Prospective memory
Prospective memory is a form of memory that involves remembering to perform a planned action or recall a planned intention at some future point in time. Prospective memory tasks are common in daily life and range from the relatively simple to extreme life-or-death situations. Examples of simple tasks include remembering to put the toothpaste cap back on, remembering to reply to an email, or remembering to return a rented movie. Examples of highly important situations include a patient remembering to take medication or a pilot remembering to perform specific safety procedures during a flight.
In contrast to prospective memory, retrospective memory involves remembering people, events, or words that have been encountered in the past. Whereas retrospective memory requires only the recall of past events, prospective memory requires the exercise of retrospective memory at a time that has not yet occurred. Prospective memory is thus considered a form of "memory of the future".
Retrospective memory involves the memory of what we know, containing informational content; prospective memory focuses on when to act, rather than focusing on informational content. There is some evidence demonstrating the role of retrospective memory in the successful execution of prospective memory, but this role seems to be relatively small.
Types
Event-based vs. time-based
There are two types of prospective memory: event-based and time-based prospective memory. Event-based prospective memory involves remembering to perform certain actions when specific circumstances occur. For example, driving past the local library cues the remembrance of the need to return an overdue book. Time-based prospective memory involves remembering to perform an action at a particular point in time. For example, seeing that it is 10:00 PM acts as a cue to watch a favorite television show.Research performed by Sellen et al. compared event-based and time-based cues on prospective memory tasks. The experimenters gave participants a place and a time and were told to press a button each time those cues appeared during the study. It was found that performance on event-based tasks was better than performance on time-based tasks, even when participants took more time to think about their responses. The difference in task performance between the two types of prospective memory suggests that the intended action was better triggered by external cues of the event-based task than internal cues of the time-based task. External cues, as opposed to internal cues, act as a prompt for better performance, making it easier to complete event-based tasks.
Types of event-based prospective memory: Immediate-execute vs. delayed-execute
McDaniel et al. further distinguished event-based prospective memory into immediate-execute tasks and delayed-execute tasks. Immediate-execute tasks involve a response as soon as a particular cue is noticed, while delayed-execute tasks involve delays between the perception of the relevant cue and the performance of the intended action. Delayed-execute tasks more commonly occur in real life when circumstances of a situation prevent intermediate action once the cue has been perceived. Research was performed by McDaniel et al., in which participants completed tasks involving various delays and interruptions between cues and responses. It was demonstrated that correct performance suffered when there was a delay or interruption during a task. However, it was further shown that the use of reminders for participants eliminated the effects of the interruption task.History and theoretical perspectives
History
Prospective memory received wide attention when Ulric Neisser included a paper presented by John A. Meacham at the 1975 American Psychological Association meeting in Chicago in his 1982 edited volume, Memory Observed: Remembering in Natural Contexts. Previously, this paper and three other articles by Meacham had received little notice. Meacham defined prospective memory as information with implications for actions to be performed in the future, such as stopping at the store on the way home, and distinguished it from retrospective memory, concerned solely with recall of information from the past. Meacham was the first to introduce this distinction, along with the term prospective memory.There is great interest about the possible mechanisms and resources that underlie the workings of prospective memory.
The preparatory attentional and memory (PAM) theory
The preparatory attentional and memory theory proposes two types of processes involved in successful prospective memory performance. The first component of this theory involves a monitoring process that begins when a person constructs an intention that is then maintained until it is performed. This monitoring component involves a capacity-consuming process, similar to those used when maintaining attention, because there is a need for the intention to be stored and maintained in memory. The second component involves the use of elements of retrospective memory processes. These elements are used to differentiate between the wanted prospective memory intention and unwanted thoughts, in an attempt to keep focus on the goal and not the other options surrounding it. Retrospective memory is also used to remember specifically what intention is supposed to be performed in the future, and the monitoring process is needed to be able to remember to perform this action at the correct condition or time.According to this theory, prospective memory should be enhanced when complete attention is given to the desired task than when attention is divided among multiple tasks. Research conducted by McDaniel et al. attempted to prove that prospective memory performance is better on focused tasks as opposed to those where attention is split. Subjects completed a prospective memory task in either a condition where full attention was given or a condition where attention was divided on other tasks. The results were consistent with the PAM theory, showing that participants' prospective memory performance was better with full attention.
However, there is a lot of scepticism that the rather complex mechanisms of the PAM theory are required for all, sometimes mundane, prospective memory tasks. In research by Reese and Cherry, participants formed an intention to act in the future, but were interrupted prior to acting on their intention when the cue was present. When participants were asked their thoughts at the moment of interruption, only 2% reported that they were thinking of the original intention. This demonstrated evidence against the PAM theory, that there is constant maintenance from the time of constructing the intention to acting upon it at the right circumstance.
Reflexive-associative theory
Further research conducted by Einstein and McDaniel in 1990, found that subjects during prospective memory tasks reported that their intention often "popped" into mind, instead of being constantly monitored and consciously maintained. Along similar lines, a theory was proposed in 2000, called the reflexive-associative theory, which states that when people create an intention for a prospective memory task, they make an association between the target cue and the intended action. Later when the target cue occurs, the automatic associative-memory system triggers the retrieval of the intended action and brings it back into conscious awareness. Therefore, as long as the target cue occurs, the association previously made will initiate the retrieval of the intended action, regardless of whether the intention is in consciousness.Multi-process model
Another theory that has been used to explain the mechanisms of prospective memory is the multi-process model proposed by McDaniel and Einstein. This theory states that prospective memory retrieval does not always need an active monitoring process but can occur spontaneously. Therefore, multiple processes can be used for successful prospective memory. Further, it was believed that it would be maladaptive to rely solely on active monitoring because it requires a lot of attentional resources. This may potentially interfere with other forms of processing that are required for different tasks during the retention interval.Prospective memory cues will lead to spontaneous retrieval of an intention when at least one of four conditions is met: the cue and target action are highly associated with each other, the cue is salient, the other processes performed during the period between cue and action of the prospective memory task direct attention to relevant cue features, or the intended action is simple. Further research has found that although many aspects of prospective memory tasks are automatic, they do involve a small amount of processing. An experiment conducted by Einstein et al. found that some participants performed slower on a filler task when performing a prospective memory task at the same time. Even though some of the participants did not engage in active monitoring, they showed nearly the same rate of success on the task, demonstrating the use of multiple processes for prospective memory performance.
Neuroanatomy
Frontal lobe
As prospective memory involves remembering and fulfilling an intention, it requires episodic memory, declarative memory, and retrospective memory, followed by supervisory executive functions. All of these are controlled by the frontal lobe which is situated at the front of the cerebral hemisphere.Studies using positron emission tomography trace a slight increase in blood flow to the frontal lobe in participants completing prospective memory tasks involving remembering a planned action, while performing other tasks. During these procedures, sites of brain activation include the prefrontal cortex, specifically the right dorsolateral, ventrolateral, and medial regions, as well as the median frontal lobe. The prefrontal cortex is responsible for holding the intention in consciousness and suppressing other internal thoughts. The median frontal lobe keeps attention focused on the planned action instead of the other tasks.
The prefrontal cortex is involved mainly in event-based as opposed to time-based prospective memory. Cheng et al. had participants with lesions in the prefrontal cortex perform event-based and time-based prospective memory tasks. They found that performance was impaired in the event-based tasks, which use event cues to trigger intentions, but not in the time-based tasks which use time cues to trigger intentions.
Other lesion studies have also shown the use of the frontal lobe in remembering and focusing on intentions. Burgess et al. studied patients with lesions to areas in the frontal lobe such as Brodmann's area 10, finding that these patients failed to follow instructions and switch attention during prospective memory tasks.