Prospective Memory: Processes, Lifespan Changes, and Neuroscience

2.45 Prospective Memory: Processes, Lifespan Changes, and Neuroscience G. O. Einstein, Furman University, Greenville, SC, USA M. A. McDaniel, Washington University, St. Louis, MO, USA R. L. Marsh, University of Georgia, Athens, GA, USA R. West, Iowa State University, Ames, IA, USA ª 2008 Elsevier Ltd. All rights reserved.

2.45.1 2.45.2 2.45.2.1 2.45.2.2 2.45.3 2.45.3.1 2.45.3.2 2.45.3.3 2.45.4 2.45.4.1 2.45.4.2 2.45.4.3 2.45.5 2.45.6 2.45.6.1 2.45.6.2 2.45.7 2.45.8 2.45.8.1 2.45.8.2 2.45.9 2.45.9.1 2.45.9.2 2.45.9.3 2.45.10 References

The Importance of Prospective Memory in Everyday Life Paradigms for Studying Prospective Memory Nonlaboratory Paradigms Laboratory Paradigms Varieties of Prospective Memory Tasks and How They Are Measured Event-Based Prospective Memory Time-Based Prospective Memory Activity-Based Prospective Memory Retrieval of Prospective Memories: Retrieval Without an Explicit Request to Remember Attentional Monitoring Theory Spontaneous Retrieval Theory Multiprocess Theory Storage of Prospective Memories: Do They Enjoy a Privileged Status in Memory? Encoding of Prospective Memories Associative Encoding Target Cue Encoding Similarities and Differences Between Prospective and Retrospective Memory Development and Prospective Memory Prospective Memory in Children Prospective Memory in Older Adults Cognitive Neuroscience of Prospective Memory Neuropsychology Functional Neuroimaging Electrophysiology Summary

Prospective memory involves remembering to perform actions in the future. Thus, remembering to buy a loaf of bread on the way home, remembering to go to the dentist for an appointment, and remembering to actually attach an attachment to an email all are examples of prospective memory. Prospective memory has often been contrasted with retrospective memory (we explore this distinction in more detail in a subsequent section), which is what is typically studied in the laboratory. Remembering the plot of a movie that you saw 2 weeks ago and remembering a

867 869 869 870 871 871 872 872 872 873 873 875 877 878 878 880 880 881 882 883 884 884 885 886 888 888

list of words presented in an experiment are examples of retrospective memory.

2.45.1 The Importance of Prospective Memory in Everyday Life An interesting feature of prospective memory is that it is prevalent in everyday life and central to normal functioning, and yet it is an area that until recently has been neglected by memory researchers. In 867

868 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

reflecting on the activities in our typical day, it is easy to realize the enormous number of prospective memory demands that permeate our lives. From remembering to take vitamins and medication in the morning to remembering meetings, appointments, and errands throughout the day, our lives are full of prospective memory demands. Consistent with this impression that prospective memory demands are ubiquitous, Crovitz and Daniel (1984), in a study in which they asked students to record in a diary all instances of forgetting over a 1-week period, found that about half of the reported instances of forgetting were prospective in nature. Not only do prospective memory demands permeate our lives, but successful remembering is also critical to normal and efficient functioning. Consider that one-third of older adults take three or more medications on a regular basis (Morell et al., 1997). Problems in remembering to take these medications could have serious health consequences and could threaten independent living. Consider also that prospective memory demands are often the cause of mistakes and accidents at work (Reason, 1990). Indeed, Nowinski et al. (2003), in examining voluntary reports of cockpit incidents from pilots to the Aviation Safety Reporting System, found that 74 of the 75 memory failures in their sample were prospective in nature. From the other side of airline safety, imagine the consequences of prospective memory failure for a busy air traffic controller, who gets the thought to reroute an airplane but cannot do so immediately because she is engaged in another activity and therefore must hold on to the intention until she is free. As another example, despite the best intentions of conscientious surgical teams, roughly once a year in a large hospital, they accidentally leave foreign instruments such as sponges and clamps in a patient. The patient shown in Figure 1 complained of abdominal pain and nausea 8 months after a hernia surgery. As you can see, a scan revealed that the surgical team had forgotten to remove a 16-cm clamp from his abdominal area. More generally, Tulving (2004) theorizes that a forward-looking mind that is capable of imagining and anticipating the future is critical to human survival. He assumes that this subjective and conscious apprehension of the future is mediated by the episodic memory system, and he labels this ability proscopic chronesthesia. Moreover, he believes that this ability is unique to humans and that the evolution of this ability was necessary for the creation of human culture. Prospective memory is among the

Figure 1 Scan showing a 16-cm clamp left in the abdominal area of a patient. From Dembitzer A and Lai EJ (2003) Retained surgical instrument. N. Engl. J. Med. 348–228.

important functions of chronesthetic consciousness. The idea here is that basic survival as well as rich human-like social relationships benefit from those who are capable of appreciating the future, planning for it, and later remembering to perform planned actions. In the 1980s, a few researchers (e.g., Harris, 1984; Craik, 1986) started proposing that the retrospective memory literature had not addressed fundamental issues in prospective memory and, as such, alerted researchers to the gap in our understanding of prospective memory. As can be seen in Figure 2, the number of articles and chapters on prospective memory (collapsed over 2-year intervals) has risen dramatically since that time. The increased interest has been driven by a number of factors, including the realization that prospective remembering is critical to our everyday leisure and work lives, the growing awareness that important components of prospective memory tend not to be studied in the typical retrospective memory experiment or captured in conventional neuropsychological assessments of memory, the development of laboratory paradigms for studying prospective

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

80

869

The growth of prospective memory research

70

PsycINFO citations

60 50 40 30 20 10 0 < ’89 ’89-’90 ’91-’92 ’93-’94 ’95-’96 ’97-’98 ’99-’00 ’01-’02 ’03-’04 Two year periods Figure 2 References to prospective memory over recent years in the PsychINFO database. From Marsh RL, Cook GI, and Hicks JL (2006a) An analysis of prospective memory. In: Ross BH (ed.) The Psychology of Learning and Motivation, Vol. 46, pp. 115–153. San Diego: Academic Press.

memory, theoretical progress on the cognitive processes that support prospective memory as well as interest in how these processes change across the lifespan, and the development of imaging techniques for understanding the neural basis of prospective memory. We focus on these factors in this chapter.

2.45.2 Paradigms for Studying Prospective Memory By and large, explicit retrospective memory tasks involve presenting people with materials to learn and then, at some later point, putting the participants in what Tulving (1983) calls a retrieval mode and directing them to search memory for the previously learned information. For example, in the standard cued recall task, participants might be asked to learn pairs of items (e.g., dog/grass, table/binder, etc.). After a delay, the experimenter presents the first member of the pair and explicitly asks the participants to search memory for the associated second member of each pair. On the surface, many prospective memory tasks resemble this cuedrecall scenario. Consider, for example, remembering to give your friend Patty a message. It is likely that you form an association between Patty and the message (i.e., Patty/message), and then after a delay, when Patty

occurs, you need to retrieve the message. A major difference between this and the retrospective cued recall task, however, is that in the prospective memory task no one puts the participant in a retrieval mode and asks her or him to search memory when the target cue occurs (i.e., Patty). Instead, upon seeing Patty, successful remembering requires that the participant remember to retrieve the intention on her or his own. It is this feature of prospective memory that led Craik (1986) to characterize prospective memory as being especially high in self-initiated retrieval. Thus, in designing a research paradigm for studying prospective memory, it is critical to include this self-initiated component of requiring subjects to remember on their own (see McDaniel and Einstein, 2007, Chapter 1, for additional defining features of prospective memory tasks).

2.45.2.1

Nonlaboratory Paradigms

The earliest methods for investigating prospective memory were conducted outside of the laboratory. For example, Meacham and Singer (1977) asked college students to return postcards on specified days and found, among other results, that stronger incentives led to better prospective memory. Other studies (West, 1988; Maylor, 1990) asked subjects to telephone the experimenter at particular times. Another

870 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

approach is to examine the success with which people remember to carry out their own intentions. For example, Marsh et al. (1998b) asked subjects to list their planned activities for the next week (along with the importance of each). One week later, they asked them to indicate which intentions had been carried out and which had not (and to try to explain why these were not performed). In the medication adherence literature, researchers have asked people to adhere to their medication regimen and then put their pills in electronic medication bottles that record the date and time (over a 6-month period) every time the bottle cap is removed (see Park and Kidder, 1996, for a description). As reflected in these studies, nonlaboratory paradigms have the potential to examine prospective memory under highly naturalistic conditions. One limitation of this approach, however, is that it is difficult to assess and/or control the strategies that subjects use in particular situations. For example, in the Meacham and Singer (1977) postcard study, some of the student subjects may have remembered using purely cognitive strategies, others may have used calendars, and still others may have given the post-cards to their parents to return for them. Thus, it is difficult to hone in on the mechanism by which incentives improve prospective remembering. Imagine also comparing older and younger adults and finding that the older adults remember more often than the younger adults (a typical finding in naturalistic studies; see Henry et al., 2004). This type of paradigm does not allow you to determine whether the better prospective memory for older adults was a result of more effective cognitive processes related to prospective memory, greater use of external aids, or both. In recent years, researchers have been creative in elaborating nonlaboratory paradigms, and this has Table 1 1 2 3 4 5 6

enabled them to begin exploring these processes. Kvavilashvili and Fisher (2007), for example, asked subjects to remember to call the experimenter 1 week later. They additionally asked them to record in a diary all thoughts related to the prospective memory intention over the 1-week period. Among other findings, Kvavilashvili and Fisher found that related cues (such as walking past a telephone pole) tended to spontaneously trigger thoughts of the intention. Sellen et al. (1997) gave their participants, all of whom were employees working in a single building, a prospective memory intention to perform for several days (e.g., to perform an action whenever they were in a particular room in the building). Moreover, the participants wore badges and were instructed to click their badge whenever they thought of the intention. There were sensors in the building that enabled the researchers to determine the location of the badge when it was clicked. Interestingly, participants were more likely to think of their intention when they were in transition (e.g., walking from one room to another) than when they were settled in a particular room (i.e., engaged by a task). Although these nonlaboratory paradigms have advantages over laboratory techniques in the sense that they tend to more closely approximate real-world prospective memory demands, ultimately they do not allow the precise control over independent and extraneous variables that is afforded by laboratory techniques. We now outline the basic laboratory paradigm that has been used.

2.45.2.2

Laboratory Paradigms

The essence of laboratory tests of prospective memory has been to busily engage participants in an ongoing task and to give them an intention to perform at some later time (see Table 1 for the major

A typical laboratory paradigm for studying prospective memory

Present participants with instructions and practice trials for an ongoing task (e.g., pleasantness rating). Present participants with the prospective memory (PM) instructions (e.g., press a designated key whenever you see the word ‘rake’ in the context of the ongoing task). A delay is introduced during which participants perform other activities (e.g., do other memory tasks and/or fill out demographics forms). Reintroduce the ongoing task (pleasantness rating) without reminding participants of the PM task. The PM target (‘rake’) occurs several times in the ongoing task, and PM performance is measured by the proportion of times participants remember to press the designated key when the target occurs. To verify that forgetting was a result of PM failure rather than retrospective memory failure, participants are queried at the end of the experiment for their memory of the task demands.

From Einstein GO and McDaniel MA (2005) Prospective memory: Multiple retrieval processes. Curr. Dir. Psychol. Sci. 14: 286–290.

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

phases of a typical experiment, and see Einstein and McDaniel, 1990, for a specific example). Successful prospective memory requires that one remembers to perform an intended action (the prospective component) and also the contents of the intention (i.e., that the target item is ‘rake’ and the particular response key to press; the retrospective component). In explicit retrospective memory tasks, experimenters challenge the retrospective component. That is, they present participants with a body of material and then test how much is retained. In prospective memory tasks, the retrospective content is usually kept simple, and the question is whether participants will remember to perform the action at the appropriate moment or time period. This is done so that one can be fairly certain that omissions are the result of prospective memory failures as opposed to forgetting the contents of the intention. Indeed, it is important to verify this by testing participants at the end of the experiment for their memory of the prospective memory task demands. Prospective memory failures occur when participants fail to perform the intended action and yet later show complete memory for the task demands (i.e., the retrospective component). This basic paradigm seems to capture the processes that are involved in many everyday prospective memory demands. For example, consider the prospective memory task described earlier: the task of remembering to give your friend Patty a message. After forming the intention, there is a delay during which we become engaged by the demands of life (i.e., the ongoing task), and the interest is in whether we will remember to give the message when we later see Patty (i.e., the prospective memory target). Within this general paradigm, researchers have manipulated a number of variables, including the emphasis on the ongoing and prospective memory task (Marsh et al., 2005), whether the cue for initiating the action is an event, a time, or an activity (e.g., Einstein et al., 1995), the nature of the cue (e.g., whether the cue is distinctive; McDaniel and Einstein, 1993), the length of the delay (e.g., Hicks et al., 2000), and the demands on the participant while encoding the intention and at the point of retrieval (e.g., Einstein et al., 1997; Marsh and Hicks, 1998). Despite the widespread use of some variation of this basic laboratory paradigm, it is important to realize that it does not capture all real-world prospective memory processes. For example, planning is minimized as the experimenter tells the subject when to perform the action. Also, Dismukes (2007) points out that many everyday prospective memory demands, unlike those in laboratory tasks, are embedded in well-learned and

871

highly sequenced routines. For instance, a pilot’s typical sequence of actions prior to take off may be to perform a checklist of actions, then set the flaps to take-off position, and then taxi to the runway. For an experienced pilot, this sequence has been performed thousands of times in just this order, and the completion of the checklist and the perceptual environment prior to taxiing are strong cues for setting the flaps to the take-off position. There has been little research examining this kind of heavily cued habitual prospective memory task or what happens on those rare occasions when the action must be performed out of sequence (e.g., when weather conditions require that the pilot delay the setting of the flaps until after taxiing, when the normal kinesthetic and perceptual cues are no longer present). In theory, however, these kinds of conditions can be created in the laboratory either through training or by taking advantage of long-standing habits. Thus, while it is clear that existing tasks have been and continue to be useful for understanding basic processes involved in the encoding, storage, and retrieval of prospective memories, we look forward to the development of other laboratory paradigms for examining prospective memory under a broader set of conditions.

2.45.3 Varieties of Prospective Memory Tasks and How They Are Measured 2.45.3.1

Event-Based Prospective Memory

Although there are some grey areas when defining prospective memory tasks (see McDaniel and Einstein, 2007, Chapter 1), the field seems to have focused the research on three main types of tasks. The lion’s share of the research has examined event-based prospective memory in which the rememberer offloads the intention onto some external environmental cue or cues. An example of an event-based task is the one described in the previous section of pressing a key when the target word ‘rake’ is encountered while performing an ongoing task. A real-world example would be the task of stopping to buy stamps when driving by the post office. Usually performance on an event-based task is measured as the proportion of cues detected and responded to in the manner requested when the intention was formed. Cues can either be specific or general, such as responding to particular words and constructs or to more general categories of items such as fruits or U.S. presidents. The responses could be as simple as marking a response sheet in a particular way, pressing a special key on a keyboard, or rapping on the table when an item is detected.

872 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

2.45.3.2

Time-Based Prospective Memory

Another form of prospective memory has been labeled time-based intentions because the intended actions relate to time in some way. The intention could be a relative measure, such as returning a phone call in 30 min, or it could be related to clock time, as in attending a meeting at 1.30 p.m. (note that if the target time were associated with an event or activity and one of these features triggered the intention rather than the monitoring of time, it would not be classified as a time-based task). Not much is known about the mechanisms underlying timebased prospective memory. Most of the work that has been done appeals to a test-wait-test-exit model (see Kvavilashvili and Fisher, 2007). Here the rememberer executes a time check, which is presumably on the first several occasions too early and thus necessitates a cyclical waiting period before another time check is made. As Kvavilashvili and Fisher have so eloquently stated, the problem with this model is that it does not specify what causes a person to engage in a time check in the first place. They conducted a diary study with a long-term time-based intention and found that many remindings were related to chance encounters with objects and language that were direct reminders of the time-based intention. They also found that many such retrievals of the time-based intention came to mind unbidden. We do know that the most successful individuals at time-based prospective memory tasks check the clock frequently in the period just prior to a required response (Einstein et al., 1995). However, that still does not specify what psychological process is responsible for the clock check in the first place, and this is especially true when a participant records in a diary that there was not an external or internal trigger of the time-based intention. Like event-based prospective memory, how many responses are successful is the usual dependent variable, although some metric of being early versus late is also a common variation. Of course, when measured, the distribution of clock checking can also be very informative as well.

2.45.3.3 Activity-Based Prospective Memory Finally, the third common form of prospective memory measures what is called activity-based prospective memory (e.g., Schaeffer et al., 1998). With this type of intention, people intend on doing one activity after finishing another one. For example,

intending on walking the dog after the evening news would represent an activity-based intention. Although this might seem to be a habitual intention, whether something is novel or habitual depends on the frequency with which it is carried out, and this applies equally well to event-based and time-based tasks. There have not been many experimentally based studies on activity-based prospective memory, probably because there is some theoretical ambiguity about whether this is just a special form of an eventbased task, with the conclusion of one task serving as the event that signals responding. However, this ambiguity highlights a very important point concerning prospective memory, namely, the rememberer can form an intention in any of these three different ways, and each will have varying success depending on tasks and conditions that prevail on that occasion. Take the simple intention of purchasing a birthday card. One could write oneself a note and hope that seeing the note was sufficient to accomplish the task (an event-based task). One could formulate the intention to run to the store right after lunch in order to carry out the purchase (an activity-based intention). Or, one could plan a specific deviation of one’s day and commit to leaving the office at 5.00 p.m. to carry out the task (a time-based task). All three formulations are prospective memory tasks, but they will vary in the success rate depending on the individual and the conditions surrounding the performance interval (e.g., seeing the note but being late for work or for a class). The important point is that a desire to accomplish some goal can be linked to various future contexts in a variety of ways depending on whether the rememberer gives some serious consideration to what formulation will be best (for a more detailed treatment of prospective memory and contextual associations see Marsh et al., in press).

2.45.4 Retrieval of Prospective Memories: Retrieval Without an Explicit Request to Remember A central problem in prospective memory is in understanding how we initiate an intended action at the appropriate moment. This is an interesting question because models of retrospective memory retrieval (e.g., recall and recognition) start with the assumption that people have been put in a retrieval mode and have been explicitly directed to search their memory for previously encoded information. As discussed earlier, prospective memory is different

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

in the sense that we form an intention to perform an action at some later point and then get busily involved in other activities. How, then, do we remember to perform the action in response to that event? Because the majority of the research has investigated retrieval on event-based tasks, this is our focus in this section. Following, we consider two opposing theories that address this question and then present a compromise view. (For those interested in research and theorizing on retrieval of timebased prospective memories, we recommend the following sources: Harris and Wilkins, 1982; Harris, 1984; Ceci and Bronfenbrenner, 1985; Block and Zakay, 2006; Kvavilashvili and Fisher, 2007.). 2.45.4.1

Attentional Monitoring Theory

The attentional monitoring view assumes that some of our attentional and/or working memory resources need to be devoted to monitoring the environment for the target event in order for retrieval to occur. According to this view, successful prospective memory requires that an attentional system like Shallice and Burgess’s (1991) supervisory attentional system monitors the environment in light of our prospective memory demands. When a target event is detected, this system interrupts the ongoing activity, evaluates whether the conditions for performing the action are appropriate, and if so initiates the appropriate actions. The most thoroughly developed statement of this view is Smith and Bayen’s (Smith, 2003; Smith and Bayen, 2004, 2006) preparatory attentional and memory (PAM) theory. According to this theory, when we form an intention, we initiate a capacity-consuming preparatory attentional process that monitors environmental events by initiating recognition checks to determine whether the events are instances of the prospective memory target. For example, consider the task presented in Table 1, in which the prospective memory task is to press the slash key when the target word ‘rake’ occurs while performing the ongoing pleasantness rating task. According to the PAM theory, preparatory processes involve initiating a recognition check for each item to determine whether it is an instance of the target event and could also include rehearsing the target event. According to this theory, forgetting occurs when people fail to maintain their attention on the intention and therefore fail to initiate recognition checks, or when there is a recognition failure (see Smith and Bayan 2004, 2006, for a multinomial model that measures these two parameters). Smith takes a strong

873

position on the necessity of monitoring for successful prospective memory, arguing that ‘‘capacity must be devoted to the prospective memory task in the form of monitoring before a target event occurs if the target is to be recognized as a signal or an opportunity to perform the prospective memory action’’ (Smith, 2003, p. 359). Because this view assumes that people are using attentional resources to monitor the environment for target events when they have a prospective memory intention, this view clearly predicts that adding a prospective memory task to an ongoing task should produce task interference (i.e., slowing on the ongoing task). Continuing with the example, the idea is that the pleasantness ratings for nontarget items will be slower because subjects are additionally monitoring these items for the prospective memory target event while they are performing the pleasantness ratings. Smith (2003, Experiment 1) provided strong support for this view when she found that participants were approximately 300 ms slower in performing a lexical decision task when they were also performing a prospective memory task compared with when they were performing the lexical decision task alone. Task interference to the ongoing task has been found repeatedly and with other types of ongoing tasks (Smith and Bayen, 2004) and in other labs (Marsh et al., 2003; Einstein et al., 2005). Moreover, Smith (2003) found that individuals who showed more task interference (i.e., more slowing on the ongoing task as a result of performing the prospective memory task) had higher prospective memory, thereby indicating that monitoring is important for prospective memory retrieval. The monitoring view is also supported by research showing that dividing attention during retrieval lowers prospective memory (Einstein et al., 1997; Park et al., 1997; Marsh and Hicks, 1998). Marsh and Hicks have shown that divided attention tasks that required central executive resources, but not ones that increased the demands of articulatory suppression or visuospatial involvement, reduced prospective memory performance. A straightforward interpretation of these results is that dividing attention compromises monitoring processes that are needed to identify prospective memory targets. 2.45.4.2

Spontaneous Retrieval Theory

A different way to think about prospective memory retrieval is to assume that the occurrence of the target event can trigger remembering even when no

874 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

resources are devoted to the intention at the time that the target event occurs (Einstein and McDaniel, 1996; McDaniel and Einstein, 2000; McDaniel et al., 2004; Einstein et al., 2005). Much like walking by a friend can reflexively trigger the recollection of an amusing past episode with the friend (when there was no prior intention to remember that episode prior to encountering the friend), according to the spontaneous view, it is the occurrence of the cue that triggers processes that lead to retrieval of the intended action. Within this view, then, monitoring or preparatory attentional processes are not necessary for successful retrieval. In this section, we briefly review two theoretical mechanisms by which spontaneous retrieval can be accomplished. One theory, called the reflexiveassociative theory (Einstein and McDaniel, 1996; McDaniel and Einstein, 2000; McDaniel et al., 2004), assumes that relatively automatic processes can underlie prospective memory retrieval. The idea is that during planning, people form an association between the target cue and the intended action (e.g., an association between the target word ‘rake’ and the action to press the slash key). Later, when the target event is processed in the context of the ongoing task, an automatic associative system (like the one proposed by Moscovitch [1994] and presumed to be mediated by the hippocampal system) retrieves the intended action and delivers it to consciousness. According to Moscovitch, the hippocampal system is an associative module that mediates associative encoding and associative retrieval. If we have formed a good association between the target cue and the intended action, and if the cue is fully processed at retrieval, then this associative module should rapidly, obligatorily, and with few cognitive resources deliver the intended action (press the slash key) to consciousness. There are several results that are consistent with this theory. One comes from introspective reports of participants who often remark that the thought to perform the intended action appeared to pop into their mind while performing the ongoing task (Einstein and McDaniel, 1990). Also, Reese and Cherry (2002) found very little evidence that participants were monitoring while performing an ongoing task. They probed participants at various points during the ongoing task and asked them to indicate what they were thinking about. Both younger and older adults rarely indicated thinking about the prospective memory task (less than 5% of the time, compared with reporting thoughts of the ongoing

task about 69% of the time). Even so, prospective memory performance was at a reasonable level (about 60%). Also consistent with the spontaneous retrieval theory is the finding that subjects who demonstrate no costs or task interference when performing an ongoing task (and are therefore unlikely to be monitoring) can still exhibit very high levels (93%) of prospective memory (Einstein et al., 2005, Experiment 4). We should also note that the previously described findings of negative effects of dividing attention on prospective memory do not unambiguously argue against spontaneous retrieval. At this point in our research, it is not clear exactly how dividing attention affects performance. For example, dividing attention may interfere with full processing of the target event, which may be essential for good spontaneous or associative retrieval (Moscovitch, 1994). Or, it may not interfere with retrieval of the intention but, instead, may increase working memory demands to such a degree that participants have difficulty selecting the retrieved intention and scheduling the intended action while it is still activated in working memory (Einstein et al., 1997). The discrepancy plus attribution theory also explains how retrieval can occur spontaneously and in the absence of monitoring. It assumes that the processing of the target event leads to a feeling that there is something significant about the event, and this in turn leads to a search of memory for an explanation of its significance. Depending on how well the intention was encoded, this search at retrieval can lead to the realization that the event is a cue for an intended action. According to Whittlesea and Williams (2001a,b), people chronically evaluate the quality and coherence of their processing, and they are sometimes sensitive to the discrepancy between the actual quality of processing and the expected quality of processing in that context. This sense of discrepancy is alerting and begs for an explanation, which in the context of a recognition task could lead to the interpretation that the item has been seen before. McDaniel et al. (2004) proposed that these processes can also explain prospective memory retrieval. Specifically, the idea is that the target event, on the basis of its initial processing during the encoding of the intention, will, when it appears again in the context of the ongoing task, be processed more fluently (than other items in the ongoing task), and this discrepancy is likely to elicit a sense of significance. In turn, this noticing can lead to a search of memory for the source of the significance, and this can lead to

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

the realization that the event is a cue for an intended action. There has been recent support for this theory from research manipulating the prior exposure of the target item relative to the ongoing task items. McDaniel et al (2004) created a high-discrepancy condition by presenting the target words during the initial instruction and not preexposing the nontarget items. That is, none of the ongoing task items appeared in a preceding list-learning task, but the prospective memory target item appeared during the instructions for the prospective memory task items. In this condition, the target item should have been processed more fluently relative to the ongoing task items and thus should have produced discrepancy and a sense of significance. In the lowdiscrepancy condition, the ongoing task items were preexposed in a preceding list learning task. Thus, there should have been less discrepancy in the fluency of processing the target items relative to ongoing-task items. Consistent with the discrepancy attribution theory, prospective memory performance was better in the high-discrepancy condition than in the low-discrepancy condition. Breneiser and McDaniel (2006) have recently provided additional support for this theory by showing that it is not simply greater familiarity for the target item but, rather, the discrepancy between the actual quality of processing and the expected quality of processing that is critical for determining a sense of significance. They found that preexposing ongoing task items four times each in a preceding list-learning task relative to one preexposure for the target items (high-discrepancy condition) led to better prospective memory performance than one preexposure of both the target and ongoing task items (lowdiscrepancy condition). Other evidence consistent with the general idea that discrepancy can stimulate a search for significance comes from research showing that manipulations that increase the noticing of the target event, such as making the target event distinctive (e.g., a target word presented in upper case letters with the ongoing task items in lower case letters), produced very high prospective memory performance (McDaniel and Einstein, 1993; Brandemonte and Passolunghi, 1994). 2.45.4.3

Multiprocess Theory

So, which processes do we rely on for prospective remembering? According to the multiprocess view (McDaniel and Einstein, 2000; see also Einstein and

875

McDaniel, 2005; Einstein et al., 2005; McDaniel and Einstein, 2007: Chapter 4), there are many reasons to believe that the human cognitive system uses both monitoring and spontaneous retrieval processes for prospective remembering. First, given the prevalence and importance of prospective memory demands in the real world, it would be adaptive to have a system that relies on multiple processes for prospective memory retrieval and thus increases the chances that we will remember under a variety of conditions. Second, given that the delays between forming an intention and the opportunity to execute the intention are often substantial (on the order of several hours or more), it would seem maladaptive to have a system that relied exclusively on capacity consuming monitoring processes for successful retrieval. In Smith’s (2003) research, for example, monitoring for target events slowed down lexical decision times by about 45% (Experiment 1). If we relied entirely on monitoring processes for successful prospective remembering, then the efficiency with which we performed the intervening ongoing activities in our lives would be severely compromised. Third, the view that participants sometimes (perhaps most often) rely on spontaneous retrieval processes fits with Bargh and Chartrand’s (1999) theory that we have a limited capacity for conscious control over behavior and therefore much prefer to rely on automatic or unconscious processes. Consistent with this idea, several studies have shown that exerting conscious control over behavior in one phase of an experiment leads subjects to expend less conscious effort in a later phase (e.g., Baumeister et al., 1998). From this perspective, the cognitive system is limited in the extent to which it is able to maintain controlled monitoring of the environment for target events. Fourth, the idea that we sometimes rely on spontaneous retrieval processes and sometimes augment these processes with capacity-consuming monitoring processes has the potential to explain some apparently inconsistent results. For example, although dividing attention often interferes with prospective memory, there are conditions under which dividing attention has no effect on performance (McDaniel et al., 2004). An explanation of this pattern of results is that dividing attention will interfere with prospective memory primarily in those conditions in which monitoring is useful for prospective memory retrieval but will have minimal effects under those conditions in which spontaneous retrieval processes are effective in producing retrieval.

876 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

There are three assumptions to the multiprocess view. One is that prospective remembering can be supported by several different kinds of processes ranging from strategic monitoring of the environment to spontaneous retrieval processes. A second assumption is that the process that people rely on in a particular situation and the effectiveness of that process for producing retrieval depend on a host of factors, including the nature of the prospective memory demand, the demands and characteristics of the ongoing task, and the characteristics of the individual. For example, if people can anticipate that they will later encounter a salient retrieval cue for prospective memory, they are more likely to rely on spontaneous retrieval processes. If, on the other hand, it would be catastrophic to forget the intended action and the delays are fairly brief, people may initiate and maintain an active monitoring strategy over the delay interval. A third assumption, and in line with the theory of Bargh and Chartrand (1999) noted above, the multiprocess theory assumes that people have a bias to rely on spontaneous retrieval processes. As just noted, according to the multiprocess theory, certain conditions make it more likely that the presence of the target event spontaneously triggers retrieval of the intention (McDaniel and Einstein, 2000; see McDaniel and Einstein, 2007: Chapter 4, for further discussion of relevant variables).

Assuming good encoding of the intention, an important variable, for example, is the extent to which the ongoing task encourages focal processing of the target event. This idea, which is an extension of the retrospective memory theory of transfer-appropriate processing (see more about this later, and see Morris et al., 1977), is that spontaneous retrieval is likely to occur to the extent that the ongoing task directs attention to the target event and encourages processing of those features that were processed at encoding or planning (see Table 2 for examples of conditions McDaniel and Einstein believe do and do not encourage focal processing). On the other hand, with nonfocal cues, spontaneous retrieval is less likely, and successful retrieval is more dependent on monitoring for the target event. The multiprocess theory assumes that subjects are generally sensitive to the conditions that lead to spontaneous retrieval (e.g., focal cues) and those that demand active monitoring for the target event (e.g., nonfocal cues). This idea is similar to that of Marsh et al. (2003; see also Marsh et al., 2006), who believe that subjects develop an allocation policy that is based on their perceived difficulty of performing the ongoing task and the prospective memory activities. For example, if subjects believe that the prospective memory task will be difficult, they will allocate attentional resources to monitoring for the

Table 2 Representative examples of task conditions, some of which have been used in published research, that we assume are high and low in focal processing Processing

Ongoing task

Prospective memory task

Nonfocal

Words were presented in the center of a computer monitor and participants had to learn them for recall tests that occurred at unpredictable times. Participants had to keep track of the number of occurrences of each background screen pattern.

Respond when you see a particular background pattern (background pattern changes every 3 s). Respond when you see a particular background pattern (background pattern is changed every 3 s).

Nonfocal Focal

Lexical decision task Lexical decision task

Respond to items from the animal category. Respond to the word ‘cat.’

Nonfocal

Pairs of words were presented, and participants decided whether the word on the left was a member of the category on the right. Pairs of words were presented, and participants decided whether the word on the left was a member of the category on the right.

Respond to the syllable ‘tor.’

Pictures of famous faces were presented, and the task was to name the face. Pictures of famous faces were presented, and the task was to name the face.

Respond when you see a face with eyeglasses.

Focal

Focal

Nonfocal Focal

Respond to the word ‘tortoise.’

Respond when you see a face with the first name of John.

From Einstein GO and McDaniel MA (2005) Prospective memory: Multiple retrieval processes. Curr. Dir. Psychol. Sci. 14: 286–290.

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

target event. Marsh et al. believe that this allocation policy is dynamic and varies in response to subjects’ changing perceptions of the difficulty of prospective memory and ongoing tasks change.

2.45.5 Storage of Prospective Memories: Do They Enjoy a Privileged Status in Memory? Because prospective memories are formed with the goal of later retrieving them in the appropriate context, some researchers have suggested that they may have special storage properties. Indeed, Goschke and Kuhl’s (1993) seminal work suggests that intentions may hold privileged status in memory. In their work, participants were asked to learn pairs of scripted actions for, say, clearing a messy desk or setting a table (e.g., actions might be: distribute the cutlery, polish the glass, light the candle, etc.). After learning, participants were told that one script in the pair would have to be performed later. In an immediate recognition test, latencies were faster to words coming from the to-be-performed script as opposed to the neutral script about which there was no prospective intention. Marsh et al. (1998a) replicated this decreased latency effect using a lexical decision task but also discovered that if the assessment of activation came after performing the script, then latencies were slower to the already-performed script as compared with the neutral script. Applying the standard interpretation that faster latencies are associated with information being more accessible in memory, Goschke and Kuhl concluded that prospective memories enjoy a privileged status in memory, whereas Marsh et al. concluded additionally that a prospective memory, once completed, goes into a state of being temporarily inhibited, which could be ecologically adaptive in planning what activities one has to do next. There are converging reports to suggest that prospective memories reside in a privileged state. For example, Maylor et al. (2000) asked younger and older adults to list their plans for the coming week and also to list what they completed in the previous week. The conditions under which they did so were speeded, and participants were asked to write two or three words to describe each future intention or each completed intention. Consistent with the intention superiority effect (ISE), younger adults listed more future plans than they did completed activities, ostensibly because the future plans were more

877

available in memory. In contrast, the older adults did not. Lebiere and Lee (2002) modeled Marsh et al.’s (1998) data using the ACT-R assumptions (Anderson and Lebiere, 1998) that prospective memories represent a goal node in that model. According to ACT-R, goal nodes receive constant sources of activation, and this facet of the model would account for their higher accessibility in memory. In measuring cue interference, Marsh et al. (2002b) found that prospective memory cues that were missed (i.e., that were not detected and that had received no prospective memory response) in a lexical decision task were responded to more quickly than control-matched items. Because they used a categorical intention to respond to animals, Marsh et al. assumed that they had found a more specific version of the ISE. That is, because intention-related material has privileged accessibility, it is processed more quickly even when the cue does not elicit a prospective memory response (but see West et al., 2005). Marsh et al. (2008) have recently reported a related, very provocative finding. In this study, participants were asked to pay attention to a visual stream of words and actively ignore the information presented in an auditory channel. The participants were also given the prospective memory task of responding to a categorical intention (e.g., vegetables) when an exemplar appeared in the visual channel of information. Participants were then tested on their memory for only information presented in the to-be-ignored auditory channel. Recognition of intention-related material in the to-be-ignored channel was significantly better than control-matched material in the same channel. Marsh et al. interpreted these results as consistent with the ISE, in which intention-related material gains more obligatory access to consciousness than comparable material about which there is no intentionality. As an alternative to the ACT-R account, if one assumes a network model of memory, then whenever plans and intentions are considered or otherwise brought into consciousness, some small amount of activation might accrue to other plans and intentions, and this process could keep them in a higher baseline resting state. Combined with a view that prospective memories are revisited from time to time, whereas retrospective memories probably receive fewer such rehearsals, then perhaps some confluence of these different explanations is what actually confers a special status on prospective memories. Of course, this general perspective is not without its opponents. In their original report, Marsh et al. (1998; see also

878 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

Marsh et al., 1999) were somewhat skeptical that a critic would necessarily adopt the notion that prospective memories were stored in a more accessible fashion. They argued that an alternative conception of the ISE is that prospective memories reside as declarative representations with the same level of baseline activation in their resting state as do retrospective memories. As such, prospective memories may be able to be revived faster because they are more elaborately encoded or because they are related to one’s self schema. Also, Freeman and Ellis (2003) report boundary conditions on the ISE. In their report, they used subject-performed tasks (e.g., clap your hands), and they found an ISE only with verbal encoding and not if people learned the tasks motorically. Consequently, the ISE may be a verbal learning phenomenon. If so, this finding may not really constrain the generality of the effect because most of our everyday intentions are self-generated from thoughts. There are no published reports contravening the ISE other than Maylor et al.’s (2000) failure to find the effect in older adults and Freeman and Ellis’s (2003) failure to find it with motoric encoding. Unfortunately, this does not mean that the ISE is not a major contributor to the file drawer problem. After the Marsh et al. (1998) article appeared, Richard Marsh was contacted by many people for stimulus materials expressing an interest in testing older adult populations in order to assess whether older adults fail to inhibit after completing a prospective memory task. Because none of these reports have appeared in the last decade, one cannot help but wonder just how robust the ISE truly is. Of the many effects found in prospective memory, the ISE stands alone because it is a tantalizing proposition that the human memory system would have evolved to single out our ancestors’ intentions as privileged material. Of course, from an evolutionary perspective, it would be advantageous if our ancestors who were proactive about finding food, water, shelter, and a mate survived and thrived more readily as opposed to being reactive toward these basic needs. The ISE is one of those phenomena in the realm of prospective memory that needs to be scrutinized more carefully than it has been in the scientific record to date. Only a handful of reports have been published on the effect, but any theoretical influence the ISE has on clock checking or the probability of an event-based cue being recognized needs to be based on a deeper understanding of the basic phenomenon and why it occurs.

2.45.6 Encoding of Prospective Memories The work on encoding has reflected two general orientations: (1) the influence on prospective memory performance of instructions or experimental conditions that guide encoding of the intention to perform an action in the future (including encoding of the target event that signals the appropriateness of performing the intention) and (2) the nature of planning processes that people display in the absence of instructions directing specific encodings. Most of the research has centered on the first topic, and accordingly our review concentrates on that research.

2.45.6.1

Associative Encoding

A primary finding is that instructions or conditions that foster associative encoding of the target cue and the intended action tend to improve prospective memory performance. This finding resonates well with the reflexive associative theory presented earlier. Several aspects of this finding merit amplification. First, as is elaborated later, associative-encoding manipulations do not always produce improvements in prospective memory, and this may be because of the nature of laboratory tasks. In laboratory prospective memory tasks, where the participants are instructed to perform an intended action in the presence of a particular cue event, it is especially likely that people are spontaneously encoding a target cue–intended action association. Consequently, instructions specifically designed to augment such associative encoding could be redundant with the encoding already engaged by participants. A second key pattern is that prospective memory effects of at least one type of associative-encoding manipulation may be accompanied by signatures of spontaneous retrieval. This pattern is consistent with the reflexive-associative theory described earlier that assumes that retrieval of an encoded target cue– intention association can be mediated by an automatic associative memory system. One general technique to stimulate associative encoding that people can be instructed to use is an implementation intention (Gollwitzer, 1999). An implementation intention specifies situational cues for initiating an intended action and a technique to link these specific cues to the intention by using a condition-action statement such as: If situation x arises, I will perform y. However, in the experimental

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

work on prospective memory, laboratory instantiations of an implementation intention have varied. Cohen and Gollwitzer’s (2007) implementation intention required subjects to write down three times the implementation intention (e.g., ‘‘If I see the word window at any point in the task [lexical decision], I will say wrapper as fast as possible!’’). The implementation intention produced a significant advantage in prospective memory over a standard prospective memory instruction that simply told participants to say a response word upon seeing the cue word (but without repetitive writing of the instruction), even though the standard instruction group displayed relatively high prospective memory performance. In other experiments, the implementation intention involved both saying aloud the condition–action statement and a period of encoding (typically 30 s) during which subjects imagined themselves performing the intended action upon seeing the target cue (Chasteen et al., 2001). Prospective memory performance improved under these conditions relative to a control not given implementation intention instructions for both younger adults (Howard et al., 2006) and older adults (Chasteen et al., 2001). Furthermore, it appears that the imagery encoding alone is not sufficient to produce the benefits (Einstein et al., 2003, Experiment 3; Howard et al., 2006, Experiment 2), even though imagery encoding would presumably be fostering associative linkages between the target event and the behavior (McDaniel and Pressley, 1987). Thus, based on current evidence, it seems that the full implementation intention procedure (imagery plus the if . . . then statement) is most likely to create positive effects of this kind of associative-encoding instruction. It is important to note, however, that the full implementation intention procedure does not always yield improvements in prospective memory (Kardiasmenos et al., 2004; Bennett et al., 2005; see also Chasteen et al., 2001; Howard et al., 2006, for other instances of null effects with implementation intentions). These findings dovetail with the first point made above. Participants under standard prospective memory instructions may at least sometimes spontaneously form good associative encodings of the target cue–intention action, thereby rendering experimenter-instructed associative encoding procedures unnecessary. Another possibility is that even when implementation intentions do not affect levels of prospective memory, the processes underlying prospective

879

memory retrieval may be altered. Under standard prospective memory instructions, attention-demanding retrieval processes (e.g., monitoring) might be recruited (processes that in some cases support relatively high levels of prospective memory; McDaniel et al., 2006; Cohen and Gollwitzer, 2007), whereas with an implementation intention, encoding relatively automatic retrieval processes may prevail (see section 2.45.4 for details of these processes). The limited evidence is consistent with this possibility. For instance, in Cohen and Gollwitzer (2007), response times to the ongoing activity (lexical decision) did not differ between the implementation intention condition and a control for which there was no prospective memory task (implicating relatively spontaneous retrieval processes), yet in the standard prospective memory condition, the response times were significantly longer relative to the no-prospective memory control (this cost implicating a demanding process for prospective memory). Further, Howard et al. (2006, Experiment 2) substantially increased the demands of the ongoing activity (by requiring random number generation as a secondary task). Prospective memory performance significantly declined relative to a condition without the demanding ongoing activity (random number generation was not required) with standard prospective memory instructions but not with implementation intention instructions. The benefits of focusing encoding on the association between the target cue and the intended action are underscored by another type of finding. In one paradigm, after encoding the prospective memory intention, participants were interrupted several times during the ongoing task and re-presented with aspects of the prospective memory instructions (Guynn et al., 1998, Experiment 3). Some participants were presented with only the target cues, others were presented with the intention, and still others were presented with the target cues and the associated intended action. In all cases, participants were instructed to think only about the information presented. Thus, these conditions reflect additional encoding of target cues, the intention, or both. The differences in prospective memory performance as a function of the type of additional encoding were pronounced. Additional encoding of target cues alone and intention alone produced relatively low performance (36% and 56% prospective memory responding, respectively), whereas additional encoding of the target cue–intention pairs promoted high prospective remembering (82%).

880 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

2.45.6.2

Target Cue Encoding

An interesting aspect of the above results is that repeated encoding of target cues produced no increases in prospective remembering relative to a single-encoding control condition. Ample evidence indicates, however, that the quality of the target-cue encoding plays a role in successful prospective remembering. Paralleling the retrospective memory literature, semantic encoding of the target cue tends to improve prospective memory performance relative to nonsemantic encoding (McDaniel et al., 1998, Experiment 3), generating the target cue at encoding improves prospective remembering relative to reading the target cue (Matthews, 1992; RobinsonRiegler, 1994, Experiment 1), and presenting the referent of the target cue as a picture at encoding produces better prospective memory performance than presenting the cue as a word (even when the presentation of the cue during retrieval is in a different modality than at encoding; McDaniel et al., 1998, Experiment 2). Similarly, dividing attention during encoding of the target-cue significantly attenuates prospective remembering (Einstein et al., 1997). Further, elaboration of the target-cue prior to its specification as a prospective memory target event appears to enhance prospective remembering. In one study, prior to the prospective memory instructions, some participants repeatedly generated the target cue (from word fragments or anagrams). These participants evidenced high levels of prospective memory under both standard and demanding ongoing task demands. In contrast, participants who generated words that were not subsequently used as targets displayed a significant reduction in prospective memory when ongoing task demands became more challenging (Guynn and McDaniel, in press; see Mantyla, 1994, for a similar finding). It is worth noting that the positive effects of elaborative encoding of the target cue are entirely compatible with the theories of prospective memory retrieval reviewed in the preceding section. Such encoding would be expected to lead to better recognition of the cue during the retrieval period (assuming the PAM theory) or to create more discrepancy between subsequent processing of the target cue and nontarget events (assuming the discrepancyattribution processes), thereby facilitating noticing of the target cue in the retrieval context. Even the reflexive-associative approach assumes that interaction of the cue with a memory trace (e.g., the intended

action) is facilitated by initial encodings that are more semantic or distinctive (Moscovitch, 1994).

2.45.7 Similarities and Differences Between Prospective and Retrospective Memory Given the formal distinction between prospective and retrospective memory, it may be tempting to focus on their differences and perhaps even to appeal to different memory systems; however, this approach would overlook many similarities as well as undercut our exploration of how our rich conceptualization of retrospective memory can help us understand prospective memory (see Marsh et al., 2006, for a more detailed treatment of the similarities and differences between retrospective and prospective memory). As a fundamental starting point, consider that prospective memories share three basic stage-like histories with retrospective memories, namely, encoding, retrieval, and any changes that occur over a retention interval (as reflected in the content of the previous sections; cf. Ellis, 1996). Intentions occur as a function of direct requests from others, or they are self-initiated. No work to date has experimentally examined the fate of these two basic types of intentions. However, even a cursory analysis or Gedanken experiment would suggest that the former type should go unfulfilled more frequently than the latter (with notable exceptions arising such as not breaking social contracts). The reason for this is twofold. First, self-generated information may undergo more rehearsals because it is self-referential in nature. Second, prospective memories that are self-referential may be more elaborately encoded and better linked to present and future contexts. More generally, for both of the same reasons that self-defined intentions may be completed more often than requests from others, prospective memories may be more durable than retrospective memories as a consequence of the manner in which they are encoded and/or rehearsed (see West and Krompinger, 2005, for an empirical approach designed to maximize similarities in order to identify fundamental differences). To elaborate, when an intention is formed, a host of self-referential information is stored, such as why we want to complete the task, the costs and benefits of doing (or not doing) so, the current context, and the future context we might be in at the time of completion. Because material that is related to one’s self is better remembered (e.g., Klein and Kihlstrom,

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

1986), prospective memories may be more durable than otherwise equivalent retrospective memories. More elaborated intentions that are stored more durably in memory also should have a higher probability of coming to mind during the retention interval. Just like a retrospective memory, the more frequently a memory is rehearsed, the better it will be recalled on a subsequent occasion (called retrieval sensitivity by Ma¨ntyla¨, 1994). So, based on the properties of encoding, one cannot make a blanket statement that all prospective memories will be remembered more faithfully than retrospective memories, only that on average, the amount of effort expended in creating a prospective memory could be greater than in creating a simple, everyday retrospective memory. In addition, the contextual details surrounding retrospective memories are usually lost quite quickly (e.g., Bornstein and LeCompte, 1995), whereas they often form the core of a prospective memory. For example, we often plan to fulfill a prospective memory in a particular context, and therefore, a prospective memory will have linked with it at least two contexts (the environment during formation and the one in which we expect to do it). These can serve as important retrieval cues to fulfilling intentions, and when contexts mismatch our expectations, then the consequences can be very grave indeed for intention completion (Cook et al., 2005). As we said earlier, retrieving intentions is usually a self-initiated act, whereas many times retrieving retrospective memories is not. Of course, exceptions to this rule exist, such as when a third party queries you about your intentions (e.g., ‘‘Got plans for this weekend?’’). Nevertheless, when we rely on retrieval cues, many of the principles of prospective memory appear to mimic what has been found with retrospective memory. For example, if one has the intention to respond to a word such as ‘bat’ (as in baseball), then receiving the cue as bat (as in mammal) leads to much worse prospective memory (McDaniel et al., 1998). A form of transferappropriate processing is also found in what is known as task-appropriate processing (Marsh et al., 2000; West and Craik, 2001; Maylor et al., 2002). If the features of the ongoing task focus one on the correct aspects of the prospective memory cue, intention retrieval is more successful. As such, a semantic intention to respond to words denoting animals is more successful if the ongoing task encourages semantic, as opposed to orthographic, processing of the items. Also, resource sharing during retrieval appears to have similar effects on prospective and

881

retrospective memories. Dividing attention during either encoding or retrieval generally reduces retrospective memory (Baddeley et al., 1984; Craik et al., 1996) and prospective memory (e.g., Einstein et al., 1997, 1998; McDaniel et al., 2004). One possible difference is that some forms of event-based prospective memory require difficult, centrally mediated divided attention tasks to observe lower rates of responding to prospective memory tasks (Marsh and Hicks, 1998). Finally, prospective and retrospective memories both share the property that they will change over the course of a retention interval. Obviously, an unrehearsed memory will grow weaker over time and eventually be forgotten. However, most people review their intentions periodically as a part of their daily mental life. Alternatively, cues in the environment can remind us of intentions, such as the sight of one’s vehicle serving as a reminder to have the oil changed. These periodic reminders of intentions only serve to strengthen their representation, as we argued earlier. Most retrospective memories do not enjoy such periodic revisitation and more likely fall into desuetude, thereby requiring increasingly stronger retrieval cues over time to recover that information.

2.45.8 Development and Prospective Memory Although there has been much interest in examining prospective memory from developmental perspectives, most of it has been conducted with older adults. This focus on older adults is probably a result of the obvious practical importance of understanding how aging affects prospective memory (e.g., to help inform health care issues related to prospective memory such as medication adherence), but also in response to compelling theoretical issues. We briefly review first the literature with children and then the research with older adults. As might be expected, the research generally shows that older children outperform younger children and younger adults outperform older adults on prospective memory tasks. However, it is also clear that the age differences vary greatly across prospective memory tasks and that there are some tasks on which no age differences are found. Thus, an interesting theoretical and applied challenge for prospective memory researchers is to understand those conditions that are and are not especially difficult for younger children and older adults.

882 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

Before reviewing this literature, we briefly raise a methodological issue that is important to consider when examining developmental trends in prospective memory. Given that prospective memory tasks are embedded in ongoing tasks and that demanding ongoing tasks have been shown to interfere with prospective memory (Marsh and Hicks, 1998), it is important to control the demands of the ongoing task across age groups. Otherwise, differences in prospective memory could stem from the ongoing task being functionally more demanding for younger children or for older adults (see Einstein et al., 1997; Kvavilashvili and Fisher, 2007, for discussion of this issue). 2.45.8.1

Prospective Memory in Children

Even though there is not a plethora of existing research on prospective memory in children, several interesting results have emerged, and these seem to be stimulating increasing interest (e.g., see Kliegel et al., in press; Kvavilashvili et al., in press). Recent studies examining event-based prospective memory in 5- and 7-year old children generally suggest that age differences are larger on tasks that require more controlled or strategic processes. All of these studies used a variation of Kvavilashvili et al.’s (2001) prospective memory task of asking children to name pictures from stacks of pictures for Morris the Mole because he does not see very well (the ongoing task). The prospective memory task was to hide any picture of animals from Morris because he was scared of them. Kvavilashvili et al. varied whether the animal pictures appeared in the middle or the end of the stack. Five- and 7-year old children both remembered about 75% of the time when the target was at the end of the stack, but the older children did much better than the younger children when the target was in the middle. Thus, the older children were better able to inhibit the ongoing activity in order to perform the intended action. When inhibition was not needed, however, the younger children were as capable of remembering as the older children. To directly study strategic processes, Stokes et al. (2007) manipulated whether the target event was focal or nonfocal. Children in their study were presented with cards (with four pictures on each card) and asked to name the circled picture on each card (the ongoing task). The prospective memory task was to hide the card if there was an animal on it. In the focal condition, animals always appeared as the circled picture, and thus the ongoing task requirement

to name the picture forced processing of the target pictures, which in turn could trigger spontaneous retrieval. In the nonfocal condition, the target picture always occurred in a noncircled location, and thus subjects had to remember to monitor the other locations for the target picture. Whereas the prospective memory performance of the older children was nearly perfect regardless of the cuing condition (around 95%), prospective memory was much higher for the younger children in the focal condition (68%) than in the nonfocal condition (20%). Consistent with this pattern, McGann et al. (2005) found high performance and no differences between 5- and 7-year old children with salient target pictures (when the pictures were larger than others) but higher performance for the older children (relative to the younger children) with nonsalient target pictures. All of these studies suggest that some prospective memory conditions are more difficult for younger children than others. Consistent with the general developmental trend showing that younger children have more limited attentional and working memory resources (e.g., Guttentag, 1984) and with the multiprocess theory (McDaniel and Einstein, 2000), younger children seem to have greater difficulty with prospective memory tasks that require active monitoring of the environment and inhibiting the demands of the ongoing task. Very little research has examined time-based prospective memory in children. An interesting question with this kind of task is whether children can develop and maintain a clock checking strategy in the absence of a cue to trigger remembering. Ceci and Bronfenbrenner (1985) asked 10- and 14-year-old children either to remember to remove cupcakes from the oven or to remove cables from a battery charger exactly 30 min later. The children performed these tasks either at home or in the laboratory. During the 30-min interval, they were engaged in an entertaining video game, and there was a wall clock at their back. This arrangement allowed the researchers to record monitoring of the clock. Interestingly, most children developed a monitoring strategy, but the strategy varied across the laboratory and home contexts. In the lab, the children monitored the time increasingly more often as the target time approached. In the home setting, children tended to adopt what Ceci and Bronfenbrenner described as a more adaptive U-shaped monitoring pattern. That is, they monitored frequently initially (presumably to calibrate the passage of time) and then very little after that except for the last 5 min before the target

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

time (at which point they monitored frequently). This strategy is adaptive in the sense that it frees up resources for the ongoing video task. Although the large majority of both 10- and 14-year-olds remembered on time, late responding was associated with less strategic monitoring. In light of the surprising finding that very young children (2 years old) can show very good prospective memory for tasks that they consider important (e.g., buying candy at the store; Sommerville et al., 1983), it would be interesting to explore the conditions and age at which strategic monitoring develops. 2.45.8.2 Adults

Prospective Memory in Older

As noted earlier, the majority of the developmental research has focused on aging issues (for recent papers, see Henry et al., 2004; McDaniel and Einstein, 2007: Chapter 7; McDaniel et al., in press; Phillips et al., 2007; Wilson and Park, 2007). This interest was motivated by both practical and theoretical considerations. The applied concerns included that good prospective memory may be especially important for older adults who often have health-related prospective memory needs like remembering to take medication. Craik’s (1986) theory, suggesting that prospective memory should be very difficult for older adults, provided the theoretical thrust. Noting that aging affects some retrospective memory tasks more than others, Craik proposed that aging disrupts self-initiated retrieval processes, and therefore that older adults need greater environmental support or external cuing for accomplishing retrieval. This theory helps explain why age differences are often larger with free recall than recognition tasks. Because prospective memory is not accompanied by an external request to remember (i.e., subjects are not put in a retrieval mode), Craik theorized that prospective memory should be especially demanding in terms of self-initiated retrieval and thus particularly difficult for older adults. The findings remind us that prospective memory is not a unitary concept and that age differences vary as a function of the nature of the task demands and the contexts in which they are performed. One pattern is what Phillips et al. (2007) describe as the age prospective memory paradox, which is the finding that older adults generally perform more poorly on prospective memory tasks in the lab but perform as well as or better than younger adults in naturalistic settings (e.g., remembering to mail postcards or to call the experimenter on designated days). Indeed,

883

Wilson and Park (2007) discuss the high medication adherence of older adults in the face of declining cognitive functioning as another paradox (but see Insel et al., 2006, for evidence of modest levels of medication adherence by older adults). It is not currently clear what produces this reversal of performance across naturalistic and laboratory settings, but Phillips et al. and others (e.g., Kvavilashvili and Fisher, 2007) have suggested several possible explanations including age differences in conscientiousness, views regarding the importance of punctuality, busyness and structure of lifestyle, perceptions of task importance, and use of reminders (see also Wilson and Park, 2007). Another possible explanation is that older adults have greater control over the pacing of their ongoing activities in natural settings (McDaniel et al., in press). Even in laboratory settings, however, there is a large range of age effects. Many studies show large age-related deficits in prospective memory (e.g., Maylor et al., 1999), whereas some show modest or no age-related declines in prospective memory (e.g., Einstein and McDaniel, 1990; Cherry and LeCompte, 1999). Henry et al.’s (2004) meta-analysis revealed an interesting pattern that prospective memory tasks that required greater degrees of controlled or strategic processing (i.e., ones with less external support, and thus ones that required greater monitoring) were associated with larger age effects than those that could be accomplished by relatively automatic retrieval processes (i.e., those with good external cues that could support spontaneous retrieval processes). From a cursory interpretation of Craik’s (1986) theory, this should not happen; all prospective memory tasks should be difficult for older adults. From a deeper analysis, however, if one considers prospective memory to be a general label for a variety of specific tasks that differ in the extent to which they are cued by environmental events, the data may be consistent with the theory. The data also appear consistent with the multiprocess theory, which assumes that, depending on the conditions, people rely on monitoring versus spontaneous retrieval processes to different degrees in different kinds of prospective memory tasks. This is important as it relates to aging because working memory and attentional resources that are assumed to be needed for monitoring are thought to decline with age (Craik, 1986), whereas relatively automatic retrieval processes may remain relatively intact with age (McDaniel et al., in press).

884 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

To evaluate this interpretation, Reese (2004) tested younger and older adults and varied whether the prospective memory cues were focal or nonfocal (see Table 2; recall that focal cues are thought to stimulate spontaneous retrieval processes, whereas nonfocal cues are thought to require monitoring for successful retrieval). The ongoing task involved remembering short lists of words, and as every new word appeared, the background pattern of the screen changed. In the focal condition, subjects were asked to press a designated key whenever they saw a particular word, whereas in the nonfocal condition subjects were asked to press a designated key whenever a particular background pattern occurred. Consistent with the multiprocess theory prediction, Reese found that the size of the age difference depended on the type of prospective memory cue such that the age difference was smaller with the focal cue (80% for younger vs. 49% for older) than for the nonfocal cue (80% younger vs. 17% older). Sometimes there is no age difference with focal cues (e.g., Einstein and McDaniel, 1990; Cherry and LeCompte, 1999; McDaniel et al., in press) and sometimes, as in this particular experiment, the age difference is reduced but not eliminated (see also Rendell et al., 2007, Experiment 1). Possible explanations for the existence of age differences in some experiments even with a focal cue conclude that younger adults may be more likely to engage in monitoring and thereby increase the chances of retrieval, and that spontaneous retrieval processes may not be entirely spared with age. In addition to tasks with nonfocal cues, prospective memory tasks that seem to pose special problems for older adults seem to be time-based tasks (Henry et al., 2004), habitual prospective memory tasks (ones in which the intended action is performed repeatedly; Einstein et al., 1998), and those in which the retrieved intention cannot be performed immediately and must be delayed (as when a person remembers to take her/his medication in the bathroom but then needs to maintain the intention until she/he gets to the kitchen; see McDaniel et al., 2003). In closing this section, we note again the striking finding that the magnitude of the age differences varies greatly across studies. We suspect that we will better understand this pattern as we examine the processes that are recruited for different prospective memory tasks and how aging affects these processes.

2.45.9 Cognitive Neuroscience of Prospective Memory Building upon the considerable advances that have been made in our understanding of the cognitive processes underlying the realization of delayed intentions, significant progress has been made in identifying the functional neuroanatomy of prospective memory. The neural basis of prospective memory has been investigated using complimentary methodologies within the neuropsychological, functional neuroimaging, and electrophysiological traditions. Study in these domains has revealed a number of neurological and psychiatric conditions that are associated with impaired prospective memory as well as illuminating the temporal dynamics of the functional neuroanatomy of prospective memory.

2.45.9.1

Neuropsychology

Studies using the neuropsychological approach reveal that impairments of prospective memory are observed in a variety of neurological and psychiatric disorders including traumatic brain injury (TBI; Shum et al., 1999), stroke (Cockburn, 1995), epilepsy (Palmer and McDonald, 2000), multiple sclerosis (Bravin et al., 2000), Parkinson’s disease (Kliegel et al., 2005), schizophrenia (Shum et al., 2004), and substance abuse (Hefferman et al., 2001). Additionally, other evidence has revealed individual differences in prospective memory associated with genetic expression (Driscoll et al., 2005; Singer et al., 2006). Together, work in the area of neuropsychology converges with several themes that arise from the cognitive psychological literature. A number of studies reveal that damage to or disruption of neural networks involving the prefrontal cortex results in impaired prospective memory (Cockburn, 1995; Burgess et al., 2000). This finding is consistent with evidence revealing that prospective memory covaries with the efficiency of executive functions (typically thought to be dependent on the functional integrity of the prefrontal cortex) and the availability of working memory capacity (Marsh and Hicks, 1998). Also, disruption of the medial temporal lobe memory network results in impaired prospective memory (Palmer and McDonald, 2000). This finding is consistent with theoretical models of prospective memory wherein similar processes are thought to support prospective memory and explicit episodic

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

memory (Einstein and McDaniel, 1996; Guynn et al., 2001). The effects of mild to severe TBI on prospective memory have been considered in a number of studies. This research reveals negative effects of TBI on measures of time-, event-, and activity-based prospective memory (Shum et al., 1999) that increase with the severity of the injury (McCauley and Levin, 2004). TBI has an adverse effect on multiple phases of prospective memory including intention formation, re-instantiation, and execution, and it may have a lesser effect on intention retention (Kliegel et al., 2004). Consistent with this finding, individuals with TBI can benefit from reminders that are inserted in the middle of task performance (McCauley and Levin, 2004). The magnitude of the effect of TBI on prospective memory is equivalent when focal and nonfocal prospective cues are used (SchmitterEdgecombe and Wright, 2004), possibly indicating that patients do not benefit from spontaneous processes underlying the recognition of prospective cues (Einstein et al., 2005). There is also some evidence that indices of monitoring for prospective cues may be relatively intact in patients with TBI (Shum et al., 1999; McCauley and Levin, 2004). Studies examining the effects of TBI on prospective memory have revealed a mixed neuropsychological profile, with some, but not other, groups of patients demonstrating impairments of episodic or declarative memory, processing speed, and executive functions (Kliegel et al., 2004; Schmitter-Edgecombe and Wright, 2004; Mathias and Mansfield, 2005), making it difficult to ascertain whether there is a core deficit underlying the effects of TBI on prospective memory. There is growing evidence that disruption of the frontostriatal dopamine system leads to impaired prospective memory. At least two studies reveal that schizophrenia can produce deficits of time-, event-, and activity-based prospective memory (Shum et al., 2004; Kumar et al., 2005). The effect of schizophrenia may result from a disruption of the representation of intentions as the intention superiority effect is reduced or absent in patients with this disorder (Kondel, 2002), or from a reduction in the efficiency of strategic monitoring processes (Elvevag et al., 2003; Shum et al., 2004). There is also some evidence that prospective memory is disrupted in Parkinson’s disease (PD; Katai et al., 2003). Furthermore, the effect of PD on prospective memory may result from a reduction in the efficiency of processes supporting the formation and realization of intentions rather than processes supporting the

885

representation of an intention in memory (Katai et al., 2003; Kliegel et al., 2005). Finally, data from two studies indicate that the recreational abuse of MDMA, or Ecstasy – which is known to be toxic to dopaminergic and serotonergic neurons (Ricaurte et al., 2002) – results in both self-reported (Heffernan et al., 2001) and laboratory-based (Zakzanis et al., 2003) prospective memory deficits.

2.45.9.2

Functional Neuroimaging

Data from studies using functional neuroimaging methods generally converge with those from the neuropsychological literature. Specifically, PET and fMRI studies reveal activation of a broadly distributed neural network during the performance of prospective memory tasks that includes the rostral and lateral frontal cortex, structures within the medial temporal lobe, parietal cortex, and the thalamus (Okuda et al., 1998; Burgess et al., 2001; Simons et al., 2006). Functional neuroimaging techniques also reveal neural correlates of processes that may distinguish prospective memory from working memory, vigilance, and divided attention (Reynolds et al., 2003; De Bruycker et al., 2005). Evidence from one line of research reveals that the recruitment of rostral frontal cortex is important for the realization of delayed intentions (Figure 3;

Figure 3 Functional activation differentiating (execution þ expectation) – ongoing alone (a–c) and execution – expectation (d) conditions. Parts (a) and (b) portray activation within lateral rostral PFC, (c) portrays activation in right lateral prefrontal cortex, and (d) portrays thalamic activation. Adapted from Burgess PW, Quayle A, and Frith CD (2001) Brain regions involved in prospective memory as determined by positron emission tomography. Neuropsychologia 39: 545–555.

886 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

Burgess et al., 2001, 2003). In tasks requiring eventbased prospective memory, the lateral rostral frontal cortex is consistently activated, while the medial rostral frontal cortex is often deactivated (Burgess et al., 2003). In contrast, in tasks requiring time-based prospective memory, this pattern may be reversed, revealing activation of medial rostral frontal cortex and deactivation of lateral rostral frontal cortex (Okuda et al., 2001). Variation in the respective roles of the lateral and medial rostral frontal cortex across a variety of tasks has served as the impetus for the development of the Gateway hypothesis, wherein rostral frontal cortex is believed to play a role in switching the focus of one’s attention between stimulus-dependent and stimulusindependent aspects of information processing that may be critical for the realization of delayed intentions (Burgess et al., 2005). For instance, as applied to the typical prospective memory paradigm, the rostral frontal cortex may support the ability to switch from a focus on attributes of a stimulus that are relevant to performance of the ongoing activity to a focus on attributes of a stimulus that are internally represented, such as the cue-intention association. Using PET, Burgess et al. (2001, 2003) sought to determine whether the rostral frontal cortex was involved in the maintenance or realization of delayed intentions. In the baseline condition of these studies, individuals simply performed one of three ongoing activities; in the expectation condition, individuals anticipated the presentation of prospective cues, but cues were never presented; in the execution condition, individuals anticipated prospective cues – and cues were in fact presented. A comparison of neural recruitment in the expectation þ execution conditions versus the baseline condition revealed bilateral recruitment in lateral rostral frontal cortex, right parietal cortex, and the precuneus region, while a comparison of neural recruitment in the expectation and execution conditions did not reveal activation in these regions. This finding led to the suggestion that rostral frontal cortex was associated with cognitive processes that support the maintenance of an intention during the delay period (e.g., preparatory processing, Smith, 2003), rather than processes related to the realization of an intention once the prospective cue was detected (Burgess et al., 2001). fMRI has also been used to examine item-level or event-related neural recruitment associated with processes underlying prospective memory. Evidence from one study reveals what may reflect a neural correlate of item checking described in the strategic monitoring account of prospective memory (Guynn, 2003; Smith,

2003). De Bruycker et al. (2005) compared neural activity for ongoing activity stimuli when the ongoing activity was performed in isolation or when it was performed in the context of a prospective memory task. This comparison revealed increased activation in the medial and lateral extrastriate cortex for ongoing activity stimuli presented during the prospective memory condition relative to the ongoing activity condition. This basic finding was replicated by Reynolds et al. (2003), who observed decreased activation for prospective cues that were presented in a prospective memory condition relative to a simple vigilance condition. The decrease in activation for prospective memory cues from the prospective memory condition to the vigilance condition is consistent with the idea that the addition of a prospective memory component to a task may require the reallocation of processing resources between the prospective and ongoing components of the task (Smith, 2003; Marsh et al., 2006b).

2.45.9.3

Electrophysiology

Studies incorporating the event-related potential (ERP) methodology have sought to address three fundamental issues related to the neural basis of event-based prospective memory. First, work in this area has sought to identify the temporal dynamics of the neural correlates of prospective memory. Second, investigations in this area have sought to determine whether the neural correlates of prospective memory can be distinguished from other modulations of the ERPs related to target processing. Third, other investigations have sought to link the neural correlates of prospective memory to cognitive processes described in theories of prospective memory. Work examining the temporal dynamics of the neural correlates of prospective memory has consistently revealed three modulations of the ERPs that are associated with the realization of delayed intentions (Figure 4; N300, parietal old–new effect, and prospective positivity; West et al., 2001; West and Krompinger, 2005). The N300 reflects a phasic negativity over the occipital-parietal region of the scalp that typically emerges between 300 and 400 ms after onset of the prospective cue and is often accompanied by a positivity over the midline frontal region of the scalp (West et al., 2001; West and Ross-Munroe, 2002). The amplitude of the N300 is greater for prospective hits than for prospective misses, leading to the suggestion that it is associated with processes

Prospective Memory: Processes, Lifespan Changes, and Neuroscience

Occipital-parietal + N300 +

–

Parietal + –

Prospective positivity – Prospective cue Ongoing activity Figure 4 Grand average ERPs and scalp topography maps as viewed from above, demonstrating the time course and topography of the N300 and prospective positivity. Adapted from West and Wymbs (2004) and West and Covell (2001).

supporting the detection of prospective cues (West and Ross-Monroe, 2002). The N300 is elicited by prospective cues that are defined by letter case, color, and word identity, indicating that it reflects a relatively generic process that is associated with prospective memory (West et al., 2001; West et al., 2003; West and Krompinger, 2005). The parietal old–new effect and prospective positivity reflect enhanced positivity over the parietal region of the scalp between 400 and 1000 ms after stimulus onset (West et al., 2001; West and Krompinger, 2005). The parietal old–new effect reflects a relatively general process that is associated with item recognition in recognition memory (Rugg, 2004) and prospective memory paradigms; the prospective positivity is more specific to prospective memory and may reflect processes that serve to coordinate the prospective and ongoing components of the task once the prospective cue is detected and the intention is retrieved from memory (West and Krompinger, 2005). An example of research addressing the second issue is portrayed in a study comparing the prospective positivity and the P3 component. Given similarities between the time course and topography of the prospective positivity and P3 component, one might wonder whether the prospective positivity reflects a general index of target categorization in prospective memory paradigms (West et al., 2003). To examine this question, West et al. (2006)

887

examined the effects of working memory load on the amplitude of the prospective positivity and the P3 component. The logic of the study was this: If the prospective positivity and P3 arise from the activity of similar processes, then both should be sensitive to working memory load (Gevins et al., 1996); in contrast, if the prospective positivity and P3 reflect distinct processes, then there may be differential effects of working memory load on these two modulations of the ERPs. The data from this study support the latter hypothesis, as the amplitude of the P3 for target stimuli decreased with increasing working memory load (Figure 5), while the amplitude of the prospective positivity was unaffected by increasing working memory load (West and Bowry, 2005; West et al., 2006). These data demonstrate that that the neural correlates of prospective memory, in this case the prospective positivity, can be dissociated from processes that are more generally related to target categorization or selection. Following from work examining the temporal dynamics of processes underlying prospective

1-Back +

– 3-Back +

– Prospective cue N-back target Nontarget Figure 5 Grand average ERPs for prospective cue, N-back target, and nontarget trials at electrode, Pz demonstrating the effect of N-back load on the P3, but not the prospective positivity. The filled arrow marks the P3, and the unfilled arrow marks the prospective positivity. Adapted from West R, Bowry R, and Krompinger J (2006) The effects of working memory demands on the neural correlates of prospective memory. Neuropsychologia 44: 197–207.

888 Prospective Memory: Processes, Lifespan Changes, and Neuroscience

memory, other investigations have sought to determine whether modulations of the ERPs associated with the realization of delayed intentions possess the characteristics of cognitive processes described in theories of prospective memory. Two such studies have examined the influence of the working memory demands of the ongoing activity and strategic monitoring on the N300 (West et al., 2006; West, in press a). Based on strategic monitoring accounts of prospective memory, the amplitude of the N300 was expected to decrease as the working memory demands of the ongoing activity increased; in contrast, based on the discrepancy plus search account, the N300 was not expected to be sensitive to working memory load. The application of partial least squares analysis (McIntosh et al., 1996) – which allows one to decompose the effects of different experimental manipulations on the ERPs into a set of orthogonal latent variables – revealed that the N300 was expressed by two latent variables (West et al., 2006): one that was sensitive to N-back load and expressed the N300, but not the prospective positivity, and one that was insensitive to N-back load and expressed the N300 and prospective positivity. The results of this study reveal two important findings. First, consistent with the multiprocess view of prospective memory, these data reveal that both relatively automatic and more resource demands processes contribute to the detection of prospective cues. Second, these data reveal that the N300 and prospective positivity may be coupled to one another, a finding that is consistent with the general architecture of the discrepancy plus search theory (West, in press b).

2.45.10 Summary Although ignored for many years, and indeed characterized as a forgotten topic 25 years ago (Harris, 1984, p. 71), research since that time has proven prospective memory to be an experimentally tractable and theoretically exciting area. Laboratory and nonlaboratory paradigms have been developed to examine prospective remembering under a variety of situations, and theoretical issues are stimulating rich understanding of the cognitive processes and neural mechanisms underlying prospective memory. Because the memory literature has focused on memory tasks in which experimenters initiate retrieval by putting subjects in a retrieval mode, it has ignored the important capability of humans to plan for future events and then later perform them

in the appropriate circumstance. It appears that this self-initiated characteristic of prospective memory has important implications for considering optimal encoding, storage, and retrieval processes (see Ellis, 1996; Dobbs and Reeves, 1996). As our understanding of prospective memory has developed, and consistent with contextualistic views of memory (Jenkins, 1979), it also appears that prospective memory is not a unitary concept and, instead, that different processes are involved in different prospective memory tasks. We believe that it will be important, for both theoretical and applied concerns, to carefully examine these processes and the extent to which they are prominent in different prospective memory tasks.

References Anderson JR and Lebiere C (1998) The Atomic Components of Thought. Mahwah NJ: Erlbaum. Baddeley A, Lewis V, Eldridge M, and Thosmson N (1984) Attention and retrieval from long-term memory. J. Exp. Psychol. Gen. 113: 518–540. Bargh JA and Chartrand TL (1999) The unbearable automaticity of being. Am. Psychol. 54: 462–479. Baumeister RF, Bratslavsky E, Muraven M, and Tice DM (1998) Ego depletion: Is the active self a limited resource? J. Pers. Soc. Psychol. 74: 1252–1265. Bennett LR, Clawson DM, and Kardiasmenos KS (2005) The retrospective component of prospective memory: Relationship to prospective-component success. Poster presented at the 46th Annual Meeting of the Psychonomic Society Toronto ON. Block RA and Zakay D (2006) Prospective remembering involves time estimation and memory processes. In: Glicksohn J and Myslobodsky MS (eds.) Timing the Future: The Case for a Time-Based Prospective Memory, pp. 25–49. London: World Scientific. Bornstein BH and LeCompte DC (1995) A comparison of forgetting for source and item recognition. Psychon. Bull. Rev. 2: 254–259. Brandimonte MA and Passolunghi MC (1994) The effect of cuefamiliarity, cue-distinctiveness and retention interval on prospective remembering. Q. J. Exp. Psychol. Hum. Exp. Psychol. 47(A): 565–588. Bravin JH, Kinsella GJ, Ong B, and Vowels L (2000) A study of performance of delayed intentions in multiple sclerosis. J. Clin. Exp. Neuropsychol. 22: 418–429. Breneiser JE and McDaniel MA (2006) Discrepancy processes in prospective memory retrieval. Psychon. Bull. Rev. 13: 837–841. Burgess PW, Veitch E, de Lacy Costello A, and Shallice T (2000) The cognitive and neuroanatomical correlates of multitasking. Neuropsychologia 38: 848–663. Burgess PW, Quayle A, and Frith CD (2001) Brain regions involved in prospective memory as determined by positron emission tomography. Neuropsychologia 39: 545–555. Burgess PW, Scott SK, and Frith CD (2003) The role of the rostral frontal cortex (area 10) in prospective memory: A lateral versus medial dissociation. Neuropsychologia 41: 906–918.

Prospective Memory: Processes, Lifespan Changes, and Neuroscience Burgess PW, Simons JS, Dumontheil I, and Gilbert SJ (2005) The gateway hypothesis of rostral prefrontal cortex (area 10) function. In: Duncan J, Phillips L, and McLeod P (eds.) Measuring the Mind: Speed Control and Age, pp. 217–248, Oxford: Oxford University Press. Ceci SJ and Bronfenbrenner U (1985) ‘‘Don’t forget to take the cupcakes out of the oven’’: Prospective memory, strategic time-monitoring and context. Child Dev. 56: 152–164. Chasteen AL, Park DC, and Schwarz N (2001) Implementation intentions and facilitation of prospective memory. Psychol. Sci. 12: 457–461. Cherry KE and LeCompte DC (1999) Age and individual differences influence prospective memory. Psychol. Aging 14: 60–76. Cockburn J (1995) Task interruption in prospective memory: A frontal lobe function. Cortex 31: 87–97. Cohen AL, and Gollwitzer PM (in press) The cost of remembering to remember: Cognitive load and implementation intentions influence ongoing task performance. In: Kliegel M, McDaniel MA, Einstein GO (eds.) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives, Mahwah NJ: Erlbaum. Cook GI, Marsh RL, and Hicks JL (2005) Associating a timebased prospective memory task with an expected context can improve or impair intention completion. App. Cogn. Psychol. 19: 345–360. Craik FIM (1986) A functional account of age differences in memory. In: Clix F and Hangendorf H (eds.) Human Memory and Cognitive Capabilities: Mechanisms and Performances, pp. 409–422. Amsterdam: Elsevier. Craik FIM, Govoni R, Naveh-Benjamin M, and Anderson ND (1996) The effects of divided attention on encoding and retrieval processes in human memory. J. Exp. Psychol. Gen. 125: 159–180. Crovitz HF and Daniel WF (1984) Measurements of everyday memory: Toward the prevention of forgetting. Bull. Psychon. Soc. 22: 413–414. De Bruycker W, Verhoef B, d’Ydewalle G, and Orban GA (2005) Brain Regions Associated with Retention and Retrieval in Event-Based Prospective Memory. Paper presented at the Second International Conference on Prospective Memory Zurich Switzerland. Dembitzer A and Lai EJ (2003) Retained surgical instrument. N. Engl. J. Med. 348–228. Dismukes RK (in press) Prospective memory in aviation and everyday settings. In: Kliegel M, McDaniel MA, and Einstein GO (eds.) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives, Mahwah, NJ: Erlbaum. Dobbs AR and Reeves MB (1996) Prospective memory: More than memory. In: Brandimonte M, Einstein G, and McDaniel M (eds.) Prospective Memory: Theory and Applications, pp. 199–226. Hillsdale, NJ: Erlbaum. Driscoll I, McDaniel MA, and Guynn MJ (2005) Apolipoprotein E and prospective memory in normally aging adults. Neuropsychology 19: 28–34. Einstein GO and McDaniel MA (1990) Normal aging and prospective memory. J. Exp. Psychol. Learn. Mem. Cogn. 16: 717–726. Einstein GO and McDaniel MA (1996) Retrieval processes in prospective memory: Theoretical approaches and some new empirical findings. In: Brandimonte M, Einstein GO, and McDaniel MA (eds.) Prospective Memory: Theory and Applications, pp. 115–142. Mahwah, NJ: Lawrence Erlbaum. Einstein GO and McDaniel MA (2005) Prospective memory: Multiple retrieval processes. Curr. Dir. Psychol. Sci. 14: 286–290. Einstein GO, McDaniel MA, Richardson SL, Guynn MJ, and Cunfer AR (1995) Aging and prospective memory: Examining

889

the influences of self-initiated retrieval processes. J. Exp. Psychol. Learn. Mem. Cogn. 21: 996–1007. Einstein GO, McDaniel MA, Smith RE, and Shaw P (1998) Habitual prospective memory and aging: Remembering intentions and forgetting actions. Psychol. Sci. 9: 284–288. Einstein GO, McDaniel MA, Thomas R, et al. (2005) Multiple processes in prospective memory retrieval: Factors determining monitoring versus spontaneous retrieval. J. Exp. Psychol. Gen. 134: 327–342. Einstein GO, McDaniel MA, Williford CL, Pagan JL, and Dismukes RK (2003) Forgetting of intentions in demanding situations is rapid. J. Exp. Psychol. Appl. 9: 147–162. Einstein GO, Smith RE, McDaniel MA, and Shaw P (1997) Aging and prospective memory: The influence of increased task demands at encoding and retrieval. Psychol. Aging 12: 479–488. Ellis J (1996) Prospective memory or the realization of delayed intentions: A conceptual framework for research. In: Brandimonte M, Einstein G, and McDaniel M (eds.) Prospective Memory: Theory and Applications, pp. 1–51. Hillsdale, NJ: Erlbaum. Elvevag B, Maylor EA, and Gilbert AL (2003) Habitual prospective memory in schizophrenia. BioMed Centr. Psychiatry 3: 9. www.biomedcentral.com/1471: 244X/3/9. Freeman JE and Ellis J (2003) The representation of delayed intentions: A prospective subject-performed task? J. Exp. Psychol. Learn. Mem. Cogn. 29: 976–992. Gevins A, Smith ME, Le J, et al. (1996) High resolution evoked potential imaging of the cortical dynamics of human working memory. Electroencephalogr. Clin. Neurophysiol. 98: 327–348. Gollwitzer PM (1999) Implementation intentions: Strong effects of simple plans. Am. Psychol. 54: 493–503. Goschke T and Kuhl J (1993) Representation of intentions: Persisting activation in memory. J. Exp. Psychol. Learn. Mem. Cogn. 19(5): 1211–1226. Guttentag RE (1984) The mental effort requirement of cumulative rehearsal: A developmental study. J. Exp. Child Psychol. 37: 92–106. Guynn MJ (2003) A two-process model of strategic monitoring in event-based prospective memory: Activation/retrieval mode and checking. Int. J. Psychol. 38: 245–256. Guynn MJ and McDaniel MA (2007) Target pre-exposure eliminates the effect of distraction on event-based prospective memory. Psychon. Bull. Rev. 14: 484–488. Guynn MJ, McDaniel MA, and Einstein GO (1998) Prospective memory: When reminders fail. Mem. Cogn. 26: 287–298. Guynn MJ, McDaniel MA, and Einstein GO (2001) Remembering to perform intentions: A different type of memory? In: Zimmer HD, Cohen RL, Guynn MJ, Engelkamp J, Kormi-Nouri R, and Foley MA (eds.) Memory for Action: A Distinct Form of Episodic Memory? pp. 25–48. Oxford: Oxford University Press. Harris JE (1984) Remembering to do things: A forgotten topic. In: Harris JE and Morris PE (eds.) Everyday Memory, Actions and Absent-Mindedness, pp. 71–92. London: Academic Press. Harris JE and Wilkins AJ (1982) Remember to do things: A theoretical framework and an illustrative experiment. Hum. Learn. 1: 123–136. Heffernan TM, Jarvis H, Rodgers J, Scholey AB, and Ling J (2001) Prospective memory, everyday cognitive failures and central executive function in recreational users of Ecstasy. Hum. Psychopharmacol. Clin. Exp. 16: 607–612. Henry JD, MacLeod MS, Phillips H, and Crawford JR (2004) A meta-analytic review of prospective memory and aging. Psychol. Aging 19(1): 27–39. Hicks JL, Marsh RL, and Cook GI (2005) Task interference in time-based, event-based and dual intention prospective memory conditions. J. Mem. Lang. 53: 430–444.

890 Prospective Memory: Processes, Lifespan Changes, and Neuroscience Hicks JL, Marsh RL, and Russell EJ (2000) The properties of retention intervals and their affect on retaining prospective memories. J. Exp. Psychol. Learn. Mem. Cogn. 26: 1160–1169. Howard DC, McDaniel MA, and Butler KM (2006) Implementation Intentions and Prospective Memory in Young Adults. Paper presented at the Annual Meeting of the Psychonomic Society, Houston, TX. Insel K, Morrow D, Brewer B, and Figueredo A (2006) Executive function, working memory and medication adherence among older adults. J. Gerontol. Psychol. Sci. 61(2): 102–107. Jenkins JJ (1979) Four points to remember: A tetrahedral model of memory. In: Cermak LS and Craik FIM (eds.) Levels of Processing in Human Memory, pp. 429–446. Hillsdale NJ: Erlbaum. Kardiasmenos KS, Clawson DM, Wilken JA, and Wallin MT (2004) Effects of Implementation Intentions on Prospective Memory Performance. Poster presented at the 45th Annual Meeting of the Psychonomic Society, Minneapolis, MN. Katai S, Maruyama T, Hashimoto T, and Ikeda S (2003) Event based and time based prospective memory in Parkinson’s disease. J. Neurol. Neurosurg. Psychiatry 74: 704–709. Kliegel M, Eschen A, and Thone-Otto AI (2004) Planning and realization of complex intentions in traumatic brain injury and normal aging. Brain Cogn. 56: 43–54. Kliegel M, Mackinlay R, and Jager T (in press) A lifespan approach to the development of complex prospective memory. In: Kliegel M, McDaniel MA, Einstein GO Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives, Mahwah, NJ: Erlbaum. Kliegel M, Phillips LH, Lemke U, and Kopp UA (2005) Planning and realisation of complex intentions in patients with Parkinson’s disease. J. Neurol. Neurosurg. Psychiatry 76: 1501–1505. Klein SB and Kilstrom JF (1986) Elaboration, organization and the self-reference effect in memory. J. Exp. Psychology: Gen. 115: 26–38. Kok A (2001) On the utility of P3 amplitude as a measure of processing capacity. Psychophysiology 38: 557–577. Kondel TK (2002) Prospective memory and executive function in schizophrenia. Brain Cogn. 2: 405–410. Kumar D, Nizamie HS, and Jahan M (2005) Event-based prospective memory in schizophrenia. J. Clin. Exp. Neuropsychol. 27: 867–872. Kvavilashvili L and Fisher L (2007) Is time-based prospective remembering mediated by self-initiated rehearsals? Role of incidental cues, ongoing activity, age and motivation. J. Exp. Psychol. Gen. 136: 112–132. Kvavilashvili L, Kyle F, and Messer DJ (in press) The development of prospective memory in children: Methodological issues, empirical findings and future directions. In: Kliegel M, McDaniel MA, Einstein GO (eds.) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives, Mahwah, NJ: Erlbaum. Kvavilashvili L, Messer DJ, and Ebdon P (2001) Prospective memory in children: The effects of age and task interruption. Dev. Psychol. 37: 418–430. Lebiere C and Lee FJ (2002) Intention superiority effect: A context-switching account. Cogn Sys Res 3: 57–65. Ma¨ntyla¨ T (1994) Remembering to remember: Adult age differences in prospective memory. J. Gerontol. 49: 276–282. Marsh RL, Cook GI, and Hicks JL (2006a) An analysis of prospective memory. In: Ross BH (ed.) The Psychology of Learning and Motivation, vol. 46, pp. 115–153. San Diego: Academic Press.

Marsh RL, Cook GI, Meeks JT, Clark-Foos A, and Hicks JL (2007) Memory for intention-related material presented in a channel. Mem. Cogn. 5: 1197–1204. Marsh RL, Hancock TW, and Hicks JL (2002a) The demands of an ongoing activity influence the success of event-based prospective memory. Psychon. Bull. Rev. 9: 604–610. Marsh RL and Hicks JL (1998) Event-based prospective memory and executive control of working memory. J. Exp. Psychol. Learn. Mem. Cogn. 24: 336–349. Marsh RL, Hicks JL, and Bink ML (1998a) Activation of completed, uncompleted and partially completed intentions. J. Exp. Psychol. Learn. Mem. Cogn. 24: 350–361. Marsh RL, Hicks JL, and Bryan ES (1999) The activation of unrelated and cancelled intentions. Mem. Cogn. 27: 320–327. Marsh RL, Hicks JL, and Cook GI (2005) On the relationship between effort toward an ongoing task and cue detection in event-based prospective memory. J. Exp. Psychol. Learn. Mem. Cogn. 29: 861–870. Marsh RL, Hicks JL, and Cook GI (2006b) Task interference from prospective memories covaries with contextual associations of fulfilling them. Mem. Cogn. 34: 1037–1045. Marsh RL, Hicks JL, Cook GI, Hansen JS, and Pallos AL (2003) Interference to ongoing activities covaries with the characteristics of an event-based intention. J. Exp. Psychol. Learn. Mem. Cogn. 29: 861–870. Marsh RL, Hicks JL, and Hancock TW (2000) On the interaction of ongoing cognitive activity and the nature of event-based intention. Appl. Cogn. Psychol. 14: 529–541. Marsh RL, Hicks JL, and Landau JD (1998b) An investigation of everyday prospective memory. Mem. Cogn. 26: 633–643. Marsh RL, Hicks JL, and Watson V (2002b) The dynamics of intention retrieval and coordination of action in event-based prospective memory. J. Exp. Psychol. Learn. Mem. Cogn. 28: 652–660. Mathias JL and Mansfield KM (2005) Prospective and declarative memory problems following moderate and severe traumatic brain injury. Brain Inj. 19: 271–282. Matthews RD (1992) Are Retrospective and Prospective Memory Related? Master’s Thesis, University of North Carolina Greensboro. Maylor EA (1990) Age and prospective memory. Q. J. Exp. Psychol. 42A: 471–493. Maylor EA (1996) Age-related impairment in an event-based prospective memory task. Psychol. Aging 11: 74–78. Maylor EA, Darby RJ, and Della Salla S (2000) Retrieval of performed versus to-be-performed tasks: A naturalistic study of the intention superiority effect in normal aging and dementia. Appl. Cogn. Psychol. 14: S83–S98. McCauley SR and Levin HS (2004) Prospective memory in pediatric traumatic brain injury: A preliminary study. Dev. Neuropsychol. 25: 5–20. McDaniel MA and Einstein GO (1993) The importance of cue familiarity and cue distinctiveness in prospective memory. Memory 1: 23–41. McDaniel MA and Einstein GO (2000) Strategic and automatic processes in prospective memory retrieval: A multiprocess framework. Appl. Cogn. Psychol. 14: S127–S144. McDaniel MA and Einstein GO (2007) Prospective Memory: An Overview and Synthesis of an Emerging Field. Thousand Oaks, CA: Sage. McDaniel MA and Einstein GO (eds.) (2007) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives. Mahwah, NJ: Erlbaum. McDaniel MA, Einstein GO, and Jacoby LL (2007) New considerations in aging and memory: The glass may be half full. In: Craik FIM and Salthouse TA (eds.) The Handbook of Aging and Cognition, pp. 251–310, 3rd edn. Mahwah, NJ: Erlbaum.

Prospective Memory: Processes, Lifespan Changes, and Neuroscience McDaniel MA, Einstein GO, and Rendell PG (in press) The puzzle of inconsistent age-related declines in prospective memory: A multiprocess explanation. In: Kliegel M, McDaniel MA, and Einstein GO (eds.) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives. Mahwah, NJ: Erlbaum. McDaniel MA, Einstein GO, Stout AC, and Morgan Z (2003) Aging and maintaining intentions over delays: Do it or lose it. Psychol. Aging 18(4): 807–822. McDaniel MA, Guynn MJ, Einstein GO, and Breneiser JE (2004) Cue focused and automatic-associative processes in prospective memory. J. Exp. Psychol. Learn. Mem. Cogn. 30: 605–614. McDaniel MA and Pressley M (1987) Imagery and Related Mnemonic Processes: Theories, Individual Differences and Applications. New York: Springer. McDaniel MA, Robinson-Riegler B, and Einstein GO (1998) Prospective remembering: Perceptually driven or conceptually driven processes? Mem. Cogn. 26: 121–134. McGann D, Defeyter MA, Ellis JA, and Reid C (2005) Prospective memory in children: The effects of age and target salience. Paper presented at the 2nd International Prospective Memory Conference, Zurich, Switzerland. McIntosh AR, Bookstein FL, Haxby JV, and Grady CL (1996) Spatial pattern analysis of functional images using partial least squares. Neuroimage 3: 143–157. Meacham JA and Singer J (1977) Incentive effects in prospective remembering. J. Psychol. Interdiscipl. Appl. 97: 191–197. Morrell RW, Park DC, Kidder DP, and Martin M (1997) Adherence to antihypertensive medications across the life span. Gerontologist 37: 609–619. Morris CD, Bransford JD, and Franks JJ (1977) Levels of processing versus transfer appropriate processing. J. Verb. Learn. Verb. Behav. 16: 519–533. Moscovitch M (1994) Memory and working with memory: Evaluation of a component process model and comparisons with other models. In: Schacter DL and Tulving E (eds.) Memory Systems, pp. 269–310. Cambridge, MA: MIT Press. Nowinski JL, Holbrook JB, and Dismukes RK (2003) Human memory and cockpit operations: An ASRS study. Proceedings of the 12th International Symposium on Aviation psychology, pp. 888–893. Dayton, OH: The Wright State University. Retrieved October 20, 2006, from http://humanfactors.arc.nasa.gov/ihs/flightcognition/Publications/ Nowinski_etal_ISAP03.pdf Okuda J, Fujii T, Ohtake H, et al. (2001) Brain mechanisms underlying human prospective memory. In: Yamadori A, Kawashima R, Fujii T, and Suzuki K (eds.) Frontiers in Human Memory, pp. 79–96. Sendai, Japan: Tohoku University Press. Okuda J, Fujii T, Yamadori A, et al. (1998) Participation of the prefrontal cortices in prospective memory: Evidence from a PET study in humans. Neurosci. Lett. 253: 127–130. Palmer HM and McDonald S (2000) The role of frontal and temporal lobe processes in prospective memory. Brain Cogn. 44: 103–107. Park DC, Hertzog C, Kidder DP, Morell RW, and Mayhorn CB (1997) Effect of age on event-based and time-based prospective memory. Psychol. Aging 12: 314–327. Park DC and Kidder DP (1996) Prospective memory and medication adherence. In: Brandimonte M, Einstein GO, and McDaniel MA (eds.) Prospective Memory: Theory and Applications, pp. 1–22. Mahwah, NJ: Erlbaum. Phillips LH, Henry JD, Martin M (in press) Adult aging and prospective memory: The importance of ecological validity. In: Kliegel M, McDaniel MA, Einstein GO (eds.) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives, Mahwah, NJ: Erlbaum.

891

Reason JT (1990) Human Error. Cambridge, MA: Cambridge University Press. Reese CM (2004) Age and Focal Processing in Event-Based Prospective Memory. Paper presented at the Cognitive Aging Conference, Atlanta, GA. Reese CM and Cherry KE (2002) The effects of age, ability and memory monitoring on prospective memory task performance. Aging Neuropsychol. Cogn. 9: 98–113. Rendell PG, McDaniel MA, Forbes RD, and Einstein GO (2007) Age-related effects in prospective memory are modulated by ongoing task complexity and relation to target cue. Aging Neuropsycho. Cogn. 3: 236–256. Reynolds J, West R, and Braver T (2003) Differentiation of prospective memory and working memory using a mixed state and event-related fMRI design. J. Cogn. Neurosci. Suppl. p. 147. Ricaurte GA, Yuan J, Hatzidimitriou Cord BJ, and McCann UD (2002) Severe dopaminergic neurotoxicity in primates after a common recreational dose regimen of MDMA (‘‘Ecstasy’’). Science 297: 2260–2263. Robinson-Riegler MB (1994) The Recognition-Recall Hypothesis of Prospective Memory. PhD Thesis, Purdue University. Rugg MD (2004) Retrieval processes in human memory: Electrophysiological and fMRI evidence. In: Gazzaniga MS (ed.) The Cognitive Neurosciences, 3rd edn., pp. 727–737. Cambridge MA: MIT Press. Schaeffer EG, Kozak MV, and Sagness K (1998) The role of enactment in prospective remembering. Mem. Cogn. 26: 644–650. Shallice T and Burgess P (1991) Deficits in strategy application following frontal lobe damage in man. Brain 114: 727–741. Schmitter-Edgecombe M and Wright MJ (2004) Event-based prospective memory following severe closed-head injury. Neuropsychology 18: 353–361. Sellen AJ, Louie G, Harris JE, and Wilkins AJ (1997) What brings intentions to mind? An in situ study of prospective memory. Memory 5: 483–507. Shum D, Ungvari GS, Tang W-K, and Leung JP (2004) Performance of schizophrenia patients on time-, event- and activity-based prospective memory tasks. Schizophr. Bull. 30: 693–701. Shum D, Valentine M, and Cutmore T (1999) Performance of individuals with severe long-term traumatic brain injury on time-, event- and activity-based prospective memory tasks. J. Clin. Exp. Neuropsychol. 21: 49–58. Simons JS, Scho¨lvinck ML, Gilbert SJ, Frith CD, and Burgess PW (2006) Differential components of prospective memory? Evidence from fMRI. Neuropsychologia 44: 1388–1397. Singer JJ, Falchi M, MacGregor AJ, Cherkas LF, and Spector TD (2006) Genome-wide scan for prospective memory suggests linkage to chromosome 12q22. Behav. Genet. 36: 18–28. Smith RE (2003) The cost of remembering to remember in event-based prospective memory: Investigating the capacity demands of delayed intention performance. J. Exp. Psychol. Learn. Mem. Cogn. 29: 347–361. Smith RE and Bayen UJ (2004) A multinomial model of eventbased prospective memory. J. Exp. Psychol. Learn. Mem. Cogn. 30: 756–777. Smith RE and Bayen UJ (2006) The source of adult age differences in event-based prospective memory: A multinomial model approach. J. Exp. Psychol. Learn. Mem. Cogn. 32: 623–635. Somerville SC, Wellman HM, and Cultice JC (1983) Young children’s deliberate reminding. J. Genet. Psychol. 143: 87–96. Stokes S, Pierroutsakos S, and Einstein G (2007) Remembering to Remember: Strategic and Spontaneous Processes in

892 Prospective Memory: Processes, Lifespan Changes, and Neuroscience Children’s Prospective Memory. Paper presented at the Meeting of the Society for Research in Child Development, Boston, MA. Tulving E (1983) Elements of Episodic Memory. New York: Oxford University Press. Tulving E (2004) Memory, Consciousness and Time. Keynote address presented at the 16th Annual Convention of the American Psychological Society, Chicago, IL. West RL (1988) Prospective memory and aging. In: Gruneberg MM, Morris PE, and Sykes RN (eds.) Practical Aspects of Memory, vol. 2, pp. 119–125. Chichester, UK: Wiley. West R (2005) The neural basis of age-related decline in prospective memory. In: Cabeza R, Nyberg L, and Park D (eds.) Cognitive Neuroscience of Aging, pp. 246–264. New York: Oxford University Press. West R (in press a) Towards a cognitive neuroscience of prospective memory. In: Kliegel M, McDaniel MA, and Einstein GO (eds.) Prospective Memory: Cognitive Neuroscience Developmental and Applied Perspectives. Mahwah, NJ: Erlbaum West R (in press b) The influence of strategic monitoring on the neural correlates of prospective memory. Mem. Cogn. West R and Bowry R (2005) Effects of aging and working memory demands on prospective memory. Psychophysiology 42: 698–712. West R, Bowry R, and Krompinger J (2006) The effects of working memory demands on the neural correlates of prospective memory. Neuropsychologia 44: 197–207. West R and Craik FIM (1999) Age-related decline in prospective memory: The roles of cue accessibility and cue sensitivity. Psychol. Aging 14: 264–272. West R and Craik FIM (2001) Influences on the efficiency of prospective memory in younger and older adults. Psychol. Aging 16: 682–696.

West R and Covell E (2001) Effects of aging on event-related neural activity related to prospective remembering. Neuroreport 12: 2855–2858. West R, Herndon RW, and Crewdson SJ (2001) Neural activity associated with the realization of a delayed intention. Cogn. Brain Res. 12: 1–10. West R and Krompinger J (2005) Neural correlates of prospective and episodic memory. Neuropsychologia 43: 418–433. West R, Krompinger J, and Bowry R (2005) Disruptions of preparatory attention contribute to failures of prospective memory. Psychon. Bull. Rev. 12: 502–507. West R and Ross-Munroe K (2002) Neural correlates of the formation and realization of delayed intentions. Cogn. Affect. Behav. Neurosci. 2: 162–173. West R and Wymbs N (2004) Is detecting prospective cues the same as selecting targets? An ERP study. Cogn. Affective Behav. Neurosci. 4: 354–363. West R, Wymbs N, Jakubek K, and Herndon RW (2003) Effects of intention load and background context on prospective remembering: An event-related brain potential study. Psychophysiology 40: 260–276. Whittlesea BWA and Williams LD (2001a) The discrepancyattribution hypothesis: I. The heuristic basis of feelings of familiarity. J. Exp. Psychol. Learn. Mem. Cogn. 27: 3–13. Whittlesea BWA and Williams LD (2001b) The discrepancyattribution hypothesis: II. Expectation, uncertainty, surprise and feelings of familiarity. J. Exp. Psychol. Learn. Mem. Cogn. 27: 14–33. Wilson EAH and Park D (in press) Prospective memory and health behaviors: Context trumps cognition. In: Kliegel M, McDaniel MA, Einstein GO (eds.) Prospective Memory: Cognitive, Neuroscience, Developmental and Applied Perspectives, Mahwah, NJ: Erlbaum. Zakzanis KK, Young DA, and Campbell Z (2003) Prospective memory impairment in abstinent MDMA (‘‘Ecstasy’’) users. Cogn. Neuropsychiatry 8: 141–153.