Time-based prospective memory (PM) refers to remembering to perform deferred actions at a specified time in the future. Event-based PM refers to remembering to perform deferred actions when a target cue is encountered in the future. It has been well-established in the event-based PM literature that having a PM requirement exacts a cost to the ongoing task. However, the few studies in time-based PM that have investigated costs to ongoing tasks have produced contradictory findings (e.g. Hicks et al., 2005; Waldum & Sahakyan, 2012; Marsh et al., 2006; Jägar & Kliegel, 2008). The overarching goal was to explore how participants perform time-based PM task, specifically, the extent to which internal and external control processes are employed and needed to perform time-based task successfully. External control refers to external factors (e.g. clock) while internal control refers to internal time keeping mechanisms (e.g. internal clock) used to maintain the intent to respond and make prospective timing estimates. The first aim of my research was to examine the contradictory findings of cost in time-based PM retrieval by using a single PM intention. The second aim of my research was to investigate the effects of explicit reminders on PM accuracy, cost, and clock checking behavior. The third aim of my research was to examine the effect of matched or mismatched expectations of an explicit reminder on PM accuracy, cost, and clock checking behavior. In particular, I examined whether participants expecting a reminder were able to localize their clock checking and costs to the time period after the reminder occurred. The fourth aim of my research was to examine the effects of implicit reminders on PM accuracy, cost, and clock checking behavior.
The aim of Experiment 1 was to examine whether having a time-based intention exacted a cost to the ongoing task and also to examine the effects of a reminder on PM accuracy and cost under standard conditions (i.e. when clock checking was not discouraged). The results of Experiment 1 indicated no significant cost to the ongoing task with a PM requirement when clock checking frequency was high, and this was attributed to greater reliance on external control processes to track the passage of time. PM performance was numerically but not statistically better in the reminder condition than the no reminder condition. Having a PM reminder did not influence cost to the ongoing task, but a reminder encouraged participants to check the clock immediately after the reminder was presented. Hence it is concluded that a PM reminder did not have a significant impact on PM performance, but it reminded participants to perform clock checks immediately after the reminder was encountered.
In Experiment 2, participants were discouraged from checking the clock because it was believed that the high number of clock checks (M = 22) performed in Experiment 1 could have externalized the control needed to perform the PM task. The absence of significant costs in the PM conditions of Experiment 1 could be attributed to unlimited clock access. The results of Experiment 2 indicated that significant costs were found in the PM conditions, which suggested that the internal timing mechanism employed was attentionally demanding. PM performance was numerically but not statistically better in the reminder than no reminder condition and participants were likely to check the clock immediately after a reminder occurred. Consistent with Experiment 1, the PM reminder did not influence cost to the ongoing task. Experiment 2 demonstrated increased cost when participants had to rely on internal control to maintain the intent to respond and make prospective timing estimates.
Experiment 3 examined how participants’ meta-cognitive beliefs regarding the presentation of a reminder would influence costs and clock checking. In particular, I examined whether participants expecting a reminder were able to localize clock checking (external control) and costs (internal control) to the time period after the presentation of the reminder. Participants were informed that a reminder would occur during the experiment, and the actual reminder presentation was either given or withheld. The results of Experiment 3 indicated that PM performance was significantly better in the PM reminder condition than the PM no reminder condition, but clock checking instruction did not predict PM accuracy. Consistent with Experiments 1 and 2, no cost to the ongoing task was found in the standard clock condition but significant costs were observed in the discourage clock condition.
Experiment 4 examined whether implicit cues were effective reminders of the time-based PM task. Three implicit cues (clock, watch, hours) known to elicit response ‘time’ in free association were embedded in the ongoing task. The findings of Experiment 4 revealed that participants were unable to use the implicit cues to activate the concept, which would trigger the PM intent as evidenced by the absence of clock checking immediately following the presentation of the implicit cues. It was possible that participants were unable to detect the implicit cues because they were not instructed to expect reminders during the experiment. The results of Experiment 4 indicated that PM performance in reminder condition was slightly more accurate than no reminder condition; however, this difference did not reach significance, possibly due to a lack of statistical power.
In summary, the present research revealed how individuals externalized and internalized control and how these types of control influenced the way they performed a time-based PM task. It also demonstrated that a having an external reminder improved PM performance compared to a no reminder condition. Metacognitive beliefs about reminder presentation did not help participants localize clock checking and costs to the time period after the presentation of the reminder. Further research needs to be conducted on implicit cues to determine their effects in the retrieval of time-based PM intention. The results from the four experiments highlighted the importance of external versus internal control and how reminders influenced the retrieval strategies in time-based PM.