Deterioration of frontal lobe function in normal aging: influences of fluid intelligence versus perceptual speed.

A group of young participants were compared with 2 groups of older participants (young-old, 65-74 years and old-old, 75 years or over) on a range of frontal lobe tasks. They were also assessed on the Digit Symbol Substitution Test (DSST), a test of digit cancellation (DC), the AH4 test of fluid intelligence, and the National Adult Reading Test (NART)-a measure of crystalized intelligence. Reliable age differences on all frontal measures except word fluency (FAS) were found. However, age effects were radically attenuated when either DSST speed or Alice Heim 4 (AH4) performance was used as a covariate. In contrast, DC and NART attenuated age-related variance to a much lesser degree. The authors conclude that a large proportion of age-related variance on measures of frontal lobe function may be attributed to a more general factor characterized jointly by DSST and AH4 performance.