Non-word repetition and vocabulary in Kuwaiti Arabic-speaking children with down syndrome and typically developing children

OVERVIEW

Non-word repetition (NWR) is one of the most effective predictors of language impairments in children as it has been found to correlate with various language measures and the association between NWR and vocabulary is well documented in typically developing (TD) studies. However, there is a dire need for investigations of language skills in Kuwaiti Arabic individuals with Down Syndrome, and this study set out to fill a gap in this field.

METHOD

In this paper, we compare the vocabulary and NWR skills of a group of 48 individuals with DS aged 6-20 years to a group of 44 TD children aged 3-10 years matched on nonverbal IQ. Furthermore, we investigate the correlations among these language measures in the two groups and examine whether NWR can predict receptive and expressive vocabulary in these two groups.

RESULT

Results found DS participants performed significantly less than the TD group on the three language measures (receptive vocabulary t(90)= -3.17, p < .01, expressive vocabulary t(90)= -3.27, p < .01, and NWR t(90)= -8.32, p < .01). Moreover, there were strong correlations between NWR and vocabulary (receptive and expressive) in the TD group but not the DS group.

CONCLUSION

Findings supported the working memory model and the phonological processing account for the TD group. On the other hand, the poor association between NWR and vocabulary in the DS group might be due to poor phonological discrimination difficulties and speech discrimination difficulties.

An experiment on measuring awareness of stuttering in individuals with Down syndrome

BACKGROUND

Awareness of stuttering is likely to depend upon the development of the metalinguistic skill to discriminate between fluent speech and stuttering and the ability to identify one's own speech as fluent or stuttered. Presently, little is known about these abilities in individuals with Down syndrome (DS).

PURPOSE

This study investigates whether individuals with DS and typically developing (TD) children who stutter and who do not stutter differ in their ability to discriminate between fluent speech and stuttering. The second purpose of this study is to discover if this ability is correlated with their self-identification ability.

METHOD

An experiment to investigate awareness with tasks for discrimination of stuttering and self-identification was developed. It was administered to 28 individuals (7-19 years) with DS, 17 of them stutter and 11 do not, and 20 TD children (3-10 years), 8 of them stutter and 12 do not. Skills to discriminate stuttering were compared between these groups and correlated with self-identification within these groups. The influence of stuttering severity and developmental/chronological age on their ability to discriminate was also investigated.

RESULTS

The ability to discriminate does not differ significantly between the DS and TD group, but is highly influenced by developmental age. This ability correlates with self-identification but only for the TD individuals who speak fluently.

CONCLUSION

The ability to discriminate matures around the age of 7 and conscious awareness may rely on this ability. Differences between the present findings and earlier studies suggest that differentiation in levels and types of awareness is warranted.

Executive function in Down syndrome: A meta-analysis

BACKGROUND

Executive function (EF) refers to a set of cognitive processes involved in goal-oriented behavior-especially inhibition, attention shifting, and working memory. EF has been identified as a probable area of difficulty in Down syndrome (DS), but the exact nature of the difficulty has not been well-established.

AIMS

The meta-analysis sought to confirm or disconfirm EF as an area of difficulty in DS and elucidate an EF profile.

METHODS AND PROCEDURES

A random-effects meta-analysis was conducted on 57 studies that compared a group with DS to a typically developing (TD) mental age matched group on one or more executive function tasks. Heterogeneity was examined and moderators analyzed.

OUTCOMES AND RESULTS

The overall mean weighted effect size was large (d = -0.87), indicating poorer EF in groups with DS vs TD groups. Heterogeneity was significant, and moderator analysis revealed an EF profile with a very large effect for verbal WM/STM, a large effect for shifting, and moderate effects for inhibition and nonverbal WM/STM. Skewness analysis suggested that mean effect sizes might have been dampened, especially for WM/STM and shifting.

CONCLUSIONS AND IMPLICATIONS

Individuals with DS display a pronounced difficulty in EFs; implications for interventions and future research are discussed.

What predicts nonword repetition performance?

Despite the widespread use of nonword repetition in child neuropsychological research and clinical practice, the specific cognitive, linguistic and motor processes that contribute to variability in performance are unclear. The aim of this work was to determine the role of phonological memory, word reading, oromotor sequencing, and oromotor control on nonword repetition performance in the context of children's speech and language abilities. Ninety one children between the ages of 9 and 11 years, with a broad range of speech and language abilities participated in the study. Hierarchical regression was used to a) evaluate the contribution of phonological memory, word reading, oromotor sequencing and oromotor control to nonword repetition and b) determine whether speech and/or language ability moderated the relationship between these specific skills and nonword repetition performance. Results showed all four predictor variables were related to nonword repetition performance, accounting for 59% of variance. The variable with the strongest association with nonword repetition was phonological memory, followed by oromotor sequencing ability, word reading, and oromotor control. Contrary to expectations, neither speech nor language ability were significantly associated with the degree to which these specific skills were drawn upon to perform the nonword repetition task. These findings underline the multidimensional nature of the nonword repetition task and provide further evidence of the major contributions made by phonological memory, word reading, speech sequencing and control to performance on this task. Further, findings suggest that speech and language ability, as measured here, do not significantly influence the skills employed for nonword repetition performance.

Verbal Agreement Inflection in German Children With Down Syndrome

PURPOSE

The study aims to explore whether finite verbal morphology is affected in children/adolescents with Down syndrome (DS), whether observed deficits in this domain are indicative of a delayed or deviant development, and whether they are due to phonetic/phonological problems or deficits in phonological short-term memory.

METHOD

An elicitation task on subject-verb agreement, a picture-naming task targeting stem-final consonants that also express verbal agreement, a nonword repetition task, and a test on grammar comprehension were conducted with 2 groups of monolingual German children: 32 children/adolescents with DS (chronological age M = 11;01 [years;months]) and a group of 16 typically developing children (chronological age M = 4;00) matched on nonverbal mental age.

RESULTS

Analyses reveal that a substantial number of children/adolescents with DS are impaired in marking verbal agreement and fail to reach an acquisition criterion. The production of word-final consonants succeeds, however, when these consonants do not express verbal agreement. Performance with verbal agreement and nonword repetition are related.

CONCLUSIONS

Data indicate that a substantial number of children/adolescents with DS display a deficit in verbal agreement inflection that cannot be attributed to phonetic/phonological problems. The influence of phonological short-term memory on the acquisition of subject-verb agreement has to be further explored.

Memory profiles in Down syndrome across development: a review of memory abilities through the lifespan

Down syndrome (DS) is associated with a variety of cognitive impairments, notably memory impairments. Due to the high prevalence rates of early-onset dementia associated with DS, it is imperative to understand the comprehensive development of memory impairments beginning in childhood and into adulthood, as this may help researchers identify precursors of dementia at earlier stages of development and pinpoint targets for memory intervention. The current paper provides a systematic, developmentally focused review of the nature of memory difficulties in DS across the lifespan. Specifically, this review summarizes what is known about long-term, short-term, and working memory abilities (distinguishing between verbal and nonverbal modalities) in DS, compared to both mental age-matched typically developing peers and individuals with other forms of intellectual disability (ID) at three developmental stages (i.e., preschool, adolescence, and adulthood). Additionally, this review examines the degree of impairment reported relative to typically developing mental age-matched peers in the existing literature by examining effect size data across memory domains as a function of age. With few exceptions, memory abilities were impaired across the lifespan compared to mental age-matched typically developing peers. Relative to other groups with ID, research findings are mixed. Our review of the literature identified a scarcity of memory studies in early childhood, particularly for STM and WM. In adulthood, research was limited in the LTM and WM domains and very little research has compared memory abilities in older adults with DS to those with typical development. Looking to the future, longitudinal studies could provide a better understanding of the developmental trajectory of memory abilities in DS, and the possible associations between memory abilities and real-world functioning. This research could ultimately inform interventions to improve independence and overall quality of life for those with DS and their families.

Receptive vocabulary analysis in Down syndrome

The present study is an in-depth examination of receptive vocabulary in individuals with Down syndrome (DS) in comparison to control groups of individuals of similar nonverbal ability with typical development (TD) and non-specific etiology intellectual disability (ID). Verb knowledge was of particular interest, as it is known to be a predictor of later syntactic development. Fifty participants with DS, aged 10-21 years, 29 participants with ID, 10-21 years, and 29 participants with TD, 4-9 years, completed measures of receptive vocabulary (PPVT-4), nonverbal ability (Leiter-R), and phonological memory (Nonword Repetition subtest of the CTOPP). Groups were compared on percentage correct of noun, verb and attribute items on the PPVT-4. Results revealed that on verb items, the participants with ID performed significantly better than both participants with DS and TD, even when overall receptive vocabulary ability and phonological memory were held constant. Groups with DS and TD showed the same pattern of lexical knowledge, performing better on nouns than both verbs and attributes. In contrast, the group with ID performed similarly on nouns and verbs, but worse on attributes.

Reading comprehension in children with Down syndrome

Two studies aimed to investigate the reading comprehension abilities of 14 readers with Down syndrome aged 6 years 8 months to 13 years relative to those of typically developing children matched on word reading ability, and to investigate how these abilities were associated with reading accuracy, listening comprehension, phonological awareness and vocabulary knowledge. Study 1 confirmed significantly poorer passage-reading comprehension than the typically developing group. In an experimental task, readers with Down syndrome understood fewer written sentences than the typical group and, contrary to prediction, received no advantage from printed sentences compared to spoken sentences, despite the lower memory load. Reading comprehension was associated with listening comprehension, word reading and phonological awareness in DS. Vocabulary knowledge was also associated with reading comprehension, mediated by word reading and nonverbal cognitive abilities. Study 2 investigated the longitudinal relationships between reading and language measures in the readers with DS over around 22 months. Time 1 listening comprehension and phonological awareness predicted Time 2 reading comprehension but there was no evidence that reading or reading comprehension predicted Time 2 language scores or phonological awareness, and no evidence that readers had acquired greater depth of vocabulary.

Early hearing loss and language abilities in children with Down syndrome

BACKGROUND

Although many children with Down syndrome experience hearing loss, there has been little research to investigate its impact on speech and language development. Studies that have investigated the association give inconsistent results. These have often been based on samples where children with the most severe hearing impairments have been excluded and so results do not generalize to the wider population with Down syndrome. Also, measuring children's hearing at the time of a language assessment does not take into account the fluctuating nature of hearing loss in children with Down syndrome or possible effects of losses in their early years.

AIMS

To investigate the impact of early hearing loss on language outcomes for children with Down syndrome.

METHODS & PROCEDURES

Retrospective audiology clinic records and parent report for 41 children were used to categorize them as either having had hearing difficulties from 2 to 4 years or more normal hearing. Differences between the groups on measures of language expression and comprehension, receptive vocabulary, a narrative task and speech accuracy were investigated.

OUTCOMES & RESULTS

After accounting for the contributions of chronological age and nonverbal mental age to children's scores, there were significant differences between the groups on all measures.

CONCLUSIONS & IMPLICATIONS

Early hearing loss has a significant impact on the speech and language development of children with Down syndrome. Results suggest that speech and language therapy should be provided when children are found to have ongoing hearing difficulties and that joint audiology and speech and language therapy clinics could be considered for preschool children.

Differences on morphological and phonological processing between typically developing children and children with Down syndrome

It is widely acknowledged that people with Down syndrome (Ds) have less highly developed morphosyntactic abilities than typically developing (TD) children. However, little is known about the morphological processing of this population. In this paper we carry out two experiments in which the morphological Base Frequency (BF) effect is explored in both groups. The aim of the experiments is to carry out an in-depth exploration of morphological processing in children with Ds and TD children. In the first experiment children performed a definition task; in the second children had to provide a plural form for singular words. The results show a significant BF effect in only the first experiment. In the second experiment this morphological variable does not reach significance, but the variable we called Ending phoneme (a phonological variable that refers to the last phoneme of the bases prior to the addition of plural morphemes) does. The results also show that children with Ds score significantly below the two control groups in both experiments, with no significant differences between control groups. We go on to discuss morphological processing in children with and without Ds, the role of the two tasks carried out (paying special attention to the role played by working memory), and the possible relationship between our results and morphosyntactic deficits described in the literature.

Contributions of phonological and verbal working memory to language development in adolescents with fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. Although language delays are frequently observed in FXS, neither the longitudinal course of language development nor its cognitive predictors are well understood. The present study investigated whether phonological and working memory skills are predictive of growth in vocabulary and syntax in individuals with FXS during adolescence. Forty-four individuals with FXS (mean age = 12.61 years) completed assessments of phonological memory (nonword repetition and forward digit recall), verbal working memory (backward digit recall), vocabulary, syntax, and nonverbal cognition. Vocabulary and syntax skills were reassessed at a 2-year follow-up. In a series of analyses that controlled for nonverbal cognitive ability and severity of autism symptoms, the relative contributions of phonological and working memory to language change over time were investigated. These relationships were examined separately for boys and girls. In boys with FXS, phonological memory significantly predicted gains in vocabulary and syntax skills. Further, verbal working memory was uniquely associated with vocabulary gains among boys. In girls with FXS, phonological and working memory skills showed no relationship with language change across the 2-year time period. Our findings indicate that, for adolescent boys with FXS, acquisition of vocabulary and syntax may be constrained by the ability to maintain and manipulate phonological representations online. Implications for the identification and treatment of language disorders in this population are discussed. The present study is the first to identify specific cognitive mechanisms contributing to language growth over time in individuals with FXS.

Evidence for preserved novel word learning in Down syndrome suggests multiple routes to vocabulary acquisition

PURPOSE

Three studies investigated novel word learning, some requiring phonological production, each involving between 11 and 17 individuals with Down syndrome, and between 15 and 24 typically developing individuals matched for receptive vocabulary. The effect of stimuli wordlikeness and incidental procedure-based memory demands were examined to see whether these may account for an apparent impairment in word learning in Down syndrome demonstrated in earlier research.

METHOD

Paired associate word and nonword learning tasks were presented, requiring participants to learn the names of novel characters. The nonword stimuli varied in the degree of wordlikeness in 2 studies. A third study investigated extraneous task demand.

RESULTS

Across 3 studies, there was no suggestion of a word learning deficit associated with Down syndrome (η(2)(p) for the main effect of group of .03, .11, and .03, respectively), despite the level of phonological representation required. There was evidence that novel word learning by participants with Down syndrome exceeded that which their verbal short-term memory capacity would predict.

CONCLUSIONS

Vocabulary acquisition in Down syndrome may not rely on verbal short-term memory to the same extent as in typically developing children, lending support to the suggestion that new word learning may be underpinned by an additional memory process.

Verbal short-term memory deficits in Down syndrome: phonological, semantic, or both?

The current study examined the phonological and semantic contributions to the verbal short-term memory (VSTM) deficit in Down syndrome (DS) by experimentally manipulating the phonological and semantic demands of VSTM tasks. The performance of 18 individuals with DS (ages 11-25) and 18 typically developing children (ages 3-10) matched pairwise on receptive vocabulary and gender was compared on four VSTM tasks, two tapping phonological VSTM (phonological similarity, nonword discrimination) and two tapping semantic VSTM (semantic category, semantic proactive interference). Group by condition interactions were found on the two phonological VSTM tasks (suggesting less sensitivity to the phonological qualities of words in DS), but not on the two semantic VSTM tasks. These findings suggest that a phonological weakness contributes to the VSTM deficit in DS. These results are discussed in relation to the DS neuropsychological and neuroanatomical phenotype.

Research review: crossing syndrome boundaries in the search for brain endophenotypes

The inherent imprecision of behavioral phenotyping is the single most important factor contributing to the failure to discover the biological factors that are involved in psychiatric and neurodevelopmental disorders (e.g., Bearden & Freimer, 2006). In this review article we argue that in addition to an appreciation of the inherent complexity at the biological level, a rather urgent task facing behavioral scientists involves a reconsideration of the role that clinical syndromes play in psychological theorizing, as well as in research into the biological basis of cognition and personality. Syndrome heterogeneity, cross-syndrome similarities and syndrome comorbidities question the relevance of syndromes to biological research. It is suggested that the search for brain endophenotypes, intermediate between genes and behavior, should be based on cross-syndrome, trait classification. Cohort selection should rest on behavioral homogeneity, enabling, when necessary, syndrome heterogeneity.

A preliminary study of speech discrimination in youth with Down syndrome

Few studies have examined the ability of individuals with learning disabilities, in general, or with Down syndrome, specifically, to discriminate speech. The purpose of this study was compare the speech discrimination abilities of eight children with Down syndrome (aged 5.7 to 12.8 years) to seven nonverbal mental-age matched controls (aged 4.0 to 5.3 years). A computer program presented the speech discrimination task using a two-cued alternative forced choice procedure. On each trial, the participants heard four successive synthesized speech syllables, with the first and last stimuli being the same and serving as the cue. The results indicated children with Down syndrome differed from their nonverbal mental-age matched peers in their ability to discriminate two of the five pairs, but not in the manner predicted. The relationship between speech discrimination, phonological memory, and speech-language development is also discussed.