Speech timing and verbal short-term memory: Evidence for contrasting deficits in Down syndrome and Williams syndrome

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Abstract

This study explored the degree of verbal short-term memory deficit among individuals with Down syndrome and Williams syndrome, and the extent to which any such impairment could be accounted for by a relative slowing of rehearsal and output processes. Measures of serial recall and detailed assessments of speeded articulation for short and long words were assessed among these two populations, and controls. Both clinical groups showed an impairment in serial recall. Among individuals with Williams syndrome this deficit could be explained in terms of a general slowing in speech rate. However, although aspects of speeded articulation were delayed among individuals with Down syndrome, this could not account for the extent of impairment in their verbal short-term memory performance. The implications of these findings for the source of impaired verbal short-term memory associated with Down syndrome, and for the word length effect at different levels of development, are discussed.

Section snippets

Participants

Four groups of participants took part in this study, individuals with Down syndrome and individuals with the Williams syndrome phenotype of a similar average age, as well as two samples of typically developing children. The group of individuals with Down syndrome consisted of 14 children and teenagers, six male and eight female, aged between 9 years 8 months and 18 years 8 months. All individuals had confirmed trisomy 21 without mosaicism, and were recruited from local schools for children with

Preliminary analyses

The reliability of the short-term memory and articulation time measures was assessed in the whole sample of 60 individuals, prior to further separate analyses of each clinical group and their associated controls. Split-half reliability was calculated for recall of both short and long words by comparing the number of trials correct calculated across the first two and the last two trials at each span length. Spearman–Brown reliability estimates for short word and long word recall trials were .86

Discussion

The main aim of this study was to explore the impact of speech production skills on short-term memory performance among individuals of a comparable age, but with two different developmental disorders, Williams syndrome and Down syndrome. Although data from these two populations were not analysed together in the above analyses, because of the difficulties of equating these groups on any meaningful matching variable (cf. Klein & Mervis, 1999), the fact that both groups were themselves matched to

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    We are grateful to the members of the Down Syndrome Association and Williams Syndrome Foundation who took part in this work, and to the staff and pupils of the following schools for their help and cooperation: Air Balloon Infants School, Bristol; Cheddar Grove Primary School, Bristol; Fosse Way School, Midsomer Norton; Kingsweston School, Bristol; Raysfield Junior School, Chipping Sodbury; Ravenswood School, Nailsea. We thank Jon Brock for his helpful comments on an earlier version of the manuscript. This collaboration was initiated while Nelson Cowan was supported by a Benjamin Meaker Visiting Professorship from the University of Bristol, UK, and by NIH Grant R01 HD-21338 from the United States.

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