the relationship between vocabulary, grammar, and false belief task performance in children with...

The relationship between vocabulary, grammar,and false belief task performance in childrenwith autistic spectrum disorders and children

with moderate learning difficulties

Naomi Fisher, Francesca Happe, and Judy DunnSGDP Research Centre, Institute of Psychiatry, King’s College, London, UK

Background: The aim of this study was to examine the relationship between language and theory ofmind in children with autistic spectrum disorders (ASD) and children with moderate learning difficulties(MLD). Previous studies have found a strong association between language and theory of mind in arange of groups, but mostly have not included measures of both grammar and vocabulary; includingthese enables us to speculate about the causal direction of the relationship. Methods: Fifty-eightchildren with ASD and 118 children with MLD were given standardised assessments of vocabulary andgrammar, along with standard theory of mind tasks. Results: The relationship between language andtheory of mind was more evident in children with ASD than in those with MLD, and grammar was aparticularly strong predictor of theory of mind performance in children with ASD. Children with MLDperformed better on false belief (FB) tasks than did children with ASD, and their performance was morepredictable across the different theory of mind tasks. Conclusions: Language, in particular grammar,and theory of mind appear to be more strongly related in children with ASD than in those with MLD. Wespeculate that this relationship may be causal, with some grammatical understanding being a pre-cursor of theory of mind. The implications of these findings are discussed in relation to possible routesfor compensatory strategies for mentalising in children with ASD. Keywords: Autistic spectrum dis-orders, moderate learning difficulties, theory of mind, language. Abbreviations: TROG: Test forReception of Grammar; BPVS: British Picture Vocabulary Scale; ToM: Theory of mind; FB: false belief;ASD: autistic spectrum disorder; MLD: moderate learning difficulties.

The relationship between language and theory ofmind (the ability to attribute representational mentalstates) has been of increasing interest in recent years.A wide range of studies have shown a strong rela-tionship in young normally developing children (e.g.,Astington & Jenkins, 1999; Cutting & Dunn, 1999;Dunn, Brown, Slomkowski, Tesla, & Youngblade,1991; Hughes, 1998). The relationship between lan-guage and theory of mind (ToM) is evident using awide range of measures, from standardised syntaxmeasures (Astington & Jenkins, 1999), to meanlength of utterance andmeasures of mental state talk(Dunn et al., 1991). There has been some debate as tothe nature of this relationship, in particular whetherit is in any way causal, and if so in what direction theeffect might go. There are three basic possibilitiesthat may explain the relationship between languageand theory of mind: first, that language may be ne-cessary or facilitatory in the development of a theoryof mind; second, a theory of mind (or precursors to it)may be necessary for language development; andthird, there may be no direct causal association, withthe observed relationship due to some third factor.

The evidence from normally developing childrensuggests that the first option is the most likely; earlylanguage appears to predict later theory of mind(e.g., Astington & Jenkins, 1999). There has beensome debate over the route that this could take, with

some authors suggesting that grammar, and specif-ically complement syntax (the embedded clausesinherent in sentences containing mental statesverbs, e.g., he thinks that the horse is in the garden)is a necessary precursor to theory of mind (De Vil-liers, 2000). Others argue that language is importantbecause it provides children with access to the socialworld, experiences of mental state talk and theopportunity to learn about the mental states of oth-ers. Dunn and Brophy (2002), for example, suggestthat discourse and conversation are cruciallyimportant for a child’s developing understanding ofmind, and that the properties of specific relationshipsthat the child has (e.g., with their parents or peers)predict individual differences in later ToM.

It is also theoretically possible, and not incompat-iblewith theabove evidence, that earlyunderstandingof mind predicts later language gains. Whilst the ToMtested at age 4–5 years by standard false belief (FB)tasks is quite obviously not necessary for languagedevelopment, since most children are talking fluentlyby that age, early socio-cognitive skills such as jointattention could be a necessary precursor to languagedevelopment. A child may have to have some under-standing of the intentionality of other people in orderto learn language (e.g., Baldwin & Saylor, 2002;Bloom, 2000; Tomasello & Farrar, 1986). The re-lationship between language and theory of mind in

Journal of Child Psychology and Psychiatry 46:4 (2005), pp 409–419 doi: 10.1111/j.1469-7610.2004.00371.x

� Association for Child Psychology and Psychiatry, 2004.Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA

children with autistic spectrum disorders (ASD) hasalso been a source of some interest (Happe, 1995;Ozonoff, Pennington, & Rogers, 1991; SparrevohnTager-Flusberg & Sullivan, 1994). Autism is charac-terised by a triad of impairments in socialisation,communication and imagination (Wing & Gould,1979), and the majority of individuals with ASD failbasic ToM tasks (seeBaron-Cohen, 2000 for a review).Children with ASD who pass basic ToM tasks have amuch higher language level than those who fail, andappear to require a higher level of language thannormally developing children to pass (Happe, 1995).There has been the suggestion that language mayprovide childrenwith ASDwith an alternative route tosome understanding of mind (Tager-Flusberg, 2000).If this is the case, then the relationship between lan-guage and theory of mind should be stronger in chil-dren with ASD than in those who are developingnormally, orwhohave other developmental disorders.It would also mean that findings from children withASD could not be generalised to normal development,and vice versa.

The present study investigated the relationshipbetween language and theory of mind in a largesample of children with ASD, and a sample of chil-dren with moderate learning difficulties (MLD), usingtwo standardised measures of language, a receptivevocabulary measure and a receptive grammarmeasure. As discussed above, a causal relationshipbetween language and theory of mind may go ineither direction. An aim of this study was to elucidatethe relationship between language and theory ofmind both in ASD and in children with MLD.

When it comes to clarifying the direction of therelationship between language and theory ofmind, anassociation between vocabulary and theory of mind(such as that found by Happe, 1995) is ambiguous.This isbecausewhilst some level of vocabularymaybenecessary for the acquisition of a theory of mind, it isequally possible that possessing a theory of mindfacilitates the acquisition of vocabulary. Learningwords via the usual ostensive routemay require someunderstanding of the speaker’s intentions andmentalstates, in order to deduce the intended referent(Bloom, 2000). A relationship between ToM andgrammar, on the other hand, is more indicative of aspecific causal direction, since it is unlikely that ToMis required for the acquisition of grammatical struc-tures, except in an indirect way through vocabulary.Therefore a relationship between grammar and ToM,over and above that seen with vocabulary, wouldsuggest a causal role for language in ToM develop-ment. In this way, a correlational study such as thatreported in the present paper may give some indica-tion of causal direction when measures of bothgrammar and vocabulary are included.

By comparing and contrasting childrenwith ASD tothose with MLD, this study aimed to identify differ-ences in the relationship between language and ToMin the two groups. The hypotheses were that language

would be a better predictor of theory of mind per-formance in ASD than in MLD, and that grammarwould predict theory of mind performance in ASD,indicating a causal role for language. An additionalaim was to identify ‘floor’ language scores belowwhich children invariably failed FB tasks, as well asscores above which all children would pass. For thisreason, children with verbal mental ages of lowerthan 4 years were not excluded, since to excludethem would impose an artificial floor in both groups.

A final aim was to investigate the relative difficultyof the different FB tasks, for both children with ASDand those with MLD. This is not only interesting froma methodological viewpoint, it may also give us ahandle on factors that might be causing task failurein the two groups. In order to investigate this, theperformance of those individuals who performedinconsistently across tasks was analysed.

Method

The participants in this study were 176 children andadolescents, recruited from eight schools for childrenwith special educational needs in the greater Londonarea. All children for whom parental consent was ob-tained and who were at school during the testing weretested, but for inclusion in this study theyhad topass thecontrol question for at least one of the two theory ofmindtasks. Five children with ASD did not reach this criterionand so were excluded from the study. The tasks used inthis study served as a screening tool for a theory of mindtraining project, reported elsewhere (Fisher & Happe, inpress). A consequence of this is that manymore childrenwith MLD were tested than those with ASD, in order toobtain the required number of ToM failers.

The ASD group contained 44 children who had re-ceived a primary diagnosis of autism or an autisticspectrum disorder from a psychiatrist or psychologist,and 5 children with a diagnosis of Asperger’s Syndrome.The remaining 9 (who were from a single school andwho were all being educated in classes for children withautistic spectrum disorders) were described on theirstatements of special educational needs as having so-cial and communication disorders. These children wereassigned to the ASD group after completion of achecklist of symptoms based on DSM-IV, after discus-sion with their teachers. The results were unchangedwhen these 9 children were excluded from the analysis,and so data for the full sample will be reported. Therewere therefore 58 children in total in the ASD group.

The remaining 118 children had non-autistic mod-erate learning difficulties and made up the MLD group.They were all being educated in schools for childrenwith special educational needs, and were of mixedaetiologies. Children with fragile-X syndrome, or anysuggestion of an ASD were excluded from this group.

Procedure

All the children were tested individually by the re-searcher in a quiet room in their school. The testing

410 Naomi Fisher, Francesca Happe, and Judy Dunn

session typically took 25 minutes. Language and FBtasks were alternated, and the order of each languageand FB task was counterbalanced.

Measures

British Picture Vocabulary Scale 2nd edition (BPVSII). Receptive vocabulary was assessed using the BPVSII (Dunn, Dunn, Whetton, & Burley, 1999). In this test,children are shown four pictures and asked to point tothe picture that best tells the meaning of a word. Itemsbecome progressively harder. The test is discontinuedwhen a child makes 8 errors in a group of 12. Rawscores were converted to a VMA using the tables in themanual.

Test for Reception of Grammar (TROG). Receptivegrammar was assessed using the TROG (Bishop, 1989).This task involves presenting the child with four pic-tures, and asking them to indicate which picture goeswith a sentence containing a grammatical construct.Items are arranged in blocks of 4, all of which test thesame grammatical construct, and a child is consideredto have failed a block if they fail a single item within theblock. If the child fails 5 consecutive blocks the test isdiscontinued. Raw scores (number of blocks) wereconverted to an age-equivalent (or VMA) score, accord-ing to the manual.

False belief (FB) tasks. Two different FB tasks wereused, counterbalanced in order. One was a picture bookversion of the standard unexpected transfer task(Baron-Cohen et al.’s ‘Sally-Anne task’ (1985)). Thecharacters were a girl called Sally and a boy calledDavid. Children were asked a FB question, a justifica-tion question and two control (memory and reality)questions. They were only credited with passing the FBquestion if they also passed both controls.

The second test was a standard deceptive box taskusing a Smarties tube containing a pencil (Hogrefe,Wimmer, & Perner, 1986). Children were asked bothabout another person’s FB and about their own FB priorto the tube being opened. They were only credited withpassing the FB questions if they also passed a realitycontrol question.

There were therefore 3 FB questions asked, althoughonly two FB tasks were carried out. Potential scoresranged from 0 to 3.

Table 1 gives the age, gender and language charac-teristics of the two groups. The age-equivalent scoreswere used for the language measures. Children whosescores fell below the lowest age equivalent score were

credited with a value one unit below the floor value. Thisproblem only applied to the TROG VMA score, and avalue of 3.92 (i.e., 3 years 11 months) was used. Thisapplied to all children who passed fewer than 5 blocks,which applied to 8 children in the ASD group and 7children in the MLD group.

A one-way ANOVA showed no significant differencesbetween the groups on either of the language measures.There was a significant difference in CA (F ¼ 18.37,df ¼ 179, p < .001).

Results

Firstly, the number of children passing each FB taskin each group will be compared statistically. Thecharacteristics of FB ‘passers’ and ‘failers’ will thenbe reported and the relationship between languageand FB performance analysed using logistic regres-sion and scatter plots.

How many children passed each FB question?

Table 2 gives the number and percentage of particip-ants who passed or failed each individual FB ques-tion. Those who failed the control question werecounted as missing for that task only. Two-tailed chi-square tests were used to compare the number ofparticipants in each group who passed each taskversus the number who failed. For the Sally–Davidtask, the difference approached but did not reachsignificance (v2 ¼ 2.94, df ¼ 1, p ¼ .09). For bothSmarties questions the difference was highly signi-ficant (Self v2 ¼ 20.75 df ¼ 1, p < .001; Other v2 ¼15.02, df ¼ 1, p < .001).

Did the FB tasks vary in difficulty?

Performance on the various tasks varied greatly,particularly in the MLD group, with over 86% pass-ing the Smarties self question, but only 63% passingthe Sally–David task. In order to look at the relativedifficulty of the tasks, the number who performedinconsistently across the FB tasks were compared. Ifthose inconsistently performing individuals consist-ently failed one task rather than another, it wouldindicate that this task was systematically harder for

Table 1 Age, gender and language characteristics for the ASDand MLD groups; mean (s.d.) range

ASD (n ¼ 63) MLD (n ¼ 118)

CA (years) 10.74 (2.35) 12.13 (1.75)5.58–16.17 5.25–14.58

BPVS VMA 7.28 (3.19) 7.58 (1.95)3.58–16.67 2.67–10.58

TROG VMA 6.05 (2.36) 6.07 (1.60)3.92–11.00 3.92–10.00

Gender (boys/girls) 53/5 76/42

Table 2 Performance on the different FB tasks, split by group.Number (percentage) of participants who passed, failed. Thosewho failed the control questions are excluded from that taskonly

Task

ASD(total n ¼ 58)

MLD(total n ¼ 118)

pass fail pass fail

Sally–David(unexpected transfer)

25 (49%) 26 (51%) 66 (63%) 38 (37%)

Smarties other(deceptive box)

28 (49%) 29 (51%) 90 (78%) 25 (22%)

Smarties self(deceptive box)

31 (54%) 26 (46%) 99 (86%) 16 (14%)

Language and theory of mind 411

the group. Table 3 gives the numbers of inconsist-ently performing participants who showed eachpattern of passing and failing.

Since the number of children who performedinconsistently was small, non-parametric statisticswere used. McNemar’s test showed that there was nosystematic difference in task difficulty for the ASDgroup (all p-values > .38), but that in the MLD groupthere was a significant difference between the num-bers passing Smarties self and other (p < .05), be-tween Sally–David and Smarties other (p < .01) andbetween Sally–David and Smarties self (p < .001).That is, when children performed inconsistently,they were highly likely to find the Smarties selfquestion easier than Smarties other, and bothSmarties questions easier than the Sally–David task.Further investigation of the profile of performancebetween different tasks showed that over 60% ofthose children with MLD who performed incon-sistently failed only the Sally–David task, whilstpassing both Smarties tasks. Only 19% of the ASDgroup showed a similar pattern of performance.Table 4 gives the number of inconsistently perform-ing participants who passed each combination oftasks.

Characteristics of FB ‘passers’, as compared to FB‘failers’

In order to ease comparison between the groups andwith previous studies (e.g., Happe, 1995) a pass/failvariable was created. Children were credited withpassing FB only if they passed all possible FBquestions on which they had passed the controlquestions. For the majority of children this meantthat they had to pass 3 FB questions. However, thosechildren who failed a control question were scored aspassing if they passed all the FB tasks on which theypassed the control – i.e., either one or two questions.

This applied to seven children in the MLD grouponly. On this criterion, 15 of the ASD group (24%),and 65 (55%) of the MLD group were credited withpassing FB. This difference was highly significant(v2 ¼ 16.29, df ¼ 1, p ¼ .001). The group character-istics of these ‘passers’ and ‘failers’ are shown inFigure 1. Inspection of Figure 1 suggests that thepassers and failers in the ASD group differed onlanguage ability more than did passers and failers inthe MLD group: there was a difference of over 4 yearson BPVS and TROG VMA in the ASD group in con-trast to a difference of only about one year in theMLD group. A similar pattern emerges on thestandardised measures. A one-way ANOVA showedthat in the ASD group, passers and failers differedsignificantly on the BPVS score (F (1,56) ¼ 36.51,p < .001) and the TROG score (F (1,56) ¼ 116.75,p < .001). There was a trend towards a difference onCA (F (1,56) ¼ 2.97, p ¼ .09). In the MLD group, aone-way ANOVA showed significant differences be-tween the passers and failers in CA (F ¼ 6.36, df ¼1,116, p < .05), BPVS score (F ¼ 10.37, df ¼ 1,116,p < .01) and TROG score (F ¼ 10.88, df ¼ 1,116,p < .01).

In order to get some idea of the magnitude of thedifferences, effect sizes (d) were calculated for bothgroups. In the ASD group effect size ‘d’ for differencesbetween passers and failers ranged from 1.50 to 2.87(with the TROG having higher effect sizes than theBPVS), indicating very large effect sizes (Cohen,1969, suggests that .8 or above should be consideredlarge). In the MLD group d ranged from .23 to .59,indicating low to moderate effects.

Language and false belief performance

Table 5 gives the correlations between total score onfalse belief tasks, age, and language characteristicsin each participant group. Fisher’s z transformationshowed that the full correlations between FB · CAand FB · BPVS did not differ significantly betweenthe MLD group and the ASD groups. The full corre-lations between FB and the TROG, however, weresignificantly different at the p ¼ .05 level (z r1)r2 ¼3.47, with a score above 1.96 indicating signific-ance).

The figures in brackets are the partial correlationswith the other two variables accounted for. In theASD group, only the correlation between the TROGand FB remained significant, whilst in the MLDgroup correlations between BPVS, TROG and FBboth remained significant, although with muchlower effect sizes than in the ASD group.

Table 4 Number (percentage) of inconsistently performing participants passing each task. ASD in bold

Taskspassed

Smartiesself only

Smartiesother only

Sally–Davidonly

Smarties self &other

Smarties self &Sally–David

Smarties other &Sally–David

ASD 8 (27%) 3 (10%) 6 (23%) 5 (17%) 2 (7%) 2 (7%)MLD 5 (13%) 2 (5%) 2 (5%) 23 (61%) 5 (13%) 1 (3%)

Table 3 Number of inconsistently performing participantswith ASD (in bold) and MLD who passed a particular taskwhilst failing another

Passed

Sally–David Smarties other Smarties self

ASD FailedSally–David 8 13Smarties other 8 11Smarties self 8 8

MLD FailedSally–David 25 28Smarties other 7 12Smarties self 3 3


These correlations are reported as background tothe following logistic regression analyses.

Since the standard deviation in performance onthe language measures appeared to be greater in theASD group, subgroups were created which excludedall children who obtained a VMA greater than10 years on the BPVS. This resulted in groups of 47children with ASD and 110 children with MLD, whohad more comparable standard deviations on thelanguage measures (BPVS MLD s.d ¼ 1.85, ASD ¼1.78; TROG MLD s.d. ¼ 1.54, ASD ¼ 1.83). Thesegroups did differ significantly on both the BPVS(MLD mean ¼ 7.38, ASD mean ¼ 6.03; p < .01) andthe TROG (MLD mean ¼ 5.33, ASD mean ¼ 5.93;p < .05). The correlations between language, chrono-logical age and FB performance were repeated withthese subgroups. The correlations between FB andchronological age (ASD r ¼ .25, p ¼ .09; MLD r ¼.27, p < .01) and FB and BPVS (ASD r ¼ .43, p < .01;MLD r ¼ .46, p < .01) were not significantly different,but the correlations between FB and TROG (ASD r ¼.67, p < .01; MLD r ¼ .43, p < .01) were significantlydifferent at the p ¼ .05 level, using Fisher’s z trans-formation (z r1)r2 ¼ 2.44).

Logistic regression analyses were performed toinvestigate predictors of FB performance in thetwo groups. Of primary interest was whether thegrammar measure (the TROG) predicted perform-ance on FB over and above vocabulary (BPVS) andage. A forced-entry logistic regression was per-formed, with age and BPVS scores entered first, fol-lowed by TROG scores. In the ASD group age wasentered in the first block with a non-significantimprovement (v2 ¼ 2.92, df ¼ 1, p ¼ .09). In Block 2BPVS score was then added with an improvement(v2 ¼ 22.17, df ¼ 1, p < .001), and was found to be asignificant predictor of ToM performance (ß ¼ .69,df ¼ 1, p < .001). In the final block TROG score wasadded with an improvement (v2 ¼ 17.58, df ¼ 1,p < .001). In Block 3 TROG score alone was a sig-nificant predictor of ToM performance (ß ¼ 1.27,df ¼ 1, p ¼ .01). This final model using BPVS scoreand TROG score predicted 89.7% of cases (i.e.,whether they passed or failed) correctly. When theBPVS and the TROG were entered in the reverse or-der, then in Block 2 the TROG was added with animprovement (v2 ¼ 39.64, df ¼ 1, p < .001), whilst inBlock 3 the BPVS was added with no improvement(v2 ¼ .11, df ¼ 1, p ¼ .74).

In the MLD group the same analysis was run. InBlock 1, CA was added with significant improvement(v2 ¼ 5.98, df ¼ 1, p < .05). In Block 2, BPVS scorewas added with an improvement (v2 ¼ 4.42, df ¼ 1,p < .05). In the final block (when the TROG score wasadded) there was no significant improvement in themodel (v2 ¼ 1.59, df ¼ 1, p ¼ .21). None of the 3predictors were uniquely significant in this model (allp-values were greater than .22). In Block 2, the BPVSscore alone was a significant predictor (ß ¼ .25,df ¼ 1, p < .05). This model, using BPVS score only,

Figure 1 Age and language levels of FB ‘passers’ and ‘failers’ split by diagnostic groupSignificant differences between passers and failers within each diagnostic group are marked as follows: ***p < .001;**p < .01; *p < .05.

Table 5 Correlations between FB, age and language for theASD and MLD groups (partial correlations with other two var-iables partialled out, e.g., for FB · CA with TROG and BPVSpartialled out)

ASD (n ¼ 58) MLD (n ¼ 118)

FB · CA .41** (.20) .34** (.09)FB · BPVS VMA .67** (.11) .50** (.23*)FB · TROG VMA .77** (.57**) .46** (.20*)

*p < .05; **p < .01.


predicted 65% of cases correctly. When the BPVSand TROG were added in reverse order, then in Block2 the TROG was added with an improvement (v2 ¼6.20, df ¼ 1, p < .05), and in Block 3 (when the BPVSwas added) there was no significant improvement inthe model (v2 ¼ .48, df ¼ 1, p ¼ .48) and none of the3 variables were independent predictors.

To summarise, in the ASD group grammar pre-dicted FB performance over and above vocabulary,and language predicted FB performance well, whilstin the MLD group neither grammar nor vocabularypredicted FB over and above the other, and languagewas not as strong a predictor of FB as in the ASDgroup.

Scatter plots of language against theory of mind

To examine the relationship between the two lan-guage measures and FB performance at a moreindividual level, scatter plots were inspected, show-ing TROG VMA against age, with markers set bywhether the participant passed or failed FB. Figure 2shows these plots.

Inspection of Figure 2 suggested that passers andfailers in the ASD group were more easily distin-guished by the TROG score than were passers andfailers in the MLD group. This is in line with themeans displayed in Figure 1. In the ASD group noparticipant with a TROG VMA of less than 5.75 years

(38 individuals) passed FB, whilst all those with aTROG VMA equal to or above 10 years (10 indi-viduals) passed. A dividing line at a VMA of 6 yearswould divide passers and failers with the exceptionof four children. In the case of CA, no child youngerthan 9.08 years passed FB (14 individuals), butthere was no upper threshold – the oldest participantin the study failed at the age of 16.17 years. In theMLD group the relationship was far less clear. Indi-viduals with TROG VMA scores of 4 years passed FB,and 20 individuals with scores less than 5.75 passed(the threshold in the ASD group). At the other end ofthe ability range there was no more clarity: oneparticipant with a TROG VMA of 10.00 still failed FB.All children (3 individuals) with a CA of less than7.25 years failed.

Figure 3 gives the equivalent graphs for the BPVSVMA. From Figure 3 it can be seen that the BPVSdistinguished between passers and failers less wellthan the TROG, but it still divided the groups moreclearly in the ASD group than in the MLD group. Inthe ASD group all participants with a BPVS VMA ofless than 4.92 failed (13 individuals). A single childpassed with a BPVS VMA of 4.92, but no one elsepassed with a score of less than 6.67. All childrenwith scores higher than 10 years 11 months passed(7 individuals).

In the MLD group again the pattern is less clear.One participant passed FB with a BPVS VMA of only

ASD

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Figure 2 Scatter plots of FB passers and failers onTROG VMA v. CA

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Figure 3 Scatter plots of passers and failers on BPVSVMA v. CA


3.08 years. No children in the group had a BPVSVMA of more than 10.58, but one child with this VMAstill failed FB.

Discussion

Language and theory of mind

The major area of interest in this study was therelationship between language and false belief per-formance in children with ASD and MLD. In thepresent study, which included much larger and morerepresentative groups than previous studies (Happe,1995; Tager-Flusberg & Sullivan, 1994; Sparrevohn& Howie, 1995), false belief performance correlatedsignificantly with both BPVS and TROG scores inboth the ASD and MLD groups. Language, particu-larly grammar, and performance on false belief taskswere more strongly related in children with ASD ascompared to those with MLD.

In a logistic regression model, language predictedFB performance correctly in 90% of the ASD group,but only 65% of the MLD group. Vocabulary was asignificant predictor of FB performance in childrenwith ASD, but grammar was the best predictor,predicting FB performance over and above vocabu-lary. The opposite was not true. In contrast, in theMLD group the pattern was far less clear – logisticregression models including age, vocabulary andgrammar did not fit particularly well, and whicheverof vocabulary and grammar was entered firstemerged as the best predictor. This suggests that theelement that predicted false belief performance wascommon to both tasks. This element could be ageneral language competence measure, or it may bea general ability factor. Since no non-verbal abilitymeasure was included in this study we cannot dis-tinguish between these options. Scatter plots, too,suggested that in the ASD group there was a clearrelationship between language level and FB per-formance for both the TROG and the BPVS, whilstthe relationship in the MLD group was far less pre-dictable. Individuals with MLD passed and failed atevery level of TROG and BPVS VMA.

This study found that children with ASD with agrammatical level below 5.75 years invariably failedat least one of the FB tasks, whilst those with agrammar level above 10 years invariably passed allof them. Other studies have not looked at the rela-tionship between grammar and theory of mind in thesame way. Happe’s (1995) study with 70 participantswith ASD found that no one with a verbal mental ageas measured by the BPVS of lower than 5.5 yearspassed, and that no one with a level of 11.58 years orhigher failed. The equivalent BPVS VMA findingsfrom this present study were about 6–8 monthslower in both cases. The present findings differedfrom those of Happe (1995) in that Happe found nocorrelation between BPVS performance and FB inchildren with MLD, whilst the present study found

highly significant correlations between BPVS scoresand FB. Happe’s sample does not appear to havebeen substantially different to the children includedin the present study; although the average BPVSverbal mental age was about 11

2 years lower in Hap-pe’s study, the range was very similar. Happe (1995)did, however, have a much smaller sample than thepresent study (35 children as compared to 118); inaddition, her study included only two false beliefquestions, and therefore the potential range of theoryof mind performance was smaller in her study thanin the present one.

There is, of course, always the possibility that anassociationbetween languageand theory ofmindmaysimply to be due to the linguistic demands of thetheory of mind tasks. This cannot be completely ruledout, since non-verbal theory of mind tasks were notincluded in this study. However, it is extremely un-likely that this is the case in children with ASD, sincenormally developing children pass these tests by theage of 4, yet a child with ASDappears to need a level ofgrammar nearly 2 years above that to have even achance of passing. The existence of a third factorinfluencing both language and FB is a possibility,although themostplausible candidates –suchas jointattention–aresoclosely linked toToMthat to separatetheir influences seems impossible. Other factors suchas family background can be partialled out withoutthe association disappearing (Cutting&Dunn, 1999).

As argued in the introduction, a relationship be-tween vocabulary and FB understanding tells uslittle about the causal direction of the relationship.However, although it may be necessary to have acertain level of grammatical knowledge to acquire anunderstanding of FB, it is less easy to see how adeficit in ToM would prevent grammatical gains ex-cept by delaying general language acquisition, inwhich case vocabulary and grammar should beequally affected (and equally strongly related toToM). The special association between grammar andFB performance found here, and elsewhere (e.g.,Tager-Flusberg & Sullivan, 1994), therefore suggeststhat some elements of language may be necessary forFB success in children with ASD, rather than viceversa. The findings from this study support claimsby Happe (1995) and Tager-Flusberg and Sullivan(1994) that language may be particularly importantin the development of FB understanding in individ-uals with ASD, and suggests that grammar may playa special role. It would be over-simplistic, however,to suggest that the two options as to the causaldirection of the relationship are completely separate,and that the interactions between language andtheory of mind may not go in both directions. Whilstthe transition to a representational theory of mind(as measured by FB tasks) may require language,earlier forms of social understanding may be neces-sary for early language development, which arethemselves necessary for, or at least facilitatory of,ToM development.


How might language influence ToM developmentin ASD? It is possible that language skills give chil-dren with ASD access to social experiences andinteractions that enable them to develop someunderstanding of mind. Conversation and discourseare certainly crucially important in the developmentof a theory of mind in typically developing children(Dunn & Brophy, 2002). However, the case of chil-dren with ASD may be different, since it appears thatthey can have good receptive language skills (farbeyond those required by typically developing chil-dren) and yet still not develop a theory of mind. It ispossible that in the case of children with ASD, lan-guage itself may provide a structure for developingrepresentational understanding. Happe (1995) andTager-Flusberg (2000) suggest that children withASD may use cognitive strategies to develop someunderstanding of mind in a way that is not neces-sary for normally developing children (or presuma-bly children with MLD), and that language mayprovide the structure for this logical reasoning). Asdiscussed in the introduction, De Villiers (2000)suggests that complement syntax specifically is anecessary precursor of theory of mind. Tager-Flus-berg (2002) suggests that in the case of autism,complement syntax of communication verbs may becrucially important, since they give children a con-crete way to experience different perspectives. So, forexample, a child can learn that ‘Jonny said thatthere were monsters under his bed’, and canunderstand that Jonny may be wrong about this,but that he still said it, thus introducing perspectivetaking and providing a structure for an embeddedfalse belief (or in this case, false statement) withoutthe necessity for an understanding of abstractmental state verbs.

This strong relationship between syntax and the-ory of mind was seen only in the ASD group in thisstudy and should be interpreted with caution. Inparticular, De Villiers (e.g., 2002) argues that com-plement syntax is a necessary precursor for theory ofmind in all groups, but our data cannot test thisclaim. De Villiers postulates that this distinctionbetween the truth value of the complement and thetruth value of the whole phrase is the crucial elementthat enables children to consider different perspect-ives and thus gain a ToM. However, since in Englishthe only verbs that take a tensed complement aremental state and communication verbs, it is hard totease apart the causal direction – use of these com-plements may indicate the existence of a ToM, ratherthan being a precursor to it. In contrast, in Germanthe non-representational verb ‘want’ takes a tensedcomplement, and Perner, Sprung, Zauner, andHaider (2003) have shown that young childrenunderstand and use it well before they use repre-sentational verbs such as ‘think that’ or pass FBtasks. De Villiers counters this by pointing out thateven though verbs such as ‘want’ take a tensedcomplement in German, this complement does not

have the potential for different truth values thatit would in the case of a verb such as ‘think’and therefore does not provide a fair comparison(De Villiers, 2002).

It seems to be the case that De Villiers’ account as itstands cannot account for the emerging ToM com-petence in all groups – Woolfe, Want, and Siegal(2002) found that deaf children who were late signersperformed worse on theory of mind tasks than thosewho were native signers even when they were equatedfor syntactic ability. However, it may have particularrelevance in the case of high functioning childrenwith ASD who we speculate may be less able to usenormal conversational and social cues to acquire anunderstanding of mind and therefore have to use thealternative route suggested by Tager-Flusberg.

As the measure of grammar used in this study didnot contain any mental state or communicationverbs our data cannot directly test De Villiers’ orTager-Flusberg’s theories. The strong relationshipbetween the TROG scores and FB performance inchildren with ASD in this study may be due to theTROG measuring good general grammatical ability,which is presumably related to complement syntax(although were that to be the case we might expectthose with a grammar level of 4 or above to pass,since this is the age when normally developing chil-dren acquire complement syntax). Alternatively therelationship between the TROG and ToM may bebecause grammar in fact has a wider importance inthe development of ToM. It is interesting to speculateas to what this might be. If children with ASD areusing an alternative cognitive strategy to developsome understanding of mind, then it is possible thatthis strategy requires some of the same abilities asthe TROG. In particular, the ability to hold some-thing in mind may be important. Later items in theTROG require a degree of embedding and of holdingin mind – for example, item 65, ‘not only the bird butalso the flower is blue’, requires the child to hold inmind the first part of the sentence whilst attending tothe second part, and then to integrate the final ‘isblue’ with both earlier parts.

There are therefore several alternative optionswhich may explain our findings, and further studiesare needed to clarify the relationship further.

False belief performance in ASD and MLD

Whilst children with ASD performed less well on FBtasks than non-autistic children matched on VMA(74% of the ASD group failed at least one FB task, ascompared to only 45% of the MLD group), a surpris-ingly large proportion of the MLD group still failed FBtasks, and a significant proportion of the ASD grouppassed. This corresponds to other studies (e.g., Yi-rmiya, Erel, Shaked, & Solomonica-Levi, 1998) andappears to pose a problem for a theory of mindhypothesis of autism. If difficulties in theory of mindcan account for the pattern of deficits that are unique


to autism, those difficulties should be both specificto, and universally found in, autistic spectrum dis-orders. If they are not, it is problematic to explain whyother children who have theory of mind difficulties donot display the characteristic pattern of difficulties inareas such as socialisation and communication seenin children with ASD. However, it is important, per-haps, to differentiate between the behavioural per-formance and the underlying cognitive competence.

The presence of some children with ASD who passFB tasks is problematic for the universality of thetheory of mind account of autism. It is thereforeimportant to identify whether passing an FB taskindicates a genuine understanding of mind in somechildren with ASD, or whether it reflects nothingmore than chance or task-specific strategies. Chil-dren with ASD who pass ToM tasks still demonstratemany of the characteristic social impairments asso-ciated with ASD, and their ability to pass FB tasksdoes not mean that their social difficulties are re-solved. This has led some researchers to suggest thata child with ASD passing an FB task simply reflectsover-exposure to the tasks, or task-specific strat-egies (e.g., Frith, Morton, & Leslie, 1991). However,there is evidence that some of those who pass FBtasks do in fact show more socially insightful beha-viour such as taking hints, lying and cheating (Frith,Happe, & Siddons, 1994). It therefore seems likelythat some, at least, of these children have not simplylearnt to pass FB tasks, but do actually have a betterunderstanding of minds than do the majority ofchildren with ASD, albeit not a good enough under-standing to completely overcome their social andcommunication difficulties.

The specificity of the ToM deficit in ASD is a topicof debate, and some authors have argued that adeficit in FB performance can be seen in othergroups with learning difficulties (Yirmiya, Erel,Shaked, & Solomonica-Levi, 1998; Zelazo, Burack,Benedetto, & Frye, 1996). This study found somesupport for that view. Since we did not have a controlgroup of normally developing children, it was notpossible to directly contrast our non-autistic groupwith children’s normal development. However, it isstriking that 45% of the MLD group failed at leastone FB question, even though the majority of themhad VMA scores of over 4 years (only 10 children inthe MLD group had either a TROG or BPVS VMA ofless than 4 years), the age at which a normallydeveloping child would be expected to pass. Even ifall children with either a TROG or BPVS VMA of5 years or less were excluded from the analysis(taking 5 years as a conservative estimate of when anormally developing child would be expected to passa FB test), 39% of the remaining MLD group (32individuals) still failed. There are a number of poss-ible explanations for their poor performance.

One option is that some childrenwithMLDdid havegenuine difficulties in ToM. Yirmiya et al. (1998)suggest that ToM deficits may be present but less

severe in individuals with MLD than in children withASD.However, neither their data nor the present datacan resolve this issue, since there is no real measureof the severity of the deficit; instead the data reflectsthe number of childrenwhopassed or failed the tasks.Alternatively, it may be that childrenwithMLD fail FBtasks for other reasons. Frith, Happe, and Siddons(1994) found that in children with MLD, FB perform-ance did not relate to teacher ratings of real-life socialadaptation, suggesting that FB tasks may not be agood measure of true social cognitive ability in thisgroup. It is possible that children with MLD are sim-ilar to normally developing 3-year-olds who fail FBtests despite demonstrating relatively competent so-cial understanding through speech and behaviour(Bartsch&Wellman, 1995). However, thosewithMLDin this sample were obviously not equivalent to nor-mally developing 3-year-olds in that they mostly hadlanguage levels (and, presumably, general develop-mental levels) far above that of the average 3-year-old.It has been suggested that normally developing 3-year-olds may fail FB tasks due to executive difficul-ties (e.g., Roth & Leslie, 1998), and these may also bea source of problems for some of this group of childrenwith MLD. More specifically, candidates for executivefactors that limit performance on FB tasks could in-clude inhibitory control or flexibility. Although therewere no executive tasks in this study that would en-able us to look directly at the relationship between FBperform-ance and executive function in children withMLD, it may be possible to gain some clues as to whatit might mean to pass or fail an FB task in childrenwith MLD by looking at their relative performanceacross the 3 questions. If we look at those individualswho perform inconsistently across the FB tasks, wecanmake some estimate of the relative difficulty of thetasks. Whilst in the ASD group there were no differ-ences between performance on any of the 3 questions(which is what we would expect if children sometimespassed a single task by chance), in the MLD groupthere was a clear hierarchy, with the Sally–David taskbeing hardest, the Smarties (other) next hardest, andthe Smarties (self) easiest. Since the Sally–David taskand the Smarties (other) task are assumed to makevery similar ToM demands (both asking the child topredict themistaken belief of another), but were quitedifferent in administration style, the difference inrelative difficulty between these two tasks is likely toreflect task-specific factors, suggesting that factorsother than ToM difficulties may lead to some childrenwith MLD failing the tasks. However, the Smarties(other) and Smarties (self) questions are from thesame task, and differ in their ToM demands ratherthan in any task-specific factors, with one requiringthe child to rememberhis or her own false belief whilstthe other requires the child to predict another’s mis-taken belief. Therefore the relative difference in diffi-culty between these two questions may indicate thatsome children with MLD do in fact have difficulties inToM, and that the majority of these children find


remembering their own false belief easier than pre-dicting another’s.

This leaves us with a picture where some childrenwith MLD are failing FB tasks due to task-specificfactors, but others (and probably a small minority)have genuine difficulties in theory of mind. Thenature of these difficulties, and their implications fortheir everyday-life social functioning, are yet to beelucidated. If we consider the MLD children whoperformed inconsistently on FB tasks in this study,61% of these individuals passed both Smarties taskswhilst failing the Sally–David task, suggesting thattask factors specific to the Sally–David task led totheir inconsistent performance. If we therefore countthese children as having failed a ToM task for task-specific reasons, rather than because of genuineToM problems, the number of children who might beconsidered to have genuine ToM problems in theMLD group is reduced to 29 (25%). Fourteen of thesechildren failed all the FB tasks, whilst the other 15failed at least one out of the two Smarties questions.The comparable percentage in the ASD group is 59%,even though, as argued above, there is little evidencethat failure on the Sally–David task is due to task-specific factors in this group, and therefore the ori-ginal estimate of 74% is likely to be more accurate inthis case. This apparent vulnerability of childrenwith MLD to task-specific factors has implicationswhen equating failure on any particular false belieftask with a lack of a theory of mind.

Whilst we can speculate about the causal rela-tionship between language and theory of mind fromthis study, in order to investigate the issue moreclosely further longitudinal studies are necessary. Inaddition, it would be useful to include a measure ofcomplement syntax in order to look at specific rela-tionships between different aspects of syntax andtheory of mind. It would also be useful to includemeasures of possible third factors, for example gen-eral ability, in order to eliminate the possibility thatthese factors account for the observed relationshipbetween language and theory of mind.

To summarise, this study found that language, andespecially grammar, was strongly related to FB per-formance in ASD.We speculate that thismay indicatethat individuals with ASD are using alternative, lin-guistically based, routes to representational thought.

Acknowledgements

The work reported here was carried out by NaomiFisher as partial fulfilment of the requirements for adoctoral degree, during which she was supported bya Medical Research Council studentship.

Correspondence to

Naomi Fisher, PO77, Psychology Department, Insti-tute of Psychiatry, King’s College, SE5 8AF, London,

UK; Tel: +44 (0) 20 7848 0224; Fax: +44 (0) 20 78480866; Email: [email protected]

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Manuscript accepted 4 March 2004


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