Cross-sectional and longitudinal relationships among age, cognition, and processing speed

Cross-sectional and longitudinal age effects on cognitive function were exa mined in 302 older adults followed longitudinally. Processing speed was rel ated to cognitive performance at cross-section, and change in speed predict ed within-person longitudinal cognitive decline. Statistical control of pro cessing speed greatly reduced cross-sectional age effects but did not atten uate longitudinal aging effects. This difference in processing speed's abil ity to account far cross-sectional and longitudinal age effects is discusse d in the context of theories of cognitive aging and methodological and stat istical issues pertaining to the cross-sectional and longitudinal study of cognitive aging.