PROCESSING SPEED, WORKING-MEMORY, AND FLUID INTELLIGENCE - EVIDENCE FOR A DEVELOPMENTAL CASCADE

Processing speed, working memory capacity, and fluid intelligence were assessed in a large sample (N = 214) of children, adolescents, and yo ung adults (ages 7 to 19 years). Results of path analyses revealed tha t almost half of the age-related increase in fluid intelligence was me diated by developmental changes in processing speed and working memory , and near ly three fourths of the improvement in working memory was m ediated by developmental changes in processing speed. Moreover, even w hen age-related differences in speed, working memory, and fluid intell igence were statistically controlled, individual differences in speed had a direct effect on working memory capacity, which, in turn, was a direct determinant of individual differences in fluid intelligence.