Developmental trajectories of spatial-sequential and spatial-simultaneous working memory in Down syndrome.

BACKGROUND: Working memory (WM) is generally considered an area of weakness in the cognitive profile associated with Down syndrome (DS). The great majority of studies explored WM in this population through a comparison with typical development (TD) on the basis of mental age or developmental level. However, it is also relevant to understand how these skills develop and whether such development could be more related to chronological or developmental level. In the present study, we explored cross-sectional developmental trajectories of spatial-sequential and spatial-simultaneous WM in individuals with DS across chronological age and developmental level. Typically developing children (TD) of similar mental age were also included as a comparison group. METHODS: Eighty-four individuals with DS (aged between 7 and 30 years) and 327 children with TD (aged between 4 and 8 years) were administered with tasks to assess spatial-sequential and spatial-simultaneous WM, together with tasks to assess both general verbal and spatial developmental levels. RESULTS AND CONCLUSION: Performance in spatial-simultaneous WM task was lower compared with spatial-sequential WM task in both groups. In the case of individuals with DS, the developmental trajectories of chronological age are better described through a segmented model showing increased performance until approximately 13 years of age, followed by a rather flat progress. In the case of TD children, developmental trajectories are better described through a linear model in the spatial-simultaneous WM task when chronological age is considered; in the spatial-sequential WM, the increase in performance with age was however characterised by a discontinuity at age 6. The increase in performance followed a linear pattern in both groups (DS and TD) without substantial differences between the types of measure used (verbal vs. spatial) when the developmental level is considered.

Using Z and age-equivalent scores to address WISC-IV floor effects for children with intellectual disability.

BACKGROUND: The Wechsler Intelligence Scale for Children - Fourth Edition often produces floor effects in individuals with intellectual disability. Calculating respondents' Z or age-equivalent scores has been claimed to remedy this problem. METHOD: The present study applied these methods to the Wechsler Intelligence Scale for Children - Fourth Edition scores of 198 individuals diagnosed with intellectual disability. Confirmatory factor analysis and profile analysis were conducted using a Bayesian approach. RESULTS: The intelligence structure in intellectual disability resembled the one previously reported for typical development, suggesting configural but not metric invariance. When Z or age-equivalent scores (but not traditional scaled scores) were used, the average profile resembled the one previously reported for other neurodevelopmental disorders. CONCLUSIONS: Both methods avoided any floor effects, generating similar but not identical profiles. Despite some practical and conceptual limitations, age-equivalent scores may be easier to interpret. This was true even for a subgroup of individuals with more severe disabilities (mean IQ < 43).

Environment learning from virtual exploration in individuals with down syndrome: the role of perspective and sketch maps.

BACKGROUND: Spatial knowledge about an environment is an important determinant of ability to move effectively within it and of personal autonomy. Individuals with Down's syndrome (DS) have difficulty managing configural visuospatial information. METHOD: Twenty-nine individuals with DS and 29 typically developing (TD) children, matched for mental age, learned about environments through virtual exploration using a route or survey view. A sketch map of the environment was or was not presented before exploration. Then the acquisition of configural knowledge (landmark locations) and route retracing were tested. RESULTS: Individuals with DS were able to acquire configural knowledge through virtual exploration in all presentation conditions, and generally performed no worse than matched TD children. However, they were not able to benefit from the conditions that facilitated acquisition of configural knowledge in TD children, that is, seeing a sketch map before exploring and exploring in survey (rather than route) view. As regards route retracing, individuals with DS paused more often than controls and tended to travel longer paths, which made them slower overall. CONCLUSIONS: DS reduces children's ability to benefit from additional survey information and may be related to difficulty in elaborating configural/simultaneous information.