total number of vocalizations
coded in each group was substantial (CAS: 2481 nonresonant, 495 resonant; TYP: 784 nonresonant, 942 resonant).
After all resonant vocalizations were broadly transcribed with IPA, consonants were categorized by place, manner, and
voicing, being counted in a participant’s inventory only if they appeared at least twice (Stoel-Gammon, 1987). Resonant
vocalizations were also categorized into one of eight syllable shapes (V, CV, VC, CVC, VCV, CVCV, VCVC, and ‘‘Other’’). The
‘‘Other’’ category included chains of repetitive and variegated canonical babble, consonant clusters, and strings of resonant
contextually understandable sentences (e.g., ‘‘I go home’’).
2.1.4. Reliability
Reliability between each investigator for diagnosis of CAS was 100%. Each investigator independently reviewed each
participant’s evaluation and discussed the scoring of the Mayo 10 with the other investigator. The diagnosis of participant
CASM1 was also independently confirmed by a nationally recognized expert in CAS.
Reliability(Cohen’skappa) wascalculated for10% of thetotalvocalizations withfour graduate studentstrained in phonetics
and infant transcription by the first author. Reliability for the number of utterances was high for both the CAS (k = .85–.89) and
TYP (k = .85–.93) groups. Point-to-point reliability for consonant transcription was 83.3–92.9% (CAS) and 83.8–96.7% (TYP),
and for syllable shapes, 83.3–95.3% (CAS) and 95.2–97.0% (TYP). Additional reliability was obtained by asking three SLPs
experiencedinearly intervention(M = 23years, range12–34years) tocode2.5–5%randomlyselectedtokensasnonresonantor
resonant. Average point-to-point reliability was 96.8% (CAS) and 95.5% (TYP). High reliability across multiple variables
indicated not only consistency of measurements but that the perceptual quality of the videotapes was sufficient for analysis.
3. Results
All results were calculated based on the number of minutes of videotape in which the participant was visible on camera
and clearly audible to the coder. For calculations involving consonants and their features, results were based on the minutes
of videotape available after 7 months of age, just before the earliest (8 months) onset of resonant consonants among all
participants. Measures of volubility were based on all 24 months. See Appendix B for a list of missing data. For each group
(CAS and TYP), the following means were found for each of three variables (number of different consonant singletons/
minute, different place features/minute, and different manner classes/minute): (a) group monthly mean representing a
group’s average number of different consonant singletons/place features/manner classes per minute each month, and (b)
group grand mean signifying a group’s overall average between 7 and 24 months for the number of different consonant
singletons/place features/manner classes per minute. Two other cumulative calculations across the experimental period
were made for each group: (a) a group proportional grand mean reflecting the proportional use of each type of place feature
and manner class, and (b) the group grand percentage of voiceless consonants.
M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–6250
3.1. Volubility
Volubility was calculated as number of vocalizations per minute of video. Mann–Whitney U analysis showed no
significant group differences across the 24 months in group monthly means of volubility(defined as the number of resonant
and nonresonant productions) (CAS M = 4.00, SD = 1.50; TYP M = 4.90, SD = 1.98). After a Bonferroni correction for Type
1 error (.05/3 = .016) and dividing the two-tailed p value in half to derive the one-tailed p value needed to test directional
hypotheses (Leventhal & Huynh, 1996), significant between group differences were found for resonant vocalizations (CAS
M = .60, SD = .75; TYP M = 2.61, SD = 2.72) (Mann–Whitney U = 163.00, z = �2.618, n1 = 4, n2 = 2, p = .005 one-tailed exact,
r = 1.07) and nonresonant vocalizations (CAS M = 3.38, SD = 1.62; TYP M = 2.26, SD = 1.69) (Mann–Whitney U = 174.00,
z = �2.351, n1 = 4, n2 = 2, p = .009 one-tailed exact, r = .96). The TYP group produced more resonant productions than the CAS
group while the CAS group produced more nonresonant productions than the TYP group. However, because the home videos
tended to capture events that parents wished to preserve, the frequency of nonresonant vocalizations such as laughing may
have, in these small sample sizes, artificially inflated any ‘‘true’’ between-group difference.
3.2. Consonant singleton inventories
Significant differences were apparent between the CAS and TYP group grand means (CAS M = .12, SD = .02; TYP M = .65,
SD = .21) for the average number of different consonants used per minute between 7 and 24 months (Fig. 1). Statistically
significant differences were found for group monthly means between the two groups (Mann–Whitney U = 22.000,
z = �3.435, n1 = 4, n2 = 2, pbetween group differences for group monthly
means were found (Mann–Whitney U = 33.000, z = �2.925, n1 = 4, n2 = 2, p = .002 one-tailed exact, r = 1.194). The moving
means time series regression analysis of group monthly means (Fig. 4) shows that the CAS group used 2–3 times fewer
different manner classes per minute each month than did the TYP group.
The group proportional grand mean for manner classes revealed the TYP group favored the use of stops (56%), followed by
glides (16%), fricatives (14%), nasals (12%), rhotics (1%), laterals (1%), and affricates (delayed onset
of words, and inconsistent productions in the context of high average receptive language skills. Speech therapy was initiated
at 19 months for twice a week.
M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–6256
The singleton consonant inventory of CASM1 was dominated by/b, d, m, n/, and although he demonstrated glides at
15 months, they did not appear again until age 22 months. He also had no fricatives or voiceless phones during the
experimental period and also depended on C and CV syllable shapes for utterances.
CASM2: CASM2 and CASM3 are dizygotic twins. There is an older cousin diagnosed with CAS but no other familial history
of speech-language difficulty. Labor was induced at 37 weeks and the twins were born via caesarian section. Neither twin
was reported to have difficulty with early feeding or swallowing. Parents reported that for both infants, babbling appeared
‘‘typical’’ but the onset of words was slow with first words not appearing until 18 months. CASM3 appeared to have fewer
productions than CASM2 and though intelligibility to family members was poor for both twins, it seemed slightly more
frustrating for CASM3. Delays in speech and fine motor skills initiated early intervention services for both boys at age 2;
6 months; speech therapy was provided twice a week.
The singleton consonant inventories of CASM2 and CASM3 consisted of/b, d, g, m, h, l, w, j/and/t, d, k, g, h, j, s/, respectively.
However, unlike CASF1 and CASM1, each of the twins (a) used glides frequently during the experimental period; (b)
appeared to ‘‘lose’’ phones (nasals for both participants,/l/for CASM2, and/t, k, g, s/for CASM3), and (c) used the voiceless
fricative/h/periodically from the onset of resonant phones to 24 months. For both, the dominant syllable structures were V
and CV, though strings of canonical babble (‘‘Other’’) were occasionally evident toward age 2, the time at which early
intervention began due to unintelligibility and significant expressive output delays.
4. Discussion
Although much has been learned about CAS from the limited longitudinal single-subgroup studies of older children with
the disorder (Davis et al., 2005; Jacks et al., 2006; Marquardt et al., 2004), little is known about whether infants and toddlers
later diagnosed with the disorder present any differently than those with typical speech sound skills. Parents and
investigators report that infants and toddlers later diagnosed with CAS seem to be unusually ‘‘quiet’’ babies, present reduced
and/or preferred consonant and vowel inventories, and use limited syllable shapes. Parents often seek speech therapy
services to address these concerns, but there have been no quantifiable data to assist in our understanding of these
observations. Findings from the current study, notwithstanding significant limitations to its methodological design, provide
the first empirical corroboration of these reports.
Our hypothesis that infants and toddlers later diagnosed with CAS would demonstrate lower overall volubility than the
comparison group was not supported and there was no statistical difference in the number of vocalizations (regardless of
type) per minute between the two groups. However, consistent with parent reports that infants and toddlers later diagnosed
with CAS are relatively ‘‘silent’’ and babbled very little (Aziz et al., 2010), we found statistically significant differences
between the CAS and TYP groups in the frequency/minute of resonant sounds (speech-like productions which could be
transcribed using IPA). On average, infants and toddlers in the CAS group used 3.4 times fewer resonant sounds than the
comparison group and the average onset of those productions was delayed (CAS onset = 13.5 months; TYP onset = 9 months).
Reduced frequency of resonant sounds in infancy and toddlerhood is not unexpected for infants and toddlers later diagnosed
with CAS. Among the many proposed characteristics which aid in diagnosis of the disorder in older children are severe,
irregular, and persistent difficulties with the ambient sound system, including, but not limited to inconsistency and/or
variability of errors, reduced intelligibility, and nonphonemic productions (Hall, Jordan, & Robin, 1993; Shriberg, Aram, &
Kwiatkowski, 1997b).
Statistical analysis also revealed statistically significant differences in the frequency/minute for nonresonant
productions, with more nonresonant productions produced by the CAS group. We suggest two possibilities for this result.
Perhaps nonresonant productions are a compensatory strategy for communicative intent for infants and toddlers later
diagnosed with CAS when resonant productions are reduced or difficult to make. It is also possible that these results are
simply an artifact of individual characteristics of participants in this investigation and/or what parents chose to videotape.
Further study on nonresonant productions in children with CAS is needed.
Our second hypothesis, that infants and toddlers later diagnosed with CAS would demonstrate fewer and less diverse
consonants than the comparison group, was supported in the findings. The CAS group used, on average, 2–3 times fewer
different consonants, place features, and manner classes each month in the first 24 months of life than the TYP group. Around
age two, the gap in the number of different consonant singletons widened with the CAS group having 4–5 times fewer
different consonant singletons than the comparison group. This result is not unexpected given that when children are
diagnosed with CAS at an older age, predominant error types are omissions (Jacks et al., 2006; Lewis, Freebairn, Hansen,
Iyengar, et al., 2004; Shriberg et al., 1997a).
Individual profiles of the phonetic inventory of the participants in the CAS group showed variability in the specific
phonemes attained, but inventories were always highly restricted. Moreover, as has been discussed in studies of older
children with CAS, the phonetic inventories for infants and toddlers later diagnosed with CAS were qualitatively different
from the TYP group (Jacks et al., 2006; Shriberg et al., 1997a). Inventories implied that both groups in this limited data set
‘‘lost consonants’’ – consonants which appeared once did not always regularly reappear. However, consistent phones
produced by the CAS group consisted only of Early-8/m, b, j, n, w, d, p, h/consonants, whereas in the TYP group, they
represented the Early-8/m, b, j, n, w, d, p, h/, Middle-8/t, k, g, v/, and Late-8/r, s/. This slow trajectory of phonetic development
in infants and toddlers later diagnosed with CAS is, apparently, a phenomenon to which parents are sensitive and may
partially explain why they may seek speech therapy for their child well before the disorder is diagnosed. However, it is not
M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–62 57
uncommon for early intervention to be denied to toddlers with restricted phonetic inventories because they are perceived by
SLPs, pediatricians, and multi-disciplinary team leaders as ‘‘late talkers’’ who will recover.
Although parents of infants and toddlers later diagnosed with CAS have not noted a lack of any particular sound class, our
results revealed several distinct differences between the CAS and comparison groups. (a) Both the CAS and comparison
groups demonstrated stops, nasals, and glides in the first 24 months of life, but the CAS group used statistically significantly
fewer fricatives than the comparison group. This result supports a recent report that no fricative use by 18 months was
associated with a slower expressive language developmental trajectory as measured by vocabulary, sentence length, and
grammar (Sotto, Redle, Bandaranayake, Neils-Strunjas, & Creaghead, 2014). As evident in Table 1, participants in the CAS
group demonstrated lower mean length of utterance and lower vocabulary scores (though still within normal limits) than
the comparison group. (b) A major difference between the CASand TYP groups was the trajectory of voiceless phone
production. If coordinative organization of the oral and laryngeal articulators is requisite to attain the necessary timing to
produce voiceless targets (Catts & Jensen, 1983; Grigos, 2009), then our results support the notion that orolaryngeal timing
may be particularly difficult in the CAS population (Grigos, Case, & Elias, 2012). (c) Production of/h/(the only glottal phone)
was statistically significant between the groups, but further study is needed to determine whether difficulty was synergistic
across its voiceless, glottal fricative features or was particularly related to production of any one of those features.
Finally, our results are consistent with our third hypothesis, and with parent reports, that infants and toddlers later
diagnosed with CAS demonstrate fewer and limited syllable structures (Aziz et al., 2010; Davis, Jakielski, & Marquardt, 1998;
Davis & Velleman, 2000; Le Normand et al., 2000). As expected, both the TYP and CAS groups produced a preponderance of
simple monosyllabic and disyllabic syllable shapes during the experimental period (Ingram, 1978). Similar to reports of older
children with CAS, the experimental group preferred simple monosyllables such as V and CV to disyllables, rarely used
complex syllable shapes, and demonstrated a notable lack of final consonant production (Jacks et al., 2006; Lewis, Freebairn,
Hansen, Iyengar, et al., 2004; Shriberg et al., 1986, 1997a). Lack of final consonant production may be indicative of difficulty
with longer and more difficult syllable shapes than V or CV.
The apparent ‘‘regression’’ of V and possibly ‘‘Other’’ syllable shapes is consistent with parental reports that older children
with the disorder progress erratically in speech development or lose speech milestones (Teverovsky et al., 2009). However,
regression of syllable shape in very young children has not been documented to date and requires additional investigation.
For the infants and toddlers later diagnosed with CAS, we would expect to find difficulty with the acquisition of the
ambient sound system. A number of longitudinal studies of young children have connected (a) the use of consonants at
1 year old and the children’s later phonological skills, (b) a correlation between the diversity of syllable and sound types for
children aged 6 months–1.2, (c) and the amount of vocalization under 6 months of age to performance on speech and
language tests at age 5.0 (Stoel-Gammon, 1992). Moreover, children who have more resonant prelinguistic vocalizations
(especially of the canonical kind) will have a greater repertoire of ‘‘building blocks’’ available for later word production
(Stoel-Gammon, 2011). Nonetheless, it is important to consider that not all infants and toddlers in the experimental group
followed group trends or presented with the same phonetic repertoires. Individual differences were apparent, consistent
with well-documented variability in infant and toddler speech sound development.
Although this investigation was not meant to test different theoretical perspectives of CAS, the findings reported here are
in concordance with the theory of CAS as a genetically based core deficit in speech motor skill (Shriberg et al., 1997a). Some
investigators (Guenther, 2006; Terband, Maassen, Guenther, & Brumberg, 2009) have suggested that for infants and toddlers
later diagnosed with CAS, this deficit arises because they are less likely to engage in early sound exploration needed to
develop the motor programs (or synaptic maps) that eventually produce target sounds of the ambient language. The acoustic
and somatosensory feedback acquired during sound explorations such as babbling, critical to establishing the feedforward
programs needed for articulatory movements, may be more difficult for infants and toddlers later diagnosed with CAS to
obtain. Recent evidence offered by Iuzzini-Seigel, Hogan, Guarino, and Green (2015) provides support for impaired
feedforward programs in older children with CAS (ages 6.1–17.6) but there has been little evidence of such impaired
programs in infants and toddlers later diagnosed with the disorder. The present study suggests that for very young children
with CAS, differences in early sound exploration appear at the onset of consonant singleton production, thereby limiting the
child’s capacity for continued and/or future sound exploration. Robust effect sizes for differences in the acquisition of
consonants as well as across multiple manner, place, and voiceless phoneme features provide some evidence of the extent to
which they appear to fail to engage in this exploration.
5. Limitations and future research needs
A significant limitation is that this pilot investigation did not include a comparison group of infants and toddlers later
diagnosed with a non-CAS speech sound disorder (SSD) (e.g., phonological delay, articulation disorder). Although the effect
sizes between the CAS and TYP groups in this study were strong and corroborated parent and investigator reports that
infants and toddlers later diagnosed with CAS have atypical consonant and syllable development, a non-CAS SSD comparison
group is essential if results are to go beyond corroboration and provide potential early diagnostic criteria. To meet this need,
we have begun a large-scale comparative study of three groups of infants and toddlers (those later diagnosed with CAS, later
diagnosed with non-CAS SSD, and those with typical speech sound skills).
Another consideration is that low sample size in both groups might not have provided sufficient opportunity for
vocalization tokens to appear. However, resonant productions from low sample sizes can be reasonably identified with
M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–6258
relatively small monthly samples (Molemans, Van Den Berg, Severen, & Gillis, 2012) and in this investigation we obtained
more hours of videotape for the CAS group than the TYP group to allow for sufficient tokens in the experimental group. The
fact that there were substantially more tokens from the TYP group than the experimental group across multiple variables
suggested that the token number was sufficient for analysis, and that the results may have underreported any differences
between the two groups; but it is also possible that additional recording time from the TYP group would have revealed more
‘‘quiet’’ time in this population, reducing apparent differences between the groups. Additional study with larger sample sizes
is needed to explicate this possibility.
Third, this investigation only considered the consonant and syllable inventories of the participants and, as was the case in
previous longitudinal studies of older children with CAS, analysis of vowel skills and phonetic variability of this sample set is
needed. These studies are anticipated. Finally, all participants were identified as White (Non-Hispanic). They came from
three states but each participant lived in a suburban environment with two parents each having a college degree and
additional study with a more ethnically and socioeconomically diverse sample is needed.
6. Conclusion
Results of this investigation support parent and investigator reports that infants and toddlers later diagnosed with CAS
present differently from those with typical speech sound skills, specifically in (a) lower frequency/minute of resonant
vocalizations, (b) delayed onset of resonant consonant singletons, (c) and limited syllable structures. Findings were also
statistically significant for the frequency/minute of nonresonant vocalizations. Although consonant inventory profiles were
variable and individual, infants and toddlers later diagnosed with CAS used significantly fewer phones than the comparison
group and generally had difficulty with the fricative manner class and possibly the glottal placement feature. Moderate to
strong effect sizes for all manner and place features indicate additional study with larger sample sizes isneeded. All infants
and toddlers later diagnosed with CAS demonstrated difficulty with voiceless productions. Syllable shapes were dominated
by V and CV, with possible regression of V and ‘‘Other’’ shapes. Results may partially explain why some parents of infants and
toddlers later diagnosed with CAS seek speech therapy services before the diagnosis of CAS is made.
Acknowledgements
The authors gratefully acknowledge Lindsay Booker, Samantha Capece, Cara McGilvray, Danielle Moss, and Emily Wright
for their assistance, Rebecca McCauley and Kathy Jakielski for their commentary, and thank the participants and their
families for their participation. The work of Samantha Capece and Emily Wright was partially supported through
Undergraduate Summer Student Research Grants from The College of Saint Rose.
Appendix A
Table A1
Table A1
Example: Mayo 10 clinical signs for childhood apraxia of speech adapted across eight speech tasks.
�4 signs in �3 Speech Tasks = CAS
Instructions: if a ‘‘sign’’ (below)
is seen at least two times
within a ‘‘task’’ (right), put
check in corresponding box
kRepeat
1-Syllable
Words (R1S)
kRepeat
2-Syllable
Words (R2S)
kRepeat
3+ Syllable
Utterance
(RMS)
Articulation
Test (ART)
Connected
Speech
Sample
(CSS)
lDDK
(DDK)
mPhonation
Task (PHO)
nStress
Task (ST)
TOTAL SIGNS:
If sign appears
in at least one
speaking task, put +
sign in this column.
aVowel distortions (VW) U U +
bDistorted substitutions (DS)
cDifficulty w/initial artic configurations or
transitionary movement gestures (AT)
dLexical or phrasal stress errors (SE) U U +
eSyllable segregation or word segregation (SG)
fGroping (GR) U U +
gIntrusive Schwa (IS)
hVoicing Errors (VE) U U +
iSlow speech rate and/or slow DDK (SR)
jIncreased difficulty with multi-syllabic words (ID)
TOTAL SPEAKING TASKS: if a column has at least
one check, put + sign in corresponding box in
this row
+ + + + TOTAL SIGNS = 4
TOTAL TASKS = 4
a Vowel distortion error (did not ‘‘sound right’’). b Nondevelopmental consonantal distortions from inaccurate articulatory placement. c Difficulty with articulatory movement between segments or difficulty
achieving the initial articulatory gesture of a segment in a word. d Stress errors on a multisyllabic word or in a phrase (e.g., [?hæ?pi] vs. [?hæ?pi]). e Articulatory movement from one syllable to the next is disrupted
and production sounds ‘‘halting.’’ f Effortful attempts to find the correct articulatory posture. g Epenthesis in multisyllabic words or phrases. h Errors on voicing contrasts. i Unusually slow productions and/or below
norms for diadochokinetic rates. j Increased articulatory errors (vowel errors, distortions, stress errors, segmentation, intrusive schwa, voicing contrast, consistency) as word length increases. k Repeating 1-, 2-, or 3-
syllable words in Dynamic Evaluation of Motor Speech Skill (DEMSS) or Kaufman Speech Praxis for Children (Kaufman, 1995). l Diadochokinetic task (Robbins & Klee, 1987). m Phonation of sustained ‘‘ah’’. n Informal
assessment of stress production on 2+ syllable words taken from (DEMSS) or word list inventory provided by parents.
M
.
 O
v
erb
y
,
 S.S.
 C
a
sp
a
ri
 /
 Jo
u
rn
a
l
 o
f
 C
o
m
m
u
n
ica
tio
n
 D
iso
rd
ers
 5
5
 (2
0
1
5
)
 4
4
–
6
2
 
5
9
M. Overby, S.S. Caspari / Journal of Communication Disorders 55 (2015) 44–6260
Appendix B
Table B1
Table B1
Missing data for participants.
Participant Months for which no data available
CASF1 11
CASM1 8, 10, 11, 15, 16, 18, 20, 23, 24
CASM2 2, 3, 4, 5, 10, 12, 16, 18
CASM3 2, 3, 4, 5, 10, 12, 16, 18
TYPF1 9
TYPM1
Appendix C. Continuing Education Questions
True or False: Reduced vocal output in infants and toddlers later diagnosed with CAS is well-documented.Which of the
following may be a reason parents of infants and toddlers later diagnosed with CAS seek early intervention services before any
condition is diagnosed?
(A) b
eing unusually ‘‘quiet’’ babies with little use of resonant sounds
(B) la
ck of voiced phones
(C) p
reponderance of disyllables over monosyllable syllable shapes
(D) d
isparity between consonant and vowel inventories
The current study found evidence for differences between infants and toddlers with typical speech sound skills and those later
diagnosed with CAS in:
(A) o
verall volubility
(B) fr
equency of resonant sounds
(C) fr
equency of stops and glides
(D) fr
equency of the use of the velar place feature
True or False: The consonant singleton inventories of participants later diagnosed with CAS were qualitatively and quantitatively
different than the comparison group.In the current study, participants later diagnosed with CAS demonstrated:
(A) d
ifficulty with fricatives
(B) e
arly differences which can be used to diagnose infants and toddlers with CAS
(C) e
vidence of possible regression of V and CV syllable shapes
(D) A
ll of the above
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