Speed of processing, control of processing, working memory and crystallized and fluid intelligence: Evidence for a developmental cascade.

The present study investigated the causal relations among age, speed of processing, control of processing, working memory and intelligence, fluid and crystallized. 158 participants aged from 7 to 18 years old completed a large battery of tests measuring latent factors of speed, control of processing and working memory. Intelligence was assessed using the Wechsler Abbreviated Scale of Intelligence. Structural equation modeling was performed to determine whether there is a cognitive-developmental cascade in which age-related increases in processing speed lead to improvements in control of processing that leads to increases in working memory, and whether improved working memory, in turn, leads to increases in both fluid and crystallized intelligence. Several alternative models of a different cascade order of the above factors were also tested. The results of the present study provide evidence of a cognitive-developmental cascade, confirming that this model describes cognitive development during childhood and adolescence. • The results confirm a cognitive-developmental cascade. • Our models demonstrate that developmental increases in WM contribute directly to the improvement of children's intelligence. • Age-changes in processing speed and control of processing do not contribute directly to increases in intelligence. • There is a causal chain connecting directly WM with fluid and crystallized intelligence. • Processing speed and control of processing influence indirectly fluid and crystallized intelligence. [ABSTRACT FROM AUTHOR]