From mind wandering to involuntary retrieval: Age-related differences in spontaneous cognitive processes

Highlights

• Frequency of mind-wandering and involuntary retrieval decreases with increasing age.

• Evidence for relatively preserved spontaneous prospective memory retrieval.

• Cognitive control, motivation and current concerns may contribute to age difference.

Abstract

The majority of studies that have investigated the effects of healthy aging on cognition have focused on age-related differences in voluntary and deliberately engaged cognitive processes. Yet many forms of cognition occur spontaneously, without any deliberate attempt at engaging them. In this article we review studies that have assessed age-related differences in four such types of spontaneous thought processes: mind-wandering, involuntary autobiographical memory, intrusive thoughts, and spontaneous prospective memory retrieval. These studies suggest that older adults exhibit a reduction in frequency of both mind-wandering and involuntary autobiographical memory, whereas findings regarding intrusive thoughts have been more mixed. Additionally, there is some preliminary evidence that spontaneous prospective memory retrieval may be relatively preserved in aging. We consider the roles of age-related differences in cognitive resources, motivation, current concerns and emotional regulation in accounting for these findings. We also consider age-related differences in the neural correlates of spontaneous cognitive processes.

Introduction

The effects of healthy aging on cognition have been studied over many years, and it is now well established that increasing age is associated with changes in several cognitive domains including episodic memory, autobiographical memory, working memory and attention (Craik and Salthouse, 2000). However, the majority of studies of aging cognition to date have focused on age-related differences in voluntary and deliberately engaged cognitive processes. For example, in a typical episodic memory experiment, participants are asked to voluntarily recall a list of items seen earlier and in studies of autobiographical memory, participants are typically instructed to recall experiences from their everyday lives. Yet many forms of cognition occur spontaneously, without any deliberate attempt at engaging them. For instance, numerous studies during the past decade have shown that when people are asked to perform a cognitive task in the laboratory, they often spontaneously focus on task-irrelevant thoughts, an activity known as mind-wandering (MW; Smallwood and Schooler, 2015). Indeed, recent evidence suggests close to 50% of our daily lives may be spent engaging in MW (Killingsworth and Gilbert, 2010). Despite its prevalence, however, relatively little is known about age-related changes in MW. Similarly, researchers have also delineated other spontaneous thought types such as involuntary autobiographical memory (IAM; Berntsen, 2009), intrusive thoughts (Rachman, 1981), intrusive memories (Holmes et al., 2004), involuntary semantic memories (Kvavilashvili and Mandler, 2004), spontaneously recurring tunes or “earworms” (Beaman and Williams, 2010), déjà vu (Brown, 2003) and some forms of prospective memory (PM) (McDaniel and Einstein, 2000). But we still know relatively little about the effects of aging on these forms of spontaneous cognition.

Despite the relatively modest amount of evidence available concerning the effects of aging on spontaneous cognition, we believe that the time is right to review what is known on this topic, for at least three reasons. First, interest in the general topic of spontaneous cognition has increased rapidly during recent years in both psychology and neuroscience (e.g., Andrews-Hanna et al., 2010; Christoff et al., 2011; O’Callaghan et al., 2015; Smallwood and Schooler, 2015), and the trend seems likely to continue. Second, the emergence of studies on MW in older adults during the past few years (e.g., Jackson and Balota, 2012; Krawietz et al., 2012; Maillet and Rajah, 2013; Nagamatsu et al., 2013; Staub et al., 2014) suggests an increasing focus on spontaneous cognition among cognitive aging researchers. Third, although studies of different spontaneous thought types are typically pursued independently of one another, we think that it is useful to consider them together in order to encourage questions and future investigations about similarities and differences among these processes as a function of aging. In the current review, we focus on four types of spontaneous cognitive processes for which some systematic evidence exists regarding cognitive aging: MW, IAM, intrusive thoughts and spontaneous PM retrieval. We will focus primarily on age-related differences in MW because this type of spontaneous cognition has been studied most extensively. By contrast, there has been virtually no research on age-related differences in earworms or involuntary semantic memory, so we do not consider these phenomena further. Similarly, there is little research on intrusive memories in older adults other than in the context of post-traumatic stress disorder (Clapp and Beck, 2012). Because the present review is concerned with healthy aging, consideration of psychological disorders is beyond our scope. Finally, we do not consider déjà vu, but refer interested readers to a recent overview of age-related differences in this phenomenon (Moulin et al., 2014).

When examining the literatures on MW, IAM, spontaneous PM and intrusive thoughts, one may notice differences in which aspects of spontaneous cognition have been most extensively investigated in each. For example, meta-awareness has been a topic of much interest in the MW literature ever since early studies demonstrated that MW often occurs without it (Schooler et al., 2004). In the IAM literature, there has been considerable interest on elucidating what cues trigger these spontaneous thoughts. Both laboratory and naturalistic studies have found that most IAM have identifiable triggers that tend to predominantly be external (i.e. triggered by an environmental stimulus or event) rather than internal (i.e. triggered by one's train of thought) (Berntsen, 1996, Schlagman and Kvavilashvili, 2008). In the PM literature, it was emphasized early on that PM can occur both spontaneously or deliberately, and researchers expended much effort in developing methodologies to assess spontaneity of thoughts (Einstein et al., 2005, McDaniel and Einstein, 2000). These differences in which aspects of thoughts have been most extensively studied in each literature likely reflect differences in research trends, as well as differences in methodologies used, rather than actual differences between the phenomena of interest. For example, a recent study suggests that similar to MW, intrusive thoughts can also occur without meta-awareness (Takarangi et al., 2014). In the MW literature, there has recently been a surge of interest in identifying triggers for MW (e.g., Smallwood, 2013), with studies showing that, similar to findings from the IAM literature (e.g., Schlagman and Kvavilashvili, 2008), the content of off-task thoughts can be modulated by task stimuli (McVay and Kane, 2013, Plimpton et al., 2015). There has also been a resurgence of interest in distinguishing between spontaneous and deliberate MW (e.g., Seli et al., 2015a, b), a topic that has been of interest for some time in the PM literature. These findings highlight that MW, IAM, spontaneous PM, and intrusive thoughts may share much in common, and that greater insight regarding age-related differences in spontaneous thoughts may emerge from considering these phenomena together rather than separately.

Two broad theories of cognitive changes with aging are particularly relevant for making predictions regarding age-related differences in spontaneous cognitive processes: the inhibition deficit theory (Hasher and Zacks, 1988) and the reduced cognitive resources theory (Craik, 1983, Craik, 1986, Craik and Byrd, 1982). The inhibition deficit theory of aging suggests that reduced inhibitory abilities in older adults facilitate the initial entrance into working memory of information that is off the goal path, and the prolonged maintenance of such information in working memory (Hasher and Zacks, 1988). Off-goal path thoughts include environmental distractions, evaluations of ongoing events (e.g., “this is not the best talk he’s given) and thoughts/plans unrelated to ongoing events (e.g., “I need to remember to make dinner reservations after the talk”). Thus, the inhibitory deficit theory leads to the prediction that older adults may be more likely than young adults to exhibit off-task spontaneous thoughts. There is some evidence that supports this idea, at least indirectly. For example, studies in which young and older adults produce narrative discourse indicate that older adults are more likely than young to spontaneously produce “off-topic” details that are not relevant to the main topic at hand (e.g., Arbuckle and Gold, 1993; Trunk and Abrams, 2009), and related findings have been reported in studies that require young and old adults to produce extended narratives that involve remembering past experiences, imagining future experiences, or describing a scene (Gaesser et al., 2011; Madore et al., 2014; for review, see Schacter et al., 2013). By contrast, some of the earliest direct evidence concerning MW suggested that older adults exhibit a reduction in MW compared to young adults (e.g., Giambra, 1989; Singer, 1961), a result seemingly inconsistent with predictions made based on the basis of the inhibitory deficit theory.

These findings may instead be more consistent with a second theory of aging that emphasizes a reduction in cognitive resources in older adults (Craik, 1983, Craik, 1986, Craik and Byrd, 1982, Lindenberger and Mayr, 2014). Craik (1986) argued that cognitive resources are particularly needed in tasks that provide minimal environmental support and instead rely on self-initiated processing. Thus Craik proposed that, because older adults have fewer cognitive resources compared to young adults, they should be particularly impaired in tasks requiring a high level of self-initiated processing, but minimally impaired in tasks with high environmental support. In the MW literature, it has been suggested that if older adults spend a greater proportion of their cognitive resources on an ongoing task or external activity compared to young adults, then they may have fewer resources left over to exhibit MW compared to young (e.g., Giambra, 1989; Krawietz et al., 2012; Maillet and Rajah, 2013). In the PM literature, the same theory has been used to suggest that older adults should exhibit preserved PM in tasks that rely on spontaneous processing of a PM cue (e.g. when the PM intention of pressing a special key is spontaneously triggered by a target word), but that older adults may exhibit reduced behavioral performance in tasks relying on deliberate PM (McDaniel and Einstein, 2000). In considering why the reduced cognitive resources theory of aging has been used to predict both an age-related reduction in one spontaneous thought type (MW) and the preservation of another (PM), it is important to note that while MW is task-irrelevant, cue-driven PM is thought to occur spontaneously as part of the ongoing task. Thus, from a reduced cognitive resource perspective, it may be argued that older adults should exhibit intact spontaneous processing of PM cues since this does not require the use of cognitive resources beyond those already used to perform the ongoing task, whereas older adults should exhibit reduced MW since MW does require additional processing resources. A related and more general prediction would be that spontaneous thinking that is cued by environmental stimuli in the focus of attention is preserved in aging, while spontaneous thinking that is environment-independent is reduced.

As we discuss in this article, there is now increasing evidence that factors other than cognitive resources, such as age-related differences in task interest, current concerns, and emotional regulation, may also play an important role in explaining age-related differences in frequency of spontaneous thoughts. In the following sections, we review, in turn, studies that have examined psychological and behavioral characteristics of MW, IAM, intrusive thoughts and spontaneous PM retrieval in young and old adults. Next, we review studies that have used neuroimaging to assess effects of aging on the neural correlates of these thought types. We conclude by integrating findings across these different literatures and linking them to observations from related studies of cognitive aging.