Intraindividual variability (IIV) in cognitive speed, or moment-to-moment changes in ability, is a developmental phenomenon indicative of neurological integrity that increases gradually across adulthood. Past research has shown that IIV negatively covaries with cognitive performance, in which higher IIV at one occasion is associated with poorer…

Age differences in intellect as reflected by performance on the Wechsler Adult Intelligence Scale (Revised) (WAIS-R) were evaluated for persons aged 20 to 74 years. Educational attainment levels were held constant. The WAIS-R sample included 1,480 men and women in the following seven age groups--20-24 years (n=250), 25-34 years (n=250), 35-44…

A major issue concerning adult intellectual development is whether intellectual decline in late adulthood is uniform or ability-specific. Differential patterns of ability decline were analyzed by comparing data on longitudinal age change over the age range from 53 to 81 years from two successive 14-year periods (1956-1970 and 1970-1984). The…

This report reviews a theoretically inspired empirical investigation of individual differences in knowledge, abilities, and nonability traits as part of an ongoing effort to better understand adult intellectual development and to develop more accurate measures of adult intelligence. Twenty Knowledge Scales were constructed, drawing on…