What Reduced Mind Wandering in Older Adults Can Tell Us About the Cognitive Mechanisms of Mind Wandering
Christina Bruckmann University of Amsterdam
Abstract
Although the negative consequences of off-task though can be grave, we spend about 10% to 60% of our daily lives mind wandering (Killingsworth & Gilbert, 2010; Kane et al., 2007; Seli, Beaty et al., 2018). Though several theories have been proposed, the origin of mind wandering is still contested. Moreover, the estimates of mind wandering frequency are based almost
exclusively on samples of young adults and numerous studies have demonstrated that the frequency of mind wandering declines with age (Jordão, Ferreira-Santos, Pinho, & Jacques, 2019). This reduction in mind wandering across the life span strikes as counterintuitive when one considers the prevalent assumption that the origins of mind wandering lie in executive function (e.g. McVay & Kane, 2010). However, any theory that aims to provide a comprehensive explanation for mind wandering would have to account for this observation. The aim of this literature review is to illustrate and discuss various approaches seeking to explain the origin of mind wandering, while using the reduction of mind wandering with age as a common factor against which the explanatory powers of each theory are compared. Overall, most theories can accurately predict the reduction of mind wandering frequency in old age. The predictions are based on distinct components for each theory however, allowing for future experimental designs to entangle the origin of this age-dependent tendency. While theories of executive function have been prevalent in the past, novel approaches such as the local sleep theory present promising alternative views.
What Reduced Mind Wandering in Older Adults Can Tell Us About the Cognitive Mechanisms of Mind Wandering
Although the mechanisms of attention have been a subject of research for decades, the experience itself that occurs during moments of attentional lapses has only more recently received attention (Callard, Smallwood, Golchert, & Margulies, 2013). These task-unrelated thoughts have been broadly summarized under the term mind wandering (Smallwood & Schooler, 2015) and seemingly lead to mostly negative outcomes in a variety of situations. Higher instances of mind wandering are robustly associated with decreased performance on a wide range of tasks (e.g. sustained attention: Stawarczyk & D'Argembeau, 2016, reading comprehension: Smallwood, McSpadden, & Schooler, 2008; selective attention: Thomson, Seli, Besner, & Smilek, 2014), have been linked to negative mood (Maillet et al., 2018) and
neuroticism (Kane et al., 2017; Robison, Gath, & Unsworth, 2017; but Robison, Miller, & Unsworth, 2020), and have been implicated in several psychopathologies (Marchetti, Koster, Klinger, & Alloy, 2016). Outside of laboratory settings, mind wandering has been shown to have detrimental consequences, such as risky driving behavior (Albert et al., 2018; Yanko & Spalek, 2013) and car accidents (Galéra et al., 2012; Gil-Jardiné et al., 2017), as well as poor academic performance (Smallwood, Fishman, & Schooler, 2007; Unsworth, McMillan, Brewer, & Spillers, 2012; Wammes, Seli, Cheyne, Boucher, & Smilek, 2016). However, it is important to note that comparatively few studies have investigated the benefits of mind wandering, and there is some evidence that mind wandering can temporarily increase creative thinking and problem-solving skills (Baird et al., 2012; Wang et al., 2017). For a comprehensive review of positive and negative consequences of mind wandering, see Mooneyham and Schooler (2013).
Although the negative consequences of mind wandering can be grave, we seemingly spend a large proportion of our daily lives mind wandering, with estimates ranging from 10% to
60% (Killingsworth & Gilbert, 2010; Kane et al., 2007; Seli, Beaty et al., 2018). In light of the negative consequences associated with mind wandering, the question arises why we engage in it so frequently. Several theories have been proposed, though none has yet been able to sufficiently explain all facets of mind wandering, and the origin of mind wandering is still contested.
Moreover, the above-mentioned estimates of mind wandering frequency are based almost exclusively on samples of young adults, whereas several studies have demonstrated that the frequency of mind wandering changes with age. Older adults (>60 years) have been shown to consistently report fewer instances of mind wandering compared to young adults (<30 years) during a variety of tasks (Jordão et al., 2019). This reduction in mind wandering across the life span strikes as counterintuitive when one considers the prevalent assumption that the origins of mind wandering lie in executive function (e.g. McVay & Kane, 2010). As fluid cognition, including cognitive control and executive functioning, declines with age (Harada, Love, & Triebel, 2013; McCabe, Roediger, McDaniel, Balota, & Hambrick, 2010; Spreng & Turner, 2019), it appears reasonable to therefore expect mind wandering episodes to increase with age. Studies illustrating an age-dependent effect in the opposite direction poses an explanatory challenge for current theories of mind wandering.
The aim of this literature review is to illustrate and discuss various approaches seeking to explain the origin of mind wandering, while using a reduction in mind wandering with age as a common factor against which the explanatory powers of each theory are compared. In the following, I will first review the evidence for reduced mind wandering in older adults.
Subsequently, different cognitive and behavioral components that have been implicated in the most prominent theories of mind wandering will be highlighted to discuss in how far these aspects could account for a decreased incidence of mind wandering with age. This will be done alongside a general overview of evidence for and against each theory. Specifically, I will discuss
changes in old age in light of the aspects of executive function, situational and dispositional factors, as well as the more recently suggested factor of local sleep. Lastly, I will highlight some of the methodological challenges that mind wandering research faces and consider in how far these difficulties could impact scientific findings.
Suitable studies using the keywords mind wandering and off-task thought were included, with a focus on behavioral studies. Though there is an emerging interest in the neural correlates of mind wandering, exploring the recent neuroscientific findings is beyond the scope of this review. Thus, while some facets of the neuroscientific results have been included when necessary, this review deals primarily with behavioral findings.
Changes in Mind Wandering Across the Lifespan.
While research in the field of mind wandering has been carried out primarily with young adults, mind wandering in older adults has received ample attention in recent years after
previous, seemingly paradoxical, findings indicated a reduction in mind wandering in old age (Giambra, 1989). Examining the aging brain and its influence on mind wandering might help elucidate the neural and cognitive components involved in the phenomenon. While few studies have been longitudinal in nature, studies comparing older and younger participants consistently find that older adults report fewer mind-wandering episodes during reading tasks (Jackson & Balota, 2012; Krawietz, Tamplin, & Radvansky, 2012),sustained attention tasks (Fountain-Zaragoza, Puccetti, Whitmoyer, & Prakash, 2018; Jackson & Balota, 2012; Staub, Doignon-Camus, Bacon, & Bonnefond, 2014; Zavagnin, Borella, & Beni, 2014), and memory tasks (Maillet & Rajah, 2013). This trend has been shown to extend past laboratory settings into daily life (Maillet et al., 2018).
Beyond the research indicating an overall decline in mind wandering frequency with age, several studies have investigated whether this tendency is exclusive to certain types of mind wandering or represents a more global phenomenon. Seli, Maillet, Smilek, and colleagues (2017) focused on the distinction between intentional and unintentional mind wandering, hypothesizing that the age-dependent reduction in mind wandering does not present uniformly across both types. However, contrary to their predictions, younger adults reported both more intentional as well as unintentional episodes of mind wandering, suggesting a rather general trend. Further, McVay and colleagues (2013) investigated task-related interference and task-unrelated thought separately and found that while older adults reported fewer task-unrelated thoughts, they experienced significantly more task-related interference compared to younger adults. Considering the age-related decline in cognitive abilities, this finding seems to contradict
research by Randall, Oswald, and Beier, (2014) who found that individuals with lower executive abilities are more likely to mind wander, whereas those with higher executive abilities more frequently engage in task-related thought. Indeed, Maillet and Rajah (2013) reported that even task-related thoughts decrease with age.
Possible alternative explanations for fewer reported mind wandering episodes in old age have been investigated. For example, Frank, Nara, Zavagnin, Touron, and Kane (2015) studied the possibility that older adults might be less inclined to report episodes of mind-wandering compared to young adults, rather than truly experiencing fewer. The research team used eye-tracking as well as comprehension tests to validate older adults’ reports of reduced mind-wandering and found that fewer reported incidences of mind mind-wandering correlated with improved comprehension during a reading task, as well as fewer eye-movement patterns indicative of mind wandering. Thus, it appears that the findings illustrating a reduced rate of mind wandering in older adults cannot be explained by a lower willingness to report mind
wandering episodes. Further, the finding that older adults mind wander less appears to be in line with research showing that reduced mind wandering episodes are also characteristic of some age-related neurodegenerative disorders, such as dementia (O’Callaghan, Shine, Hodges, Andrews-Hanna, & Irish, 2017). Taken together, these results suggest that mind wandering occurs most commonly in a young and healthy brain while progressive degeneration is negatively correlated with the frequency of mind wandering.
Why do we mind-wander and why do older people mind wander less?
The explanations for why mind wandering is such a pervasive phenomenon in our daily lives and for why older people mind wander less are likely to go hand-in-hand. A theory sufficiently explaining the origin of mind wandering must be able to account for the observed reduction of mind wandering in old age. Different cognitive and neural aspects have been implicated in the phenomenon of mind wandering; executive functions (McVay & Kane, 2010; Smallwood & Schooler, 2006), situational and dispositional factors, such as motivation (Seli et al., 2020), boredom (Shephard, 2019), neuroticism (Kane et al., 2017; Robison et al., 2017), or current concerns (McVay & Kane, 2010), and more recently the incidence of local sleep (Andrillon et al., 2019). Examining how each of these factors changes with age and reviewing the evidence for their involvement in mind wandering can not only shine a light on the validity of current theories of mind wandering, but possibly also explain the reduction of mind wandering in old age.
The Executive System. One of the cognitive components most commonly implicated in mind wandering is the executive system. More specifically, attention, inhibition, and working memory capacity have been frequently associated with the occurrence of mind wandering (e.g. McVay & Kane, 2009; Pereira, Gurguryan, & Ristic, 2020; Robison & Unsworth, 2017). These
findings led to a variety of theories aiming to explain mind wandering in relation to the executive functions. While there are several theories that have been proposed, I will focus here on the main two opposing approaches; theories of executive resources and of cognitive failure. Schooler and Smallwood (2006) who were some of the first to hypothesize about the origin of mind
wandering, suggested that mind wandering might arise primarily through available executive resources which are currently not taken up by task demands. Contrary to this, McVay and Kane (2010) proposed that mind wandering represents a failure of executive control allowing attention to be allocated to internally-generated thoughts, away from current task demands. In the
following, these two theories regarding mind wandering as either executive function or executive failure will be examined separately.
Executive Function. The most prominent theory stating that mind wandering is a process relying on executive resources comes from Schooler and Smallwood (2006). Their theory posits that mind wandering and task performance compete for the same executive resources and mind wandering thus draws on executive functions. Two testable predictions can be derived from their theory; (1) if the task demands increase, less executive control is free to be devoted to mind wandering and thus the frequency of mind wandering should decrease, (2) if tasks become automatized through practice, they should require fewer executive resources and allow for increased rates of mind wandering. Both hypotheses have been supported by empirical evidence. For example, Forster and Lavie (2009) demonstrated that increasing perceptual load during a task reduced the frequency of mind wandering. Similar results have been reported by
Smallwood, Nind, and O’Connor (2009) and more recently by Seli, Konishi, Risko, and Smilek (2018). Further, in study by Mason and colleagues (2007) participants reported more mind wandering episodes during practiced task blocks compared to novel blocks, despite the tasks being identical. This finding supports predictions made by the executive resource theory,
suggesting that during automated tasks more executive resources are free to be devoted to mind wandering.
Similarly, in what can be considered an extension to this theory, Smallwood and
Andrews-Hanna (2013) proposed the context-regulation theory, which states that individuals will aim to regulate the frequency of their mind wandering episodes based on current task demands to minimize the detrimental impact of distraction on task performance. If task demands are low, mind wandering frequency increases, whereas it decreases when task demands are too high to allow for resources being dedicated to mind wandering. While the two theories do have distinct characteristics, Smallwood and Schooler’s, and Smallwood and Andrew-Hanna’s theories will be discussed jointly under the umbrella of an executive resource approach here.
There is some evidence for these theories. Whereas mind wandering has been frequently associated with performance deficits, Thomson, Besner, and Smilek (2013) reported no impact of mind wandering episodes on task performance during a Stroop task and a reading task, theorizing that participants were able to find an optimal balance between mind wandering and task focus by engaging in mind wandering only when the current task demands allowed for it. Similarly, Burdett, Charlton, and Starkey (2019) studied mind wandering reports of drivers during different sections of a familiar road and found that mind wandering was reported most frequently during parts of the road that were least likely to be the site of car accidents in the following five years. This pattern would suggest that drivers mind wander specifically in situations that do not require their full attention and when additional cognitive resources are available. Further, mind wandering episodes were least likely to occur during narrative shifts of a short movie, indicating that a changing story line reduces mind wandering either by capturing attention or preventing boredom (Faber, Radvansky & D'Mello, 2018). Direct evidence for a strategic allocation of executive resources to mind wandering also comes from a study by
Jackson and Ballota (2012) who specifically investigated age-related differences. While older adults reported fewer instances of mind wandering compared to younger adults across a variety of tasks, no significant difference in sustained attention performance was found. These results support the hypothesis that mind wandering is most commonly engaged in when the attentional task demands allow for it.
Regarding the aging brain, a theory of cognitive resources would likely predict a
reduction of mind wandering in old age through two routes; as fluid intelligence decreases, more cognitive resources have to be dedicated to current task demands and thus less capacity is
available for mind wandering. Additionally, overall capacity of executive function has been shown to decrease with age (McCabe et al., 2010), thus even if similar resources have to be dedicated to a task by younger and older adults, less excess capacity would be available to older adults for mind wandering. This is in line with the observed age-dependent trend in mind wandering. Therefore, the cognitive resource theory can accurately predict reduced mind wandering in old age.
Despite this, the theory is not without its caveats. One of the biggest challenges that any theory focusing on executive resources faces is the rather consistent evidence that individuals with low working memory (WM) capacity tend to mind wander more, rather than less (McVay & Kane, 2009; Randall et al., 2014). While this finding seems to be directly in accordance with theories that explain mind wandering as a failure of the executive system, the effect should be reversed from an executive resource perspective; if mind wandering relies on executive resources, that should lead to an increased occurrence of mind wandering in individuals with higher executive capabilities as they have more attentional resources available during the same task demands compared to those with fewer resources . Yet, the evidence regarding the relation between WM capacity and mind wandering is not entirely clear, as some studies also report
opposite effects during low demand tasks (Levinson, Smallwood, & Davidson, 2012; but see replication by Meier, 2019). If higher WM capacity is associated with more mind wandering during low-demand tasks and the effect reverses for high-demand tasks as the results by Levinson suggest, this would not contradict the context-regulation hypothesis. However, Robison and Unsworth (2017) reported a negative correlation between WM capacity and mind wandering, even during low-demand tasks.
Further evidence against a significant role of executive resources in facilitating mind wandering episodes comes from other studies investigating how task difficulty influences the tendency to mind wander. Feng, D’Mello, and Graesser (2013) found that participants were more likely to report mind wandering episodes when reading a difficult text than when reading a more easily comprehensible text. This finding presents a direct contradiction to the predictions of Smallwood and Schooler’s theory (2006), as an easy text would allow for more attentional resources to be available and would likely not be challenging enough to keep the participants interested.
Executive Failure. Conversely, mind wandering has also been proposed to be a consequence of executive failure, rather than relying on executive resources. One of the most influential theories regarding mind wandering as executive failure is the control failure x current concerns theory (McVay & Kane, 2010). This theory posits that mind wandering arises from the failure of the executive system to prevent internally-generated thoughts about current concerns from drawing attentional resources away from task-demands. Categorizing mind wandering as an unwanted lapse of attention or cognitive control would provide a clear illustration as to why it is so pervasive in our lives despite the negative consequences associated with it. Several studies have provided evidence for the involvement of the two components of the control failure x
current concerns theory in mind wandering. In the following, I will discuss the evidence for the aspect of control failure and executive function, the involvement of current concerns will be discussed at a later point.
The importance of executive function in the prevention of mind wandering episodes has been implicated by two main findings. Firstly, mind wandering has been frequently associated with WM capacity. Overall, individuals with higher working memory capacity tend to mind wander less (McVay & Kane, 2009; Randall et al., 2014), though as discussed above, this association is not always as clear cut and appears to be influenced by situational factors such as task-difficulty (e.g. Levinson et al., 2012). In a similar vein, Robison and Unsworth (2015) reported that increased WM capacity appears to provide resistance to distraction, whether that distraction comes from internally-generated thoughts or from external sources. Participants with high WM capacity were less likely to report distractions during a reading task and showed better text comprehension. Secondly, a strong argument in favor of the involvement of control failure in the generation of mind wandering episodes is the rather robust positive correlation between mind wandering and activity of the default mode network (DMN; e.g. Kajimura, Kochiyama, Nakai, Abe, & Nomura, 2016; Philippi et al., 2020). Mind wandering has been correlated with DMN activity in a variety of contexts and tasks, while separate research has established the anti-correlational relationship between the DMN and task-positive networks involved in attention and cognitive control processes (Fox et al., 2005); if the DMN is active, activity in the task-positive networks is suppressed, and vice versa. This oppositional relationship would support the theory that when mind wandering occurs and the DMN is active, cognitive control processes and attention are inhibited, though the exact order and causality cannot be established from these findings. However, the reliance of mind wandering and executive function on anti-correlational
networks, does seem to directly contradict Smallwood and Schooler’s theory that both processes draw on the same resources.
In contrast to the predictions made by theories based on cognitive failure, Drescher, Bussche, and Desender (2018) reported no correlation between the level of cognitive control, as assessed by a conflict task, and the frequency of mind wandering, calling the role of executive control in preventing mind wandering into question. Pereira, Gurguryan, & Ristic (2020) showed that while mind wandering led to poor academic performance in students scoring low on the trait of effortful control, the correlation was reversed for those with high trait-level effortful control; these students showed higher academic performance when reported mind wandering frequency during class was also high. Thus, while cognitive control does seem to protect against the negative consequences of mind wandering, no correlation was found between cognitive control and the frequency of mind wandering episodes, casting doubt on whether all aspects of mind wandering, including frequency, can be explained through control failure.
It is unclear how the control failure approach could account for the observed age-related changes in mind wandering. Indeed, reduced mind wandering in old age appears to be one of the biggest challenges for a theory of executive failure. As executive capacities decline with age (Harada et al., 2013; McCabe et al., 2010; Spreng & Turner, 2019), the most-straight forward prediction for age-related changes in mind wandering would be an increase in mind wandering frequency due to deficits in cognitive control abilities. While this prediction directly contradicts the commonly reported findings, taking a more differential approach might allow for the
executive failure hypothesis to accurately predict reduced mind wandering in old age. For example, whereas aging is associated with declines in inhibitory control and selective attention (Spreng & Turner, 2019) which would suggest an increased tendency to mind wander, there is also evidence for an age-dependent decline in the ability of maintaining representations outside
of the focus of attention (Dorbath & Titz, 2011). If representations outside of the focus of attention cannot be maintained, this could mean that older adults would often not be able to generate the interfering off-task thoughts that result in mind wandering. In this case, cognitive control would not be crucial for older adults to keep their mind on-task, as few or no internally-generated distractions are present. This hypothesis matches findings regarding the DMN, illustrating that functional DMN connectivity declines even during tasks in healthy aging (Cieri & Esposito, 2018), hinting that fewer off-tasks thoughts might be generated by older adults. Further, Maillet and colleagues (2020) have demonstrated that while older adults are more likely to be distracted by an external input, they are less likely to be influenced by internally-generated thoughts compared to younger adults. Thus, while reduced mind wandering in old age is not readily explainable by general executive failure, component-specific deficits might provide an explanation for the findings in old age which seemingly contradict the executive failure hypothesis.
This example illustrates the bigger issue with theories explaining mind wandering as a failure or function of the executive system. While an in-depth discussion about healthy cognitive aging and its influence on executive capacities is beyond the scope of this review, it is important to mention that not all aspects of the executive system display the same age-related changes. The common distinction between ‘crystallized’ intelligence increasing with age while ‘fluid’
intelligence declines is a helpful, but simplified view (Salthouse, 2010). As the executive system comprises several components which are differentially affected by age, it is rather difficult to make exact predictions for mind wandering in old age based on theories regarding the executive system. This heterogeneity of executive functions and the extent to which they are impacted by healthy cognitive aging could explain the seemingly contradictory and complicated findings of studies investigating mind wandering and executive function, as well as age related changes.
Lastly, it is important to mention that while theories of cognitive failure and cognitive function appear to be mutually exclusive, there have been efforts to reconcile the two seemingly competing ideas. For example, Marcusson-Clavertz, Cardeña, and Terhune (2016) investigated whether the content of mind wandering episodes could predict their relation to executive resources. They found that while positive mind wandering content appeared to be the result of excess cognitive resources and was not associated with impairments in task performance,
negative mind wandering episodes were strongly correlated with working memory capacity. This valence-dependent account of mind wandering could indicate that not all mind wandering arises through the same mechanisms, providing a possible approach to reconcile the two executive theories. Further, there are theories attempting to bridge the two approaches (e.g. Thomson, Besner, & Smilek, 2015).
Situational and Dispositional Factors. Beyond cognitive abilities, individual
differences in mind wandering have been linked to several situational and dispositional factors, such as boredom (Shephard, 2019), motivation (Seli et al., 2020), mood (Kane et al., 2017; Robison et al., 2017), and concerns (McVay & Kane, 2010). Few theories of mind wandering focus on these factors exclusively, yet they are implicated in a variety of different mind wandering accounts. In the following, three of the most prevalent factors will be highlighted; boredom, motivation, and mood.
Boredom. One of the situational factors that has been hypothesized to play a role in mind wandering is boredom. For instance, Shepherd (2019) proposed that boredom might be the main cause of mind wandering. He suggests that when the current task is deemed not rewarding enough, the mind searches for a more rewarding goal and turns to mind wandering. Boredom has also been implicated in other theories, such as Smallwood and Schooler’s theory regarding the executive system (2006); the availability of additional attentional resources is difficult to
entangle from the subjective feeling of boredom. While evidence in favor as well as against a boredom account of mind wandering will be discussed at a later point, the prediction the theory would make for older adults is rather straightforward: older adults report fewer instances of mind wandering as they are less prone to boredom and are more engaged by the task. However,
whether this is the case and older adults indeed experience boredom less often is challenging to answer, as research regarding changes in boredom-proneness across the lifespan is sparse.
One of the few studies investigating boredom across several age groups was conducted by Chin, Markey, Bhargava, Kassam, and Loewenstein (2017). The large experience-sampling study included just under 4000 US Americans and found that boredom is more prevalent in younger compared to older people. An earlier study by Harris (2000) did not find any significant correlation between reported boredom and age, though the age-range of the participants was not sufficiently broad, and most were university students, making the findings difficult to generalize. Overall, due to the lack of systematic research, it is not possible at the moment to obtain a clear picture of changes in boredom proneness across the lifetime. Preliminary findings do seem to indicate a decline of boredom with age.
However, whereas the relation of old age and boredom is not entirely clear, several pieces of evidence support the hypothesis of an involvement of boredom in mind wandering. For
example, evidence discussed previously in light of Smallwood and Schooler’s theory (2006) could also be interpreted in support of Shepherd’s theory. As it is not clear in how far there is a difference between boredom and excess executive resources, Danckert and Merrifield’s (2016) findings that car drivers mind wander mainly during less risky parts of their commute, as well as Faber and colleagues’ study (2018) showing that mind wandering is reduced during narrative shifts in a movie could be viewed as support for Shepherd’s theory.
While mind wandering seems to occur at times without any detrimental consequences, the stark discrepancy between these results and the large body of research illustrating a detrimental effect of mind wandering on task performance (e.g. Stawarczyk & D'Argembeau, 2016, Smallwood et al., 2008; Thomson et al., 2014) as well as the association with car accidents (Galéra et al., 2012; Gil-Jardiné et al., 2017) cannot be neglected. A frequent negative impact of mind wandering might be more in line with Shepherd’s view, rather than that of Smallwood and Schooler, as mind wandering resulting from boredom does not have to arise primarily when it is adaptive.
Moreover, a distinction between available resources and boredom could be drawn by studies investigating how task difficulty influences the tendency to mind wander. Feng and colleagues (2013) found that participants were more likely to report mind wandering episodes when reading a difficult text than when reading a more easily comprehensible text. This finding presents a direct contradiction to the predictions of Smallwood and Schooler, since an easy text would allow for more attentional resources to be available and would likely not be challenging enough to keep the participants interested. However, since levels of perceived boredom were not assessed in the study by Feng and colleagues (2013), one could argue that impaired
comprehension during the difficult reading task would make it more difficult for participants to immerse themselves in the material, thus creating boredom and increasing mind wandering episodes. Indeed, findings by Xu and Metcalfe (2016) suggest a curvilinear relationship between mind wandering and task difficulty, with moderate task demands leading to the least amount of mind wandering by optimally recruiting mental capacities and reducing boredom associated with too easy or overwhelming tasks. Results from a large experience-sampling study by Chin and colleagues (2017) show that boredom is most likely to arise in monotonous or difficult situations, in line with a boredom interpretation of Xu and Metcalfe’s findings.
Evidence against a boredom account of mind wandering comes from Robison and colleagues (2020) who investigated the relation between boredom and mind wandering directly. The researchers observed no significant correlation between boredom proneness and intentional or unintentional mind wandering on several tasks; neither during high- nor low-demand
conditions. Thus, while Shepherd’s theory (2019) seems promising, more research is needed to support the association between boredom and mind wandering, as well as determining its implications for old age. It is important to emphasize however, that a boredom account of mind wandering and theories based on executive function are not mutually exclusive, as there is evidence that these two aspects are linked (Danckert & Merrifield, 2016).
Motivation. A factor related to boredom which has also been implicated in mind
wandering is motivation. While there are no theories directly focusing on motivation as a factor of mind wandering, extensive research has shown that motivation is negatively associated with mind wandering (Seli, Schacter, Risko, & Smilek, 2017; Seli et al., 2020; Unsworth &
McMillan, 2013). Further, as motivation has been linked to executive control (Etienne, 2010; Pessoa, 2009) motivation is implicated in theories of mind wandering based on executive function, such as the cognitive control x current concerns theory by McVay and Kane (2010). Regarding the current topic of mind wandering in old age, motivation has been proposed as a possible moderator of the changes in mind wandering propensity (Seli et al., 2020). Older adults have generally reported higher task-related motivation than younger adults (Ceccato, Lecce, Cavallini, Vugt, & Ruffman, 2019; Seli et al., 2020; Staub et al., 2014), and scored higher on conscientiousness (Donnellan & Lucas, 2008; Jackson & Balota, 2012), which likely affects motivation to perform a task well. Thus, combined with the findings that motivation is negatively correlated with mind wandering frequency (Seli, Schacter, Risko, & Smilek, 2017), one would predict that older adults are less prone to mind wander, which is in line with empirical findings.
Indeed, significant evidence for the role of motivation not only in the occurrence of mind wandering, but also in the age-dependent changes in mind wandering comes from a recent study by Seli and colleagues (2020). The research team specifically tested the hypothesis that older adults might mind wander less due to higher motivation to complete the task successfully. With an attention task and no reward-specific instructions, they first replicated the established finding of reduced mind wandering in old age. This age-dependent difference diminished however, when motivation was externally induced in younger people by giving rewards for better performance, suggesting that at least part of the differences in mind wandering propensity can be attributed to differences in motivation. Nonetheless, even after controlling for motivation, younger adults still mind wandered more than older adults, indicating that other factors might be involved in age-dependent differences. Similar findings have been reported by Frank and colleagues (2015) who found that motivation partially mediated the age differences in task-unrelated thoughts, though could not fully account for the differences observed.
Further evidence suggesting that these differences in mind wandering frequency cannot fully be accounted for by differences in motivation comes from a previous study by Seli, Schacter, Risko, and Smilek (2017) showing that both unintentional and intentional mind wandering reduce with age. Should motivation play a significant role in the occurrence of mind wandering, one would predict that intentional mind wandering would be affected selectively by differences in motivation. Yet, there is evidence that increasing motivation can decrease the occurrence of both intentional and unintentional mind wandering (Seli, Schacter, Risko, & Smilek, 2017), indicating that even if motivation cannot provide a full explanation, individual differences in mind wandering can indeed be driven significantly by differences in motivation.
Negative Mood and Current Concerns. Another attempt at explaining mind wandering has arisen from the rather consistent evidence that mind wandering goes hand-in-hand with
negative mood (Poerio, Totterdell, & Miles, 2013; Robison et al., 2017; Ruby, Smallwood, Engen, & Singer, 2013). Causal evidence for this connection comes from a study by Smallwood, Fitzgerald, Miles, and Phillips (2009) who induced either a positive, a negative, or a neutral mood in participants before they performed a sustained attention task. The researchers found that negative mood induction led to significantly more frequent mind wandering episodes during the subsequent task than either a neutral or a positive mood. However, the causality also seems to be reversed in some instances, as the content of mind wandering episodes has been shown to have an influence on subsequent mood (Killingsworth & Gilbert, 2010; Poerio et al., 2013).
These findings have led researchers to propose that mind wandering might be a consequence of negative emotions and that individual differences in the propensity of mind wandering can be explained through individual differences in disposition and mood. This theory was originally proposed by Klinger (1971; 2009) but has since been extended upon most
prominently in the cognitive control x current concerns framework by McVay & Kane (2010), the first component of which has already been discussed above. Within this view, mind
wandering arises when cognitive control fails and internally-generated thoughts about current concerns draw attention away from current task demands. To keep within the scope of the current review, negative mood, neuroticism, and current concerns will be grouped together and discussed as a single factor.
Indirect evidence for an involvement of negative affect and concerns in mind wandering comes from a study illustrating that higher trait neuroticism is associated with increased mind wandering frequency (Robison et al., 2017). As individuals high in neuroticism are predisposed to experience worries and feelings of anxiety (Muris, Roelofs, Rassin, Franken, & Mayer, 2005), this finding appears to support the hypothesis that individuals with more concerns mind wander more frequently. Crosswell, Coccia, and Epel (2020) demonstrated that persistent stress in daily
life, caused by circumstances such as a stressful job, was associated with higher reported incidents of mind wandering which in turn also correlated with a more negative mood. Thus, current concerns in the form of daily life stress appear to facilitate the occurrence of mind wandering as predicted by the current concerns x control failure theory. Shining light on the causality between current concerns and mind wandering, Kopp, D’Mello, & Mills (2015) have shown that by prompting participants to think about their short-term plans, it was possible to increase the reported mind wandering episodes during a following reading task. The extent however, to which short term plans can be considered current concerns is unclear. Seeing as mind wandering episodes are consistently marked by future-oriented thought (Baird, Smallwood, & Schooler, 2011), it appears likely that priming future-thoughts leads to an increased tendency to elaborate on these thoughts during the following task. The control condition in which
participants were prompted to name car parts does not sufficiently control for the possibility that future priming itself could be the cause of increased mind wandering rather than the focus on current concerns. Indeed, anticipation of either neutral or negative future events seems to impact the frequency of mind wandering equally strong (Stawarczyk, Majerus, & D’Argembeau, 2013). Participants expecting to perform a stressful task did not report more mind wandering episodes than those anticipating performing a non-stressful task, suggesting that it might be future-oriented thought per se that triggers mind wandering, rather than negative emotion.
Furthermore, Ottaviani, Shapiro, and Couyoumdjian (2013) argued that a strong association between negative mood and mind wandering is unlikely, considering the general pervasiveness of the phenomenon in our daily lives (Killingsworth & Gilbert, 2010; Kane et al., 2007; Seli, Beaty, et al., 2018). Rather, they suggest, mind wandering is associated with a dysphoric mental state predominantly in cases of rumination rather than in general instances of mind wandering. This distinction is not always made in studies investigating mind wandering
and thus rumination might be a confounding factor when investigating the relation between mind wandering and negative mood.
Despite the conflicting evidence regarding a primary role of negative affect and current concerns in the origin of mind wandering, theories based on this factor would likely make accurate predictions regarding mind wandering in old age. Building on the finding that individuals less prone to neuroticism mind wander less frequently (Robison et al., 2017), a reduction in mind wandering is in line with findings that trait neuroticism decreases with age (Donnellan & Lucas, 2008). Further, regarding state neuroticism and negative mood, older adults have been shown to report negative affect less frequently and fewer concerns (Parks, Klinger, & Perlmutter, 1989) compared to younger adults. Thus, a current concern perspective could
account for reduction of mind wandering in old age. Specifically, whereas McVay and Kane’s account of executive failure struggles to explain this phenomenon, their cognitive control x concerns theory as a whole can sufficiently explain reduced mind wandering in old age as older adults appear to have fewer current concerns than younger adults.
Local Sleep. A rather recent theory which approaches mind wandering from an entirely different angle was proposed by Andrillon and colleagues (2019). Their theory posits that it could be the phenomenon of local sleep that is the root cause of mind wandering episodes. Local sleep is defined as the occurrence of sleep-like slow waves at the level of neuronal populations (Andrillon et al., 2019) and while it has been studied mainly during sleep (Nir et al., 2011; Nobili et al., 2011) it has also been shown to occur during periods of wakefulness (Bernardi et al., 2015; Quercia, Zappasodi, Committeri, & Ferrara, 2018). Specifically, local sleep is thought to arise as a result of the build-up of sleep pressure (Muto et al., 2016) and has been linked to region
specific task demands (Bernardi et al., 2015; Goel, Abe, Braun, & Dinges, 2014; Hung et al., 2013). Based on these findings, Andrillon and colleagues (2019) theorize that local sleep
episodes during wakefulness could induce mind wandering periods; when a certain brain region has been used extensively in a certain task, local sleep occurs which leads to the phenomenology of mind wandering. Thus, while mind wandering does lead to a decrease in task performance, it could be a necessary ‘refresher-mechanism’ the adaptive use of which would be relieving exhausted brain regions. Indeed, local sleep as well as mind wandering have been consistently associated with temporary deterioration in task performance (local sleep: Quercia et al., 2018; Vyazovskiy et al., 2011; mind wandering: Mooneyham & Schooler, 2013) and the longer a task is being performed, the more frequent mind wandering becomes (Krimsky, Forster, Llabre, & Jha, 2017). Andrillon’s theory shows parallels to the dynamic framework proposed by Christoff, Irving, Fox, Spreng, and Andrews-Hanna (2016) who suggest that mind wandering and dreaming might both lie on spectrum of related mental activity and phenomenology.
Due to the recency of the interest in local sleep research, not much information on the phenomenon is available (Krueger, Nguyen, Dykstra-Aiello, & Taishi, 2019) and as of yet, it appears there are only two studies investigating the link between mind wandering and local sleep specifically which have been published as preprints (Andrillon, Burns, MacKay, Windt,
Tsuchiya, 2020; Jubera-Garcia, Vermeylen, Peigneux, Gevers, & van Opstal, 2020). As this makes a well-founded evaluation of the local sleep theory challenging, in the following I will also be discussing related factors, such as sleep pressure or slow wave activity, rather than local sleep specifically. The occurrence of local sleep has been shown to increase with time spend awake and sleep-pressure (Bernardi et al., 2015; Muto et al., 2016; Vyazovskiy et al., 2011), therefore increased tiredness can be reasonably hypothesized to correlate with increased occurrence of local sleep.
Indirect support for a local sleep account of mind wandering comes from studies
et al., 2017; Risko, Anderson, Sarwal, Engelhardt, & Kingstone, 2011; Thomson et al., 2014). This same pattern has been found for local sleep occurrence during wakefulness; the longer a certain task is being performed, the more likely the incidence of local sleep in that same region becomes (Hung et al., 2013), suggesting a possible task-dependent connection between mind wandering and local sleep. To investigate this, Esperanza and colleagues (2020) studied whether local use-dependent activity can induce mind wandering episodes, as predicted by the local sleep theory. For this, participants performed three sessions of a visual task during which the target stimuli were presented in one visual quadrant only. For a fourth session, the target was shifted to a different quadrant. The team hypothesized that if use-dependent local sleep triggers mind wandering episodes, which in turn impact performance, a decrement in performance and
increased mind wandering should be observed during the first three sessions, while performance would be restored and mind wandering less frequent in the last session. Their results confirmed these predictions when an objective measure of mind wandering was used, though with a subjective measure the results failed to reach significance.
More direct evidence comes from results by Andrillon and colleagues (2020), who tracked self-reported mind wandering during task performance and correlated mind wandering episodes with EEG signatures indicative of local sleep. They found a significant correlation between the participants’ subjective report of mind wandering, behavioral markers of attentional lapses and neural signatures of local sleep. Further, they could even distinguish above chance between mind wandering and mind blanking through the region in which local sleep was detected. These two studies combined lend tentative support to the local sleep account of mind wandering.
Further support for the local sleep theory is provided by findings regarding related factors such as sleep pressure or region-specific errors in task performance. Similarly to mind
wandering, local sleep occurrence has been linked to commission of region-specific errors during laboratory tasks. Patterns of local sleep in frontal areas have been associated with inhibitory lapses (Bernardi et al., 2015), whereas local sleep in perceptual areas has been linked to impaired reaction during a visual task (Nir et al., 2017). Further, sleep pressure is positively correlated with the frequency of local sleep episodes (Muto et al., 2016), as well as with mind wandering (Carciofo, Du, Song, & Zhang, 2014; Madiouni, Lopez, Gély-Nargeot, Lebrun, & Bayard, 2020), suggesting a possible connection between the two.
To approximate the predictions a local sleep account would make for mind wandering frequency in older adults, one can examine the changes in sleepiness and slow wave sleep associated with old age. Generally, older adults tend to report spending less time asleep compared to younger adults (Klerman & Dijk, 2008; Landolt & Borbély, 2001; Ohayon, Carskadon, Guilleminault, & Vitiello, 2004). Whether this is due to reduced sleep need or the inability to stay asleep is unclear at the moment. However, current evidence seems to be favoring the second option (Mander, Winer, & Walker, 2017). Reduced duration and quality of sleep could potentially lead to increased sleepiness and higher sleep pressure during the day, predicting an increased propensity for mind wandering with age. The opposite seems to be true however; older adults routinely report less daytime sleepiness and show fewer signs of sleep pressure (Dijk, Groeger, Stanley, & Deacon, 2010; Mander et al., 2017), which are both predictors of local sleep. Further, old age has been associated with changes in slow wave activity (Carrier et al., 2011). Older adults spent less time per night in stages of slow wave sleep (Dijk et al., 2010; Landolt & Borbély, 2001; Varga et al., 2016) and the reduction of episodes of slow wave sleep decreases less rapidly across the night, suggesting impaired homeostatic sleep regulation
(Mander et al., 2017). This lower inclination to experience slow wave activity might translate to decreased local slow wave activity also during wakefulness, i.e. local sleep, and in turn lead to
fewer mind wandering episodes. Taking this stance, the local sleep account of mind wandering appears to be in line with findings of reduced mind wandering in old age. However, drawing a definite conclusion about the predictions local sleep theory makes for mind wandering in older adults would be premature without studies directly investigating local sleep occurrence in older adults. For example, despite the global changes in sleep patterns seen in old age, a rodent study by McKillop and colleagues (2018) did not find any effects of aging on local cortical responses to sleep deprivation, illustrating the need for further research into the effects of age on local sleep.
There are some findings that pose an issue for the local sleep account of mind wandering. For example, the studies already described above investigating the relation between mind
wandering and motivation have shown that increasing motivation can reduce mind wandering (Seli, Schacter, Risko, & Smilek, 2017; Seli et al., 2020; Unsworth & McMillan, 2013). Should mind wandering occur as a result of task-dependent regional depletion, as the local sleep theory suggests, this is unlikely to be reversible through increased motivation. However, as the research into local sleep is scarce, it might be the case that local sleep during wakefulness only sets in when the current environment allows for it, akin to the context regulation theory. In this case, motivation might raise the importance of a task and prevent the occurrence of local sleep.
Another piece of evidence challenging the local sleep theory are results from a study by Stawarczyk and D’Argembeau (2016) who found that sleepiness and mind wandering have an independent and additive influence on task performance. As sleepiness has been shown to increase occurrences of local sleep (Muto et al., 2016; Vyazovskiy et al., 2011), one would expect the effects of sleepiness and mind wandering on task performance to be entangled if sleepiness was indeed an indirect cause of mind wandering as local sleep theory predicts. Even stronger evidence against a local sleep account of mind wandering comes from a study by Choi,
Geden, and Feng (2017), who investigated the relationship between task modality and modality of mind wandering content. If local sleep arises through region-specific fatigue through task demands (Hung et al., 2013), one would predict that the resulting mind wandering episode makes use of unrelated mental resources to provide a recovery period for the brain region implicated in current task demands. However, Choi and colleagues (2017) found that participants were more likely to report visual mind wandering when performing visual tasks, compared to tasks engaging other modalities.
Overall, although there are still difficulties to be overcome, there appears to be ample support for Andrillon’s local sleep theory. However, while the theory seems promising, research both into local sleep itself as well as its relation to mind wandering is scarce. The same applies when discussing the predictions a local sleep account would make for mind wandering in old age. Yet, current findings tentatively support a local sleep explanation for reduced mind wandering with age in line with established results, and future research is expected to further shine light on the explanatory power of this recent theory.
Discussion
Whereas mind wandering is common in every-day life (Killingsworth & Gilbert, 2010; Kane et al., 2007; Seli, Beaty, et al., 2018), scientific interest in this field of research is relatively new (Callard et al., 2013). Several theories aiming to explain the origin of the phenomenon have been proposed, but as of now, there is no comprehensive explanation for why and how mind wandering occurs. The evidence for and against each account appears to be largely inconsistent and difficult to interpret, preventing a conclusive evaluation. Surprisingly, one of the most replicated findings within mind wandering research has been a reduced frequency of mind wandering in old age (Jordão et al., 2019). This rather striking finding represents an intriguing
opportunity to test and compare the hypotheses different theories would make for mind
wandering in old age, as any theory aiming to explain mind wandering would have to account for this reduction.
Despite many researchers describing a reduction of mind wandering as counterintuitive or surprising, most theories can successfully account for this age-related development. Out of the theories discussed above, reduced mind wandering in old age seems to present a challenge primarily for theories based on executive failure, such as the control failure x cognitive concerns theory by McVay and Kane (2010). Should mind wandering occur when the executive system fails to prevent internally-generated thoughts to enter awareness and draw away attentional resources from task demands, this would most likely predict an increase in mind wandering in old age. However, this contradiction with empirical findings can be circumvented specifically within McVay and Kane’s theory through the second component. While cognitive control declines with age, older adults might mind wander less due to a lack of current concerns. Thus, like most other theories, also McVay and Kane’s theory could sufficiently explain reduced mind wandering in old age.
One factor strongly implicated in age-differences but not considered in the majority of theories is motivation. As motivation has been shown to mediate a large proportion of the age-related variations in mind wandering propensity, incorporating this aspect in general theories of mind wandering appears to be a valuable next step in broadening current explanations of mind wandering. Whereas motivation does not have to take the role of a primary explanatory factor, exploring its association with aspects currently implicated in mind wandering, such as local sleep or cognitive control might extend the explanatory power of theoretical approaches.
While the aim of this review was to link theories to empirical findings, to clearly establish which of the theories can best account for reduced mind wandering in old age, an
experiment set up to specifically investigate this issue would be needed. Though most theories could successfully explain age-related changes, their explanations are each based on separate cognitive and situational components, the involvement of which in age-related changes could be directly examined through targeted experimental designs.
Additionally, while not the focus of this review, age-related pathology might help explain the patterns observed in healthy aging. For instance, there appears to be a further decrease in mind wandering occurrence in dementia patients compared to healthy older adults. During low-demand as well as higher low-demand tasks, patients with dementia report less frequent mind
wandering and more on-task thoughts than age-matched healthy controls (Gyurkovics, Balota, & Jackson, 2018; Jackson, Fagan, Holtzman, Balota, & Morris, 2012; O’Callaghan et al., 2017; but Haj et al., 2019). There is no direct evidence that reduction in mind wandering in pathological samples occurs through the same mechanisms as the reduction in healthy aging. However, should the underlying causes for the trend of reduced mind wandering be identical across both groups, this would suggest that mind wandering is primarily a function of healthy, young brains and by extension might serve a yet to be determined adaptive function, despite its impact on performance.
Further, should the underlying mechanisms of decrease mind wandering be comparable, this would render several explanatory approaches for this phenomenon rather unlikely. For example, whereas there is evidence that older adults show increased task-based motivation (Ceccato et al., 2019; Seli et al., 2020; Staub et al., 2014) compared to younger adults, this does likely not extend to dementia patients. Thus, differences in motivation might not be able to fully account for differences in mind wandering propensity. Two theories that could reliably explain also these findings from dementia patients are the executive resource theory by Smallwood and Schooler (2006), as well as the local sleep theory by Andrillon and colleagues (2019).
Specifically, executive function has been shown to further decline in dementia patients compared to healthy older adults (Johns et al., 2009), suggesting that they have even fewer excess resources available to engage in mind wandering. Similarly, dementia patients also appear to experience a reduction in night-time slow wave sleep (Lim, Gerstner, & Holtzman, 2014), which could imply a role of local sleep occurrence in mind wandering. Thus, exploring mind wandering not only in healthy older adults, but also continuing the recent interest in mind wandering in patient
populations is a promising route to determine the validity of the different theories of mind wandering.
Limitations and Challenges
There are several challenges and limitations in mind wandering research yet to be overcome. Most importantly, while the findings that older adults mind wandering less has been replicated in numerous studies and appears largely uncontested, one must take into account the lack of longitudinal research. Most studies investigating age-related differences in mind wandering are cross-sectional, allowing for the possibility that a reduction in mind wandering occurs through generational, rather than age-differences. However, one of the few longitudinal studies which examined 93 women and 169 men over 6 to 8 years revealed a trend strikingly similar to cross-sectional studies, supporting the notion that mind wandering propensity decreases with age (Giambra, 1993).
Further, in this review as well as in the majority of prior research, mind wandering has been treated as a unified concept, comprising all thoughts unrelated to current task demands. While it has already been implied at several points throughout this review, it is important to emphasize that recent views consider mind wandering a more heterogeneous concept (Seli, Maillet, et al., 2017; Seli, Kane, Metzinger et al., 2018; Seli, Kane, Smallwood et al., 2018;
Wang et al., 2017). For instance, mind wandering can be intentional or unintentional (Seli, Risko, Smilek, & Schacter, 2016) and the two types have been shown to be clearly dissociable (Seli, Carriere, & Smilek, 2014; Seli, Risko, & Smilek, 2016; Vannucci & Chiorri, 2018). Moreover, mind wandering episodes can differ in content, whether they are past- or future-focused, have a positive or negative valence, or are self- or other-referential (Smallwood et al., 2011; Smallwood, & Andrews-Hanna, 2013; Stawarczyk, Cassol, & D'Argembeau, 2013). There is evidence that different types of mind wandering can relate differently to behavioral and neural components; for example, intentional mind wandering is more often associated with future-oriented content compared to spontaneous mind wandering (Seli, Ralph, Konishi, Smilek, & Schacter, 2017).
Additionally, mind wandering is not always clearly differentiated from similar or related concepts, such as daydreaming or rumination. To address these issues, Seli and colleagues (Seli, Maillet, et al., 2017; Seli, Kane, Metzinger, et al., 2018; Seli, Kane, Smallwood et al., 2018) advocate for a family-resemblance approach; as long as clear working definitions are provided, they argue, all these phenomena can be summarized under the broad umbrella-term ‘mind wandering’. In contrast, Christoff and colleagues (2018) contend that this approach could increase methodological variety and could promote overgeneralization of findings, wherefore a clear-cut definition of mind wandering is needed. Overall, there is no consensus as of yet
regarding what constitutes ‘mind wandering’ and a variety of working-definitions is used across studies, rendering comparisons of findings difficult. Moreover, this heterogeneity in the nature of mind wandering could indicate that there might not be one unifying theory of mind wandering, as different types of mind wandering could require different explanations. Thus, the search for an overarching explanation for the origin of mind wandering might be misguided. The various theories discussed above, each supported as well as contested by substantial evidence, are an
indication that a more precise definition of mind wandering in theoretical perspectives and in future research is needed to shed light on the origin(s) of mind wandering.
Beyond definitional concerns, several methodological difficulties render systematic investigation of mind wandering challenging. While some laboratory findings have been replicated in daily life settings (e.g. McVay, Kane, & Kwapil, 2009), among which the finding that older people mind wander less frequently (Maillet et al., 2018), most research has been carried out in a controlled setting during attention tasks. As some comparative studies report discrepancies between results from laboratory and real-life settings (Kane et al., 2017; Linz, Pauly, Smallwood, & Engert, 2019), it is unclear as of yet to what extent findings are generalizable across contexts. Theories of mind wandering will have to take into account findings from all settings and test their hypotheses in different contexts, so as to not overgeneralize laboratory findings.
Further, while there is evidence that probing people for mind wandering has no impact on the reported frequency of mind wandering (Wiemers & Redick, 2018), a potential drawback of current mind wandering studies is the reliance on self-report. Whether mind wandering episodes are probe-caught or self-caught, subjective insight on behalf of the subjects is required, which has been shown to be subject to several biases (Seli, Carriere, Levene, & Smilek, 2013; Weinstein, 2017). This is especially a concern when the definition of mind-wandering or task-unrelated thought is not clearly outlined, and the phrasing and frequency of probes vary between studies. A recent review reported 69 different varieties of mind wandering probes across 145 studies in 105 different articles (Weinstein, 2017), underlining the extent of methodological inconsistency. Unclarity in the way a question is framed as well as subjective judgements about what does and does not constitute a mind wandering episode could influence results, specifically in studies investigating individual differences. A tentative solution is the attempt to establish
psychophysical and neuroscientific markers of mind wandering, such as eye gaze patterns (Frank et al., 2015), pupillometry measures (Pelagatti, Binda, & Vannucci, 2019), and activity of the default mode network (e.g. Mason et al., 2007). However, self-report measures are still employed in the majority of studies.
Taken together, the definitional and methodological inconsistencies across studies make a systematic comparison and evaluation of current findings challenging and could be the cause of the often-conflicting findings found in different studies. While there has been a recent push for a more structured and standardized approach (Seli, Maillet, et al., 2017), the field of mind
wandering research is comparatively young and evolving rapidly (Callard et al., 2013); standardized practices and definitions have yet to be established.
Conclusion
In conclusion, the majority of theories can accurately predict the reduction of mind wandering frequency in old age. The predictions are based on distinct components for each theory however, allowing for future experimental designs to entangle the origin of this age-dependent tendency. For the moment, comparing different studies and theories of mind
wandering presents a challenging endeavor due to the inconsistency of research methods across studies. Future research will benefit from a more nuanced approach, taking into account the heterogeneity of mind wandering. While theories of executive resources have been prevalent in the past, novel approaches such as the local sleep theory present promising alternative views.
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