Processing speed, working memory and reasoning ability from childhood to old age

The study investigated whether theoretical causative relations among declining cognitive abilities during adulthood and old age conform to a literal reversal of improving cognitive development during childhood. Children aged 8–14 years (n = 240) and adults aged 18–87 (n = 238) completed the same battery of psychometric tests, which defined latent traits for processing speed, working memory, and reasoning ability. Speeded performance improved during childhood and slowed across the adult range. Childhood performance was well described by a developmental cascade, whereby increasing chronological age is accompanied by faster processing speed, which influences improved working memory, which in turn influences improving reasoning ability. However, although adult performance resembled a cascade with diminishing reasoning ability mediated by processing speed and working memory, this was not a mirror image of the cascade for children. The main difference with adults was a direct causal path between age and working memory. Post hoc analysis located this among adults aged 55 years and over. This suggests that, whereas childhood cognitive development is substantially mediated by processing speed, declining reasoning ability in old age is influenced by slower processing speed but also by age-related change(s) influencing working memory that are independent from processing speed.