Child Development, January/February 2016, Volume 87, Number 1, Pages 143–153
Theory of Mind in Children With Specific Language Impairment: A Systematic Review and Meta-Analysis Kristine Kahr Nilsson and Kristine Jensen de L opez Aalborg University
The relation between language and theory of mind (ToM) has been debated for more than two decades. In a similar vein, ToM has been examined in children with specific language impairment (SLI), albeit with inconsistent results. This meta-analysis of 17 studies with 745 children between the ages of 4 and 12 found that children with SLI had substantially lower ToM performance compared to age-matched typically developing children (d = .98). This effect size was not moderated by age and gender. By revealing that children with SLI have ToM impairments, this finding emphasizes the need for further investigation into the developmental interface between language and ToM as well as the extended consequences of atypical language development.
Theory of mind (ToM), which is the ability to attribute mental states to self and others in order to explain behaviors (Premack & Woodruff, 1978), develops gradually during childhood as a sequence of developmental accomplishments (Wellman & Liu, 2004). Joint attention in infancy as well as intentionality and pretend play in toddlerhood have been discussed as early precursors of ToM (Miller, 2006). A marked change toward a more complex ToM occurs around the age of 4 when children become able to pass false-belief tests, which demonstrates knowledge of beliefs as mental entities that can deviate from reality and between individuals (Wellman, Cross, & Watson, 2001). During the school years children begin to master second-order ToM, which entails recursive reasoning about two individuals’ sequential thinking as in “Emma thinks that John thinks” (Miller, 2009). ToM development continues in later childhood and adolescence as evidenced by an increasing understanding of emotional and nonliterate meanings of utterances and behaviors (Choudhury, Blakemore, & Charman, 2006; Peterson, Wellman, & Slaughter, 2012). Research, which suggests that ToM abilities are associated with social skills, peer acceptance, and cooperativeness (Caputi, Lecce, Pagnin, & Banerjee, 2012; Dunn & Cutting, 1999; Slaughter, Dennis, &
We are grateful to the scholars who took time and effort to provide us with additional information to be used in the metaanalysis. Their contribution has been crucial in the making of this review and meta-analysis. Correspondence concerning this article should be addressed to Kristine Kahr Nilsson, Center for Developmental & Applied Psychological Science (CeDAPS), Department of Communication and Psychology, Aalborg University, Aalborg, Denmark. Electronic mail may be sent to [email protected].
Pritchard, 2002; Watson, Nixon, Wilson, & Capage, 1999), emphasizes the potentially adaptive nature of ToM and hence the importance of insights into its developmental underpinnings. Language and ToM Language is one of the most researched developmental domains in relation to ToM. A meta-analysis synthesizing 104 cross-sectional studies found a moderate correlation (r = .43) between children’s performance on language and false-belief tests (Milligan, Astington, & Dack, 2007). Different lines of research furthermore indicate that language may exert a facilitating role in children’s ToM development. For instance, longitudinal studies on preschool children consistently found that language abilities predicted later false-belief performance, whereas false-belief performance did not predict later language abilities (Astington & Jenkins, 1999; de Villiers & Pyers, 2002; Slade & Ruffman, 2005). Likewise, from experimental training studies it emerged that merely exposing children to systematic training on linguistic tasks was sufficient to cause improvement in their false-belief performance (Lohmann & Tomasello, 2003; Sellabona et al., 2013). Further evidence is provided by the consistent finding that deaf children of deaf parents have better ToM abilities than deaf children of hearing parents (Peterson & Siegal, 2000; Schick, de Villiers, de Villiers, & Hoffmeister, 2007), thus emphasizing © 2015 The Authors Child Development © 2015 Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2016/8701-0012 DOI: 10.1111/cdev.12462
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the importance of linguistic environment and especially parent–child communication in facilitating children’s ToM development (Schick et al., 2007). Theoretical perspectives disagree on which aspect of language is essential for ToM development (Astington & Baird, 2005). From the lexical-semantic perspective, it has been argued that the understanding of mental state words, such as want, belief, and think, acquired through conversation with adults, leads children to develop the necessary representations for understanding unobservable mental states in themselves and others (Bartsch & Wellman, 1995). From another perspective, represented by linguistic determinism theory, certain syntactical abilities are essential for the acquisition of ToM. More specifically, children must master the use of tensed complement clauses embedded under believe or communication verbs such as think and say (e.g., “I think Peter is sleeping”) in order to represent events as points of view that can be judged against reality (de Villiers, 2005). Thus, mastering sentential complements is therefore considered a prerequisite for false-belief understanding. From a third perspective, it is not linguistic abilities per se that promote ToM development, but rather the communication that linguistic abilities allow. Proponents of this view argue that conversational exchanges promote ToM development because they expose children to other’s perspectives and convey the fact that such can differ (Dunn & Brophy, 2005; Harris, 2005). Different lines of research have, respectively, supported the importance of mental state vocabulary (e.g., Ruffman, Slade, & Crowe, 2002), sentential complements (e.g., de Villiers & Pyers, 2002), and communicative exchanges (e.g., Ontai & Thompson, 2002) in children’s ToM development. Due to inconclusive results from research comparing these aspects of language, it is still uncertain if any takes precedence in influencing ToM development (e.g., Lohmann & Tomasello, 2003; Sellabona et al., 2013). In contrast to the outlined perspectives, other researchers have questioned the importance of language in ToM development. For instance, Perner, Zauner, and Sprung (2005) argued that children’s conceptual understanding of perspectives precedes their ability to talk about perspectives and therefore doubted a determining role of language in ToM development. Supporting this argument, preferential looking research indicates that toddlers exhibit some understanding of false beliefs before having acquired the linguistic ability to express such beliefs verbally (e.g., Onishi & Baillargeon, 2005). Researchers from the domain-specific approach
have also questioned the importance of language, albeit on different grounds. They have particularly emphasized cases of adults with aphasia who retained their ToM abilities despite severe language impairments as evidence for language and ToM being separate domains (Colle, Baron-Cohen, & Hill, 2007; Siegal & Varley, 2006). As is evident, different views on how language relates to ToM stem from different theoretical assumptions. Although the empirical literature on the relation between ToM and language is extensive and simultaneously supports different views, there has been limited progress toward developing consensus on this subject. Moreover, additional factors potentially influencing the association between language and ToM such as developmental timing and gender have not been adequately considered. Thus, altogether much remains to be understood about the complex connection between language and ToM. Language Impairment and ToM Further empirical evidence on this subject comes from the field of language and speech pathology. A vast amount of research has demonstrated that children with autism spectrum disorder (ASD) have ToM deficits (Yirmiya, Erel, Shaked, & SolomonicaLevi, 1998). There is, however, no agreement on how these ToM deficits relate to the language impairments also found in ASD (e.g., Colle et al., 2007; Durrleman & Franck, 2015). Some research suggests that language abilities and especially sentential complements are linked to the ToM performance of children with ASD (Durrleman & Franck, 2015; Fisher, Happe, & Dunn, 2005). Such findings has led to the speculation that children with ASD rely on linguistic routes as a shortcut for ToM reasoning without employing the social-perceptual processes that typically developing (TD) children use (Fisher et al., 2005; Tager-Flusberg & Joseph, 2005). From this perspective, ASD may not be the most enlightening case for exploring connections between language and ToM that apply to children in general. Another language impairment disorder that has received increasing attention in research on ToM is specific language impairment (SLI). Children are diagnosed with SLI when they display marked language impairments on standardized tests, despite normal nonverbal intelligence and no apparent neurological or sensory dysfunction (Leonard, 1998). SLI has been found to be prevalent affecting approximately 7% of children in kindergarten (Tomblin et al., 1997). Ample evidence further sug-
Theory of Mind in Children With SLI
gests that SLI often persists into adulthood (e.g., Poll, Betz, & Miller, 2010). The causes of SLI are unknown, but are likely to include a heritable component (Bishop, 2006). As the term indicates, SLI is defined specifically by language impairments. According to Leonard (2014), this specificity makes SLI an optimal natural experiment for investigating language development. More specifically, by exemplifying what happens to development when language is critically delayed, SLI elucidates the importance of language for children’s broader development across different domains. Thus, from this perspective, SLI may be used as a methodological vantage point for exploring the developmental interface between language and ToM. Furthermore, as SLI involves different types of language impairments, including deficits in lexical semantics, syntax, and pragmatics (e.g., Bishop, Chan, Adams, Hartley, & Weir, 2000; McGregor et al., 2012), research on SLI may also inform the debate on how language influences ToM development. Yet, before embarking upon such endeavors, a necessary initial step is to provide an overall evaluation of the ToM abilities of children with SLI. Studies unambiguously indicate that children with SLI have better ToM abilities than children with ASD (e.g., Loukusa, M€akinen, Kuusikko-Gauffin, Ebeling, & Moilanen, 2014; Ziatas, Durkin, & Pratt, 1998). However, whether children with SLI differ from TD children is unclear. In some studies, children with SLI were found to have lower ToM abilities than TD children (e.g., Andres-Roqueta, Adrian, Clemente, & Katsos, 2013; Farrant, Fletcher, & Maybery, 2006), whereas in other studies no such difference emerged (e.g., Farmer, 2000; Miller, 2001; Ziatas et al., 1998). The conclusions drawn from these studies were all based on statistical significance, despite the fact that many had very small samples and therefore low statistical power to detect significant results. In order to overcome this limitation and clarify if and to what extent children with SLI have ToM impairments, we conducted a systematic review and meta-analysis of studies comparing TD children and children with SLI in terms of ToM performance. Due to the inconsistency of past studies, we did not adopt any prior hypotheses about the direction or magnitude of the effect. To further understand the result of the meta-analysis, two moderator analyses were also conducted. Previous findings suggest that the association between language and ToM increases as children’s ToM understanding progresses (Grazzani & Ornaghi, 2012; Peterson et al., 2012). Thus, language abilities may
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exert a stronger influence on ToM abilities when such become advanced. On this account, any potential gap in ToM abilities between children with SLI may be assumed to widen with age and age was therefore analyzed as a moderator of the differences between the two groups. Emerging research points to gender differences in ToM including different brain activity patterns during ToM reasoning (Frank, Baron-Cohen, & Ganzel, 2015) and different performance profiles on ToM tests with some tests favoring females (e.g., Calero, Salles, Semelman, & Sigman, 2013) and others males (e.g., Russell, Tchanturia, Rahman, & Schmidt, 2007). In consideration of such findings, as well as the higher prevalence of SLI in boys than girls (Tomblin et al., 1997), the role of gender was investigated in a second moderator analysis.
Method In order to ensure transparency and methodological quality, the systematic review and meta-analysis followed the recommendations proposed by Preferred Reporting Items for Systematic Reviews and Meta-Analysis (Moher, Liberati, Tetzlaff, & Altman, 2009). Search Strategies An extensive literature search was performed, incorporating different search strategies. Initially, the databases PsychInfo and PubMed were searched using different related terms in order to increase the sensitivity of the search. The terms SLI, developmental language disorder, developmental dysphasia, and speech, language, and communication needs were entered separately in combination with each of the following subject words: theory of mind, false belief, mental states, and mentalize, which in some studies has been used synonymously with ToM (e.g., Sharp & Venta, 2012). Thereafter, reference lists from the collected articles as well as from review articles and books on the subject were examined for potentially eligible studies. Finally, the Internet was searched with the specific aim of identifying unpublished studies and studies accepted for publication and in press. The searches covered all previously published studies from the first available date until March 11, 2015, when the last search was conducted. Only documents written in English were considered. Study eligibility and quality were assessed by the two authors independently and inclusion of studies was based on consensus.
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Inclusion Criteria To be included in the review, studies were required to meet the following five inclusion criteria. First, the studies had to compare children with SLI and TD children in terms of ToM performance. Second, the diagnosis of SLI was required to meet the aforementioned criteria proposed by Leonard (1998). Third, the two comparison groups were required to be matched in terms of chronological age. Fourth, the participants had to be children. In agreement with other systematic reviews (e.g., Shields et al., 2007), a mean age of 12 was used as a cutoff age for childhood marking the approximate starting point of puberty. Fifth, the statistical information required for the computation of effect size (e.g., samples sizes, means, and standard deviations) had to be available either in the published material or upon request to the respective authors. Coding For the studies meeting the inclusion criteria, the following information was coded: (a) country of study; (b) sample size, mean age, and gender distribution in the SLI and TD samples, respectively; (c) ToM test(s), which were grouped into the following three categories: (i) false-belief tests, which were differentiated by subtypes partially inspired by the coding scheme used by Milligan et al. (2007), (ii) advanced ToM tests such as the Strange Stories Test (Happe, 1994), and (iii) multiple ToM tests involving five or more different task types, such as the Theory-of-Mind Scale (Wellman & Liu, 2004); and (d) statistical information for computing effect sizes. If the studies contained results from more than one ToM test, composite scores were used. Data Analysis The meta-analysis was performed using Comprehensive Meta-Analysis Version II (Borenstein, Hedges, Higgins, & Rothstein, 2004). The statistical results from all the included studies were converted into Cohen’s d, also known as standardized mean difference. For interpretation of the effect sizes, the conventional definitions were used, d = .20, small; d = .50, medium; and d = .80, large (Cohen, 1988). The directions of the results were quantified as negative and positive mean effect sizes indicating, respectively, lower and higher ToM performance in the children with SLI compared to TD children. There are two main computational models in meta-
analysis. One is the fixed effect model (FEM), which assumes that studies’ results reflect a true mean and that variation is due to sampling error alone. The other is the random effects model (REM), which infers that variation across findings reflects real differences between studies, but that an overall mean can be estimated by accounting for this heterogeneity. Accordingly, the REM accounts for both withinand between-study variability, whereas the FEM only accounts for the former (Borenstein, Hedges, Higgins, & Rothstein, 2009). When there are many potential sources of heterogeneity, as there often are in psychological research with children, the REM is considered appropriate. The REM was therefore selected as the computational model for the present review, although results from both models were presented for transparency. The moderator analyses of age and gender were performed using REM metaregression analyses. Both of these variables were treated as continuous moderators with gender quantified as the percentage of females in the sample. Heterogeneity was assessed using the Q statistic, which evaluates whether the distribution of effect sizes is homogeneous, and the I2 statistic, which estimates the proportion of variance due to between-study heterogeneity. As recommended by Higgins, Thompson, Deeks, and Altman (2003), I2 values around 25%, 50%, and 75% were interpreted as a low, medium, and high levels of heterogeneity, respectively. Publication bias is a serious threat to the validity of systematic reviews and meta-analyses and should therefore be considered carefully. It occurs when the results of published research are systematically unrepresentative of the results from all of the research that has been conducted on the subject (Rothstein, Sutton, & Borenstein, 2005). Such bias is commonly reflected by the fact that statistically significant findings are more likely to be published than nonsignificant findings (Easterbrook, Berlin, Gopalan, & Matthews, 1991). A number of graphical and statistical procedures have been developed with the aim of assessing publication bias. For this review, publication bias was assessed in two ways. First, the fail-safe number method was used to estimate the number of unpublished studies with mean effects of zero that would cause the mean effect size to drop to a nonsignificant level (Rosenthal, 1979). A satisfactory fail-safe number is required to exceed Rosenthal’s (1979) tolerance level, which is the number of included studies times 5 plus 10 (5k + 10). Second, publication bias was examined with inferential statistics using Begg’s test and Egger’s test. Both of these tests assess funnel plot
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asymmetry, which is assumed to imply the presence of publication bias.
Results Results of the Literature Search A flowchart that visually depicts the search process is provided in Figure S1 in the online Supporting Information. Once duplicates had been removed, the search produced 63 records. A screening of all titles and abstracts identified 28 studies potentially eligible for inclusion. Of these studies, 19 initially met the inclusion criteria. However, for 2 of them additional information required for the computation of effect sizes could not be obtained. Thus, in total, 17 studies were included in the meta-analysis. The information coded for each of these studies is presented in Table 1. The total sample comprised 745 children of which 329 were children, with SLI and 416 were TD children. Four of the studies were published in dissertations (Goldman, 2002; Holmes, 2002; Stich, 2010; Tucker, 2004) and the rest in international peer-reviewed journals. In most of the studies, false-belief tests were used as measures of ToM abilities. As described in Table 1, the research in this meta-analysis was conducted across eight different countries: Australia, Canada, Finland, Germany, Holland, Spain, the United Kingdom, and the United States. Results of the Meta-Analysis A forest plot containing a detailed breakdown of each of the studies’ effect size statistics is presented in Figure S2 in the online Supporting Information. Although the effect sizes varied, they all pointed in the same direction, with lower ToM performance in children with SLI compared to TD children. The results for the two computational models are presented in Table 2. The REM showed that children with SLI had significantly lower ToM performance compared to TD children (p < .001) and that the effect size for this difference was large (d = .98). Although mathematically different, the FEM produced a comparable result (p < .001, d = .96). The distribution of effect sizes was found to be heterogeneous (Q = 35.74, p = .003) with a medium proportion of between-study heterogeneity (I2 = 55.23%). The REM metaregression analyses revealed that neither age (z = .835, p = .404) nor gender (z = .270, p = .788) was a significant moderator of the studies’ effect sizes. Additional tests supported the validity of the results. The tests of funnel plot
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asymmetry, Egger’s test (p = .530) and Begg’s test (p = .564), were both nonsignificant, hence indicating a low probability of publication bias. Furthermore, the computed fail-safe number was found to be 599, which greatly exceeded Rosenthal’s tolerance level of 95 for this metaanalysis.
Discussion This empirical review revealed that children with SLI have substantially lower ToM performance than age-matched TD children. Age and gender did not emerge as moderators and therefore did not provide any additional explanation of the result. From the perspective of atypical development, the finding of the meta-analysis lends further support for an association between language and ToM. Moreover, as SLI can be conceived as exemplifying development under the condition of critical language delays (Leonard, 2014), it also suggests that there is a potential interface between language and ToM development where impairment in one domain extends into the other. On a more general level, this finding can therefore be interpreted as emphasizing the importance of normal language development in promoting ageappropriate ToM abilities. Considering the specificity of SLI, language impairment offers the most immediate explanation of lower ToM abilities in children with SLI. The exact mechanism through which language impairment influences ToM development in these children cannot, however, be inferred due to the lack of longitudinal investigations on this subject. Studies documenting moderate to strong associations between language and ToM within samples of children with SLI, nevertheless, support a link between these domains in this population (Andres-Roqueta et al., 2013; Farmer, 2000; Farrar et al., 2009; Holmes, 2002; Stich, 2010). In two of these studies, specific linguistic correlates of ToM were also examined, hence informing the unsettled debate on this subject (e.g., Astington & Baird, 2005). Regression analyses revealed that grammatical ability was the strongest linguistic predictor of ToM performance in children with SLI (Andres-Roqueta et al., 2013; Farrar et al., 2009). Thus, grammatical difficulties that are prevalent in SLI (Bishop, 2014) may be implicated in the ToM impairments of these children. Importantly, though, as the measures of grammatical ability employed in these studies encompass both receptive and expressive grammar, they may tap into
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Table 1 Studies Comparing Children With Specific Language Impairment (SLI) and Typically Developing (TD) Children in Terms of Theory of Mind (ToM) Performance Sample characteristics SLI Study
Country
TD
n
Age (M)
Females (n)
n
Age (M)
Females (n)
Type of ToM task
Andres-Roqueta et al. (2013) Farmer (2000)
Spain
31
5.40
12
31
5.40
12
False beliefs: CL, UI
United Kingdom
16
10.55
1
8
11.04
3
Farrant et al. (2006) Farrant, Maybery, and Fletcher (2012) Gillott, Furniss, and Walter (2004) Goldman (2002) Guiberson and Rodriguez (2013) Hanley et al. (2014) Holmes (2002)
Australia Australia
20 30
5.24 5.25
7 4
20 90
5.10 5.12
8 46
False beliefs: SO Advanced ToM Multiple ToM False beliefs: SO, UI
United States
15
10.25
2
15
10.26
2
United States United States
12 22
11.17 4.25
3 6
12 24
10.91 4.41
3 10
False beliefs: CL, UI False beliefs: UI
United Kingdom Canada
14 43
9.60 6.15
2 15
16 49
9.97 6.02
10 23
Loukusa et al. (2014) Miller (2001) Miller (2004) Norbury (2005) Stich (2010) Tucker (2004) van Buijsen et al. (2011) Ziatas et al. (1998)
Finland United Kingdom United Kingdom United Kingdom Germany Australia Holland Australia
18 10 15 12 22 10 27 12
6.20 5.60 4.92 10.87 6.86 4.05 6.70 6.92
5 1 5 1 9 2 9 4
25 10 15 30 22 10 27 12
6.07 5.60 5.00 10.36 6.99 4.07 6.70 6.42
5 5 8 14 9 0 11 4
False beliefs: BD, CL, UI False beliefs: CL, SO Advanced ToM Multiple ToM False beliefs: CL False beliefs: CL False beliefs: SO Multiple ToM False beliefs: CL, UI False beliefs: BD, CL, UI False beliefs: CL
Advanced ToM
Note. False-belief tests: BD = belief–desire; CL = change of location; SO = second order; UI = unexpected identity.
Table 2 Results From the Random Effects Model and the Fixed Effect Model
Model:
Random effects model Fixed effect model
Number of studies (k)
Sample size SLI/TD (n)
17 17
329/416 329/416
Mean weighted effect size (d)
.98 .96
95% CI lower/ upper limits
1.23/ 0.74 1.12/ 0.80
z score
7.88 11.92
p
< .001 < .001
Note. SLI = specific language impairment; TD = typically developing.
general language abilities rather than any discrete linguistic ability. Thus, narrower and more independent measures of language are required before any specific mechanism can be identified. While the presented studies may give the impression that language and ToM are straightforwardly connected, they may not necessarily be if their connection is better explained by a common denominator. Despite being defined by nonverbal intelligence within the normal range, SLI has in
recent years been associated with general processing difficulties such as executive function deficits (Henry, Messer, & Nash, 2012), although these may be confined to the verbal modality (Archibald & Gathercole, 2007). In two studies within this metaanalysis, executive functioning (i.e., sustained attention and working memory) correlated significantly with ToM performance in the children with SLI. Nevertheless, when executive functioning and general linguistic abilities were analyzed simultane-
Theory of Mind in Children With SLI
ously, general linguistic abilities emerged as the strongest predictor of ToM performance (AndresRoqueta et al., 2013; Holmes, 2002). Accordingly, language impairments may provide a more satisfactory explanation of ToM impairments in children with SLI compared to the executive function deficits also found in these children. Among other common denominators potentially underlying both language and ToM impairments are etiological mechanisms. In twin studies, the association between ToM and verbal ability was found to be attributable to a common effects of shared genes as well as shared environment (Hughes et al., 2005; Ronald, Viding, Happe, & Plomin, 2006). Impairments in language and ToM may therefore be conjoined in SLI through shared genetic and environmental effects. As regards the genetic component, it is noteworthy that variants within the CNTNAP2 gene confer increased risk of both SLI and ASD (Alarc on et al., 2008; Vernes et al., 2008). However, whether the ToM impairments in SLI are attributable to an etiological overlap with ASD (i.e., a disorder defined by ToM deficits) is contentious due to the unclear overlap between these disorders (Bishop, 2010). When interpreting the findings of this review, some methodological aspects merit consideration. While ToM tests claim to tap into an underlying ToM competence, it has been argued that performance factors may interfere with this objective (e.g., Yazdi, German, Defeyter, & Siegal, 2006). In research on SLI, it is particularly relevant to consider any potential constraints posed by verbal aspects of a given test or experiment. The linguistic demands of the ToM tests administered in included studies may, however, not have compromised the results for a number of reasons. First, the verbal instructions were generally simple and usually supplemented by visual aids such as pictograms, drawings, and video clips. Second, initial pretests or control questions were employed to verify the children’s memory capabilities and comprehension of the tasks. Accordingly, the children with SLI presumably met the requirements of the administered ToM tests. Third, to further address this issue some of the included studies compared the children’s performances across verbal and less verbal ToM tasks. Children with SLI performed better on some of the less verbal ToM tasks, although some results went against this pattern (Miller, 2001, 2004; van Buijsen, Hendriks, Ketelaars, & Verhoeven, 2011). Moreover, in the study by Holmes (2002), children with SLI were found to be equally different from the TD children on verbal and less verbal ToM tasks. Thus, altogether, no consistent patterns were found.
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When taking all of these aspects into consideration, the finding of this review most likely indicates that children with SLI have real ToM impairments that cannot be explained by the verbal demands of ToM tests. Deficit or Delay? Tager-Flusberg and Joseph (2005) differentiate between two components of ToM: a social-perceptual component, which is the innate preference for human stimuli, and a social-cognitive component, which is the ability to draw inferences about mental phenomena by integrating different kinds of information. Moreover, they argue that the ToM impairments in children with ASD are due to deficits within the social-perceptual component. In light of the present finding, it is relevant to question whether the same applies to SLI. Two studies that bear upon this question found that children with SLI and TD children exhibited similar eye gaze patterns when viewing social situations, whereas children with ASD exhibited a markedly different gaze pattern with less attention to faces and gazes shifting to the periphery of social scenes (Hanley et al., 2014; Hosozawa, Tanaka, Shimizu, Nakano, & Kitazawa, 2012). Thus, the ToM impairments of children with SLI may not be attributable to profound deficits in social perception, as it appears to be the case in children with ASD. In a similar vein, some of the studies included in the meta-analysis found that the ToM performance of children with SLI was comparable to an additional control group consisting of languagematched children of a younger age (Andres-Roqueta et al., 2013; Miller, 2001, 2004; Ziatas et al., 1998). These results were interpreted as suggesting that the lower ToM abilities in children with SLI reflect a developmental delay rather than a developmental deficit. Although this interpretation seems persuasive, it should be noted that developmental delays vary in degree and complexity. The ToM impairments in SLI may not be just a temporary lag. In two studies, adolescents and adults who had been diagnosed with SLI as children exhibited markedly lower ToM abilities than age-matched TD controls (Botting & Conti-Ramsden, 2008; Clegg, Hollis, Mawhood, & Rutter, 2005). Thus, the ToM impairments of children with SLI may potentially become an enduring characteristic that extends beyond childhood. Furthermore, as ToM is considered a crucial tool for understanding social situations (Astington, 2001), the ToM impairments of children with SLI may conceivably play a role in their poorer social outcomes such as their tendency to have poorer social skills
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(Fujiki, Brinton, & Todd, 1996), be more socially withdrawn (Fujiki, Brinton, Hart, & Fitzgerald, 1999), and be at a higher risk of peer victimization (Redmond, 2011) and bullying (Knox & Conti-Ramsden, 2003). Thus, further investigations into the concurrent and longitudinal consequences of ToM impairments in children with SLI are warranted. Conclusion This empirical review demonstrates that children with SLI perform considerably below the level of age-matched TD children on ToM tests. This finding therefore supports an association between language and ToM from the perspective of atypical development. Furthermore, it also questions the boundaries of SLI as a language disorder and calls for further research into the developmental interface between language and ToM as well as the potentially extended consequences of language impairments. The finding of this review also merits clinical consideration. Previous studies, involving TD children and children with ASD, found that ToM abilities can be improved with systematic training (e.g., Gevers, Clifford, Mager, & Boer, 2006; Lohmann & Tomasello, 2003; Sellabona et al., 2013). Similar interventions aiming to improve the ToM abilities of children with SLI may be contemplated as an adjunct to conventional language programs. References References marked with an asterisk indicate studies included in the meta-analysis. Alarc on, M., Abrahams, B. S., Stone, J. L., Duvall, J. A., Perederiy, J. V., Bomar, J. M., & Geschwind, D. H. (2008). Linkage, association, and gene-expression analyses identify CNTNAP2 as an autism susceptibility gene. American Journal of Human Genetics, 82, 150–159. doi:10.1016/ j.ajhg.2007.09.005 *Andres-Roqueta, C., Adrian, J. E., Clemente, R. A., & Katsos, N. (2013). Which are the best predictors of theory of mind delay in children with specific language impairment? International Journal of Language & Communication Disorders, 48, 726–737. doi:10.1111/1460-6984.12045 Archibald, L., & Gathercole, S. (2007). The complexities of complex memory span: Storage and processing deficits in specific language impairment. Journal of Memory and Language, 57, 177–194. doi:10.1016/j.jml.2006.11.004 Astington, J. W. (2001). The future of theory-of-mind research: Understanding motivational states, the role of language, and real-world consequences. Commentary on “Meta-analysis of theory-of-mind development: The truth about false belief.” Child Development, 72, 685–687. doi:10.1111/1467-8624.00305
Astington, J. W., & Baird, J. A. (2005). Introduction: Why language matters. In J. W. Astington & J. Baird (Eds.), Why language matters for theory of mind (pp. 3–25). New York, NY: Oxford University Press. Astington, J. W., & Jenkins, J. M. (1999). A longitudinal study of the relation between language and theory-ofmind development. Developmental Psychology, 35, 1311– 1320. doi:10.1037/0012-1649.35.5.1311 Bartsch, K., & Wellman, H. M. (1995). Children talk about the mind. Oxford, UK: Oxford University Press. Bishop, D. V. M. (2006). What causes specific language impairment in children? Current Directions in Psychological Science, 15, 217–221. doi:10.1111/j.1467-8721.2006. 00439.x Bishop, D. V. M. (2010). Overlaps between autism and language impairment: Phenomimicry or shared etiology? Behavior Genetics, 40, 618–629. doi:10.1007/s10519010-9381-x Bishop, D. V. M. (2014). Problems with tense marking in children with specific language impairment: Not how but when. Philosophical Transactions of the Royal Society, Biological Science, 369, 1–8. doi:10.1098/rstb.2012.0401 Bishop, D. V. M., Chan, J., Adams, C., Hartley, J., & Weir, F. (2000). Conversational responsiveness in specific language impairment: Evidence of disproportionate pragmatic difficulties in a subset of children. Development and Psychopathology, 12, 177–199. doi:10.1017/S09545794 00002042 Borenstein, M., Hedges, L., Higgins, J., & Rothstein, H. (2004). Comprehensive meta-analysis version 2: A computer program for research synthesis [Computer software]. Englewood, NJ: Biostat. Borenstein, M., Hedges, L. V., Higgins, J., & Rothstein, H. R. (2009). Introduction to meta-analysis. Chichester, UK: Wiley. Botting, N., & Conti-Ramsden, G. (2008). The role of language, social cognition, and social skill in the functional social outcomes of young adolescents with and without a history of SLI. British Journal of Developmental Psychology, 26, 281–300. doi:10.1348/026151007X235891 Calero, C. I., Salles, A., Semelman, M., & Sigman, M. (2013). Age and gender dependent development of theory of mind in 6- to 8-years old children. Frontiers in Human Neuroscience, 7, 281. doi:10.3389/fnhum.2013. 00281 Caputi, M., Lecce, S., Pagnin, A., & Banerjee, R. (2012). Longitudinal effects of theory of mind on later peer relations: The role of prosocial behavior. Developmental Psychology, 48, 257–270. doi:10.1037/a0025402 Choudhury, S., Blakemore, S., & Charman, T. (2006). Social cognitive development during adolescence. Social Cognitive and Affective Neuroscience, 1, 165–174. doi:10. 1093/scan/nsl024 Clegg, J., Hollis, C., Mawhood, L., & Rutter, M. (2005). Developmental language disorders: A follow-up in later adult life. Cognitive, language and psychosocial outcomes. Journal of Child Psychology and Psychiatry, 46, 128–149. doi:10.1111/j.1469-7610.2004.00342.x
Theory of Mind in Children With SLI Cohen, J. (1988). Statistical power analysis for the behavioral sciences. Hillsdale, NJ: Erlbaum. Colle, L., Baron-Cohen, S., & Hill, J. (2007). Do children with autism have a theory of mind? A non-verbal test of autism vs. specific language impairment. Journal of Autism and Developmental Disorders, 37, 716–723. doi:10.1007/s10803-006-0198-7 de Villiers, J. G. (2005). Can language acquisition give children a point of view? In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 186–219). New York, NY: Oxford University Press. de Villiers, J. G., & Pyers, J. E. (2002). Complements to cognition: A longitudinal study of the relationship between complex syntax and false-belief-understanding. Cognitive Development, 17, 1037–1060. doi:10.1016/ S0885-2014(02)00073-4 Dunn, J., & Brophy, M. (2005). Communication, relationships, and individual differences in children’s understanding of mind. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 50– 69). Oxford, UK: Oxford University Press. Dunn, J., & Cutting, A. L. (1999). Understanding others, and individual differences in friendship interactions in young children. Social Development, 8, 201–219. doi:10.1111/1467-9507.00091 Durrleman, S., & Franck, J. (2015). Exploring links between language and cognition in autism spectrum disorders: Complement sentences, false belief, and executive functioning. Journal of Communication Disorders, 54, 15–31. doi:10.1016/j.jcomdis.2014.12.001 Easterbrook, P. J., Berlin, J. A., Gopalan, R., & Matthews, D. R. (1991). Publication bias in clinical research. Lancet, 337, 867–872. doi:10.1016/0140-6736(91)90201-Y *Farmer, M. (2000). Language and social cognition in children with specific language impairment. Journal of Child Psychology and Psychiatry, 42, 627–636. doi:10.1111/ 1469-7610.00649 *Farrant, B., Fletcher, J., & Maybery, M. (2006). Specific language impairment, theory of mind, and visual perspective taking: Evidence for simulation theory and the developmental role of language. Child Development, 77, 1842–1853. doi:10.1111/j.1467-8624.2006.00977 *Farrant, B. M., Maybery, M. T., & Fletcher, J. (2012). Language, cognitive flexibility, and explicit false belief understanding: Longitudinal analysis in typical development and specific language impairment. Child Development, 83, 223–235. doi:10.1111/j.1467-8624.2011.01681.x Farrar, M. J., Johnson, B., Tompkins, V., Easters, M., Zilisi-Medus, A., & Bengino, J. P. (2009). Language and theory of mind in preschool children with specific language impairment. Journal of Communication Disorders, 42, 428–441. doi:10.1016/j.jcomdis.2009.07.001 Fisher, N., Happe, F., & Dunn, J. (2005). The relationship between vocabulary, grammar, and false belief task performance in children with autistic spectrum disorders and children with moderate learning difficulties. Journal of Child Psychology and Psychiatry, 46, 409–419. doi:10.1111/j.1469-7610.2004.00371.x
151
Frank, C. K., Baron-Cohen, S., & Ganzel, B. L. (2015). Sex differences in the neural basis of false-belief and pragmatic language comprehension. NeuroImage, 15, 300– 311. doi:10.1016/j.neuroimage.2014.09.041 Fujiki, M., Brinton, B., Hart, C. H., & Fitzgerald, A. H. (1999). Peer acceptance and friendship in children with specific language impairment. Topics in Language Disorders, 19, 34–48. doi:10.1097/00011363-199902000-00005 Fujiki, M., Brinton, B., & Todd, C. M. (1996). Social skills of children with specific language impairment. Language, Speech, and Hearing Services in Schools, 27, 195– 202. doi:10.1044/0161-1461.2703.195 Gevers, C., Clifford, P., Mager, M., & Boer, F. (2006). A theory-of-mind-based social-cognition training program for school-aged children with pervasive developmental disorders: An open study of its effectiveness. Journal of Autism and Developmental Disorders, 36, 567–571. doi:10.1007/s10803-006-0095-0 *Gillott, A., Furniss, F., & Walter, A. (2004). Theory of mind ability in children with specific language impairment. Child Language Teaching and Therapy, 20, 1–11. doi:10.1191/0265659004ct260oa *Goldman, S. (2002). Unshared lives: Fictional and personal narrative productions in high-functioning autistic children (Doctoral dissertation). Available from ProQuest Dissertations and Theses Database. (UMI No. 3047222) Grazzani, I., & Ornaghi, V. (2012). How do use and comprehension of mental-state language relate to theory of mind in middle childhood? Cognitive Development, 27, 99–111. doi:10.1016/j.cogdev.2012.03.002 *Guiberson, M., & Rodriguez, B. L. (2013). False belief understanding in language impaired and typically developing Spanish seeking preschoolers from lower income backgrounds. Early Education and Development, 24, 517–535. doi:10.1080/10409289.2012.693429 *Hanley, M., Riby, D. M., McCormack, T., Carty, C., Coyle, L., Crozier, N., . . . Robinson, J. (2014). Attention during social interaction in children with autism: Comparison to specific language impairment, typical development, and links to cognition. Research in Autism Spectrum Disorders, 8, 908–924. doi:10.1016/j.rasd.2014.03.020 Happe, F. (1994). An advanced test of theory of mind: Understanding of story characters’ thoughts and feelings by able autistic, mentally handicapped, and normal children and adults. Journal of Autism and Developmental Disorders, 24, 129–154. doi:10.1007/ BF02172093 Harris, P. L. (2005). Conversation, pretense, and theory of mind. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 70–83). New York, NY: Oxford University Press. Henry, L. A., Messer, D. J., & Nash, G. (2012). Executive functioning in children with specific language impairment. Journal of Child Psychology and Psychiatry, 53, 37– 45. doi:10.1111/j.1469-7610.2011.02430.x Higgins, J. P., Thompson, S. G., Deeks, J. J., & Altman, D. G. (2003). Measuring inconsistency in meta-analyses.
152
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British Medical Journal, 327, 557–560. doi:10.1136/ bmj.327.7414.557 *Holmes, A. M. (2002). Theory of mind and behaviour disorders in children with specific language impairment (Doctoral dissertation). Available from Available from ProQuest Dissertations and Theses database. (UMI No. AAINQ64711) Hosozawa, M., Tanaka, K., Shimizu, T., Nakano, T., & Kitazawa, S. (2012). How children with specific language impairment view social situations: An eye tracking study. Pediatrics, 129, e1453–e1460. doi:10.1542/ peds.2011-2278 Hughes, C., Jaffee, S. R., Happe, F., Taylor, A., Caspi, A., & Moffitt, T. E. (2005). Origins of individual differences in theory of mind: From nature to nurture? Child Development, 76, 356–370. doi:10.1111/j.1467-8624.2005.00 850_a.x Knox, E., & Conti-Ramsden, G. (2003). Bullying risks of 11-year-old children with specific language impairment (SLI): Does school placement matter? International Journal of Language & Communication Disorders, 38, 1–12. doi:10.1080/13682820304817 Leonard, L. (1998). Children with specific language impairment. Cambridge, MA: MIT Press. Leonard, L. (2014). Children with specific language impairment and their contribution to the study of language development. Journal of Child Language, 41, 38– 47. doi:10.1017/S0305000914000130 Lohmann, H., & Tomasello, M. (2003). The role of language in the development of false belief understanding: A training study. Child Development, 74, 1130–1144. doi:10.1111/1467-8624.00597 *Loukusa, S., M€akinen, L., Kuusikko-Gauffin, S., Ebeling, H., & Moilanen, I. (2014). Theory of mind and emotion recognition skills in children with specific language impairment, autism spectrum disorder and typical development: Group differences and connection to knowledge of grammatical morphology, word-finding abilities and verbal working memory. International Journal of Language and Communication Disorders, 49, 498– 507. doi:10.1111/1460-6984.12091 McGregor, K. K., Berns, A. J., Owen, A. J., Michels, S. A., Duff, D., Bahnsen, A. J., & Lloyd, M. (2012). Associations between syntax and the lexicon among children with or without ASD and language impairment. Journal of Autism and Developmental Disorders, 42, 35–47. doi:10.1007/s10803-011-1210-4 *Miller, C. A. (2001). False belief understanding in children with specific language impairment. Journal of Communication Disorders, 34, 73–86. doi:10.1016/S0021-9924 (00)00042-3 *Miller, C. A. (2004). False belief and sentence complement performance in children with specific language impairment. International Journal of Language and Communication Disorders, 39, 191–213. doi:10.1080/ 13682820310001616994 Miller, C. A. (2006). Developmental relationships between language and theory of mind. American Journal of
Speech-Language Pathology, 15, 142–154. doi:10.1044/ 1058-0360(2006/014) Miller, S. A. (2009). Children’s understanding of secondorder mental states. Psychological Bulletin, 135, 749–773. doi:10.1037/a0016854 Milligan, K., Astington, J. W., & Dack, L. A. (2007). Language and theory of mind: Meta-analysis of the relation between language ability and false belief understanding. Child Development, 78, 622–646. doi:10.1111/j.14678624.2007.01018.x Moher, D., Liberati, A., Tetzlaff, J., & Altman, D. G., & the PRISMA Group. (2009). Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement. PLoS Medicine, 6. doi:10.1371/journal.pmed1000097 *Norbury, C. F. (2005). The relationship between theory of mind and metaphor: Evidence from children with language impairment and autistic spectrum disorder. British Journal of Developmental Psychology, 23, 383–399. doi:10.1348/026151005X26732 Onishi, K. H., & Baillargeon, R. (2005). Do 15-month-old infants understand false beliefs? Science, 8, 255–258. doi:10.1126/science.1107621 Ontai, L. L., & Thompson, R. A. (2002). Patterns of attachment and maternal discourse effects on children’s emotion understanding from 3 to 5 years of age. Social Development, 11, 433–450. doi:10.1111/1467-9507.00209 Perner, J., Zauner, P., & Sprung, M. (2005). What does “that” have to do with points of view? Conflicting desires and “want” in German. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 220–245). Oxford, UK: Oxford University Press. Peterson, C. C., & Siegal, M. (2000). Insights into theory of mind from deafness and autism. Mind & Language, 15, 123–145. doi:10.1111/1468-0017.00126 Peterson, C. C., Wellman, H. M., & Slaughter, V. (2012). The mind behind the message: Advancing theory-ofmind scales for typically developing children, and those with deafness, autism, or Asperger syndrome. Child Development, 83, 469–485. doi:10.1111/j.14678624.2011.01728 Poll, G. H., Betz, S. K., & Miller, C. A. (2010). Identification of clinical markers of specific language impairment in adults. Journal of Speech, Language, and Hearing Research, 53, 414–429. doi:10.1044/1092-4388(2009/080016) Premack, D., & Woodruff, G. (1978). Does the chimpanzee have a theory of mind? Behavioral and Brain Sciences, 1, 515–526. doi:10.1017/S0140525X00076512 Redmond, S. M. (2011). Victimization among students with specific language impairment, attention-deficit/ hyperactivity disorder, and typical development. Language, Speech, and Hearing Services in Schools, 42, 520– 535. doi:10.1044/0161-1461(2011/10-0078) Ronald, A., Viding, E., Happe, F., & Plomin, R. (2006). Individual differences in theory of mind ability in middle childhood and links with verbal ability and autistic
Theory of Mind in Children With SLI traits: A twin study. Social Neuroscience, 1, 412–425. doi:10.1080/17470910601068088 Rosenthal, R. (1979). The file drawer problem and tolerance for null results. Psychological Bulletin, 86, 638–641. doi:10.1037/0033-2909.86.3.638 Rothstein, H. R., Sutton, A. J., & Borenstein, M. (Eds.). (2005). Publication bias in meta-analysis Prevention, assessment and adjustments. Hoboken, NJ: Wiley. Ruffman, T., Slade, L., & Crowe, E. (2002). The relation between children’s and mothers’ mental state language and theory-of-mind understanding. Child Development, 73, 734–751. doi:10.1111/1467-8624.00435 Russell, T. A., Tchanturia, K., Rahman, Q., & Schmidt, U. (2007). Sex differences in theory of mind: A male advantage on Happe’s “cartoon” task. Cognition & Emotion, 21, 1554–1564. doi:10.1080/02699930601117096 Schick, B., de Villiers, P., de Villiers, J. G., & Hoffmeister, R. (2007). Language and theory of mind: A study of deaf children. Child Development, 78, 376–396. doi:10.1111/j.1467-8624.2007.01004.x Sellabona, E. S., Sanchez, C. R., Majoral, E. V., Guitart, M. E., Caballero, F. S., & Ortiz, J. S. (2013). Labelling improves false belief understanding. A training study. Spanish Journal of Psychology, 16, E6. doi:10.1017/ sjp.2013.8 Sharp, C., & Venta, A. (2012). Mentalizing problems in children and adolescents. In N. Midgley & I. Vrouva (Eds.), Mind the child: Mentalization-based interventions with children, young people and their families (pp. 35–53). London, UK: Routledge. Shields, L., Zhou, H., Pratt, J., Taylor, M., Hunter, J., & Pascoe, E. (2007). Family-centered care for hospitalized children aged 0–12 years. Cochrane Database of Systematic Reviews, 10, CD004811. doi:10.1002/ 14651858.CD004811.pub2 Siegal, M., & Varley, R. (2006). Aphasia, language, and theory of mind. Social Neuroscience, 1, 167–174. doi:10.1080/17470910600985597 Slade, L., & Ruffman, T. (2005). How language does (and does not) relate to theory of mind: A longitudinal study of syntax, semantics, working memory and false belief. British Journal of Developmental Psychology, 23, 117–141. doi:10.1348/026151004X21332 Slaughter, V., Dennis, M. J., & Pritchard, M. (2002). Theory of mind and peer acceptance in preschool children. British Journal of Developmental Psychology, 20, 545–564. doi:10.1348/026151002760390945 *Stich, M. (2010). Theory of mind and pretend play in children with specific language impairment (Doctoral dissertation). Available from ProQuest Dissertations and Theses database. (UMI No. AAINR72302) Tager-Flusberg, H., & Joseph, R. M. (2005). How language facilitates the acquisition of false belief understanding in children with autism. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 298– 319). New York, NY: Oxford University Press. Tomblin, J. B., Records, N. L., Buckwalter, P., Zhang, X., Smith, E., & O’Brien, M. (1997). Prevalence of specific
153
language impairment in kindergarten children. Journal of Speech, Language and Hearing Research, 40, 1245–1260. doi:10.1044/jslhr.4006.1245 *Tucker, L. (2004). Specific language impairment and theory-ofmind: Is normal language development an essential precursor for on time theory-of-mind development? Unpublished manuscript, University of Western Australia, Perth, WA. *van Buijsen, M., Hendriks, A., Ketelaars, M., & Verhoeven, L. (2011). Assessment of theory of mind in children with communication disorders: Role of presentation mode. Research in Developmental Disabilities, 32, 1038–1045. doi:10.1016/j.ridd.2011.01.036 Vernes, S. C., Newbury, D. F., Abrahams, B., Winchester, L., Nicod, J., Groszer, M., . . . Fisher, S. (2008). A functional genetic link between distinct developmental language disorders. New England Journal of Medicine, 359, 2337–2345. doi:10.1056/NEJMoa0802828 Watson, A. C., Nixon, C. L., Wilson, A., & Capage, L. (1999). Social interaction skills and theory of mind in young children. Developmental Psychology, 35, 386–391. doi:10.1037/0012-1649.35.2.386 Wellman, H. M., Cross, D., & Watson, J. (2001). Metaanalysis of theory of mind development: The truth about false belief. Child Development, 72, 655–684. doi:10.1111/1467-8624.00304 Wellman, H. M., & Liu, D. (2004). Scaling of theory-ofmind tasks. Child Development, 75, 523–541. doi:10.1111/j.1467-8624.2004.00691.x Yazdi, A. A., German, T. P., Defeyter, M. A., & Siegal, M. (2006). Competence and performance in belief-desire reasoning across two cultures: The truth, the whole truth and nothing, but the truth about false belief? Cognition, 100, 343–368. doi:10.1016/j.cognition.2005.05.004 Yirmiya, N., Erel, O., Shaked, M., & Solomonica-Levi, D. (1998). Meta-analysis comparing theory of mind abilities in individuals with autism, individuals with mental retardation, and normally developing individuals. Psychological Bulletin, 124, 283–307. doi:10.1037/00332909.124.3.283 *Ziatas, K., Durkin, K., & Pratt, C. (1998). Belief term development in children with autism, Asperger syndrome, specific language impairment and normal development: Links to theory of mind. Journal of Child Psychology and Psychiatry, 39, 755–763. doi:10.1111/1469-7610.00374
Supporting Information Additional supporting information may be found in the online version of this article at the publisher’s website: Figure S1. Flow Diagram of the Search and Inclusion of Studies in the Meta-Analysis (Adapted From PRISMA; Moher et al., 2009) Figure S2. Forest Plot Depicting the Effect Sizes and Related Statistics of the Studies in the MetaAnalysis
Theory of Mind in Children With Specific Language Impairment: A Systematic Review and Meta-Analysis Kristine Kahr Nilsson and Kristine Jensen de L opez Aalborg University
The relation between language and theory of mind (ToM) has been debated for more than two decades. In a similar vein, ToM has been examined in children with specific language impairment (SLI), albeit with inconsistent results. This meta-analysis of 17 studies with 745 children between the ages of 4 and 12 found that children with SLI had substantially lower ToM performance compared to age-matched typically developing children (d = .98). This effect size was not moderated by age and gender. By revealing that children with SLI have ToM impairments, this finding emphasizes the need for further investigation into the developmental interface between language and ToM as well as the extended consequences of atypical language development.
Theory of mind (ToM), which is the ability to attribute mental states to self and others in order to explain behaviors (Premack & Woodruff, 1978), develops gradually during childhood as a sequence of developmental accomplishments (Wellman & Liu, 2004). Joint attention in infancy as well as intentionality and pretend play in toddlerhood have been discussed as early precursors of ToM (Miller, 2006). A marked change toward a more complex ToM occurs around the age of 4 when children become able to pass false-belief tests, which demonstrates knowledge of beliefs as mental entities that can deviate from reality and between individuals (Wellman, Cross, & Watson, 2001). During the school years children begin to master second-order ToM, which entails recursive reasoning about two individuals’ sequential thinking as in “Emma thinks that John thinks” (Miller, 2009). ToM development continues in later childhood and adolescence as evidenced by an increasing understanding of emotional and nonliterate meanings of utterances and behaviors (Choudhury, Blakemore, & Charman, 2006; Peterson, Wellman, & Slaughter, 2012). Research, which suggests that ToM abilities are associated with social skills, peer acceptance, and cooperativeness (Caputi, Lecce, Pagnin, & Banerjee, 2012; Dunn & Cutting, 1999; Slaughter, Dennis, &
We are grateful to the scholars who took time and effort to provide us with additional information to be used in the metaanalysis. Their contribution has been crucial in the making of this review and meta-analysis. Correspondence concerning this article should be addressed to Kristine Kahr Nilsson, Center for Developmental & Applied Psychological Science (CeDAPS), Department of Communication and Psychology, Aalborg University, Aalborg, Denmark. Electronic mail may be sent to [email protected].
Pritchard, 2002; Watson, Nixon, Wilson, & Capage, 1999), emphasizes the potentially adaptive nature of ToM and hence the importance of insights into its developmental underpinnings. Language and ToM Language is one of the most researched developmental domains in relation to ToM. A meta-analysis synthesizing 104 cross-sectional studies found a moderate correlation (r = .43) between children’s performance on language and false-belief tests (Milligan, Astington, & Dack, 2007). Different lines of research furthermore indicate that language may exert a facilitating role in children’s ToM development. For instance, longitudinal studies on preschool children consistently found that language abilities predicted later false-belief performance, whereas false-belief performance did not predict later language abilities (Astington & Jenkins, 1999; de Villiers & Pyers, 2002; Slade & Ruffman, 2005). Likewise, from experimental training studies it emerged that merely exposing children to systematic training on linguistic tasks was sufficient to cause improvement in their false-belief performance (Lohmann & Tomasello, 2003; Sellabona et al., 2013). Further evidence is provided by the consistent finding that deaf children of deaf parents have better ToM abilities than deaf children of hearing parents (Peterson & Siegal, 2000; Schick, de Villiers, de Villiers, & Hoffmeister, 2007), thus emphasizing © 2015 The Authors Child Development © 2015 Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2016/8701-0012 DOI: 10.1111/cdev.12462
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the importance of linguistic environment and especially parent–child communication in facilitating children’s ToM development (Schick et al., 2007). Theoretical perspectives disagree on which aspect of language is essential for ToM development (Astington & Baird, 2005). From the lexical-semantic perspective, it has been argued that the understanding of mental state words, such as want, belief, and think, acquired through conversation with adults, leads children to develop the necessary representations for understanding unobservable mental states in themselves and others (Bartsch & Wellman, 1995). From another perspective, represented by linguistic determinism theory, certain syntactical abilities are essential for the acquisition of ToM. More specifically, children must master the use of tensed complement clauses embedded under believe or communication verbs such as think and say (e.g., “I think Peter is sleeping”) in order to represent events as points of view that can be judged against reality (de Villiers, 2005). Thus, mastering sentential complements is therefore considered a prerequisite for false-belief understanding. From a third perspective, it is not linguistic abilities per se that promote ToM development, but rather the communication that linguistic abilities allow. Proponents of this view argue that conversational exchanges promote ToM development because they expose children to other’s perspectives and convey the fact that such can differ (Dunn & Brophy, 2005; Harris, 2005). Different lines of research have, respectively, supported the importance of mental state vocabulary (e.g., Ruffman, Slade, & Crowe, 2002), sentential complements (e.g., de Villiers & Pyers, 2002), and communicative exchanges (e.g., Ontai & Thompson, 2002) in children’s ToM development. Due to inconclusive results from research comparing these aspects of language, it is still uncertain if any takes precedence in influencing ToM development (e.g., Lohmann & Tomasello, 2003; Sellabona et al., 2013). In contrast to the outlined perspectives, other researchers have questioned the importance of language in ToM development. For instance, Perner, Zauner, and Sprung (2005) argued that children’s conceptual understanding of perspectives precedes their ability to talk about perspectives and therefore doubted a determining role of language in ToM development. Supporting this argument, preferential looking research indicates that toddlers exhibit some understanding of false beliefs before having acquired the linguistic ability to express such beliefs verbally (e.g., Onishi & Baillargeon, 2005). Researchers from the domain-specific approach
have also questioned the importance of language, albeit on different grounds. They have particularly emphasized cases of adults with aphasia who retained their ToM abilities despite severe language impairments as evidence for language and ToM being separate domains (Colle, Baron-Cohen, & Hill, 2007; Siegal & Varley, 2006). As is evident, different views on how language relates to ToM stem from different theoretical assumptions. Although the empirical literature on the relation between ToM and language is extensive and simultaneously supports different views, there has been limited progress toward developing consensus on this subject. Moreover, additional factors potentially influencing the association between language and ToM such as developmental timing and gender have not been adequately considered. Thus, altogether much remains to be understood about the complex connection between language and ToM. Language Impairment and ToM Further empirical evidence on this subject comes from the field of language and speech pathology. A vast amount of research has demonstrated that children with autism spectrum disorder (ASD) have ToM deficits (Yirmiya, Erel, Shaked, & SolomonicaLevi, 1998). There is, however, no agreement on how these ToM deficits relate to the language impairments also found in ASD (e.g., Colle et al., 2007; Durrleman & Franck, 2015). Some research suggests that language abilities and especially sentential complements are linked to the ToM performance of children with ASD (Durrleman & Franck, 2015; Fisher, Happe, & Dunn, 2005). Such findings has led to the speculation that children with ASD rely on linguistic routes as a shortcut for ToM reasoning without employing the social-perceptual processes that typically developing (TD) children use (Fisher et al., 2005; Tager-Flusberg & Joseph, 2005). From this perspective, ASD may not be the most enlightening case for exploring connections between language and ToM that apply to children in general. Another language impairment disorder that has received increasing attention in research on ToM is specific language impairment (SLI). Children are diagnosed with SLI when they display marked language impairments on standardized tests, despite normal nonverbal intelligence and no apparent neurological or sensory dysfunction (Leonard, 1998). SLI has been found to be prevalent affecting approximately 7% of children in kindergarten (Tomblin et al., 1997). Ample evidence further sug-
Theory of Mind in Children With SLI
gests that SLI often persists into adulthood (e.g., Poll, Betz, & Miller, 2010). The causes of SLI are unknown, but are likely to include a heritable component (Bishop, 2006). As the term indicates, SLI is defined specifically by language impairments. According to Leonard (2014), this specificity makes SLI an optimal natural experiment for investigating language development. More specifically, by exemplifying what happens to development when language is critically delayed, SLI elucidates the importance of language for children’s broader development across different domains. Thus, from this perspective, SLI may be used as a methodological vantage point for exploring the developmental interface between language and ToM. Furthermore, as SLI involves different types of language impairments, including deficits in lexical semantics, syntax, and pragmatics (e.g., Bishop, Chan, Adams, Hartley, & Weir, 2000; McGregor et al., 2012), research on SLI may also inform the debate on how language influences ToM development. Yet, before embarking upon such endeavors, a necessary initial step is to provide an overall evaluation of the ToM abilities of children with SLI. Studies unambiguously indicate that children with SLI have better ToM abilities than children with ASD (e.g., Loukusa, M€akinen, Kuusikko-Gauffin, Ebeling, & Moilanen, 2014; Ziatas, Durkin, & Pratt, 1998). However, whether children with SLI differ from TD children is unclear. In some studies, children with SLI were found to have lower ToM abilities than TD children (e.g., Andres-Roqueta, Adrian, Clemente, & Katsos, 2013; Farrant, Fletcher, & Maybery, 2006), whereas in other studies no such difference emerged (e.g., Farmer, 2000; Miller, 2001; Ziatas et al., 1998). The conclusions drawn from these studies were all based on statistical significance, despite the fact that many had very small samples and therefore low statistical power to detect significant results. In order to overcome this limitation and clarify if and to what extent children with SLI have ToM impairments, we conducted a systematic review and meta-analysis of studies comparing TD children and children with SLI in terms of ToM performance. Due to the inconsistency of past studies, we did not adopt any prior hypotheses about the direction or magnitude of the effect. To further understand the result of the meta-analysis, two moderator analyses were also conducted. Previous findings suggest that the association between language and ToM increases as children’s ToM understanding progresses (Grazzani & Ornaghi, 2012; Peterson et al., 2012). Thus, language abilities may
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exert a stronger influence on ToM abilities when such become advanced. On this account, any potential gap in ToM abilities between children with SLI may be assumed to widen with age and age was therefore analyzed as a moderator of the differences between the two groups. Emerging research points to gender differences in ToM including different brain activity patterns during ToM reasoning (Frank, Baron-Cohen, & Ganzel, 2015) and different performance profiles on ToM tests with some tests favoring females (e.g., Calero, Salles, Semelman, & Sigman, 2013) and others males (e.g., Russell, Tchanturia, Rahman, & Schmidt, 2007). In consideration of such findings, as well as the higher prevalence of SLI in boys than girls (Tomblin et al., 1997), the role of gender was investigated in a second moderator analysis.
Method In order to ensure transparency and methodological quality, the systematic review and meta-analysis followed the recommendations proposed by Preferred Reporting Items for Systematic Reviews and Meta-Analysis (Moher, Liberati, Tetzlaff, & Altman, 2009). Search Strategies An extensive literature search was performed, incorporating different search strategies. Initially, the databases PsychInfo and PubMed were searched using different related terms in order to increase the sensitivity of the search. The terms SLI, developmental language disorder, developmental dysphasia, and speech, language, and communication needs were entered separately in combination with each of the following subject words: theory of mind, false belief, mental states, and mentalize, which in some studies has been used synonymously with ToM (e.g., Sharp & Venta, 2012). Thereafter, reference lists from the collected articles as well as from review articles and books on the subject were examined for potentially eligible studies. Finally, the Internet was searched with the specific aim of identifying unpublished studies and studies accepted for publication and in press. The searches covered all previously published studies from the first available date until March 11, 2015, when the last search was conducted. Only documents written in English were considered. Study eligibility and quality were assessed by the two authors independently and inclusion of studies was based on consensus.
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Inclusion Criteria To be included in the review, studies were required to meet the following five inclusion criteria. First, the studies had to compare children with SLI and TD children in terms of ToM performance. Second, the diagnosis of SLI was required to meet the aforementioned criteria proposed by Leonard (1998). Third, the two comparison groups were required to be matched in terms of chronological age. Fourth, the participants had to be children. In agreement with other systematic reviews (e.g., Shields et al., 2007), a mean age of 12 was used as a cutoff age for childhood marking the approximate starting point of puberty. Fifth, the statistical information required for the computation of effect size (e.g., samples sizes, means, and standard deviations) had to be available either in the published material or upon request to the respective authors. Coding For the studies meeting the inclusion criteria, the following information was coded: (a) country of study; (b) sample size, mean age, and gender distribution in the SLI and TD samples, respectively; (c) ToM test(s), which were grouped into the following three categories: (i) false-belief tests, which were differentiated by subtypes partially inspired by the coding scheme used by Milligan et al. (2007), (ii) advanced ToM tests such as the Strange Stories Test (Happe, 1994), and (iii) multiple ToM tests involving five or more different task types, such as the Theory-of-Mind Scale (Wellman & Liu, 2004); and (d) statistical information for computing effect sizes. If the studies contained results from more than one ToM test, composite scores were used. Data Analysis The meta-analysis was performed using Comprehensive Meta-Analysis Version II (Borenstein, Hedges, Higgins, & Rothstein, 2004). The statistical results from all the included studies were converted into Cohen’s d, also known as standardized mean difference. For interpretation of the effect sizes, the conventional definitions were used, d = .20, small; d = .50, medium; and d = .80, large (Cohen, 1988). The directions of the results were quantified as negative and positive mean effect sizes indicating, respectively, lower and higher ToM performance in the children with SLI compared to TD children. There are two main computational models in meta-
analysis. One is the fixed effect model (FEM), which assumes that studies’ results reflect a true mean and that variation is due to sampling error alone. The other is the random effects model (REM), which infers that variation across findings reflects real differences between studies, but that an overall mean can be estimated by accounting for this heterogeneity. Accordingly, the REM accounts for both withinand between-study variability, whereas the FEM only accounts for the former (Borenstein, Hedges, Higgins, & Rothstein, 2009). When there are many potential sources of heterogeneity, as there often are in psychological research with children, the REM is considered appropriate. The REM was therefore selected as the computational model for the present review, although results from both models were presented for transparency. The moderator analyses of age and gender were performed using REM metaregression analyses. Both of these variables were treated as continuous moderators with gender quantified as the percentage of females in the sample. Heterogeneity was assessed using the Q statistic, which evaluates whether the distribution of effect sizes is homogeneous, and the I2 statistic, which estimates the proportion of variance due to between-study heterogeneity. As recommended by Higgins, Thompson, Deeks, and Altman (2003), I2 values around 25%, 50%, and 75% were interpreted as a low, medium, and high levels of heterogeneity, respectively. Publication bias is a serious threat to the validity of systematic reviews and meta-analyses and should therefore be considered carefully. It occurs when the results of published research are systematically unrepresentative of the results from all of the research that has been conducted on the subject (Rothstein, Sutton, & Borenstein, 2005). Such bias is commonly reflected by the fact that statistically significant findings are more likely to be published than nonsignificant findings (Easterbrook, Berlin, Gopalan, & Matthews, 1991). A number of graphical and statistical procedures have been developed with the aim of assessing publication bias. For this review, publication bias was assessed in two ways. First, the fail-safe number method was used to estimate the number of unpublished studies with mean effects of zero that would cause the mean effect size to drop to a nonsignificant level (Rosenthal, 1979). A satisfactory fail-safe number is required to exceed Rosenthal’s (1979) tolerance level, which is the number of included studies times 5 plus 10 (5k + 10). Second, publication bias was examined with inferential statistics using Begg’s test and Egger’s test. Both of these tests assess funnel plot
Theory of Mind in Children With SLI
asymmetry, which is assumed to imply the presence of publication bias.
Results Results of the Literature Search A flowchart that visually depicts the search process is provided in Figure S1 in the online Supporting Information. Once duplicates had been removed, the search produced 63 records. A screening of all titles and abstracts identified 28 studies potentially eligible for inclusion. Of these studies, 19 initially met the inclusion criteria. However, for 2 of them additional information required for the computation of effect sizes could not be obtained. Thus, in total, 17 studies were included in the meta-analysis. The information coded for each of these studies is presented in Table 1. The total sample comprised 745 children of which 329 were children, with SLI and 416 were TD children. Four of the studies were published in dissertations (Goldman, 2002; Holmes, 2002; Stich, 2010; Tucker, 2004) and the rest in international peer-reviewed journals. In most of the studies, false-belief tests were used as measures of ToM abilities. As described in Table 1, the research in this meta-analysis was conducted across eight different countries: Australia, Canada, Finland, Germany, Holland, Spain, the United Kingdom, and the United States. Results of the Meta-Analysis A forest plot containing a detailed breakdown of each of the studies’ effect size statistics is presented in Figure S2 in the online Supporting Information. Although the effect sizes varied, they all pointed in the same direction, with lower ToM performance in children with SLI compared to TD children. The results for the two computational models are presented in Table 2. The REM showed that children with SLI had significantly lower ToM performance compared to TD children (p < .001) and that the effect size for this difference was large (d = .98). Although mathematically different, the FEM produced a comparable result (p < .001, d = .96). The distribution of effect sizes was found to be heterogeneous (Q = 35.74, p = .003) with a medium proportion of between-study heterogeneity (I2 = 55.23%). The REM metaregression analyses revealed that neither age (z = .835, p = .404) nor gender (z = .270, p = .788) was a significant moderator of the studies’ effect sizes. Additional tests supported the validity of the results. The tests of funnel plot
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asymmetry, Egger’s test (p = .530) and Begg’s test (p = .564), were both nonsignificant, hence indicating a low probability of publication bias. Furthermore, the computed fail-safe number was found to be 599, which greatly exceeded Rosenthal’s tolerance level of 95 for this metaanalysis.
Discussion This empirical review revealed that children with SLI have substantially lower ToM performance than age-matched TD children. Age and gender did not emerge as moderators and therefore did not provide any additional explanation of the result. From the perspective of atypical development, the finding of the meta-analysis lends further support for an association between language and ToM. Moreover, as SLI can be conceived as exemplifying development under the condition of critical language delays (Leonard, 2014), it also suggests that there is a potential interface between language and ToM development where impairment in one domain extends into the other. On a more general level, this finding can therefore be interpreted as emphasizing the importance of normal language development in promoting ageappropriate ToM abilities. Considering the specificity of SLI, language impairment offers the most immediate explanation of lower ToM abilities in children with SLI. The exact mechanism through which language impairment influences ToM development in these children cannot, however, be inferred due to the lack of longitudinal investigations on this subject. Studies documenting moderate to strong associations between language and ToM within samples of children with SLI, nevertheless, support a link between these domains in this population (Andres-Roqueta et al., 2013; Farmer, 2000; Farrar et al., 2009; Holmes, 2002; Stich, 2010). In two of these studies, specific linguistic correlates of ToM were also examined, hence informing the unsettled debate on this subject (e.g., Astington & Baird, 2005). Regression analyses revealed that grammatical ability was the strongest linguistic predictor of ToM performance in children with SLI (Andres-Roqueta et al., 2013; Farrar et al., 2009). Thus, grammatical difficulties that are prevalent in SLI (Bishop, 2014) may be implicated in the ToM impairments of these children. Importantly, though, as the measures of grammatical ability employed in these studies encompass both receptive and expressive grammar, they may tap into
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Table 1 Studies Comparing Children With Specific Language Impairment (SLI) and Typically Developing (TD) Children in Terms of Theory of Mind (ToM) Performance Sample characteristics SLI Study
Country
TD
n
Age (M)
Females (n)
n
Age (M)
Females (n)
Type of ToM task
Andres-Roqueta et al. (2013) Farmer (2000)
Spain
31
5.40
12
31
5.40
12
False beliefs: CL, UI
United Kingdom
16
10.55
1
8
11.04
3
Farrant et al. (2006) Farrant, Maybery, and Fletcher (2012) Gillott, Furniss, and Walter (2004) Goldman (2002) Guiberson and Rodriguez (2013) Hanley et al. (2014) Holmes (2002)
Australia Australia
20 30
5.24 5.25
7 4
20 90
5.10 5.12
8 46
False beliefs: SO Advanced ToM Multiple ToM False beliefs: SO, UI
United States
15
10.25
2
15
10.26
2
United States United States
12 22
11.17 4.25
3 6
12 24
10.91 4.41
3 10
False beliefs: CL, UI False beliefs: UI
United Kingdom Canada
14 43
9.60 6.15
2 15
16 49
9.97 6.02
10 23
Loukusa et al. (2014) Miller (2001) Miller (2004) Norbury (2005) Stich (2010) Tucker (2004) van Buijsen et al. (2011) Ziatas et al. (1998)
Finland United Kingdom United Kingdom United Kingdom Germany Australia Holland Australia
18 10 15 12 22 10 27 12
6.20 5.60 4.92 10.87 6.86 4.05 6.70 6.92
5 1 5 1 9 2 9 4
25 10 15 30 22 10 27 12
6.07 5.60 5.00 10.36 6.99 4.07 6.70 6.42
5 5 8 14 9 0 11 4
False beliefs: BD, CL, UI False beliefs: CL, SO Advanced ToM Multiple ToM False beliefs: CL False beliefs: CL False beliefs: SO Multiple ToM False beliefs: CL, UI False beliefs: BD, CL, UI False beliefs: CL
Advanced ToM
Note. False-belief tests: BD = belief–desire; CL = change of location; SO = second order; UI = unexpected identity.
Table 2 Results From the Random Effects Model and the Fixed Effect Model
Model:
Random effects model Fixed effect model
Number of studies (k)
Sample size SLI/TD (n)
17 17
329/416 329/416
Mean weighted effect size (d)
.98 .96
95% CI lower/ upper limits
1.23/ 0.74 1.12/ 0.80
z score
7.88 11.92
p
< .001 < .001
Note. SLI = specific language impairment; TD = typically developing.
general language abilities rather than any discrete linguistic ability. Thus, narrower and more independent measures of language are required before any specific mechanism can be identified. While the presented studies may give the impression that language and ToM are straightforwardly connected, they may not necessarily be if their connection is better explained by a common denominator. Despite being defined by nonverbal intelligence within the normal range, SLI has in
recent years been associated with general processing difficulties such as executive function deficits (Henry, Messer, & Nash, 2012), although these may be confined to the verbal modality (Archibald & Gathercole, 2007). In two studies within this metaanalysis, executive functioning (i.e., sustained attention and working memory) correlated significantly with ToM performance in the children with SLI. Nevertheless, when executive functioning and general linguistic abilities were analyzed simultane-
Theory of Mind in Children With SLI
ously, general linguistic abilities emerged as the strongest predictor of ToM performance (AndresRoqueta et al., 2013; Holmes, 2002). Accordingly, language impairments may provide a more satisfactory explanation of ToM impairments in children with SLI compared to the executive function deficits also found in these children. Among other common denominators potentially underlying both language and ToM impairments are etiological mechanisms. In twin studies, the association between ToM and verbal ability was found to be attributable to a common effects of shared genes as well as shared environment (Hughes et al., 2005; Ronald, Viding, Happe, & Plomin, 2006). Impairments in language and ToM may therefore be conjoined in SLI through shared genetic and environmental effects. As regards the genetic component, it is noteworthy that variants within the CNTNAP2 gene confer increased risk of both SLI and ASD (Alarc on et al., 2008; Vernes et al., 2008). However, whether the ToM impairments in SLI are attributable to an etiological overlap with ASD (i.e., a disorder defined by ToM deficits) is contentious due to the unclear overlap between these disorders (Bishop, 2010). When interpreting the findings of this review, some methodological aspects merit consideration. While ToM tests claim to tap into an underlying ToM competence, it has been argued that performance factors may interfere with this objective (e.g., Yazdi, German, Defeyter, & Siegal, 2006). In research on SLI, it is particularly relevant to consider any potential constraints posed by verbal aspects of a given test or experiment. The linguistic demands of the ToM tests administered in included studies may, however, not have compromised the results for a number of reasons. First, the verbal instructions were generally simple and usually supplemented by visual aids such as pictograms, drawings, and video clips. Second, initial pretests or control questions were employed to verify the children’s memory capabilities and comprehension of the tasks. Accordingly, the children with SLI presumably met the requirements of the administered ToM tests. Third, to further address this issue some of the included studies compared the children’s performances across verbal and less verbal ToM tasks. Children with SLI performed better on some of the less verbal ToM tasks, although some results went against this pattern (Miller, 2001, 2004; van Buijsen, Hendriks, Ketelaars, & Verhoeven, 2011). Moreover, in the study by Holmes (2002), children with SLI were found to be equally different from the TD children on verbal and less verbal ToM tasks. Thus, altogether, no consistent patterns were found.
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When taking all of these aspects into consideration, the finding of this review most likely indicates that children with SLI have real ToM impairments that cannot be explained by the verbal demands of ToM tests. Deficit or Delay? Tager-Flusberg and Joseph (2005) differentiate between two components of ToM: a social-perceptual component, which is the innate preference for human stimuli, and a social-cognitive component, which is the ability to draw inferences about mental phenomena by integrating different kinds of information. Moreover, they argue that the ToM impairments in children with ASD are due to deficits within the social-perceptual component. In light of the present finding, it is relevant to question whether the same applies to SLI. Two studies that bear upon this question found that children with SLI and TD children exhibited similar eye gaze patterns when viewing social situations, whereas children with ASD exhibited a markedly different gaze pattern with less attention to faces and gazes shifting to the periphery of social scenes (Hanley et al., 2014; Hosozawa, Tanaka, Shimizu, Nakano, & Kitazawa, 2012). Thus, the ToM impairments of children with SLI may not be attributable to profound deficits in social perception, as it appears to be the case in children with ASD. In a similar vein, some of the studies included in the meta-analysis found that the ToM performance of children with SLI was comparable to an additional control group consisting of languagematched children of a younger age (Andres-Roqueta et al., 2013; Miller, 2001, 2004; Ziatas et al., 1998). These results were interpreted as suggesting that the lower ToM abilities in children with SLI reflect a developmental delay rather than a developmental deficit. Although this interpretation seems persuasive, it should be noted that developmental delays vary in degree and complexity. The ToM impairments in SLI may not be just a temporary lag. In two studies, adolescents and adults who had been diagnosed with SLI as children exhibited markedly lower ToM abilities than age-matched TD controls (Botting & Conti-Ramsden, 2008; Clegg, Hollis, Mawhood, & Rutter, 2005). Thus, the ToM impairments of children with SLI may potentially become an enduring characteristic that extends beyond childhood. Furthermore, as ToM is considered a crucial tool for understanding social situations (Astington, 2001), the ToM impairments of children with SLI may conceivably play a role in their poorer social outcomes such as their tendency to have poorer social skills
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(Fujiki, Brinton, & Todd, 1996), be more socially withdrawn (Fujiki, Brinton, Hart, & Fitzgerald, 1999), and be at a higher risk of peer victimization (Redmond, 2011) and bullying (Knox & Conti-Ramsden, 2003). Thus, further investigations into the concurrent and longitudinal consequences of ToM impairments in children with SLI are warranted. Conclusion This empirical review demonstrates that children with SLI perform considerably below the level of age-matched TD children on ToM tests. This finding therefore supports an association between language and ToM from the perspective of atypical development. Furthermore, it also questions the boundaries of SLI as a language disorder and calls for further research into the developmental interface between language and ToM as well as the potentially extended consequences of language impairments. The finding of this review also merits clinical consideration. Previous studies, involving TD children and children with ASD, found that ToM abilities can be improved with systematic training (e.g., Gevers, Clifford, Mager, & Boer, 2006; Lohmann & Tomasello, 2003; Sellabona et al., 2013). Similar interventions aiming to improve the ToM abilities of children with SLI may be contemplated as an adjunct to conventional language programs. References References marked with an asterisk indicate studies included in the meta-analysis. Alarc on, M., Abrahams, B. S., Stone, J. L., Duvall, J. A., Perederiy, J. V., Bomar, J. M., & Geschwind, D. H. (2008). Linkage, association, and gene-expression analyses identify CNTNAP2 as an autism susceptibility gene. American Journal of Human Genetics, 82, 150–159. doi:10.1016/ j.ajhg.2007.09.005 *Andres-Roqueta, C., Adrian, J. E., Clemente, R. A., & Katsos, N. (2013). Which are the best predictors of theory of mind delay in children with specific language impairment? International Journal of Language & Communication Disorders, 48, 726–737. doi:10.1111/1460-6984.12045 Archibald, L., & Gathercole, S. (2007). The complexities of complex memory span: Storage and processing deficits in specific language impairment. Journal of Memory and Language, 57, 177–194. doi:10.1016/j.jml.2006.11.004 Astington, J. W. (2001). The future of theory-of-mind research: Understanding motivational states, the role of language, and real-world consequences. Commentary on “Meta-analysis of theory-of-mind development: The truth about false belief.” Child Development, 72, 685–687. doi:10.1111/1467-8624.00305
Astington, J. W., & Baird, J. A. (2005). Introduction: Why language matters. In J. W. Astington & J. Baird (Eds.), Why language matters for theory of mind (pp. 3–25). New York, NY: Oxford University Press. Astington, J. W., & Jenkins, J. M. (1999). A longitudinal study of the relation between language and theory-ofmind development. Developmental Psychology, 35, 1311– 1320. doi:10.1037/0012-1649.35.5.1311 Bartsch, K., & Wellman, H. M. (1995). Children talk about the mind. Oxford, UK: Oxford University Press. Bishop, D. V. M. (2006). What causes specific language impairment in children? Current Directions in Psychological Science, 15, 217–221. doi:10.1111/j.1467-8721.2006. 00439.x Bishop, D. V. M. (2010). Overlaps between autism and language impairment: Phenomimicry or shared etiology? Behavior Genetics, 40, 618–629. doi:10.1007/s10519010-9381-x Bishop, D. V. M. (2014). Problems with tense marking in children with specific language impairment: Not how but when. Philosophical Transactions of the Royal Society, Biological Science, 369, 1–8. doi:10.1098/rstb.2012.0401 Bishop, D. V. M., Chan, J., Adams, C., Hartley, J., & Weir, F. (2000). Conversational responsiveness in specific language impairment: Evidence of disproportionate pragmatic difficulties in a subset of children. Development and Psychopathology, 12, 177–199. doi:10.1017/S09545794 00002042 Borenstein, M., Hedges, L., Higgins, J., & Rothstein, H. (2004). Comprehensive meta-analysis version 2: A computer program for research synthesis [Computer software]. Englewood, NJ: Biostat. Borenstein, M., Hedges, L. V., Higgins, J., & Rothstein, H. R. (2009). Introduction to meta-analysis. Chichester, UK: Wiley. Botting, N., & Conti-Ramsden, G. (2008). The role of language, social cognition, and social skill in the functional social outcomes of young adolescents with and without a history of SLI. British Journal of Developmental Psychology, 26, 281–300. doi:10.1348/026151007X235891 Calero, C. I., Salles, A., Semelman, M., & Sigman, M. (2013). Age and gender dependent development of theory of mind in 6- to 8-years old children. Frontiers in Human Neuroscience, 7, 281. doi:10.3389/fnhum.2013. 00281 Caputi, M., Lecce, S., Pagnin, A., & Banerjee, R. (2012). Longitudinal effects of theory of mind on later peer relations: The role of prosocial behavior. Developmental Psychology, 48, 257–270. doi:10.1037/a0025402 Choudhury, S., Blakemore, S., & Charman, T. (2006). Social cognitive development during adolescence. Social Cognitive and Affective Neuroscience, 1, 165–174. doi:10. 1093/scan/nsl024 Clegg, J., Hollis, C., Mawhood, L., & Rutter, M. (2005). Developmental language disorders: A follow-up in later adult life. Cognitive, language and psychosocial outcomes. Journal of Child Psychology and Psychiatry, 46, 128–149. doi:10.1111/j.1469-7610.2004.00342.x
Theory of Mind in Children With SLI Cohen, J. (1988). Statistical power analysis for the behavioral sciences. Hillsdale, NJ: Erlbaum. Colle, L., Baron-Cohen, S., & Hill, J. (2007). Do children with autism have a theory of mind? A non-verbal test of autism vs. specific language impairment. Journal of Autism and Developmental Disorders, 37, 716–723. doi:10.1007/s10803-006-0198-7 de Villiers, J. G. (2005). Can language acquisition give children a point of view? In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 186–219). New York, NY: Oxford University Press. de Villiers, J. G., & Pyers, J. E. (2002). Complements to cognition: A longitudinal study of the relationship between complex syntax and false-belief-understanding. Cognitive Development, 17, 1037–1060. doi:10.1016/ S0885-2014(02)00073-4 Dunn, J., & Brophy, M. (2005). Communication, relationships, and individual differences in children’s understanding of mind. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 50– 69). Oxford, UK: Oxford University Press. Dunn, J., & Cutting, A. L. (1999). Understanding others, and individual differences in friendship interactions in young children. Social Development, 8, 201–219. doi:10.1111/1467-9507.00091 Durrleman, S., & Franck, J. (2015). Exploring links between language and cognition in autism spectrum disorders: Complement sentences, false belief, and executive functioning. Journal of Communication Disorders, 54, 15–31. doi:10.1016/j.jcomdis.2014.12.001 Easterbrook, P. J., Berlin, J. A., Gopalan, R., & Matthews, D. R. (1991). Publication bias in clinical research. Lancet, 337, 867–872. doi:10.1016/0140-6736(91)90201-Y *Farmer, M. (2000). Language and social cognition in children with specific language impairment. Journal of Child Psychology and Psychiatry, 42, 627–636. doi:10.1111/ 1469-7610.00649 *Farrant, B., Fletcher, J., & Maybery, M. (2006). Specific language impairment, theory of mind, and visual perspective taking: Evidence for simulation theory and the developmental role of language. Child Development, 77, 1842–1853. doi:10.1111/j.1467-8624.2006.00977 *Farrant, B. M., Maybery, M. T., & Fletcher, J. (2012). Language, cognitive flexibility, and explicit false belief understanding: Longitudinal analysis in typical development and specific language impairment. Child Development, 83, 223–235. doi:10.1111/j.1467-8624.2011.01681.x Farrar, M. J., Johnson, B., Tompkins, V., Easters, M., Zilisi-Medus, A., & Bengino, J. P. (2009). Language and theory of mind in preschool children with specific language impairment. Journal of Communication Disorders, 42, 428–441. doi:10.1016/j.jcomdis.2009.07.001 Fisher, N., Happe, F., & Dunn, J. (2005). The relationship between vocabulary, grammar, and false belief task performance in children with autistic spectrum disorders and children with moderate learning difficulties. Journal of Child Psychology and Psychiatry, 46, 409–419. doi:10.1111/j.1469-7610.2004.00371.x
151
Frank, C. K., Baron-Cohen, S., & Ganzel, B. L. (2015). Sex differences in the neural basis of false-belief and pragmatic language comprehension. NeuroImage, 15, 300– 311. doi:10.1016/j.neuroimage.2014.09.041 Fujiki, M., Brinton, B., Hart, C. H., & Fitzgerald, A. H. (1999). Peer acceptance and friendship in children with specific language impairment. Topics in Language Disorders, 19, 34–48. doi:10.1097/00011363-199902000-00005 Fujiki, M., Brinton, B., & Todd, C. M. (1996). Social skills of children with specific language impairment. Language, Speech, and Hearing Services in Schools, 27, 195– 202. doi:10.1044/0161-1461.2703.195 Gevers, C., Clifford, P., Mager, M., & Boer, F. (2006). A theory-of-mind-based social-cognition training program for school-aged children with pervasive developmental disorders: An open study of its effectiveness. Journal of Autism and Developmental Disorders, 36, 567–571. doi:10.1007/s10803-006-0095-0 *Gillott, A., Furniss, F., & Walter, A. (2004). Theory of mind ability in children with specific language impairment. Child Language Teaching and Therapy, 20, 1–11. doi:10.1191/0265659004ct260oa *Goldman, S. (2002). Unshared lives: Fictional and personal narrative productions in high-functioning autistic children (Doctoral dissertation). Available from ProQuest Dissertations and Theses Database. (UMI No. 3047222) Grazzani, I., & Ornaghi, V. (2012). How do use and comprehension of mental-state language relate to theory of mind in middle childhood? Cognitive Development, 27, 99–111. doi:10.1016/j.cogdev.2012.03.002 *Guiberson, M., & Rodriguez, B. L. (2013). False belief understanding in language impaired and typically developing Spanish seeking preschoolers from lower income backgrounds. Early Education and Development, 24, 517–535. doi:10.1080/10409289.2012.693429 *Hanley, M., Riby, D. M., McCormack, T., Carty, C., Coyle, L., Crozier, N., . . . Robinson, J. (2014). Attention during social interaction in children with autism: Comparison to specific language impairment, typical development, and links to cognition. Research in Autism Spectrum Disorders, 8, 908–924. doi:10.1016/j.rasd.2014.03.020 Happe, F. (1994). An advanced test of theory of mind: Understanding of story characters’ thoughts and feelings by able autistic, mentally handicapped, and normal children and adults. Journal of Autism and Developmental Disorders, 24, 129–154. doi:10.1007/ BF02172093 Harris, P. L. (2005). Conversation, pretense, and theory of mind. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 70–83). New York, NY: Oxford University Press. Henry, L. A., Messer, D. J., & Nash, G. (2012). Executive functioning in children with specific language impairment. Journal of Child Psychology and Psychiatry, 53, 37– 45. doi:10.1111/j.1469-7610.2011.02430.x Higgins, J. P., Thompson, S. G., Deeks, J. J., & Altman, D. G. (2003). Measuring inconsistency in meta-analyses.
152
Kahr Nilsson and Jensen de L opez
British Medical Journal, 327, 557–560. doi:10.1136/ bmj.327.7414.557 *Holmes, A. M. (2002). Theory of mind and behaviour disorders in children with specific language impairment (Doctoral dissertation). Available from Available from ProQuest Dissertations and Theses database. (UMI No. AAINQ64711) Hosozawa, M., Tanaka, K., Shimizu, T., Nakano, T., & Kitazawa, S. (2012). How children with specific language impairment view social situations: An eye tracking study. Pediatrics, 129, e1453–e1460. doi:10.1542/ peds.2011-2278 Hughes, C., Jaffee, S. R., Happe, F., Taylor, A., Caspi, A., & Moffitt, T. E. (2005). Origins of individual differences in theory of mind: From nature to nurture? Child Development, 76, 356–370. doi:10.1111/j.1467-8624.2005.00 850_a.x Knox, E., & Conti-Ramsden, G. (2003). Bullying risks of 11-year-old children with specific language impairment (SLI): Does school placement matter? International Journal of Language & Communication Disorders, 38, 1–12. doi:10.1080/13682820304817 Leonard, L. (1998). Children with specific language impairment. Cambridge, MA: MIT Press. Leonard, L. (2014). Children with specific language impairment and their contribution to the study of language development. Journal of Child Language, 41, 38– 47. doi:10.1017/S0305000914000130 Lohmann, H., & Tomasello, M. (2003). The role of language in the development of false belief understanding: A training study. Child Development, 74, 1130–1144. doi:10.1111/1467-8624.00597 *Loukusa, S., M€akinen, L., Kuusikko-Gauffin, S., Ebeling, H., & Moilanen, I. (2014). Theory of mind and emotion recognition skills in children with specific language impairment, autism spectrum disorder and typical development: Group differences and connection to knowledge of grammatical morphology, word-finding abilities and verbal working memory. International Journal of Language and Communication Disorders, 49, 498– 507. doi:10.1111/1460-6984.12091 McGregor, K. K., Berns, A. J., Owen, A. J., Michels, S. A., Duff, D., Bahnsen, A. J., & Lloyd, M. (2012). Associations between syntax and the lexicon among children with or without ASD and language impairment. Journal of Autism and Developmental Disorders, 42, 35–47. doi:10.1007/s10803-011-1210-4 *Miller, C. A. (2001). False belief understanding in children with specific language impairment. Journal of Communication Disorders, 34, 73–86. doi:10.1016/S0021-9924 (00)00042-3 *Miller, C. A. (2004). False belief and sentence complement performance in children with specific language impairment. International Journal of Language and Communication Disorders, 39, 191–213. doi:10.1080/ 13682820310001616994 Miller, C. A. (2006). Developmental relationships between language and theory of mind. American Journal of
Speech-Language Pathology, 15, 142–154. doi:10.1044/ 1058-0360(2006/014) Miller, S. A. (2009). Children’s understanding of secondorder mental states. Psychological Bulletin, 135, 749–773. doi:10.1037/a0016854 Milligan, K., Astington, J. W., & Dack, L. A. (2007). Language and theory of mind: Meta-analysis of the relation between language ability and false belief understanding. Child Development, 78, 622–646. doi:10.1111/j.14678624.2007.01018.x Moher, D., Liberati, A., Tetzlaff, J., & Altman, D. G., & the PRISMA Group. (2009). Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement. PLoS Medicine, 6. doi:10.1371/journal.pmed1000097 *Norbury, C. F. (2005). The relationship between theory of mind and metaphor: Evidence from children with language impairment and autistic spectrum disorder. British Journal of Developmental Psychology, 23, 383–399. doi:10.1348/026151005X26732 Onishi, K. H., & Baillargeon, R. (2005). Do 15-month-old infants understand false beliefs? Science, 8, 255–258. doi:10.1126/science.1107621 Ontai, L. L., & Thompson, R. A. (2002). Patterns of attachment and maternal discourse effects on children’s emotion understanding from 3 to 5 years of age. Social Development, 11, 433–450. doi:10.1111/1467-9507.00209 Perner, J., Zauner, P., & Sprung, M. (2005). What does “that” have to do with points of view? Conflicting desires and “want” in German. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 220–245). Oxford, UK: Oxford University Press. Peterson, C. C., & Siegal, M. (2000). Insights into theory of mind from deafness and autism. Mind & Language, 15, 123–145. doi:10.1111/1468-0017.00126 Peterson, C. C., Wellman, H. M., & Slaughter, V. (2012). The mind behind the message: Advancing theory-ofmind scales for typically developing children, and those with deafness, autism, or Asperger syndrome. Child Development, 83, 469–485. doi:10.1111/j.14678624.2011.01728 Poll, G. H., Betz, S. K., & Miller, C. A. (2010). Identification of clinical markers of specific language impairment in adults. Journal of Speech, Language, and Hearing Research, 53, 414–429. doi:10.1044/1092-4388(2009/080016) Premack, D., & Woodruff, G. (1978). Does the chimpanzee have a theory of mind? Behavioral and Brain Sciences, 1, 515–526. doi:10.1017/S0140525X00076512 Redmond, S. M. (2011). Victimization among students with specific language impairment, attention-deficit/ hyperactivity disorder, and typical development. Language, Speech, and Hearing Services in Schools, 42, 520– 535. doi:10.1044/0161-1461(2011/10-0078) Ronald, A., Viding, E., Happe, F., & Plomin, R. (2006). Individual differences in theory of mind ability in middle childhood and links with verbal ability and autistic
Theory of Mind in Children With SLI traits: A twin study. Social Neuroscience, 1, 412–425. doi:10.1080/17470910601068088 Rosenthal, R. (1979). The file drawer problem and tolerance for null results. Psychological Bulletin, 86, 638–641. doi:10.1037/0033-2909.86.3.638 Rothstein, H. R., Sutton, A. J., & Borenstein, M. (Eds.). (2005). Publication bias in meta-analysis Prevention, assessment and adjustments. Hoboken, NJ: Wiley. Ruffman, T., Slade, L., & Crowe, E. (2002). The relation between children’s and mothers’ mental state language and theory-of-mind understanding. Child Development, 73, 734–751. doi:10.1111/1467-8624.00435 Russell, T. A., Tchanturia, K., Rahman, Q., & Schmidt, U. (2007). Sex differences in theory of mind: A male advantage on Happe’s “cartoon” task. Cognition & Emotion, 21, 1554–1564. doi:10.1080/02699930601117096 Schick, B., de Villiers, P., de Villiers, J. G., & Hoffmeister, R. (2007). Language and theory of mind: A study of deaf children. Child Development, 78, 376–396. doi:10.1111/j.1467-8624.2007.01004.x Sellabona, E. S., Sanchez, C. R., Majoral, E. V., Guitart, M. E., Caballero, F. S., & Ortiz, J. S. (2013). Labelling improves false belief understanding. A training study. Spanish Journal of Psychology, 16, E6. doi:10.1017/ sjp.2013.8 Sharp, C., & Venta, A. (2012). Mentalizing problems in children and adolescents. In N. Midgley & I. Vrouva (Eds.), Mind the child: Mentalization-based interventions with children, young people and their families (pp. 35–53). London, UK: Routledge. Shields, L., Zhou, H., Pratt, J., Taylor, M., Hunter, J., & Pascoe, E. (2007). Family-centered care for hospitalized children aged 0–12 years. Cochrane Database of Systematic Reviews, 10, CD004811. doi:10.1002/ 14651858.CD004811.pub2 Siegal, M., & Varley, R. (2006). Aphasia, language, and theory of mind. Social Neuroscience, 1, 167–174. doi:10.1080/17470910600985597 Slade, L., & Ruffman, T. (2005). How language does (and does not) relate to theory of mind: A longitudinal study of syntax, semantics, working memory and false belief. British Journal of Developmental Psychology, 23, 117–141. doi:10.1348/026151004X21332 Slaughter, V., Dennis, M. J., & Pritchard, M. (2002). Theory of mind and peer acceptance in preschool children. British Journal of Developmental Psychology, 20, 545–564. doi:10.1348/026151002760390945 *Stich, M. (2010). Theory of mind and pretend play in children with specific language impairment (Doctoral dissertation). Available from ProQuest Dissertations and Theses database. (UMI No. AAINR72302) Tager-Flusberg, H., & Joseph, R. M. (2005). How language facilitates the acquisition of false belief understanding in children with autism. In J. W. Astington & J. A. Baird (Eds.), Why language matters for theory of mind (pp. 298– 319). New York, NY: Oxford University Press. Tomblin, J. B., Records, N. L., Buckwalter, P., Zhang, X., Smith, E., & O’Brien, M. (1997). Prevalence of specific
153
language impairment in kindergarten children. Journal of Speech, Language and Hearing Research, 40, 1245–1260. doi:10.1044/jslhr.4006.1245 *Tucker, L. (2004). Specific language impairment and theory-ofmind: Is normal language development an essential precursor for on time theory-of-mind development? Unpublished manuscript, University of Western Australia, Perth, WA. *van Buijsen, M., Hendriks, A., Ketelaars, M., & Verhoeven, L. (2011). Assessment of theory of mind in children with communication disorders: Role of presentation mode. Research in Developmental Disabilities, 32, 1038–1045. doi:10.1016/j.ridd.2011.01.036 Vernes, S. C., Newbury, D. F., Abrahams, B., Winchester, L., Nicod, J., Groszer, M., . . . Fisher, S. (2008). A functional genetic link between distinct developmental language disorders. New England Journal of Medicine, 359, 2337–2345. doi:10.1056/NEJMoa0802828 Watson, A. C., Nixon, C. L., Wilson, A., & Capage, L. (1999). Social interaction skills and theory of mind in young children. Developmental Psychology, 35, 386–391. doi:10.1037/0012-1649.35.2.386 Wellman, H. M., Cross, D., & Watson, J. (2001). Metaanalysis of theory of mind development: The truth about false belief. Child Development, 72, 655–684. doi:10.1111/1467-8624.00304 Wellman, H. M., & Liu, D. (2004). Scaling of theory-ofmind tasks. Child Development, 75, 523–541. doi:10.1111/j.1467-8624.2004.00691.x Yazdi, A. A., German, T. P., Defeyter, M. A., & Siegal, M. (2006). Competence and performance in belief-desire reasoning across two cultures: The truth, the whole truth and nothing, but the truth about false belief? Cognition, 100, 343–368. doi:10.1016/j.cognition.2005.05.004 Yirmiya, N., Erel, O., Shaked, M., & Solomonica-Levi, D. (1998). Meta-analysis comparing theory of mind abilities in individuals with autism, individuals with mental retardation, and normally developing individuals. Psychological Bulletin, 124, 283–307. doi:10.1037/00332909.124.3.283 *Ziatas, K., Durkin, K., & Pratt, C. (1998). Belief term development in children with autism, Asperger syndrome, specific language impairment and normal development: Links to theory of mind. Journal of Child Psychology and Psychiatry, 39, 755–763. doi:10.1111/1469-7610.00374
Supporting Information Additional supporting information may be found in the online version of this article at the publisher’s website: Figure S1. Flow Diagram of the Search and Inclusion of Studies in the Meta-Analysis (Adapted From PRISMA; Moher et al., 2009) Figure S2. Forest Plot Depicting the Effect Sizes and Related Statistics of the Studies in the MetaAnalysis
