How much of age-related changes in fluid and visual-spatial problem solving relate to processing speed?

Cognitive aging across the lifespan has long been of interest to intelligence researchers. Recent research has examined cognitive aging on the most up-to-date and widely used measure of adult intelligence, the WAIS-5, using both cross-sectional and quasi-longitudinal methodologies. The results of both investigations agreed with a large body of literature, with both problem-solving ability and processing speed declining precipitously across the 20–90-year age range. The present WAIS-5 study utilized the same database (adults ages 20–90 years, n = 1660) to gain greater insight into the interplay between problem solving and processing speed. Specifically, we asked: Do adults' scores on problem-solving tasks continue to change substantially with increasing age, even after controlling for processing speed? Furthermore, are the findings comparable for fluid versus visual-spatial problem-solving tasks, for males and females, and for different portions of the age range? Basic findings of the MANOVAs (Indexes) and MANCOVA (subtests) revealed the impact of processing speed on the age-related changes in problem solving. During the period of mild decrease in problem-solving ability (ages 20–60), covarying processing speed reduced the age-related changes by roughly 20–35%; during the period of substantial decrease (ages 60–90), that reduction jumped to approximately 80%. Overall, the findings were similar for fluid and visual-spatial problem-solving tasks, and for males versus females. In general, WAIS-5 results accord well with previous research on the WAIS-IV, although that earlier study did not evaluate the impact of speed on fluid versus visual-spatial problem solving or its role at different portions of the age range.