Is epileptiform activity related to developmental language disorder? Findings from the HelSLI study

Objective

To study if interictal epileptiform discharges (IEDs) are associated with language performance or pre-/perinatal factors in children with developmental language disorder (DLD).

Methods

We recorded routine EEG in wake and sleep in 205 children aged 2.9-7.1 years with DLD, without neurologic diseases or intellectual disability. We examined the language performance of the children and collected data on pre-/perinatal factors.

Results

Interictal epileptiform discharges were not associated with lower language performance. Children with so-called "rolandic", i.e. centrotemporoparietal, IEDs had better language skills, but age explained this association. Most pre-/perinatal factors evaluated did not increase the risk of rolandic IEDs, except for maternal smoking (OR 4.4, 95% CI 1.4-14). We did not find electrical status epilepticus during slow-wave sleep (ESES)/spike-and-wave activation in sleep (SWAS) in any children.

Conclusions

Interictal epileptiform discharges are not associated with lower language performance, and ESES/SWAS is not common in children with DLD.

Significance

Routine EEGs do not bring additional information about language performance in children with DLD who do not have any neurologic diseases, seizures, intellectual disability, or regression of language development.

Cross-Sectional and Longitudinal Associations Between Quality of Parent-Child Interaction and Language Ability in Preschool-Age Children With Developmental Language Disorder

PURPOSE

This study explores whether the quality of parent-child interaction is associated with language abilities cross-sectionally and longitudinally up to preschool-age among children with developmental language disorder (DLD).

METHOD

Participants were 97 monolingual children with DLD and their parents from the Helsinki Longitudinal SLI study, HelSLI (baseline, age in years;months, M = 4;3, SD = 0;10), of which 71 pairs were followed longitudinally (age in years;months, M = 6;6, SD = 0;5). Video recordings from three play sessions were scored for child, parent, and dyadic behavior using Erickson's sensitivity scale protocol and mutually responsive orientation at baseline. Children's expressive and receptive language and language reasoning ability were assessed at baseline, and expressive and receptive language were assessed at follow-up.

RESULTS

At baseline, engaged child behavior, parent's supportive guidance, and fluent and attuned dyadic behavior were associated with better receptive language ability, and engaged child behavior and dyadic synchrony were positively associated with language reasoning ability in 3- to 6-year-olds. The child's positive engagement and fluent and attuned dyadic behavior at baseline were associated with better expressive and receptive language abilities at follow-up in 6- to 7-year-olds, respectively.

CONCLUSIONS

Fluent and attuned dyadic behavior is associated with better receptive language ability in preschool-age children. Parent behavior alone was not associated with language ability. A connected and mutually attuned parent-child relationship could be a protective factor for language development for children with DLD.

Language acquisition of early sequentially bilingual children is moderated by short-term memory for order in developmental language disorder: Findings from the HelSLI study

BACKGROUND

The role of domain-general short-term memory (STM) in language development remains controversial. A previous finding from the HelSLI study on children with developmental language disorder (DLD) suggested that not only verbal but also non-verbal STM for temporal order is related to language acquisition in monolingual children with DLD.

AIMS

To investigate if a similar relationship could be replicated in a sample of sequentially bilingual children with DLD. In addition to the effect of age, the effect of cumulative second language (L2) exposure was studied.

METHODS & PROCEDURES

Sixty-one 4-6-year-old bilingual children with DLD and 63 typically developing (TD) bilingual children participated in a cross-sectional study conducted in their L2. Children completed novel game-like tests of visual and auditory non-verbal serial STM, as well as tests of cognitive functioning and language. Interactions of STM for order with age and exposure to L2 (Finnish) were explored as explanatory variables.

OUTCOMES & RESULTS

First, the improvement of non-verbal serial STM with age was faster in sequentially bilingual TD children than in bilingual children with DLD. A similar effect was observed for L2 exposure. However, when both age and exposure were considered simultaneously, only age was related to the differential growth of non-verbal STM for order in the groups. Second, only in children with DLD was better non-verbal serial STM capacity related to an improvement in language scores with age and exposure.

CONCLUSIONS & IMPLICATIONS

The results suggest that, as previously found in Finnish monolingual children, domain-general serial STM processing is also compromised in bilingual children with DLD. Further, similar to the monolingual findings, better non-verbal serial STM was associated with greater language improvement with age and exposure, but only in children with DLD, in the age range studied here. Thus, in clinical settings, assessing non-verbal serial STM of bilingual children could improve the detection of DLD and understanding of its non-linguistic symptoms.

WHAT THIS PAPER ADDS

What is already known on the subject Both phonological and non-verbal STM have been associated with DLD in monolingual and sequentially bilingual children. Monolingual children with DLD have also shown slower non-verbal serial STM development than TD children. What this study adds to existing knowledge Sequentially bilingual TD children's non-verbal serial STM improves more between ages 4 and 7 years than that of their peers with DLD, replicating a finding for monolingual children with DLD. Better non-verbal serial STM was especially associated with early receptive language development in sequentially bilingual children with DLD. L2 exposure showed largely comparable effects with age. These results support the hypothesis that a domain-general serial STM deficit is linked to DLD. What are the potential or actual clinical implications of this work? Non-verbal assessment of STM for serial order in sequentially bilingual children with DLD could benefit the development of better tailored therapeutic interventions.

Structure of Cognitive Functions in Monolingual Preschool Children With Typical Development and Children With Developmental Language Disorder

Purpose Developmental language disorder (DLD) is defined by persistent difficulties with language, but a growing body of evidence suggests that it is also associated with domain-general and nonverbal information-processing deficits. However, the interconnections between cognitive functions, both nonverbal and language related, are still unclear. With the aim of gaining more comprehensive insight into the cognitive deficits related to DLD, we investigated and compared the cognitive structure of children with DLD and typically developing (TD) children. Method As a part of the Helsinki longitudinal SLI study, monolingual Finnish preschoolers (N = 154; TD group: n = 66, DLD group: n = 88) were assessed with 23 tasks measuring nonverbal and verbal reasoning, language processing, memory, visuomotor functions, attention, and social cognition. Exploratory factor analysis and structural equation modeling were performed to examine latent constructs and to test measurement invariance between the TD and DLD groups. Results Measurement invariance was not found across the TD and DLD groups. Best fitting structure for TD children included factors reflecting verbal abilities, processing speed/short-term memory, visuomotor functions, and visuoconstructive abilities/nonverbal reasoning. The DLD group's structure comprised nonverbal abilities, naming/expressive language, verbal comprehension, and verbal/declarative memory. Conclusions The findings suggest that the structure of cognitive functions differs in TD children and children with DLD already at preschool age. Nonverbal functions seem more unified, whereas verbal functions seem more varying in preschoolers with DLD compared to TD children. The results can be used in future research for prognosis of DLD and planning interventions.

Short-Term Memory for Serial Order Moderates Aspects of Language Acquisition in Children With Developmental Language Disorder: Findings From the HelSLI Study

Previous studies of verbal short-term memory (STM) indicate that STM for serial order may be linked to language development and developmental language disorder (DLD). To clarify whether a domain-general mechanism is impaired in DLD, we studied the relations between age, non-verbal serial STM, and language competence (expressive language, receptive language, and language reasoning). We hypothesized that non-verbal serial STM differences between groups of children with DLD and typically developing (TD) children are linked to their language acquisition differences. Fifty-one children with DLD and sixty-six TD children participated as part of the HelSLI project in this cross-sectional study. The children were 4-6-year-old monolingual native Finnish speakers. They completed several tests of language and cognitive functioning, as well as new game-like tests of visual and auditory non-verbal serial STM. We used regression analyses to examine how serial STM moderates the effect of age on language. A non-verbal composite measure of serial visual and auditory STM moderated cross-sectional development of receptive language in the children with DLD. This moderation was not observed in the TD children. However, we found more rapid cross-sectional development of non-verbal serial STM in the TD children than in the children with DLD. The results suggest that children with DLD may be more likely to have compromised general serial STM processing and that superior non-verbal serial STM may be associated with better language acquisition in children with DLD.

L2 vocabulary acquisition of early sequentially bilingual children with TD and DLD affected differently by exposure and age of onset

BACKGROUND

Language exposure is known to be a key factor influencing bilingual vocabulary development in typically developing (TD) children. There is, however, a lack of knowledge in terms of exposure effects in children with developmental language disorder (DLD) and, especially, in interaction with age of onset (AoO) of second language acquisition.

AIMS

In the Helsinki longitudinal SLI study (HelSLI), we investigated the receptive and expressive second language (L2) vocabulary performance and cross-sectional vocabulary development of sequentially bilingual children with TD and DLD in order to resolve whether the groups could be differentiated based on their vocabulary performance. More importantly, we examined the effects of AoO and exposure in the vocabulary performance of these two bilingual groups.

METHODS & PROCEDURES

A total of 70 children with DLD from a hospital clinic and 82 with TD from kindergartens were recruited. Children were 3-7 years old with different AoOs for the L2 and varying degrees of language exposure. Multiple regression analysis was used to compare the groups in two receptive and three expressive vocabulary tests while considering the effects of AoO and language exposure.

OUTCOMES & RESULTS

Children with TD outperformed children with DLD in both receptive and expressive vocabulary measures. Exposure predicted vocabulary but AoO did not. The effect of exposure was different in TD and DLD groups in receptive but not in expressive vocabulary. Additionally, the interaction of exposure and AoO was found for receptive vocabulary, but similarly in both groups. With increasing exposure, a difference in performance between the groups became more notable in receptive vocabulary compared with the expressive vocabulary.

CONCLUSIONS & IMPLICATIONS

Bilingual children with TD and DLD can be differentiated by using L2 vocabulary tests when exposure is taken into consideration. Non-significant AoO effects in 3-7 year olds suggest flexibility in terms of when to start L2 immersion. However, exposure is important, and especially children with DLD would need a substantial amount of it relative to their TD peers, so that they would not fall even further behind over time. Differences in benefiting from exposure in receptive mode might offer clinicians and kindergarten personnel an insight for evaluating challenges in bilingual development. Severe challenges in vocabulary development in the DLD group also call for both individually targeted small-group activities for learning words as well as strategies for strengthening vocabulary in various environments and everyday life situations. What this paper adds What is already known on the subject Language exposure is often found to explain more of the variation compared with AoO in early L2 vocabulary. On the other hand, it has been suggested by some researchers, but not all, that AoO effects would be found. Exposure and AoO might also interact differently depending on the task and whether the development is typical or disordered. Contrary to the clinical observation, diagnostic value of receptive vocabulary has often been questioned. What this paper adds to existing knowledge This study indicates that receptive vocabulary might be useful in differentiating bilingual TD and DLD. Language exposure effects differ between TD and DLD groups, but depending on task. Lower performance, but also slower cross-sectional development, is found in receptive vocabulary for children with DLD. Interaction between language exposure and AoO stresses the importance of taking both into consideration when studying bilingual development. What are the potential or actual clinical implications of this work? L2 vocabulary tests can be used in differentiating bilingual children with TD and DLD when exposure is taken into consideration. Difficulties using exposure and, hence, slower development in children with DLD suggest that especially receptive vocabulary might be diagnostic by the accumulating exposure. Investing in ways of supporting vocabulary development through small-group activities and in everyday situations of bilingual children at risk of DLD is highly recommended. This is important to prevent them from incrementally falling further behind their TD peers over time. A limited AoO effect suggests that families have more flexibility in terms of when to place their child in L2 immersion in their early years.

Project DyAdd: Non-linguistic Theories of Dyslexia Predict Intelligence

Two themes have puzzled the research on developmental and learning disorders for decades. First, some of the risk and protective factors behind developmental challenges are suggested to be shared and some are suggested to be specific for a given condition. Second, language-based learning difficulties like dyslexia are suggested to result from or correlate with non-linguistic aspects of information processing as well. In the current study, we investigated how adults with developmental dyslexia or ADHD as well as healthy controls cluster across various dimensions designed to tap the prominent non-linguistic theories of dyslexia. Participants were 18–55-year-old adults with dyslexia (n = 36), ADHD (n = 22), and controls (n = 35). Non-linguistic theories investigated with experimental designs included temporal processing impairment, abnormal cerebellar functioning, procedural learning difficulties, as well as visual processing and attention deficits. Latent profile analysis (LPA) was used to investigate the emerging groups and patterns of results across these experimental designs. LPA suggested three groups: (1) a large group with average performance in the experimental designs, (2) participants predominantly from the clinical groups but with enhanced conditioning learning, and (3) participants predominantly from the dyslexia group with temporal processing as well as visual processing and attention deficits. Despite the presence of these distinct patterns, participants did not cluster very well based on their original status, nor did the LPA groups differ in their dyslexia or ADHD-related neuropsychological profiles. Remarkably, the LPA groups did differ in their intelligence. These results highlight the continuous and overlapping nature of the observed difficulties and support the multiple deficit model of developmental disorders, which suggests shared risk factors for developmental challenges. It also appears that some of the risk factors suggested by the prominent non-linguistic theories of dyslexia relate to the general level of functioning in tests of intelligence.

Understanding developmental language disorder - the Helsinki longitudinal SLI study (HelSLI): a study protocol

BACKGROUND

Developmental language disorder (DLD, also called specific language impairment, SLI) is a common developmental disorder comprising the largest disability group in pre-school-aged children. Approximately 7% of the population is expected to have developmental language difficulties. However, the specific etiological factors leading to DLD are not yet known and even the typical linguistic features appear to vary by language. We present here a project that investigates DLD at multiple levels of analysis and aims to make the reliable prediction and early identification of the difficulties possible. Following the multiple deficit model of developmental disorders, we investigate the DLD phenomenon at the etiological, neural, cognitive, behavioral, and psychosocial levels, in a longitudinal study of preschool children.

METHODS

In January 2013, we launched the Helsinki Longitudinal SLI study (HelSLI) at the Helsinki University Hospital ( http://tiny.cc/HelSLI ). We will study 227 children aged 3-6 years with suspected DLD and their 160 typically developing peers. Five subprojects will determine how the child's psychological characteristics and environment correlate with DLD and how the child's well-being relates to DLD, the characteristics of DLD in monolingual versus bilingual children, nonlinguistic cognitive correlates of DLD, electrophysiological underpinnings of DLD, and the role of genetic risk factors. Methods include saliva samples, EEG, computerized cognitive tasks, neuropsychological and speech and language assessments, video-observations, and questionnaires.

DISCUSSION

The project aims to increase our understanding of the multiple interactive risk and protective factors that affect the developing heterogeneous cognitive and behavioral profile of DLD, including factors affecting literacy development. This accumulated knowledge will form a heuristic basis for the development of new interventions targeting linguistic and non-linguistic aspects of DLD.

Sluggish cognitive tempo in children and adolescents with higher functioning autism spectrum disorders: Social impairments and internalizing symptoms

Sluggish cognitive tempo (SCT) was introduced in 1980s in the field of attention deficit hyperactivity disorder (ADHD). Studies indicate that symptoms of SCT are separate from symptoms of ADHD and independently associated with multiple domains of functioning in clinical groups and in typical development. We assessed whether similar pattern would apply to higher functioning autism spectrum disorders (ASD). Children with higher functioning ASD (N = 55; 5-15 years) were divided into the ASD+High SCT (n = 17), the ASD+Medium SCT (n = 18) and the ASD+Low SCT (n = 20) groups based on parent-rated daydreaming and slowness on the Five to Fifteen questionnaire (FTF). The groups were compared on SCT-related impairments found in previous studies: social skills, academic functioning, psychiatric symptoms, and processing speed. Assessment methods were the FTF, the Development and Well-Being Assessment, and the Coding subtest of the WISC-III. The ADHD symptoms were statistically controlled due to the overlap between SCT and ADHD. The ASD+High SCT and ASD+Medium SCT groups were significantly more likely to have the most pronounced social impairments, and the ASD+High SCT group had significantly higher rate of internalizing disorders compared to the ASD+Low SCT group. Our results suggest that children with higher functioning ASD and high or medium levels of SCT symptoms could be at higher risk for psychosocial impairments than children with higher functioning ASD with low levels of SCT symptoms. Co-occurring ADHD symptoms do not explain the finding. Recognizing SCT symptoms in higher functioning ASD would be important to targeting preventive support.

Child and family-related predictors of psychological outcomes in children adopted from abroad; what is the role of caregiver time?

International adoptees need to cope with stressful transitions and to develop secure attachment with their caregivers at the same time. Although most children adopted from abroad adjust fine, they are at increased risk of psychological problems. We investigated whether both child and family-related factors are associated with later psychological problems and whether the length of time spent at home after adoption before daycare moderates these associations among internationally adopted children in Finland (FinAdo, Finnish Adoption Study). The sample consisted of 1,265 children (708 girls, 557 boys) who arrived in Finland before they started school (mean age 2 years at arrival). Later behavioral problems were measured using the Child Behavior Check List (CBCL). According to our results, male gender, older age, child's early clinical symptoms (problems of sensory processing) and single parenthood were associated with later behavioral problems measured by CBCL scores. Longer stay at home before the start of daycare or school modified these results. Longer stay at home was associated with less later behavioral externalizing problems in girls but not in boys compared to those who spent a shorter time at home.

Teacher Ratings of Executive Function Difficulties in Finnish Children with Combined and Predominantly Inattentive Symptoms of ADHD

School-age children with difficulties in executive functions (EFs) are at risk for substantial academic impairment and poorer developmental outcome. Although Attention Deficit Hyperactivity Disorder (ADHD) is generally associated with weaknesses in EFs, a relatively minimal amount is known about school-related EF difficulties and differences between ADHD subtypes. The present study examined teacher ratings of EF behaviors in 7- to 15-year-old Finnish children with combined symptoms of ADHD (ADHD-C; n = 189), predominantly inattentive symptoms (ADHD-I; n = 25), and no ADHD (n = 691). The teacher ratings showed that both ADHD groups had more EF difficulties than controls. Ratings also indicated specific EF profiles for the ADHD subtypes, students with ADHD-I having more wide-ranging EF difficulties in attention as well as initiation, planning, and execution of actions than children with ADHD-C. According to the present findings, the school-related EF difficulties of children with ADHD-I need to be specifically acknowledged. Teacher ratings seem to be sensitive indicators of EF difficulties and distinguish between different kinds of EF profiles. In clinical practice, rating scales with reliable psychometric properties and normative data relevant to the specific cultural environment should be employed.

Neurocognitive performance of children with higher functioning autism spectrum disorders on the NEPSY-II

This study examined patterns of strengths and weaknesses in the neurocognitive performance of children with higher functioning autism spectrum disorder (ASD). The participants were 30 children with higher functioning ASD ranging from 6 to 11 years, and 60 typically developing (TD) children, who were matched with the children with higher functioning ASD in terms of age, gender, and maternal education. The TD children were drawn from the Finnish standardization sample for the NEPSY-II. The cognitive abilities of the children with higher functioning ASD were assessed with the WISC-III, and the neurocognitive performance of the children with higher functioning ASD and TD children on the NEPSY-II was compared. The children with higher functioning ASD were found to have strengths in verbal reasoning skills with respect to the population mean and weaknesses in set-shifting, verbal fluency, and narrative memory in comparison with the TD children. Minor weaknesses were also observed in facial memory and fine and visuomotor skills.

Preschoolers' recognition of emotional expressions: relationships with other neurocognitive capacities

We cross-sectionally examined the development of the ability to recognize facial expressions of emotions in preschool-aged children and the relationship between this ability and other neurocognitive capacities, that is, attention/executive functions, language, memory/learning, sensorimotor functions, theory of mind, and visuospatial processing. Children aged 3 to 6 years with no significant developmental deficits (N = 370) were assessed with a nonverbal matching task of emotion recognition ability: The Affect Recognition subtest from the NEPSY-II. The relationship between emotion recognition ability and other neurocognitive capacities was analyzed using correlation, regression, and commonality analyses. The results showed that (a) emotion recognition ability improved with age-this development decelerating mildly between ages 5 and 6-(b) emotion recognition ability correlated with all other neurocognitive capacities, and (c) language, attention/executive functions, and theory of mind were significant predictors of emotion recognition ability in the regression analysis. As revealed by the commonality analysis, and in contrast to most previous studies, language was the most important predictor of nonverbal emotion recognition ability. These results suggest that nonverbal emotion matching is an early maturing skill that develops in relation to other neurocognitive capacities, especially linguistic ability.

Simultaneity learning in vision, audition, tactile sense and their cross-modal combinations

Latencies of sensory neurons vary depending on stimulus variables such as intensity, contrast, distance and adaptation. Therefore, different parts of an object and simultaneous environmental events could often elicit non-simultaneous neural representations. However, despite the neural discrepancies of timing, our actions and object perceptions are usually veridical. Recent results suggest that this temporal veridicality is assisted by the so-called simultaneity constancy which actively compensates for neural timing asynchronies. We studied whether a corresponding compensation by simultaneity constancy could be learned in natural interaction with the environment without explicit feedback. Brief stimuli, whose objective simultaneity/non-simultaneity was judged, consisted of flashes, clicks or touches, and their cross-modal combinations. The stimuli were presented as two concurrent trains. Twenty-eight adult participants practised unimodal (visual, auditory and tactile) and cross-modal (audiovisual, audiotactile and visuotactile) simultaneity judgement tasks in eight sessions, two sessions per week. Effects of practice were tested 7 months later. All tasks indicated improved judgements of simultaneity that were also long-lasting. This simultaneity learning did not affect relative temporal resolution (Weber fraction). Transfer of learning between practised tasks was minimal, which suggests that simultaneity learning mechanisms are not centralised but modally specific. Our results suggest that natural perceptual learning can generate simultaneity-constancy-like phenomena in a well-differentiated and long-lasting manner and concomitantly in several sensory systems. Hebbian learning can explain how experience with environmental simultaneity and non-simultaneity can develop the veridicality of perceived synchrony.

Crossmodal temporal processing acuity impairment aggravates with age in developmental dyslexia

Temporal processing has been found to be impaired in developmental dyslexia. We investigated how aging affects crossmodal temporal processing impairment with 39 dyslexic and 40 fluent 20-59-year-old readers. Cognitive temporal acuity was measured at millisecond levels in six tasks. They consisted of order judgments of two brief non-speech stimulus pulses, the stimuli being audiotactile, visuotactile and audiovisual, and of simultaneity/nonsimultaneity detection of the pulses in two parallel three-pulse trains. Temporal acuity declined with age in both reading groups and its impairment was observed in developmental dyslexia. A new finding was that the crossmodal temporal impairment, directly relevant to reading, increased with age. The age-related exacerbation suggests a developmental neuronal deficit, possibly related to magnocells, which exists before dyslexia and is its ontogenetic cause.

Differential development of attention and executive functions in 3- to 12-year-old Finnish children

The developmental sequence of attention and executive functions (EFs) was studied by utilizing normative data from four hundred 3- through 12-year-old Finnish children. Data from 10 subtests measuring impulse control and inhibition of irrelevant responses, auditory and visual attention, visual search, planning, and verbal and visual fluency were included. The development proceeded sequentially, from motor inhibition and impulse control to functions of selective and sustained attention, and finally to EFs of fluency. Significant relations between gender and development and between parent education and development were found in several subtests. In a factor analysis, inhibition, auditory attention, visual attention, and the EF of fluency clustered into separate factors. The developmental staging and clustering of functions suggests that, although inhibition, attention, and EFs are highly interrelated cognitive functions, their developmental sequences are separate from one another. The development of basic inhibitory functions precedes the development of more complex functions of selective attention, and EFs continue to develop into adolescence.

Developmentally impaired processing speed decreases more than normally with age

Several studies show that although function may recover after brain damage the insult can nevertheless cause accelerated deterioration in old age. This has been interpreted as indicating reduced neuronal capacity to counteract age-related decline with plastic changes. Psychosocial and compensatory factors obscure the neuronal explanation. Since the speed of processing sequential temporal information is impaired in developmental dyslexia, we investigated its dependence on age (20-59 years) in psychosocially comparable groups of dyslexic and fluent readers using six tasks. Processing speed was impaired in dyslexia and decreased with age. The decrement was faster in dyslexic than normal readers in processing periodic stimuli. No exacerbation occurred in reading and other experiential factors. Our results, therefore, support the neuronal explanation.

Rate of information segregation in developmentally dyslexic children

Slowed processing of sequential perceptual information is related to developmental dyslexia. We investigated this unimodally and crossmodally in developmentally dyslexic children and controls ages 8-12 years. The participants judged whether two spatially separate trains of brief stimuli, presented at various stimulus onset asynchronies (SOA) in one or two senses, were synchronous or not. The stimulus trains consisted of light flashes in vision, clicks in audition, and indentations of the skin in the tactile sense. The dyslexic readers required longer SOAs than controls for successful performance in all six comparisons. The crossmodal spatiotemporal resolution of the groups differed more than unimodal performance. The dyslexic readers' segregation performance was also less differentiated than that of the controls. Our results show that not only sensory but also polysensory nonverbal information processing is temporally impaired in dyslexic children.