Time-based prospective remembering: interference and facilitation in a dual task

The aim of this study was to analyse prospective memory behaviour when people have to fulfil two different intentions whose retention intervals partially over- lapped. More specifically, the purpose of the study was to explore the effects of a secondary PM task (either time-based or event-based) on performance of a main time-based PM task. Four embedded conditions were tested: two event-based ones and two time-based ones. The time- and event-based interpolated tasks differed in how closely their target time was to the 20-minute response required by the main time-based task (16th and 19th min., respectively). The results indicated that when a main time-based prospective memory task shares a portion of the retention interval with a second time-based prospective task, this overlapping facilitated performance on the main task. However, the interpolated tasks appeared to be affected by the moment in which they were administered during the execution of the main time-based task. More specifically, a decrease in the interpolated task performance was observed when this was time-based and had to be executed very closely to the target time of the main task. On the contrary, when the two tasks were different (event-based vs. time-based), there was neither interference, nor facilitation.