Genetically dissociated components of working memory: evidence from Down's and Williams syndrome.

Wang and Bellugi [J clin exp Neuropsychol 1994;16:317 22] have suggested that Down's and Williams syndrome might be associated with specific and contrasting working memory deficits; with impaired verbal short-term memory in Down's syndrome, and a visuo-spatial short-term memory deficit in Williams syndrome. In two studies we examine whether these apparent deficits might simply be a consequence of the general pattern of learning difficulties associated with these disorders. Experiment 1 compared verbal and visuo-spatial short-term memory abilities in these groups, using analysis of covariance to control for mental age differences. In Experiment 2 individuals with Williams syndrome were matched to control groups for non-verbal mental age, and the short-term memory abilities of these matched groups were compared. The results of both experiments are broadly consistent with those reported by Wang and Bellugi, and support the view that working memory can be dissociated into separate subsystems.