Vocabulary profiles of children with specific language

Vocabulary pro les of children with speci c language impairment Rachel F Hick, Kate L Joseph, Gina Conti-Ramsden and Ludovica Serratrice School of Education, University of Manchester, Manchester, UK and Brian Faragher University of Manchester Institute of Science and Technology, Manchester, UK

Abstract This study investigates vocabulary development over one year for three young children with speci c language impairment (SLI). Rate of vocabulary development and use of nouns and verbs relative to total vocabulary is compared with a larger sample of younger, typically developing children. Communicative Development Inventory (CDI) data were collected and results provided a typically developing trajectory against which the children with SLI could be compared. The two groups show similar growth curves at these early stages. Findings are discussed with reference to previous work on vocabulary development and methodological differences between parental report and naturalistic data collection.

Introduction Children with Speci c Language Impairment (SLI) demonstrate signi cant language dif culties in absence of other factors that often accompany language problems, for example hearing impairment, neurological damage, autistic tendencies, low non-verbal IQ, oral structure or motor abnormalities. Children are usually initially identi ed by a delay in the onset of rst words and multi-word combinations that is not explained by any of the aforementioned Address for correspondence: Gina Conti-Ramsden, Human Communication and Deafness, School of Education, University of Manchester, Oxford Road, Manchester, M13 9PL. E-mail: [email protected] # Arnold 2002

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factors. They are likely to continue to have persistent dif culties with language throughout development, showing later problems with syntactic structure and grammatical morphology. Therefore, as the child ages, the evidence for SLI, as opposed to a more transient language delay, becomes stronger. Previous studies of vocabulary development in children with SLI have examined both general delays of vocabulary overall, such as the onset of rst words (Trauner et al., 1995) and speci c delays within different word classes, such as particular dif culty with acquiring verbs (Fletcher and Peters, 1984; Rice et al., 1994). Although children with SLI start producing language at a later stage than typically developing children, there is a substantial amount of variation in the age at which they produce their rst words. A recent review by Leonard (1998) re ects the heterogeneity present in SLI. This corresponds to the wide range of individual differences also found in vocabulary development in the normal population (Fenson et al., 1994). There are some dif culties inherent in the study of early vocabulary development in SLI, owing to problems in identifying such children at an early age. Some studies, such as that by Trauner et al. (1995) have addressed this issue by using retrospective reports from parents of children identi ed with SLI at a later age. However, these do not give a true indication of the early language development of the child. The alternative, and the approach taken in this study, is to nd young children with signi cant language dif culties who appear to be at a ‘high risk’ of having SLI, i.e. they have expressive and receptive language dif culties, show no evidence of explanatory factors for their language dif culties, as discussed above, are not of low socioeconomic status, and may also have some history of language dif culties within the family. Using such a combination of exclusionary and inclusionary criteria, it is reasonable to assume that at least at this stage of development, children tting this pro le are demonstrating a speci c language disorder, hence can be described as having SLI, if only for research purposes. Given that children with SLI are late in acquiring their rst words, it is interesting to examine whether the early forms used by these children differ from those of children following a more typical developmental trajectory. There is evidence that the distributions of lexical types is similar for children with SLI and typically developing children. Leonard et al. (1982) found that general nominals accounted for just over half of all lexical types whereas words referring to actions and properties constituted approximately one-tenth of forms for both children with and without SLI. Despite reports of similar lexical distributions in children with SLI and typically developing children early on, evidence suggests that differences emerge between the groups at the onset of multi-word speech. In particular, Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015

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children with SLI show persistent dif culties in verb use, in comparison to their use of other lexical items. Children with SLI have been found to produce fewer verb types than typically developing children (Fletcher and Peters, 1984). In a study comparing children with their typically developing younger siblings, matched on Mean Length of Utterance (MLU), Conti-Ramsden and Jones (1997) found that the children with SLI used verbs less frequently and nouns more frequently than their siblings. In a detailed examination of verb types used by children with SLI, Watkins et al. (1993) reported a tendency for children with SLI to rely on a handful of high frequency verb types, which overlapped with the high frequency types used by typically developing children. Differences between children with SLI and their typically developing peers have also been noted in the use of the noun- and verb-related morphology. For example, it has been reported that children with SLI show a particularly protracted development of verbal tense markers (Rice et al., 1995). This result is supported by the nding that children with SLI used more unin ected verb forms than their MLU-matched younger siblings in contexts that required the use of an in ected verb form. For example, the children with SLI were more likely than their siblings to say ‘man live here’ than ‘man lives here’, or ‘I play that yesterday’ rather than ‘I played that yesterday’ (ContiRamsden and Jones, 1997). Much of the available evidence for differences between the use of nouns and verbs in children with SLI and typically developing children has come from analyses of naturalistic data. There are advantages and disadvantages to this method of data collection. On the one hand, there are no constraints on the situation and the child is free to produce any word that s=he might know at any time. In addition, there are no task demands (such as those that exist in controlled experiments) so children in naturalistic settings may feel more at ease and may talk more readily. On the other hand, in most research studies, naturalistic interaction is usually con ned to one speci c situation: mothers and children playing. Therefore the information pertaining to vocabulary development is restricted to a speci c dyadic context in which a limited set of words is used. More importantly, this method is not ideal for use with very early language-learners, who may be less talkative and produce less informative, useful speech samples. It is for this reason that it is bene cial to supplement data from naturalistic studies with converging evidence from parental report measures. A number of studies have used parental report measures to investigate vocabulary development in detail, with respect to individual differences between children and the acquisition of various lexical categories. The MacArthur Communicative Development Inventory (CDI) has proved a Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015

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useful tool for tracking vocabulary development in both typical and atypical populations (Fenson et al., 1994). It has been used to measure speci c aspects of vocabulary development, such as rate of development of individual vocabulary items (Fenson et al., 1994) as well as noun and predicate development relative to total vocabulary (Bates et al., 1994). The CDI (Fenson et al., 1993) consists of a checklist of words divided into semantic categories, created on the basis of data on the frequency of usage of different words by children. On the toddler version (designed for typically developing children between 16 and 30 months), parents are asked to mark the words that the child both understands and says, whereas the infant version (for typically developing children aged 9 to 16 months) asks also for words that the child understands but does not yet produce. The current study is only concerned with the words that children are reported to produce. There are advantages associated with using parental report measures such as the CDI. First, it is possible to obtain good estimates of normative vocabulary development as the measure can be administered to a large sample. Second, there is evidence that CDI scores correlate with other measures of language learning, such as laboratory tests of comprehension (Dale et al., 1989). Third, parents have access to a larger data set of child language (and therefore a wider range of vocabulary) than do researchers who sample speech at weekly or fortnightly intervals. Finally Williams et al. (2001) investigated potential differences between parental report on the CDI for children from higher and lower SES backgrounds and found the measure to be reliable for both groups. However, there has also been some criticism of the parental report method of data collection. For example, Tomasello and Mervis (1994) argued that the CDI lacks face validity and may encourage parents to overestimate their child’s knowledge of vocabulary. Proponents of the CDI have defended the tool with regard to this, arguing that although parents may overestimate their child’s knowledge of vocabulary, their reports still re ect the relative pattern of the child’s strengths and weaknesses (Dale, 1991; Weitzner-Lin, 1996). With particular reference to the use of parental report measures with populations with language impairment, Boynton Hauerwas and Addison Stone (2000) argued that parents’ estimations of their children’s language abilities may play a role in both identifying children in need of special educational services and facilitating language stimulation and intervention techniques in the home. That is, if parents are able to monitor their children’s progress with a reasonable degree of accuracy, they can become more involved in the therapy process by sharing their observations with professionals in schools and language units (Dale, 1996). The reliability and validity of the MacArthur CDI have been investigated in relation to its use with groups with Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015


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language impairments. Parental report measures were found to correlate with the language skills demonstrated by children with SLI in both language samples and standardized language tests (Fenson et al., 1994; Thal et al., 1999). In addition, there is agreement between CDI scores and estimations of children’s language level made by speech and language pathologists (Hadley and Rice, 1993). Thus, as Boynton Hauerwas and Addison Stone (2000) point out, the bene ts and shortcomings of the CDI are similar for its application to both children with language impairment and those with more typical development. That is, despite the fact that parents may overestimate their children’s language skills, CDI scores still appear to correlate well with other measures of language, such as standardized tests. Having said this, there is little research in the UK involving children with SLI and the use of the CDI. Consequently, the present study was designed to ll this gap and aimed to: 1. Track the vocabulary development of three children with SLI over time. 2. Investigate separately the development of nouns and verbs. 3. Compare the developmental trajectories for a large control group of typically developing children with the three children with SLI. There have been a number of adaptations of the MacArthur CDI developed speci cally for use with English-speaking children in the UK. These include the Oxford CDI (Hamilton et al., 2000) and the Newcastle CDI (Klee and Harrison, 2001). It is essential to note that differences have been found between the CDI scores obtained by British and American children, with British infants from both the Oxford and Newcastle areas demonstrating lower scores for both comprehension and production than American infants of the same age. Therefore in order to provide a fair comparison, it is necessary to compare British children with SLI with their British typically developing counterparts, rather than norms obtained from American children. For this reason the current study uses normative data from the Oxford CDI.

Method Participants CDI data were analysed for three children with SLI. Two boys (Nathan and Dan) and one girl (Grace) participated in the study (names used are pseudonyms). The CDI information was collected longitudinally over a period of 12 months (Nathan), 14 months (Grace) and 15 months (Dan). At the beginning of data collection Nathan was aged 34 months, Grace 39 months Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015

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and Dan 30 months and by the end the three children were aged 46, 53 and 45 months respectively. The children were recruited from speech and language therapists in the North West of England and were all receiving therapy for the duration of the study. They were enrolled on the basis of both receptive and expressive language delay, in the absence of hearing impairment or known neurological damage. All children showed normal social interaction behaviours as measured by the Autistic Screening Questionnaire (Berument et al., 1999) and they all scored above 90 on the Leiter International Performance Scale (Leiter, 1969). Receptive language level was also measured using the Reynell Developmental Language Scales (Edwards et al., 1997) and all children received percentile scores of below 16, indicating a severe receptive delay. All three children and their families were monolingual speakers of English and there was some family history of speech and=or language impairment in all cases. All three lived in pleasant residential areas, and had plenty of toys and stimulation at home. Together with the education and occupation information for the parents, this suggests that the children did not come from deprived or low SES backgrounds (see Table 1 for background and also socio-economic characteristics). As the standard exclusionary criteria for SLI were met by all three children, and they were showing both expressive and receptive problems, it was felt that at this stage these children were at a ‘high risk’ for showing persistent language dif culties. Additionally, in order to gain further information on the language characteristics of the three children, various psycholinguistic tasks were administered throughout the duration of the project. Certain tasks, for example the Clinical Evaluation of Language Fundamentals (CELF-Preschool, Wiig et al., 1992) had to be administered later in the study as they placed higher linguistic demands on the children. These tasks were not administered to the typically developing group, as all psychometrics used were standardized and the rationale behind inclusion of the tests was to look for dif culties within the group considered to have SLI, in areas other than parental report of expressive vocabulary. The British Picture Vocabulary Scale (BPVS) (Dunn et al., 1997) was used to measure receptive vocabulary. This involves the child selecting the correct pictorial representation of a spoken item out of four options. The Expressive Vocabulary Test (EVT) (Williams, 1997) was included as it provided another measure of expressive vocabulary to corroborate the parental report measure. The CELF-Preschool was conducted. This consists of six sub-tests that target different aspects of both receptive and expressive language, such as grammatical awareness and ability to repeat strings of words. Table 2 presents the test scores for the children with SLI. Although the results of these tests will not be Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015

2 GCSE=O Level Homemaker GCSE=O Level Supervisor Older sister (7 years) No Older sister undergoing speech and language therapy

0 GCSE=O Level Beautician GCSE=O Level Policeman Older brother (6 years) No Older brother had speech therapy for a stammer early in development but has fully recovered Yes Yes

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62

Mother report of good hearing

F 8.2.2000 39 53

M 18.10.99 30 45

Sex Date of enrolment Age at enrolment (months) Age at end of study (months) No. of words at enrolment (MacArthur CDI) ASQ score Mother’s education Mother’s occupation Father’s education Father’s occupation Siblings (age) Birth complications Family history of language problems

Grace

Dan

Child name

Table 1 Background information for the three children with SLI

Yes

5 GCSE=O Level Homemaker GCSE=O Level Supervisor Older sister (6 years) No Older male cousin underwent speech and language therapy

76

M 17.11.99 34 46

Nathan


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Dan

IQ ˆ 129 10 9 58 47 53 75 75 50 70 16 75 25 34

Centile score (unless speci ed) 4;0 3;4 3;11 3;6 3;8 4;3 4;3 4;3 4;3 4;3 4;3 4;3 4;3 4;3

Age of child

*NA denoted that child was not administered this test at the time of the project.

3;6 2;6 3;5 3;1 3;3 3;9 3;9 3;9 3;9 3;9 3;9 3;9 3;9 3;9

Age of child

Test results for the three children with SLI

Leiter Reynell comprehension Reynell expression BPVS EVT CELF Linguistic concepts (CELF) Basic concepts (CELF) Sentence structure (CELF) Receptive language (CELF) Recalling sentences (CELF) Formulating labels (CELF) Word structure (CELF) Expressive language (CELF)

Test

Table 2

Grace

IQ ˆ 113 1 1 4 21 4 1 37 16 10 1 16 1 2

Centile score (unless speci ed) 3;10 2;10 NA* 3;4 3;4 3;4 3;4 3;4 3;4 3;4 3;4 3;4 3;4 3;4

Age of child

IQ ˆ 117 1 NA* 55 68 47 63 63 95 82 16 37 5 16

Centile score (unless speci ed)

Nathan

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analysed as this project focuses on the parental report data, they serve to outline general cognitive and linguistic pro les of the three children. That is, the results of the tests and tasks indicate that the three children appear to have signi cant language problems beyond their delays in vocabulary development. Data for the typically developing children were taken from the Oxford Babylab database produced at Oxford University as part of an ongoing investigation into vocabulary development. CDI data have been collected from children between the ages of 9 and 27 months by the Oxford researchers (see Hamilton et al., 2000, for further details). For the purpose of our comparisons, we used data from 260 children aged 15–27 months as before 15 months the typically developing children hardly used any verbs. Table 3 shows the spread of children across each monthly age range. All the children included in the database were exposed to English only and none had any major medical problems. Procedure and materials Mothers of the three children with SLI completed the CDI approximately every month for 12 months. This CDI was based on the version of the MacArthur CDI by Fenson et al. (1994) (at the beginning of data collection, the Oxford version was not available) and was identical with the exception of a few American terms (e.g., jello, pretzel) that had been either excluded or changed to an English form. Mothers were asked to read through the list and tick any of the words that their child said. The same copy of the CDI was used each month so that a cumulative record of vocabulary development could be Table 3 Number of typically developing children at each monthly age range

Age (months) 15 16 17 18 19 20 21 22 23 24 25 26 27

Number of children (total ˆ 260) 57 11 48 46 1 7 11 16 31 25 4 2 1


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gained for each child. These three longitudinal records were then compared with the large (cross-sectional) data set provided by the Oxford researchers. Although these two data collection methods differ, to our knowledge there are no large longitudinal data sets collected for typically developing children. Thus it was felt that a cross-sectional data set of a relatively large number of children at different ages would provide reliable information on the general trend of vocabulary development over this age range with which the data on the three children in this study could be compared. The mothers of the 260 typically developing children each completed the CDI for their child on one occasion. The CDI used by the mothers of the typically developing children was the Oxford CDI (Hamilton et al., 2000). This checklist was compared with the one used on the children with SLI and any words present in only one of the lists were removed. This left information on 398 words, of which 65 were verbs and 217 were nouns. It was in the performance on these words that the two groups of children (SLI and typically developing) were compared. Hence both groups were effectively compared on identical lists of words, despite administration of slightly different versions of the CDI. For the typically developing children, each child’s total number of words spoken and the number of these that were verbs and nouns were entered into a new database. This generated information on proportions of verbs and nouns for differing total vocabularies (due to the range of ages of the children selected). This was then used to calculate a curve representing number of verbs and nouns relative to total number of words against which the longitudinal data for each of the three children with SLI could be compared.

Results The analysis on the CDI data focused on the development of verb and noun use relative to the total number of words that each child was reported to say. Rate of noun development has previously been considered in this way in typically developing children (see Bates et al., 1994), hence it seemed appropriate to use this method and this type of comparison avoided many of the dif culties involved in ‘matching’ groups of children with SLI and typically developing children on measures such as MLU or language age. Many of the youngest children in the typically developing group had only just begun to use any meaningful speech. Although the children with SLI were severely delayed in their expressive language development, they already had between 60 and 120 words in their total vocabulary at the start of the study. Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015


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This difference can be seen in the scatterplots in Figures 1 and 2 below, where most of the data for the typically developing children are clustered in the bottom left-hand corner. The aim in this investigation was to explore whether the children with SLI were using equivalent amounts of nouns and verbs as typically developing children with the same total vocabulary size. It might be expected for example, in light of some of the studies discussed previously, that the children with SLI learn verbs at a slower rate than typically developing younger children. Figure 1 shows total number of verbs for all the children, relative to their total vocabularies. A polynomial non-linear regression line was tted to the data, and the best t was a cubic curve. As the scatterplot below indicates, all three children with SLI appear to show a similar rate of verb development relative to total vocabulary as the typically developing younger group. Con dence intervals of 95% were calculated for the curve of the typically developing group. The data for the children with SLI on the whole falls within these limits. Some of Nathan’s points fall slightly below and some of Dan’s are slightly above the con dence interval curves. However, as can be seen from the scatterplot, some of the points for the typically developing children also

Figure 1

Verb vocabulary development in children with SLI and controls


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Figure 2 Noun vocabulary development in children with SLI and controls

fall above and below the 95% con dence interval lines. Therefore the data are taken to indicate that both the typically developing group and the group with SLI are following a similar developmental trajectory for verb use. Figure 2 plots the total number of nouns for each child relative to total vocabulary. Again, a cubic curve was found to be the best t for the data and the rate of noun development compared to total vocabulary development looks very similar for both groups of children. Con dence intervals at 95% indicated that nearly all the data for the children with SLI fall within these limits. One of Grace’s points is slightly outside the upper con dence interval line but, as with the verb data, this is to no greater degree than some of the points in the typically developing group and hence the conclusion that the two groups did not differ in the rate of noun development is upheld.

Discussion The results of this investigation indicate that, based on parental report, the rate of vocabulary development over time in the three children with SLI with Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015


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respect to nouns and verbs does not appear to differ from that of typically developing younger children. Although the children with SLI are severely delayed in their acquisition of vocabulary, once their vocabulary does begin to develop, during the early stages it follows a similar course to that of typically developing children. It should be remembered that this study was limited to analysis involving a total vocabulary of 400 words. The children with SLI in this study do not seem to show any particular delay in the acquisition of verbs or nouns relative to children with the same total vocabulary. This is in line with research into early vocabulary development of children with SLI. Leonard et al. (1982) also found a similar distribution of lexical types in children with SLI and typically developing controls. It may be that the dif culties children with SLI appear to have with verbs are only evident at later stages of development and from analyses on naturalistic speech data (Conti-Ramsden and Jones, 1997; Watkins et al., 1993). Additionally, the CDI collects no information on frequency of use of words or whether or not the words are successfully used in the context of sentences. Children with SLI may correctly produce single vocabulary items but have much more dif culty when these have to be combined into multi-word phrases. The children with SLI in the current study still demonstrate severe delay in all areas of vocabulary acquisition as they are older than the typically developing controls. This suggests that the development of expressive vocabulary may be an important therapeutic aim. Evidence from a systematic review of intervention techniques suggests that both parent-administered and clinical treatment can yield improvements in the expressive language of children with SLI (Law et al., 1998). It may be pertinent here that the CDI can be an informative measure of the vocabulary development of children with SLI, but that the dif culties children appear to demonstrate in the use of verbs and verbal morphology in naturalistic speech contexts are more complex than problems with the single vocabulary items, and hence are not evidenced by such a form of data collection.

Conclusions Overall, based on vocabulary measures, the three children with SLI in this study appear to show a large delay in vocabulary development, but a similar rate of development of nouns and verbs to children who are younger but have the same size total vocabulary, as measured by the CDI. That is to say, once the children with SLI begin to produce vocabulary items, their rate of development of verbs and nouns relative to total vocabulary is similar to Downloaded from clt.sagepub.com at University of Manchester Library on June 24, 2015

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younger typically developing controls, at least as far as word types are concerned. It needs to be remembered nonetheless that the CDI is limited in the information it provides about children’s actual vocabulary use in naturalistic conversational contexts. Despite the cautions discussed above, the CDI could be an informative tool for speech and language therapy services, as suggested by Dale (1996). Parents may nd it encouraging to keep a checklist of words that their child is beginning to use, rather than focusing on the child’s limitations, and it may stimulate interest in teaching the child items on the list. The CDI may provide a richer sample of spoken vocabulary than that elicited in therapy or teaching sessions, particularly in cases where the child is reticent. The CDI may also be a useful way of assessing a particular vocabulary. Once collated, the inventory provided by the CDI can be used in establishing the words the child knows for planning teaching or therapy. Acknowledgements This research was supported by the Economic and Social Research Council, ESRC (grant number R000237767). Our special thanks go to the three children with SLI and their families who participated in the study.

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