The extent to which increasing age is associated with impairment in cognitive function, termed cognitive aging, may have been overestimated in prior studies. The inclusion of individuals with severe or uncontrolled systemic medical illness or prodromal neurodegenerative disease in normal aging samples is likely to bias estimates toward lower cognitive performance and inflate estimates of variability.
Unbiased estimates of cognitive aging in 658 adults aged 60–84, who underwent rigorous screening to ensure their general and cognitive health, were computed. The first study screened the psychometric properties of a battery of neuropsychological tests in order to identify those with optimal properties to evaluate cognitive aging. The second study used the selected tests to compare baseline performance within 5-year age bands from 60 to 84.
The first study identified a battery of 12 tests that provided reliable measures of memory, psychomotor speed, attention, and executive function and were appropriate for investigating age-related cognitive changes. The second study observed moderate to large age-related impairment for performance on tests of complex psychomotor function, category fluency, verbal learning, and verbal and visual memory. No, or only small, age effects were observed for working memory, phonemic fluency, learning of visual information, and reaction time.
These data suggested that while increasing age is associated with impairment in cognitive function, this impairment is less severe and is evident only on more complex neuropsychological tests than estimated previously in samples selected using less rigorous criteria to ensure cognitive health.