Effective external reminders impair the practice effect of time-based prospective memory.

The practice effect of time-based prospective memory (TBPM) refers to the phenomenon that TBPM task performance can be significantly improved by repetitive behavioural training. However, reminders are a common strategy for people to perform TBPM tasks in daily life. A large amount of evidence shows that reminders can improve TBPM performance when individuals pay less attention to time information. However, the present study was the first to explore whether external reminders might simultaneously impede the practice effect of TBPM. In this study, 81 undergraduate students were randomly assigned to control group (N = 27, M  = 20.00, SD  = 1.04), reminder group (N = 26, M  = 20.35, SD  = 1.70) and non-reminder group (N = 28, M  = 20.25, SD  = 1.17). In the training stage, the reminder group could receive effective external reminders, while the non-reminder group could not. The results of the training stage revealed that compared with the non-reminder group, the reminder group had fewer time monitoring times and better TBPM performance. In the testing stage, when reminders were removed from the reminder group, we found that compared with the control group without TBPM training, the TBPM performance of the reminder group failed to improve, while that of the non-reminder group improved significantly. Meanwhile, the time estimation ability of the reminder group was not as improved as that of the non-reminder group.