Implicit procedural learning in fragile X and Down syndrome

Background Procedural learning refers to rule‐based motor skill learning and storage. It involves the cerebellum, striatum and motor areas of the frontal lobe network. Fragile X syndrome, which has been linked with anatomical abnormalities within the striatum, may result in implicit procedural learning deficit. Methods To address this issue, a serial reaction time (RT) task including six blocks of trials was performed by 14 individuals with fragile X syndrome, 12 individuals with Down syndrome and 12 mental age‐matched control subjects. The first (B1) and fifth (B5) blocks were random whereas the others (B2, B3, B4 and B6) consisted of a repeated 10‐step sequence. Results were analysed by Kruskal–Wallis one‐way analysis of variance and Wilcoxon signed‐rank test. Results For patients with fragile X syndrome, the RT was highly suggestive of preserved implicit learning as a significant difference was observed between blocks B5 and B6 (P = 0.009). However, the difference of RT between B4 and B5 did not reach significance, possibly due to a subgroup of individuals who did not learn. In contrast, in the Down syndrome group, RT decreased significantly between B4 and B5 (W = 2; P = 0.003) but not between the last ordered block (B6) and the last random block (B5), suggesting a weakness in procedural learning which was sensitive to the interfering random block. Conclusion implicit learning is variable in genetic syndromes and therefore relatively independent of general intellectual capacities. The results are discussed together with previous reports.     

A specific deficit in visuospatial simultaneous working memory in Down syndrome

Background   Recent studies have demonstrated that individuals with Down syndrome (DS) present both central and verbal working memory deficits compared with controls matched for mental age, whereas evidence on visuospatial working memory (VSWM) has remained ambiguous. The present paper uses a battery of VSWM tasks to test the hypothesis that individuals with DS can also encounter specific difficulties in VSWM.
Method   Four tasks were administered to 34 children and adolescents with DS and 34 controls matched for verbal mental age. In two of these tasks, participants had to remember a series of locations sequentially presented on a matrix (spatial-sequential WM); in another two, they had to remember locations simultaneously presented (spatial-simultaneous WM).
Results and Conclusions   Results showed that individuals with DS are poorer than controls in the spatial-simultaneous tasks, but not in the spatial-sequential tasks. These findings were not due to a difference in speed of visuospatial processing. In fact, when performances of the two groups in VSWM were compared using speed measures as covariates, differences between groups remained. It is suggested that the simultaneous VSWM deficit of individuals with DS could be due to the request for processing more than one item at a time.     

Using developmental trajectories to examine verbal and visuospatial short-term memory development in children and adolescents with Williams and Down syndromes

Williams (WS) and Down (DS) syndromes have been associated with specifically compromised short-term memory (STM) subsystems. Individuals with WS have shown impairments in visuospatial STM, while individuals with DS have often shown problems with the recall of verbal material. However, studies have not usually compared the development of STM skills in these domains, in these populations. The present study employed a cross-sectional developmental trajectories approach, plotting verbal and visuospatial STM performance against more general cognitive and chronological development, to investigate how the domain-specific skills of individuals with WS and DS may change as development progresses, as well as whether the difference between STM skill domains increases, in either group, as development progresses. Typically developing children, of broadly similar cognitive ability to the clinical groups, were also included. Planned between- and within-group comparisons were carried out. Individuals with WS and DS both showed the domain-specific STM weaknesses in overall performance that were expected based on the respective cognitive profiles. However, skills in both groups developed, according to general cognitive development, at similar rates to those of the TD group. In addition, no significant developmental divergence between STM domains was observed in either clinical group according to mental age or chronological age, although the general pattern of findings indicated that the influence of the latter variable across STM domains, particularly in WS, might merit further investigation.     

Featural versus configural face processing in a rare genetic disorder: Williams syndrome

Background Williams syndrome (WMS) is a rare genetic disorder with an estimated prevalence of 1 in 20 000 live births. Among other characteristics, WMS has a distinctive cognitive profile with spared face processing and language skills that contrasts with impairment in the cognitive domains of spatial cognition, problem solving and planning. It remains unclear whether individuals with WMS process faces using a featural strategy that focuses on features or a configural strategy that takes into consideration the contour of a face and spatial relations between features. Methods To investigate face processing in WMS, the tasks specifically probe unfamiliar face matching by using a design that includes manipulations in face presentation (thatcherised and non‐thatcherised), face orientation (upright and inverted) and face valence (happy and neutral expression) in a match‐to‐target face recognition design. The sample consisted of 20 participants with WMS, 10 participants with non‐specific developmental delay (IQ‐matched) and 10 normal control participants (chronological age‐matched). Results Similar to normal controls, WMS performed best when faces were presented upright. The results show while the WMS group did not perform as well as their typically developing counterparts, they did significantly better than the IQ‐matched developmentally delayed group. WMS did not show an accuracy advantage for inverted faces commonly understood as an index for featural face processing, nor did they perform better on thatcherised inverted face conditions whereby featural processing is forced. Furthermore, no accuracy advantage was observed for positively valenced (happy) faces in the WMS group. Conclusion These results are consistent with previous work showing a configural face processing approach in WMS, a strategy that is also utilised by normal controls.     

Implicit and explicit olfactory memory in people with and without Down syndrome

This study examined differences in implicit and explicit memory performance between people with Down syndrome (DS), their siblings, children matched on mental age, and university undergraduates, using olfactory stimuli. The DS and mental-age matched participants were also compared on two tasks of executive function. The data revealed implicit memory for olfactory stimuli. Further, people with DS performed similarly to each control group on the implicit memory task, but performed significantly poorer than all control groups on the explicit memory task. Impairment to executive functioning was identified as a possible cause of this deficit in explicit memory as people with DS performed more poorly than the mental-age matched controls on both tasks of executive function.     

Systematic review of cognitive development across childhood in Down syndrome: implications for treatment interventions

Background There is conjecture regarding the profile of cognitive development over time in children with Down syndrome (DS). Characterising this profile would be valuable for the planning and assessment of intervention studies. Method A systematic search of the literature from 1990 to the present was conducted to identify longitudinal data on cognitive trajectories in children with DS. Results Thirteen studies were identified: six assessed overall cognitive performance and seven assessed specific cognitive domains. Studies assessing IQ reported a decline across time. Studies assessing change in cognitive domains were, for the most part, not interpretable because of large age ranges in samples obscuring age‐specific data. Conclusion The current literature has only begun to describe typical cognitive developmental trajectories in children with DS; additional research is needed to clarify this topic.     

Effect of musical experience on verbal memory in Williams syndrome: evidence from a novel word learning task

Williams syndrome (WS) is a neurogenetic developmental disorder characterized by an increased affinity for music, deficits in verbal memory, and atypical brain development. Music has been shown to improve verbal memory in typical individuals as well as those with learning difficulties, but no studies have examined this relationship in WS. The aim of our two studies was to examine whether music can enhance verbal memory in individuals with WS. In Study 1, we presented a memory task of eight spoken or sung sentences that described an animal and identified its group name to 38 individuals with WS. Study 2, involving another group of individuals with WS (n = 38), included six spoken or sung sentences that identified an animal group name. In both studies, those who had participated in formal music lessons scored significantly better on the verbal memory task when the sentences were sung than when they were spoken. Those who had not taken formal lessons showed no such benefit. We also found that increased enjoyment of music and heightened emotional reactions to music did not impact performance on the memory task. These compelling findings provide the first evidence that musical experience may enhance verbal memory in individuals with WS and shed more light on the complex relationship between aspects of cognition and altered neurodevelopment in this unique disorder.     

Long-term memory for verbal and visual information in Down syndrome and Williams syndrome: performance on the Doors and People test

Previous studies have suggested that Williams syndrome and Down syndrome may be associated with specific short-term memory deficits. Individuals with Williams syndrome perform relatively poorly on tests of visuo-spatial short-term memory and individuals with Down syndrome show a relative deficit on verbal short-term memory tasks. However, these patterns of impairments may reflect the impact of generally impaired visuo-spatial processing skills in Williams syndrome, and verbal abilities in Down syndrome. The current study explored this possibility by assessing long-term memory among 15 individuals with Williams syndrome and 20 individuals with Down syndrome using the Doors and People test, a battery which assesses recall and recognition of verbal and visual information. Individuals' performance was standardised for age and level of intellectual ability with reference to that shown by a sample of 110 typically developing children. The results showed that individuals with Down syndrome have no differential deficits in long-term memory for verbal information, implying that verbal short-term memory deficits in this population are relatively selective. Instead both individuals with Down syndrome and with Williams syndrome showed some evidence of relatively poor performance on tests of long-term memory for visual information. It is therefore possible that visuo-spatial short-term memory deficits that have previously been demonstrated in Williams syndrome may be secondary to more general problems in visuo-spatial processing in this population.     

Emotion recognition by children with Down syndrome: A longitudinal study

Abstract

Background According to the literature, children with Down syndrome (DS) have difficulties recognising facial expressions. Yet abilities to recognise emotional expressions are often assessed in tasks that imply comprehension of words for emotions. We investigated the development of these abilities in children with DS in a longitudinal study that did not involve lexical knowledge of emotions.

Method Children with DS and nonspecific intellectual disability and typically developing children matched for developmental age (DA) were assessed once a year over 3 years. They were asked to recognise the facial expression of an emotion after hearing a vocalisation.

Results In each annual session, children with DS were not significantly different from others at recognising emotions. Their abilities to discriminate basic emotions improved significantly and to a similar extent to those of other children.

Conclusion The findings indicate that children with DS develop emotion recognition abilities similarly to other children of the same DA.     

Numeracy for adults with Down syndrome: it's a matter of quality of life

Background Numeracy development is widely accepted as critical for adults in the general community which is equally the case for adults with Down syndrome. This paper reports some of the findings of a study including the research question: What is the justification for numeracy development for adults with Down syndrome? Investigating this question led to the search for a framework to support the ongoing development of numeracy. Method The research used a case study methodology. Five adults were observed and interviewed in two contexts each. The data were analyzed to identify links to the quality of life model. Results The research illustrates how a quality of life approach can be used to justify and guide the lifelong development of numeracy. Data from the case studies linked numeracy to quality of life under the principles of personal contexts, variability, life-span perspective, values, choices and personal control, perceptions and self-image. Conclusions The principles of quality of life can provide a framework for the development of numeracy in the context of adulthood and Down syndrome. Preparation for the numeracy needs of a long and satisfying adulthood should begin in early childhood, continue in schools with the teaching of underlying mathematics concepts and skills, and be modified and refined throughout adulthood by the use of a numeracy development plan. Carers and professionals interacting in the contexts need to adopt a teaching role for numeracy.     

Verbal short-term memory in individuals with congenital articulatory disorders: new empirical data and review of the literature

Background To investigate the nature of the articulatory rehearsal mechanism of the Articulatory Loop in Baddeley's Working Memory model, it seems particularly important to study individuals who developed a deficit (dysarthria) or total abolition (anarthria) of the ability to articulate language following a cerebral lesion. Method In this study, a forced‐choice recognition procedure for word sequences of increasing length was used to evaluate verbal short‐term memory in nine individuals with severe congenital motor and verbal disabilities (seven anarthric and two severely dysarthric) and associated intellectual disability (ID) and 30 normal children of comparable mental age. Results The normal children exhibited classical phonological similarity effects (better performance on acoustically dissimilar than on similar word lists), word length (greater accuracy on two‐syllable than on four‐syllable word lists) and frequency of occurrence (an advantage of high‐frequency over low‐frequency words). Instead, all of these effects were lacking in the experimental group. Conclusions These data suggest that persons with congenital anarthria/dysarthria and ID present defective maturation at many levels of the Articulatory Loop and reduced contribution of semantic‐lexical processing in the temporary retention of phonological sequences. It is likely that in these individuals both communicative deficits and ID play a role in the impaired development of verbal short‐term memory abilities.     

Behaviour problems and adults with Down syndrome: childhood risk factors

Background Studies of people with intellectual disability suggest that several individual characteristics and environmental factors are associated with behaviour disorder. To date there are few studies looking at risk factors within specific syndromes and the relationship between early risk markers and later behaviour disorder. The key aim of the study was to determine if childhood risk factors were predictors of severe behaviour disorder in young adults with Down syndrome. Materials and methods A longitudinal cohort study of 50 people with Down syndrome was assessed with the same behavioural measure used in both childhood and adult life. The early risk factors which were assessed included childhood functioning, childhood psychopathology and early family environment as determined by measures of parental mental health, quality of parental marriage and social background. Results Childhood psychopathology and functioning were associated with severe behaviour disorder in adult life whereas childhood family environment was not. Conclusions Children with Down syndrome at risk for severe behaviour disorder in adult life may be identified in childhood and appropriate interventions offered to reduce their risk.     

Verbal short‐term memory shows a specific association with receptive but not productive vocabulary measures in Down syndrome

Background

Verbal short‐term memory (STM) capacity has been considered to support vocabulary learning in typical children and adults, but evidence for this link is inconsistent for studies in individuals with Down syndrome (DS). The aim of this study was explore the role of processing demands on the association between verbal STM and vocabulary measures in DS, by comparing receptive vocabulary measures with high STM processing demands to productive vocabulary measures with low STM processing demands.

Method

Forty‐seven adults with Down syndrome were administered receptive vocabulary and productive vocabulary tasks, as well as measures of verbal STM abilities and intellectual efficiency.

Results

Bayesian regression analyses showed that verbal STM abilities were strongly and specifically associated with receptive vocabulary measures but not productive lexical abilities after controlling for intellectual efficiency, and this is despite the fact that vocabulary abilities as measured by receptive and productive vocabulary tasks were closely associated.

Conclusions

In Down syndrome, verbal STM abilities may be predictive of specific task demands associated with receptive vocabulary tasks rather than of vocabulary development per se.     

Language acquisition in special populations: a comparison between Down and Williams syndromes

To investigate the relationship between language acquisition and cognition, we evaluated linguistic abilities in 12 Italian-speaking children with Williams syndrome (WS) and 12 with Down syndrome (DS) of comparable global cognitive level. Another control group included 12 typically developing (TD) children, matched for mental age. Linguistic measures included a parent questionnaire to assess vocabulary, a verbal comprehension test, a sentence repetition test and MLU calculated on spontaneous production. No dissociation was evident between lexical and cognitive abilities, but specific morphosyntactic difficulties emerged both in comprehension and production in children with DS. Individuals with WS, albeit less compromised than DS, also had difficulty in the phrase repetition task and, particularly, using content words. Our results demonstrate that the linguistic abilities of infants with WS are not above their cognitive level and that language development in these special populations is not only delayed, but follows a different developmental trajectory.