Changes in intellectual functioning associated with normal aging.

Declines in IQ scores with advancing age have been observed in each successive revision of the Wechsler Intelligence Scales. This study examined age-related changes on the fourth edition of the Wechsler Adult Intelligence Scale and compared these to the effects seen on the 1955, 1981, and 1997 standardizations of the scales. The most pronounced declines were in measures of processing speed and nonverbal reasoning. Declines in nonverbal reasoning were similar on timed and un-timed measures. Verbal abilities remained relatively stable across the life span. General intelligence as assessed by the Full Scale IQ was reduced about 1 SD by age 75 when corrections for age were removed. Age-related declines have become less pronounced since 1955, particularly on measures of processing speed. This effect was essentially linear, unrelated to concurrent IQ increases in the general population, and paralleled a 9-year increase in life expectancy during this time period.