The purpose of this study was to examine determinants of time-monitori
ng to clarify the cognitive process in prospective memory tasks (i.e.,
tasks which require the timely execution of a previously intended act
ion). Thirty-two participants were asked to perform future activities
three minutes after the start of backgound tasks, and their time-monit
oring responses were recorded. The results showed that higher motivati
on and less cognitive load led to higher time-monitoring frequency and
better performance in prospective memory tasks. However, with time pr
esentation, time-monitoring frequency could be reduced, while the perf
ormance in prospective memory tasks was improved. The findings indicat
e that information which facilitates the maintenance of inner time mod
el is an important factor for effective time-monitoring. This study su
ggested that frequency of time-monitoring could be regarded as a criti
cal factor in the theoretical analysis of prospective memory tasks.