Different origin of auditory and phonological processing problems in children with language impairment: evidence from a twin study

Frequency discrimination deficits in people with specific language impairment: reliability, validity, and linguistic correlates

The reliability and validity of a frequency discrimination (FD) task were tested in 16 people with specific language impairment (SLI) and 16 people with normal spoken language (controls). The FD thresholds of the 2 groups indicated that FD thresholds for 25-ms and 250-ms tones were remarkably stable across 18 months. The FD thresholds were lower for control listeners than for listeners with SLI for both duration conditions, and the FD thresholds for both groups of listeners were lower for 250-ms tones than for 25-ms tones. Moreover, the FD thresholds were influenced little by nonperceptual, task-related abilities (e.g., paired-associative learning, memory for temporal order, sustained attention, and control of attention) of the listener groups. The significant group difference between the mean FD thresholds of the SLI and control groups was explained by a subgroup of people with SLI who had particularly poor thresholds compared with those of controls and the majority of the SLI group. This subgroup did not differ from the remainder of the SLI sample in terms of age or nonverbal ability but was characterized by very poor reading that was associated with poor phonemic awareness.

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'.

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.

Developmental Dyslexia and Specific Language Impairment: Same or Different?

Developmental dyslexia and specific language impairment (SLI) were for many years treated as distinct disorders but are now often regarded as different manifestations of the same underlying problem, differing only in severity or developmental stage. The merging of these categories has been motivated by the reconceptualization of dyslexia as a language disorder in which phonological processing is deficient. The authors argue that this focus underestimates the independent influence of semantic and syntactic deficits, which are widespread in SLI and which affect reading comprehension and impair attainment of fluent reading in adolescence. The authors suggest that 2 dimensions of impairment are needed to conceptualize the relationship between these disorders and to capture phenotypic features that are important for identifying neurobiologically and etiologically coherent subgroups.

A comparison of language abilities in adolescents with Down syndrome and children with specific language impairment

This article compared the language profiles of adolescents with Down syndrome (DS) and children with specific language impairment matched for nonverbal cognitive ability, and investigated whether similar relationships could be established between language measures and other capacities in both groups. Language profiles were very similar: Expressive language was more affected than language comprehension, and grammar was more affected than vocabulary in both domains. Both groups were impaired on tests of grammatical morphology and phonological memory. There were some differences between the groups, but these could be attributed to other features of development of people with DS.

Deciphering the genetic basis of speech and language disorders

A significant number of individuals have unexplained difficulties with acquiring normal speech and language, despite adequate intelligence and environmental stimulation. Although developmental disorders of speech and language are heritable, the genetic basis is likely to involve several, possibly many, different risk factors. Investigations of a unique three-generation family showing monogenic inheritance of speech and language deficits led to the isolation of the first such gene on chromosome 7, which encodes a transcription factor known as FOXP2. Disruption of this gene causes a rare severe speech and language disorder but does not appear to be involved in more common forms of language impairment. Recent genome-wide scans have identified at least four chromosomal regions that may harbor genes influencing the latter, on chromosomes 2, 13, 16, and 19. The molecular genetic approach has potential for dissecting neurological pathways underlying speech and language disorders, but such investigations are only just beginning.

Otitis media and tympanostomy tube insertion during the first three years of life: developmental outcomes at the age of four years

OBJECTIVE

In a long-term, prospective study, we set out to determine whether otitis media in the first 3 years of life persisting for periods currently considered developmentally threatening actually results in later impairments of children's cognitive, language, speech, or psychosocial development; whether prompt insertion of tympanostomy tubes prevents or lessens any such impairments; and whether, irrespective of causality, associations exist between persistent early-life otitis media and later developmental impairments. This report describes findings in study participants at the age of 4 years.

METHODS

We enrolled 6350 healthy infants from 2 to 61 days of age at urban hospitals and 2 small-town/rural and 4 suburban private pediatric practices. We regularly evaluated the children for the presence of middle-ear effusion (MEE) throughout their first 3 years of life by pneumatic otoscopy, supplemented by tympanometry; we monitored the validity of the otoscopic observations on an ongoing basis; and we treated children for otitis media according to specified guidelines. In the clinical trial component of the study, we randomly assigned 429 children who met specified minimum criteria regarding the persistence of MEE to undergo tympanostomy tube insertion either promptly or after a defined extended period if MEE remained present. In the associational component of the study, we selected a representative sample of 241 children who ranged from having no MEE to having MEE the cumulative duration of which fell just short of meeting randomization criteria for the clinical trial. In 397 (92.5%) of the children in the clinical trial and in 234 (97.1%) of the children in the representative sample, we assessed cognitive, language, speech, and psychosocial development at the age of 4 years, using formal tests, conversational samples, and parent questionnaires.

RESULTS

In children in the randomized clinical trial, there were no statistically significant differences in mean (+/-standard deviation) scores (higher denotes more favorable) favoring the early-treatment group over the late-treatment group on the General Cognitive Index of the McCarthy Scales of Children's Abilities (97 +/- 14 and 98 +/- 14, respectively); the Peabody Picture Vocabulary Test-Revised, a measure of receptive language (90 +/- 15 vs 92 +/- 16); the Nonword Repetition Test, a measure of phonological memory (66 +/- 12 vs 70 +/- 12); the Number of Different Words, a measure of word diversity (150 +/- 34 vs 150 +/- 31); the Mean Length of Utterance in Morphemes, a measure of sentence length and grammatical complexity (3.4 +/- 0.8 vs 3.4 +/- 0.7); or the Percentage of Consonants Correct-Revised, a measure of speech-sound production (92 +/- 5 vs 93 +/- 5). There were also no significant differences in ratings (higher denotes less favorable) on the Parenting Stress Index-Short Form (Total Stress scores: 68 +/- 18 vs 65 +/- 17) or the Child Behavior Checklist (Total Problem T scores: 50 +/- 10 vs 49 +/- 10). In the associational component of the study, correlations between the children's durations of MEE and their developmental outcomes were generally weak and, in most instances, nonsignificant. Exceptions, after adjustment for sociodemographic variables and for hearing thresholds at the time of developmental testing, consisted of a significant negative correlation between children's cumulative durations of MEE in their first 3 years of life and scores on the McCarthy Verbal subscale, and significant positive correlations between durations of MEE and scores on 2 measures of parent-child stress. The percentage of variance in these scores explained by time with MEE beyond that explained by sociodemographic variables ranged from 1.6% to 3.3%. In both the randomized clinical trial and the associational component, sociodemographic variables seemed to be the most important factors influencing developmental outcomes, and in both components, the results at 4 years of age were consistent with the results that had been obtained at 3 years of age.

CONCLUSIONS

In otherwise healthy children who are younger than 3 years and have persistent MEE within the duration limits that we studied, prompt insertion of tympanostomy tubes does not measurably improve developmental outcomes at 4 years of age. In such children, persistent MEE within the duration limits that we studied is negligibly associated with and probably does not affect developmental outcomes at 4 years of age.

Developmental dyslexia: specific phonological deficit or general sensorimotor dysfunction?

Dyslexia research now faces an intriguing paradox. It is becoming increasingly clear that a significant proportion of dyslexics present sensory and/or motor deficits; however, as this 'sensorimotor syndrome' is studied in greater detail, it is also becoming increasingly clear that sensory and motor deficits will ultimately play only a limited role in a causal explanation of specific reading disability.

Genetic evidence for bidirectional effects of early lexical and grammatical development

This article addresses the autonomy hypothesis of vocabulary and grammar and bootstrapping mechanisms in early language development. Two birth cohorts of 1,505 and 1,049 same-sex twin pairs from the UK were assessed at 2 and 3 years on grammar and vocabulary, using adapted versions of the MacArthur Communicative Development Inventory. Vocabulary and grammar correlate strongly at both 2 and 3 years in both cohorts. Multivariate genetic modeling reveals a consistently high genetic correlation between vocabulary and grammar at 2 and 3 years. This finding suggests the same genetic influences operate for both vocabulary and grammar, a finding incompatible with traditional autonomy hypothesis, at least in early acquisition. Crosslagged longitudinal genetic models indicate both lexical and syntactical bootstrapping operate from 2 to 3 years.

Diagnostic accuracy and test-retest reliability of nonword repetition and digit span tasks administered to preschool children with specific language impairment

To assess diagnostic accuracy and test-retest reliability, two forms of a nonword repetition task were administered to 22 preschool children with specific language impairment (SLI) and to 22 age- and gender-matched children with normal language (NL). Results were compared with performance on a digit span task and norm-referenced test scores. Nonword repetition scores provided excellent sensitivity and specificity for discriminating between groups. Scores on both nonword repetition and digit span tasks improved significantly from first to second administrations for both groups, but remained relatively stable at the third administration. The SLI group appeared to benefit more from repetition than the NL group. Acceptable levels of test-retest reliability were achieved for the digit span task, but not for the NL group on the nonword repetition task. These preliminary findings suggest that with further refinement to improve test-retest reliability, nonword repetition holds promise as a diagnostic measure for SLI in preschool children.

EDUCATIONAL OBJECTIVES

As a result of this activity, the participant will be able to (1) describe the content and administration of nonword repetition tasks; (2) explain why evidence of test-retest reliability is necessary before a measure may be considered reliable for diagnostic purposes; and (3) accurately compare the sensitivity and specificity of the nonword repetition task utilized in this study to standardized language test scores.

The perception of "sine-wave speech" by adults with developmental dyslexia

Numerous studies have shown that, as a group, children or adults with developmental dyslexia perceive isolated syllables or words abnormally. Continuous speech containing reduced acoustic information also might prove perceptually difficult to such listeners. They might, however, exploit the intact syntactic and semantic features present in whole utterances, thereby compensating fully for impaired speech perception. "Sine-wave speech" sentences afford a test of these competing possibilities. The sentences contain only 4 frequency-modulated sine waves, lacking many acoustic cues present in natural speech. Adults with and without dyslexia were asked to orally reproduce 9 sine-wave utterances, each occurring in 4 immediately successive trials. Participants with dyslexia reported fewer words than did control listeners. Practice, phonological contrasts, and word position affected both groups similarly. Comprehension of sine-wave sentences seems impaired in many, but not all, adults with dyslexia. A reduced auditory memory capacity may contribute to this deficit.

Semantic representation and naming in children with specific language impairment

When 16 children with SLI (mean age = 6;2) and 16 normally developing age-mates named age-appropriate objects, the SLI cohort made more naming errors. For both cohorts, semantic misnaming and indeterminate responses were the predominant error types. The contribution of limited semantic representation to these naming errors was explored. Each participant drew and defined each item from his or her semantic and indeterminate error pools and each item from his or her correctly named pool. When compared, the drawings and definitions of items from the error pools were poorer, suggesting limited semantic knowledge. The profiles of information included in definitions of items from the correct pool and the error pools were highly similar, suggesting that representations associated with misnaming differed quanlitatively, but not qualitatively, from those associated with correct naming. Eleven members of the SLI cohort also participated in a forced-choice recognition task. Performance was significantly lower on erroneous targets than on correctly named targets. When performance was compared across all three post-naming tasks (drawing, defining, recognition), the participants evinced sparse semantic knowledge for roughly half of all semantic misnaming and roughly one third of all indeterminate responses. In additional cases, representational gaps were evident. This study demonstrates that the degree of knowledge represented in the child's semantic lexicon makes words more or less vulnerable to retrieval failure and that limited semantic knowledge contributes to the frequent naming errors of children with SLI.

Profiles of grammatical morphology and sentence imitation in children with specific language impairment and Down syndrome

The purpose of the present study was to examine the grammatical morphology and sentence imitation performance of two different groups of children with language impairment and to compare their performance with that of children learning language typically. Expressive use of tense-bearing and non-tense-related grammatical morphemes was explored. Children with specific language impairment (SLI), with Down syndrome (DS), and with typical language development (TL) were matched on mean length of utterance (MW). Performance was compared primarily on composite measures of tense, tense inflections, and non-tense morphemes, as well as on the Sentences subtest of the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R; D. Wechsler, 1989). Exploratory analyses were completed on a set of 11 individual grammatical morphemes as a follow-up to the principal analyses. As predicted, the children with SLI performed significantly more poorly than the children with TL on all three composite measures. In addition, the DS group exhibited significantly weaker performance than did the TL group on the tense inflections and non-tense morpheme composites. Although there were no statistically reliable differences between the SLI and DS groups on any morpheme measure, the groups were not comparably weak in their use of the regular post, -ed; the irregular third person singular morphemes (e.g., has, does); the present progressive, -ing; or the use of modals. The SLI and DS groups both performed more poorly than did the TL group on the sentence imitation task.

The role of genes in the etiology of specific language impairment

Although specific language impairment (SLI) often runs in families, most pedigrees are not consistent with a single defective gene. Before progress can be made in molecular genetics, we need a better understanding of which aspects of SLI are heritable. Twin studies are useful in allowing us to distinguish genetic from environmental influences. This point is illustrated with a study in which twins were given tests of nonword repetition (regarded as an index of phonological short-term memory) and auditory processing. Children with SLI were impaired on both measures, but these deficits had different origins. Auditory processing problems showed no evidence of genetic influence, whereas the nonword repetition deficit was highly heritable. Future genetic studies of SLI may be most effective if they use measures of underlying cognitive processes, rather than relying on conventional psychometric definitions of disorder.

LEARNING OUTCOMES

Information in this manuscript will serve to (1) equip readers with an elementary understanding of methods used in molecular genetic studies of language impairment; (2) familiarise readers with the logic of twin studies in behavioural genetics, using both categorical and quantitative methods; (3) illustrate the importance of phenotype definition for genetic research, and the usefulness of genetic methods in illuminating theoretical relationships between deficits associated with SLI; (4) show how genetically informative methods can be used to study environmental as well as genetic influences on impairment.

FOXP2 is not a major susceptibility gene for autism or specific language impairment

The FOXP2 gene, located on human 7q31 (at the SPCH1 locus), encodes a transcription factor containing a polyglutamine tract and a forkhead domain. FOXP2 is mutated in a severe monogenic form of speech and language impairment, segregating within a single large pedigree, and is also disrupted by a translocation in an isolated case. Several studies of autistic disorder have demonstrated linkage to a similar region of 7q (the AUTS1 locus), leading to the proposal that a single genetic factor on 7q31 contributes to both autism and language disorders. In the present study, we directly evaluate the impact of the FOXP2 gene with regard to both complex language impairments and autism, through use of association and mutation screening analyses. We conclude that coding-region variants in FOXP2 do not underlie the AUTS1 linkage and that the gene is unlikely to play a role in autism or more common forms of language impairment.

Genetic factors and neurocognitive traits

Genetic contributions to phenotypic variation in general intelligence have been studied extensively. Less research has been conducted on genetic contributions to specific cognitive abilities, such as attention, memory, working memory, language, and motor functions. However, the existing data indicate a significant role of genetic factors in these abilities. Stages of information processing, such as sensory gating, early sensory registration, and cognitive analysis, also show evidence of genetic contributions. Recent molecular studies have begun to identify candidate genes for specific cognitive functions. Future research, identifying endophenotypes based on cognitive profiles of neuropsychiatric disorders, may also assist in the detection of genes that increase susceptibility to major psychiatric disorders.

A genomewide scan identifies two novel loci involved in specific language impairment

Approximately 4% of English-speaking children are affected by specific language impairment (SLI), a disorder in the development of language skills despite adequate opportunity and normal intelligence. Several studies have indicated the importance of genetic factors in SLI; a positive family history confers an increased risk of development, and concordance in monozygotic twins consistently exceeds that in dizygotic twins. However, like many behavioral traits, SLI is assumed to be genetically complex, with several loci contributing to the overall risk. We have compiled 98 families drawn from epidemiological and clinical populations, all with probands whose standard language scores fall > or =1.5 SD below the mean for their age. Systematic genomewide quantitative-trait-locus analysis of three language-related measures (i.e., the Clinical Evaluation of Language Fundamentals-Revised [CELF-R] receptive and expressive scales and the nonword repetition [NWR] test) yielded two regions, one on chromosome 16 and one on 19, that both had maximum LOD scores of 3.55. Simulations suggest that, of these two multipoint results, the NWR linkage to chromosome 16q is the most significant, with empirical P values reaching 10(-5), under both Haseman-Elston (HE) analysis (LOD score 3.55; P=.00003) and variance-components (VC) analysis (LOD score 2.57; P=.00008). Single-point analyses provided further support for involvement of this locus, with three markers, under the peak of linkage, yielding LOD scores >1.9. The 19q locus was linked to the CELF-R expressive-language score and exceeds the threshold for suggestive linkage under all types of analysis performed-multipoint HE analysis (LOD score 3.55; empirical P=.00004) and VC (LOD score 2.84; empirical P=.00027) and single-point HE analysis (LOD score 2.49) and VC (LOD score 2.22). Furthermore, both the clinical and epidemiological samples showed independent evidence of linkage on both chromosome 16q and chromosome 19q, indicating that these may represent universally important loci in SLI and, thus, general risk factors for language impairment.

Motor immaturity and specific speech and language impairment: evidence for a common genetic basis

Previous studies have found an association between motor immaturity and specific language impairment in children. Data from two twin studies were used to address the question of whether these linked deficits have a common etiology. Study 1 involved 57 MZ and 22 DZ pairs where one or both twins had specific speech/language impairment. A control group of 173 single-born children was also tested. Motor skill was assessed using a tapping task, which was carried out with left and right hands. Tapping scores were converted to scaled scores adjusted for age and sex. Unaffected twins and single-born controls did not differ in motor skill, but twins with speech and/or language impairments obtained significantly poorer tapping scores than controls. Bivariate DeFries-Fulker analysis pointed to shared genetic influence on tapping speed and a measure of speech production accuracy. In study 2, 37 twin pairs from study 1 were retested 2-3 years later and combined with 100 twin pairs from a general population sample. A timed peg-moving task was used to assess motor skill. Children with combined speech and language impairments obtained poorer peg-moving scores than unaffected children. Bivariate DeFries-Fulker analysis found significant shared genetic variance for impairments on peg-moving and on a test of nonword repetition. It is concluded that genes that put the child at risk for communicative problems also affect motor development, with the association being most evident when speech production is affected.

Auditory processing and the development of language and literacy

This paper considers evidence for basic auditory processing impairments associated with dyslexia and specific language impairment, against a back-drop of findings from studies of the normal development of auditory and phonological processing. A broad range of auditory impairments have been implicated in the aetiology of these language-learning disorders, including deficits in discriminating the temporal order of rapid sequences of auditory signals, elevated thresholds for frequency discrimination and for detection of amplitude and frequency modulation, impaired binaural processing and increased susceptibility to backward masking. Current evidence is inconsistent, but suggests that not all children with language difficulties have non-verbal auditory processing impairments, and for those that do, the impact on language development is poorly understood. Some implications for clinical practice are discussed.

Rapid auditory processing and phonological ability in normal readers and readers with dyslexia

According to a prominent theory, the phonological difficulties in dyslexia are caused by an underlying general impairment in the ability to process sequences of rapidly presented, brief sounds. Two studies examined this theory by exploring the relationships between rapid auditory processing and phonological processing in a sample of 82 normally reading children (Study 1) and by comparing 17 children with dyslexia to chronological-age and reading-age control participants on these tasks (Study 2). In the normal readers, moderate correlations were found between the measure of rapid auditory processing (Auditory Repetition Task, or ART) and phonological ability. On the ART, the dyslexia group performed at a level similar to that of the reading-age control group but obtained scores that were significantly below those of the chronological-age control group. This difference was due to a subgroup of 4 children in the dyslexia group who had particular difficulty with the ART. The phonological skills of these individuals were not worse than those of the children in the dyslexia group who were unimpaired on the ART. The discussion argues that there is no evidence that phonoogical difficulties are secondary to impairments of rapid auditory processing, as measured by the ART, and highlights the need to examine the strategic and cognitive demands involved in tasks of rapid auditory processing.

Auditory perceptual processing in people with reading and oral language impairments: current issues and recommendations

A popular hypothesis holds that specific reading disability (SRD) and specific language impairment (SLI) result from an impaired ability to process rapid and brief sounds. However, the results of experiments that have tested this hypothesis are incongruous. A number of factors could explain these contradictory findings, including the questionable reliability and validity of rapid auditory processing tasks, individual differences in the auditory processing abilities of SRD and SLI populations, the age of listeners, the quality of control groups, and the relationship between verbal and non-verbal auditory processing abilities. These issues highlight the need for future studies to (1) establish the reliability and validity of psychophysical tasks used to assess rapid auditory processing; (2) report the rapid auditory processing scores of individuals rather than just group means; (3) include a wide range of reading and spoken language tests to determine the literacy and oral language profile of people who demonstrate an auditory processing deficit; (4) include clinical comparison groups to determine whether a rapid auditory processing deficit is related specifically to written and spoken language impairments; and (5) examine the relationship between low-level non-verbal, verbal, and phonological processing abilities.

Genetic basis of cognitive disability

The importance of genetic influences on cognitive disability has been recognized for a long time, but molecular analysis has only recently begun to yield insights into the pathogenesis of this common and disabling condition. The availability of genome sequences has enabled the characterization of the chromosomal deletions and trisomies that result in cognitive disability, and mutations in rare single-gene conditions are being discovered. The molecular pathology of cognitive disability is turning out to be as heterogeneous as the condition itself, with unexpected complexities even in apparently simple gene-deletion syndromes. One remarkable finding from studies on X-linked mental retardation is that mutations in different small guanosine triphosphate (GTP)-binding proteins result in cognitive disability without other somatic features. Advances are also being made in cognitive disability with polygenic origins, such as dyslexia and autism. However, the genetic basis of mild intellectual disability has yet to be satisfactorily explained.

Genetic and environmental risks for specific language impairment in children

Specific language impairment (SLI) is the term used to refer to unexplained difficulties in language acquisition in children. Over the past decade, there has been rapid growth of evidence indicating that genes play an important part in the aetiology of SLI. However, further progress in elucidating the role of genes in causing SLI is limited by our lack of understanding of the phenotype. Studies to date have been hampered by the fact that we do not know whether SLI should be treated as a discrete disorder or a continuous variable, let alone which measures should be used to identify cases, or how many subtypes there are. Recent research suggests that theoretically motivated measures of underlying processes may be better than conventional clinical diagnoses for identifying aetiologically distinct types of language impairment. There has been a tendency for researchers to embrace parsimony and look for a single cause of SLI-or in any event, to identify different subtypes, each with a different single cause. Research is reviewed that suggests that may not be a fruitful approach to SLI, and that an approach in terms of multiple risk and protective factors, which is widely adopted in medicine, is more realistic.

An emergent account of language impairments in children with SLI: implications for assessment and intervention

While current theoretical accounts of language impairments in children with specific language impairment (SLI) provide clear direction with regard to intervention goal setting, these same accounts say little with regard to the intervention process. Current developments in connectionist modeling and the extension of principles of dynamical systems theory to cognitive and language development have resulted in a new theory of language development known as emergentism. In contrast to traditional formal linguistic accounts, the emergentist view holds that language is a dynamic evolving system that can be represented as a distribution of probabilistic information. Language acquisition, from this perspective, emerges from the child's simultaneous integration of multiple acoustic, linguistic, social and communicative cues within the context of the communicative interaction. An alternative account of SLI grounded within this emergentist view is presented, and preliminary implications are explored with respect to assessment and intervention.

Follow-up of children with early expressive phonology disorders

Fifty-two children identified at age 4 to 6 years as demonstrating a moderate to severe expressive phonology disorder were followed to the third and fourth grades. Children were classified into two groups based on the presence of an early phonology disorder in isolation (P) or the presence of a phonology disorder with other language problems (PL). At follow-up, articulation measures failed to differentiate the groups; however, the PL group performed more poorly than the P group on measures of phoneme awareness, language, reading decoding, reading comprehension, and spelling. The P group demonstrated poor spelling skills relative to their reading and language abilities, suggesting residual spelling weaknesses in these children. The PL group reported more nuclear family members with speech-language disorders and with reading disorders than the P group. Findings support previous research linking early language disorders with later reading difficulties.

Nonlinguistic perceptual deficits associated with reading and language disorders

Recent behavioral evidence supports the idea that some individuals with reading and language disorders are impaired in their perception of nonlinguistic auditory and visual information. More sophisticated measurement paradigms and analysis techniques are leading to a clearer understanding of these deficits and to possibilities for their remediation.

Nonword repetition performance in school-age children with and without language impairment

This study examined nonword repetition performance in a population-based sample of school-age children. A total of 581 second graders who were participating in a longitudinal, epidemiologic investigation of specific language impairment (SLI) were administered the Nonword Repetition Task (NRT) developed by Dollaghan & Campbell (1998). Performance was examined according to second-grade diagnostic category, presence/absence of language impairment, and treatment status. Results indicated that children with language impairment, as well as those in intervention, exhibited deficient nonword repetition skills compared to normal language controls. Findings also confirmed that the NRT is a culturally nonbiased measure of language processing. Results from likelihood ratio analyses indicated that NRT performance, though not sufficient on its own, may provide a useful index to assist in ruling in or ruling out language disorder.

Auditory temporal processing impairment: neither necessary nor sufficient for causing language impairment in children

Fourteen twin pairs, aged 8 to 10 years, were tested 3 times over 12 months; they included 11 children with language impairment (LI), 11 control children matched on nonverbal ability and age, and 6 co-twins who did not meet criteria for LI or control status. Thresholds were estimated for detecting a brief backward-masked tone (BM), detection of frequency modulation (FM), and pitch discrimination using temporal cues (deltaf0). Both BM and FM thresholds improved with training, and by the 2nd test session, FM thresholds were in the adult range. There were marked individual differences on BM and deltaf0 and, for both tasks, performance correlated with Tallal's Auditory Repetition Task administered 2 years previously. However, no auditory measure gave significant differences between LI and control groups; performance was influenced more by nonverbal than language ability. Some children did have a stable pattern of poor performance on certain auditory tasks, but their good FM detection raised questions about whether processing of auditory temporal information is abnormal. We found no evidence that auditory deficits are a necessary or sufficient cause of language impairments.

Cognitive approaches to the development of short-term memory

The capacity to retain information for brief periods of time increases dramatically during the childhood years. The increases in temporary storage of speech-based material that take place in the period spanning the pre-school years and adolescence reflect complex changes in many of the different component processes, including perceptual analysis, construction and maintenance of a memory trace, retention of order information, rehearsal, retrieval and redintegration. Another crucial capacity that undergoes a similar striking development is complex working memory, the ability to manipulate and store material simultaneously. Possible sources of age-related changes in working memory include increases in processing efficiency and attentional capacity, and task-switching. These two short-term memory systems might play significant but distinct roles in supporting the acquisition of knowledge and skills during childhood. Whereas phonological short-term memory is linked specifically with the learning of the phonological structures of new words, complex working memory appears to support processing and learning in a wide range of contexts, in both childhood and adulthood.