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Contrasting Profiles of Language Development in Children withWilliams and Down Syndromes

Naomi G. Singer Harris a, Ursula Bellugi b, Elizabeth Bates c,Wendy Jones b, Michael Rossen b

a San Diego State University, Department of Psychology; University of California San Diego,Department of Psychiatry, San Diego, CA 92093

b The Salk Institute for Biological Studies, Laboratory for Cognitive Neuroscience, La Jolla, CA92037

c University of California San Diego, Departments of Psychology and Cognitive Science, SanDiego, CA 92093

In D. Thal & J. Reilly, (Eds.), Special issue on Origins ofCommunication Disorders, Developmental Neuropsychology,

1 9 9 7 , 13(3), 345-370.

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Contrasting Profiles of Language Development in Children withWilliams and Down Syndromes

Abstract

We describe language acquisition in two distinct genetically based syndromes. Parents of children with Williams syndrome(WMS) and Down syndrome (DNS) were given the MacArthur Communicative Development Inventory (CDI), a parental reportmeasure of child language development. Although both groups of children were found to be equally delayed according to norma-tive standards, differential patterns of language acquisition emerged. Early in language development,, the groups were differenti-ated primarily by a proclivity for gesture production by the children with DNS. Later in language development,, the groups werecleaved by grammatical development, where the children with WMS displayed a significant advantage over children with DNS.These findings are striking given the marked differences observed between adolescents and adults with WMS and DNS, whereparticipants with WMS exhibit linguistic skills superior to those of matched DNS controls despite significant but comparablecognitive deficits.

Williams syndrome (WMS), a genetically based neuro-developmental disorder, is characterized by a uniqueneuropsychological profile in which language appearsto “decouple” from other higher cognitive functions(Bellugi, Bihrle, Jernigan, Trauner, & Doherty, 1990;Bellugi, Bihrle, Neville, Jernigan, & Doherty, 1992;Bellugi, Wang & Jernigan, 1994; Karmiloff-Smith,Klima, Bellugi, Grant, & Baron-Cohen, 1995; Mervis& Bertrand, in press; Wang & Bellugi, 1993). Despiteaverage IQ scores ranging from 50 to 70, adolescentsand adults with WMS display surprisingly good mas-tery of complex linguistic structures, as compared toDown syndrome (DNS) participants matched for ageand IQ. Furthermore, individuals with WMS have pro-found spatial cognitive deficits that exceed their levelsof general cognitive impairment; a notable exception tothis is their relatively unimpaired performance on testsof facial recognition (Bellugi et al., 1992, 1994; Jones,Singer, Rossen, & Bellugi, 1993). In addition, indi-viduals with WMS tend to be quite sociable and affec-tively expressive (Reilly, Klima, & Bellugi, 1991;Udwin & Yule, 1990). These factors all contribute to ahighly unusual neuropsychological profile exhibitingpeaks and valleys of higher cognitive functioning.

The contrast between WMS and DNS goes beyonddifferent behavioral profiles. Both syndromes have aunique genetic basis: DNS generally involves an addi-tional chromosomeS recently has been understood asdeletion of one copy of the gene for elastin on Chromo-some 7, plus surrounds (Ewart et al., 1993; Morris,1995). The incidence of WMS (1 in 25,000) is consid-erably rarer than that of DNS, however (1 in 600). Inaddition, magnetic resonance imaging studies indicatethat each syndrome appears to leave its own distinctmorphological “stamp” on the brain, with WMS exhib-iting relatively spared frontal, limbic, and cerebellarregions, and DNS exhibiting relatively preserved basalganglia and diencephalic structures (Jernigan, Bellugi,Sowell, Doherty, & Hesselink, 1993;

Wang, Hesselink, Jernigan, Doherty, & Bellugi,1992). Thus, multiple levels of investigation point tobehavioral, neuroanatomic, and genetic distinctionsbetween these two neurodevelopmental disorders, pro-viding clues to the relation between genes, brain, andbehavior.

A missing piece thus far has been research on theearly acquisition of language and other cognitive func-tions, and the developmental profiles of these two syn-dromes. As described above, most of the research todate has examined individuals with WMS and DNS inadolescence and adulthood. Studies of younger chil-dren with WMS and DNS are of particular importancebecause by examining differences between the twosyndromes in the early stages of cognitive and languagedevelopment, insights can be obtained into the factorsresponsible for the very different neuropsychologicalprofiles evidenced in the steady state. Critical ques-tions which drive such investigations of younger chil-dren with WMS and DNS are: What happens early indevelopment that leads these two groups to such verydifferent end points? How do their developmental tra-jectories differ? By examining differential aspects oflanguage development in WMS and DNS, the presentstudy is one of the first and is the largest to begin toaddress these important questions.

A considerable amount of research has focused onlanguage development in DNS, with investigators pri-marily noting “delays” rather than “deviance”. Al-though there is general consensus that language is moreimpaired than other cognitive abilities in individualswith DNS, and that differences between linguistic andnon-linguistic cognitive development tend to increasewith chronological age, there is some controversy re-garding the nature of the language deficit in DNS (cf.Chapman, 1993; Fowler, 1993). The literature indi-cates, however, that production deficits tend to exceedcomprehension deficits, and that grammar appears to bedisproportionately affected (Beeghly & Cicchetti, 1987;Beeghly, Weiss-Perry, & Cicchetti, 1990; Chapman,1995; Fowler, 1990; Miller, 1987, 1992).

In contrast, there has been relatively little researchpublished on early stages of language development inWMS. One study found that performance of children

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with WMS on language items on the Bayley Scales ofInfant Intelligence exceeded their performance on non-language items, while the reverse was true for childrenwith DNS (Mervis and Bertrand, in press). Similarly, astudy of language and symbolic gesture in two youngchildren with WMS uncovered deviant relations be-tween language and symbolic gesture that are consistentwith the unusual relation between language and cogni-tion in older individuals with WMS (Thal, Bates, andBellugi, 1989). Studies also report different relationsbetween linguistic development and purportedly linkednon-linguistic cognitive development in children withWMS (e.g., lack of pointing before first referential ob-ject word; Mervis and Bertrand, in press; Goodman,1994, 1995). These studies all involve small groups ofchildren, yielding results that are not always consistent.One recent longitudinal study found considerable vari-ability in language acquisition in three children withWMS (Mervis et al., 1995). While such longitudinalanalyses of language acquisition are informative, theytypically involve small samples. Larger samples areneeded to more clearly identify global patterns of lan-guage development in WMS, and to overcome prob-lems with variability which often plague small samples.The present study, using a cross-sectional design, is thefirst to involve large numbers of children with WMSand DNS in order to address these issues.

There are a number of possibilities for what thetrajectories of language development could be like inWMS and DNS: a) consistent with the striking differ-ences in the steady state, in which WMS display farmore sophisticated mastery of language than their DNScounterparts, we might expect a developmental trajec-tory in which children with WMS are from the outsetmore adept at language acquisition than children withDNS; b) alternatively, based on comparable levels ofgeneral cognitive impairment, we might speculate thatchildren with WMS and DNS are equivalently delayedin language acquisition; c) finally, due to the complexand multifaceted nature of language, differences in lan-guage development between WMS and DNS may occuracross linguistic domains, within linguistic domains, oralong boundaries which divide linguistic domains. Thisstudy seeks to address these possibilities, as well as thequestions raised above: what happens during languagedevelopment to take these two groups to such very dif-ferent linguistic end points? How do their patterns oflanguage development compare?

METHODS

Instrumentation

All data for this study were collected using theMacArthur Communicative Development Inventory(CDI), a widely used parental report measure of lan-guage development ( Fenson et al., 1993, 1994).

The CDI has two scales -- a Words and Gesturesscale, which assesses the onset of communication skills(for normally developing children between 8 and 16

months of age), and a Words and Sentences scale,which assess later developing communication skills,including grammatical development (for normally de-veloping children between 16 and 30 months of age).Both scales were utilized in the present study.

Words and Gestures scale. Part 1 of the Wordsand Gestures scale consists of a checklist of 396 wordswhich have been found to be the first to appear in thereceptive and expressive vocabularies of normally de-veloping English-speaking children between the ages of8 and 16 months ( Fenson et al., 1993). Next to eachword item, the parent is asked to indicate if their childa) “understands” the word, or b) “understands and says”the word. The checklist is divided into 19 semanticcategories: sound effects, animal names, vehicle names,toys, food items, articles of clothing, body parts, furni-ture, household objects, outside things and places to go,people, routines and games, verbs, words for time, ad-jectives, pronouns, question words, prepositions, andquantifiers. In Part 2 of the Words and Gestures scale,the child’s use of intentional gestures (e.g., pointing,showing) and referential/representational gestures (e.g.,putting telephone to ear) is assessed. Gestures of thistype are of interest because they have been found tocorrelate with the onset of language comprehensionand/or language production in normally developingchildren.

Words and Sentences scale. Part I of the Wordsand Sentences scale consists of a checklist of 689 wordsthat are typically produced by normally developingEnglish-speaking children between the ages of 16 and30 months (this includes 396 words from the Wordsand Gestures scale). Next to each word item the parentis asked to indicate if their child “says” the word. Thesame 19 semantic categories that are found on theWords and Gestures scale are represented on the Wordsand Sentences scale, with two additional categories forauxiliary verbs (i.e. “helping verbs”), and conjunctions.

Part II of the Words and Sentences scale assessesthe acquisition of grammar. Specifically, parents areasked if their child has begun to combine words; possi-ble answers include “not yet”, “sometimes”, or “often”.If the parent indicates that their child has begun tocombine words they are then asked to provide examplesof the three longest sentences that they have recentlyheard their child say. In addition, parents are providedwith a checklist of nouns and verbs in both regular andirregular inflected forms in order to assess the onset ofinflectional morphology. Finally, grammatical com-plexity is assessed by presenting 37 sentence pairs, eachof which represents a minimal contrast in grammaticalcomplexity which are typical examples of early multi-word combinations. For example, some pairs index theattainment of bound morphemes (e.g., “two shoe” vs.“two shoes”; “doggie kiss me” vs. “doggie kissed me”),some index free morphemes (e.g., “baby crying” vs.

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“baby is crying”; “cookie mommy” vs. “cookie formommy”), and some index sentence embeddings andnoun phrases (e.g., “don’t read book” vs. “don’t wantyou read that book”; “want cookies” vs. “want cookiesand milk”). The parent simply marks “the one thatsounds most like the way your child talks right now”.The analyses presented in this study will address theproduction checklist, examples of the child’s longestutterances and the grammatical complexity measure, aswell as a parental report measure of mean length ofutterance (MLU).

For both the Words and Gestures scale and theWords and Sentences scale, normative data also areprovided for associations between the various dimen-sions of language development assessed by the CDI.This enables an examination of one dimension of lan-guage development in the context of another (e.g., wordproduction in the context of gesture production; gram-matical complexity in the context of word production).Naturally, there will be variability in the extent towhich these dimensions are associated in different chil-dren; furthermore, the strength of associations are likelyto vary at different time points in development. Byproviding normative information about these associa-tions at different time points in language development,the CDI enables one to look for potential dissociationsbetween domains of language, dissociations which notonly indicate extremes of normal language develop-ment, but are particularly likely to be found in atypicalpopulations such as WMS and DNS. The CDI providesthis normative information in the form of “dissociationpercentiles”, which indicate where a given child“ranks” compared to the normative CDI sample. Forexample, for “word production relative to word com-prehension,” a child who scores in the 80th percentile isproducing more words than 80 percent of the childrenin the CDI normative sample who were comprehendingthe same number of words as she (indicating high pro-duction relative to comprehension); accordingly, a childwho scores in the 20th percentile is only producingmore words than 20 percent of the children in the CDInormative sample who were comprehending the samenumber of words as she (indicating low productionrelative to comprehension). The more extreme the dis-sociation percentile (whether high or low), the largerthe dissociation between the two domains, with 50thpercentile indicating no dissociation whatsoever rela-tive to the normative sample.

Participants

The participants, 54 children with WMS and 39 chil-dren with DNS, are part of an ongoing longitudinal in-vestigation of language acquisition. The WMS group iscomprised of 30 males and 24 females, and the DNSgroup is comprised of 23 males and 16 females. For thedata points reported in this study, participants ranged inage from 12 months to 76 months. Participants wererecruited through the Williams Syndrome Association

and Down Syndrome Association (through advertise-ments in the national and regional newsletters), as wellas through medical and other professional contacts.Because of the nature of the study, diagnostic informa-tion was acquired through parental report. Participantswith DNS were included if parents indicated that diag-nosis had been confirmed by chromosomal analysis.Participants with WMS were included if they had beendiagnosed with Williams syndrome and did not evi-dence any confounding developmental abnormalities.Many of the children have been administered both theWords and Gestures scale and the Words and Sentencesscale of the CDI. This paper presents cross-sectionaldata from the children’s first data points on each scale,resulting in 74 WMS data points and 58 DNS datapoints.

Procedure

Through initial contact with parents, the child’s ap-proximate level of language development was ascer-tained in order to determine the appropriate CDI scaleto administer. If parents indicated that their child wasproducing less than 50 words and was not yet combin-ing words, the Words and Gestures form was sent. Ifparents indicated that their child was producing morethan 50 words or was combining words, the Words andSentences form was sent. If it was not clear what levelof language development the child had reached, parentswere asked to complete both scales. Parents weremailed the CDI along with a self-addressed, postagepaid envelope for its return. Instructions for complet-ing the CDI are stated clearly on the form itself, and acover letter accompanied the questionnaire and pro-vided the telephone number of a researcher who as-sisted parents with any questions or comments regard-ing the questionnaire.

RESULTS

Whole-Sample Results Across Both Scales

As a first pass through the data, pooling all data pointsacross both forms of the CDI enabled an examination ofthe sample as a whole. This is important because dif-ferent patterns of results on the two forms could poten-tially be caused by sampling effects due to having the“more advanced” children receive the Words and Sen-tences scale. Because of differences between the forms,the only variable on which data points can be comparedacross forms is language age-equivalent scores basedon the normative data for the CDI. After excludingdata points for which a child had both the Words andGestures and Words and Sentences scales administeredat the same age, our sample for this analysis contained69 WMS data points and 54 DNS data points (9 datapoints were excluded, 5 WMS and 4 DNS, with thehigher score being retained for each child). Table 1indicates characteristics of the sample.

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A one-way analysis of variance (ANOVA) yieldedno differences between the two syndrome groups over-all in age F (1, 122) = 0.896, ns. There was a trend forthe children with WMS to produce larger absolutenumbers of words F (1, 122) = 3.4, p = .07; however,this could be related to the fact that there were morechildren with WMS than DNS who completed theWords and Sentences scale, which has a higher ceilingfor number of words produced (maximum is 689, ver-sus 396 for the Words and Gestures scale). Thus, lan-guage age-equivalence, based on the CDI normativesample, is a more appropriate anchor on which to com-pare the two groups. Analysis by one-way ANOVAyielded no difference between the two groups in overalllanguage age-equivalence F(1, 122) = 0.954, ns. Theindividual data points depicted in Figure 1 illustrate thatoverall the two syndrome groups appear to be produc-ing similar numbers of words throughout the age rangesampled here. Importantly, although there is variability,these children are on average 20 months behind theirnormally developing peers with regard to expressivelanguage.

Following the initial analysis of all data pointscombined, the two scales were analyzed separately inorder to examine the more detailed information aboutlanguage development that the CDI provides. Unlessotherwise indicated, analyses were conducted usingone-way ANOVA, with syndrome as the independentvariable.

Words and Gestures Scale: The Onset of Symbolic Communication

Overall findings. A total of 66 data points initiallywere obtained for the Words and Gestures Scale (34WMS and 32 DNS). After excluding those childrenwho were producing more than 300 words, consideredto be “ceiling” for this scale, 60 data points remained(32 WMS and 28 DNS). Table 2 describes characteris-tics of the sample both before and after this exclusion.

The analyses discussed below included only chil-dren producing 300 words or less on the CDI Wordsand Gestures scale. No significant group differenceswere found with regard to age, number of words com-prehended or number of words produced, F(1, 59) =0.37, 1.8 and 0.07 respectively, ns. Group differencesdid emerge, however, with regard to total number ofgestures, F(1, 59) = 9.9, p< .01. The children withDNS produced significantly more gestures than did thechildren with WMS (see Figure 2). The mean languageage for the WMS group was 14.5 months, and the meanlanguage age for the DNS group was 15.4 monthsF(1,59) = 0.70, ns. Importantly, both groups of chil-dren were delayed relative to normal children, fallingwell below the 10th percentile according to the CDInormative sample (Figure 3).

Relation between components of early lan-guage development. The relations among compre-

hension, production, and gesture in WMS and DNS alsoare informative, as they may yield clues to mechanismswhich may differentiate the two syndromes either fromone another or from normal children. As mentionedearlier, the CDI provides normative data for indices ofdissociation among these three components of earlylanguage, in the form of percentile scores which indi-cate where a given child “ranks” relative to the CDInormative sample. In addition to enabling one to lookfor potential dissociations among domains of languagedevelopment, these percentile scores allow for an ex-amination of the relations among various language pa-rameters intraindividually, rather than relying on sam-ple means.

Three dissociation percentile scores were examinedfor the Words and Gestures scale: 1) word productionlevel given the child’s word comprehension, 2) gesturelevel given the child’s word comprehension, and 3)gesture level given the child’s word production. Table2 provides the means and standard deviations for thesevariables (some children (2 DNS, 5 WMS) had missingvalues for the production/comprehension variable, be-cause the dissociation percentiles can not be derivedreliably for those children near the floor or ceiling ofthe normative tables). Results indicated that relative tonormally developing children, on average children withWMS and DNS had similar relations between wordcomprehension and word production, F(1, 52) = 0.151,ns. That is, relative to normal children at the samecomprehension levels, the WMS group was on averageat the 63rd percentile for word production, while theDNS group was at the 60th percentile. Two-tailed bi-nomial tests indicated that many more children in theWMS group were above the 50th percentile than ex-pected by chance (21/27 were above 50th percentile, p= .004) and somewhat more children in the DNS groupwere above the 50th percentile than expected by chance(18/26 were above 50th percentile, p = .05). A chisquare analysis revealed no significant difference be-tween groups on this parameter X2 (1, N = 53) = 0.5, ns.

The relation between word comprehension andgestures and between word production and gestures wasdifferent for the two syndrome groups, however. Re-sults indicated that relative to normally developingchildren, children with DNS on average had signifi-cantly more gestures given their word comprehensionand word production levels than did children withWMS. F(1, 59) = 10.2 and 11.3 respectively, p < .01 forboth analyses. Furthermore, the children with DNS inthis sample gestured more than most normal children doat similar comprehension and word production levels.The DNS group was on average at the 77th percentilefor gestures relative to normal children at the samecomprehension levels, and at the 80th percentile rela-tive to children at the same production levels, while theWMS group was at the 55th percentile for gesturesrelative to normal children at the same comprehensionand production levels. Two-tailed binomial tests indi-

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cated that many more children in the DNS group wereabove the 50th percentile on these variables than ex-pected by chance (25/28 were above 50th percentile,p<.0001, while no more children in the WMS groupwere above or below the 50th percentile than expectedby chance (14 of 32 were below 50th percentile, p = ns;a chi square analysis revealed significant differencesbetween groups on these parameters X2(1, N = 60) =8.03 for both analyses, p< .01. Figure 4 depicts therelationships among word production, word compre-hension, and gesture for the two syndrome groups.

Differences between children producing lessthan 50 words and children producing more than50 words. Because of the relatively large word pro-duction range in the samples, it is instructive to look atchildren in the earliest stages of word production (<50words) separately from those who have larger produc-tive vocabularies (>50 words). Productive vocabularyof 50 was used as a cutoff because prior to this lexicallevel most children are at the one-word stage, which isconsidered to be a fairly homogeneous stage of lan-guage development (e.g., Nelson, 1973). As it turnsout, results were different in the two subsamples, anddifferent from the sample as a whole. Table 3 listscharacteristics of the two subsamples.

In the subsample of children with productive vo-cabularies less than 50 words, those with DNS tendedto comprehend more, F(1, 36) = 3.8, p = .06; producedsignificantly more words, F(1, 36) = 14.4, p < .001, andgestured more, F(1, 36) = 8.6, p < .01 than did the chil-dren with WMS. In contrast, in the subsample of chil-dren with productive vocabularies greater than 50words, word comprehension and word production werenot different in the two syndrome groups, F(1, 22) =0.846 and 0.577 respectively, ns, while the DNS par-ticipants still gestured significantly more than thosewith WMS, F(1, 22) = 13.1, p < .01 (see Figure 5).These differential findings in the children producingless than 50 words versus those producing more than 50words may have been influenced in part by the pres-ence of a number of WMS data points in our samplefrom older children who were still in the very firststages of language development. It is possible thatthese older children may in fact not have “classic”WMS (i.e., deletion of one copy of the elastin gene), ormay be more affected (i.e., may have a larger deletion).Studies are currently under way to tease apart suchvariability in the phenotypic presentation of WMS.Nevertheless, these findings suggest the possibility thatin the earliest stages of language acquisition childrenwith DNS may have an advantage over children withWMS, an advantage which attenuates as the childrenacquire larger vocabularies (and subsequently begin todevelop grammar). This finding, if replicated, would beextraordinary in that it would represent a complete re-

versal of the later linguistic profile of individuals withWMS and DNS.

Summary of indings from Words and Gestures scale of the CDI.

Taken together, the current findings indicate that thereare minimal differences between children with WMSand children with DNS early in language development,with the notable exception of gestures, in which thecommunicative abilities of children with DNS outstripthose of children with WMS. At this earlier stage ofcommunicative development, if anything, children withDNS may have an overall advantage over children withWMS, an advantage which fades as productive vo-cabulary increases. Although there is considerablevariability, both groups of children are significantlydelayed in their language development. We now turnto the next stage in language acquisition, the develop-ment of grammar. As we will see, it is here where therelative advantage shifts.

Words and Sentences Scale: The Emergence of Grammar

Overall findings, word production. A total of 58data points initially were obtained for the Words andSentences Scale (35 WMS and 23 DNS). After exclud-ing those children who were producing more than 600words, considered to be “ceiling” for this scale, 48 datapoints remained (27 WMS, 21 DNS). Table 4 describescharacteristics of the sample both before and after thisexclusion.

Before excluding data points from those children atceiling on the scale, results indicated that the childrenwith WMS produced significantly more words thanthose with DNS, F(1, 57) = 4.41, p < .05. Withoutthese data points, this difference diminished to a trend,F(1, 47) = 2.12, p = .15. The children who completedthis form of the CDI were on average 15 months olderthan those who completed the Words and Gesturesform, and they were producing on average 200 morewords. The mean language age for the WMS groupwas 22.7 months, and the mean language age for theDNS group was 21 months, F (1, 47) = 2.5, ns. Thus,this more linguistically advanced group was still quitedelayed in language development, with both syndromegroups falling well outside of typical developmentallimits. The analyses discussed below utilized thosechildren producing 600 words or less on the CDI Wordsand Sentences scale. When the children at ceiling wereincluded, the differences that emerged in grammaticaldevelopment were magnified.

Grammatical development . The CDI providesseveral measures of grammatical development. As de-scribed earlier, grammatical complexity is indexed by achecklist of 37 pairs of contrasting phrases, for whichthe parent is asked to indicate “which sounds the mostlike what the child is producing now”. The score on

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this measure of complexity is the total number of wordpairs for which it is indicated that the child is currentlysaying the more complex phrase of the pair. Thismeasure of grammatical complexity has been shown tocorrelate strongly with laboratory measures of meanlength of utterance (MLU) in normally developing chil-dren (r= .88 at 20 months, r= .76 at 24 months; Fensonet al., 1994). As depicted in Figure 6, the children withWMS achieved significantly higher scores on thisgrammatical complexity measure of the CDI than thosewith DNS, F(1, 47) = 7.9, p < .01.

Examining a child’s mean length of utterance(MLU) has a long history in the child language litera-ture and has been widely used as an indicator of achild’s level of grammar (Brown, 1973; Miller, 1981).Accordingly, another index of grammatical develop-ment on the CDI is the mean length in morphemes ofthe three longest utterances (M3L) that the child hasproduced recently according to the parent (see Fensonet al., 1994, for a discussion of this measure as an indexof MLU). In our sample of children with WMS andDNS, strong differences in the M3L emerged (see Fig-ure 6). Children with WMS produced significantlylonger utterances than their DNS counterparts, F (1, 43)= 12.9, p < .001, complementing the finding of morecomplexity in the speech of children with WMS ascompared to children with DNS. Sample sentencesfrom matched WMS and DNS participants shown inFigure 7 highlight these differences.

Relation between word production and gram-mar. The differences in grammar between childrenwith WMS and children with DNS are striking. Nev-ertheless, because of the trend for children with WMSto say more words than those with DNS, it could beargued that this difference is what accounts for the dif-ference in grammatical complexity and phrase length.Fortunately, the CDI provides normative data for indi-ces of “dissociation” between word production and thecomplexity measure, and between word production andM3L. As with the dissociation measures for the Wordsand Gestures Scale, these variables allow for an intrain-dividual comparison of word production and grammar,which is more appropriate than using group means.Two such variables were used for examining grammati-cal development on the Words and Sentences Scale,each expressed in the form of a percentile score: 1)sentence complexity given the child’s word production,and 2) M3L given the child’s word production. As de-scribed earlier, the dissociation percentiles indicatewhere a given child “ranks” compared to the normativeCDI sample.

Table 4 provides the means and standard deviationsfor the dissociation variables, which are depictedgraphically in Figure 6. As with the Words and Ges-tures Scale, some children had missing values for thesevariables (7 DNS, 4 WMS for production/complexity, 1DNS, 3 WMS for production/M3L) because the per-

centiles cannot be derived reliably for those childrennear the floor or ceiling of the normative tables. Re-sults indicated that relative to normally developingchildren, children with WMS displayed more gram-matical complexity F(1, 36) = 6.9, p < .05, and had alonger M3L, F(1, 42) = 4.1, p < .05, for their level ofword production than did children with DNS (Figure 6).In fact, the children with WMS were on average nodifferent than normally developing children with re-gards to the relation between the numbers of words theyproduced and their grammatical development; if any-thing, they tended to produce longer utterances than domost normally developing children at their lexical lev-els (16 of 23 children with WMS were above 50th per-centile for M3L relative to word production, two-tailedbinomial probability = .06; 9 of 20 children with DNSwere above 50th percentile, p = n s; X2(1, N = 43) =2.65, p = .10. In contrast, the children with DNS wereon average quite different from normally developingchildren in this regard; if anything, their speech wasmarked by far less grammatical complexity than that ofmost normally developing children at their lexical lev-els (11/14 children with DNS were below 50th percen-tile for grammatical complexity relative to word pro-duction, two-tailed binomial probability = .04; 13 of 23children with WMS were above the 50th percentile, p =

ns; X2 (1, N = 37) = 4.37, p < .05).

Combining Words: An additional index of language development.

Combining words is a critical stage of language devel-opment in normal children, although little is knownabout this important linguistic milestone in atypicallydeveloping populations. The CDI assesses word com-binations by having parents indicate if their child iscombining words “often”, “sometimes”, or “not yet”.To create “dissociation percentiles” from the CDI nor-mative database, percentile ranks for word productionwere generated for each “level” of word combinations(E. Bates, personal communication 1/94). In otherwords, a child who was combining words “sometimes”would receive a percentile rank based on how his wordproduction level compared to the normative childrenwho also were combining words “sometimes”. A highpercentile rank would indicate that he was producingmore words than most normal children are when theyare at the point where they are only combining words“sometimes” (i.e., he may be considered to be a lin-guistically “late” combiner); conversely, a low percen-tile rank would indicate that he was producing fewerwords than most normal children are when they are atthe point where they are combining words “sometimes”(i.e., he may be considered to be a linguistically “preco-cious” combiner). While these measures are admittedly“rough”, they do enable an examination of this impor-tant index of language development.

As it turned out, however, no differences were re-vealed in the relation between word combinations and

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word production levels in WMS and DNS, F(1, 47) =1.5, ns. On average, children with WMS were at the52nd percentile relative to normally developing chil-dren, while children with DNS were at the 42nd per-centile. Two-tailed binomial tests indicated that forboth groups, no more children were above or below the50th percentile than expected by chance (16 of 27 chil-dren with WMS were above the 50th percentile, p = ns,9 of 21 children with DNS were above the 50th percen-tile, p = ns); a chi-square analysis also revealed no sig-nificant difference between groups on this parameter,X2 (1, N = 48) = 1.27, ns.

Summary of findings with Words and Sen-tences scale of the CDI. In the group of older andmore linguistically advanced children, those with WMSwere producing more words than those with DNS. Thisfinding could be an extension of results from the Wordsand Gestures scale, which indicated progressive im-provement once language gets under way in WMS.Importantly, however, when higher production levelswere controlled for individually using normativelybased dissociation percentile scores, significant differ-ences in grammatical development persisted. Regard-less of number of words produced, children with WMSdisplayed grammatical skills far superior to their DNScounterparts. Moreover, once they reached this level oflinguistic development, the children with WMS ap-peared to display a normal grammatical developmentaltrajectory relative to word production, whereas the chil-dren with DNS continued to evidence delayed gram-matical development (see Figure 8). It is quite intrigu-ing that despite their relative language delay, childrenwith WMS not only surpass children with DNS ingrammatical development, but they may actually beginachieving grammatical milestones at a normal rate.Equally intriguing is the strong dissociation betweenlexical and grammatical development in DNS, sug-gesting a deviant pattern of language development thathas not been reported for other groups. These differen-tial patterns will be explored in more detail.

DISCUSSION

In this study, we sought to gain information re-garding the emerging linguistic abilities of childrenwith WMS as compared to DNS against a large sampleof normative data acquired through the MacArthurCommunicative Development Inventory. The data re-veals that, despite variability, initially both groups ofchildren are equally delayed in acquisition of words (anaverage of two years’ delay for both groups). Firstwords appear in these children at about the same timethat non-retarded children begin to combine words thatthey already have in their lexicon. This equivalentlydelayed language acquisition in WMS and DNS is sur-prising, because it is not at all predictive of the later

differences these two syndrome groups evidence in lin-guistic abilities.

Despite equivalent language delay, two intriguingdifferences did emerge between groups, namely, anearly gesture advantage for the DNS group, and a latergrammatical advantage for the WMS group. The pro-clivity of the children with DNS for gesturing was avery robust finding. A preference for gestural expres-sion over verbal expression in children with DNS hasbeen noted previously in the literature (see Miller, 1987for a brief discussion). However, as sign language is acommunicative modality that is widely taught to youngchildren with DNS (Miller, 1987, 1992), “gestures” onthe CDI perhaps could have been confounded with useof signs in this study. Nevertheless, it is possible thattheir apparent “overgesturing” may be a compensatorystrategy used by the children with DNS for their de-layed word production. Furthermore, that children withDNS may be relatively good at extracting sensory detailfrom the visual communicative context may relate tofindings of significantly better visual-spatial short-termmemory in adolescents with DNS as compared to age-and IQ-matched adolescents with WMS (Wang & Bel-lugi, 1994).

In contrast, several investigators have noted thatchildren with WMS appear to be selectively “ages-tural”; they do not evidence the communicative ges-tures that normally developing children do prior to theonset of first words (Mervis & Bertrand, in press), andthey display significantly fewer gestures during freeplay than age-matched children with DNS and lan-guage-matched normal controls (Goodman, 1994,1995). Furthermore, Thal et al. (1989) reported that 2young children with WMS displayed dissociations insymbolic gesture that were unlike anything observed innormal children or children with specific language de-lay. That the current study failed to find evidence ofimpoverished gesturing by children with WMS couldbe due to the way in which the CDI assesses gesturing,which may not be as sensitive as observational or labo-ratory measures. For example, the CDI assesses thenumber of gestures the children have in their “gesturallexicon”, rather than frequency of use of gestures.

Whereas children with DNS may compensate fortheir poverty of spoken language by the use of gestures,children with WMS may compensate by their “affectivestyle”, tending to be overly engaging with social part-ners. For example, Bertrand, Mervis, and colleagues(1993) have noted that children with WMS spend aninordinate amount of time focused on an adult partner’sface, relative to normally developing children. Olderchildren and adolescents with WMS are similarly capti-vated by social partners; their narratives are rich andcomplex, containing a variety of devices for engagingthe listener (Reilly et al., 1991; Bellugi, Jones,Harrison, Rossen & Klima, 1995). Individuals withWMS are not merely adept at “reading” affect from asocial partner, however; recent studies demonstrate that

9

both children and adults with WMS are able to inferanother’s emotions or mental state without the aid ofaffective prosodic or facial cues (Singer, Delehanty,Reilly, & Bellugi, 1993; Karmiloff-Smith et al., 1995).Whatever reasons may underlie the differences in ges-ture between WMS and DNS, a better understanding ofthe relation between language development and gesture(an area which is currently under investigation by manyresearchers) will help to elucidate the significance ofthese differences.

Regarding the early grammatical abilities of chil-dren with WMS, because our research has found re-markably preserved grammatical skills in adolescentswith WMS, we speculated how early in language de-velopment this advantage/preservation would evidenceitself. The present study provides evidence to supportpreservation of early grammatical skills for childrenwith WMS who have advanced beyond the earlieststages of language development, in marked contrastwith their DNS counterparts, who are much slower todevelop grammar. Thus, even when no advantage wasfound in the total number of words produced by chil-dren with WMS, they were clearly superior to the chil-dren with DNS in their grammatical achievements. It isworth noting that the differences in language acquisi-tion between WMS and DNS could have emerged atany point, including first words. The fact that gram-matical development is what differentiates the twogroups is an extremely provocative finding, given theirdiffering linguistic profiles evidenced later in life. It isalso quite surprising that in the domain of language weobserve an early profile of marked delay in WMSwhich is not predictive of the rich and complex linguis-tic abilities seen later in development. Further studiesof language development throughout childhood are un-der way to link this early profile with the adolescentand adult profile (Jones, Rossen & Bellugi, 1995;Jones, et al., 1993; Singer, Jones & Bellugi, 1995).

Another trend in early language developmentwhich has been noted by researchers and parents ofchildren with WMS is that some of the children seem tosay more than they actually comprehend. Although thecurrent study did not completely replicate these find-ings (the WMS children in our sample were on averagein the 63rd percentile for word production relative toword comprehension), we have acquired numerous an-ecdotes from parents that do attest to this phenomenon.In fact, a number of parents have indicated that on theCDI Words and Gestures form, in addition to the wordchecklist columns understands and understands andsays, they need a separate column for says, but does notunderstand! Further investigation of this possibilityclearly is needed.

Although this study contributes to existing knowl-edge about language acquisition in atypical populationsby providing extensive information about language de-velopment in large samples of children with contrastinggenetic disorders, there are several limitations that must

be kept in mind. First, the cross-sectional nature of thestudy is able to uncover patterns of language develop-ment in the two populations, but not developmentaltrajectories. Longitudinal studies, currently under wayin our laboratory, will complement the findings pre-sented herein and enable us to better address develop-mental trajectories in the two syndrome groups. Sec-ond, the fact that the current data are based on parentalreport rather than experimental observations could po-tentially introduce some bias, particularly if parentshave a tendency to overestimate their child’s linguisticcapabilities. Numerous studies, however, have docu-mented the validity of the CDI for assessing languagedevelopment through parent report (see Fenson et al.,1994), and any parental bias that did exist would not beexpected to differ between syndrome groups. Third,although the mailing procedure by which the data werecollected enabled us to amass the largest sample ofchildren with WMS ever studied, this technique hasinherent limitations such as lack of control over accu-racy of the data and homogeneity of the sample. Webelieve, however, that this limitation is offset by thelarge sample sizes, which are quite unusual for studiesof such rare genetic syndromes. In fact, this study pro-vides the largest sample of children with WMS in thisdevelopmental range that has ever been studied, pro-viding crucial information that complements ongoingobservational studies in our own lab and others. Fur-thermore, the basic developmental trends identified inthis study are compatible with other observationalstudies (e.g., Chapman, 1995; Goodman, 1994, 1995;Mervis and Bertrand, in press; Mervis et al., 1995).

A final note pertains to unavoidable sampling is-sues facing a cross-sectional study such as the presentone. In determining where to “dive in” to our assay oflanguage development in a syndrome as rare as WMS,we distributed the CDI to as many parents as we couldcontact. When we examined our returns, there appearedoverall to be more variability in the WMS group than inthe DNS group. This could be due to differences inbase rates of the syndromes, such that a fuller range ofthe WMS population was sampled than of the DNSpopulation. The WMS sample was drawn from a na-tional sample while the DNS sample was drawn from alocal sample, which could also confer more variabilityon the WMS sample. Finally, although both syndromeshave clear clinical manifestations, it is only in the pastyear that a genetic probe for WMS has become clini-cally available, which enables children to be identifiedas having WMS at an earlier age than when we com-pleted the collection of data for this study. Because ofthis, it is possible that some children in our sample maynot have classic WMS; studies of variability in the phe-notypic expression of WMS are currently under way,and should help address sampling issues in the future.Longitudinal studies with matched samples of WMSand DNS are also under way to confirm and expand thecurrent findings.

10

CONCLUSIONS

This study represents one of the largest investiga-tions to date of emerging language in two geneticallybased neurodevelopmental disorders, and provides thelargest group of young children with WMS ever stud-ied. Despite striking differences in the linguistic abili-ties of adolescents and adults with WMS and DNS, theresults presented herein indicate that both syndromegroups are equally delayed in the onset of language.Early in language development, the groups are differ-entiated primarily by a proclivity for gesture productionby the children with DNS. Later in language develop-ment, the groups are cleaved by grammatical develop-ment, where the children with WMS display a signifi-cant advantage over children with DNS. That individu-als with WMS may display normally developing lan-guage with the advent of grammar, while those withDNS display what could almost be termed “agrammati-cism”, highlights the importance of grammar for humanlanguage, and raises intriguing questions about geneticinfluences on brain and language development. Thisstudy is one of the first to examine these broader issuesof language development in WMS as compared withDNS. Longitudinal studies are under way to assist inidentifying developmental trajectories for patternswhich may differentiate language acquisition processesin the two syndromes. The relation between gesturesand words in WMS and DNS is also being examined inmore detail, as well as characteristics of the early lexi-con in WMS and DNS as compared to normally devel-oping children. Expanding these investigations to in-clude other atypical populations, such as autistic chil-dren and children with focal lesions (e.g., this volume),will provide further opportunities to view variationwithin and across components of early language,thereby enhancing our understanding of language de-velopment and its neural underpinnings.

ACKNOWLEDGMENTS

This research was supported in part by grants from theNational Institutes of Health to Ursula Bellugi (RO1HD 26022 and 1 P01 HD 33113-01) and to ElizabethBates (P50 NS22343 and P01 DC01289); from the OakTree Philanthropic Foundation to Ursula Bellugi; and agrant from the March of Dimes Foundation to the SalkInstitute.

Special thanks to the parents of children with Williamssyndrome and Down syndrome who participated in thisstudy, as well as the Williams Syndrome Associationand the Down Syndrome Association. Our thanks alsoto Judy Goodman, Valerie Loewe, Paul Wang, JudyReilly, and Edward S. Klima for their help and valuablecomments.

Please address correspondence to Ursula Bellugi, Labo-ratory for Cognitive Neuroscience, The Salk Institutefor Biological Studies, 10010 North Torrey Pines Road,La Jolla, CA 92037.

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LANGUAGE DEVELOPMENT IN CHILDREN WITH WMS AND DNS

Table 1.

Sample Characteristics: Both CDI Scales Combined

WMS (n=69) DNS (n=54)M (SD) M (SD)

Age (months) 41 (14) 39 (11)

Word Production 217 (222) 150 (172)

Language Age 19.5 (6.8) 18.4 (5.2)(in months)

Language Delay 21.5 (12.4) 20.3 (8.9)(in months)

Note : M = mean, SD = standard deviation; All comparisons n.s. (at p = .05)

LANGUAGE DEVELOPMENT IN CHILDREN WITH WMS AND DNS

Table 2.

Sample Characteristics: Words and Gestures Scale

All Subjects Production <300 wordsWMS (n=34) DNS (n=32) WMS (n=32) DNS (n=28)

M (SD) M (SD) M (SD) M (SD)

Age (months) 34 (11.2) 34 (9.7) 34 (11.5) 32 (9.1)

Word Compreh. 173 (115) ** 224 (118) 163 (111) 201 (107)

Word Production 77 (101) 93 (119) 61 (82)56 (69)

Gesture Production 35 (15)* 47 (14) 34 (14) * 45 (14)

Comp/Prod % 63 (29.3) 60 (26)63 (29.3) 60 (26)

Comp/Gest % 57 (30.5) * 79 (20.2) 55 (30.5) * 77 (20.9)

Prod/Gest % 56 (32.7) * 81 (21.1) 55 (33)* 80 (22.1)

Note : M = mean, SD = standard deviation

* p<.05

** p<.10

LANGUAGE DEVELOPMENT IN CHILDREN WITH WMS AND DNS

Table 3.Words and Gestures Scale: Subjects Producing Fewer vs. Greater than 50 Words

Production <50 words Production >50 wordsWMS (n=19) DNS (n=18) WMS (n=13) DNS (n=10)

M (SD) M (SD) M (SD) M (SD)

Age (months) 34.6 (14.4) 28.8 (8.14) 33 (5.7) ** 38.5 (7.5)

Word Compreh. 96 (82.2) * 154 (96.7) 260 (65.9) 286 (67.2)

Word Production 5.3 (6.1) * 21.2 (17.2) 143 (70.8) 118.6 (83.3)

Gesture Production 27 (13)* 40 (15) 44 (8.4) * 55 (4.6)

Comp/Prod % 51.5 (30.7) 51.8 (27.8) 83 (11.6) 76 (12.4)

Comp/Gest % 55 (30.8) ** 72 (23.3) 57 (31.3) * 87 (11.6)

Prod/Gest % 55 (33.2) ** 75 (25.8) 55 (34)* 90 (6.9)

Note : M = mean, SD = standard deviation* p<.05** p<.10

LANGUAGE DEVELOPMENT IN CHILDREN WITH WMS AND DNS

Table 4.Sample Characteristics: Words and Sentences Scale

All Subjects Production <600 wordsWMS (n=35) DNS (n=23) WMS (n=27) DNS (n=21)

M (SD) M (SD) M (SD) M (SD)

Age (months) 47 (13.5) 47 (8.7) 45 (13)46 (7.7)

Word Production 366 (208) * 252 (195) 280 (152) 215 (159)

Gram. Complexity 13 (14)* 3 (7.8) 7 (9.1) * 1.2 (2.2)

Prod/Complex % 52 (23.7) * 32 (22.2) 52 (23.7) * 32 (22.2)

MLU 6.2 (4) * 3.4 (2.3) 4.9 (2.4) * 2.9 (.84)

Prod/MLU % 64 (26.3) * 47 (30.8) 64 (26.3) * 47 (30.8)

Note : M = mean, SD = standard deviation

* p<.05