Sentence memory of individuals with Down's syndrome and typically developing children

Background Individuals with Down's syndrome (DS) have an auditory short-term memory span disproportionately shorter than the non-verbal mental age (MA). This study evaluated the Baddeley model's claim that verbal short-term memory deficits might arise from slower speaking rates (and thus less material rehearsed in a 2 s passive store) by using the sentence memory subtest of the Stanford-Binet. Previous work had shown digit span recall speaking rate to be comparable to the examiner's slow rate (one syllable per second) for both DS and language-matched participants. Method Thirty individuals with DS were compared to two control groups [non-verbal MA-matched and mean length of utterance (MLU)-matched] on the sentence span and speaking rate for the longest verbatim recalled sentence. Sentence stimuli were presented at a normal speaking rate. Results The DS group had shorter sentence memory span than the MA-matched group and a faster, rather than slower, speaking rate (syllables per second) than the MLU-matched controls. Conclusions Language production level accounted for a substantial portion of the variance in the sentence memory span in the DS group. Thus, language production skill, rather than speaking rate, predicts variability in verbal memory span.