Optimal time-of-day and consolidation of learning in younger and older adults.

The current study investigated the relationship between intraindividual variability and associative learning in younger and older adults. The authors hypothesized that higher levels of intraindividual variability would be associated with a reduction in the benefits of practice during learning, and that nonoptimal testing times would magnify these effects. Results indicated that older adults showed an increase in reaction time (RT) standard deviation (SD) relative to mean RT in the evening. Although time-of-day did not have a significant effect on rate of learning or total learning, intraindividual variability did predict learning rate of younger adults at nonoptimal testing times. Results are discussed in light of theoretical models of aging and learning.