Cycles in speed-working memory-G relations: Towards a developmental-differential theory of the mind
AuthorDemetriou, Andreas P.
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This article presents three studies, two of them longitudinal, which investigated the relations between age, processing speed, working memory (WM), and fluid intelligence (g f) from 4 to 16years of age. Structural equation modeling showed that speed was a powerful covariate of age (~-.6 to -.7) from 4 to 13years, declining thereafter (to ~-.2). WM was stably related to speed through the whole age-span studied (~-.4 to -.5). A large part (59%) of age-related changes in g f (83%) from 4 to 7years and a lower but significant part later on, especially in adolescence (~10-20% out of ~40-50%), were mediated by WM. However, with speed and age controlled, WM was almost fully commensurate with g f (~.9), from about the age of 8-9years onwards. A series of models suggested an ever present efficiency level defined by speed and control and a representational level defined by WM and gf, which are increasingly differentiated with development. All processes develop in cycles concerted by a dynamic G. Change in each process over time originated from within the processes themselves and G, in proportions varying with developmental phase. Overall, speed signified age-associated changes in processing capabilities, partly expressed in WM expansions and g f reconstructions. An overarching model is proposed integrating differential with developmental theories of human intelligence. © 2012 Elsevier Inc.