The structure of language abilities at 4 years: a twin study

The cognitive science of language diversity: achievements and challenges

Linguistics needs to embrace all the way down a key feature of language: its diversity. In this paper, we build on recent experimental findings and theoretical discussions about the neuroscience and the cognitive science of linguistic variation, but also on proposals by theoretical biology, to advance some future directions for a more solid neurocognitive approach to language diversity. We argue that the cognitive foundations and the neuroscience of human language will be better understood if we pursue a unitary explanation of four key dimensions of linguistic variation: the different functions performed by language, the diversity of sociolinguistic phenomena, the typological differences between human languages, and the diverse developmental paths to language. Succeeding in the cognitive and neurobiological examination and explanation of these four dimensions will not only result in a more comprehensive understanding of how our brain processes language, but also of how language evolved and the core properties of human language(s).

Preschool Verbal and Nonverbal Ability Mediate the Association Between Socioeconomic Status and School Performance

We compared the extent to which the long‐term influence of family socioeconomic status (SES) on children's school performance from age 7 through 16 years was mediated by their preschool verbal and nonverbal ability. In 661 British children, who completed 17 researcher‐administered ability tests at age 4.5 years, SES correlated more strongly with verbal than nonverbal ability (.39 vs. .26). Verbal ability mediated about half of the association between SES and school performance at age 7, while nonverbal ability accounted for a third of the link. Only SES, but not verbal or nonverbal ability, was associated with changes in school performance from age 7 to 16. We found that SES‐related differences in school performance are only partly transmitted through children's preschool verbal abilities.

Twins Early Development Study: A Genetically Sensitive Investigation into Behavioral and Cognitive Development from Infancy to Emerging Adulthood

The Twins Early Development Study (TEDS) is a longitudinal twin study that recruited over 16,000 twin-pairs born between 1994 and 1996 in England and Wales through national birth records. More than 10,000 of these families are still engaged in the study. TEDS was and still is a representative sample of the population in England and Wales. Rich cognitive and emotional/behavioral data have been collected from the twins from infancy to emerging adulthood, with data collection at first contact and at ages 2, 3, 4, 7, 8, 9, 10, 12, 14, 16, 18 and 21, enabling longitudinal genetically sensitive analyses. Data have been collected from the twins themselves, from their parents and teachers, and from the UK National Pupil Database. Genotyped DNA data are available for 10,346 individuals (who are unrelated except for 3320 dizygotic co-twins). TEDS data have contributed to over 400 scientific papers involving more than 140 researchers in 50 research institutions. TEDS offers an outstanding resource for investigating cognitive and behavioral development across childhood and early adulthood and actively fosters scientific collaborations.

Hearing me hearing you: Reciprocal effects between child and parent language in autism and typical development

Language development in typically developing children (TD) has traditionally been investigated in relation to environmental factors, while language in children with autism spectrum disorder (ASD) has primarily been related to child-based factors. We employ a longitudinal corpus of 32 preschoolers with ASD and 35 linguistically matched TD peers recorded over 6 visits (ranging between 2 and 5 years of age) to investigate the relative importance of child-based and environmental factors in language development for both populations. We also investigate the reciprocal interaction between children's response to parents' input, and parents' response to children's production. We report six major findings. (1) Children's production of word types, tokens, and MLU increased across visits, and were predicted by their Expressive Language (EL) (positively) and diagnosis (negatively) from Visit 1. (2) Parents' production also increased across visits, and was predicted by their child's nonverbal cognition (positively) and diagnosis (negatively) from Visit 1. (3) At all visits and across groups, children and parents matched each other in lexical and syntactic production; (4) Parents who produced longer MLUs during a given visit had children who produced more word types and tokens, and had longer MLUs, at the subsequent visit. (5) When both child EL at Visit 1 and parent MLU were included in the model, both contributed significantly to future child language; however, EL accounted for a greater proportion of the variance. (6) Finally, children's speech significantly predicted parent speech at the next visit. Taken together, these results draw more attention to the importance of child-based factors in the early language development of TD children, and to the importance of parental language factors in the early language development of children with ASD.

Stability of core language skill from infancy to adolescence in typical and atypical development

Command of language is a fundamental life skill, a cornerstone of cognitive and socioemotional development, and a necessary ingredient for successful functioning in society. We used 15-year prospective longitudinal data from the Avon Longitudinal Study of Parents and Children to evaluate two types of stability of core language skill in 5036 typically developing and 1056 atypically developing (preterm, dyslexic, autistic, and hearing impaired) children in a multiage, multidomain, multimeasure, multireporter framework. A single core language skill was extracted from multiple measures at multiple ages, and this skill proved stable from infancy to adolescence in all groups, even accounting for child nonverbal intelligence and sociability and maternal age and education. Language skill is a highly conserved and robust individual-differences characteristic. Lagging language skills, a risk factor in child development, would profitably be addressed early in life.

Investigation of the language tasks to include in a short-language measure for children in the early school years

BACKGROUND

The inaccurate estimation of language difficulties by teachers suggests the benefit of a short-language measure that could be used to support their decisions about who requires referral to a speech-language therapist. While the literature indicates the potential for the development of a short-language measure, evidence is lacking about which combination of language tasks it should include.

AIMS

To understand the number and nature of components/language tasks that should be included in a short-language measure for children in the early school years.

METHODS & PROCEDURES

Eight language tasks were administered to participants of the Early Language in Victoria Study (ELVS) at ages 5 (n = 995) and 7 (n = 1217). These included six language tasks measured by an omnibus language measure (which comprised a direction-following, morphological-completion, sentence-recall, sentence-formation, syntactic-understanding and word-association task) and a non-word repetition and a receptive vocabulary task, measured by two task-specific language measures. Scores were analyzed using principal component analysis (PCA), the Bland and Altman method, and receiver operating characteristic (ROC) curve analysis.

OUTCOMES & RESULTS

PCA revealed one main component of language that was assessed by all language tasks. The most effective combination of two tasks that measured this component was a direction-following and a sentence-recall task. It showed the greatest agreement with an omnibus language measure and exceeded the criterion for good discriminant accuracy (sensitivity = 94%, specificity = 91%, accuracy = 91%, at 1 SD (standard deviation) below the mean).

CONCLUSIONS & IMPLICATIONS

Findings support the combination of a direction-following and a sentence-recall task to assess language ability effectively in the early school years. The results could justify the future production of a novel short-language measure comprising a direction-following and a sentence-recall task to use as a screening tool in schools and to assess language ability in research participants.

Stability of core language skill across the first decade of life in children at biological and social risk

BACKGROUND

Command of language is a fundamental skill, a cornerstone of multiple cognitive and socioemotional aspects of development, and a necessary ingredient of successful adjustment and functioning in society. Little is known about the developmental stability of language in at-risk youth or which biological and social risk factors moderate stability.

METHODS

This four-wave 10-year prospective longitudinal study evaluated stability of core language skill in 1,780 children in varying categories of biological and social risk in a multiage, multidomain, multimeasure, and multireporter framework.

RESULTS

Structural equation modeling supported loadings of diverse age-appropriate measures of child language on single latent variables of core language skill at 15 and 25 months and 5 and 11 years, respectively. Core language skill was stable over the first decade of life; significant and comparable stability coefficients were obtained for children with diverse biological and social risks, including poor health, welfare status, teen motherhood, ethnicity, gender, birth order, and families that changed in income and maternal education over the study period; stability in language was strong even accounting for child nonverbal intelligence and social competence, maternal education and language, and the family home environment.

CONCLUSIONS

Core language skill varies in stability with age but is robustly stable in children regardless of multiple biological and social risk factors.

Language Outcomes in Young Children with Mild to Severe Hearing Loss

OBJECTIVES

This study examined the language outcomes of children with mild to severe hearing loss during the preschool years. The longitudinal design was leveraged to test whether language growth trajectories were associated with degree of hearing loss and whether aided hearing influenced language growth in a systematic manner. The study also explored the influence of the timing of hearing aid fitting and extent of use on children's language growth. Finally, the study tested the hypothesis that morphosyntax may be at particular risk due to the demands it places on the processing of fine details in the linguistic input.

DESIGN

The full cohort of children in this study comprised 290 children who were hard of hearing (CHH) and 112 children with normal hearing who participated in the Outcomes of Children with Hearing Loss (OCHL) study between the ages of 2 and 6 years. CHH had a mean better-ear pure-tone average of 47.66 dB HL (SD = 13.35). All children received a comprehensive battery of language measures at annual intervals, including standardized tests, parent-report measures, and spontaneous and elicited language samples. Principal components analysis supported the use of a single composite language score for each of the age levels (2, 3, 4, 5, and 6 years). Measures of unaided (better-ear pure-tone average, speech intelligibility index) and aided (residualized speech intelligibility index) hearing were collected, along with parent-report measures of daily hearing aid use time. Mixed modeling procedures were applied to examine the rate of change (227 CHH; 94 children with normal hearing) in language ability over time in relation to (1) degree of hearing loss, (2) aided hearing, (3) age of hearing aid fit and duration of use, and (4) daily hearing aid use. Principal components analysis was also employed to examine factor loadings from spontaneous language samples and to test their correspondence with standardized measures. Multiple regression analysis was used to test for differential effects of hearing loss on morphosyntax and lexical development.

RESULTS

Children with mild to severe hearing loss, on average, showed depressed language levels compared with peers with normal hearing who were matched on age and socioeconomic status. The degree to which CHH fell behind increased with greater severity of hearing loss. The amount of improved audibility with hearing aids was associated with differential rates of language growth; better audibility was associated with faster rates of language growth in the preschool years. Children fit early with hearing aids had better early language achievement than children fit later. However, children who were fit after 18 months of age improved in their language abilities as a function of the duration of hearing aid use. These results suggest that the language learning system remains open to experience provided by improved access to linguistic input. Performance in the domain of morphosyntax was found to be more delayed in CHH than their semantic abilities.

CONCLUSION

The data obtained in this study largely support the predictions, suggesting that mild to severe hearing loss places children at risk for delays in language development. Risks are moderated by the provision of early and consistent access to well-fit hearing aids that provide optimized audibility.

Genetic and Environmental Links Between Natural Language Use and Cognitive Ability in Toddlers

Although the phenotypic correlation between language and nonverbal cognitive ability is well-documented, studies examining the etiology of the covariance between these abilities are scant, particularly in very young children. The goal of this study was to address this gap in the literature by examining the genetic and environmental links between language use, assessed through conversational language samples, and nonverbal cognition in a sample of 3-year-old twins (N = 281 pairs). Significant genetic and nonshared environmental influences were found for nonverbal cognitive ability and language measures, including mean length of utterance and number of different words, as well as significant genetic covariance between cognitive ability and both language measures.

A genome-wide sib-pair scan for quantitative language traits reveals linkage to chromosomes 10 and 13

Although there is considerable evidence that individual differences in language development are highly heritable, there have been few genome-wide scans to locate genes associated with the trait. Previous analyses of language impairment have yielded replicable evidence for linkage to regions on chromosomes 16q, 19q, 13q (within lab) and at 13q (between labs). Here we report the first linkage study to screen the continuum of language ability, from normal to disordered, as found in the general population. 383 children from 147 sib-ships (214 sib-pairs) were genotyped on the Illumina(®) Linkage IVb Marker Panel using three composite language-related phenotypes and a measure of phonological memory (PM). Two regions (10q23.33; 13q33.3) yielded genome-wide significant peaks for linkage with PM. A peak suggestive of linkage was also found at 17q12 for the overall language composite. This study presents two novel genetic loci for the study of language development and disorders, but fails to replicate findings by previous groups. Possible reasons for this are discussed.

A Randomized Trial of 12-Week Interventions for the Treatment of Developmental Phonological Disorder in Francophone Children

PURPOSE

This study was designed to test the relative efficacy of different combinations of intervention approaches when targeting speech production accuracy and phonological awareness skills. All children received individual speech therapy, a home program, and a small-group phonological awareness intervention.

METHOD

Sixty-five 4-year-olds with a developmental phonological disorder received these intervention components in different combinations over 12 weeks, resulting in 4 groups: output-oriented individual intervention and articulation practice home program, output-oriented individual intervention and dialogic reading home program, input-oriented individual intervention and articulation practice home program, and input-oriented individual intervention and dialogic reading home program.

RESULTS

A significant interaction of the individual treatment condition and the home program condition was observed for 2 outcome measures: targeted feature match (which reflected changes in speech production accuracy for features and word shape structures that were targeted in therapy) and explicit phonological awareness skills.

CONCLUSION

In this context, in which the children received a brief period of direct therapy and a home program component provided sequentially, the most effective strategy was to teach the parents to use treatment procedures at home that were congruent with the direct therapy component.

A randomised trial of granulocyte-macrophage colony-stimulating factor for neonatal sepsis: childhood outcomes at 5 years

OBJECTIVE

We performed a randomised trial in very preterm, small for gestational age (SGA) babies to determine if prophylaxis with granulocyte macrophage colony stimulating factor (GM-CSF) improves outcomes (the PROGRAMS trial). GM-CSF was associated with improved neonatal neutrophil counts, but no change in other neonatal or 2-year outcomes. As subtle benefits in outcome may not be ascertainable until school age we performed an outcome study at 5 years.

PATIENTS AND METHODS

280 babies born at 31 weeks of gestation or less and SGA were entered into the trial. Outcomes were assessed at 5 years to determine neurodevelopmental and general health status and educational attainment.

RESULTS

We found no significant differences in cognitive, general health or educational outcomes between 83 of 106 (78%) surviving children in the GM-CSF arm compared with 81 of 110 (74%) in the control arm. Mean mental processing composite (equivalent to IQ) at 5 years were 94 (SD 16) compared with 95 (SD 15), respectively (difference in means -1 (95%CI -6 to 4), and similar proportions were in receipt of special educational needs support (41% vs 35%; risk ratio 1.2 (95% CI 0.8 to 1.9)). Performance on Kaufmann-ABC subscales and components of NEPSY were similar. The suggestion of worse respiratory outcomes in the GM-CSF group at 2 years was replicated at 5 years.

CONCLUSIONS

The administration of GM-CSF to very preterm SGA babies is not associated with improved or more adverse neurodevelopmental, general health or educational outcomes at 5 years.

TRIAL REGISTRATION NUMBER

ISRCTN42553489.

Stability of core language skill from early childhood to adolescence: a latent variable approach

This four-wave prospective longitudinal study evaluated stability of language in 324 children from early childhood to adolescence. Structural equation modeling supported loadings of multiple age-appropriate multisource measures of child language on single-factor core language skills at 20 months and 4, 10, and 14 years. Large stability coefficients (standardized indirect effect = .46) were obtained between language latent variables from early childhood to adolescence even when accounting for child nonverbal intelligence and social competence and maternal verbal intelligence, education, speech, and social desirability. Stability coefficients were similar for girls and boys. Stability of core language skill was stronger from 4 to 10 to 14 years than from 20 months to 4 years, so early intervention to improve lagging language is recommended.

Specific language impairment: a convenient label for whom?

BACKGROUND

The term 'specific language impairment' (SLI), in use since the 1980s, describes children with language impairment whose cognitive skills are within normal limits where there is no identifiable reason for the language impairment. SLI is determined by applying exclusionary criteria, so that it is defined by what it is not rather than by what it is. The recent decision to not include SLI in DSM-5 provoked much debate and concern from researchers and clinicians.

AIMS

To explore how the term 'specific language impairment' emerged, to consider how disorders, including SLI, are generally defined and to explore how societal changes might impact on use the term.

METHODS & PROCEDURES

We reviewed the literature to explore the origins of the term 'specific language impairment' and present published evidence, as well as new analyses of population data, to explore the validity of continuing to use the term.

OUTCOMES & RESULTS AND CONCLUSIONS & IMPLICATIONS

We support the decision to exclude the term 'specific language impairment' from DSM-5 and conclude that the term has been a convenient label for researchers, but that the current classification is unacceptably arbitrary. Furthermore, we argue there is no empirical evidence to support the continued use of the term SLI and limited evidence that it has provided any real benefits for children and their families. In fact, the term may be disadvantageous to some due to the use of exclusionary criteria to determine eligibility for and access to speech pathology services. We propose the following recommendations. First, that the word 'specific' be removed and the label 'language impairment' be used. Second, that the exclusionary criteria be relaxed and in their place inclusionary criteria be adopted that take into account the fluid nature of language development particularly in the preschool period. Building on the goodwill and collaborations between the clinical and research communities we propose the establishment of an international consensus panel to develop an agreed definition and set of criteria for language impairment. Given the rich data now available in population studies it is possible to test the validity of these definitions and criteria. Consultation with service users and policy-makers should be incorporated into the decision-making process.

Sentence repetition is a measure of children's language skills rather than working memory limitations

Sentence repetition tasks are widely used in the diagnosis and assessment of children with language difficulties. This paper seeks to clarify the nature of sentence repetition tasks and their relationship to other language skills. We present the results from a 2-year longitudinal study of 216 children. Children were assessed on measures of sentence repetition, vocabulary knowledge and grammatical skills three times at approximately yearly intervals starting at age 4. Sentence repetition was not a unique longitudinal predictor of the growth of language skills. A unidimensional language latent factor (defined by sentence repetition, vocabulary knowledge and grammatical skills) provided an excellent fit to the data, and language abilities showed a high degree of longitudinal stability. Sentence repetition is best seen as a reflection of an underlying language ability factor rather than as a measure of a separate construct with a specific role in language processing. Sentence repetition appears to be a valuable tool for language assessment because it draws upon a wide range of language processing skills.

Generalist genes and cognitive abilities in Chinese twins

This study considered how far nonverbal cognitive, language and reading abilities are affected by common genetic influences in a sample of 312 typically developing Chinese twin pairs aged from 3 to 11 years. Children were individually given tasks of Chinese word reading, receptive vocabulary, phonological memory, tone awareness, syllable and rhyme awareness, rapid automatized naming, morphological awareness and orthographic skills, and Raven's Colored Progressive Matrices. Factor analyses on the verbal tasks adjusted for age indicated two factors: Language as the first factor and Reading as the second factor. Univariate genetic analyses indicated that genetic influences were substantial for nonverbal cognitive ability and moderate for language and reading. Multivariate genetic analyses showed that nonverbal cognitive ability, language and reading were influenced by shared genetic origins, although there were specific genetic influences on verbal skills that were distinct from those on nonverbal cognitive ability. This study extends the Generalist Genes Hypothesis to Chinese language and reading skills, suggesting that the general effects of genes could be universal across languages.

Norway's high-quality center care reduces late talking in high- and low-risk groups

OBJECTIVES

To examine whether attendance in Norwegian high-quality center care in the first 3 years of life buffers the negative effects of biomedical risk factors on children's late talking (LT) at 3 years of age.

METHODS

Data on 75,128 children from the Norwegian Mother and Child Cohort Study were analyzed and include information on child care arrangements, LT, and a variety of covariates. A biomedical risk group (N = 6893) was constructed on the basis of information from the Medical Birth Registry of Norway on children's Apgar scores 5 minutes after birth, birth weight, and gestational age. Late talking was reported by mothers when their children were 3 years old.

RESULTS

In line with previous research, children born with biomedical risk factors were at higher risk for LT at age 3 years than children born without biomedical risk factors. Child care arrangement at age 1 was not significantly related to LT at age 3 years. At both 1.5 and 3 years of age, center care attendance was related to a reduced chance of LT, independently of whether the children were in the biomedical risk group or not. However, our main hypothesis was not confirmed. Center care attendance did not buffer the negative effects of biomedical risk factors on LT for boys or girls (all p > .05).

CONCLUSION

Although attendance in Norwegian center care is positive for children's language development in general, it does not buffer the negative effects of biomedical risk factors on children's LT.

Longitudinal stability in genetic effects on children's conversational language productivity

PURPOSE

The authors examined the longitudinal stability of genetic and environmental influences on children's productive language sample measures during the early school-age years.

METHOD

Twin study methodology with structural equation modeling was used to derive univariate estimates of additive genetic (A), shared environmental (C), and nonshared environmental (E) effects on language measures at each of 2 time points, based on 487 twins at the 1st-grade time point and 387 twins at the 2nd-grade time point. To address questions of stability over time, the authors used longitudinal latent factor analysis.

RESULTS

Stability in the Conversational Language factor was accounted for almost entirely by shared genetic effects between 1st and 2nd grade, meaning no new genetic effects were observed at the 2nd time point. In contrast, nonshared environmental effects were entirely time point specific, meaning whatever nonshared environmental influences were operating at the first time point were not influencing individual variation in the language factor at the second time point.

CONCLUSION

The discussion in this article centers on possible candidates for both genetic and nonshared environmental effects as well as implications for clinical practice and future research.

Twins' Early Development Study (TEDS): A Multivariate, Longitudinal Genetic Investigation of Language, Cognition and Behavior Problems from Childhood Through Adolescence

The Twins' Early Development Study (TEDS) is a large-scale longitudinal study of twins from early childhood through adolescence. Since its conception, TEDS has had as its focus the study of problematic development within the context of normal variation, mainly in the development of language, cognitive and academic abilities and behavior problems from multivariate quantitative and molecular genetic perspectives. TEDS twins have been assessed at 2, 3, 4, 7, 9, 10 and (currently) 12 years of age, and DNA collected from more than 12,000 children. Identified from birth records of twins born in the United Kingdom between 1994 and 1996, more than 15,000 pairs of twins originally enrolled in TEDS, and well over 13,000 pairs — representative of the UK population — remain involved in the study to date. Similar to many other twin and adoption studies, TEDS data indicate that both genetic and environmental influences are important in nearly all areas of behavioral development. Multivariate genetic analyses allow researchers to go beyond this basic nature–nurture question, and TEDS results suggest that, especially in the area of learning abilities and disabilities, genes are generalists and environments are specialists. That is, genes largely contribute to similarity in performance within and between learning abilities and disabilities and across age, whereas the environment contributes to differences in performance. Quantitative genetic findings such as these chart the course for molecular genetic research. The TEDS dataset is proving valuable in genome-wide association research that tries to identify some of the many genes responsible for the ubiquitous heritability of behavior.

Defining the genetic architecture of human developmental language impairment

Language is a uniquely human trait, which poses limitations on animal models for discovering biological substrates and pathways. Despite this challenge, rapidly developing biotechnology in the field of genomics has made human genetics studies a viable alternative route for defining the molecular neuroscience of human language. This is accomplished by studying families that transmit both normal and disordered language across generations. The language disorder reviewed here is specific language impairment (SLI), a developmental deficiency in language acquisition despite adequate opportunity, normal intelligence, and without any apparent neurological etiology. Here, we describe disease gene discovery paradigms as applied to SLI families and review the progress this field has made. After review the evidence that genetic factors influence SLI, we discuss methods and findings from scans of the human chromosomes, including the main replicated regions on chromosomes 13, 16 and 19 and two identified genes, ATP2C2 and CMIP that appear to account for the language variation on chromosome 16. Additional work has been done on candidate genes, i.e., genes chosen a priori and not through a genome scanning studies, including several studies of CNTNAP2 and some recent work implicating BDNF as a gene x gene interaction partner of genetic variation on chromosome 13 that influences language. These recent developments may allow for better use of post-mortem human brain samples functional studies and animal models for circumscribed language subcomponents. In the future, the identification of genetic variation associated with language phenotypes will provide the molecular pathways to understanding human language.

Literacy outcomes of children with early childhood speech sound disorders: impact of endophenotypes

PURPOSE

To demonstrate that early childhood speech sound disorders (SSD) and later school-age reading, written expression, and spelling skills are influenced by shared endophenotypes that may be in part genetic.

METHOD

Children with SSD and their siblings were assessed at early childhood (ages 4-6 years) and followed at school age (7-12 years). The relationship of shared endophenotypes with early childhood SSD and school-age outcomes and the shared genetic influences on these outcomes were examined.

RESULTS

Structural equation modeling demonstrated that oral motor skills, phonological awareness, phonological memory, vocabulary, and speeded naming have varying influences on reading decoding, spelling, spoken language, and written expression at school age. Genetic linkage studies demonstrated linkage for reading, spelling, and written expression measures to regions on chromosomes 1, 3, 6, and 15 that were previously linked to oral motor skills, articulation, phonological memory, and vocabulary at early childhood testing.

CONCLUSIONS

Endophenotypes predict school-age literacy outcomes over and above that predicted by clinical diagnoses of SSD or language impairment. Findings suggest that these shared endophenotypes and common genetic influences affect early childhood SSD and later school-age reading, spelling, spoken language, and written expression skills.

Children who read words accurately despite language impairment: who are they and how do they do it?

Some children learn to read accurately despite language impairments (LI). Nine- to 10-year-olds were categorized as having LI only (n = 35), dyslexia (DX) only (n = 73), LI + DX (n = 54), or as typically developing (TD; n = 176). The LI-only group had mild to moderate deficits in reading comprehension. They were similar to the LI + DX group on most language measures, but rapid serial naming was superior to the LI + DX group and comparable to the TD. For a subset of children seen at 4 and 6 years, early phonological skills were equally poor in those later classified as LI or LI + DX. Poor language need not hinder acquisition of decoding, so long as rapid serial naming is intact; reading comprehension, however, is constrained by LI.

How does the mind work? Insights from biology

Cognitive scientists must understand not just what the mind does, but how it does what it does. In this paper, I consider four aspects of cognitive architecture: how the mind develops, the extent to which it is or is not modular, the extent to which it is or is not optimal, and the extent to which it should or should not be considered a symbol-manipulating device (as opposed to, say, an eliminative connectionist network). In each case, I argue that insights from developmental and evolutionary biology can lead to substantive and important compromises in historically vexed debates.

Gene × Environment interactions in speech sound disorder predict language and preliteracy outcomes

Few studies have investigated the role of gene × environment interactions (G × E) in speech, language, and literacy disorders. Currently, there are two theoretical models, the diathesis–stress model and the bioecological model, that make opposite predictions about the expected direction of G × E, because environmental risk factors may either strengthen or weaken the effect of genes on phenotypes. The purpose of the current study was to test for G × E at two speech sound disorder and reading disability linkage peaks using a sib-pair linkage design and continuous measures of socioeconomic status, home language/literacy environment, and number of ear infections. The interactions were tested using composite speech, language, and preliteracy phenotypes and previously identified linkage peaks on 6p22 and 15q21. Results showed five G × E at both the 6p22 and 15q21 locations across several phenotypes and environmental measures. Four of the five interactions were consistent with the bioecological model of G × E. Each of these four interactions involved environmental measures of the home language/literacy environment. The only interaction that was consistent with the diathesis–stress model was one involving the number of ear infections as the environmental risk variable. The direction of these interactions and possible interpretations are explored in the discussion.

The genetic bases of speech sound disorders: evidence from spoken and written language

The purpose of this article is to review recent findings suggesting a genetic susceptibility for speech sound disorders (SSD), the most prevalent communication disorder in early childhood. The importance of genetic studies of SSD and the hypothetical underpinnings of these genetic findings are reviewed, as well as genetic associations of SSD with other language and reading disabilities. The authors propose that many genes contribute to SSD. They further hypothesize that some genes contribute to SSD disorders alone, whereas other genes influence both SSD and other written and spoken language disorders. The authors postulate that underlying common cognitive traits, or endophenotypes, are responsible for shared genetic influences of spoken and written language. They review findings from their genetic linkage study and from the literature to illustrate recent developments in this area. Finally, they discuss challenges for identifying genetic influence on SSD and propose a conceptual framework for study of the genetic basis of SSD.

Distinct genetic influences on grammar and phonological short-term memory deficits: evidence from 6-year-old twins

Children with language impairments have limitations of phonological short-term memory (STM) and have distinctive problems with certain aspects of grammar. Both deficits have been proposed as phenotypic markers of heritable language impairment. We studied 173 twin pairs, selected to be over-representative of children with risk of developmental language impairment, using a battery of standardized language and intelligence tests, a test of nonword repetition to index phonological STM and two elicitation tasks to assess use of verb tense marking. As predicted, the phonological STM and the verb tense measures both discriminated children with risk of language impairment from low risk children, and DeFries-Fulker analysis showed that impairments on both tasks were significantly heritable. However, there was minimal phenotypic and etiological overlap between the two deficits, suggesting that different genes are implicated in causing these two kinds of language difficulty. From an evolutionary perspective, these data are consistent with the view that language is a complex function that depends on multiple underlying skills with distinct genetic origins.

Dimensions of early speech sound disorders: A factor analytic study

The goal of this study was to classify children with speech sound disorders (SSD) empirically, using factor analytic techniques. Participants were 3-7-year olds enrolled in speech/language therapy (N = 185). Factor analysis of an extensive battery of speech and language measures provided support for two distinct factors, representing the skill dimensions of articulation/phonology and semantic/syntactic skills. To validate these factors, 38 of the children were followed to school age to re-evaluate speech and language skills and assess reading/spelling achievement. The validity of the two factors was supported by their differential associations with school-age reading and spelling achievement, persistence of SSD, and affection status in family members. A closer relationship of the family member to the proband and male gender predicted higher odds of a disorder. The findings suggest that articulation/phonology and language abilities are at least partially independent in children with SSD and that these constructs have distinct clinical and biological correlates.

LEARNING OUTCOMES

The reader will develop knowledge about subtypes of speech sound disorders, understand the relationship between early speech sound disorders and later reading and spelling difficulties, and obtain information concerning familial transmission of speech sound disorders.

Genetic influences on specific versus nonspecific language impairment in 4-year-old twins

The present study addresses the distinction between specific (SLI) and nonspecific (NLI) language impairment at an etiological level by estimating the relative genetic and environmental contributions to language impairment in children with SLI and NLI. Drawing on a large longitudinal twin study, we tested a sample of 356 four-and-a-half-year-old children with low language ability and their twin partners at home on a range of language and nonverbal measures. For children whose language and nonverbal abilities were both low (NLI), genetic influence on language impairment was moderate and shared environmental influence was substantial. A similar pattern emerged for children whose language difficulties occurred in apparent isolation (SLI), although there was a trend for the genetic effects to be smaller for SLI than for NLI: Group heritability was .18 for SLI and .52 for NLI. Probandwise cross-concordances were suggestive of some genetic overlap between these two groups, but not with a subgroup of children with more severe cognitive delay.

Association analysis of mild mental impairment using DNA pooling to screen 432 brain-expressed single-nucleotide polymorphisms

We hypothesize that mild mental impairment (MMI) represents the low extreme of the same quantitative trait loci (QTLs) that operate throughout the distribution of intelligence. To detect QTLs of small effect size, we employed a direct association strategy by genotyping 432 presumably functional nonsynonymous single-nucleotide polymorphisms (nsSNPs) identified from public databases on DNA pools of 288 cases and 1025 controls. In total, 288 MMI cases were identified by in-home administration of McCarthy Scales of Children's Abilities to 836 twin pairs selected from a community sample of more than 14 000 children previously screened for nonverbal cognitive delay using parentally administered tests. Controls were selected from the community sample representing the full range of nonverbal intelligence. SNPs showing at least 7% allele frequency differences between case and control DNA pools were tested for their association with the full range of nonverbal intelligence using five DNA subpools, each representing quintiles of the normal quantitative trait scores from the 1025 controls. SNPs showing linear associations in the expected direction across quintiles using pooled DNA were individually genotyped for the 288 cases and 1025 controls and analyzed using standard statistical methods. One SNP (rs1136141) in HSPA8 met these criteria, yielding a significant (P=0.036) allelic frequency difference between cases and controls for individual genotyping and a significant (P=0.013) correlation within the control group that accounts for 0.5% of the variance. The present SNP strategy combined with DNA pooling and large samples represents a step towards identifying QTLs of small effect size associated with complex traits in the postgenomic era when all functional polymorphisms will be known.

Generalist Genes and Learning Disabilities

The authors reviewed recent quantitative genetic research on learning disabilities that led to the conclusion that genetic diagnoses differ from traditional diagnoses in that the effects of relevant genes are largely general rather than specific. This research suggests that most genes associated with common learning disabilities--language impairment, reading disability, and mathematics disability--are generalists in 3 ways. First, genes that affect common learning disabilities are largely the same genes responsible for normal variation in learning abilities. Second, genes that affect any aspect of a learning disability affect other aspects of the disability. Third, genes that affect one learning disability are also likely to affect other learning disabilities. These quantitative genetic findings have far-reaching implications for molecular genetics and neuroscience as well as psychology.

Genetic, environmental, and gender effects on individual differences in toddler expressive language

In this article, the authors examined the genetic and environmental factors influencing expressive language development in a sample of 386 toddler twin pairs participating in the Wisconsin Twin Project. Expressive language was assessed using 2 measures from the MacArthur Communicative Development Inventories-Short Form: Total Vocabulary and Two-Word Combination Use (L. Fenson et al., 2000). A sex-limitation structural equation model estimated the contribution of genetics, shared environment, and nonshared environment to individual variation. For vocabulary, heritability was higher for boys than for girls (20% vs. 8%). For word combination use, heritability was higher for girls (28% vs. 10%). However, the majority of individual variation in both boys and girls could be attributed to shared environment (54%-78%).

Factors affecting the appearance of 'twin language': An original language naturally developing within twin pairs

OBJECTIVES

The appearance of 'twin language' has been highlighted as a reason for delayed language development in twins. 'Twin language' is a unique language understandable only within the pair, and not by their mother or others. The purpose of this study was to examine and clarify the factors affecting the appearance of 'twin language'.

METHODS

A mailed questionnaires survey was conducted in 2733 mothers of twins. Of them, 1395 mothers returned the questionnaires. The core questionnaire asked for data on birth weight, age at first spoken word, whether the twins were as alike as two peas in a pod, household members and non-verbal play. Logistic regression analysis was used in this study.

RESULTS

Out of the 1395 pairs included in this analysis, 598 pairs (42.9%) showed the appearance of a 'twin language'. When the 598 pairs were divided by whether the twin pair was exactly alike or not, there were 112 opposite sex pairs, 105 not-alike male pairs, 106 not-alike female pairs, 129 exactly alike male pairs and 140 exactly alike female pairs. Namely, 38.4% of the opposite sex pairs, 40.4% of the not-alike male pairs, 39.3% of the not-alike female pairs, 47.6% of the exactly alike male pairs and 48.4% in the exactly alike female pairs had a twin language. By multivariate logistic regression analysis controlling for twins' age, it was found that 'twin language' was significantly more frequent in exactly alike twin pairs, pairs with non-verbal play, and pairs with fewer older siblings.

CONCLUSIONS

These findings suggest that three factors (whether the twin pair is exactly alike or not, older siblings, non-verbal play) affect the appearance of 'twin language'.

Psychopathology in the postgenomic era

We are rapidly approaching the postgenomic era in which we will know all of the 3 billion DNA bases in the human genome sequence and all of the variations in the genome sequence that are ultimately responsible for genetic influence on behavior. These ongoing advances and new techniques will make it easier to identify genes associated with psychopathology. Progress in identifying such genes has been slower than some experts expected, probably because many genes are involved for each phenotype, which means the effect of any one gene is small. Nonetheless, replicated linkages and associations are being found, for example, for dementia, reading disability, and hyperactivity. The future of genetic research lies in finding out how genes work (functional genomics). It is important for the future of psychology that pathways between genes and behavior be examined at the top-down psychological level of analysis (behavioral genomics), as well as at the bottom-up molecular biological level of cells or the neuroscience level of the brain. DNA will revolutionize psychological research and treatment during the coming decades.

Genetic and environmental influence on language impairment in 4-year-old same-sex and opposite-sex twins

BACKGROUND

We investigated the aetiology of language impairment in 579 four-year-old twins with low language performance and their co-twins, members of 160 MZ twin pairs, 131 same-sex DZ pairs and 102 opposite-sex DZ pairs.

METHODS

Language impairment in 4-year-olds was defined by scores below the 15th percentile on a general factor derived from an extensive language test battery. Language impairment of different degrees of severity was investigated by using multiple cut-offs below the 15th percentile.

RESULTS

DeFries-Fulker extremes analysis indicated that language impairment as measured by the general language scale is under strong genetic influence. In addition, group differences heritability showed an increasing trend (from 38% to 76%) as a function of severity of language impairment. Although more boys are impaired than girls, incorporating opposite-sex DZ pairs into the analysis found neither quantitative nor qualitative differences between boys and girls in genetic and environmental aetiologies.

CONCLUSIONS

Language impairment at four years is heritable. This finding replicates previous research on language impairment and extends it by showing that language impairment is heritable in twins selected from a representative community sample. Despite the mean difference between boys and girls, genetic and environmental influences are quantitatively and qualitatively similar for language impairment for boys and girls. For both boys and girls, heritability appears to be greater for more severe language impairment, indicating stronger influence of genes at the lower end of language ability.

Genetic and environmental mediation of the relationship between language and nonverbal impairment in 4-year-old twins

This study of 4-year-old twins investigated the genetic and environmental origins of comorbidity between language impairment and nonverbal ability by testing the extent to which language impairment in one twin predicted nonverbal ability in the co-twin. Impairment of language ability was defined as scores below the 15th percentile on a general language scale derived from a battery of diverse language tests. Four hundred thirty-six children, members of 160 monozygotic (MZ) and 131 same-sex dizygotic (DZ) twin pairs, were identified as language impaired. Language-impaired probands also suffered significant impairments in nonverbal ability. DeFries-Fulker extremes analysis showed evidence for substantial genetic mediation of the phenotypic relationship between language impairment and poor nonverbal ability in that language problems in one twin predicted poor nonverbal ability in the co-twin, much more so for MZ twins than for DZ twins. This finding held even when we excluded those children with language impairment whose nonverbal score indicated general cognitive delay. These results point to a general genetic factor that includes both language and nonverbal problems.

Outcomes of early language delay: I. Predicting persistent and transient language difficulties at 3 and 4 years

Parent-based assessments of vocabulary, grammar, nonverbal ability, and use of language to refer to post and future (displaced reference) were obtained for 8,386 twin children at 2 years of age. Children with 2 year vocabulary scores below the 10th centile were designated the early language delay (ELD) group, and their outcomes at 3 and 4 years were contrasted with the remainder of the sample, the typical language (TL) group. At 3 and 4 years old, children were designated as language impaired if their scores fell below the 15th centile on at least 2 of the 3 parent-provided language measures: vocabulary, grammar, and use of abstract language. At 3 years, 44.1% of the ELD group (as compared to 7.2% of the TL group) met criteria for persistent language difficulties, decreasing slightly to 40.2% at 4 years (as compared to 8.5% of the TL group), consistent with previous reports of frequent spontaneous resolution of delayed language in preschoolers. Although relations between language and nonverbal abilities at 2 years and outcome at 3 and 4 years within the ELD group were highly statistically significant, effect sizes were small, and classification of outcome on the basis of data on 2-year-olds was far too inaccurate to be clinically useful. Children whose language difficulties persisted were not necessarily those with the most severe initial difficulties. Furthermore, measures of parental education and the child's history of ear infections failed to substantially improve the prediction.