Prospective memory (PM) is the ability to execute a planned action in the future (e.g., remembering to take medication before going to bed). Prior work has suggested that PM failure can account for 50-80% of reported memory problems. Research has also shown that PM becomes increasingly impaired in the Alzheimer's disease (AD) process. To our knowledge, most PM studies use PM accuracy as a measure of PM performance. However, examining the speed of the response as it relates to the AD process remains relatively unexplored. In this study, we examined both PM accuracy and speed in healthy aging, mild cognitive impairment (MCI), and AD.

Participants included healthy older controls (N=65), persons with MCI (N=70), and persons with AD (N=11). The PM task was embedded within a working memory task as PM demands often occur during an ongoing activity in everyday life. For the working memory component of the PM task, participants were shown a series of words and asked to continuously monitor the words while maintaining the last 3 in memory. All words were displayed within 1 of 6 background patterns. For the PM component, participants were asked to press "1" on the keyboard whenever they were shown a particular background pattern on the screen. PM abilities were measured using the median response time and total accuracy.

Age was correlated with PM accuracy. An ANCOVA, controlling for age, and examining the impact of diagnosis on PM accuracy, was significant. Post-hoc tests revealed a trend toward the AD and MCI groups being less accurate than healthy controls. In contrast to accuracy, age was not related to PM speed. An ANOVA examining the impact of diagnosis on PM accuracy found that the AD group responded faster than healthy controls. The MCI group did not show differences in speed from the healthy control and AD groups.

Overall, the pattern of results differed in accuracy and speed of PM performance. There was a trend for the MCI and AD groups being less accurate than the controls, with no difference in performance between the MCI and AD groups. However, the AD group responded more quickly than the controls, which may have impacted their accuracy. These findings indicate that PM performance differences among groups can be detected by examining speed and not just accuracy. As speed appears to be an essential aspect involved in PM performance, future research should consider incorporating speed as a measure of PM performance when examining PM differences in populations.