Poster #46 - Comparing cross-sectional and longitudinal trajectories for vocabulary and nonverbal reasoning in Williams syndrome

• In Event: 2-163 - Poster Session 08
  In Poster Session: PS 08 Section - Developmental Disabilities

Integrative Statement

Introduction: Williams syndrome (WS) is a rare neurodevelopmental disorder that affects approximately 1 in 20,000 live births. Historically, language abilities in WS have been characterised as ‘spared’ or ‘preserved’ (e.g., Bellugi et al. 1990) in the context of a developmental delay or impaired overall level of cognitive functioning (see, e.g., Karmiloff-Smith et al., 2003, for an overview) and in contrast to robust evidence for particular difficulties in visuospatial processing (Mervis et al., 2000). However, reviews of the literature (e.g., Brock, 2007) indicate a more complex picture, with almost all areas of language developing atypically and performance levels in line or below those predicted by mental age. Developmental research in WS are often cross-sectional and very small in size, largely due to the sheer rarity of the population. However, by amalgamating data from different researchers for the most commonly used standardized tests – the British Picture Vocabulary Scale (BPVS) and Raven's Coloured Progressive Matrices (RCPM, a test of nonverbal reasoning) – it has been possible to explore the development of verbal and nonverbal abilities both cross-sectionally and longitudinally involving far larger participant numbers than usually viable in WS research.

Method: Cross-sectional and longitudinal datasets have been pooled together from several research groups with long histories of investigating WS across the UK, using Annette Karmiloff-Smith’s large historical database as the core. The cross-sectional data presented here involve 90 individuals with WS, aged between 5 and 39 years. BPVS and RCPM scores were available for the same 90 participants. The datasets presented for the longitudinal data were not of the same individuals, though the groups overlapped substantially. For the BPVS, data were available for 22 participants with at least 8 time points for each; they were aged 4 to 44 years. For the RCPM, data were available for 20 participants with at least 7 time points for each; they were aged 9 to 50 years.

Results: Cross-sectional data: curve-fitting of the BPVS dataset indicated that a power curve best fitted the data, reflecting a gently asymptotic and significant developmental increase of mental-age equivalent with increasing chronological-age, with 35% of the variance in the dataset was explained by the model. For RCPM, the best fit was also a power curve, but this explained only 4% of variance: there was no significant increase of mental-age with chronological-age. Longitudinal data: data for each individual were analysed using Kendall-Tau. For BPVS, only 5 individuals showed reliable development; for RCPM, development was evident for only 3 people.

Discussion: While cross-sectional methods suggest slow and steady improvements over the lifespan for verbal but not nonverbal abilities, longitudinal analyses tell a very different story: individuals have markedly different developmental trajectories from one another, with most not clearly ones of improvement. We will apply Bayesian analyses to examine whether these ‘flat’ trajectories reflect a true plateau. We will also include older participants to assess the possibility of cognitive decline.

Authors

• Harry R M Purser, Kingston University London
  Non-Presenting Author

• Michael S. C. Thomas, University of London
  Non-Presenting Author

• Emily K. Farran, University College London
  Non-Presenting Author

• Annette Karmiloff-Smith, Birkbeck, University of London
  Non-Presenting Author

• Jo Van Herwegen, Kingston University
  Presenting Author