Visual filtering and covert orienting in persons with Down syndrome

Visual filtering in time and space among persons with Down syndrome

BACKGROUND

Individuals with Down syndrome (DS) appear to perform at a level that is commensurate with developmental expectations on simple tasks of selective attention. In this study, we examine how their selective attention is impacted by target changes that unfold over both time and space. This increased complexity reflects an attempt at greater ecological validity in an experimental task, as a steppingstone for better understanding attention among persons with DS in real-world environments.

METHODS

A modified flanker task was used to assess visual temporal and spatial filtering among persons with DS (n = 14) and typically developing individuals (n = 14) matched on non-verbal mental age (mental age = 8.5 years). Experimental conditions included varying the stimulus onset asynchronies between the onset of the target and flankers, the distances between the target and flankers, and the similarity of the target and flankers.

RESULTS

Both the participants with DS and the typically developing participants showed slower reaction times and lower accuracy rates when the flankers appeared closer in time and/or space to the target.

CONCLUSION

No group differences were found on a broad level, but the findings suggest that dynamic stimuli may be processed differently by those with DS. Implications of the findings are discussed in relation to the developmental approach to intellectual disability originally articulated by Ed Zigler.

A meta-analysis of the executive function components inhibition, shifting, and attention in intellectual disabilities

BACKGROUND

Executive function is a concept for higher-order cognitive functions, which have the role of controller and modulator of cognitive abilities. The consensus in the literature is that people with an intellectual disability perform significantly lower on executive function tasks than groups matched on chronological age. The comparison with groups matched on mental age is less clear. Therefore, the objective of this meta-analysis was to investigate to what extent executive function is impaired in people with intellectual disability compared with a typically developing control group matched on mental age. It was also investigated if the executive function component and intellectual disability aetiology moderated the effect.

METHODS

Eligibility criteria were participants with intellectual disability (IQ ≤ 75) without a dual diagnosis; a comparison group matched on mental age; executive function outcome reported in a group comparison study design with n ≥ 10. Working memory tasks and ratings of executive function were not included. The literature search yielded 6637 potentially interesting articles. Twenty-six studies (with 99 effect sizes) including 1395 participants were included in the quantitative synthesis.

RESULTS

A multilevel random-effects meta-analysis found that people with intellectual disability performed statistically significantly lower than the mental age-matched group on the executive function tasks, g = -0.34, 95% confidence interval = [-0.53, -0.16]. However, the heterogeneity between effect sizes was large. The intellectual disability aetiology moderator was significant, but it only reduced the heterogeneity marginally.

CONCLUSION

The overall conclusion is that individuals with an intellectual disability have more problems with executive function tasks than mental age-matched controls. Limitations are the large unexplained variance and the remarkably high number (69) of different tests that were used, which make more detailed conclusions problematic. This meta-analysis implies that future studies need to be of better quality, to have higher power, and to a higher degree use the same executive function tests.

Visuo-attentional correlates of Autism Spectrum Disorder (ASD) in children with Down syndrome: A comparative study with children with idiopathic ASD

BACKGROUND

Children with Down syndrome (DS) are at increased likelihood of Autism Spectrum Disorder (ASD) relative to the general population. To better understand the nature of this comorbidity, we examined the visuo-attentional processes associated with autistic trait expression in children with DS, focusing specifically on attentional disengagement and visual search performance.

METHOD

We collected eye-tracking data from children with DS (n = 15) and children with idiopathic ASD (iASD, n = 16) matched according to chronological age. Seven children with DS had a formal clinical diagnosis of ASD (DS+ASD).

RESULTS

In children with iASD, but not DS, higher autistic trait levels were associated with decreased temporal facilitation on a gap-overlap task, implying increased visuospatial orienting efficiency. In all cases, higher autistic trait levels were associated with improved visual search performance according to decreased target detection latency. On a visual search task, children with DS+ASD outperformed their peers with DS-ASD, mirroring the phenotypic advantage associated with iASD. We found no evidence of a relationship between attentional disengagement and visual search performance, providing preliminary evidence of a differentiation in terms of underlying visuo-attentional mechanism.

CONCLUSION

We illustrate the value of progressing beyond insensitive behavioural measures of phenotypic description to examine, in a more fine-grained way, the attentional features associated with ASD comorbidity in children with DS.

Attention allocation to facial expressions of emotion among persons with Williams and Down syndromes

Individuals with Williams syndrome and those with Down syndrome are both characterized by heightened social interest, although the manifestation is not always similar. Using a dot-probe task, we examined one possible source of difference: allocation of attention to facial expressions of emotion. Thirteen individuals with Williams syndrome (mean age = 19.2 years, range = 10-28.6), 20 with Down syndrome (mean age = 18.8 years, range = 12.1-26.3), and 19 typically developing children participated. The groups were matched for mental age (mean = 5.8 years). None of the groups displayed a bias to angry faces. The participants with Williams syndrome showed a selective bias toward happy faces, whereas the participants with Down syndrome behaved similarly to the typically developing participants with no such bias. Homogeneity in the direction of bias was markedly highest in the Williams syndrome group whose bias appeared to result from enhanced attention capture. They appeared to rapidly and selectively allocate attention toward positive facial expressions. The complexity of social approach behavior and the need to explore other aspects of cognition that may be implicated in this behavior in both syndromes is discussed.

Rule-based category learning in Down syndrome

Rule-based category learning was examined in youths with Down syndrome (DS), youths with intellectual disability (ID), and typically developing (TD) youths. Two tasks measured category learning: the Modified Card Sort task (MCST) and the Concept Formation test of the Woodcock-Johnson-III ( Woodock, McGrew, & Mather, 2001 ). In regression-based analyses, DS and ID groups performed below the level expected for their nonverbal ability. In cross-sectional developmental trajectory analyses, results depended on the task. On the MCST, the DS and ID groups were similar to the TD group. On the Concept Formation test, the DS group had slower cross-sectional change than the other 2 groups. Category learning may be an area of difficulty for those with ID, but task-related factors may affect trajectories for youths with DS.

Visual-spatial processing in children and adolescents with Down's syndrome: a computerized assessment of memory skills

BACKGROUND

Several studies have identified better visual-spatial than verbal memory skills in children with Down's syndrome (DS); however, research in both typical development and DS points to a relative dissociation between visual and spatial memory processing, questioning the notion of a unitary visual-spatial memory construct. The insufficient and often contradictory results regarding the visual-spatial memory domain probably reflect the heterogeneity of memory tests employed by these studies and the different memory systems that they evaluate.

METHOD

We administered five visual-spatial memory tasks from the Cambridge Neuropsychological Test Automated Battery (CANTAB) to 25 children with DS and to 25 controls matched for mental age (MA) and basic psychomotor speed and accuracy. The memory tasks measure spatial span, visual and spatial recognition, paired associates learning and self-ordered search abilities.

RESULTS

The results confirm the relative sparing of the spatial short-term memory (STM) capacity in children with DS; however, as memory load increases, in recognition tasks, or when visual and spatial demands are combined, their performance is impaired compared with MA controls. The same impairment is generated by additional executive demands in the self-ordered search task, although search strategy is similar to the one presented by MA controls.

CONCLUSIONS

We did not find support for a visual vs. spatial dissociation in recognition memory. Performance impairment in the visual-spatial domain parallels the increase in working memory (WM) load or in the executive demands of the task. Possible neurobiological implications of the observed performance on the CANTAB tasks are also considered.

Differences in visual orienting between persons with Down or fragile X syndrome

The voluntary and reflexive orienting abilities of persons with Down syndrome and fragile X syndrome, at average MA levels of approximately 4 and 7 years, were compared with an RT task. Reflexive orienting abilities appeared to develop in accordance with MA for the participants with Down syndrome but not for those with fragile X syndrome. However, both groups showed delayed voluntary orienting. The group differences in reflexive orienting at the low MA level reinforce the practice of separating etiologies and highlight the contribution of rudimentary attentional processes in the study of individuals with mental retardation.

Spatial representation and attention in toddlers with Williams syndrome and Down syndrome

The nature of the spatial representations that underlie simple visually guided actions early in life was investigated in toddlers with Williams syndrome (WS), Down syndrome (DS), and healthy chronological age- and mental age-matched controls, through the use of a "double-step" saccade paradigm. The experiment tested the hypothesis that, compared to typically developing infants and toddlers, and toddlers with DS, those with WS display a deficit in using spatial representations to guide actions. Levels of sustained attention were also measured within these groups, to establish whether differences in levels of engagement influenced performance on the double-step saccade task. The results showed that toddlers with WS were unable to combine extra-retinal information with retinal information to the same extent as the other groups, and displayed evidence of other deficits in saccade planning, suggesting a greater reliance on sub-cortical mechanisms than the other populations. Results also indicated that their exploration of the visual environment is less developed. The sustained attention task revealed shorter and fewer periods of sustained attention in toddlers with DS, but not those with WS, suggesting that WS performance on the double-step saccade task is not explained by poorer engagement. The findings are also discussed in relation to a possible attention disengagement deficit in WS toddlers. Our study highlights the importance of studying genetic disorders early in development.