What links verbal short-term memory performance and vocabulary level? Evidence of changing relationships among individuals with learning disability

Two studies are presented that adopt a novel approach to determining whether verbal short-term memory performance is causally related to vocabulary acquisition in childhood. This involves examining whether verbal short-term memory measures are more closely related to the absolute level of individuals’ vocabulary, or the rate at which vocabulary has been attained. In a first study, two groups of individuals with learning disability, who differed in age but were matched for vocabulary knowledge at around the 8-year-old equivalent level, showed comparable verbal short-term memory performance. However, a second study showed that in less developed individuals functioning around the 5-year-old level of vocabulary development, matching for vocabulary knowledge did not equate verbal short-term memory performance across groups differing in chronological age. This pattern is consistent with the view that variance in verbal short-term memory performance is causally related to individual differences in vocabulary acquisition, but only early on in development.