Although much recent research has focused on event-based prospective memory (PM), fewer studies have compared event- and time-based PM. In the current study, two experiments were conducted to directly compare ongoing task costs of focal and non-focal event-based tasks with a time-based task. In the second experiment, an external reminder of the task was present to test whether this reduced the cost of the time-based task. PM accuracy was significantly greater for the focal conditions, as predicted. Response times (RT) were highest in the non-focal tasks, with similar RTs in the focal and time-based tasks. Clock check frequency was significantly related to making a PM response in the time-based task, with clock checks increasing as the 7 min target time approached. While time-based tasks may be more difficult to complete, they do not seem to result in the speed cost to an ongoing task that non-focal PM tasks do.
Keywords: Prospective memory; cognitive cost; monitoring; time estimation.