Differential effects of delay on time-based prospective memory in younger and older adults.

The current study measured forgetting in a time-based, naturalistic prospective memory (PM) task. In Experiment 1, younger and older participants were asked to mail a stamped postcard on a date that was delayed 1, 2, 5, 14, or 28 days in the future. In Experiment 2, a different sample of older participants completed the same task with similar delays to replicate results for the older sample in Experiment 1. Overall, older participants were more likely than younger participants to mail the postcard on time. In addition, delay affected on-time return rates more for the younger participants than the older participants. Younger participants' return rates illustrated the typical forgetting curve seen in numerous retrospective memory studies (i.e., rapid decline at shorter delays and slower decline for longer delays). However, older participants' return rates only declined at the longest delays. These results indicate that time-based PM performance declines with an increase in delay, but the form of the decline may differ across age groups.