Elsevier

Psychiatry Research

Volume 226, Issue 1, 30 March 2015, Pages 14-22
Psychiatry Research

Review article
The effect of implementation intention on prospective memory: A systematic and meta-analytic review

https://doi.org/10.1016/j.psychres.2015.01.011Get rights and content

Highlights

  • Implementation intention can improve PM in different groups of participants.

  • Implementation intention can improve PM in clinical/sub-clinical population.

  • The combined verbal and imagery implementation intention has a larger effect.

  • There was no significant difference in focal or non-focal PM conditions.

Abstract

Prospective memory (PM) refers to remembering to perform a planned action at a future time. Implementation intention is an encoding method in the form of “if situation Y is encountered, then I will initiate the goal-directed behavior X”. It has been applied to improve PM performances. The present study conducted a systematic and meta-analytic review on the effect and mechanism of implementation intention on PM. In the meta-analysis, 36 comparisons were included. The results showed that for healthy young adults, the overall effect of implementation intention in improving PM performances was significant with a medium effect size (d=0.445). The combined verbal and imagery form of implementation intention had a relatively larger effect size (d=0.590). For older adults, implementation intention had a medium to large effect size on their PM performances (d=0.680). As for the mechanism, implementation intention seemed to reduce ongoing task performances in young adults as reflected by longer reaction time (d=0.224) though the effect size was small. The present study supports the positive effect of implementation intention on PM. The mechanism and potential implications of this promising strategy especially for clinical/sub-clinical people are discussed.

Introduction

Prospective memory (PM) refers to remembering to carry out intended actions at a future time (Einstein and McDaniel, 1990). There are five main phases of PM: (a) intention formation; (b) intention maintenance; (c) cue recognition and intention retrieval; (d) intention execution; and (e) evaluation of outcome (Ellis, 1996). In a typical PM experiment, participants are instructed to engage in two tasks: the ongoing and PM tasks. They are required to execute intended PM actions when PM cues appear while undertaking the ongoing task. According to the nature of the PM cue, there are two types of PM: time-based (executing the intentions at a particular time), and event-based (executing the intentions when an event cue appears) (Einstein and McDaniel, 1990, Einstein and McDaniel, 1996, Einstein et al., 1995, Okuda et al., 2007). In recent years, PM has received increasing attention by researchers due to its importance in daily life, for example, remembering to attend a meeting on time, to turn off the stove after cooking, or take medicine. PM failures may cause unwanted and undesirable consequences. Unfortunately, many studies have found that people often show PM forgetting (Crovitz and Daniel, 1984, Terry, 1988) and individuals such as older people and patients with mental disorders suffer even more serious PM problems (Henry et al., 2004, Wang et al., 2009).

Implementation intention is an encoding method to promote behaviors in the form of “if situation Y is encountered, then I will initiate the goal-directed behavior X” (Gollwitzer, 1999, Gollwitzer and Sheeran, 2006). Gollwitzer, 1993, Gollwitzer, 1996, Gollwitzer, 1999 put forward implementation intention to help people to achieve intentions and goals. This method includes two components: (a) anticipation of a suitable occasion to initiate the response (the “if” part) and (b) identification of a response that promotes goal attainment (the “then” part). It specifies the exact situation and plans the particular actions for achieving the goal. To achieve a goal, people have to form a goal intention like “I intend to achieve the outcome Z” (Gollwitzer and Sheeran, 2006). Implementation intention creates a strong mental representation of the situation and a strong linkage between situation and response that makes it easy to execute the behaviors. It helps people to overcome the gaps between the intentions and the actual behaviors. A meta-analysis of the impact of implementation intention on goal achievement showed that the effect size was medium to large (d=0.65) (Gollwitzer and Sheeran, 2006). PM actually shares some similar characteristics with goal achievement and can be considered a type of goal achievement related task. For example, to accomplish a PM task, people need to form and execute intentions. In addition, it is necessary to make a plan. Because of this, researchers have begun to use implementation intention as a technique to improve PM performances. However, only two studies that specifically examined PM were included in Gollwitzer and Sheeran׳s (2006) meta-analysis study. To date, quite a number of studies have found that implementation intention was effective in improving PM performances (Breneiser, 2009, McDaniel et al., 2008, McDaniel and Scullin, 2010, McFarland and Glisky, 2012, Meeks and Marsh, 2010, Zimmermann and Meier, 2010).

The implementation intention strategy was originally suggested by Gollwitzer (1999) as a verbal statement in the format of “if… then…”. However, with the development of different variations of this method by researchers, there are currently three main kinds of implementation intention encoding techniques: the verbal form (repeating the instructions) (e.g., Zimmermann and Meier, 2010), the imagery form (imagining the relevant scenes for 30–45 s) (e.g., Brewer et al., 2011b), and a combination of the two forms (e.g., Chasteen et al., 2001, McDaniel et al., 2008). Empirical data suggest that all three forms of implementation intention were effective in improving PM performances (Brewer et al., 2011a, McDaniel et al., 2008, Zimmermann and Meier, 2010). Although not many, some studies have compared the effectiveness of the three forms of implementation intention encoding on PM performances. Again, all three forms of implementation intention were found to be effective in improving PM performances. Nevertheless, in their study, McFarland and Glisky (2011) did not find much difference in effect among the three forms of implementation intention. Thus, they argued that sole adoption of the verbal form of implementation intention is sufficient to improve PM performances, and that the imagery instruction was not necessary. However, several studies have shown that under the combined implementation intention condition, participants were found to perform the best in completing PM tasks, albeit to the difference between the combined and other kinds of implementation intention did not reach statistical significance (Breneiser, 2009, McFarland and Glisky, 2011, Meeks and Marsh, 2010). In the present study, we aimed to conduct a systematic and meta-analytic review to examine and quantify the effect of implementation intention on PM performances and to compare the effects of the different types of implementation intention encoding techniques.

In the literature, the impact of implementation intention on PM performances has also been examined in different samples, such as young adults, older individuals and a wide range of clinical and sub-clinical groups. Until now, most of the studies about the effect of implementation intention on PM were conducted in young adults (e.g., Brewer et al., 2011b, McDaniel et al., 2008, McDaniel and Scullin, 2010, Meeks and Marsh, 2010). For older people, implementation intention has been found to significantly improve PM performances in both laboratory (Chasteen et al., 2001, McFarland and Glisky, 2011) and real life conditions (Burkard et al., 2014a, Liu and Park, 2004). Nevertheless, negative findings have also been reported (Schnitzspahn and Kliegel, 2009). There were also a few studies in clinical and sub-clinical groups (Chen et al., 2014, Grilli and McFarland, 2011, Kardiasmenos et al., 2008, Kretschmer et al., 2014). Thus in the current study, we also aimed to conduct a systematic and meta-analytic review to evaluate and summarize the effect of implementation intention in different populations, including healthy young adults and older adults. Due to the limited number of studies and the mixed types of clinical and sub-clinical samples, we aimed to briefly describe the effect of implementation intention on PM in these samples.

The underlying mechanisms of implementation intention in promoting PM remain unclear and controversial. There are mainly three viewpoints. The first one, as suggested by Gollwitzer (1999), is that a strong link between intention and the cue is set up by implementation intention. Therefore an individual would automatically detect the cue and execute the intention when the cue appears. From this perspective, the effect of implementation intention on PM is an automatic process without any reliance on cognitive resources (Breneiser, 2009, Brewer et al., 2011b, McDaniel et al., 2008, McFarland and Glisky, 2012).

The second viewpoint suggests that implementation intention makes individuals perceive the PM task as more important and allocate more cogntive resources to the PM task. Therefore, with the change of cognitive resources, the ongoing task performances would decrease while the PM performances increase. Support for this viewpoint comes from empirical findings that showed participants in implementation intention group had better PM performances while their ongoing task performances were significantly poorer than those in standard PM instruction group (Brewer and Marsh, 2010, Meeks and Marsh, 2010, Smith et al., 2014, Zimmermann and Meier, 2010).

The third viewpoint was put forward recently by McDaniel and Scullin (2010). They believed that the ongoing task in previous studies (e.g., Chasteen et al., 2001, McDaniel et al., 2008) was not challenging enough, and people had sufficient cognitive resources to perform the ongoing task without any cost. They suggested that implementation intention may associate the PM cues and the intentions strongly, and stimulate spontaneous retrieval of the intended actions when PM cues appeared (McDaniel et al., 2008, McDaniel and Scullin, 2010). However, apart from the retrieval of the intention, other processes might still need cognitive resources to accomplish the PM task, such as changing attention from the ongoing task to PM task. Therefore the effect of implementation intention on PM was not an entirely automatic process, but a complex process with both automatic and controlled processes.

Recently, Smith et al. (2014) reviewed previous studies and suggested that when PM cues were non-focal (does not share cognitive processing with ongoing task), implementation intention encoding would bring ongoing task cost. On the contrary, when the PM cues were focal (share similar cognitive processing with ongoing task), no cost would show. They further conducted experiments in non-focal PM tasks and found that implementation intention did bring ongoing task cost. In summary, the mechanism of implementation intention affecting PM is still under debate, and we would try to summarize previous study results to explore the mechanism with meta-analysis.

Due to the inconsistent findings about the effect of implementation intention on PM, the present study aimed to conduct a systematic and meta-analytic review of the effect of implementation intention on PM. First, we conducted a meta-analysis of studies that include different participants (both healthy young and older adults) and the effect sizes of implementation intention on PM in each group. Second, we compared the effect of three forms of implementation intention on PM performances. Third, for different types PM cues (focal and non-focal), we also compared the effect sizes of implementation intention on PM performances. Fourth, we analyzed the effect of implementation intention on ongoing task performances (in focal/non-focal PM cue conditions) and tried to explore the underlying mechanism of implementation intention. Finally, due to the small number of studies, we decided to conduct a descriptive review (with calculated effect size for each study) of the effect of implementation intention on PM performances in clinical/sub-clinical populations. The aims were to quantitatively evaluate and summarize the effect of implementation intention on PM in different populations, to compare the effect of three forms of implementation intention encoding, and to evaluate the underlying mechanism of implementation intention effect.

Section snippets

Literature search

Two approaches were used to identify relevant articles. First, a number of keywords (viz., implementation intention+prospective memory) were used to search the following database: Elsevier, EBSCO, Springer, and PsycINFO. Second, the references of the articles resulted from the first approach were examined to identify additional papers. The time period of literature research was from 2001 (i.e., the year that implementation intention was first used in the PM area) to October 28th, 2014.

There

The effect of implementation intention on PM performances in young and older adults

For young and older adults, the results showed that implementation intention could significantly improve PM performances (see Table 2). According to Cohen׳s (1988) effect size criteria, d=0.20 is “small”, d=0.50 is “medium”, and d=0.80 is “large”. The overall meta-analysis showed that implementation intention had a medium sized effect (d=0.508, 95% confidence interval 0.419–0.597) in improving PM performances.

For young adults, the Q statistics was not significant, suggesting that the results of

Discussion

The current study provided a systematic and meta-analytic review of the effect and magnitude of implementation intention in improving PM performances. Results suggested that (1) implementation intention had a medium-sized effect in improving PM performances, and it can significantly improve PM performances in both young and older adults; (2) for the three types of implementation intention encoding, the combination of verbal and imagery was found to have a significantly larger effect than

Summary and future directions

Here we summarize the main findings of our study and discuss future directions for this area:

First, implementation intention can improve PM performances in different populations (young adults, older adults, clinical/sub-clinical people). Given that implementation intention is a useful, brief and convenient memory strategy, future studies should extent the application of wider clinical populations especially those who suffer from PM impairments such as schizophrenia. PM has been suggested to be

Conflict of interest

None.

Acknowledgments

This study was supported by Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, China (113000C136), the National Natural Science Foundation of China (#30900403), Youth Innovation Promotion Association of the Chinese Academy of Sciences (Y1CX131003), and the CAS/SAFEA International Partnership Programme for Creative Research Teams (Y2CX131003).

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