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. Author manuscript; available in PMC: 2023 Jun 3.
Published in final edited form as: Clin Linguist Phon. 2021 Jul 15;36(6):528–546. doi: 10.1080/02699206.2021.1941263

Lexicogrammatical Skills in 2-Year-Old Children with and without Repaired Cleft Palate

Marziye Eshghi 1, Reuben Adatorwovor 2, John S Preisser 3, Elizabeth R Crais 4, David J Zajac 5
PMCID: PMC8760352  NIHMSID: NIHMS1756415  PMID: 34263689

Abstract

The purpose of the current research was to compare the lexical–grammatical skills of two-year old children with and without repaired cleft palate (CP), accounting for the effect of variables such as vocabulary size at 18 months of age, maternal education level, and gender. Participants included 52 children with CP and 25 typically-developing (TD) children. The CDI-WS was employed to measure vocabulary and grammatical skills. Significant differences were observed between the CP and TD groups with respect to the number of words, word forms (irregular nouns and verbs), word endings (overuse of plural (-s) and past tense (-ed) markers), the mean number of morphemes in their three longest utterances (M3L), and sentence complexity. In addition, compared to TD children, significantly smaller proportions of children with CP were observed to use words to talk about past and future events or use words to talk about an absent object. The difference between the CP and TD groups in terms of the size of vocabulary at 24 months of age was explained by significantly smaller size of vocabulary at 18 months of age in the CP group. Among all predictors, the size of vocabulary at 18 months of age was identified as the most robust precursor of lexical and grammatical skills at 24 months of age. Gender was identified as a predictor of the M3L measure as an index for syntactic ability.

Keywords: Vocabulary, morphology, syntax, children, cleft palate

Introduction

Children with repaired cleft palate (CP) have a range of speech and language difficulties, which develop at early stages of development. Compared to infants without CP, infants with unrepaired CP were observed to produce restricted number of stop consonants, fewer multisyllabic constructions (Chapman, 1991), smaller canonical babbling ratios (Chapman, Hardin-Jones, Schulte, & Halter, 2001), smaller size of true consonant inventory (Chapman et al., 2003), and reduced composition of babbling (Lohmander, Lillvik, & Friede, 2004). Early expressive vocabulary of children with CP has been described as smaller in size (Eshghi, Dorry, Vivaldi, Crais, Vallino, Baylis, Preisser, & Zajac, 2017; Estrem & Broen, 1989; Park & Ha, 2016; Willadsen, 2013) and delayed (Scherer & D’Antonio, 1995; Scherer, Williams, & Proctor-Williams, 2008). Recently, Eshghi, Adatorwovor, Preisser, Crais, and Zajac (2019) reported that children with CP demonstrated smaller vocabulary size at 24 months of age and slower rate of vocabulary growth from 18 to 24 months of age compared to children without CP. Additionally, they identified 63% of their participants with CP to be at the 16th percentile for the CDI WS number of words at 18 months of age and 53% of their participants with CP to be below the 16th percentile at 24 months of age. They linked their findings to a number of etiological factors. In their sample, children with CP exhibited significantly lower mean sound weighted raw scores (number and frequency of sounds produced during the 30-minute recording of the CSBS-DP assessment) compared to the TD children. In addition, at least eight of their participants with CP demonstrated inconsistent VP closure for stop consonants at 18 months of age as measured by the nasal ram pressure (NRP) technique (Eshghi et al., 2017), suggesting the possibility of VP inadequacy. Of interest, among several variables they examined as potential determinants of the vocabulary growth, middle ear status significantly predicted the development of vocabulary skills across all children. Their statistical model demonstrated that abnormal middle ear status can result in approximately a 70-word decrease in the size of vocabulary.

Although the literature on the early speech and expressive vocabulary of children with CP is relatively rich, little attention has been directed toward early grammatical skills and lexical-grammatical interference in this subgroup of children. In an early cross-sectional study by Spriestersbach, Darley, and Morris (1958), 3;6 to 8;5 year old children with CP revealed smaller vocabulary size and shorter mean length of utterance (MLU) compared to normative data obtained from Templin (1957). In addition, Young, Purcell, and Ballard (2010) reported that of the 43 preschoolers with nonsyndromic cleft lip and palate (CLP), 14 children (33%) demonstrated a grammar score lower than the 20th percentile on the Singapore English Action Picture Test (SEAPT) normative data which is 23% higher than the prevalence rate in the SEAPT normative sample.

Syntactic complexity was also reported to be less advanced in children with CP (Morris, 1962), although some studies did not note any significant differences between the MLU score (Jocelyn, Penko, & Rode, 1996) and structural complexity (Spriestersbach et al.; 1958) of children with and without CP. In a recent study conducted by Boyce, Kilpatrick, Reilly, Costa, and Morgan (2018), although children with CP exhibited receptive and expressive language skills within normal limits, they showed the lowest subtest score for sentence structure as measured by the Clinical Evaluation of Language Fundamentals, Fourth Edition (CELF-4). Given that the foundation for acquiring syntax is established around the age of two, it is of considerable heuristic value to determine whether children with repaired CP follow similar developmental trajectories compared to TD children during the early stages of language acquisition.

A recent meta-analysis conducted by Lancaster et al. (2020) suggested that children with non-syndromic cleft lip and palate (NSCL/P) had significantly smaller consonant inventories, less accurate articulation, and poorer expressive and receptive language skills than their peers without NSCL/P which can persist up to age 8 years. The lower performance of children with NSCL/P in expressive language performance was more noticeable when using parent reports and observational language measures. These findings provide rationale for the current work and highlights the importance of addressing language delays as early as possible to limit later language and higher-level linguistic skills. The present research is a follow-up to our prior work in which the vocabulary growth from 18 to 24 months of age was observed to occur at slower rate in children with CP compared to their age-matched peers without CP (Eshghi et al., 2019). Because, the “vocabulary spurt” usually occurs between 18 to 24 months of age (Bates & Goodman, 2001; Fenson et al., 1994; Fernald, Pinto, Swingley, Weinberg, & McRoberts, 1998; Goldfield & Reznick, 1990; Kauschke & Hofmeister, 2002), it is plausible to hypothesize that reduced rate of vocabulary growth from18 to 24 months of age may negatively impact the capability of children with CP to make two-word and multi-word combinations and eventually produce syntactically complex constitutes. This hypothesis is based on the findings that lexical development in young children precedes the onset of combinatorial speech and it is assumed to be a prerequisite for the emergence of morphosyntactic and syntactic constitutions (Bartsch, 2006; Bates et al., 1988; Bates & Goodman, 1997; Marchman & Bates, 1994; Marchman & Thal, 2005). In other words, the transition from single-word production to combinatorial speech requires prior maturation of lexical knowledge. Continuity between lexical and grammatical development has been well explained by the critical mass hypothesis according to which abstraction of morphosyntactic patterns cannot occur unless the child’s lexicon reaches the critical mass threshold necessary to trigger grammatical development (Marchman & Bates, 1994; Bates & Goodman, 1997; Bates & Goodman, 2001). Despite the well-supported evidence for the correlation between the size of children’s early vocabulary and their later grammatical proficiency, there is equivocality in the literature with regard to the lexical–grammatical association. For instance, several studies suggest that the lexicon and grammar are two distinct language subsystems that develop autonomously in different cognitive and neural modules, and hence, the development of each language subsystem occurs independently (Pinker, 1991, Pinker & Ullman, 2002; Ullman, 2001; Ullman, Pancheva, Love, Yee, Swinney, & Hickok, 2005). On the basis of these two extreme views (i.e., tight correlation vs. no correlation between lexicon and grammar), more recent studies have provided evidence for five paths of influence that underlie the association between vocabulary and grammar: 1) a reciprocal (bidirectional) relationship between vocabulary and grammar (Dixon & Marchman, 2007; Pérez-Leroux, Castilla-Earls, & Brunner, 2012), 2) the unidirectional effect from vocabulary to grammar (Bates & Goodman, 2001), 3) the unidirectional effect from grammar to vocabulary (Brinchmann, Braeken, & Lyster, 2019), 4) correlated but uncoupled development of vocabulary and grammar (Hoff, Quinn, & Giguere, 2018), and 5) no developmental relationship between vocabulary and grammar (Ullman, 2001; Ullman et al., 2005).

The present study investigated the morphosyntactic ability of children with and without CP as the subsequent level of language development following lexical acquisition. The study pursued three aims 1) to compare the morphosyntactic skills of children with repaired CP and TD children at two-years of age; 2) to investigate the relationship between vocabulary size at 24 months of age and measures of syntactic skills at 24 months of age; and 3) to determine the effect of variables such as early size of vocabulary (at 18 months of age), MEL, and gender on morphosyntactic skills. Since the role of middle ear status in the rate of vocabulary growth from 18 to 24 months of age was determined in our previous study, in the current study, we restricted the predictor factors to the early vocabulary size, MEL, and gender to prevent overfitting by keeping the number of covariates at a reasonable proportion to our sample size. Hearing and middle ear status of the participants, however, are reported for descriptive purposes.

The impetus for controlling the effect of MEL and gender on vocabulary and grammatical development rises from the literature suggesting that both of these variables are important demographic predictors of early language development. For instance, a strong association has been reported between maternal educational levels (MEL) and early language skills such as expressive vocabulary, comprehension, and grammatical skills (Dollaghan, Campbell, Paradise, Feldman, Janosky, Pitcairn, & Kurs-Lasky, 1999; Magnuson, Sexton, Davis-Kean, Huston, 2009; Marjanovic-Umek, Bozin, Cermak, Stiglic, Bajc, & Fekonja-Peklaj, 2016; Marjanovič-Umek, Fekonja, Kranjc, & Bajc, 2008). In addition, various studies suggested that compared to children from families with higher SES, children from lower SES families have smaller vocabulary size (Arriaga, Fenson, Cronan, & Pethick, 1998; Hoff, 2003; Malin, Karberg, Cabrera, Rowe, Cristaforo & Tamis-LeMonda, 2012; Mol & Neuman, 2014), less complex utterances (Arriaga et al., 1998), and delayed onset of word combinations (Arriaga et al., 1998).

Gender also has been shown to be an influential factor in early expressive language development. Research has established that, compared to boys, girls tend to have progressively more rapid vocabulary growth (Bauer, Goldfield & Reznick, 2002; Bornstein, Hahn & Haynes; 2004; Hadley, Rispoli, Fitzgerald, & Bahnsen, 2011; Huttenlocher, Haight, Bryk, Seltzer, & Lyons, 1991) and a larger vocabulary size (Eriksson, Marschik, Tulviste, Almgren, Pérez Pereira, Wehberg, Marjanovič-Umek, Gayraud, Kovacevic, & Gallego, 2012; Marjanovič-Umek et al. 2008; Marjanovič-Umek, Fekonja-Peklaj, & Podlesek, 2012). In addition, girls were observed to outperform boys by producing longer and more grammatically complex utterances (e.g., Bornstein & Haynes, 1998; Eriksson et al., 2012; Fenson et al., 1994; Simonsen, Kristoffersen, Bleses, Wehberg, & Jørgensen, 2014). Contrary to these findings, Marjanovič-Umek et al. (2016) did not find significant differences between boys’ and girls’ vocabulary size at different ages. They reported, however, that while boys’ vocabulary consisted of more masculine-type words, girls tended to use more feminine-type words.

Findings of this study will improve our understanding about early morphosyntactic skills and developmental milestones for the transition from single word productions to sentences in children with CP. Because impaired expressive language has been shown to influence higher level language and literacy attainment in later childhood (Felsenfeld Broen, & McGue, 1994; Lewis, Freebairn, Hansen, Stein, Shriberg, Iyengar, & Taylor, 2006; Scarborough, 1990; Sices, Taylor, Freebairn, Hansen, & Lewis, 2007), if differences are found in the current study, early language intervention may attenuate the development of persistent language delay and later literacy underachievement.

Methods

Participants

The participants of this study consisted of 52 children with repaired CP (27 males, 25 females) and 25 TD children (13 males, 12 females). These children were a subset of participants enrolled in a multi-site longitudinal study designed to determine the age of stop consonant emergence in young children with cleft palate following surgical repair of the palate (Zajac et al., 2021). The larger study enrolled participants at three sites – the University of North Carolina at Chapel Hill, A. I. duPont Hospital for Children in Wilmington, DE, and Nationwide Children’s Hospital in Columbus, OH (see Zajac et al. for a breakdown of participants by gender, race, and site). The current study is a follow-up to our prior work that aimed to investigate rate of vocabulary growth from 18 to 24 months in children with CP (Eshghi et al., 2019). As such, forty of the current children with CP and all TD children were previously studied by Eshghi et al. (2019).

Children with CP ranged in age from 23.3 to 26.9 months (mean= 24.2 months, SD = 0.6). Information about birth and family history, demographics, medical history, surgical history as well as cleft classification were obtained from the primary care giver of the child at the screening visit when the child was initially enrolled in the study. Cleft type and date of palate surgery were verified from medical records. Of 52 children with repaired CP, 48 children were non-Hispanic/Latino and 4 were Hispanic/Latino. In addition, 42 children with CP were Caucasian, 2 were African-American, and 8 belonged to more than one race. None of the children with CP were born prematurely (i.e., gestation less than 36 weeks) or diagnosed with any known syndromes including Pierre Robin syndrome. With regard to the type of the cleft, 21 children had CLP and 31 had clefts of the hard and/or soft palate only. All children with CP had undergone a single surgery to repair the palate. Forty-three children had their palatal surgery by 11 months of age (mean = 9.7 months, range = 7.2 to 10.8 months) while 9 children had their palatal surgery after 11 months of age (mean = 11.8 months, range = 11.2 to 13.2 months). Oral examination was performed at the study visit to rule out the presence of oronasal fistulae. The status of VP function was objectively determined using nasal ram pressure (NRP) (see Eshghi et al., 2017, for details). Of the 52 children with CP, 43 were successfully evaluated using NRP (i.e., they tolerated wearing the pressure probe and produced stops). Of these, approximately 30 children with CP (70%) showed consistent VP closure during production of stop consonants. In addition, all but two children with CP underwent myringotomy with insertion of pressure-equalization (PE) tubes at the time of their palate surgery. Forty-seven children with CP had available audiogram data at 24 months of age, 37 of which (79%) exhibited normal hearing level as reported by the audiologists. Whereas, of 25 TD children, 22 (96%) had normal hearing level. In addition, of 45 children with CP who had available tympanogram data at 24 months of age, at least 6 children demonstrated abnormal middle ear status as indicated by type As (reduced compliance) and type C tympanogram readings. Given the data used in this study was derived from a larger multisite project, see Tables 1 and 2 in Zajac et al. (2021) for detailed demographic and clinical information about the participants.

TD children ranged in age from 23.4 to 25.1 months (mean= 23.9 months, SD = 0.4). All TD children showed normal language development at 12 months of age determined by the Communication and Symbolic Behavior Scales Developmental Profile (CSBS DP; Wetherby & Prizant, 2002) assessment tool. Please see Eshghi et al. (2019) for more information about the TD children.

All children participated in this study were from monolingual American English–speaking families. Further, all children in CP and TD groups were in good general health and had no documented sensorineural hearing loss or global developmental delays. All participants underwent bilateral tympanometry at 24 months of age to evaluate middle-ear function and/or confirm the presence of PE tubes. Tympanograms were obtained by either SLPs and/or certified audiologists at each of the sites. In addition, air-conduction hearing levels at 24 months of age for frequencies of 500, 1000, 2000, and 4000 Hz were obtained by licensed audiologists and the overall report of the hearing status was provided to the investigators. Sound field audiometry assessments were obtained in sound-attenuated booths according to pediatric assessment protocols. This study was approved by the intuitional review board (IRB) of the University of North Carolina at Chapel Hill and other involved sites.

Assessment of Vocabulary and Grammatical Skills

The MacArthur–Bates Communicative Development Inventory: Word and Sentences (CDI-WS) form (Fenson et al., 2007) is a standardized test to measure the development of the expressive language and grammar in toddlers. This parent report tool has been widely used for both clinical and research purposes in TD children as well as children with disorders (Fenson et al., 1994; Jackson-Maldonado et al., 1993; Miller, Sedey, & Miolo, 1995; Scherer & D’Antonio, 1995; Thal, Marchman, Stiles, Aram, Trauner, Nass, & Bates, 1991). Parents completed the CDI-WS at home around their child’s second birthday (mean= 24.08 months, ranged from 23.26 to 26.88 months, SD = 0.54). For most of the participants (i.e., 93%), the primary caregiver who completed the CDI-WS checklist was the mother. For the present study, the first part of the CDI-WS was used to measure the participant’s lexical (i.e., expressive vocabulary) development. This part includes the number of words produced by the child and how the child used the words. The number of words was derived from a checklist of 680 commonly used vocabulary items. The primary caregivers were asked to indicate the words that the child produced spontaneously (maximum score 680). In addition to the number of words, parents were asked to identify whether their child used words to talk about past events or people, future events, absent objects (production), or absent owner. Grammatical development was measured from the second part of the CDI-WS. Different inflectional paradigms including plural (-s), possessive (-’s), progressive (-ing), and past tense marker (-ed), as well as different word forms such as regular/irregular past tense verbs and regular/irregular plural nouns were targeted as an index of morphosyntactic development.

Syntactic knowledge of the participants and sentence complexity was measured through mean number of morphemes used in three longest utterances (M3L). To obtain information about M3L, parents were first asked whether their child already produced word combinations. If so, they were further asked to write down the three longest utterances they heard their child say. The M3L scale was then calculated by counting the number of morphemes used in each sentence and taking the mean. The investigators followed the guidelines stated in the CDI-WS manual to identify morphemes. For Sentence Complexity, CDI-WS has a list of 37 sentence pairs with the second sentence being grammatically more complex than the other sentence with regard to the use of morphosyntactic markers, auxiliary verbs, using prepositions, or embedded clauses serve to increase sentence length and complexity. From the list of 37 sentence pairs, parents were asked to identify whether they heard the child using the syntactically simpler sentence or the syntactically more complex one.

Because this study was part of a larger longitudinal study, CDI WS forms were also available when participants were 18 months of age (except for one boy and one girl with CP). For this set of data, the mean ages of participants in CP and TD groups were 17.9 months (SD= 0.4) and 17.9 months (SD= 0.5), respectively. The number of words produced at 18 months of age was used in this study to examine the association between early vocabulary size and later development of grammatical skills (the second purpose of the study).

Statistical Analyses

For the unadjusted comparisons of the cohort groups (CP, TD), two-sample t-tests were used for the outcome variables having a continuous scale (i.e., the number of words, number of irregular plural nouns and irregular past tense verbs, overuse of (-s) and (-ed) markers, M3L, and sentence complexity) and Fishers exact tests were used for the categorical outcome variables (i.e., how words were used, inflectional word endings, and if the child was observed to combine words). Pearson correlation analyses were used to examine the correlation between the number of words at 24 months of age and grammatical skills (M3L and sentence complexity) at 24 months of age.

Multiple linear regressions were used to compare TD and CP groups in covariate-adjusted models. These covariates include number of words at 18 months of age, MEL, and gender. Except for the number of words at 18 months of age which was a continuous variable, the other variables were dichotomous. MEL was categorized in two levels of holding education below Bachelor’s degree vs. Bachelor’s degree and above. The variable gender had two levels: male vs. female. P-values were compared against the 0.05 significance level a priori. SAS version 9.4 (TS1M1, SAS institute, Cary, NC) was used in all analyses.

Results

Lexical and Grammatical Skills

On average children with CP and TD produced 40.23 (SD=35.30) and 60.80 (SD=48.73) words at 18 months of age. In addition, while 48% of children with CP in the sample had mothers with high education, 92% of TD children had mothers with high education. Further, 52% of children were male (52% of children with CP and 52% of TD children). In subgroups defined according to MEL or gender, the median values for two main lexicogrammatical measures (the number of words and the M3L scale in Tables 1 and 2, respectively) were generally higher for TD than for CP children. Moreover, the lower quartile is always smaller in the CP group indicating consistently larger numbers of CP children than TD children with scores on the lower (worse) end of the scale.

Table 1:

The distribution of data for the number of words at 24 months of age based on the MEL and gender in the CP and TD groups.

Group N Lower Quartile Median Upper Quartile Mean (SD)
MEL *
Low CP 27 57 114 323 174 (162)
TD 2 NR NR NR NR
High CP 25 117 237 284 215 (122)
TD 23 178 352 421 322 (157)
Gender
Male CP 27 37 84 263 157 (150)
TD 13 232 359 475 343 (180)
Female CP 25 145 231 346 233 (130)
TD 12 167 317 390 310 (155)
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*

MEL was categorized in two levels of holding education below Bachelor’s degree vs. Bachelor’s degree and above; NR= Not Reported to preserve non-identifiability.

Table 2:

The distribution of data for the M3L scale at 24 months of age based on the MEL and gender in the CP and TD groups.

Group N Lower Quartile Median Upper Quartile Mean (SD)
MEL *
Low CP 27 1.6 2.6 3.3 2.6 (1.4)
TD 2 NR NR NR NR
High CP 25 2.6 3.6 4.3 3.4 (1.6)
TD 23 3.0 3.6 4.3 3.8 (1.6)
Gender
Male CP 27 1.0 2.3 3.6 2.6 (1.5)
TD 13 3.0 3.6 4.0 3.6 (1.4)
Female CP 25 2.7 3.3 4.0 3.4 (1.4)
TD 12 3.1 3.7 4.9 4.2 (1.7)
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*

MEL was categorized in two levels of holding education bel1ow Bachelor’s degree vs. Bachelor’s degree and above; NR= Not Reported to preserve non-identifiability.

As seen in Table 3, TD children were observed to statistically significantly outperform children with CP with respect to lexical and grammatical skills by producing, on average, a greater number of words, word forms, word endings (i.e., over use of plural (-s) and past tense (-ed) markers), making longer sentences, and sentence complexity (moderate to large effect sizes). Moreover, the 25th, 50th and 75th percentiles, respectively, for these CDI measures were higher in the TD than CP group, except for word endings where the lower quartile and median was 0 in both groups.

Table 3:

Summary statistics for lexical and grammatical development for children with CP and TD children at 24 months of age.

Lexical & Grammatical Scales Percentiles (Q1, Median, Q3) Mean (SD)
CP TD CP TD t(75) p Cohen’s d
Number of words 60, 191, 292 178, 352, 421 194 (144) 328 (166) −3.64 .001 0.89
Word forms 0, 1.5, 3.0 2.0, 3.0, 7.0 2.6 (3.7) 5.5 (5.2) −2.84 .006 0.69
Word endings 0, 0, 0 0, 0, 2.0 0.8 (2.2) 2.1 (3.4) −2.08 .041 0.51
M3L 1.9, 3.0, 3.7 3.0, 3.7, 4.3 3.0 (1.5) 3.9 (1.6) −2.35 .022 0.57
Sentence complexity 0, 3.0, 8.0 0, 5.0, 11.0 5.1 (5.8) 8.9 (10.2) −2.08 .041 0.51
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Note. Summary Statistics are shown for 52 children with cleft palate (CP) and 25 typically developing (TD) children. Word forms refer to irregular plural nouns, irregular past tense verbs. Word endings refer to overuse of (-s) and (-ed) markers. Q1, median and Q3 refer to the 25th, 50th and 75th percentiles, respectively. The sixth and seventh columns contain the pooled two-sample t-test and its p-value, respectively. Finally, the absolute value of Cohen’s d is reported (i.e. negative sign is dropped).

The proportions of children who used words to talk about past and future events, absent object (production), absent object (comprehension), and absent owner are presented in Table 4. Overall, compared to children with CP, a statistically significantly higher proportion of TD children used words to talk about past events, future events, and absent objects (production).

Table 4:

Percentage of children in CP and TD groups who used words to refer to past events, future events, absent objects (production), absent objects (comprehension), and absent owners at 24 months of age.

How words were used CP TD p
Using words to talk about past events 57.7 88.0 .007
Using words to talk about future events 57.7 88.0 .007
Using words to talk about absent objects (production) 82.7 100.0 .016
Using words to talk about absent objects (comprehension) 96.2 100.0 .77
Using words to talk about absent owners 86.5 100.0 .061
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Note: Percentages of children using words in the indicated way are shown for 52 children with cleft palate (CP) and 25 typically developing (TD) children. p is p-value from Fisher’s exact test with mid p-value adjustment.

Table 5 presents the proportion of children who used inflectional word endings and demonstrated the ability to combine words. Visual inspection of the proportions suggested that children with CP may have fallen behind the TD children with regard to the use of inflectional paradigms including plural (-s), possessive (-’s), progressive (-ing), and past tense (-ed) markers. Despite the observed trends, Fisher’s exact tests failed to show any statistically significant differences between the two groups in individual scales of inflectional word endings.

Table 5:

Percentage of children in CP and TD groups who produced inflectional word endings and the ability of children to combine words at 24 months of age.

Inflectional word endings CP TD p
Plural (-s) 62.8 75.0 .37
Possessive (-’s) 51.0 75.0 .063
Progressive (-ing) 37.3 58.3 .11
Past tense (-ed) 17.6 37.5 .062
The ability to combine words 80.8 96.0 .062
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Note. Percentages of children using word endings in the indicated way are shown for 52 children with cleft palate (CP) and 25 typically developing (TD) children. p is p-value from Fisher’s exact test with mid p-value adjustment.

Association between Lexical and Grammatical Development

Pearson correlation analyses revealed statistically significant positive associations between the size of vocabulary at 24 months of age and syntactic scales of M3L and sentence complexity in both groups. The observed correlation between the number of words and the M3L scale were 0.58 and 0.51 for CP and TD groups, respectively. The correlation between the number of words and the scale of sentence complexity were 0.58 and 0.67 for children with CP and TD children, respectively.

Predictors of Lexical-grammatical Development

The observed significant differences between the CP and TD children remained statistically significant for the mean number of words at 24 months (but not for the M3L measure), after adjusting the model for the number of words at 18 months of age, MEL, and gender (Table 6). Among the three covariates, only the vocabulary size at 18 months of age was a statistically significant predictor for the number of words at 24 months of age. However, both gender and the number of words at 18 months of age significantly predict the M3L at 24 months of age. It should be noted that in identifying predictors of lexical-grammatical development, we restricted our dependent variables to the number of words at 24 months and M3L which are the main indices of lexical and syntactic abilities respectively.

Table 6:

Multiple linear regression estimates (95% confidence intervals) for lexical and grammatical development for children with CP and TD children at 24 months of age.

Mean # words at 24 months M3L
Estimate SE 95% CI p Estimate SE 95% CI p
Intercept 286.1 44.1 [198.0, 374.2] <.001 2.88 0.49 [1.9, 3.9] <.001
CP −83.4 35.2 [−153.6, −13.1] .021 −0.35 0.39 [−1.13, 0.43] .37
Female 19.3 30.1 [−40.8, 79.3] .52 0.78 0.33 [0.11, 1.45] .023
MEL 9.3 34.6 [−59.7, 78.3] .79 0.54 0.38 [−0.22, 1.31] .17
# Words at 18 months 2.1 0.38 [1.4, 2.9] <.001 0.010 0.004 [.002, .019] .016
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Note. N=73 children (four CP children had missing # words at 18 months). CP is an indicator variable for cleft palate with typically developing children as the reference; maternal education level (MEL) is an indicator variable for mother having at least a bachelor’s degree; # words at 18 months is centered at its mean of 49.7. R-squared was 0.43 for Mean # words at 24 months and 0.22 for M3L.

Discussion

In this study we investigated the lexical and grammatical skills of two-year old children with and without repaired CP to 1) compare these groups in terms of parent-reported ability of morphosyntactic skills; 2) investigate the relationship between the size of vocabulary and measures of syntactic skills at 24 months of age; and 3) determine the effect of variables such as size of vocabulary at 18 months of age, MEL, and gender on vocabulary and grammar development at 24 months of age. Lexical and syntactic measures of the CDI-WS form were used to index lexicogrammatical abilities of children in the CP and TD groups at 24 months of age.

Children with CP were reported to produce smaller number of words, fewer word forms (irregular plural nouns and past tense verbs), fewer number of word endings, shorter utterances (lower M3L scale), and syntactically less complex sentences compared to the TD children. In addition, a smaller proportion of children with CP used words to refer to past and future events, and absent objects (production). These findings are in agreement with previous studies that reported poorer expressive vocabulary skills (Broen et al. 1998; Eshghi et al., 2019; Estrem & Broen, 1989; Park & Ha, 2016; Willadsen, 2013; Scherer and D’Antonio, 1995; Scherer et al., 2008), shorter MLU (Spriestersbach et al., 1958), and less syntactically complex utterances (Morris, 1962) in children with CP compared to non-cleft healthy controls. When our data were compared to CDI normative data obtained from English-speaking children in CDI Wordbank (an open database of children’s vocabulary development, data retrieved in April 2021), children in the TD group have a similar distribution for number of words at 24 months of age (Table 3) as the CDI normative group based on quartiles, which are 178, 352 and 421 words for the lower quartile, median and upper quartile, respectively, in the normative group. On the other hand, children in the CP group had scores much fewer number of words than the CDI normative group judging by percentiles.

The size of vocabulary at 24 months of age was correlated with syntactic measures of M3L and sentence complexity in both groups. These findings are consistent with previous studies in which vocabulary development demonstrated moderate correlations with various syntactic abilities (e.g., Marjanovič-Umek et al. 2013; Stolt et al. 2009). For instance, using the Slovenian adaptation of the CDI, Marjanovič-Umek et al. (2013) reported the correlation coefficient of 0.66 for the association between vocabulary and MLU and the correlation coefficient if 0.69 for the association between vocabulary and sentence complexity. In children with CP, slower rate of vocabulary growth, restricted size of vocabulary, and lack of lexical diversity may set the basis for poor development of grammatical skills. More specifically, children with CP were reported to have slower rate of vocabulary growth from 18 to 24 months of age (Eshghi et al., 2019) which is the time window when the vocabulary spurt is expected to occur (Bates & Goodman, 2001; Fenson et al., 1994; Fernald, et al., 1988; Goldfield & Reznick, 1990; Kauschke & Hofmeister, 2002). Because vocabulary spurt coincides with the emergence of two-word combinations and syntactic development (Frankenburg & Dodds, 1967; Nelson, 1973; Stoel-Gammon, 1998), less advance grammatical skills in children with CP can be explained by the slower rate of vocabulary growth in this population.

When the statistical model was adjusted to examine the effect of the covariates of interest, results indicated that TD and CP children with the same vocabulary size at 18 months of age still demonstrate statistically significant differences in the number of words at 24 months of age. However, there is no statistically significant between-group difference in the M3L measure of TD children and children with CP with the same vocabulary size at 18 months of age. Because of the limited sample size, this cannot be interpreted as there being no differences between the two groups in the syntactic measure of M3L, as we lacked sufficient power to detect small differences. The adjusted estimate, suggesting lower adjusted vocabulary in CP than TD children would be consistent with Eshghi et al. (2019) who reported that children with CP demonstrated smaller vocabulary size at 24 months of age and slower rate of vocabulary growth from 18 to 24 months of age compared to children without CP. Given the statistically significant unadjusted differences in vocabulary sizes at 24 months, the combination of the unadjusted and adjusted results suggests the importance of early intervention as children with CP who “catch-up” to TD children by 18 months of age in their vocabulary will likely have better lexical and grammatical skills at 24 months as vocabulary at 18 months in our analysis strongly predicted the size of vocabulary and M3L at 24 months.

Our data suggested that while gender is a predictor for the development of syntactic skills (M3L measure) at 24 months of age, it doesn’t seem to predict later lexical abilities (the number of words). On average, girls were observed to outperformed boys in the M3L measure for approximately 1 morpheme. More advanced syntactic skills in girls than boys were previously reported by numerous studies (e.g., Kovačević, Kraljević, & Cepanec, 2006).; Tse, Chan, Li, & Kwong, 2002; Umek, Fekonja, Kranjc, & Bajc, 2008).

Our null findings for the effect of gender on lexical development are consistent with prior studies conducted by Eriksson and Berglund (1999) and Marjanovič-Umek et al. (2016) in which no gender differences were observed in children’s productive vocabulary or the size of vocabulary. Our results also suggested that, MEL may not predict the trajectories of lexical and grammatical development at two years of age.

Several factors are assumed to contribute to delayed vocabulary development (Eshghi et al. 2019; Scherer & D’Antonio, 1995; Scherer et al., 2008) or smaller size of vocabulary (Eshghi, Dorry, et al., 2017; Estrem & Broen, 1989; Hardin-Jones & Chapman, 2014; Park & Ha, 2016; Willadsen, 2013) in children with CP. First and foremost, compared to infants without CP, infants with unrepaired CP have a smaller number of stop consonants and fewer multisyllabic constructions (Chapman, 1991), and smaller canonical babbling ratios (Chapman et al., 2001). More specifically, while 93% of infants without CP reached the canonical babbling stage by 9 months of age, only 57% of infants with unrepaired CP reached that stage by 9 months of age (Chapman et al., 2001). Because of the well-established continuity between phonological and lexical development in TD children (Oller, Wieman, Doyle, & Ross, 1976; Stoel-Gammon, 1985; Stoel-Gammon & Cooper, 1984; Vihman, et al., 1985) and children with CP (e.g., Chapman, et al., 2003; Eshghi et al., 2019), it is plausible to attribute less advanced lexical development (and subsequently grammatical skills) to poorer phonological skills at earlier stages of language acquisition.

Second, because children with CP are susceptible to develop fluctuating conductive hearing loss, it is logical to assume that early changes in auditory processing of speech can have detrimental effect on speech and language development. A closer look at the hearing level and the middle ear status of children in the CP group revealed that of 47 children with CP who had available audiogram data at 24 months of age, at least 10 children exhibited abnormal hearing level. In addition, of 45 children with CP who had available tympanogram data at 24 months of age, at least 6 children demonstrated abnormal middle ear status (i.e., type As and type C tympanogram readings). Therefore, it is likely that differences between the CP and TD children with regard to auditory experience, may have caused some of the later differences we observed between the two groups relevant to the lexical and grammatical skills (e.g., see Eshghi et al., (2019) for significant effect of middle ear status on the trajectory of vocabulary growth from 18 to 24 months of age).

Finally, less advanced development of vocabulary and grammar in children with CP may be also explained by the status of VP function. Of 42 children with CP who had available NRP data, 12 (about 29%) failed to achieve consistent VP closure (i.e., defined by Eshghi et al., 2017, as VP closure on at least 85% of stops) by 24 months of age. Because of the link between early phonological development and later vocabulary skills (see Stoel-Gammon, 2011, for review), it is possible that children with inconsistent VP closure lagged behind their peers with consistent VP closure in terms of early phonological development and subsequent lexical and grammatical skills. In support of this hypothesis, Broen, Devers, Doyle, Prouty, and Moller (1998) reported that VP status significantly contributed to a slower rate of word acquisition in young children with repaired cleft palate. It must be noted, however, that NRP does not provide information on the size of the VP gap. Therefore, more research is warranted to examine the effect of physiological factors (i.e., VP gap size) on the development of speech and language skills in children with CP.

Clinical Implications

The premise that grammatical development depends upon lexical maturity highlights the importance of comprehensive assessment of early language development. Findings of this research can be translated into clinical practice by emphasizing the use of criterion-referenced approaches to target language growth in general and trajectories of expressive language and grammatical skills in particular. This study supports the applicability of the CDI-WS as an assessment tool that targets both vocabulary and grammar skills in children as young as two-years of age.

Various studies have emphasized the correlation between delayed onset of expressive language and later language and academic difficulties (Felsenfeld et al., 1994; Lewis et al., 2006; Scarborough, 1990; Sices et al., 2007). Although some children with delayed onset of expressive vocabulary ultimately show spontaneous progress in vocabulary skills at a later stage of language acquisition (e.g., Dale, Price, Bishop, &Plomin, 2003; Whitehurst & Fischel, 1994), others may continue to show poor higher-level linguistic abilities (Bates, Dale, & Thal, 1995; Fernald & Marchman, 2012). Research has documented that young children with CP who show persistent slower trajectories of language growth may fail to achieve literacy and higher-level linguistic milestones at later ages (e.g., Collett, Stott-Miller, Kapp-Simon, Cunningham, & Speltz, 2010; Conrad, 2019; Richman, et al., 1988) or be at risk of developing weaker academic skills compared to children without CP (e.g., Bell, et al., 2017; Broder, Richman, & Matheson, 1998; Gallagher & Collett, 2019; Van Eeden & Stringer, 2020). Given that early speech and language interventions can improve children’s expressive language (Blakeley & Brockman, 1995; Scherer & Brothers, 2002), identifying subgroups of children with CP at risk for expressive language delay and applying a target-based speech intervention are of paramount importance. Depending on the State the child is receiving healthcare services, early intervention may be available for children prior to 18 months. For example, the state of North Carolina provides such intervention services to children with CP. In addition, different techniques such as parent-implemented interventions (Scherer, D’Antonio, & McGahey, 2008), reading-aloud to children (Duursma, Augustyn, & Zuckerman, 2008), and mother-child interactive shared reading (Westerlund & Lagerberg, 2008) have been suggested by speech-language pathologists to improve and facilitate the child’s expressive language abilities. The parent-implemented interventions, for example, can be used for children with CP as early as 18 months of age. In this technique, mothers are encouraged to use and reinforce words consisting of stop consonants in their communication with their child which in turn enhances the size of the consonant inventory and subsequently vocabulary skills (Scherer & Brothers, 2002). In addition, providing training in language stimulating activities may benefit some children with repaired CP. As reported by Scherer, et al., (2008), mothers who received specific training in modeling and expansion of target words increased the total and different number of words they used with their child. Given the relative ease of parent training procedures (e.g., video demonstrations, role-playing, and coaching from the clinician), such interventions may hold promise to facilitate vocabulary growth in some children with CP.

Limitations of the Study

It should be noted that the present study investigated lexical and grammatical skills at 24 months of age when the grammatical skills of children are still at an early stage of development. Future research is required to study the morphosyntactic skills of children with CP at later stages of language development when significant group differences may emerge for various aspects of morphology and syntax. Another shortcoming of the study pertains to the limited scope of the CDI-WS instrument to capture a true picture of the child’s syntactic ability. True syntactic competence is reflected not only through making simple and complex sentences but also through making new combinations of words to generate novel sentences. Although, the CDI-WS captures, to some extent, the ability of a child to make longer or syntactically more complex sentences, it fails to reflect mastery of expressive syntax. Additionally, because we derived lexical and grammatical measures from the same assessment battery, it is likely that the measures were correlated with each other to some degree. Finally, the small overall sample size meant our statistical analysis was underpowered to detect small effects. Also, the imbalance in maternal education levels likely impacted the unadjusted comparison of CP and TD children, whereas multivariable linear regression was used to address this issue.

Conclusion

The current study suggests that two-year-old children with repaired CP are behind their age-matched TD peers in lexical and grammatical skills. Size of vocabulary at 18 months of age was identified as a robust predictor of lexical and grammatical development at 24 months of age. This study highlights the importance of language management as early as 18 months of age by providing empirical evidence in support of the argument that vocabulary proficiency lays the basis for syntactic skills.

Acknowledgements

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The authors would like to acknowledge the contributions of Amelia Drake, Kristen Lynch, Marina Pastore Rampazzo, Daniela Vivaldi, Maureen Feldbaum, Jacqueline Dorry, Linda Vallino, Katie McGraft, Adriane Baylis, and Katie Garcia in various aspects of data collection and/or analysis.

Declaration of Interest Statement

Research reported in this publication was supported by the National Institute of Dental & Craniofacial Research of the National Institutes of Health under Award Number R01DE022566 to Dr. David Zajac. Other than this, the authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Footnotes

Part of this study was presented at the 75th Annual Meeting of American Cleft Palate Association (ACPA) in Pittsburgh, PA.

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