Prospective Memory: The Relation of Executive Function to Aging

The executive functions of the frontal lobe seem to play an integral role in the mediation of prospective memory, as suggested by the results of recent studies (Shallice & Burgess, 1991; Cockburn, 1995; Shapiro, Shapiro, Alper, & Russell, in press). In the present study two groups were examined in terms of their performance on four different prospective memory tasks. The two groups included younger adults (ages 18-21) and older adults (ages 62-80). Both groups were asked to perform each of four prospective memory tasks (an event-based, disembedded task; an event-based, embedded task; a time-based, disembedded task; and a time­ based, embedded task) webbed within a general knowledge quiz. The participants also were tested using the Stroop Test and the Wisconsin Card Sort Task, which have been acknowledged as predictors of frontal lobe dysfunction. The Kaufmann Brief Intelligence Test, the Williams Inhibition Test, and an Immediate Recall Test were also administered. The results indicate that both groups performed significantly poorer on the TD task in comparison to the ED task. This finding suggests that a. deficit in internal cuing and attentional resources may be responsible for a PM performance deficit. Prospective Memory and Aging 3 Prospective Memory: The Relation of Executive Function to Aging. Memory as a cognitive construct consists of numerous broad concepts, which researchers and theorists use to form a comprehensive understanding of what it means to remember. The most common and general understanding of memory stems from the concept of "retrospective memory" (RM). This type of memory encompasses recall of past events or information (e.g., remembering the date of your birth). RM possesses great significance to us, yet there is another type of memory that plays a different role: "prospective memory" (PM), which requires recall of an intention for performing a specific action in the future. The process of remembering to take medication epitomizes this construct; for many people (for instance, individuals with heart problems) taking medication is woven in their daily routines. Failure to remember to take medicine can often lead to serious medical complications. This example as well as many others (e.g., remembering to go to an appointment, remembering to pick up a child at a specific time from school, etc.) demonstrate the significance of such remembering. There has been surprisingly. little research on prospective memory, possibly due to theoretical problems in defining it (Searleman & Herrmann, 1994). Even though the number of studies is small the foci of existing research on prospective memory is still quite diverse; these foci include concentration on differentiating PM from RM, examination of prospective memory-specific factors (internal versus external cuing, time-based versus event-based tasks, and embedded versus disembedded designs), specific research designs (in-lab versus outside of lab, natural versus artificial tasks), comparison of PM performance in younger and older adults, and, finally, examination of PM performance in brain injured groups. Yet even with such a diverse arena, the underlying issue is the distinction between PM and RM, or possible lack thereof. Prospective Memory and Aging 4 Prospective Memory as Different from Retrospective Memory Searleman and Herrmann (1994) define prospective memory as a memory set in a future time frame, one way to differentiate PM from RM. The latter contains information from a past time frame, whereas the former involves remembering to execute an action in a future time frame. The essential question this discussion gives rise to is whether there are different mechanisms for PM and RM. Distinguishing between the two forms of memory is often a difficult and controversial endeavor. Crowder (1995) argues that PM and RM originate from the same mechanism, namely RM. He argues that all memory is inherently retrospective whereas all intentions for actions in the future are necessarily prospective. Based on this stringent criteria, Crowder suggests the term PM is misleading; an intention and memory are two theoretically different concepts. He claims that "prospective memory" consists of a retrospective memory for an action; PM is either an intention or a retrospective memory, but it cannot be both. The essential problem to this argument revolves around the execution of the action as being intended. In order for the intended action to be performed there must necessarily be a mechanism by which the specific memory of the need to act can be recalled at a specific time. Crowder (1995) fails to recognize that a memory of intention is encoded in a time-specific frame to be executed in the future. The action cannot occur independently of the specific memory. There is an intrinsic connection; and furthermore, the memory is encoded with a specific cue for retrieval. Cockburn (1995) counters Crowder's (1995) argument by focusing on this retrieval cue. According to Cockburn (1995), in order to recall the specific action that is to be performed, there must be a cue exhibiting an executive influence as to specifically when the memory is to be recalled. Executive functions include abilities such as planning, impulse control, working memory, and attentional Prospective Memory and Aging 5 control (Roberts & Pennington, 1996). PM then, might rely on planning and attention. If the action is to be carried out in the near future, one may only need to focus immediate attention on the retrieval cue for performing the action. Yet if the task is farther into the future, performance then necessitates planning the specific cues and measures that must occur prior to the action (Neisser, 1982). The crucial aspect, therefore, in differentiating PM from RM might be PM's reliance on executive functioning. Factors Significant in Prospective Remembering Using this distinction, there still seems to be some relation between prospective and retrospective memory. Einstein, Holland, McDaniel, and Guynn (1992) address this relation by discussing a componential analysis of PM. They divide PM into a retrospective component (the memory of what specific action is to be executed) and a prospective component (remembering to perform the action at a specific time). They differentiate PM from RM then in terms of the necessity of remembering to perform the action in addition to the recall of what the action is. , The crucial factor deals with how and when the memory is recalled, relating once again to cues and executive functions. The cues employed in retrieval can be either internal and self-initiated or external and initiated by the environment. Einstein and McDaniel (1990) described this dichotomy, addressing relevant experimental design issues. If there were indeed different mechanisms for PM and RM, one would expect to find no correlation between the two. In two experiments investigating retrospective and prospective memory, they found no reliable association between the two forms of memory tasks. The design of their PM task was event-based. Event-based tasks rely on the presentation of an external cue, rather than internal motivation and cuing. Einstein and McDaniel (1990) presented words to participants on a computer and asked the participants to hit a specific key on the keyboard every time the word Prospective Memory and Aging 6 "rake" appeared on the screen. As an RM measure, they instructed participants to recall all the presented words in order. The PM action, hitting the key after "rake" appeared, was externally cued by the presentation of the specific word (an event­ based PM task). Internal cues, which contain no obvious and specific external cuing, occur most often in time-based tasks (i.e., tasks that require execution of the PM action after a set period of time). For example, remembering to pick up a child after school at three o'clock or putting the laundry in the dryer in one hour relies on time-based PM with internal cuing. However, one can use an external cue as an effective PM strategy, such as writing a note as a reminder, for time-based tasks. Prospective memory actions rely upon either time-based or event-based cues. Although one focus of past research has been the differentiation of PM from RM, the distinction is strengthened through examining specifically what qualifies as a PM task, as Cockburn (1995) has done. She suggested a further distinction with relevance for both time-based and event-based tasks. PM experiments usually consist of two task types: an ongoing, filler activity and the actual PM task(s). The relation between these two types of tasks can take one of two forms: "disembedded" or "embedded. " A task that interrupts the ongoing activity (a "disembedded" task), demands that the participants switch attention from the ongoing task to the PM action. The other possibility is a PM task (an "embedded" task) which complements the ongoing activity as an extension of the task, rather than interfering. For example, signing your name in the test booklet at the end of the task. Cockburn (1995) employed both types of prospective memory tasks (embedded and disembedded tasks) in several experiments. In one specific experiment, a digit-symbol substitution task, she asked the participant to note the start time, work for three minutes, then stop (a disembedded, time-based task), and go on to a letter cancellation exercise. Upon completion of this exercise, the Prospective Memory and Aging 7 participant was to write the time of completion at the bottom of the page (an embedded, event-based task). The first PM task (to stop working after three minutes) constitutes a disembedded task requiring an interruption and redirection of attention, whereas the second task (to write the time of completion) is an embedded task. The latter task is consistent with the ongoing activity, in that it required no redirection of attention. Although research has focused strictly on time­ based, disembedded