Time-based prospective memory

Intentions whereby the execution of an action is governed by the passage of time rather than by the presence of an external cue or event are called time-based PM tasks (Einstein &

McDaniel, 1990). Intentions that need to be performed at a specific time or after a predefined period of time have elapsed both fall under this term. Typical time-based PM tasks might include remembering to attend an appointment at a specific time (e.g., 10am) or remembering to take the dinner from the oven after a cooking period has elapsed (e.g., after 20-minutes has passed). In each case, the realisation of an intention is dependent on the strategic monitoring of time. Laboratory tasks which are commonly used to investigate time-based PM involve remembering to mail items to an experimenter on a specific date (see Dobbs & Rule, 1987;

Meacham & Leiman, 1982) or remembering to complete a questionnaire at various time-intervals during the test-session (Hadjiefthvoulou et al., 2011a; for further details see Chapter 5, Section 5.2).

The estimation of time during time-based PM tasks is known as prospective timing.

Conclusions from a recent meta-analytic review (Block, Hancock & Zackay, 2010) suggests that prospective timing is dependent on an attentionally driven internal clock mechanism and not by memory for interval information (i.e., the information required to be remembered during a specific time-interval). To test this proposal, Waldum and Sahakyan (2012) gave

participants an ongoing task with a time-based PM element and asked them to produce an estimation of time after the entire time interval (Experiment 1). During the time interval, participants were required to complete a lexical decision task (ongoing task) while a number of songs were played in the background. Longer verbal time estimates were produced when participants remembered more songs from the time interval. This finding is not in concert with conclusions from Block et al. (2010) and rather suggests that prospective timing is affected by memory for interval information. One possible implication of this finding might be that people who display accuracy in terms of prospective timing do so at the expense of memory for interval information. Furthermore, this finding implies that people who remember to carry out PM tasks may do so at the expense of other ongoing everyday activities.

Early investigations of time-based PM have explored the strategies employed by people to aid prospective remembering and indeed prospective timing (Ceci &

Bronfenbrenner, 1985; Harris & Wilkins, 1982). One of the first strategies to be explicitly identified in the literature is strategic time monitoring. Strategic time monitoring can be characterised by the following three phases; a) an early calibration phase where people engage in frequent clock-monitoring in an attempt to synchronise their own psychological clocks, b) an intermediate phase where clock-monitoring is less frequent and the person concentrates on other activities, c) a scalloping phase where a period of intense clock-checking occurs a short time before the delayed intention has to be realised (Ceci &

Bronfenbrenner, 1985). Consistent with this proposal, Harris and Wilkins (1982) found that their sample of adult women engaged in frequent clock-checking behaviour shortly after being asked to complete a time-based PM task. This was followed by a period of less frequent clock-checking where the women were able to focus on other ongoing tasks. Finally, there was a strategic burst of clock-monitoring just before the delayed intention should have been realised. Importantly, time-based prospective remembering was enhanced when participants intensified their clock-monitoring behaviour towards the end of the target period.

A further study of a younger sample of 10 and 14 year old children showed similar findings (Ceci & Bronfenbrenner, 1985). Children were given the task of removing cupcakes from an oven following a 30-minute time-delay. There were two experimental conditions whereby participants either completed the task in a familiar (i.e., their own home) or an unfamiliar context (i.e., a laboratory). A clock was provided for time monitoring and children were given the opportunity to play a video game during the delay interval. Total number of

clock checks did not predict time-based PM performance. Rather, increased clock-monitoring towards the end of the baking period increased prospective remembering suggesting that this may also have increased accuracy in prospective timing. Age-related differences in time-based prospective remembering were also found. Specifically, older children (14 year olds) made more efficient use of strategic time monitoring, especially towards the end of the baking period This particular study has highlighted improved PM performance as children become young adults. However PM performance does not remain stable throughout adulthood with a growing body of literature suggesting PM performance becomes impaired in older adults.

Theoretical Models of time-based PM

An important characteristic of prospective remembering is that the recollection of an intention occurs without an explicit request for retrieval. Below several theories which attempt to explain how people might retrieve time-based intentions from memory are outlined.

Harris and Wilkins’ (1982) model of time-based PM (Test-Wait-Test-Exit; TWTE model) suggests that a PM task is encoded and a test of memory is conducted after a period of time has elapsed. If the time for retrieval is not correct, further tests of memory are conducted until a test is performed during a critical period (i.e., the time when it is appropriate for an intention to be realised). It is at this point when a person should then perform an action directed towards the realisation of an intention. This model of time-based PM assumes that the monitoring of time leads to better PM performance. Studies which have shown evidence of strategic time monitoring during time-based PM tasks and in particular during the period preceding the target time support the TWTE model (Einstein & McDaniel, 1990; Harris & Wilkins, 1982). While it is assumed that monitoring is a deliberate and self-initiated process which is reliant upon a person’s attentional resources (Einstein et al., 1995;

Park et al., 1997), the TWTE model fails to explain how a person makes themselves aware of time in the absence of cues (Sellen, Louie, Harris & Wilkins, 1997, p.484). Harris and Wilkins (1982) suggest that an intention might spontaneously appear in a person’s mind for no apparent reason. Findings which have presented self-report accounts of spontaneous recollections for real-life intentions support this possibility (Ellis & Nimmo-Smith, 1993).

Alternatively, Wilkins and Baddeley’s (1978) “Random Walk” model suggests that time-based PM retrieval is dependent entirely on incidental factors rather than self-initiated processes. The “Random Walk” model is based on the concept that the mind is a multidimensional space. They suggest that a trace which represents the intention is placed in this space when it is first formulated. However, during the time interval between the formation of an intention and its retrieval from memory, a person’s thoughts are displaced throughout this space. The areas in which a person’s thoughts become distributed are dependent upon the stimuli in the environment and the activities that they engage in during the time interval. The likelihood that an intention will be realised is increased if a person’s thoughts are located around the trace for an intention at the appropriate time for retrieval.

In a recent investigation, Kvavilashvili and Fisher (2007) examined the extent to which the TWTE model and The “Random Walk” model can explain the retrieval processes involved in event- and time-based PM. The authors compared self-reported rehearsal processes involved in time- (Study 1 and Study 2) and event-based (Study 3) PM tasks.

Participants were required to phone the experimenter at a specific time (time-based PM) or after they received a text message (event-based PM). In order to identify the underlying retrieval processes involved in PM retrieval, participants were asked to keep a record of the occasions on which they thought about an intention during a seven day time interval.

Findings confirmed assumptions of the TWTE model (Harris & Wilkins, 1982) and showed that time-based intentions were either triggered by incidental cues or appeared in a person’s mind for no obvious reason. Despite these findings, there were a few reports of self-initiated rehearsals where participants used effortful retrieval processes to aid remembering for time-based intentions.

In addition to this, Kvavilashvili and Fisher (2007) suggest that the delay period between the formation of an intention and its retrieval from memory (retention phase) can influence the retrieval process. First, they propose that a person will keep short-term intentions in their mind for the entire delay period (i.e., conscious thoughts about the intention). This suggestion is in line with Harris and Wilkins’ TWTE model (1982) in that it assumes that time-based PM tasks involve self-initiated retrieval processes. However, the process of retrieval for long-term PM tasks appears to be very different. This is because there is additional opportunity for the intention memory to dissipate over longer delay periods.

Reports from participants in Kvavilashvili and Fisher’s (2007) investigation showed low

levels of self-initiated rehearsal in long-term PM tasks. Instead, there were increased incidences of rehearsals which were triggered by incidental cues completely unrelated to the intention. Once again, this finding is consistent with assumptions of Harris and Wilkins (1982). Further evidence for this model of time-based PM comes from findings which suggest that people use incidental cues including clocks, calendars and timetables to aid time-based PM (Harris & Wilkins, 1982; Sellen et al., 1997).

While Kvavilashvili and Fisher’s (2007) investigation provides substantial support for Harris and Wilkins’ TWTE model (1982) of time-based PM, some other important conclusions must be acknowledged. The overall findings suggest that time- and event-based PM are not mediated by different retrieval processes and that thoughts about each type of intention (event- or time-based) occur through one or a combination of the following routes.

Rehearsals are either prompted by incidental cues, by self-initiated planning processes, or by no apparent triggers. In relation to this finding, it seems that the difference between the retrieval processes for time- and event-based PM is quantitative rather than qualitative. For example, the low activation levels of event-based PM tasks appear to be constant, yet sufficient to sensitise a person towards a target. Nonetheless, this level of activation may not be enough for the task to pop into one’s mind. In contrast, the activation levels of time-based tasks appear to be higher and fluctuate over time resulting in episodic conscious thoughts about the task.