Background: Many studies have indicated that individuals with Down's syndrome (DS) show a specific deficit in short-term memory for verbal information. The aim of the present study was to investigate the influence of the length of words on verbal short-term memory in individuals with DS.
Methods: Twenty-eight children with DS and 10 control participants matched for memory span were tested on verbal serial recall and speech rate, which are thought to involve rehearsal and output speed.
Results: Although a significant word-length effect was observed in both groups for the recall of a larger number of items with a shorter spoken duration than for those with a longer spoken duration, the number of correct recalls in the group with DS was reduced compared to the control subjects. The results demonstrating poor short-term memory in children with DS were irrelevant to speech rate. In addition, the proportion of repetition-gained errors in serial recall was higher in children with DS than in control subjects.
Conclusions: The present findings suggest that poor access to long-term lexical knowledge, rather than overt articulation speed, constrains verbal short-term memory functions in individuals with DS.