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The nature of the developmental association between phonological memory and vocabulary knowledge was explored in a longitudinal study. At each of 4 waves (at ages 4, 5, 6, and 8 yrs), measures of vocabulary, phonological memory, nonverbal intelligence, and reading were taken from 80 children. Comparisons of cross-lagged partial correlations revealed a significant shift in the causal underpinnings of the relationship between phonological memory and vocabulary development before and after 5 yrs of age. Between 4 and 5 yrs, phonological memory skills appeared to exert a direct causal influence on vocabulary acquisition. Subsequently, though, vocabulary knowledge became the major pacemaker in the developmental relationship, with the earlier influence of phonological memory on vocabulary development subsiding to a nonsignificant level. (PsycINFO Database Record (c) 2008 APA, all rights reserved)
Gathercole et al. (1992) studied this question.