J. Child Psychol. Psychiat. Vol. 42, No. 6, pp. 741748, 2001

Cambridge University Press

' 2001 Association for Child Psychology and PsychiatryPrinted in Great Britain. All rights reserved

00219630}01 $1500000

Psycholinguistic Markers for Specific Language Impairment (SLI)

Gina Conti-Ramsden and Nicola Botting

University of Manchester, U.K.

Brian Faragher

University of Manchester, Institute of Science and Technology, U.K.

In this study 160 children, aged 11 years with a definite history of specific languageimpairment (SLI), completed four tasks that could be potential positive psycholinguisticmarkers for this impairment : a third person singular task, a past tense task, a nonwordrepetition task, and a sentence repetition task. This allowed examination of more than onetype of marker simultaneously, facilitating both comparisons between markers and alsoevaluation of combinations of markers in relation to identifying SLI. The study alsoprovided data regarding the markers in relation to nonverbal IQ, made use of new normativedata on all tasks, and examined marker accuracy in relation to current language status. Theresults show that markers vary in accuracy, with sentence repetition (a previously unusedmarker) proving to be the most useful. This psycholinguistic marker shows high levels ofsensitivity (90%), specificity (85%), and overall accuracy (88%), as well as being able toidentify the majority of children whose current language status falls in the normal rangedespite a history of SLI.

Keywords: Specific language impairment (SLI), psycholinguistic markers, sentence rep-etition, nonword repetition.

Abbreviations: CELF: Clinical Evaluation of Language Fundamentals-Revised; CNRep:Childrens Test of Nonword Repetition; PTT: Past Tense task; RecS: Recalling Sentences ;ROC: receiver operating characteristic ; SLI: specific language impairment ; TPS: ThirdPerson Singular task.

Introduction

There has beenmuch speculation recently regarding theunderlying mechanisms of specific language impairment(SLI) and in particular whether markers can beidentified that differentiate accurately between indi-viduals with and without language disorders. This is atleast in part due to the dissatisfaction felt by research andclinical communities at the exclusionary way in whichSLI is currently diagnosed. It has also perhaps beenfuelled by the reports of significant prevalence figures forSLI of around 7% (e.g., Law, Boyle, Harris, Harkness, &Nye, 1998; Tomblin et al., 1997). The role of memory inlanguage performance has been increasingly prominentand the current status of knowledge is neatly summarisedin a recent report by Ellis-Weismer, Evans, and Hesketh(1999). The literature at present consists of modelspostulating both specific verbal memory deficits as well asgeneralised limitations in processing capacity and therelationship between these and language impairment.

Some of the skills that have recently been examined inchildren with SLI include performance on phonological

Requests for reprints to Gina Conti-Ramsden, Human Com-munication and Deafness, School of Education, University ofManchester, Oxford Road, Manchester M13 9PL, U.K.(E-mail : gina.conti-ramsden!man.ac.uk).

short-term memory tasks such as nonword repetitiontests (Bishop, North, & Donlan, 1996; Gathercole& Baddeley, 1990: Stothard, Snowling, Bishop,Chipchase, & Kaplan, 1998), which are reported tobe good indicators of underlying language difficultyeven when superficially the impairment appears to haveresolved. Interestingly, immediate verbal memory taskshave also been found to be more difficult for children withSLI (Ellis-Weismer et al., 1999). In a different vein, theability to mark syntactic tense has also been thought as apossiblemarker. Syntactic tense appears to be a particularhurdle for children with SLI throughout the primaryschool years (Marchman, Wulfeck, & Ellis-Weismer,1999; Rice & Wexler, 1996; Rice, Wexler, & Cleave,1995; Rice, Wexler, & Hershberger, 1998; for an in-depth review see Leonard, 1998).

Markers that appear to reveal underlying impairmentswhen language is adequate in daily use are particularlyimportant when attempting to trace the heritability oflanguage disorders and related clinical outcomes. Butthere are also direct clinical motivations for identifyingmarkers. They may lead therapists to try alternativeapproaches and may help to positively identify thosemost suited to intensive language provision in education.However, most markers, including the nonword rep-etition marker and immediate memory task, are notunique to specific language impairment and children withmore global learning disabilities (e.g., those with Downsyndrome) have also been shown to perform more poorly

741

742 G. CONTI-RAMSDEN, N. BOTTING, and B. FARAGHER

on these tasks (Jarrold, Baddeley, & Hewes, 2000).Interestingly, the first work to examine nonword rep-etition in children with autism appears to show amoderate deficit in this clinical group also (Kjelgaard &Tager-Flusberg, in press). Thus it may be that suchindicators are predictors only of any language impair-ment and that the specific nature of such impairmentsneeds still to be identified via a process of exclusionamethod with which neither the clinical nor academicprofessions are entirely satisfied.

Furthermore, a difficulty of immediate memory taskssuch as the ones described by Ellis-Weismer et al. (1999)is that nonverbal intelligence appears to be correlatedwith performance on these tasks for children with SLI. Incontrast, Stothard et al. (1998) found that a nonwordrepetition task did not correlate significantly with a test ofnonverbal ability (Ravens matrices). This suggests thatnonword repetition tasks may be less loaded towardsgeneral nonverbal ability and therefore this type ofmemory assessment may prove to be a more accuratemarker for language impairment.

Even more importantly, to the authors knowledge noresearch has examined more than one type of marker inparallel and analysed the relative predictive value of eachmarker or the combined power of a set of markers. Thusclinicians cannot be sure at present whether assessing twoareas of ability is of additional benefit or whether they areusing overlapping and thus unnecessary tasks for thisprocess. Combinatory analysis might also enable pre-liminary examination of the underlying skills thatmarkers tap into, such as different types of memory,knowledge, and processing abilities.

The present study set out to examine whether any ofthree previously reported clinical assessments could act aspsycholinguistic markers for a large cohort of 11-year-oldchildren who were identified as having SLI at 7 years ofage. These childrens difficulties represent the range ofspecific language impairment (as reported in Conti-Ramsden & Botting, 1999a,b; Conti-Ramsden, Crutch-ley, & Botting, 1997). In total 160 children had dataconfirming their status as SLI at 11 years. Because of thepaucity of standardised data for 11-year-old children, themarker tasks were also completed by 100 normallydeveloping age-matched children.

Three potential markers were examined. As discussedabove, nonword repetition was assessed. Tense markingability, as reported byRice et al. (1995) and by Marchmanet al. (1999), has also been identified as a key feature ofchildren with SLI. This was examined using Marchmanselicitation task and a task examining use of third personsingular (Simkin & Conti-Ramsden, 2001). Finally, asentence repetition task, the recalling sentences subtest ofthe Clinical Evaluation of Language Fundamentals-Revised, CELF-Revised (Semel, Wiig, & Secord, 1994)was used. This task was included based on the work ofTomblin, Freese, and Records (1992) with young adultswith a history of SLI. These researchers found that atelephone task involving sentence repetition discrim-inated well between young adults with a history of SLIand those without a history of SLI. We wanted to extendthis work and examine sentence repetitions as a possiblepsycholinguistic marker for children with SLI.

The analysis attempted to investigate five main issues :

(1) The independent contributions of markers to theidentification of SLI (sensitivity, specificity, andoverall accuracy).

(2) The effects on identification accuracy of combiningmarkers.

(3) The relative level of identification for each potentialmarker in relation to current language status. Inparticular examining the fact that children whosedifficulties appear to have resolved by 11 yearsshould still be marked by these variables.

(4) The relationship between markers in children witha history of SLI and in normally developingchildren.

(5) The relationship between potential markers andnonverbal intelligence.

Method

Participants

Children with SLI. A group of 242 children were identi-fied, recruited, and assessed at 7 years on a series oflanguage measures. Initial selection at 7 years is describedfully in Conti-Ramsden et al. (1997) and consisted of arandom 50% sample of all Year 2 children attendingmainstream language units. Thus, no specific SLIcriteria were used at selection, except that those withknown current hearing loss or major physical disabilitywere excluded, as were those with definite diagnoses ofautism or of moderate learning difficulties.

For the purpose of investigating markers, however, itwas felt important to make a post hoc exclusion of datafrom individuals who appeared to have resolved theirlanguage difficulties at recruitment (age 7), since we haveno firm data confirming their status as having SLI atearlier stages. In addition, children with global delay at 7years of age (defined by nonverbal scores more than 2 SDbelow population norm) were excluded. In total, 193}242children actually showed typical SLI in this way. Of these160 were seen at 11 years of age (in total 200}242 childrenparticipated at this age, thus 40 children for whom 11-year data was available were excluded due to non-SLIcharacteristics at 7 years). Forty-three children (27%)were girls and 22 children (14%) had exposure tolanguages other than English at home. The average age ofthe children was 10; 9 (SD 5 months).

Normally developing children. One hundred normallydeveloping children from three primary schools in ruraland urban settings also completed all the marker tasks(Simkin & Conti-Ramsden, 2001). The reasons for thiswas two-fold. First, the past tense, third person, andnonword repetition tasks had no normative data avail-able for this age group. Second, sensitivity and specificityanalysis, as well as between-test correlations, requiredthat all data was available for both groups, hence thechildren were also tested on the Recalling Sentencessubtest of the CELF, although this test has recentavailable norms for this age group. However, tests ofnonverbal cognition and general language ability werenot administered to these children.

Of the 100 children, 51 were girls and their mean agewas 10; 9 (SD 4 months). Children with a history ofspecial needs education were excluded from this sample.

Procedure

Following informed written consent from families,children were visited at school and assessed individuallyin a quiet room or area. Testing on marker tasks was

743PSYCHOLINGUISTIC MARKERS FOR SLI

completed as part of a wider battery of language andcognition tests, during a single visit, at the childs ownpace, and with normal school breaks. Because of the largenumber of measures used, the numbers of data pointsavailable for each language and cognition assessmentvary slightly.

Marker Tasks

Past Tense task (PTT ; Marchman et al. 1999). This is atest designed to assess correct grammatical usage of verbsin past tense form. It consists of 52 line drawings shownto the child one at a time. With each picture, the assessorreads out a sentence related to the picture, which the childmust complete. The sentences all follow the format:This boy is walking. He walks everyday. Yesterday he(walked). The items are balanced and randomized forfrequency of verbs and for regular vs. irregular forms.

Third Person Singular task (TPS ; Simkin & Conti-Ramsden, 2001). This is a test designed to assess correctgrammatical usage of verbs in third person singular form.Fifteen colour photo-cards of people at work are shownto the children one at a time. As with the past tense task,a sentence is read by the assessor and must be finished bythe child. The sentences all follow the format: Sailorssail. This man is a sailor, so everyday he (sails). This isthe second test in the battery to assess tense marking.

CELF-RRecalling Sentences subtest (RecS ; Semel,Wiig, & Secord, 1994). For this task children are given asentence and asked to repeat it verbatim. Sentencesbecome increasingly longer and more complex. Resp-onses are scored in relation to the number of errors madein each sentence.

Children s Test of Nonword Repetition (CNRep ;Gathercole & Baddeley, 1990). This is a test of verbal }phonological short-term memory consisting of 40 non-words. In this study, live presentation was used ratherthan the audiotape version. In this paradigm, the re-searcher says a nonword (e.g., barrazon) whilst hidinghis or her lips behind a screen of paper (to avoid visualstrategies being used by the child). The child must repeatthe word exactly. The researcher is not permitted torepeat the word.

Tests of Nonverbal Cognition

Children with SLI were also tested using subtests ofthe Wechsler Intelligence Scale for Children (WISC-III,Wechsler, 1992) : Block Design and Picture Completion.These are combined to form an estimated Performance ornonverbal IQ. This performance short form in par-ticular has been found to correlate well with a full IQbattery and has been used in other studies of cognitiveability and language (e.g. Sparrow & Davies, 2000).

Language Measures for Comparison of Markersacross Current Language Ability

A wide range of language tests was also completed byeach child with SLI. This battery was not intended tobe exhaustive, but to represent important areas of lan-guage development, (vocabulary expression, vocabularycomprehension, syntactic comprehension, and wordassociations}fluency) using standardised assessments.The following four measures were used: Expressive

Vocabulary Test (EVT; Williams, 1997) ; British PictureVocabulary Scale (BPVS-II ; Dunn, Dunn, Whetton, &Burley, 1998) ; Test for Reception of Grammar (TROG;Bishop, 1982) ; CELFWord Associations (Semel et al.,1994).

Results

Relationship to Performance IQ

None of the marker tasks correlated highly with Per-formance IQ in the group of children with SLI(Spearmans rho: CNRep 019; TPS 020; RecS023; PTT 030), although all relationships were stat-istically significant because of large numbers of partici-pants. This is important to note since any marker for SLIshould not be a proxy for general cognitive level.

Identification of Children with SLI Using MarkerTasks

For each marker, analyses were completed for sensi-tivity and specificity. This analysis requires that athreshold score be used as a cutoff for predicting groupmembership. Cutoff points were selected for each test ;children scoring at or below the cutoff were defined as impaired and children scoring above the cutoff wereclassified as nonimpaired. Since all the tasks in thecurrent study are relatively new (at least to the notion ofmarking clinical groups), three different thresholds wereexamined for each marker (giving a total of 12 analyses :4 markers3 cutoff values). Threshold values used weredetermined using normative data gained from the 100control children. The three cutoff points felt to be ofclinical interest were: below the 16th centile (approxi-mately 1 SD from the population mean); below the 10thcentile (approximately 125 SD from the populationmean) and below the 25th centile (approximately 2 SDfrom the mean). Centiles were used in preference tostandard deviations following statistical advice, sincedata was skewed towards ceiling for the normallydeveloping children on all tasks. Figure 1 shows thegroup distribution on each of the marker measures.

The sensitivity and specificity of each test were calcu-lated using the formulae:

Sensitivity : number of impaired children scoring belowcutoff point } total number of impaired children (i.e.,

Table 1Sensitivity, Specificity, and Accuracy of Tasks UsingVarious Thresholds

Sensitivity Specificity Overall accuracy

TPS16th 63% (98}155) 90% (90}100) 74% (188}255)10th 52% (81}155) 93% (93}100) 68% (174}255)25th 21% (33}155) 100% (100}100) 52% (133}255)

PTT16th 74% (114}154) 89% (89}100) 80% (203}254)10th 71% (109}154) 93% (93}100) 80% (202}254)25th 33% (51}154) 100% (100}100) 59% (151}254)

CNRep16th 78% (124}159) 87% (87}100) 82% (211}259)10th 74% (117}159) 92% (92}100) 81% (209}259)25th 42% (67}159) 98% (98}100) 64% (165}259)

RecS16th 90% (144}160) 85% (85}100) 88% (229}260)10th 86% (137}160) 92% (92}100) 88% (229}260)25th 54% (87}160) 99% (99}100) 72% (186}260)

744 G. CONTI-RAMSDEN, N. BOTTING, and B. FARAGHER

2.5th centile

10th centile16th centile

Key to cutoff lines:

Figure 1. Distributions, medians, and cutoffs for each marker.

probability that an impaired child will be correctlyidentified by the test true positive rate).

Specificity : number of nonimpaired children scoringabove cutoff point } total number of nonimpairedchildren (i.e., probability that a nonimpaired child will becorrectly identified by the test true negative rate).

Table 1 shows the sensitivity, specificity, and accuracyvalues for each analysis. As can be seen, the 16th centilethreshold proved to be the most favourable for correctgroup identification (although little separates the use of10th and 16th centile cutoffs). Furthermore, the markersdiffered in their accuracy of predicting children who didand did not have a history of SLI. The least useful taskwas third person singular, followed by past tense andnonword repetition. Recalling sentences was the mostaccurate marker of SLI.

The effects of using different diagnostic cutoff pointsfor each test were then evaluated using ROC (receiveroperating characteristic) curve analyses (G. Dunn, 2000).

Sensitivity and specificity were estimated for a series ofcutoff points across the full range of possible test values,and a graph of sensitivity (the true positive rate) plottedagainst [1specificity] (the false positive rate). The ROCcurve was examined to identify the best cutoff pointfor the test (i.e., the test score giving the highest sensitivitywith an acceptably high specificity level).

In this context, the area under a ROC curve is theprobability that a randomly selected nonimpaired childwill record a higher test score than a randomly selectedimpaired child.

Clearly, the higher this area is, the more accurate thetest will be. Thus, the areas under the curves werecompared across the tests to identify which was likely tobe most effective at correctly identifying impaired andnon impaired children. Table 2 shows the areas under thecurves for the four markers used in this study. Again,recalling sentences was the most predictive of the markertasks used. A sample ROC curve is shown in Fig. 2.

745PSYCHOLINGUISTIC MARKERS FOR SLI

Table 2Areas under ROC Curves for Marker Tests

TestArea underROC curve

Recalling Sentences 9227Nonword Repetition 8990Past Tense 8731Third Person Singular 8224

Figure 2. Sample ROC curve: Recalling Sentence marker.

TPS

PTT

CNRep

CELF RecS

100

90

80

70

60

50

40

30

20

10

0None 1 2 3 All 4

Number of language tests below 1 SD

% c

hild

ren

with

SLI

his

tory

iden

tifie

d

Figure 3. Identification of children with a history of SLI bycurrent language status.

Markers in Relation to Current Language Status

Using the four independent tests of language, currentlanguage ability was determined for each child with ahistory of SLI. This was done by coding each child forhow many tests fell below the 16th centile for age (using

Table 3Relationship between Marker Variables for Children withSLI (Normally Developing Children in Parentheses)

PTT TPS CNRep

RecS 62* (62)* 57* (06) 55* (34)*PTT 60* (21) 39* (39)*TPS 37* (13)

*p!01.

published test norms). In total the distribution was asfollows: 17 (11%) had no tests below; 25 (16%) had onetest below; 39 (24%) had two tests ; a further 39 (24%)had three tests ; and 40 (25%) had all four tests below thisthreshold. Figure 3 shows the accuracy of each markerin relation to different levels of current linguistic ability.It illustrates that whereas all markers are excellentidentifiers of those with concurrently severe languageimpairment, only nonword repetition and recallingsentences are able to identify those with mild or resolveddifficulties at a 50% level of accuracy or greater. This isimportant since a true marker of SLI (especially whenconsidering genetic}family history studies) shouldidentify all individuals with a history of languageimpairments.

Relationship between Markers

Correlations between marker tasks were moderate butnot as high as anticipated. Table 3 shows the Spearmansrho values for the children with SLI (and normallydeveloping children in parentheses). The results suggestthat although all markers are related to some degree, theydo not measure entirely overlapping skills. Recallingsentences is the only task to have consistently highcorrelations with all other tests.

Results for the normally developing group showedweaker correlations in general except for past tense andrecalling sentences, which were equal with Spearmansrho 062. Low correlations with all tests and the thirdperson singular task for the normally developing groupare probably due to ceiling effects on this assessment.

Combinations of Markers

Clinically, it may be useful to use two assessments incombination to positively determine specific languageimpairment. Thus we also examined the sensitivity andspecificity of pairs of marker tasks. Since the 16th centilecutoff had proved most useful in previous analyses, thisthreshold was used for all combinations. Two types ofcombinations were investigatedwhether the childscored low on either task; and whether the child scoredlow on both tasks. The results are shown in Table 4 andindicate first that the first type of combination (i.e., lowon either task) is more useful than the other type, since arequirement that both tests are low causes sensitivitylevels to drop to unacceptable levels. Second, it showsthat improved sensitivity, specificity, and overall accuracycan be gained by combining test results in this way, withlow scores on nonword repetition or recalling sentencesshowing the most impressive values. However, it shouldbe noted that the overall accuracy of using both thesetests only increases by 1% over the individual valuefound for the sentence repetition task alone.

746 G. CONTI-RAMSDEN, N. BOTTING, and B. FARAGHER

Table 4Sensitivity, Specificity, and Accuracy of Combined Tasks

Sensitivity Specificity Overall accuracy

Either-test combinationsTPS or PTT 82% (123}151) 82% (82}100) 82% (205}251)TPS or CNRep 86% (133}154) 81% (81}100) 84% (214}254)TPS or RecS 93% (144}155) 78% (78}100) 87% (222}255)PTT or CNRep 92% (140}153) 80% (80}100) 87% (220}253)PTT or RecS 93% (143}154) 78% (78}100) 87% (221}259)CNRep or RecS 96% (152}159) 78% (78}100) 89% (230}259)

Both-test combinationsTPS and PTT 54% (82}151) 97% (97}100) 71% (179}251)TPS and CNRep 55% (85}154) 96% (96}100) 71% (181}254)TPS and RecS 60% (93}155) 97% (97}100) 75% (190}255)PTT and CNRep 61% (93}153) 96% (96}100) 75% (189}253)PTT and RecS 71% (110}154) 96% (96}100) 81% (206}254)CNRep and RecS 73% (116}159) 94% (94}100) 81% (210}259)

Discussion

The present study aimed to explicitly compare andcontrast candidate psycholinguistic markers for specificlanguage impairment (SLI). In particular, four markertasks were examined covering three possible behaviouralmarkers for SLI: sentence repetition, nonword repetition,and linguistic tense marking. The study focused on datafrom 160 children who were approximately 11 years ofage with a documented history of SLI at age 7 years.

Marker Tasks, IQ, and Clinical Levels ofImpairment

A useful starting point is the possible relationship ofthe candidate psycholinguistic markers for SLI with Per-formance IQ. Bishop et al. (1996) have argued that auseful criterion for a marker is that it should be largelyindependent of IQ as one is interested in identifying thelanguage deficit in children and not their general learningability. Interestingly, we found that none of the markertasks correlated highly with Performance IQ. Asmentioned previously, all correlations were statisticallysignificant given the large number of participants in ourstudy. But an examination of the values of the corre-lations suggests a different interpretation. For example,Bishop et al. (1996) found a nonsignificant correlation of.16 between Ravens Matrices and the CNRep, a verysimilar figure to our findings of .19 correlation betweenPerformance IQ on the WISC-III and the CNRep. Thehighest value we obtained was a correlation of .30 for thePTT. Again, we would argue this is not a substantialcorrelation and previous work by Rice and colleagues(Rice et al., 1998) is in line with our findings. Hence, noneof the marker tasks showed a clear advantage in terms ofindependence from Performance IQ.

A second important starting point is the issue ofclinical levels for the identification of SLI. In the presentstudy, we examined three possible clinical cutoff pointsfor SLI. This was done because the determination of SLI,i.e. the discrepancy between language achievement andchronological age expectations, has usually been ar-bitrarily set (Tomblin, Records, & Zhang, 1996). Thus,Bloom and Lahey (1978) suggest a cutoff point of 2 SDsbelow the mean, a cutoff equivalent to below the 25thcentile. On the other hand, a number of researchers (Fey,1986; Lee, 1974; Paul, 1995; Rizzo & Stephens, 1981)have suggested the 10th centile (approximately 125

SD) as a desirable cutoff point. Furthermore, a centilescore below the 16th centile, which is approximatelyequivalent to 1 SD below the mean, has also beensuggested as a clinical cutoff point for SLI (Aram, Morris,& Hall, 1992; Records & Tomblin, 1994; Wiig, Secord, &Semel, 1992). In the present study, it was found that the16th centile cutoff (1 SD) proved to be the most usefulcutoff point for correct SLI}non-SLI identification. Thiswas in line with the work of Records and Tomblin (1994)who found that 1 SD represented the point where themajority of clinicians make the decision that a child hasSLI. Hence, 1 SD has been found to be a clinical goldstandard and the data from this study corroboratesthese findings.

Short-term Memory, SLI, and Repetition Tasks

Of particular interest are the results of the present studysuggesting that both tasks involving short-term memory,i.e., sentence repetition and nonword repetition, are thebest candidate psycholinguistic markers for SLI.

First, the present study replicates the findings byGathercole and Baddeley (1990) and Bishop et al. (1996)of a significant deficit in nonword repetition in childrenwith SLI. In addition, our results further corroboratethose findings of Bishop et al. in suggesting that thedeficits in nonword repetition are identifiable even inchildren with a documented history of SLI but whosemore overt language difficulties have resolved at the timeof the assessment. These consistent findings point to theprimacy of the deficits in children with SLI.

It is important, however, to ask the question: What,exactly, are these repetition tasks measuring? As far as thenonword repetition task is concerned, Gathercole andBaddeley (1990) regard this task as a measure ofphonological short-term memory with deficits associatedwith limitations in the capacity of a phonologicalstore and}or atypical rapid decay of items in memory.These authors have argued persuasively that outputexplanations, e.g. articulatory complexity, are not likelyexplanations for the disorder based on direct comparisonsof children with SLI and nonaffected control children.Another possibility that needs to be considered is possibledeficits in speech input, i.e. in the perceptual classificationof incoming speech. It may be argued, for example, thatdeficits in nonword repetition may reflect delayed pho-nemic awareness. However, Kamhi and Catts (1986) didnot find a significant relationship between nonword

747PSYCHOLINGUISTIC MARKERS FOR SLI

repetition and phonological awareness measures. Hence,it is unlikely that either output or input explanations playa significant role in nonword repetition deficits in childrenwith SLI.

As far as the sentence repetition task is concerned, ourdata shows an interesting and significant correlationbetween the nonword repetition task and the sentencerepetition task (recalling sentences). This replicates thefindings of Kamhi and Catts (1986) and Bishop et al.(1996). The sentence repetition task is thought to placefew demands on phonological analysis and, once again,input and output explanations do not appear to play akey role on this task (much like the nonword repetitiontask). Thus, we are again forced to consider limitation incapacity in short-term memory and}or atypical rapiddecay of items in memory as plausible explanations.Although our data cannot provide a firm answer to thequestion of the underlying deficits tapped by the sentencerepetition task, it supports the notion that impairments insentence repetition and nonword repetition involve somecommon mechanisms. We argue that these commonmechanisms are likely to involve limitations in short-termmemory.

It is also important to discuss the possible overalladvantage of sentence repetition over nonword repetitionin terms of sensitivity, specificity, and overall accuracy asa psycholinguistic marker for the identification of SLI. Itis also worth noting that the sentence repetition task iseasier to score on-line than the CNRep and so haspractical advantages. As discussed previously, it is clearthat both tasks involve short-term memory. We wouldlike to argue that the CNRep has a greater involvement ofphonological short-term memory (Bishop et al., 1996;Gathercole, 1995; Gathercole & Baddeley, 1990). Wewould also like to argue that the sentence repetition taskhas not only short-term memory involvement but alsosome involvement of prior language knowledge, whichmay be conceived as residing in long-term memory(Gathercole & Baddeley, 1993). In a sense, nonwordrepetition tasks may be considered to tap single-wordprocessing skills whereas sentence repetition tasks tapsomething of the language knowledge base of the child.This is supported by our findings of a significantcorrelation between the sentence repetition task (RecS)and the linguistic tense tasks (PTT and TPS). Inter-estingly, the CNRep did not appear to be so highlycorrelated with the aforementioned linguistic tasks (seeTable 2), pointing once again to the different nature ofprocessing it assesses.

It needs to be made clear, nonetheless, that the presentstudy examined potential psycholinguistic markers in asample of 11-year-old children with a documented historyof SLI. It is possible that at this developmental stage,sentence repetition tasks have an overall advantage overnonword repetition tasks in terms of marking SLI. Butwhether this advantage of sentence repetition over non-word repetition is evident in younger children meetingcriteria for SLI remains unanswered and open to furtherinvestigation. It is possible that different short-termmemory tasks with different biases (one biased moretowards phonological short-term memory with the othermore biased towards the linguistic knowledge base inlong-term memory) may mark language impairmentsmore accurately at different developmental stages acrossthe lifespan.

In addition, we found that the linguistic, more purelyknowledge-based tasks involving linguistic tense marking

also showed potential for being psycholinguistic markersfor SLI. In particular, the past tense task appeared tohave reasonable sensitivity, specificity, and accuracy verymuch in line with previous work by Rice and colleagues(Rice & Wexler, 1996; Rice et al., 1995). Having said this,it was evident that the linguistic tense markers were muchbetter at identifying those children who currently hadsevere language impairments and were much less suc-cessful in identifying those children with a documentedhistory of SLI but who appeared to be resolved at age 11years. In contrast, the repetition tasks (both sentencerepetition and nonword repetition) were able to identifythose with mild and resolved difficulties. Gershon andGoldin (1986) point out that genetic markers not onlyneed to be associated with the condition of interest, in thiscase SLI, but also should be state independent. In otherwords, the marker should be present when the conditionitself is no longer manifest. In this sense, linguistic tensedoes not appear to fully meet the criteria for a marker forSLI.

In conclusion, the data from the present study suggestthat deficits in repetition tasks, i.e., sentence repetition inparticular and nonword repetition, are promising psycho-linguistic markers for the SLI phenotype. Nonetheless, afinal word of caution is necessary. Although the afore-mentioned tasks are good discriminators between SLIand control groups, it is still unclear what the impact of arepetition deficit is. In terms of nonword repetition, it isknown that children with severe reading difficulties arealso impaired (Kamhi & Catts, 1986). The fact thatnonword repetition deficits appear to be a characteristicof literacy difficulties as well as SLI may point to acommon limitation of phonological short-term memoryin these children (Snowling, Bishop, & Stothard, 2000).On the other hand, work with children with more globallearning disabilities (e.g., Down syndrome; Jarrold et al.,2000) suggests that difficulties with nonword repetitionmay be more related to any language impairment andthat the specific nature of SLI still remains to beunderstood fully. In the case of sentence repetition(recalling sentences) there is a dearth of research withchildren having other developmental disorders associatedwith language impairments. There is no doubt that giventhe proposed involvement of both processing skills andthe knowledge base in sentence repetition tasks that thisshould be a fruitful area for future research in under-standing the specific or otherwise nature of SLI.

AcknowledgementsWe gratefully acknowledge the NuffieldFoundation (Grant DIR}28) for their continued financialsupport. We would like to thank Zoe$ Simkin and Emma Knoxfor their help with the data collection and we also would like tothank the schools and families who helped us with this research.

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Manuscript accepted 22 March 2001

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