The roles of working memory updating and processing speed in mediating age-related differences in fluid intelligence.

This study was conducted to investigate the relative roles of working memory updating (updating) and processing speed in mediating age-related differences in fluid intelligence. A sample of 142 normal adults between 18 and 85 years of age performed a set of updating, processing speed, and fluid intelligence tasks. Hierarchical regression analyses indicated that the proportion of unique age-related variance in updating measures was related to the complexity of speed measures. There was a larger proportion of unique age-related variance in updating measures after controlling for the variance in simpler speed measures. Moreover, structural equation modeling showed that updating mediated almost all the age-related effects on fluid intelligence. These results suggest that updating, but not speed, is the critical mediator between age and fluid intelligence. In addition, the speed mediation of age-related differences in fluid intelligence as indicated by previous studies is at least partially derived from the executive component of speed measures.