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Consonant and syllable structure patterns in childhood apraxia of speech: Developmental change in three children
Journal of Communication Disorders 39 (2006) 424–441
Consonant and syllable structure patterns in childhood apraxia of speech: Developmental change in three children Adam Jacks *, Thomas P. Marquardt, Barbara L. Davis Department of Communication Sciences and Disorders, The University of Texas at Austin, 1 University Station, Mail Code A1100, Austin, TX 78712, USA Received 2 May 2005; received in revised form 21 December 2005; accepted 22 December 2005
Abstract Changes in consonant and syllable-level error patterns of three children diagnosed with childhood apraxia of speech (CAS) were investigated in a 3-year longitudinal study. Spontaneous speech samples were analyzed to assess the accuracy of consonants and syllables. Consonant accuracy was low overall, with most frequent errors on middle- and late-developing sounds. Omissions and substitutions were the dominant error types. Analysis of syllables revealed higher frequencies of error on complex mono- and polysyllables. Multiple regression analyses revealed that consonant accuracy is predicted by syllable shape accuracy and polysyllable frequency. Improvement was noted over time, although irregular patterns of consonant and syllable-level errors persisted across the period studied. Findings suggest that consonant errors in CAS are related to syllable-level deficits, namely difficulty constructing syllabic frames for speech production targets. Learning outcomes: On the basis of this article, the reader will be able to (1) describe the deficits in consonant production demonstrated by the participants, (2) analyze the relationship between consonant production and syllable-level patterns of error and (3) consider the value of addressing syllable construction as a therapeutic goal. # 2006 Elsevier Inc. All rights reserved.
* Corresponding author. Tel.: +1 512 471 3841; fax: +1 512 232 1804. E-mail address: [email protected] (A. Jacks). 0021-9924/$ – see front matter # 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcomdis.2005.12.005
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1. Introduction Childhood apraxia of speech (CAS)1 is a disorder believed to result from impaired speech motor control (e.g. Hall, Jordan, & Robin, 1993) or impaired representation of phonological constructs (e.g. Marquardt, Sussman, & Davis, 2001). Although controversy surrounds the disorder (e.g. Forrest, 2003; Guyette & Diedrich, 1981), behavioral characteristics include a high frequency of consonant and vowel errors, error variability and prosodic differences (e.g. Davis, Jakielski, & Marquardt, 1998). Consonant errors per se are not sufficient for differential diagnosis of CAS and overlap with behavioral features identified in other childhood speech disorders (Shriberg, Aram, & Kwiatkowski, 1997). Recent research suggests that consonant errors affecting syllable structure (e.g. syllable reduction, initial and final consonant deletion) are more common in CAS than in speech disorders not identified as CAS (Lewis, Freebairn, Hansen, Iyengar, & Taylor, 2004; Shriberg et al., 1997). Analysis of consonant and syllable-level errors is needed to better understand persisting patterns of speech deficits found in children with CAS. 1.1. Consonant errors in CAS A high rate of consonant error frequently is cited as a diagnostic indicator for CAS (e.g. Davis et al., 1998; Rosenbek & Wertz, 1972; Shriberg et al., 1997; Yoss & Darley, 1974). However, consonant errors are common in almost all children with developmental speech disorders. A summary of consonant error types in representative studies of children with CAS is shown in Table 1. Several of these studies will be reviewed in more detail to provide a focused characterization of the nature of consonant production patterns in children with CAS. Studies of CAS have reported consonant errors affecting both isolated sound segments (e.g. sound substitutions) and word-level structure (e.g. consonant omissions, syllable deletions, assimilatory processes). While consonant substitutions are common in CAS and in delayed development, recent evidence suggests that syllable-level errors, such as consonant omissions may be distinctive for children with CAS (Lewis et al., 2004; Shriberg et al., 1997). For example, Shriberg et al. (1997) reported that 42% of consonant errors were omissions in younger children with CAS (ages 4.10–7.0 years) compared to 25% for children with speech delay. More recently, Lewis et al. (2004) found high proportions of initial and final consonant deletion, syllable deletion and cluster reduction in children with CAS in comparison with children with isolated speech disorders (S group) and children with both speech and language disorders (SL group). In particular, 100% of their CAS group produced final consonant deletion errors, compared to 25% and 38% for the S and SL groups, respectively. Overall, 90% of the CAS group deleted syllables, compared to 8% and 15% for the S and SL groups. Sixty percent of the CAS group simplified clusters, compared to 0% and 8% of the S and SL groups. Shriberg et al. (1997) also found that children with CAS and those with speech delay showed similar rates of error for consonants categorized as early- or late-developing 1 Childhood apraxia of speech (CAS) is known by several descriptors, including developmental apraxia of speech (DAS) and developmental verbal dyspraxia (DVD). To provide continuity with current conventions, CAS will be used as the label for the disorder (see Goffman, 2002 for a discussion of terminology).
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Table 1 Summary of consonant production studies in CAS Author
Age
N Study type
Consonant accuracy Error types Subst. Omiss. Distor. Insert. Stopp. Liq. Prolon. Syll. level SimP.
Time 1: 10.7, 11.9; 2 Longitudinal analysis of error Artic. Ageb T1: Time 2: 14.6, 15.7 patterns in two children with DVD 4.3, 3.0; T2: 5.6, 4.9 6.2–7.9 11 Analysis of feature retention in 72% PCC consonant substitutions and omissions in DAS Younger: 4.10–6.3; 14 Comparison of speech and prosody- PCC: 57%; older: 7.1–14.11 voice profiles of children with younger, suspected DAS and speech delay 77% older 5.7 1 Speech characteristics of children with suspected DAS; one child with confirmed diagnosis
Marquardt et al. (2001)
3.0–6.6
Lewis et al. (2004)
Pre-school: 4.17–5.42; school-age: 7.25–10.5
2.9–14
Bowman, Parsons, 6.1–7.4 and Morris (1984) Crary, Landess, and Towne (1984) Stackhouse and Snowling (1992) Thoonen et al. (1994) Shriberg et al. (1997) Davis et al. (1998)
3.9–13.11
50 Review of speech, language and neurol. characteristics of children with DAS 7 Analysis of phonological error patterns in DVD
20–58 errors a
10 Analysis of phonological error patterns in DVD
1 Longitudinal study of assessment and treatment in one child with DAS 10 Pre-school/school-age follow-up study of speech, language, and written language skills in children with CAS
78% PCC at 6.6
Cluster reduction Weak syll. del., cluster reduction Cluster reduction Cluster reduction, metath.
Glottal errors; omitted initial and final consonants Omitted intervocalic and final consonants, gliding Groping, glottal substitution
Place retention: 79% manner ret.: 87% voicing ret.: 95% Omitted in final; palatal fronting in older children only Assim. and syllable errors; oral posturing, lim. use of complex word shapes Velar fronting, FCD, ICD
Weak syll. del., cluster reduction
Cluster reduc., weak syll. del ICD 40% of Cluster reduct., Syll. CAS group Voicing errors 40% FCD reduct 100% syll reduc. 90% Liq simp. 80%
Note: DAS = developmental apraxia of speech, DVD = developmental verbal dyspraxia, CAS = childhood apraxia of speech, PCC = percent consonants correct, FCD = final consonant deletion, ICD = initial consonant deletion. a Goldman–Fristoe Test of Articulation (GFTA, Goldman & Fristoe, 1986). b Edinburgh Articulation Test (EAT, Anthony, Bogle, Ingram, & McIsaac, 1971, as cited by Stackhouse & Snowling, 1992).
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Rosenbek and Wertz (1972)
Other
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sounds, with lesser accuracy for middle-developing sounds by children with CAS. Assessing the accuracy of early-, middle- and late-developing sounds can potentially be used as an index to delay versus disorder in segmental acquisition patterns in children with clinically relevant speech patterns. Studies of consonant production patterns in children with CAS suggest that their errors may be qualitatively different from errors of children with other speech disorders or speech delay, especially in omissions that result in reductions in syllable complexity (Lewis et al., 2004; Shriberg et al., 1997). Consonant errors in CAS also may reflect typical patterns of error that persist past the period of development in which they emerge in typically developing children. For example, a child who produces most early- and middledeveloping sounds correctly with errors primarily for late-developing sounds may not have age-appropriate speech production, but the developmental pattern may be similar to that of younger typically developing children. Speech deficits in children with CAS frequently persist over time, to such an extent that slow progress in therapy has been used as a differential diagnostic criterion by clinicians and researchers alike (e.g. Byrd & Cooper, 1989; Ekelman & Aram, 1983; Forrest, 2003; Thoonen, Maassen, Gabreels, & Schreuder, 1994). Although there is a growing literature on CAS, there are relatively few longitudinal studies available (Davis, Jacks, & Marquardt, 2005; Lewis et al., 2004; Marquardt, Jacks, & Davis, 2004; Shriberg et al., 1997; Stackhouse & Snowling, 1992). Longitudinal studies of speech characteristics in CAS are needed to track the persistence of characteristics marking continued speech disorder relative to chronological age expectations. This is the third in a series of studies examining longitudinal change in characteristic speech deficits of children with CAS. The first two studies examined phonetic variability (Marquardt et al., 2004) and vowel production (Davis et al., 2005) over a 3-year period in three children diagnosed with CAS. In both studies, improvement was noted but vowel errors and phonetic variability remained high up to 7.5 years of age. These findings are supported by data from three other studies reporting continuing deficits in speech production relative to chronological age expectations (Lewis et al., 2004; Shriberg et al., 1997; Stackhouse & Snowling, 1992). Lewis et al. (2004) examined speech and language performance of 10 children with clinical diagnosis of CAS at pre-school (mean = 4.8 years) and at school age (mean = 8.7 years), compared with 15 children diagnosed with speech disorder and 14 children diagnosed with speech and language disorder. Results indicated improvement in standard articulation test scores for 8 of 10 children with CAS. However, metathetic and syllable deletion errors became more prominent by school age and unusual error types persisted, including initial consonant deletion, vowel and voicing errors. Stackhouse and Snowling (1992) studied speech errors of two children diagnosed with CAS at two times spanning a 4-year period (ages 10.7 and 11.9 years at study onset). Speech performance was compared to 10 younger children matched on articulation age (ages 3.0–5.6 years). Results indicated that articulation age improved for both children and number of words without error increased, although the children continued to produce many words with multiple errors even at 15–16 years of age. These two children produced many consonant substitutions like those of typically developing younger children, but had a greater number of errors affecting syllable structure (i.e. consonant deletion or cluster reduction).
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Shriberg et al. (1997) examined speech characteristics in children diagnosed with CAS using a cross-sectional methodology analyzing younger (4.10–6.3 years) and older (7.1– 14.11 years) children. They found better speech performance in the older group, including higher overall consonant accuracy and greater accuracy for middle and late-developing sounds. Rates of cluster reduction, initial stopping and liquid simplification were lower in the older group relative to the younger group, but several patterns of error remained prominent in older children with CAS, including palatal fronting, deaffrication and persistent cluster reduction and liquid simplification. Consonant and syllable-level error patterns represent persisting areas of deficit relative to chronological age expectations for children diagnosed with CAS. These deficits persist over time even with intensive therapeutic intervention. The aim of this study was to examine consonant and syllable patterns, describing both stability and change over a 3-year period in three children with CAS.
2. Method 2.1. Participants Participants were three English-speaking male children (P1–P3), selected from a large number of children referred for differential diagnosis of childhood apraxia of speech (CAS) in a long-term study of speech and language characteristics in children with the disorder (e.g. Davis et al., 1998). A team of three speech–language pathologists in a university clinical setting confirmed a positive diagnosis of CAS on the basis of a cluster of speech and language characteristics typical of the disorder, including prosodic abnormalities, vowel errors, high frequency of consonant and syllable omissions and segmental variability (Davis et al., 1998). When available, previous assessments of hearing, cognition and expressive and receptive language were used to establish participant status. Participants passed pure tone audiometric screening at octave frequencies from 250 to 4000 Hz at the beginning of the study. Review of clinical records revealed no positive history of fluctuations in auditory acuity due to middle ear disorders. An oral mechanism examination, diadochokinetic testing, and informal oral and limb praxis tests revealed no obvious signs of structural or neuromuscular impairment. Consonant and syllable production data were obtained as part of a longitudinal evaluation of speech production patterns in children with CAS. Following diagnosis, participants were assessed at 1-year intervals (Time 1–Time 3) between the ages of 4.6 and 7.7 years. Assessments included articulation testing and spontaneous speech sampling. Speech profiles for participants are shown in Table 2, including age at each assessment, scores on single-word articulation tests, accuracy of consonant and vowel production from connected speech samples, and inventories of consonant and vowel types. Consonant and vowel accuracy and inventories were determined from speech samples collected at each time interval in the study. Participant 1 (P1) had a normal developmental history with the exception of speech and language. He produced his first word at 22 months. He was diagnosed with CAS at 3.8 years. Initial neurological examination revealed oral apraxia and mild dysarthria although
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Table 2 Participant data: age, articulation test results and accuracy and inventories of consonant and vowel production at three times
P1 Age Articulation test Consonant accuracy Vowel accuracy Consonant inventory
Vowel inventory P2 Age Articulation test Consonant accuracy Vowel accuracy Consonant inventory
Vowel inventory P3 Age Articulation test Consonant accuracy Vowel accuracy Consonant inventory
Vowel inventory
Time 1
Time 2
Time 3
4.6 Profounda 69% 61% p, b, f, w, m, t, d, n, h
5.5 3rd%ileb 61% 72% p, b, f, v, w, m, t, d, s, l, n, k, , g, h, R, tR, ., r
i, I, e, æ, a, K\3, o, u, U, diph.
i, I, e, æ, a, K\3, 2, o, u, U, diph.
6.5 31%ilec 75% 85% p, b, f, v, w, m, t, d, s, ð, z, l, n, k, g, h, R, ., j, r, E, clust. i, I, e, e, æ, a, K\3, &, o, u, U, diph.
5.10 Severea 61% 75% p, b, f, v, w, m, t, d, s, z, l, n, k, , g, h, R, j, E, clust. i, I, e, e, æ, K\3, 2, &, o, u, U, diph.
6.10 4%ileb 72% 85% p, b, f, v, w, m, t, d, s, u, ð, z, l, n, k, g, h, j, E, clust. i, I, e, e, æ, a, K\3, 2, &, o, u, U, diph.
7.7 16%ileb 69% 71% p, b, f, v, w, m, t, d, s, u, ð, z, l, n, k, , g, R, tR, j, E, clust. i, I, e, æ, a, K\3, &, o, u, U, diph.
5.6 <1%ileb 34% 65% p, h, f, v, w, m, t, d, s, l, n, , h, R, clust.
6.10 <1%ileb 63% 70% p, h, f, v, w, m, t, d, s, u, ð, z, l, n, k, , g, h, R, ., j, r, E, clust. i, I, e, e, æ, a, K\3, &, o, u, U, diph.
7.5 <1%ileb 74% 76% p, h, f, v, w, m, t, d, s, u, ð, z, l, n, k, , g, h, ., j, E, clust. i, I, e, æ, a, K\3, &, o, u, U, diph.
i, I, e, e, æ, a, K\3, &, o, u, U, diph.
Note: Consonant and vowel accuracy represent relational measures derived from analysis of entire connected speech sample from each time. a Assessment of Phonological Processes-Revised (APP-R, Hodson, 1986). b Goldman–Fristoe Test of Articulation (GFTA, Goldman & Fristoe, 1986). c Khan–Lewis Phonological Assessment (KLPA, Khan & Lewis, 1986).
no signs of neuromuscular weakness were found upon follow-up oral-peripheral examinations. Between 3.5 and 5.0 years, speech and language evaluations indicated auditory comprehension generally within normal limits, although below average for elaborated sentences. Speech production was characterized by a limited number of consistent word forms, restricted phonetic repertoire, rudimentary syllable shapes and reduced ability to imitate non-verbal movements of the speech mechanism. P1 began receiving speech and language therapy at 2.2 years and continued to receive treatment at the time of the study. Treatment goals initially addressed increased accuracy of verbal communication with supplementary use of sign and communication boards to facilitate
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language and cognitive development. Subsequent goals included expanding phonemic repertoire, stabilizing consistent sound production and increasing use of more complex syllable shapes in words and phrases. P1 was seen for re-evaluation at 4.6, 5.5 and 6.5 years, making continuous gains in single-word articulation (see Table 2). Participant 2 (P2) also had a normal developmental history with the exception of speech and language. Initial speech and language evaluation at 2.6 years revealed severe deficits in receptive and expressive communication. Re-evaluation at 5.0 years revealed receptive language within normal limits with speech characterized by frequent vowel errors, final consonant deletion, errors on initial consonants, glottal stops and reduction of consonant clusters. P2 began therapy at 2.6 years and was enrolled continuously during the study. Treatment goals focused on expanding the phonemic repertoire, increasing accuracy of consonants and vowels, and increasing use of consonant clusters. Follow-up evaluations were completed at yearly intervals (ages 5.10, 6.10 and 7.7 years), with consistent gains in single-word articulation (see Table 2). Participant 3 (P3) had a normal developmental history with the exception of speech and language. He began using words between 1 and 2 years, although his mother reported that his speech was ‘unclear’. He was diagnosed with CAS at the age of 5.6 years. Speech and language evaluations conducted between of 4.2 and 5.11 years revealed profoundly impaired speech production characterized by an incomplete phonetic inventory, variable consonant and vowel errors, unusual and persistent phonological processes, inconsistency of stress and intonation, and nasality. His comprehension of single words was within normal limits, although tasks of short-term auditory memory and meta-linguistic skills indicated difficulty in repeating more than two lexical items, identifying words with greater than two syllables and identifying the different segment in CVC minimal word pairs. He began receiving speech and language therapy at 4.2 years focusing on increasing the accuracy of vowel and consonant segments and increased syllabic complexity. Evaluations for this study at 5.6, 6.10 and 7.5 years showed negligible gains in accuracy of single-word productions (see Table 2). A graduate clinician and two certified speech–language pathologists experienced in differential diagnosis of CAS collected spontaneous speech samples from each participant. Nine 1-hour samples (one sample at each of the three times for the three participants) were obtained in total. Developmentally appropriate materials including games, stories and spontaneous narratives were employed to elicit each sample. Samples were assessed as representative of the child’s connected speech patterns and language level based on parent interviews at the time of each evaluation. All verbal communication attempted during the acquisition of the spontaneous samples was transcribed by a certified speech–language pathologist using broad phonetic transcription. To enable relational analyses comparing productions to targets, only utterances with clear semantic intent were analyzed, based on the investigator’s understanding of the communication context. Transcription reliability was determined for a second, independent transcription of 10% of the utterances in each of the nine samples. Mean inter-rater agreement, based on the number of segments (consonants and vowels) transcribed identically, was 86.22% with a range of 75–96.26%. Target (i.e. attempted) consonants were coded by developmental sound class, as described by Shriberg (1993). Consonants were classified as Early-8 Sounds /mbjnwdph/, Middle-8 sounds /tEkgfvtR./ or Late-8 sounds /Ruszðlra/.
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2.2. Consonant analysis 2.2.1. Consonant accuracy Several relational analyses were used to compare child forms to word targets. Consonant accuracy was assessed by computing the percentage of consonants produced correctly compared to the number of consonants attempted during each session (i.e. percent consonants correct, PCC; Shriberg & Kwiatkowski, 1982). PCC was calculated for total consonants produced and separately for early, middle and late developing sounds (Shriberg, 1993). Phonetic targets for the children’s vowel productions were determined in consideration of allophonic variation and local dialect features. When a production was in question with respect to the potential correctness of a consonant (e.g. alveolar flap produced versus alveolar stop), the production was scored as correct. 2.2.2. Frequency of consonant error types Consonant errors were classified as substitution, omission, retroflex or cluster errors. Substitutions are errors perceived by the transcriber as a different consonant sound than the target sound. Omissions (i.e. deletion) are errors where no consonant was produced for an intended consonant target. Retroflex errors were comprised of omission or substitution of [r], frequently by an approximant, such as [w]. Cluster errors involved omission or substitution of one or more sounds in an intended consonant cluster. Relative frequencies of error types were calculated by dividing the number of errors of a given type (i.e. substitution, omission, retroflex or cluster) by the total number of consonant errors in the speech sample. Omissions were further analyzed to determine the proportion of errors occurring in word-initial, -medial or -final positions. 2.3. Syllable analysis Three analyses were completed to examine participant ability to produce syllables. Analyses included (1) frequency of occurrence of different syllable types, (2) syllable number accuracy and (3) syllable shape accuracy. Each word in the sample was coded for syllable shape and number. Syllable shape was coded with ‘C’ corresponding to a consonant, ‘V’ corresponding to a vowel; thus ‘CVCC’ is a combination of a consonant, a vowel and a two-consonant cluster. Syllable number was coded numerically, with ‘1’ corresponding to monosyllabic words, ‘2’ corresponding to disyllables and numbers greater than three corresponding to polysyllables. For the purposes of the present analysis, syllable shapes were collapsed into four categories: (1) simple monosyllables (V, CV, VC, CVC), (2) complex monosyllables (containing clusters), (3) disyllables and (4) polysyllables. 2.3.1. Syllable type frequency Syllable type frequency was computed as the proportion of words represented by a given syllable type. For example, if 50 of 100 words produced were simple monosyllables, then the frequency for simple monosyllables is 50%. Mean frequencies of syllable types for these children were compared to norms from typically developing children ages 3–6 years (Hoffman, 1982, as cited by Shriberg, Kwiatkowski, Best, Hengst, & Terselic-Weber,
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1986) and from older and younger children with CAS reported in the literature (Shriberg et al., 1997). 2.3.2. Syllable number accuracy Syllable number accuracy is the proportion of words in which the correct number of syllables is maintained. For example, if 50 words should have been produced with two syllables and 40 were produced with two syllables, then syllable length accuracy for disyllables is 40/50 = 80%. 2.4. Syllable shape accuracy Syllable shape accuracy is the proportion of words produced in which the syllable shape is maintained regardless of the correctness of consonants. For example, if the target word ‘vast’ [væst] is produced as [væRt], the syllable shape is accurate even though the lateralization of the fricative is an error.
3. Results 3.1. Consonant accuracy Consonant accuracy (i.e. percent consonants correct, PCC) for early, middle and late developing sounds and total consonants are shown in Table 3 for the three participants at the three measurement times, with comparison to younger and older children with CAS reported by Shriberg et al. (1997). Total PCC ranged from 34% (P3 Time 1) to 75% (P1 Time 3). P3, the participant with the most severe speech disorder at the beginning of the study, showed a clear pattern of improvement over time. Inconsistent patterns of improvement were found for P1 and P2 (e.g. poorest performance for P1 at Time 2 and best performance for P2 at Time 2). These longitudinal patterns are in keeping with findings of variability for the same children in a previous study (Marquardt et al., 2004). Segmental Table 3 Consonant accuracy: percent consonants correct (PCC) for developmental sound classes (Early-8, Middle-8 and Late-8) and for total consonants for each time and participant P1
Early PCC Middle PCC Late PCC Total PCC Total consonants attempted (#)
P2
P3
Shriberg et al. (1997)
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Younger CAS
Older CAS
88 19 3
77 73 27
92 83 41
78 54 43
86 88 40
76 82 50
57 21 22
70 52 66
88 74 59
82 47 13
88 85 50
68 415
58 446
74 635
60 346
72 825
68 457
31 374
61 435
73 502
57
77
Comparison values of consonant accuracy for younger and older children with CAS are from Shriberg et al. (1997). Total number of consonants attempted is listed in bold.
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variability decreased over time for P3, while P1 had highest variability at Time 2 and P2 had lowest variability at Time 2. This diverse set of results is suggestive of high sessionto-session variability in children with CAS in addition to within-session variability. Early developing consonants were more accurate than middle developing sounds, which were more accurate than late developing sounds (i.e. EDS > MDS > LDS), with the exception of P2 at Times 2 and 3, who produced middle developing sounds slightly more accurately than early sounds. Accuracy of early sounds increased modestly over time, with greater improvement for middle sounds and late-developing sounds. However, accuracy of ‘late-8’ sounds remained very low even at Time 3 in our study, similar to the older group from Shriberg et al. (1997). 3.2. Frequency of consonant error types Consonant errors were classified as omissions, substitutions, cluster errors and retroflex errors. The relative frequencies of these error types are shown in Table 4. Omissions and substitutions were the most frequent error types, with mean frequency of occurrence across sessions of 42% and 34%, respectively. Individual child data indicated that omissions and substitutions occurred with similar frequency during most sessions, with the exception of P1 at Time 1 and P3 at Times 1 and 3 where omissions clearly predominated. While omissions were the predominant error type, the relative frequency of omissions decreased over time for all participants. Retroflex and cluster errors were less frequent, with mean frequencies of 14% and 9%. Retroflex errors were infrequent, although considerable variation in their occurrence was noted. For example, relative frequency of retroflex errors increased steadily over time for P1. Variability in retroflex error frequency appears to be related to several factors, including decreases in other error types (e.g. omissions), poor retroflex accuracy overall (mean = 15%) and inconsistency in the number of retroflex consonants attempted (Table 5). Accuracy and frequency of consonant clusters are shown in Table 6. Cluster accuracy varied from 0% to 48%, with a longitudinal tendency towards increased accuracy; cluster accuracy was 0% for all children at Time 1, and ranged from 39% to 48% at Time 3. Errors typically involved omission of one of the consonants, indicative of a more general
Table 4 Frequency of consonant error types: percent occurrence of omission, substitution, cluster and retroflex errors are listed for each time and participant P1 Time 1 Omission Substitution Cluster Retroflex Total errors (#)
P2 Time 2
Time 3
Time 1
P3 Time 2
Time 3
Time 1
Time 2
Time 3
69 18 8 4
27 40 17 16
26 35 10 29
41 44 5 9
33 42 9 16
36 35 10 19
55 26 7 12
46 42 11 1
47 26 8 18
134
187
164
138
233
148
257
170
136
Total number of consonant errors produced is listed in bold.
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Table 5 Retroflex consonant accuracy P1
[r] Accuracy (%) Opportunities (#)
P2
P3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
0 6
31 42
29 66
0 13
5 40
0 28
3 31
60 5
4 26
Percent accuracy of retroflex consonants and number of opportunities for each time and participant.
Table 6 Consonant cluster accuracy P1
Cluster accuracy (%) Opportunities (#)
P2
Time 1
Time 2
0 11
P3
Time 3
Time 1
Time 2
Time 3
6
48
0
0
42
34
33
7
20
26
Time 1
Shriberg et al. (1997) Time 2
Time 3
Younger CAS
Older CAS
0
22
39
39
69
18
23
18
Percent accuracy of consonant clusters and number of opportunities each time and participant. Comparison values of consonant accuracy for younger and older children with CAS are from Shriberg et al. (1997).
phenomenon of syllable shape reduction. This pattern will be examined in more detail in the analysis of syllable shape accuracy. 3.3. Omission error analysis The frequency of omissions in initial, medial and final position was analyzed (Fig. 1). Final consonants were more often omitted than initial or medial consonants, with the exception of P1 at Time 2, where medial consonants were omitted nearly as often as final
Fig. 1. Omission errors by word position (initial, medial, final) for each time and participant.
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consonants, and P3 at Time 1, where initial, medial and final positions had similar omission frequencies. Initial consonant deletion errors were comparatively infrequent but were exhibited by all three participants at each measurement point. Syllables were examined to explore the relationship between syllable complexity and consonant production accuracy. Syllables were analyzed for frequency of syllable types, syllable number accuracy and syllable shape accuracy. 3.4. Syllable type frequency Mean syllable type frequencies for the participants in this study, for younger and older children with CAS from Shriberg et al. (1997), and for typically developing children ages 3–6 years (Hoffman, 1982, as cited by Shriberg et al., 1986) are shown in Table 7. Surprisingly, the children with CAS produced fewer simple monosyllabic words (e.g. CV, V, VC, CVC) and more complex monosyllables, disyllables and polysyllables than the comparison groups of typically developing children and other children with CAS. This unexpected finding may be an unintended artifact of the spontaneous speech sampling process, with examiners unintentionally attempting to elicit longer or more complex syllable types or encouraging the repetition of such words. 3.5. Syllable number accuracy Syllable number accuracy is shown in Table 8. Participants generally maintained the targeted number of syllables in their productions, especially for monosyllables and disyllables. Target words with three syllables or more (i.e. polysyllables) were less accurate. Individual data points indicate low polysyllable number accuracy for P1 at Time 1, P2 at Time 2 and P3 at Time 1. P1 showed reduced monosyllable accuracy at Time 2, typically adding an additional vowel to create a disyllable. This finding is supported by higher than expected frequency of disyllables produced by P1 at Time 2. 3.6. Syllable shape accuracy Syllable shape accuracy is shown in Table 9. Simple monosyllables were most often produced with the correct syllable shape, followed by disyllables, complex monosyllables and polysyllables. However, even simple monosyllables (CV, V, VC and CVC) were produced with the correct target syllable shape in only 75% of attempted words when averaged across participant and time. Disyllables were produced with the correct syllable shapes on slightly more than 50% of attempts, while complex monosyllables (one or more consonant clusters) and polysyllables had correct syllable shape in approximately onethird of attempts. 3.7. Relationship of syllable patterns to consonant accuracy A multiple regression analysis was completed with participant, time, frequency of syllable types (simple monosyllable, complex monosyllable, disyllable and polysyllable), syllable number accuracy and syllable shape accuracy as predictors of consonant accuracy.
436
Syllable type frequency (%) Simple monosyll. Complex monosyll. Disyllable Polysyllable
P1
P2 P3 CAS mean Typ. mean Shriberg et al. (1997) syll. freq. Younger CAS Older CAS Time 1 Time 2 Time 3 Time 1 Time 2 Time 3 Time 1 Time 2 Time 3 syl. freq. 71 1 26 1
59 14 25 2
73 19 8 <1
57 15 21 7
68 16 14 2
50 21 21 7
61 18 12 9
71 12 14 2
72 13 13 3
Total words produced (#) 269
231
361
195
452
254
187
266
263
65 14 17 4
74 11 14 1
75 9 15 2
72 11 15 2
Mean frequency of simple and complex monosyllables, disyllables and polysyllables for each time and participant. Mean syllable type frequencies for children with CAS are averaged across sessions. Mean syllable type frequencies for typically developing children are adapted from Shriberg et al. (1986). Comparison values of consonant accuracy for younger and older children with CAS are from Shriberg et al. (1997). Total number of words produced is listed in bold.
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Table 7 Syllable type frequency
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Table 8 Syllable number accuracy Syllable length accuracy (%)
P1
Monosyllable Disyllable Polysyllable Total words produced (#)
P2
P3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
98 94 33
86 100 100
94 97 100
99 98 92
96 87 56
96 94 94
99 61 19
99 97 80
100 91 86
269
231
361
195
452
254
187
266
263
CAS mean syll. # acc.
96 91 73
Accuracy of word length for each time and participant. Mean word length accuracy for children with CAS is averaged across sessions. Total number of words produced is listed in bold.
Syllable shape accuracy alone accounted for 87% of the variance in consonant accuracy (F(1,7) = 45.8, p < 0.001). Fig. 2 shows the prediction of consonant accuracy from syllable shape accuracy, with data pooled across times and participants. The data indicate a positive relationship, with low syllable shape accuracy predicting low consonant accuracy and high syllable shape accuracy predicting high consonant accuracy. A second multiple regression analysis was completed to predict the effect of syllable type frequency on consonant accuracy. The independent variables of participant, time and syllable type frequencies (e.g. simple monosyllable, complex monosyllable, disyllable and polysyllable) were entered as predictors of consonant accuracy. In this analysis, frequency of polysyllables accounted for 47.0% of the variance in consonant accuracy (F(1, 7) = 6.20, p < 0.05); inclusion of the other variables did not significantly improve the fit of the model. Fig. 3 shows the effect of polysyllable frequency on consonant accuracy, with data pooled across times and participants. High occurrence of polysyllables predicted lower consonant accuracy, suggesting an effect of word length on consonant production accuracy that is relatively independent of participant differences and variation over the longitudinal course of the study. Although consonant errors do not necessarily result in syllable shape errors, in this study of children with CAS, consonant accuracy is strongly linked with syllable construction errors and patterns of syllable production. Table 9 Syllable shape accuracy Syllable shape accuracy (%)
Simple monosyll. Complex monosyll. Disyllable Polysyllable Total words produced (#)
P1
P2
P3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
72 25 73 0
74 6 34 20
80 55 83 100
67 83 63 31
89 56 55 11
82 46 57 67
58 18 30 13
75 12 63 0
75 45 53 29
269
231
361
195
452
254
187
266
263
CAS mean syll. shape acc.
75 39 57 30
Accuracy of syllable shapes for each time and participant. Mean syllable shape accuracy for children with CAS is averaged across sessions. Total number of words produced is listed in bold.
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Fig. 2. Linear regression of consonant accuracy on syllable shape accuracy: percent consonants correct is predicted from percent accuracy of syllable shapes, with data pooled across times and participants.
Fig. 3. Linear regression of consonant accuracy on polysyllable frequency: percent consonants correct is predicted from percent occurrence of polysyllables, with data pooled across times and participants.
4. Discussion Childhood apraxia of speech is unique in its severity and persistence. Observations in this longitudinal study of three children with CAS are consistent with previous findings of consonant errors but also suggest error patterns similar to those found in younger typically developing children. These three children presented with a severe speech disorder characterized by high rates of consonant omission and substitution errors. In accord with frequent consonant omissions, analysis of syllable shape accuracy reflected impaired ability to construct accurate word shapes.
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The high rate of consonant omissions confirms several previous findings that omissions are common in children with CAS. Shriberg et al. (1997) and Lewis et al. (2004) suggested that omissions may be a distinguishing characteristic of CAS due to the relatively high occurrence of omissions in children with CAS relative to children with other speech disorders. In the present study, omission errors were accounted for almost exclusively by deletion of the final consonant in words, regardless of the number of syllables, representing a consistent pattern of syllabic error. Syllable accuracy analyses showed that simple monosyllables were the only syllable shape consistently produced correctly, suggesting that persistent omission errors likely represent a deficit in syllabic construction rather than sound-specific errors. The longitudinal course of CAS, while generally favorable, is marked by betweensession variability. The current series of longitudinal studies revealed session-to-session variability, with one child showing improvement from Time 1 to Time 2 and declining slightly at Time 3 (Participant 2) while another declined from Time 1 to Time 2 and improved at Time 3 (Participant 1). The only child showing consistent gains from session to session was Participant 3, the most severely impaired child. The inconsistent trajectory of improvement over time is at odds with the consistent improvements seen in single-word articulation testing for these three children. Lewis et al. (2004) reported a similar finding of improved articulation scores and intelligibility in the face of persistent errors in connected speech. Differential diagnosis of children with CAS is complicated by the observed session-tosession variability and task differences in speech performance. In the face of the difficulties inherent to collecting and analyzing multiple samples of connected speech, spontaneous sampling in CAS remains important on the grounds of ecological validity, i.e. it more closely reflects day-to-day speech production than single-word articulation testing (Morrison & Shriberg, 1992). Additionally, spontaneous sampling facilitates the analysis of vowel errors, variability and prosodic differences, frequently cited hallmark characteristics of CAS. Best practice for differential diagnosis of CAS should include assessment on multiple occasions, using both single-word testing and spontaneous sampling. To date, no single therapeutic regimen has proven consistently successful in treating CAS (Hall, 2000), due in part to incomplete understanding of the disorder. The present work shows that children with CAS have difficulty constructing appropriate syllable frames for target words, resulting in high rates of omission errors. This result, along with previous work showing that children with CAS have difficulty processing syllabic information (Marquardt, Sussman, Snow, & Jacks, 2002), demonstrates a clear need to address syllabic awareness and construction in treatment. Childhood apraxia of speech may be caused by a confluence of developmental factors, including immature motor control processes as well as irregular development of concurrently developing representational substrates for speech production. To date, most studies of CAS have focused on the important task of describing proposed clinical correlates for differential diagnosis from other speech disorder categories. Future work should evaluate competing theoretical frameworks to support an account of the disorder consistent with the persistent deficits observed. Both understanding of the underlying nature of the disorder and careful description of differential diagnostic behavioral correlates are important to developing effective treatment regimens.
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Appendix A. Continuing education questions 1. Children with childhood apraxia of speech (CAS): a. are no different in their consonant errors than children with speech delay or other speech sound disorders. b. are more likely to produce sound substitutions than children with other speech disorders. c. are more likely to produce omissions than children with other speech disorders. d. are more likely to simplify liquids than children with other speech disorders. e. produce more distortion than substitution or omission errors. 2. Which of the following consonant errors is related to syllable-level error patterns? a. consonant harmony. b. omissions. c. substitutions. d. distortions. e. b and c. 3. The results of this study show that children with CAS: a. have more difficulty producing late-developing than early-developing consonants. b. rarely make consonant errors that affect syllable structure. c. frequently simplify clusters and delete final consonants. d. have normal prosodic patterns during phrase production. e. a and c. 4. Over the period of 3 years, consonant and syllable production of children in this study: a. improved consistently over time. b. declined consistently over time. c. showed inconsistent patterns over time. d. remained constant at baseline level. e. was related to lexical retrieval deficits. 5. Results of the study suggest that treatment for consonant deficits in CAS should focus primarily on activities to improve: a. non-speech lip and tongue movement. b. individual consonant articulation. c. correct syllable shapes. d. grammatical forms for phrases and sentences. e. non-speech oral motor coordination.
References Bowman, S. N., Parsons, C. L., & Morris, D. A. (1984). Inconsistency of phonological errors in developmental verbal dyspraxic children as a factor of linguistic task and performance load. Australian Journal of Human Communication Disorders, 12(2), 109–119. Byrd, K., & Cooper, E. B. (1989). Apraxic speech characteristics in stuttering, developmentally apraxic, and normal speaking children. Journal of Fluency Disorders, 14(3), 215–229. Crary, M. A., Landess, S., & Towne, R. (1984). Phonological error patterns in developmental verbal dyspraxia. Journal of Clinical Neuropsychology, 6(2), 157–170.
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Davis, B. L., Jacks, A., & Marquardt, T. P. (2005). Vowel patterns in developmental apraxia of speech: Three longitudinal case studies. Clinical Linguistics & Phonetics, 19(4), 249–274. Davis, B. L., Jakielski, K. J., & Marquardt, T. P. (1998). Developmental apraxia of speech: Determiners of differential diagnosis. Clinical Linguistics & Phonetics, 12(1), 25–45. Ekelman, B. L., & Aram, D. M. (1983). Syntactic findings in developmental verbal apraxia. Journal of Communication Disorders, 16(4), 237–250. Forrest, K. (2003). Diagnostic criteria of developmental apraxia of speech used by clinical speech–language pathologists. American Journal of Speech–Language Pathology, 12(3), 376–380. Goffman, L. (2002). Summary discussion I. In L. D. Shriberg, & T. F. Campbell (Eds.), Childhood apraxia of speech research symposium. Carlsbad, CA: The Hendrix Foundation. Goldman, R., & Fristoe, M. (1986). Goldman–Fristoe Test of Articulation. Circle Pines, MN: American Guidance Service Inc. Guyette, T. W., & Diedrich, W. M. (1981). A critical review of developmental apraxia of speech. In Lass, N. J. (Ed.). Speech and language: Advances in basic research and practice. 5 (pp.1–49). New York, NY: Academic Press. Hall, P. K. (2000). A letter to the parents of a child with developmental apraxia of speech. Part IV: Treatment of DAS. Language, Speech, & Hearing Services in Schools, 31(2), 179–181. Hall, P. K., Jordan, L. S., & Robin, D. A. (1993). Developmental apraxia of speech: Theory and clinical practice. Austin, TX: PRO-ED. Hodson, B. W. (1986). Assessment of phonological processes-revised. Austin, TX: PRO-ED. Khan, L. M. L., & Lewis, N. (1986). Khan–Lewis Phonological Assessment. Circle Pines, MN: American Guidance Service Inc. Lewis, B. A., Freebairn, L. A., Hansen, A. J., Iyengar, S. K., & Taylor, H. G. (2004). School-age follow-up of children with childhood apraxia of speech. Language, Speech, & Hearing Services in Schools, 35(2), 122–140. Marquardt, T. P., Jacks, A., & Davis, B. L. (2004). Token-to-token variability in developmental apraxia of speech: Three longitudinal case studies. Clinical Linguistics & Phonetics, 18(2), 127–144. Marquardt, T. P., Sussman, H. M., & Davis, B. L. (2001). Developmental apraxia of speech: Advances in theory and practice. In D. Vogel, & M. Cannito (Eds.), Treating disordered motor speech control (2nd ed., pp. 413– 473). Austin, TX: Pro-Ed. Marquardt, T. P., Sussman, H. M., Snow, T., & Jacks, A. (2002). The integrity of the syllable in developmental apraxia of speech. Journal of Communication Disorders, 35(1), 31–49. Morrison, J. A., & Shriberg, L. D. (1992). Articulation testing versus conversational speech sampling. Journal of Speech & Hearing Research, 35(2), 259–273. Rosenbek, J. C., & Wertz, R. T. (1972). A review of fifty cases of developmental apraxia of speech. Language, Speech, & Hearing Services in Schools, 5, 13–22. Shriberg, L. D. (1993). Four new speech and prosody-voice measures for genetics research and other studies in developmental phonological disorders. Journal of Speech, Language & Hearing Research, 36(1), 105–131. Shriberg, L. D., Aram, D. M., & Kwiatkowski, J. (1997). Developmental apraxia of speech: II. Toward a diagnostic marker. Journal of Speech Language & Hearing Research, 40(2), 286–312. Shriberg, L. D., & Kwiatkowski, J. (1982). Phonological disorders: III. A procedure for assessing severity of involvement. Journal of Speech & Hearing Disorders, 47(3), 256–270. Shriberg, L. D., Kwiatkowski, J., Best, S., Hengst, J., & Terselic-Weber, B. (1986). Characteristics of children with phonologic disorders of unknown origin. Journal of Speech & Hearing Disorders, 51(2), 140–161. Stackhouse, J., & Snowling, M. (1992). Developmental verbal dyspraxia: II. A developmental perspective on two case studies. European Journal of Disorders of Communication, 27(1), 35–54. Thoonen, G., Maassen, B., Gabreels, F., & Schreuder, R. (1994). Feature analysis of singleton consonant errors in developmental verbal dyspraxia (DVD). Journal of Speech & Hearing Research, 37(6), 1424–1440. Yoss, K. A., & Darley, F. L. (1974). Developmental apraxia of speech in children with defective articulation. Journal of Speech & Hearing Research, 17(3), 399–416.
Consonant and syllable structure patterns in childhood apraxia of speech: Developmental change in three children Adam Jacks *, Thomas P. Marquardt, Barbara L. Davis Department of Communication Sciences and Disorders, The University of Texas at Austin, 1 University Station, Mail Code A1100, Austin, TX 78712, USA Received 2 May 2005; received in revised form 21 December 2005; accepted 22 December 2005
Abstract Changes in consonant and syllable-level error patterns of three children diagnosed with childhood apraxia of speech (CAS) were investigated in a 3-year longitudinal study. Spontaneous speech samples were analyzed to assess the accuracy of consonants and syllables. Consonant accuracy was low overall, with most frequent errors on middle- and late-developing sounds. Omissions and substitutions were the dominant error types. Analysis of syllables revealed higher frequencies of error on complex mono- and polysyllables. Multiple regression analyses revealed that consonant accuracy is predicted by syllable shape accuracy and polysyllable frequency. Improvement was noted over time, although irregular patterns of consonant and syllable-level errors persisted across the period studied. Findings suggest that consonant errors in CAS are related to syllable-level deficits, namely difficulty constructing syllabic frames for speech production targets. Learning outcomes: On the basis of this article, the reader will be able to (1) describe the deficits in consonant production demonstrated by the participants, (2) analyze the relationship between consonant production and syllable-level patterns of error and (3) consider the value of addressing syllable construction as a therapeutic goal. # 2006 Elsevier Inc. All rights reserved.
* Corresponding author. Tel.: +1 512 471 3841; fax: +1 512 232 1804. E-mail address: [email protected] (A. Jacks). 0021-9924/$ – see front matter # 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcomdis.2005.12.005
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1. Introduction Childhood apraxia of speech (CAS)1 is a disorder believed to result from impaired speech motor control (e.g. Hall, Jordan, & Robin, 1993) or impaired representation of phonological constructs (e.g. Marquardt, Sussman, & Davis, 2001). Although controversy surrounds the disorder (e.g. Forrest, 2003; Guyette & Diedrich, 1981), behavioral characteristics include a high frequency of consonant and vowel errors, error variability and prosodic differences (e.g. Davis, Jakielski, & Marquardt, 1998). Consonant errors per se are not sufficient for differential diagnosis of CAS and overlap with behavioral features identified in other childhood speech disorders (Shriberg, Aram, & Kwiatkowski, 1997). Recent research suggests that consonant errors affecting syllable structure (e.g. syllable reduction, initial and final consonant deletion) are more common in CAS than in speech disorders not identified as CAS (Lewis, Freebairn, Hansen, Iyengar, & Taylor, 2004; Shriberg et al., 1997). Analysis of consonant and syllable-level errors is needed to better understand persisting patterns of speech deficits found in children with CAS. 1.1. Consonant errors in CAS A high rate of consonant error frequently is cited as a diagnostic indicator for CAS (e.g. Davis et al., 1998; Rosenbek & Wertz, 1972; Shriberg et al., 1997; Yoss & Darley, 1974). However, consonant errors are common in almost all children with developmental speech disorders. A summary of consonant error types in representative studies of children with CAS is shown in Table 1. Several of these studies will be reviewed in more detail to provide a focused characterization of the nature of consonant production patterns in children with CAS. Studies of CAS have reported consonant errors affecting both isolated sound segments (e.g. sound substitutions) and word-level structure (e.g. consonant omissions, syllable deletions, assimilatory processes). While consonant substitutions are common in CAS and in delayed development, recent evidence suggests that syllable-level errors, such as consonant omissions may be distinctive for children with CAS (Lewis et al., 2004; Shriberg et al., 1997). For example, Shriberg et al. (1997) reported that 42% of consonant errors were omissions in younger children with CAS (ages 4.10–7.0 years) compared to 25% for children with speech delay. More recently, Lewis et al. (2004) found high proportions of initial and final consonant deletion, syllable deletion and cluster reduction in children with CAS in comparison with children with isolated speech disorders (S group) and children with both speech and language disorders (SL group). In particular, 100% of their CAS group produced final consonant deletion errors, compared to 25% and 38% for the S and SL groups, respectively. Overall, 90% of the CAS group deleted syllables, compared to 8% and 15% for the S and SL groups. Sixty percent of the CAS group simplified clusters, compared to 0% and 8% of the S and SL groups. Shriberg et al. (1997) also found that children with CAS and those with speech delay showed similar rates of error for consonants categorized as early- or late-developing 1 Childhood apraxia of speech (CAS) is known by several descriptors, including developmental apraxia of speech (DAS) and developmental verbal dyspraxia (DVD). To provide continuity with current conventions, CAS will be used as the label for the disorder (see Goffman, 2002 for a discussion of terminology).
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Table 1 Summary of consonant production studies in CAS Author
Age
N Study type
Consonant accuracy Error types Subst. Omiss. Distor. Insert. Stopp. Liq. Prolon. Syll. level SimP.
Time 1: 10.7, 11.9; 2 Longitudinal analysis of error Artic. Ageb T1: Time 2: 14.6, 15.7 patterns in two children with DVD 4.3, 3.0; T2: 5.6, 4.9 6.2–7.9 11 Analysis of feature retention in 72% PCC consonant substitutions and omissions in DAS Younger: 4.10–6.3; 14 Comparison of speech and prosody- PCC: 57%; older: 7.1–14.11 voice profiles of children with younger, suspected DAS and speech delay 77% older 5.7 1 Speech characteristics of children with suspected DAS; one child with confirmed diagnosis
Marquardt et al. (2001)
3.0–6.6
Lewis et al. (2004)
Pre-school: 4.17–5.42; school-age: 7.25–10.5
2.9–14
Bowman, Parsons, 6.1–7.4 and Morris (1984) Crary, Landess, and Towne (1984) Stackhouse and Snowling (1992) Thoonen et al. (1994) Shriberg et al. (1997) Davis et al. (1998)
3.9–13.11
50 Review of speech, language and neurol. characteristics of children with DAS 7 Analysis of phonological error patterns in DVD
20–58 errors a
10 Analysis of phonological error patterns in DVD
1 Longitudinal study of assessment and treatment in one child with DAS 10 Pre-school/school-age follow-up study of speech, language, and written language skills in children with CAS
78% PCC at 6.6
Cluster reduction Weak syll. del., cluster reduction Cluster reduction Cluster reduction, metath.
Glottal errors; omitted initial and final consonants Omitted intervocalic and final consonants, gliding Groping, glottal substitution
Place retention: 79% manner ret.: 87% voicing ret.: 95% Omitted in final; palatal fronting in older children only Assim. and syllable errors; oral posturing, lim. use of complex word shapes Velar fronting, FCD, ICD
Weak syll. del., cluster reduction
Cluster reduc., weak syll. del ICD 40% of Cluster reduct., Syll. CAS group Voicing errors 40% FCD reduct 100% syll reduc. 90% Liq simp. 80%
Note: DAS = developmental apraxia of speech, DVD = developmental verbal dyspraxia, CAS = childhood apraxia of speech, PCC = percent consonants correct, FCD = final consonant deletion, ICD = initial consonant deletion. a Goldman–Fristoe Test of Articulation (GFTA, Goldman & Fristoe, 1986). b Edinburgh Articulation Test (EAT, Anthony, Bogle, Ingram, & McIsaac, 1971, as cited by Stackhouse & Snowling, 1992).
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Rosenbek and Wertz (1972)
Other
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sounds, with lesser accuracy for middle-developing sounds by children with CAS. Assessing the accuracy of early-, middle- and late-developing sounds can potentially be used as an index to delay versus disorder in segmental acquisition patterns in children with clinically relevant speech patterns. Studies of consonant production patterns in children with CAS suggest that their errors may be qualitatively different from errors of children with other speech disorders or speech delay, especially in omissions that result in reductions in syllable complexity (Lewis et al., 2004; Shriberg et al., 1997). Consonant errors in CAS also may reflect typical patterns of error that persist past the period of development in which they emerge in typically developing children. For example, a child who produces most early- and middledeveloping sounds correctly with errors primarily for late-developing sounds may not have age-appropriate speech production, but the developmental pattern may be similar to that of younger typically developing children. Speech deficits in children with CAS frequently persist over time, to such an extent that slow progress in therapy has been used as a differential diagnostic criterion by clinicians and researchers alike (e.g. Byrd & Cooper, 1989; Ekelman & Aram, 1983; Forrest, 2003; Thoonen, Maassen, Gabreels, & Schreuder, 1994). Although there is a growing literature on CAS, there are relatively few longitudinal studies available (Davis, Jacks, & Marquardt, 2005; Lewis et al., 2004; Marquardt, Jacks, & Davis, 2004; Shriberg et al., 1997; Stackhouse & Snowling, 1992). Longitudinal studies of speech characteristics in CAS are needed to track the persistence of characteristics marking continued speech disorder relative to chronological age expectations. This is the third in a series of studies examining longitudinal change in characteristic speech deficits of children with CAS. The first two studies examined phonetic variability (Marquardt et al., 2004) and vowel production (Davis et al., 2005) over a 3-year period in three children diagnosed with CAS. In both studies, improvement was noted but vowel errors and phonetic variability remained high up to 7.5 years of age. These findings are supported by data from three other studies reporting continuing deficits in speech production relative to chronological age expectations (Lewis et al., 2004; Shriberg et al., 1997; Stackhouse & Snowling, 1992). Lewis et al. (2004) examined speech and language performance of 10 children with clinical diagnosis of CAS at pre-school (mean = 4.8 years) and at school age (mean = 8.7 years), compared with 15 children diagnosed with speech disorder and 14 children diagnosed with speech and language disorder. Results indicated improvement in standard articulation test scores for 8 of 10 children with CAS. However, metathetic and syllable deletion errors became more prominent by school age and unusual error types persisted, including initial consonant deletion, vowel and voicing errors. Stackhouse and Snowling (1992) studied speech errors of two children diagnosed with CAS at two times spanning a 4-year period (ages 10.7 and 11.9 years at study onset). Speech performance was compared to 10 younger children matched on articulation age (ages 3.0–5.6 years). Results indicated that articulation age improved for both children and number of words without error increased, although the children continued to produce many words with multiple errors even at 15–16 years of age. These two children produced many consonant substitutions like those of typically developing younger children, but had a greater number of errors affecting syllable structure (i.e. consonant deletion or cluster reduction).
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Shriberg et al. (1997) examined speech characteristics in children diagnosed with CAS using a cross-sectional methodology analyzing younger (4.10–6.3 years) and older (7.1– 14.11 years) children. They found better speech performance in the older group, including higher overall consonant accuracy and greater accuracy for middle and late-developing sounds. Rates of cluster reduction, initial stopping and liquid simplification were lower in the older group relative to the younger group, but several patterns of error remained prominent in older children with CAS, including palatal fronting, deaffrication and persistent cluster reduction and liquid simplification. Consonant and syllable-level error patterns represent persisting areas of deficit relative to chronological age expectations for children diagnosed with CAS. These deficits persist over time even with intensive therapeutic intervention. The aim of this study was to examine consonant and syllable patterns, describing both stability and change over a 3-year period in three children with CAS.
2. Method 2.1. Participants Participants were three English-speaking male children (P1–P3), selected from a large number of children referred for differential diagnosis of childhood apraxia of speech (CAS) in a long-term study of speech and language characteristics in children with the disorder (e.g. Davis et al., 1998). A team of three speech–language pathologists in a university clinical setting confirmed a positive diagnosis of CAS on the basis of a cluster of speech and language characteristics typical of the disorder, including prosodic abnormalities, vowel errors, high frequency of consonant and syllable omissions and segmental variability (Davis et al., 1998). When available, previous assessments of hearing, cognition and expressive and receptive language were used to establish participant status. Participants passed pure tone audiometric screening at octave frequencies from 250 to 4000 Hz at the beginning of the study. Review of clinical records revealed no positive history of fluctuations in auditory acuity due to middle ear disorders. An oral mechanism examination, diadochokinetic testing, and informal oral and limb praxis tests revealed no obvious signs of structural or neuromuscular impairment. Consonant and syllable production data were obtained as part of a longitudinal evaluation of speech production patterns in children with CAS. Following diagnosis, participants were assessed at 1-year intervals (Time 1–Time 3) between the ages of 4.6 and 7.7 years. Assessments included articulation testing and spontaneous speech sampling. Speech profiles for participants are shown in Table 2, including age at each assessment, scores on single-word articulation tests, accuracy of consonant and vowel production from connected speech samples, and inventories of consonant and vowel types. Consonant and vowel accuracy and inventories were determined from speech samples collected at each time interval in the study. Participant 1 (P1) had a normal developmental history with the exception of speech and language. He produced his first word at 22 months. He was diagnosed with CAS at 3.8 years. Initial neurological examination revealed oral apraxia and mild dysarthria although
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Table 2 Participant data: age, articulation test results and accuracy and inventories of consonant and vowel production at three times
P1 Age Articulation test Consonant accuracy Vowel accuracy Consonant inventory
Vowel inventory P2 Age Articulation test Consonant accuracy Vowel accuracy Consonant inventory
Vowel inventory P3 Age Articulation test Consonant accuracy Vowel accuracy Consonant inventory
Vowel inventory
Time 1
Time 2
Time 3
4.6 Profounda 69% 61% p, b, f, w, m, t, d, n, h
5.5 3rd%ileb 61% 72% p, b, f, v, w, m, t, d, s, l, n, k, , g, h, R, tR, ., r
i, I, e, æ, a, K\3, o, u, U, diph.
i, I, e, æ, a, K\3, 2, o, u, U, diph.
6.5 31%ilec 75% 85% p, b, f, v, w, m, t, d, s, ð, z, l, n, k, g, h, R, ., j, r, E, clust. i, I, e, e, æ, a, K\3, &, o, u, U, diph.
5.10 Severea 61% 75% p, b, f, v, w, m, t, d, s, z, l, n, k, , g, h, R, j, E, clust. i, I, e, e, æ, K\3, 2, &, o, u, U, diph.
6.10 4%ileb 72% 85% p, b, f, v, w, m, t, d, s, u, ð, z, l, n, k, g, h, j, E, clust. i, I, e, e, æ, a, K\3, 2, &, o, u, U, diph.
7.7 16%ileb 69% 71% p, b, f, v, w, m, t, d, s, u, ð, z, l, n, k, , g, R, tR, j, E, clust. i, I, e, æ, a, K\3, &, o, u, U, diph.
5.6 <1%ileb 34% 65% p, h, f, v, w, m, t, d, s, l, n, , h, R, clust.
6.10 <1%ileb 63% 70% p, h, f, v, w, m, t, d, s, u, ð, z, l, n, k, , g, h, R, ., j, r, E, clust. i, I, e, e, æ, a, K\3, &, o, u, U, diph.
7.5 <1%ileb 74% 76% p, h, f, v, w, m, t, d, s, u, ð, z, l, n, k, , g, h, ., j, E, clust. i, I, e, æ, a, K\3, &, o, u, U, diph.
i, I, e, e, æ, a, K\3, &, o, u, U, diph.
Note: Consonant and vowel accuracy represent relational measures derived from analysis of entire connected speech sample from each time. a Assessment of Phonological Processes-Revised (APP-R, Hodson, 1986). b Goldman–Fristoe Test of Articulation (GFTA, Goldman & Fristoe, 1986). c Khan–Lewis Phonological Assessment (KLPA, Khan & Lewis, 1986).
no signs of neuromuscular weakness were found upon follow-up oral-peripheral examinations. Between 3.5 and 5.0 years, speech and language evaluations indicated auditory comprehension generally within normal limits, although below average for elaborated sentences. Speech production was characterized by a limited number of consistent word forms, restricted phonetic repertoire, rudimentary syllable shapes and reduced ability to imitate non-verbal movements of the speech mechanism. P1 began receiving speech and language therapy at 2.2 years and continued to receive treatment at the time of the study. Treatment goals initially addressed increased accuracy of verbal communication with supplementary use of sign and communication boards to facilitate
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language and cognitive development. Subsequent goals included expanding phonemic repertoire, stabilizing consistent sound production and increasing use of more complex syllable shapes in words and phrases. P1 was seen for re-evaluation at 4.6, 5.5 and 6.5 years, making continuous gains in single-word articulation (see Table 2). Participant 2 (P2) also had a normal developmental history with the exception of speech and language. Initial speech and language evaluation at 2.6 years revealed severe deficits in receptive and expressive communication. Re-evaluation at 5.0 years revealed receptive language within normal limits with speech characterized by frequent vowel errors, final consonant deletion, errors on initial consonants, glottal stops and reduction of consonant clusters. P2 began therapy at 2.6 years and was enrolled continuously during the study. Treatment goals focused on expanding the phonemic repertoire, increasing accuracy of consonants and vowels, and increasing use of consonant clusters. Follow-up evaluations were completed at yearly intervals (ages 5.10, 6.10 and 7.7 years), with consistent gains in single-word articulation (see Table 2). Participant 3 (P3) had a normal developmental history with the exception of speech and language. He began using words between 1 and 2 years, although his mother reported that his speech was ‘unclear’. He was diagnosed with CAS at the age of 5.6 years. Speech and language evaluations conducted between of 4.2 and 5.11 years revealed profoundly impaired speech production characterized by an incomplete phonetic inventory, variable consonant and vowel errors, unusual and persistent phonological processes, inconsistency of stress and intonation, and nasality. His comprehension of single words was within normal limits, although tasks of short-term auditory memory and meta-linguistic skills indicated difficulty in repeating more than two lexical items, identifying words with greater than two syllables and identifying the different segment in CVC minimal word pairs. He began receiving speech and language therapy at 4.2 years focusing on increasing the accuracy of vowel and consonant segments and increased syllabic complexity. Evaluations for this study at 5.6, 6.10 and 7.5 years showed negligible gains in accuracy of single-word productions (see Table 2). A graduate clinician and two certified speech–language pathologists experienced in differential diagnosis of CAS collected spontaneous speech samples from each participant. Nine 1-hour samples (one sample at each of the three times for the three participants) were obtained in total. Developmentally appropriate materials including games, stories and spontaneous narratives were employed to elicit each sample. Samples were assessed as representative of the child’s connected speech patterns and language level based on parent interviews at the time of each evaluation. All verbal communication attempted during the acquisition of the spontaneous samples was transcribed by a certified speech–language pathologist using broad phonetic transcription. To enable relational analyses comparing productions to targets, only utterances with clear semantic intent were analyzed, based on the investigator’s understanding of the communication context. Transcription reliability was determined for a second, independent transcription of 10% of the utterances in each of the nine samples. Mean inter-rater agreement, based on the number of segments (consonants and vowels) transcribed identically, was 86.22% with a range of 75–96.26%. Target (i.e. attempted) consonants were coded by developmental sound class, as described by Shriberg (1993). Consonants were classified as Early-8 Sounds /mbjnwdph/, Middle-8 sounds /tEkgfvtR./ or Late-8 sounds /Ruszðlra/.
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2.2. Consonant analysis 2.2.1. Consonant accuracy Several relational analyses were used to compare child forms to word targets. Consonant accuracy was assessed by computing the percentage of consonants produced correctly compared to the number of consonants attempted during each session (i.e. percent consonants correct, PCC; Shriberg & Kwiatkowski, 1982). PCC was calculated for total consonants produced and separately for early, middle and late developing sounds (Shriberg, 1993). Phonetic targets for the children’s vowel productions were determined in consideration of allophonic variation and local dialect features. When a production was in question with respect to the potential correctness of a consonant (e.g. alveolar flap produced versus alveolar stop), the production was scored as correct. 2.2.2. Frequency of consonant error types Consonant errors were classified as substitution, omission, retroflex or cluster errors. Substitutions are errors perceived by the transcriber as a different consonant sound than the target sound. Omissions (i.e. deletion) are errors where no consonant was produced for an intended consonant target. Retroflex errors were comprised of omission or substitution of [r], frequently by an approximant, such as [w]. Cluster errors involved omission or substitution of one or more sounds in an intended consonant cluster. Relative frequencies of error types were calculated by dividing the number of errors of a given type (i.e. substitution, omission, retroflex or cluster) by the total number of consonant errors in the speech sample. Omissions were further analyzed to determine the proportion of errors occurring in word-initial, -medial or -final positions. 2.3. Syllable analysis Three analyses were completed to examine participant ability to produce syllables. Analyses included (1) frequency of occurrence of different syllable types, (2) syllable number accuracy and (3) syllable shape accuracy. Each word in the sample was coded for syllable shape and number. Syllable shape was coded with ‘C’ corresponding to a consonant, ‘V’ corresponding to a vowel; thus ‘CVCC’ is a combination of a consonant, a vowel and a two-consonant cluster. Syllable number was coded numerically, with ‘1’ corresponding to monosyllabic words, ‘2’ corresponding to disyllables and numbers greater than three corresponding to polysyllables. For the purposes of the present analysis, syllable shapes were collapsed into four categories: (1) simple monosyllables (V, CV, VC, CVC), (2) complex monosyllables (containing clusters), (3) disyllables and (4) polysyllables. 2.3.1. Syllable type frequency Syllable type frequency was computed as the proportion of words represented by a given syllable type. For example, if 50 of 100 words produced were simple monosyllables, then the frequency for simple monosyllables is 50%. Mean frequencies of syllable types for these children were compared to norms from typically developing children ages 3–6 years (Hoffman, 1982, as cited by Shriberg, Kwiatkowski, Best, Hengst, & Terselic-Weber,
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1986) and from older and younger children with CAS reported in the literature (Shriberg et al., 1997). 2.3.2. Syllable number accuracy Syllable number accuracy is the proportion of words in which the correct number of syllables is maintained. For example, if 50 words should have been produced with two syllables and 40 were produced with two syllables, then syllable length accuracy for disyllables is 40/50 = 80%. 2.4. Syllable shape accuracy Syllable shape accuracy is the proportion of words produced in which the syllable shape is maintained regardless of the correctness of consonants. For example, if the target word ‘vast’ [væst] is produced as [væRt], the syllable shape is accurate even though the lateralization of the fricative is an error.
3. Results 3.1. Consonant accuracy Consonant accuracy (i.e. percent consonants correct, PCC) for early, middle and late developing sounds and total consonants are shown in Table 3 for the three participants at the three measurement times, with comparison to younger and older children with CAS reported by Shriberg et al. (1997). Total PCC ranged from 34% (P3 Time 1) to 75% (P1 Time 3). P3, the participant with the most severe speech disorder at the beginning of the study, showed a clear pattern of improvement over time. Inconsistent patterns of improvement were found for P1 and P2 (e.g. poorest performance for P1 at Time 2 and best performance for P2 at Time 2). These longitudinal patterns are in keeping with findings of variability for the same children in a previous study (Marquardt et al., 2004). Segmental Table 3 Consonant accuracy: percent consonants correct (PCC) for developmental sound classes (Early-8, Middle-8 and Late-8) and for total consonants for each time and participant P1
Early PCC Middle PCC Late PCC Total PCC Total consonants attempted (#)
P2
P3
Shriberg et al. (1997)
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Younger CAS
Older CAS
88 19 3
77 73 27
92 83 41
78 54 43
86 88 40
76 82 50
57 21 22
70 52 66
88 74 59
82 47 13
88 85 50
68 415
58 446
74 635
60 346
72 825
68 457
31 374
61 435
73 502
57
77
Comparison values of consonant accuracy for younger and older children with CAS are from Shriberg et al. (1997). Total number of consonants attempted is listed in bold.
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variability decreased over time for P3, while P1 had highest variability at Time 2 and P2 had lowest variability at Time 2. This diverse set of results is suggestive of high sessionto-session variability in children with CAS in addition to within-session variability. Early developing consonants were more accurate than middle developing sounds, which were more accurate than late developing sounds (i.e. EDS > MDS > LDS), with the exception of P2 at Times 2 and 3, who produced middle developing sounds slightly more accurately than early sounds. Accuracy of early sounds increased modestly over time, with greater improvement for middle sounds and late-developing sounds. However, accuracy of ‘late-8’ sounds remained very low even at Time 3 in our study, similar to the older group from Shriberg et al. (1997). 3.2. Frequency of consonant error types Consonant errors were classified as omissions, substitutions, cluster errors and retroflex errors. The relative frequencies of these error types are shown in Table 4. Omissions and substitutions were the most frequent error types, with mean frequency of occurrence across sessions of 42% and 34%, respectively. Individual child data indicated that omissions and substitutions occurred with similar frequency during most sessions, with the exception of P1 at Time 1 and P3 at Times 1 and 3 where omissions clearly predominated. While omissions were the predominant error type, the relative frequency of omissions decreased over time for all participants. Retroflex and cluster errors were less frequent, with mean frequencies of 14% and 9%. Retroflex errors were infrequent, although considerable variation in their occurrence was noted. For example, relative frequency of retroflex errors increased steadily over time for P1. Variability in retroflex error frequency appears to be related to several factors, including decreases in other error types (e.g. omissions), poor retroflex accuracy overall (mean = 15%) and inconsistency in the number of retroflex consonants attempted (Table 5). Accuracy and frequency of consonant clusters are shown in Table 6. Cluster accuracy varied from 0% to 48%, with a longitudinal tendency towards increased accuracy; cluster accuracy was 0% for all children at Time 1, and ranged from 39% to 48% at Time 3. Errors typically involved omission of one of the consonants, indicative of a more general
Table 4 Frequency of consonant error types: percent occurrence of omission, substitution, cluster and retroflex errors are listed for each time and participant P1 Time 1 Omission Substitution Cluster Retroflex Total errors (#)
P2 Time 2
Time 3
Time 1
P3 Time 2
Time 3
Time 1
Time 2
Time 3
69 18 8 4
27 40 17 16
26 35 10 29
41 44 5 9
33 42 9 16
36 35 10 19
55 26 7 12
46 42 11 1
47 26 8 18
134
187
164
138
233
148
257
170
136
Total number of consonant errors produced is listed in bold.
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Table 5 Retroflex consonant accuracy P1
[r] Accuracy (%) Opportunities (#)
P2
P3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
0 6
31 42
29 66
0 13
5 40
0 28
3 31
60 5
4 26
Percent accuracy of retroflex consonants and number of opportunities for each time and participant.
Table 6 Consonant cluster accuracy P1
Cluster accuracy (%) Opportunities (#)
P2
Time 1
Time 2
0 11
P3
Time 3
Time 1
Time 2
Time 3
6
48
0
0
42
34
33
7
20
26
Time 1
Shriberg et al. (1997) Time 2
Time 3
Younger CAS
Older CAS
0
22
39
39
69
18
23
18
Percent accuracy of consonant clusters and number of opportunities each time and participant. Comparison values of consonant accuracy for younger and older children with CAS are from Shriberg et al. (1997).
phenomenon of syllable shape reduction. This pattern will be examined in more detail in the analysis of syllable shape accuracy. 3.3. Omission error analysis The frequency of omissions in initial, medial and final position was analyzed (Fig. 1). Final consonants were more often omitted than initial or medial consonants, with the exception of P1 at Time 2, where medial consonants were omitted nearly as often as final
Fig. 1. Omission errors by word position (initial, medial, final) for each time and participant.
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consonants, and P3 at Time 1, where initial, medial and final positions had similar omission frequencies. Initial consonant deletion errors were comparatively infrequent but were exhibited by all three participants at each measurement point. Syllables were examined to explore the relationship between syllable complexity and consonant production accuracy. Syllables were analyzed for frequency of syllable types, syllable number accuracy and syllable shape accuracy. 3.4. Syllable type frequency Mean syllable type frequencies for the participants in this study, for younger and older children with CAS from Shriberg et al. (1997), and for typically developing children ages 3–6 years (Hoffman, 1982, as cited by Shriberg et al., 1986) are shown in Table 7. Surprisingly, the children with CAS produced fewer simple monosyllabic words (e.g. CV, V, VC, CVC) and more complex monosyllables, disyllables and polysyllables than the comparison groups of typically developing children and other children with CAS. This unexpected finding may be an unintended artifact of the spontaneous speech sampling process, with examiners unintentionally attempting to elicit longer or more complex syllable types or encouraging the repetition of such words. 3.5. Syllable number accuracy Syllable number accuracy is shown in Table 8. Participants generally maintained the targeted number of syllables in their productions, especially for monosyllables and disyllables. Target words with three syllables or more (i.e. polysyllables) were less accurate. Individual data points indicate low polysyllable number accuracy for P1 at Time 1, P2 at Time 2 and P3 at Time 1. P1 showed reduced monosyllable accuracy at Time 2, typically adding an additional vowel to create a disyllable. This finding is supported by higher than expected frequency of disyllables produced by P1 at Time 2. 3.6. Syllable shape accuracy Syllable shape accuracy is shown in Table 9. Simple monosyllables were most often produced with the correct syllable shape, followed by disyllables, complex monosyllables and polysyllables. However, even simple monosyllables (CV, V, VC and CVC) were produced with the correct target syllable shape in only 75% of attempted words when averaged across participant and time. Disyllables were produced with the correct syllable shapes on slightly more than 50% of attempts, while complex monosyllables (one or more consonant clusters) and polysyllables had correct syllable shape in approximately onethird of attempts. 3.7. Relationship of syllable patterns to consonant accuracy A multiple regression analysis was completed with participant, time, frequency of syllable types (simple monosyllable, complex monosyllable, disyllable and polysyllable), syllable number accuracy and syllable shape accuracy as predictors of consonant accuracy.
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Syllable type frequency (%) Simple monosyll. Complex monosyll. Disyllable Polysyllable
P1
P2 P3 CAS mean Typ. mean Shriberg et al. (1997) syll. freq. Younger CAS Older CAS Time 1 Time 2 Time 3 Time 1 Time 2 Time 3 Time 1 Time 2 Time 3 syl. freq. 71 1 26 1
59 14 25 2
73 19 8 <1
57 15 21 7
68 16 14 2
50 21 21 7
61 18 12 9
71 12 14 2
72 13 13 3
Total words produced (#) 269
231
361
195
452
254
187
266
263
65 14 17 4
74 11 14 1
75 9 15 2
72 11 15 2
Mean frequency of simple and complex monosyllables, disyllables and polysyllables for each time and participant. Mean syllable type frequencies for children with CAS are averaged across sessions. Mean syllable type frequencies for typically developing children are adapted from Shriberg et al. (1986). Comparison values of consonant accuracy for younger and older children with CAS are from Shriberg et al. (1997). Total number of words produced is listed in bold.
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Table 7 Syllable type frequency
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Table 8 Syllable number accuracy Syllable length accuracy (%)
P1
Monosyllable Disyllable Polysyllable Total words produced (#)
P2
P3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
98 94 33
86 100 100
94 97 100
99 98 92
96 87 56
96 94 94
99 61 19
99 97 80
100 91 86
269
231
361
195
452
254
187
266
263
CAS mean syll. # acc.
96 91 73
Accuracy of word length for each time and participant. Mean word length accuracy for children with CAS is averaged across sessions. Total number of words produced is listed in bold.
Syllable shape accuracy alone accounted for 87% of the variance in consonant accuracy (F(1,7) = 45.8, p < 0.001). Fig. 2 shows the prediction of consonant accuracy from syllable shape accuracy, with data pooled across times and participants. The data indicate a positive relationship, with low syllable shape accuracy predicting low consonant accuracy and high syllable shape accuracy predicting high consonant accuracy. A second multiple regression analysis was completed to predict the effect of syllable type frequency on consonant accuracy. The independent variables of participant, time and syllable type frequencies (e.g. simple monosyllable, complex monosyllable, disyllable and polysyllable) were entered as predictors of consonant accuracy. In this analysis, frequency of polysyllables accounted for 47.0% of the variance in consonant accuracy (F(1, 7) = 6.20, p < 0.05); inclusion of the other variables did not significantly improve the fit of the model. Fig. 3 shows the effect of polysyllable frequency on consonant accuracy, with data pooled across times and participants. High occurrence of polysyllables predicted lower consonant accuracy, suggesting an effect of word length on consonant production accuracy that is relatively independent of participant differences and variation over the longitudinal course of the study. Although consonant errors do not necessarily result in syllable shape errors, in this study of children with CAS, consonant accuracy is strongly linked with syllable construction errors and patterns of syllable production. Table 9 Syllable shape accuracy Syllable shape accuracy (%)
Simple monosyll. Complex monosyll. Disyllable Polysyllable Total words produced (#)
P1
P2
P3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
Time 1
Time 2
Time 3
72 25 73 0
74 6 34 20
80 55 83 100
67 83 63 31
89 56 55 11
82 46 57 67
58 18 30 13
75 12 63 0
75 45 53 29
269
231
361
195
452
254
187
266
263
CAS mean syll. shape acc.
75 39 57 30
Accuracy of syllable shapes for each time and participant. Mean syllable shape accuracy for children with CAS is averaged across sessions. Total number of words produced is listed in bold.
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Fig. 2. Linear regression of consonant accuracy on syllable shape accuracy: percent consonants correct is predicted from percent accuracy of syllable shapes, with data pooled across times and participants.
Fig. 3. Linear regression of consonant accuracy on polysyllable frequency: percent consonants correct is predicted from percent occurrence of polysyllables, with data pooled across times and participants.
4. Discussion Childhood apraxia of speech is unique in its severity and persistence. Observations in this longitudinal study of three children with CAS are consistent with previous findings of consonant errors but also suggest error patterns similar to those found in younger typically developing children. These three children presented with a severe speech disorder characterized by high rates of consonant omission and substitution errors. In accord with frequent consonant omissions, analysis of syllable shape accuracy reflected impaired ability to construct accurate word shapes.
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The high rate of consonant omissions confirms several previous findings that omissions are common in children with CAS. Shriberg et al. (1997) and Lewis et al. (2004) suggested that omissions may be a distinguishing characteristic of CAS due to the relatively high occurrence of omissions in children with CAS relative to children with other speech disorders. In the present study, omission errors were accounted for almost exclusively by deletion of the final consonant in words, regardless of the number of syllables, representing a consistent pattern of syllabic error. Syllable accuracy analyses showed that simple monosyllables were the only syllable shape consistently produced correctly, suggesting that persistent omission errors likely represent a deficit in syllabic construction rather than sound-specific errors. The longitudinal course of CAS, while generally favorable, is marked by betweensession variability. The current series of longitudinal studies revealed session-to-session variability, with one child showing improvement from Time 1 to Time 2 and declining slightly at Time 3 (Participant 2) while another declined from Time 1 to Time 2 and improved at Time 3 (Participant 1). The only child showing consistent gains from session to session was Participant 3, the most severely impaired child. The inconsistent trajectory of improvement over time is at odds with the consistent improvements seen in single-word articulation testing for these three children. Lewis et al. (2004) reported a similar finding of improved articulation scores and intelligibility in the face of persistent errors in connected speech. Differential diagnosis of children with CAS is complicated by the observed session-tosession variability and task differences in speech performance. In the face of the difficulties inherent to collecting and analyzing multiple samples of connected speech, spontaneous sampling in CAS remains important on the grounds of ecological validity, i.e. it more closely reflects day-to-day speech production than single-word articulation testing (Morrison & Shriberg, 1992). Additionally, spontaneous sampling facilitates the analysis of vowel errors, variability and prosodic differences, frequently cited hallmark characteristics of CAS. Best practice for differential diagnosis of CAS should include assessment on multiple occasions, using both single-word testing and spontaneous sampling. To date, no single therapeutic regimen has proven consistently successful in treating CAS (Hall, 2000), due in part to incomplete understanding of the disorder. The present work shows that children with CAS have difficulty constructing appropriate syllable frames for target words, resulting in high rates of omission errors. This result, along with previous work showing that children with CAS have difficulty processing syllabic information (Marquardt, Sussman, Snow, & Jacks, 2002), demonstrates a clear need to address syllabic awareness and construction in treatment. Childhood apraxia of speech may be caused by a confluence of developmental factors, including immature motor control processes as well as irregular development of concurrently developing representational substrates for speech production. To date, most studies of CAS have focused on the important task of describing proposed clinical correlates for differential diagnosis from other speech disorder categories. Future work should evaluate competing theoretical frameworks to support an account of the disorder consistent with the persistent deficits observed. Both understanding of the underlying nature of the disorder and careful description of differential diagnostic behavioral correlates are important to developing effective treatment regimens.
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Appendix A. Continuing education questions 1. Children with childhood apraxia of speech (CAS): a. are no different in their consonant errors than children with speech delay or other speech sound disorders. b. are more likely to produce sound substitutions than children with other speech disorders. c. are more likely to produce omissions than children with other speech disorders. d. are more likely to simplify liquids than children with other speech disorders. e. produce more distortion than substitution or omission errors. 2. Which of the following consonant errors is related to syllable-level error patterns? a. consonant harmony. b. omissions. c. substitutions. d. distortions. e. b and c. 3. The results of this study show that children with CAS: a. have more difficulty producing late-developing than early-developing consonants. b. rarely make consonant errors that affect syllable structure. c. frequently simplify clusters and delete final consonants. d. have normal prosodic patterns during phrase production. e. a and c. 4. Over the period of 3 years, consonant and syllable production of children in this study: a. improved consistently over time. b. declined consistently over time. c. showed inconsistent patterns over time. d. remained constant at baseline level. e. was related to lexical retrieval deficits. 5. Results of the study suggest that treatment for consonant deficits in CAS should focus primarily on activities to improve: a. non-speech lip and tongue movement. b. individual consonant articulation. c. correct syllable shapes. d. grammatical forms for phrases and sentences. e. non-speech oral motor coordination.
References Bowman, S. N., Parsons, C. L., & Morris, D. A. (1984). Inconsistency of phonological errors in developmental verbal dyspraxic children as a factor of linguistic task and performance load. Australian Journal of Human Communication Disorders, 12(2), 109–119. Byrd, K., & Cooper, E. B. (1989). Apraxic speech characteristics in stuttering, developmentally apraxic, and normal speaking children. Journal of Fluency Disorders, 14(3), 215–229. Crary, M. A., Landess, S., & Towne, R. (1984). Phonological error patterns in developmental verbal dyspraxia. Journal of Clinical Neuropsychology, 6(2), 157–170.
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