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Abstract

This article reviews the hypothesis that mind wandering can be integrated into executive models of attention. Evidence suggests that mind wandering shares many similarities with traditional notions of executive control. When mind wandering occurs, the executive components of attention appear to shift away from the primary task, leading to failures in task performance and superficial representations of the external environment. One challenge for incorporating mind wandering into standard executive models is that it often occurs in the absence of explicit intention--a hallmark of controlled processing. However, mind wandering, like other goal-related processes, can be engaged without explicit awareness; thus, mind wandering can be seen as a goal-driven process, albeit one that is not directed toward the primary task.
The Restless Mind
Jonathan Smallwood
University of Aberdeen
Jonathan W. Schooler
University of British Columbia
This article reviews the hypothesis that mind wandering can be integrated into executive models of
attention. Evidence suggests that mind wandering shares many similarities with traditional notions of
executive control. When mind wandering occurs, the executive components of attention appear to shift
away from the primary task, leading to failures in task performance and superficial representations of the
external environment. One challenge for incorporating mind wandering into standard executive models
is that it often occurs in the absence of explicit intention—a hallmark of controlled processing. However,
mind wandering, like other goal-related processes, can be engaged without explicit awareness; thus, mind
wandering can be seen as a goal-driven process, albeit one that is not directed toward the primary task.
Keywords: mind wandering, task-unrelated thought, stimulus-independent thought, meta-awareness,
attentional control
Introspective evidence is often suspect; yet, certain mental phe-
nomena are so self-evident their existence can hardly be ques-
tioned. Our propensity for mind wandering is such a phenomenon.
We all experience our minds drifting away from a task toward
unrelated inner thoughts, fantasies, feelings, and other musings.
Although mind wandering is ubiquitous in mental life, it has
largely escaped the interest of mainstream psychology. Indeed, we
were unable to find a single mention of the topic in a recent perusal
of cognitive psychology texts.
Perhaps part of the reason why mind wandering has escaped
mainstream attention is that research addressing the issue has been
framed in the context of a variety of disparate constructs including
task-unrelated thought (Smallwood, Baracaia, Lowe, & Obon-
sawin, 2003; Smallwood, Davies, et al., 2004; Smallwood, Obon-
sawin, Baracaia, et al., 2003; Smallwood, Obonsawin, & Heim,
2003; Smallwood, Obonsawin, & Reid, 2003; Smallwood,
O’Connor, Sudberry, & Ballantyre, 2004), task-unrelated images
and thoughts (Giambra, 1995), stimulus-independent thought
(Antrobus, 1968; Teasdale, Lloyd, Proctor, & Badgeley, 1993;
Teasdale, Segal, & Williams, 1995), mind pops (Kvavilashvili &
Mandler, 2004), and zone outs (Schooler, 2002; Schooler, Reichle,
& Halpern, 2005). These various lines of research have all ad-
dressed the basic phenomenal characteristics of mind wandering, a
shift of attention away from a primary task toward internal infor-
mation, such as memories (Smallwood, Baracaia, et al., 2003;
Smallwood, Davies, et al., 2004; Smallwood, Obonsawin, & Heim,
2003; Smallwood, O’Connor, et al., 2004; see also Christoff,
Ream, & Gabrieli, 2004). By referring to this phenomenon as mind
wandering, a term familiar to the lay person, we hope to elevate
the status of this research into mainstream psychological thinking.
Aims
In this review, we frame the literature on mind wandering in a
context that we hope will enable its integration into mainstream
models of executive attention. We propose that mind wandering is
a situation in which executive control shifts away from a primary
task to the processing of personal goals. Mind wandering shares
certain similarities with standard views of controlled processing,
however, there is an important difference. Controlled processing is
generally associated with the intentional pursuit of a goal. Mind
wandering, however, often occurs without intention (Giambra,
1995) or even awareness that one’s mind has drifted (Schooler,
2002; Schooler, Reichle, & Halpern, 2005).
Two considerations are necessary to resolve the apparent para-
dox that mind wandering involves executive control yet seems to
lack deliberate intent. First, it is likely that executive control is not
involved in the initiation of mind-wandering episodes. Rather, the
activation of goal-relevant information may occur automatically
through a process that does not require conscious intention (Bargh,
1997; Gollwitzer, 1999). Mind wandering involves executive con-
trol when a stimulus unrelated to the primary task automatically
initiates mind wandering. The absence of explicit and deliberate
intent associated with mind wandering may be enabled by the
simple fact that we often lack explicit awareness of the current
contents of our own experiences (herein termed meta-awareness;
Schooler, 2002; see also Jack & Shallice, 2001; Lambie & Marcel,
2002). Thus, mind wandering may entail situations in which indi-
viduals temporarily fail to notice that their immediate goal of task
completion has been temporarily displaced by another concern.
With the assumption that mind wandering can be accommo-
dated into executive models of attention, it is possible to derive
Jonathan Smallwood, Psychology Department, University of Aberdeen,
Aberdeen, Scotland; Jonathan W. Schooler, Psychology Department, Uni-
versity of British Columbia, Vancouver, British Columbia, Canada.
The writing of this article was supported by a grant from the U.S. Office
of Education to Erik Reichle and Jonathan W. Schooler. We are grateful to
Todd Handy, Alan Kingstone, Derek Heim, Eric Reichle, and Merrill
McSpadden for their helpful comments on earlier versions of this article.
We also thank Jason Chin, Joanne Elliott, Angela Aquino, and Helga Reid
for their help in the preparation of this article.
Correspondence concerning this article should be addressed to
Jonathan Smallwood, School of Psychology, William Guild Building,
University of Aberdeen, Aberdeen AB24 2UB, Scotland. E-mail:
j.smallwood@abdn.ac.uk
Psychological Bulletin Copyright 2006 by the American Psychological Association
2006, Vol. 132, No. 6, 946 –958 0033-2909/06/$12.00 DOI: 10.1037/0033-2909.132.6.946
946
specific predictions about how these experiences should relate to
controlled processing. First, tasks that rely heavily on controlled
processing will leave few working-memory resources available for
mind wandering because off-task thinking also requires resources.
Thus, mind wandering should be less likely to occur when the
primary task is demanding and more likely to occur when the task
is simple or automatic. Moreover, when mind wandering occurs in
demanding tasks, it should be associated with deficits in perfor-
mance because fewer resources are available to complete the
primary task.
Second, periods of mind wandering should be associated with
less accurate awareness of external information than periods of
task focus because mind wandering involves a shift of attention
away from the outside world. The shift in attention from the
primary task toward one’s memories suggests that mind wandering
is a state when information processing is decoupled from the
primary task (Smallwood, Baracaia, et al., 2003). Attention is
directed inwards during mind wandering; thus, representations of
the external environment should be superficial. In contrast, de-
tailed representations of the external environment should be avail-
able to awareness when attention is firmly directed at the current
situation.
Finally, the central challenge for incorporating mind wandering
into executive models of attention is that our mind often wanders
in the absence of explicit intention. Generally, deliberate intent is
considered a hallmark of controlled processing, so the apparent
absence of intent from mind wandering challenges the suggestion
that both mind wandering and controlled processing share
working-memory resources. This challenge can be met if one
recognizes that goal-related processes can be initiated automati-
cally (Bargh, 1997; Gollwitzer, 1999; Klinger, 1999). Assuming
that individuals have a hierarchy of goals, it is possible that mind
wandering leads to a shift of attention away from the primary task
because an alternative goal becomes activated in the absence of
attention. A crucial difference between mind wandering and stan-
dard notions of controlled processing, therefore, is that mind
wandering reflects controlled processing that is automatically ini-
tiated by a personally relevant goal. We review evidence that
individuals often fail to notice that their attention has left the
primary task and has become directed at a salient personal goal
(Giambra, 1995; Schooler, Reichle, & Halpern, 2005).
In the following sections, we review the existing literature on
mind wandering within the framework of a standard executive
model of attention, also considering how future experiments may
shed light on the processes involved in mind wandering. Before
doing so, however, we discuss the methods used to measure these
phenomena in the laboratory.
Methodological Issues for the Measurement of Mind
Wandering in the Laboratory
Verbal Reporting
In this section, we review the literature on the thought-sampling
techniques that are used to assess mind wandering (Antrobus,
1968; Giambra, 1995; Klinger, 1978; Schooler, Reichle, & Halp-
ern, 2005; Smallwood, Baracaia, et al., 2003; Smallwood, Davies,
et al., 2004; Smallwood, Obonsawin, & Reid, 2003; Smallwood,
O’Connor, et al., 2004). Self-reports cannot always be taken at
face value (Nisbett & Wilson, 1977); thus, we consider the limi-
tations and barriers that such reports impose on the study of inner
experience. Schooler and Schreiber (2004) observe that one im-
portant way to determine when self-reports accurately reflect in-
ternal states and when they may be misleading is to examine the
relation between subjective reports and behavioral and physiolog-
ical concomitants. Reliable behavioral or physiological temporal
markers for mind wandering provide important sources of validity
for these phenomena.
Methods of Thought Sampling
The most common method for investigating mind wandering is
thought sampling, assessing the inner experience of an individual
as they complete a task in a controlled experimental setting. A
similar procedure, the experience-sampling procedure, assesses
subjective experience in an ecologically valid setting (for reviews
see Csikszentmihalyi & Larson, 1987; de Vries, Dijkman-Caes, &
Delespaul, 1990; Hulburt, 1997; Shiffman, 2000). In this para-
digm, participants are asked to carry pagers during their day. An
individual’s experience is sampled at either random or quasiran-
dom intervals via the electronic device. When probed, the partic-
ipant is asked to describe his or her internal experiences, providing
detailed information on the nature of the experience and also the
context in which it occurred.
The measures of mind wandering used in empirical investiga-
tions can be grouped into two broad categories: probe-caught mind
wandering and self-caught mind wandering. In probe-caught mind
wandering, individuals are interrupted during the performance of a
task and asked to report their experiences (Giambra, 1995;
Schooler, Reichle, & Halpern, 2005). These probe-caught mind-
wandering episodes can be recorded via either computer (Antro-
bus, 1968; Giambra, 1995; Schooler, Reichle, & Halpern, 2005) or
verbal report (Smallwood, Baracaia, et al., 2003; Smallwood,
Davies, et al., 2004; Smallwood, Obonsawin, & Heim, 2003;
Smallwood, O’Connor, et al., 2004; Teasdale, Dritschell, et al.,
1995). In self-caught mind wandering, participants are asked to
monitor their awareness for off-task episodes (Cunningham,
Scerbo, & Freeman, 2000; Giambra, 1993). Self-caught mind
wandering, unlike probe-caught mind wandering, requires individ-
uals to be aware of the content of their own experiences.
Probe-caught measures have been used to examine mind wan-
dering with two different methods. In the first, the individual is
trained to recognize an example of mind wandering and is probed
at intervals throughout a task to determine whether any mind-
wandering episodes occurred during predefined intervals (Giam-
bra, 1995; Schooler, Reichle, & Halpern, 2005), typically respond-
ing with a simple yes/no judgement. We refer to this as the
self-classification probe method. The second method requires par-
ticipants to report what was passing through their mind at a point
preceding the thought probe (Teasdale, Dritschell, et al., 1995;
Teasdale et al., 1993). Before beginning the primary task, partic-
ipants are informed that thought probes will occur, but are not
informed about the category of thinking being investigated. These
verbal reports are recorded and can be coded using published
criteria (Smallwood, Obonsawin, & Reid, 2003). We refer to this
as the experimenter-classified probe method. Both sampling meth-
ods produce good estimates of mind-wandering frequency because
947
MIND WANDERING AND EXECUTIVE PROCESSES
they do not rely on participants’ awareness of their own
experiences.
The self-caught mind-wandering measure has been used to
investigate changes in mind wandering with age (Giambra, 1993,
Experiments 1 and 2) and changes in electroencephalograms
(EEGs; Cunningham et al., 2000). In addition, studies have used
retrospective measures of thought sampling, such as thought listing
(Seibert & Ellis, 1991) and questionnaire measures of off-task
thinking (Smallwood, O’Connor, et al., 2004). In these studies,
mind-wandering frequency was confounded with awareness/mem-
ory of mind wandering because the sampling measure depended on
an individual’s ability to monitor attention (Schooler, Reichle, &
Halpern, 2005). Consider the interpretation of changes in the EEG
band associated with mind wandering wherein “activity levels
recorded immediately after the reported mind wandering might be
higher because observers realize that they had been daydreaming
and must now redirect their attention back to the task at hand”
(Cunningham et al., 2000, p. 64). It is unclear whether the self-
monitoring approach indexes changes that result from engaging in
mind wandering or changes that result from catching oneself mind
wandering; thus, this method is not a good gauge of overall
mind-wandering frequency. It is possible, however, that the self-
caught method will ultimately prove useful in illuminating the
process by which individuals catch their minds wandering and
thereby shed light on how they become aware of their conscious
experiences.
Dissociations Between Methods of Thought Sampling
Both self-caught and probe-caught measures of mind wandering
provide complementary evidence about the nature of mind wan-
dering. An important research strategy, therefore, is to combine the
methods to highlight differences between mind wandering with
and without awareness. We first consider the possibility that the
manner in which mind wandering is measured influences results
and then discuss the theoretical advantages of combining self-
caught and probe-caught mind wandering in a research program.
A strong case can be made that rigorous control of participants’
beliefs regarding the purpose of an experiment is important in
psychological studies. In particular, knowledge of a psychological
phenomenon is especially important when the focus of an inves-
tigation depends on self-report (Nisbett & Wilson, 1977). It is
possible, therefore, that the self-classification method of mind-
wandering episodes (Antrobus, 1968; Giambra, 1995) in which
participants receive a description of mind wandering and are asked
to monitor their awareness for such episodes, may encourage
individuals to assign an artificially high priority to mind wander-
ing. In contrast, the experimenter-classified approach to mind
wandering (Smallwood, Baracaia, et al., 2003; Smallwood, Obon-
sawin, & Heim, 2003; Smallwood, Obonsawin, & Reid, 2003;
Teasdale, Dritschell, et al., 1995; Teasdale et al., 1993) merely
requires that individuals report what is passing through their
minds, often without overt mention of the category in question.
These ratings can be subsequently corroborated by providing par-
ticipants with a retrospective questionnaire at the end of the task.
Generally, these two measures are reliably correlated (r .60,
Smallwood, Baracaia, et al., 2003; r .50, Smallwood, Davies, et
al., 2004; r .50, Smallwood, O’Connor, et al., 2004).
Although the self-classification method of assessing mind wan-
dering may inflate estimates of mind-wandering frequency, it has
a number of important practical advantages over the experimenter-
classification approach. First, the method does not require that
individuals report detailed personal information regarding the con-
tent of their experiences, presumably reducing the potential for
demand characteristics. Second, it is considerably easier for indi-
viduals to classify their own mental experiences than it is for
experimenters to classify participants’ experiences. Considering
the potential advantages of the self-classification method, it is
important in future research to gain understanding of how partic-
ipants’ beliefs regarding the purpose of the research may bias
experimental results.
A more general methodological issue concerns the difference
between self-caught and probe-caught methods. Although self-
caught mind wandering offers important insights into participants’
meta-awareness of their off-task episodes (Schooler, 2002), its
requirement that participants continuously attend to their own
awareness has a potential methodological downside. Self-
monitoring may increase mind wandering in a manner similar to
what occurs in thought-suppression studies (Wegner, 1994). The
instruction not to think about a white bear leads to experiences of
the target at a level above baseline (for a review see Wegner, 1994;
Wenzlaff & Wegner, 2000).
Although attending to mind wandering may alter our experi-
ence, there has been little empirical support for this premise.
Schooler, Reichle, and Halpern (2005) examined mind wandering
during reading. They compared the effects of self-monitoring on
(a) the frequency of probe-caught zone outs and (b) attention to the
task, as measured by subsequent text comprehension. They com-
pared three groups: One group monitored their thoughts, a second
group was probed and also monitored their thoughts, and a final
group merely read the text. No group differences were observed in
the frequency of probe-caught mind-wandering episodes, nor did
either manipulation influence reading-comprehension scores. The
results suggest that self-monitoring did not appreciably alter the
phenomenological experience of mind wandering during text com-
prehension. Similarly, Smallwood, Baracaia, et al. (2003) demon-
strated a consistent relation between mind wandering and retrieval
from memory, irrespective of whether participants were asked to
report their thoughts when probed during a task (Experiments 1
and 2) or to retrospectively report their thoughts at the end of the
task (Experiment 3).
It should be possible to shed light on the processes underpinning
the representation of information in awareness (meta-awareness)
by combining the probe-caught and self-caught measures. The
self-caught measure requires that participants notice when their
attention has drifted from the task (Schooler, 2002). In contrast,
probe-caught mind-wandering episodes do not require awareness
and, as a result, provide a reliable baseline for the overall fre-
quency with which mind wandering occurs. Differences in re-
ported frequencies of self-caught and probe-caught mind wander-
ing should yield important insights into the intermittent nature of
conscious experience.
Schooler, Reichle, and Halpern (2005) explored mind wander-
ing during text comprehension using a combination of the probe-
caught and self-caught methods. Participants were asked to report
each episode of mind wandering, and they were periodically
probed about whether they were off-task at that moment. Schooler,
948
SMALLWOOD AND SCHOOLER
Reichle, and Halpern caught participants’ minds wandering on
approximately 13% of the trials in which they were probed. Sim-
ilar proportions of episodes without meta-awareness have been
reported with use of the thought-suppression paradigm (Fishman,
Smallwood, & Schooler, 2006). Because participants were asked
to report mind wandering as soon as possible, the probe-caught
rate indicates the proportion of time that participants lacked meta-
awareness of mind wandering.
A second research strategy is to systematically manipulate the
ratio of probe-caught and self-caught mind wandering. If monitor-
ing processes are compromised (either as a consequence of indi-
vidual differences or due to some manipulation), then self-caught
mind wandering should decrease, whereas probe-caught mind
wandering should either remain invariant or increase because
individuals fail to catch their mind wandering. Sayette, Kirchner,
Reichle, and Schooler (2006) reported results consistent with this
hypothesis. They examined the effects of alcohol— known to
reduce self-awareness (Hull, 1981)—on the frequency of both
self-caught and probe-caught mind wandering during reading.
Alcohol had a distinctly different effect as revealed by the two
measures. Participants who received alcohol reported more mind-
wandering episodes when probed than did their sober compatriots.
The inebriated participants, however, reported fewer mind-
wandering episodes than did sober participants. The probe-caught
measure was sensitive, therefore, to the overall frequency of mind
wandering (which was increased in the alcohol condition), whereas
the self-caught measure also required meta-awareness of mind
wandering (which was compromised in the alcohol condition).
In sum, evidence to date suggests that the self-caught and
probe-caught techniques used to assess mind wandering provide
valid and informative appraisals of the occurrence of mind wan-
dering. At the same time, these measures appear to reveal some-
what different aspects of the experience. The probe-caught method
provides an estimate of how often mind-wandering episodes occur,
whereas the self-caught method provides an estimate of the aware-
ness of mind wandering. In the future, it may be possible to gain
insights into the potentially distinct processes that mediate the
occurrence and awareness of mind wandering by examining dis-
crepancies between these two methods, particularly when supple-
mented with indirect measures of awareness.
Mind Wandering and Executive Processes
Controlled Processing
The first component of our hypothesis about the relation be-
tween mind wandering and executive control is that mind wander-
ing requires the coordination of information using resources under
executive control. This component is often referred to as con-
trolled processing (Baddeley, 1993). Definitions of controlled
processing emphasize four features: (a) “conscious intention of
what control will accomplish,” (b) “a sense of feeling of control,”
(c) “an expenditure of effort in the control of action,” and (d) “a
(closed-loop) monitoring of the control output” (see Wegner &
Bargh, 1998, p. 463). If mind wandering is associated with the
control of information in awareness, we can make two specific
predictions. First, tasks that rely on controlled processing should
suppress mind wandering. If the primary task requires the individ-
ual to maintain and coordinate task-relevant information in aware-
ness, then few resources will be available to coordinate a mind-
wandering episode. Second, an individual’s ability to coordinate
task-relevant information in awareness will be impaired when
mind wandering is experienced because control processes that are
normally involved in the task are directed elsewhere (see Badde-
ley, 1993). In principle, impairments resulting from mind wander-
ing should increase as a function of the controlled processing
involved in the primary task.
The experience of mind wandering and controlled processing.
This section addresses our hypothesis that mind wandering de-
creases when an individual is engaged in a primary task that
involves controlled processing. During a simple signal-detection
task, Antrobus (1968) demonstrated that mind wandering de-
creased as function of the stimulus presentation rate. The reduction
of mind wandering when stimulus presentation rate is high has
been replicated independently (Giambra, 1995; Grodsky & Giam-
bra, 1990; Smallwood, Davies, et al., 2004). A plausible explana-
tion for why increasing the stimulus presentation rate reduces mind
wandering is that the two processes compete for the same limited
working-memory resources. As more resources are allocated to the
primary task, fewer are available to support mind wandering.
Teasdale et al. (1993) hypothesized that tasks in which partic-
ipants must maintain task-relevant information in awareness
should suppress mind wandering if working memory is implicated
in the experience. Consistent with their hypothesis, mind wander-
ing occurred at a lower frequency when participants received
information for subsequent retrieval than when they verbally shad-
owed the same information (Teasdale et al., 1993). The reduction
in mind wandering occurred irrespective of whether the manipu-
lation was within the same participant (Teasdale et al., 1993,
Experiment 1) or between different participants (Teasdale et al.,
1993, Experiment 2). Moreover, mind wandering was reduced by
a simple visual-motor task relative to a control condition, suggest-
ing that suppression does not depend solely on the involvement of
the phonological loop (Teasdale, Dritschell, et al., 1995). The
authors concluded that working memory provided a “temporary
workspace for the production of thought streams consisting of
connected segments” (Teasdale et al., 1993, p. 432).
A second influence on controlled processing is practice with a
given task. Practice diminishes the need for attention in skilled
activities (Newell & Rosenbloom, 1981; Schneider & Shiffrin,
1977). Well-practiced tasks become functionally transparent (Vera
& Simon, 1993) because task-relevant information becomes rep-
resented at an increasingly abstract level (Anderson, 1983). As
tasks become skilled, fewer decisions are made consciously; for
example, skilled drivers simply drive instead of concentrating on
the relevant microbehaviors involved in driving a car (i.e., check-
ing the mirror or ensuring that the steering wheel is held in the
correct manner). Put simply, practice decreases the need for exec-
utive control in performing a task.
If practice on a task reduces the working-memory resources
allocated to the task, then mind wandering should increase as
performance becomes skilled. Experimental evidence confirms
that mind wandering increases when a task is well practiced
(Antrobus, 1968; Cunningham et al., 2000; Giambra, 1995; Small-
wood, Baracaia, et al., 2003; Smallwood, Davies, et al., 2004).
Furthermore, an increase in mind wandering in well-practiced
situations has been observed using both self-caught (Cunningham
et al., 2000) and probe-caught methods (Giambra, 1995; Small-
949
MIND WANDERING AND EXECUTIVE PROCESSES
wood, Obonsawin, & Reid, 2003) and has been observed in a
variety of contexts: simple signal detection (Cunningham et al.,
2000; Smallwood, Davies, et al., 2004), visual motor (Teasdale,
Dritschell, et al., 1995), and verbal encoding (Smallwood,
O’Connor, et al., 2004; Smallwood, O’Connor, Sudberry, & Obon-
sawin, in press). One can also observe the effects of practice at a
microlevel by examining the frequency of mind wandering in
blocks with short and long durations. Mind wandering occurs more
frequently in signal-detection and verbal encoding tasks when
blocks are of a long duration (1 min) than when they are of a short
duration (30 s; Smallwood, Obonsawin, & Reid, 2003).
One problem in interpreting the relation between mind wander-
ing and practice is that manipulations of practice confound skill
with the possibility of fatigue. A more direct test of the role of
practice in mind wandering was conducted by Teasdale, Dritschell,
et al. (1995) who examined the role of practice (a between-
participants manipulation) and time on task (a within-participants
manipulation) in the context of two tasks: a pursuit-rotor task and
a memory-load task. They found that both manipulations increased
the frequency of mind wandering (Teasdale, Dritschell, et al.,
1995, Experiment 3). Their results suggest that practice affects
mind wandering independent of fatigue.
Increased mind wandering with time on task does not generalize
to all types of tasks. Fluency tasks, for example, require that the
individual consistently generate novel information. In this case,
extensive practice does not reduce the role of controlled process-
ing. Smallwood, Obonsawin, and Reid (2003) found that block
length had no effect on mind wandering in fluency, whereas block
length increased mind wandering in simple signal detection.
Finally, not only does mind wandering increase with time on
task, the nature of thinking also changes. Practice over an extended
period yields a shift from thoughts that are related to the primary
task (e.g., an event in previous blocks of the same task) toward
thoughts related to less immediate concerns (termed experimenter-
remote concerns, see Antrobus, 1999). Comparable findings are
observed in studies investigating block length and mind wandering
(Smallwood, Obonsawin, & Reid, 2003). In simple signal-
detection and encoding tasks, moderate increases in block length
(30 60 s) are associated with a shift from thinking about ones’
own task performance toward thoughts that are unrelated to the
task (i.e., mind wandering). No change in the direction of thinking
is observed in fluency suggesting that the shift results from auto-
mating task performance.
Interference between mind wandering and controlled process-
ing. If mind wandering monopolizes working-memory re-
sources, then performance on a primary task should suffer because
few resources will be available to perform it (Baddeley, 1993). In
many of the studies described above, however, processing de-
mands were so slight that the effects of mind wandering on task
performance could not be analyzed. For example, in the studies by
Teasdale et al. (1993), participants performed at high levels of
accuracy (96%–100%), indicating that mind wandering was not
associated with poor performance.
Mind wandering is associated with poor performance, however,
when a primary task requires substantial controlled processing.
One such task is random number generation. Baddeley (1996)
argues that random number generation requires controlled process-
ing because individuals must refrain from using an automatic
response pattern (e.g., even numbers) to generate numbers in a
random order.
Teasdale, Dritschell, et al. (1995) demonstrated decrements in
random-number generation during mind wandering. Their results
are consistent with the hypothesis that mind wandering competes
with the primary task for the control and coordination of working-
memory resources; “when more control resources are allocated to
the production of stimulus-independent thoughts, fewer resources
are available to control the generation of random numbers” (Teas-
dale, Dritschell, et al., 1995, p. 558).
As outlined above, mind wandering and task performance are
unrelated in many circumstances (see Smallwood, Obonsawin, &
Heim, 2003). This is likely due to the fact that mind wandering is
frequently studied in situations in which task performance is func-
tionally transparent and can proceed without supervision by aware-
ness (see previous section). Although mind wandering can lead to
deficits on difficult tasks, these tasks reduce the frequency with which
participants report mind wandering. Without a reasonable number of
mind-wandering episodes, it is difficult to obtain reliable data con-
cerning the influence of off-task episodes on task processing.
The sustained attention to response task (SART, Robertson,
Manly, Andrade, Baddeley, & Yiend, 1997) is sufficiently simple
that attention frequently leaves the primary task, yet it is sensitive
to the tendency for participants to automate their behavior. The
SART is a simple go/no-go task. A single infrequent target is
presented (often the digit 3) amongst a background of frequent
nontargets (0 –9), and the participant is asked to respond to the
nontarget and to inhibit their response to the target. To perform
well, individuals must remain “sufficiently attentive to their re-
sponses, such that, at the appearance of a target, they can substitute
the directly antagonistic response” (Manly, Robertson, Galloway,
& Hawkins, 1999, p. 664). Performing the SART in a functionally
transparent manner should increase rather than decrease the like-
lihood of errors. In this sense, errors on the SART can be consid-
ered a behavioral example of a failure in controlled processing.
An important feature of the SART is that it is possible to
moderate the strength of the prepotent response by manipulating
the frequency of the nontarget. In principle, a low target frequency
will lead to the development of stronger prepotent responses than
a high target frequency. Responses are faster to nontargets that
precede an error than to nontargets that precede a correct response,
particularly in circumstances of low target probability (Manly et
al., 1999; Robertson et al., 1997). Errors on the SART predict
(Robertson et al., 1997) and are predicted by (Manly et al., 1999)
questionnaire measures of absentmindedness, suggesting that these
mistakes reflect a drift of attention from the primary task (Rob-
ertson et al., 1997).
Investigations of the experience of mind wandering during the
SART support the interpretation suggested by Robertson et al. (1997).
First, blocks in which mind wandering occurs are associated with
faster response times than are blocks in which attention is directed
toward the task (Smallwood, Davies, et al., 2004). Second, high levels
of mind wandering reported with retrospective questionnaires are
associated with a tendency to make an error during periods of task
disengagement. These errors are most frequent for targets with brief
stimulus durations (Smallwood, Davies, et al., 2004, Experiment 2).
Finally, the likelihood of errors when off task can be predicted by
response times in blocks in which individuals report mind wandering,
but not in blocks in which individuals are focused on the task. These
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SMALLWOOD AND SCHOOLER
findings validate the interpretation of SART performance (Robertson
et al., 1997) and confirm that participants are adopting a “mindless
stimulus-press stimulus-press style” (Manly et al., 1999, p. 662)
during mind wandering.
Summary and future directions. The evidence presented in this
section suggests trade-offs between mind wandering and task
performance. Mind wandering is reported frequently when the
primary task does not require the executive control of task-relevant
information in awareness. Moreover, it is possible to observe
subtle impairments in the efficiency of task processing when
processing and mind wandering compete for working-memory
resources. There are several areas, however, in which future re-
search could provide a more complete test of this relation.
Evidence has suggested that (a) mind wandering increases with
time on tasks that can be readily automated, and (b) mind wan-
dering interferes with the successful completion of nonautomated
tasks. It is plausible that the relation between task familiarity and
mind wandering could be tested in the following, more detailed,
manner: During the onset of a novel task, when controlled pro-
cessing is involved, mind wandering should be infrequent. When it
occurs, however, it should lead to deficits in task performance. As
task performance becomes automated, the interference between
mind wandering and task performance should decrease, and the
frequency of mind wandering should increase. This increase re-
flects the functional transparency that accompanies skill acquisi-
tion. The dynamic relation between automaticity and mind wan-
dering could be readily tested in the alphabet-addition task, a task
that is often used to examine the time course of automatic pro-
cessing (e.g. Logan & Klapp, 1991). This experiment would pro-
vide robust evidence that mind wandering is simultaneously in-
hibited by, and interferes with, the executive control of task-
relevant information in working memory.
Second, it is important to determine whether mind wandering
should be viewed as a modality-specific process or as a more
general one, as is the case for standard notions of executive
control. It is possible to address this issue through comparison of
interference between different task modalities and mind wander-
ing. Work by Teasdale et al. (1993; Teasdale, Segal, & Williams,
1995) suggested that mind wandering is suppressed by both visual-
spatial tasks and tasks with a phonological component. Similarly,
Antrobus, Singer, Goldstein, and Fortgang (1970) demonstrated
that auditory and visual tasks interfere with auditory and visual
mind-wandering episodes, respectively. In contrast, Stuyven and
van der Gouten (1995) demonstrated that a letter-generation task
suppressed mind wandering to a greater extent than either a fast or
slow random-time interval task with no verbal component. The
nature of the resources involved in mind wandering bears directly
on the extent to which mind wandering involves executive control;
thus, this issue is clearly worthy of further research. It is likely that
neuropsychological measures, such as ERP or functional magnetic
resonance imaging (fMRI), will be important in resolving this
issue by identifying the brain areas involved in the competition
between mind wandering and the primary task.
The Decoupling of Attention From the External
Environment
When the mind wanders, attention may become divided between
internal and external information, a phenomenon initially de-
scribed by John Antrobus and Jerome Singer as “decoupling” (see
also Smallwood, Obonsawin, & Heim, 2003). Mind wandering can
be viewed as a state of decoupled attention, because instead of
monitoring online sensory information, attention shifts inward and
focuses on one’s thoughts and feelings. If this hypothesis is cor-
rect, the period when the mind is wandering should be associated
with measurable differences in an individual’s access to represen-
tations of environmental stimuli. Some activities (such as reading)
involve the creation of online representations of the external task
environment. Such activities are ideal for testing our hypotheses
about mind wandering, unlike the simple tasks (e.g., signal detec-
tion) reviewed in the previous section.
In this section, we review studies of mind wandering in the
context of tasks such as reading and encoding. These studies
demonstrate that individuals have superficial representations of the
environment when their minds wander. The study of mind wan-
dering in the context of semantically rich tasks such as reading is
also important because it involves the investigation of subjective
experience in situations in which task focus is the norm rather than
the exception (see Smallwood, Obonsawin, & Heim, 2003, for a
discussion of this issue).
Mind wandering is not the only form of internally focused
attention studied in psychology. For example, research on mental
imagery, typified by the mental-rotation paradigm (Sheppard &
Metzler, 1971), also requires the shift of attention away from
sensory sources. However, in this case, attention is intentionally
directed toward the primary task. Other tasks that involve shifts of
attention away from the external environment include reasoning
(Laird, 1999) and autobiographical memory recall (Williams &
Scott, 1988). These situations may share important information-
processing characteristics with mind wandering and may ulti-
mately provide important control conditions for the investigation
of mind-wandering episodes. For example, Smallwood, O’Connor,
et al. (2004) compared mind wandering with the overt maintenance
of images in attention. The comparison between explicit imagery
and mind wandering suggested that information-processing simi-
larities exist between mind wandering and the maintenance of
dynamic images in awareness (i.e., images that change over time),
but not static ones. Tasks that involve the explicit internalization of
attention could provide a useful baseline for future neuropsycho-
logical investigations of mind wandering.
Text comprehension. Work by Grodsky and Giambra (1990)
demonstrated that the likelihood of mind wandering during reading
was positively associated with its likelihood in a simple signal-
detection task. The positive correlation between mind wandering
during reading and signal detection indicates a reasonable level of
consistency in mind wandering across two quite different contexts:
the first, a stimulus environment that is rich, and the second, a
relatively impoverished one.
Despite the consistency between mind wandering in the context
of reading and simple signal-detection tasks, the factors that de-
termined mind wandering varied across experimental situations
(Grodsky & Giambra, 1990). In signal detection, mind wandering
was more frequent during easy rather than hard blocks, whereas
mind wandering during reading was unrelated to passage diffi-
culty. Instead, mind wandering was frequent during reading when
passages were rated as uninteresting. In the context of semantically
meaningful tasks, factors such as absorption or interest, rather than
simple resource-driven factors, appear to play an important role in
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MIND WANDERING AND EXECUTIVE PROCESSES
determining when the mind wanders. The influence of interest or
absorption on mind wandering has been termed an affordance
(Smallwood, Baracaia, et al., 2003).
According to our hypotheses about the relations between mind
wandering and executive control, mind wandering leads to super-
ficial representations of the current external environment. In the
context of reading, frequent mind wandering should lead to poor
performance on measures of text comprehension. Schooler,
Reichle, and Halpern (2005) examined this issue by requiring
participants to read passages from War and Peace during which
both mind wandering (self-caught and probe caught) and text
comprehension were assessed. Comprehension was assessed im-
mediately after probes. Periods of probe-caught mind wandering
were associated with poorer text comprehension than were periods
in which attention was on task, confirming that mind wandering
interfered with participants’ ability to comprehend the text. Similar
results have been observed when mind wandering is induced by
asking participants to suppress thoughts relating to a previous
romantic relationship (Fishman et al., 2006) and when text is
presented one item at a time in a self-paced reading task (Schooler,
Smallwood, McSpadden, & Reichle, 2005). These results confirm
that superficial representations of the environment tend to occur as
attention drifts from task-relevant material.
Encoding. Research has suggested that the formation of de-
tailed episodic memories depends on the executive control of
attention during encoding. For example, dividing attention at study
reduces the formation of detailed episodic memories (Jennings &
Jacoby, 1993). In this section, we examine evidence that mind
wandering leads to a measurable difference in the quality of
episodic memories formed during encoding.
According to dual process accounts of memory, retrieval can
occur through two distinct processes (Jacoby, 1998): recollection
and familiarity (Jacoby, 1998; Jennings & Jacoby, 1993) or ex-
plicit and implicit retrieval (Szymanski & Macleod, 1996).
Broadly, recollection/explicit recall can be understood as the “con-
scious retrieval of an event” (Szymanski & Macleod, 1996, p.
165), whereas familiarity/implicit retrieval arises “when a previ-
ously encountered stimulus affects behaviour without conscious
knowledge” (Szymanski & Macleod, 1996, p. 165).
1
Both dividing
attention (Jacoby, 1998; Jennings & Jacoby, 1993) and directing
attention to superficial stimulus features (Szymanski & Macleod,
1996) impair recollection, leaving stimulus familiarity unaffected.
If mind wandering is associated with a shift of attention away
from the current environment, then subsequent retrieval may occur
via familiarity rather than recollection. Initial studies have indi-
cated that manipulations increasing mind wandering, such as in-
ducing positive or negative mood, also reduce retrieval from
memory (Seibert & Ellis, 1991). Similarly, elevated frequencies of
mind wandering are associated with high frequencies of false
alarms in immediate retrieval (Smallwood, Baracaia, et al., 2003;
Smallwood, Obonsawin, Reid, & Heim, 2002). Moreover, situa-
tions that promote high levels of encoding also encourage the
maintenance of attention on task-relevant information. In particu-
lar, the presentation of stimuli in the form of semantic categories
for subsequent recall tends to increase subsequent task perfor-
mance and decrease mind wandering, relative to either alphabetical
or randomly organized stimuli (Smallwood, Baracaia, et al., 2003;
Smallwood, Obonsawin, & Heim, 2003).
More recent evidence has demonstrated that mind wandering is
associated with a shift toward retrieval of information on the basis
of familiarity rather than recollection (Smallwood, Baracaia, et al.,
2003). The effects of mind wandering during study are robust
across a variety of different situations. For example, mind wan-
dering has been associated with elevations in familiarity, regard-
less of whether recollection/familiarity was measured at the point
of study (Smallwood, Baracaia, et al., 2003, Experiment 2) or at
retrieval using the process-dissociation procedure (Smallwood,
Baracaia, et al., 2003, Experiment 3). Second, a shift in retrieval as
a result of mind wandering has been demonstrated on word-
fragment completion (Smallwood, Baracaia, et al., 2003, Experi-
ments 1 and 2) and word-stem completion (Smallwood, Baracaia,
et al., 2003, Experiment 3) but not with simple word recognition
(Smallwood, Baracaia, et al., 2003). Third, the debilitating effects
of mind wandering on retrieval have been observed in immediate
recall (Smallwood et al., 2002) and delayed retrieval (Seibert &
Ellis, 1991; Smallwood, Baracaia, et al., 2003, Smallwood,
O’Connor, et al., 2004).
Research has also investigated whether failures in controlled
processing, defined in behavioral terms as errors, are associated
with superficial representations of the environmental context. The
relation between encoding of the environment and behavioral
lapses was addressed using a variation on the SART, called the
semantic SART (Smallwood, Heim, Riby, & Davies, 2006). In this
task, participants were asked to respond to a frequent nontarget
stimulus (a five-letter word) and inhibit their response to a target
stimulus (XXXXX). On completion of the initial task, participants
received a word-fragment completion test for words presented
during the first phase. Retrieval was measured using the process-
dissociation procedure (Jacoby, 1998). Words that were presented
before an individual made an error were equally likely to be
retrieved on the basis of familiarity or recollection. Those items
that were presented after participants made an error were more
likely to be retrieved on the basis of recollection. The pattern of
retrieval before and after an error confirms observations in the
literature that, in tasks like the SART, periods before an error
index intervals when attention is directed away from the primary
task. The rebound in recollection following an error demonstrates
that attention returns to the primary task following an explicit
failure in task performance (Manly et al., 1999; Robertson et al.,
1997).
Summary and future directions. The literature reviewed in this
section is consistent with the claim that, when the mind wanders,
attention that is normally directed toward the primary task shifts
away from the external environment, leading to more superficial
representations of the external environment than when attention is
on task. Evidence from studies of text comprehension and encod-
ing has illustrated that individuals have less detailed access to
representations of the external environment when their attention is
off task, providing support for the claim that, during mind wan-
dering, attention is decoupled from the external environment.
From a methodological perspective, the majority of the findings in
the literature measure the awareness of target stimuli indirectly.
For example, research on mind wandering during encoding often
1
For the sake of clarity, we use the terms recollection and familiarity to
refer to these phenomenon.
952
SMALLWOOD AND SCHOOLER
measures retrieval at the end of the encoding phase (e.g., Small-
wood, Obonsawin, & Heim, 2003). Given the intervening time
between the initial presentation of the stimulus and the subsequent
retrieval of the memory, it is hard to ensure that deficits result from
mind wandering and not from some other intervening variable. It
is important, therefore, for future research to address this issue
using a paradigm that measures retrieval immediately. Schooler,
Reichle, and Halpern (2005) have used this methodology to ex-
amine comprehension failures in reading, and it would be infor-
mative to use this paradigm in the context of immediate measures
of encoding.
An alternative method would be to use indirect measures of
encoding, such as ERPs, to provide temporal information about
fluctuations in an individual’s ability to encode information. Re-
cent work has provided preliminary evidence that those individuals
who report a high frequency of mind wandering show differences
in the ERP correlates of episodic memories when asked to retrieve
these stimuli (Riby, Smallwood, Cooper, Finnigan, & Annett,
2006). It would be worthwhile to explore the possibility that ERPs
could be used to detect fluctuations in awareness during the
encoding phase of a memory task.
Deliberate and Nondeliberate Processes and Mind
Wandering
Executive systems are generally involved in the deliberate con-
trol of behavior (Baddeley, 1996; Norman & Shallice, 1986).
However, we review empirical studies in this section demonstrat-
ing that people often fail to notice their minds wandering (Giam-
bra, 1995; Schooler, Reichle, & Halpern, 2005). Thus, mind wan-
dering is a paradox; mind wandering clearly shares many features
of traditional executive systems, yet some of these episodes occur
in the absence of explicit intention. Indeed, mind wandering may
occur specifically as a consequence of intentions to avoid it.
Wegner (1997) suggested that the “mind wanders as a result of our
attempts to control it” (p. 298). According to ironic processes
theory (Wegner, 1994), attempts to control awareness create con-
ditions in which the intentional control of attention is undermined,
leading in turn to an increase in the frequency of mind-wandering
episodes.
A resolution to the fact that mind wandering occurs when
executive control is engaged without deliberate intent can be
achieved by adding two assumptions to standard executive models:
(a) the assumption that individuals possess multiple goals, some of
which can be triggered automatically by salient stimuli (Bargh,
1997; Gollwitzer, 1999; see also current concerns theory in
Klinger, 1978, 1999), and (b) the assumption that consciousness
and meta-awareness are distinct (Schooler, 2002). We discuss each
assumption in turn.
Automatic goal activation. Satisfactory goal completion re-
quires that an individual’s cognitive system be sensitive to envi-
ronmental opportunities that facilitate a given behavior (Gollwit-
zer, 1999; Klinger, 1999). These goal-driven sensitivities can be
referred to as implementation intentions (Gollwitzer, 1999) or
current concerns (Klinger, 1999), and they facilitate behavior by
heightening the accessibility of goal-relevant stimuli. According to
auto-motive theory (Bargh, 1997), the heightened accessibility of
goal-relevant information results in the processing of these stimuli
preconsciously; this, in turn, leads to the direct activation of a
behavior without conscious intent (Bargh, 1997). This framework
suggests that mind wandering can occur against our best intentions
because the automatic activation of a personally relevant, but
task-unrelated, goal has temporarily drawn our attention away
from the primary task.
The automatic activation of goals has previously been applied to
mind wandering research with the current concerns framework
(Klinger, 1978, 1999). Current concerns are “hypothetical pro-
cesses active during the time that one has a goal” (Klinger, 1999,
p. 43) and elicit effects on cognition, because to commit to a goal
is to become sensitive to cues associated with the relevant behav-
ior. These goal sensitivities, in turn, lead the cognitive system to
automatically process behaviorally relevant cues (Klinger, 1999;
Nikles, Brecht, Klinger, & Bursell, 1998). Empirical evidence has
provided support for the sensitivity of attention to self- or goal-
relevant information. First, during dichotic listening, attention is
rapidly and efficiently drawn to both self-relevant stimuli (Bargh,
1982; Klinger, 1978) and goal-relevant information (Gollwitzer &
Bargh, 1996), in a manner similar to the cocktail party effect
(Cherry, 1953). Briefly presenting either self-related (Bargh, 1982)
or goal-related stimuli (Gollwitzer & Bargh, 1996) in one channel
of a dichotic listening task activates relevant adjectives in aware-
ness. Similarly, stimuli related to an individual’s current concerns
presented in one channel of a dichotic listening task leads an
individual’s attention to switch to that channel and subsequently
increases the number of thoughts related to that concern (Klinger,
1978). Therefore, it seems possible that the shift of attention away
from the external environment—mind wandering—occurs in op-
position to the goal of task completion because of the direct
activation of a personally relevant goal.
Meta-awareness. Throughout this review, we have empha-
sized the value of distinguishing between the occurrence of an
experience (experiential consciousness) and one’s explicit aware-
ness of the experience (meta-awareness, Schooler, 2002; see also
Jack & Shallice, 2001; Lambie & Marcel, 2002). This distinction
becomes particularly important when we attempt to explain how
mind wandering occurs. Empirical evidence demonstrates that
individuals often fail to recognize that their attention is off task in
both simple signal-detection (Giambra, 1995) and reading tasks
(Schooler, Smallwood, et al., 2005). Given the fact that goal-
directed processing can occur automatically, individuals may lack
meta-awareness of mind wandering in the same manner that they
occasionally fail to recognize why they engage in certain other
goal-driven acts (Bargh, 1997). Awareness will be absent in mind-
wandering episodes if goal-driven processes attract attention with-
out the individual (at least for a period of time) perceiving a
conflict.
In this final section, we consider evidence that mind-wandering
episodes occur when executive control becomes temporarily
usurped by a more personally relevant goal. The relation between
mind wandering and intention is speculative, largely because few
studies have directly addressed the relation between the directed
control of attention and mind wandering. Nonetheless, two lines of
experimental evidence shed light on whether mind wandering
occurs without intention.
First, we consider evidence demonstrating that, on occasion,
individuals describe their mind-wandering experiences as either
lacking intentionality (Giambra, 1995) or lacking awareness that
they were off task (Schooler, Reichle, & Halpern, 2005). Second,
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MIND WANDERING AND EXECUTIVE PROCESSES
we discuss the possibility that mind wandering in everyday life
plays an important role in attempts at problem solving. Evidence
suggests that personal concerns form the basis of mind wandering
and that states involving elevations in these concerns, such as
dysphoria (Ruehlman, 1985), are accompanied by high frequencies
of mind wandering (Smallwood, Davies, et al., 2004; Smallwood
et al., in press; Smallwood, Obonsawin, & Reid, 2003; Smallwood,
O’Connor, et al., 2004; Smallwood, O’Connor, & Heim, 2006).
This evidence provides a critical link between mind wandering and
the need to resolve ongoing personal problems.
Intentions, awareness, and mind wandering. Research by Gi-
ambra and colleagues examined the role of intentions in mind
wandering. They distinguished between two forms of mind wan-
dering: spontaneous and deliberate (Giambra, 1995; Grodsky &
Giambra, 1989). Spontaneous mind wandering reflects “task-
unrelated thought intrusions that spontaneously come into your
head without any effort on your part,” whereas deliberate mind
wandering reflects “intrusions that occur when you deliberately try
to think about something other than the vigilance task” (Giambra,
1995, p. 12). In the context of simple signal detection, volitional
mind wandering was reported on a greater proportion of probes
than was nonvolitional mind wandering (71% vs. 50%, respec-
tively; Giambra, 1995). This suggests that a high proportion of
mind-wandering episodes are directed toward the explicit or voli-
tional pursuit of an individual’s goals or current concerns during a
simple signal-detection task. Nonetheless, individuals reported that
they were not experiencing deliberate mind wanderings during
approximately half of the probes—in other words, individuals
were often caught mind wandering before they noticed it
themselves.
The notion that mind wandering often lacks meta-awareness is
supported by research in which the meta-cognitive status of mind
wandering was examined (Schooler, Reichle, & Halpern, 2005). In
the text-comprehension study described earlier, individuals were
unaware of the direction of their thinking on approximately 13% of
thought probes in which mind wandering was reported. Similar
frequencies (20%) have been observed with both a self-paced
word-by-word text-comprehension task (Schooler, Smallwood, et
al., 2005) and a task using alternative text (Fishman et al., 2006).
Thus, in both reading and simple signal-detection situations, indi-
viduals frequently lack meta-awareness that they are mind wan-
dering, even when specifically instructed to be vigilant for such
lapses. Empirical evidence, therefore, supports the position that a
substantial proportion of mind-wandering episodes occur without
intent.
Mind wandering and personally relevant problem solving. If
mind wandering occurs when executive control leaves the primary
task in favor of an alternative personally relevant goal, then off-
task episodes should be closely tied to problem solving. Since
Singer (1966), several authors have suggested that mind wandering
is associated with important functional consequences. In particu-
lar, mind wandering has been associated with facilitating problem
solving by the conceptual manipulation of semantic information
(Binder et al., 1999). The role of mind wandering in problem
solving is exemplified in the following quotation: “By storing and
manipulating internal information we organise what could not be
organised during stimulus presentation, solve problems that re-
quire computation over long periods of time, and create effective
plans governing behaviour in the future” (Binder et al., 1999, p.
85). Mind wandering could clearly facilitate problem solving by
helping individuals solve problems in awareness before they en-
counter them in the real world. In more general terms, this process
has been referred to as problem solving in the neural workspace
(Cleeremans & Jime´nez, 2002; Dehaene & Naccache, 2001).
2
Evidence linking mind wandering to problem solving would pro-
vide informative evidence that off-task episodes occur when a
personally relevant goal is activated in awareness.
Research supports the notion that mind wandering plays an
important functional role in resolving problems in everyday life.
When mind wandering occurs in either naturalistic (Klinger, Barta,
& Maxeiner, 1980) or laboratory settings (Klinger, 1978), individ-
uals are likely to be processing their current concerns (Klinger,
1999). First, the content of a participant’s thinking as sampled on
a day-to-day basis through the use of a pager is often associated
with the contents of the participant’s concerns as sampled by a
questionnaire. These concerns are associated with the individual’s
present life (67%), past or future life (12%), or no particular time
period (23%; Klinger & Cox, 1987). Second, an experimental
induction of a personal salient concern with extensive implications
for an individual (e.g., a broadcast indicating that China had
entered the Vietnam War) increases the likelihood of mind wan-
dering (from 0.32 to 0.45) and the frequency of errors (from .045
to .055) relative to a neutral control broadcast (Antrobus, Singer,
& Greenberg, 1966). Finally, similarities can be seen in the overlap
between the content of mind wandering and coping strategies
(Greenwald & Harder, 1995, 1997). A consistent and reliable
association has been observed between the content of mind wan-
dering experienced on a day-to-day basis and the content of
sustained fantasies evoked as a source of comfort to an individual
in situations of distress (Greenwald & Harder, 1995).
The relation between dysphoria and mind wandering provides
additional support for the claim that mind wandering occurs in the
pursuit of self-relevant goals. Dysphoria has been recently con-
ceptualized as a state of repetitive self-relevant processing (Pyszc-
zynski & Greenberg, 1987; see also Higgins, 1987). Consistent
with this emphasis on the self in depression, research suggests that
dysphoria reflects a state of elevated current concerns (Ruehlman,
1985). The current concerns of undergraduate students who were
dysphoric were less positive and less related to active goal pursuits
than those who were not dysphoric. In addition, dysphoric under-
graduate students reported a greater number of concerns than did
nondysphoric students, particularly in three areas: (a) love and sex,
(b) employment and money, and (c) mental health (Ruehlman,
1985). If mind wandering is associated with solving personal
problems, then dysphoric individuals constitute an important pop-
ulation in which to test the association between off-task thinking
and problem solving.
Mind wandering has been consistently associated with question-
naire measures of dysphoria across a wide range of tasks: encoding
(Smallwood, Obonsawin, Baracaia, et al., 2003; Smallwood,
O’Connor, et al., 2004), sustained attention (Smallwood, Davies,
et al., 2004), and word-fragment completion (Smallwood,
O’Connor, & Heim, 2006). Moreover, recent evidence has sug-
2
Similar perspectives have been advanced in evolutionary accounts of
conscious awareness, notably Dennet (1996), who emphasized the devel-
opment of infovores: organisms whose ideas can die instead of themselves.
954
SMALLWOOD AND SCHOOLER
gested that mind wandering is more frequent in a dysphoric pop-
ulation than in a nondysphoric one, and when off-task thinking
occurs in this population, it leads to physiological arousal and
inefficient information processing (Smallwood et al., in press).
Finally, recent advances in the treatment of depression—such as
mindfulness-based cognitive therapy (MBCT; Teasdale, 1999;
Teasdale et al., 2000)—provide an important source of evidence
for the association between mind wandering and on-going personal
problems. In MBCT, participants are trained in meditative tech-
niques that are focused on reducing mind wandering. MBCT
shows promise in reducing the likelihood of depressive relapse
and, posttherapy, in helping participants form more detailed auto-
biographical memories (Williams et al., 2000).
The evidence on the relation between dysphoria and mind
wandering suggests that (a) populations who have elevated per-
sonal problems are more likely to engage in mind wandering
across a wide range of tasks and (b) therapeutic interventions that
focus on reducing mind wandering are effective in reducing re-
lapse in recovering depressive individuals. Taken together, the
relation between mind wandering and dysphoria provides impor-
tant indirect evidence for the association between off-task experi-
ences and goal-resolution processes.
A recent fMRI study has provided a physiological mechanism to
explain the manner in which periods of off-task thinking may be
activated by an individual’s current concerns (Christoff et al.,
2004). In the context of neuroimaging studies, one consistent
finding has been that periods of rest resemble periods of problem-
solving activity. Recently, evidence has demonstrated that brain
activity during the resting state, presumably a period when high
frequencies of mind wandering occur, is closely related to activity
during conceptual processing (Binder et al., 1999), memory re-
trieval (Buckner, Raichle, Miezin, & Petersen, 1996), and problem
solving (Christoff & Gabrieli, 2000). Christoff et al. (2004) dem-
onstrated that periods of rest, interspersed throughout a simple
visuomotor task, showed high levels of activation in lateral pre-
frontal and visual cortex. The most robust activation during rest,
however, was observed in temporal lobe structures, including
lateral anterior and medial temporal regions. This pattern of acti-
vation was interpreted as an indication that long-term memory
processes form the basis of spontaneous thinking (Christoff et al.,
2004). The results of Christoff et al.’s study provide a plausible
physiological mechanism through which higher order goals de-
rived from our past experience may overshadow the primary goal
of task completion.
Summary and future directions. In this section, we examined
the paradoxical fact that mind wandering reflects an executive
process that occasionally occurs in the absence of intention. To
overcome this paradox, we suggested that goal-relevant processing
can be instigated automatically (Bargh, 1997; Gollwitzer, 1999)
and that individuals possess multiple goals, some of which are
unrelated to the current goal of task completion (Klinger, 1999).
When mind wandering occurs against our intentions, it is possible
that personally relevant goal-driven processes are automatically
activated, leading to the withdrawal of attention from the primary
task.
The evidence reviewed in this section demonstrates two clear
features of mind wandering that are consistent with this claim.
First, evidence shows that the mind wanders without individuals
themselves registering this fact in both simple signal-detection and
text-comprehension tasks (Giambra, 1995; Schooler, Reichle, &
Halpern, 2005). Second, evidence has suggested that personal
information from memory may form the content of mind-
wandering episodes. Moreover, those individuals who have high
frequencies of personal problems show evidence for frequent
mind-wandering episodes and periods in which attention is with-
drawn from the current situation.
One limitation of research into the relation between mind wan-
dering and executive control is that research has examined verbal
reports only. Self reports are a crude measure of awareness and are
potentially susceptible to demand characteristics. Research has
identified five markers that may index the experience of mind
wandering: (a) response time (Smallwood, Baracaia, et al., 2003;
Smallwood, Davies, et al., 2004; Smallwood, O’Connor, et al.,
2004), (b) changes in heart rate (Smallwood, Davies, et al., 2004;
Smallwood, O’Connor, et al., 2004), (c) skin conductance (Small-
wood et al., in press), (d) electro-cortical activity including both
EEGs (Cunningham et al., 2000) and ERPs (Riby et al., 2006), and
(e) fMRI activity (Christoff et al., 2004). We may be able to
exploit these physiological or behavioral markers to provide more
reliable evidence about the role of intention in mind wandering
than can be provided by the analysis of self-reports alone. In
particular, a psychophysiological contrast between self-monitored
and probe-caught mind wandering may illuminate the process by
which information becomes re-represented in awareness
(Schooler, 2002). Advances in technology such as real time fMRI
and source-localization ERP make the development of a physio-
logical marker for mind wandering a viable possibility.
A second possible direction for future research is to investigate
the emotional nature of current concerns as determinants of
whether mind-wandering episodes lack meta-awareness. Evidence
has shown that stimuli related to an individual’s current concerns
can trigger a mind-wandering episode (Klinger, 1978, 1999;
Smallwood, Davies, et al., 2004; Smallwood, Heim, et al., 2006;
Smallwood et al., in press; Smallwood, Obonsawin, Baracaia, et
al., 2003; Smallwood, O’Connor, et al., 2004) and has shown that
personally salient internal information can dominate awareness at
the expense of external task-relevant stimuli. A large body of
experimental evidence suggests that emotive material tends to
attract an individual’s attention (e.g., Ohman, Flykt, & Esteves,
2001) and may do so automatically (MacLeod, 1991; McKenna &
Sharma, 1995). If information-processing during mind wandering
is aimed at personally salient goal resolution, then the emotional
nature of this information may be responsible for whether the
subjective experience of mind wandering is associated with meta-
awareness. A study of mind wandering with and without aware-
ness by experimentally inducing positive and negative moods in
depressed and control participants could address this issue.
Conclusions and Final Thoughts
We have provided a framework for describing the empirical
evidence on mind wandering gathered over the last 30 years by
combining assumptions from previous theoretical accounts of
mind wandering (e.g., Antrobus, 1999; Klinger, 1999; Teasdale et
al., 1993; Teasdale, Dritschell, et al., 1995) with contemporary
views of executive control and meta-awareness (Jack & Shallice,
2001; Lambie & Marcel, 2002). First, we have suggested that
executive control becomes disengaged from a primary task during
955
MIND WANDERING AND EXECUTIVE PROCESSES
mind wandering and becomes directed toward the processing of
internal information, such as memories. Both the consequences
and distribution of mind wandering suggests that our minds are apt
to wander when the primary task does not require executive
control. Furthermore, when mind wandering occurs, the ability to
perform complex working-memory tasks is often impaired. Sec-
ond, in tasks such as reading and encoding, our ability to represent
task-relevant stimuli is impaired during mind wandering. This
provides evidence that mind wandering is a state of decoupled
information processing, which occurs because of a shift in atten-
tion away from the immediate environment. Finally, we speculate
that mind wandering involves both the redirection of executive
control and a failure of goal-oriented processing toward the pri-
mary task. In mind wandering, it seems that the automatic activa-
tion of a pertinent personal goal temporarily overshadows the more
immediate goal of task completion. Such goal switching may be
enabled by the tendency for experience to become decoupled from
meta-awareness, such that individuals temporarily fail to notice
that their task-related processing has been hijacked by a more
personally relevant goal.
Two questions emerge regarding the relation between executive
control and mind wandering. The first question concerns the ad-
vantages that we derive from mind wandering. Klinger (1999)
suggested that one advantage to mind wandering is that it could
foster creative problem solving. Similarly, Singer (1966) argued
that processes associated with fantasy, particularly in early life,
facilitate the development of problem-solving skills. In this article,
we have argued that mind wandering may be a mode of problem
solving. In particular, we have suggested that mind wandering is a
situation when controlled processing becomes hijacked in the
service of a goal reflecting our current concerns. If this is correct,
then this process is linked to the pursuit of ideas or problems that
have, so far, eluded solution. Considered in this light, mind wan-
dering may share important similarities with incubation processes
related to creativity. Accordingly, the experience of sudden “eu-
reka” or “ah-ha” moments (Schooler, Fallshore, & Fiore, 1995),
which apparently occur out of the blue, may sometimes occur
because mind wandering addresses more remote goals (e.g., dis-
cerning the solution to a heretofore unsolved problem). In the
future, research on mind wandering could be informed through use
of frameworks that have been successfully developed for the study
of creativity.
A second outstanding question that emerges from consideration
of the relation between executive control and mind wandering is
the specific relation between task load and mind wandering. Much
of the research on mind wandering has been influenced by a simple
limited-capacity account of cognition. However, it is clear from
this review that mind wandering requires at least two components
of cognitive processing: (a) a control process that coordinates
information within awareness and (b) a decoupling process that
allows cognitive resources to become captured by internal rather
than external information. Schooler (2002) has suggested that for
individuals to catch their minds wandering requires a self-
monitoring process that detects periods when idle cognitive re-
sources become directed to off-task material. When task demands
are low, idle cognitive processes are available for redirection to an
individual’s current concerns, thus facilitating the experience of
mind wandering; however, sufficient resources are also available
to monitor task awareness in a satisfactory manner. This could
account for the sense of focus brought about by simple
information-processing states such as meditation. When task de-
mands are high, idle processes are reduced, preventing both the
mind’s tendency to wander and the monitoring process from
operating. In the case of highly demanding tasks, however, the
absence of self-monitoring is nondetrimental because too few
resources are available to support mind wandering. At a moderate
level of task demands, however, the competition for resources will
be greatest. In these circumstances, the individual may spend a
significant period of time off task because too few resources are
available for self-monitoring. If executive control and mind wan-
dering are linked, as the evidence in this article suggests, we might
expect the relation between task load and mind wandering to
reflect this competitive process.
Although mind wandering has largely been relegated to the
backwaters of mainstream psychology, our review of the literature
has demonstrated that the phenomenon readily lends itself to
empirical investigation and directly maps onto a simple model of
executive control. Moreover, the evidence suggests that mind
wandering may be one of the most ubiquitous and pervasive of all
cognitive phenomena. Across a diverse variety of tasks, verbal
reports have indicated that between 15% and 50% of a partici-
pant’s time is spent mind wandering (15% fluency and encoding,
Smallwood, Obonsawin, & Heim, 2003; 20% reading, Schooler,
Reichle, & Halpern, 2005; and 50% simple signal detection,
Antrobus, 1968; Giambra, 1995; Smallwood, O’Connor, et al.,
2004). These ratings from laboratory tasks may be higher than
those recorded in day-to-day living, as a result of the lack of
stimulation that occurs in controlled experimental settings (Klinger
& Cox, 1987). The frequency of mind wandering, even in demand-
ing cognitive tasks such as encoding and reading, suggests that
every laboratory study is at least partially a study of mind wan-
dering. It seems that, in almost any cognitive task, mind wandering
inevitably accounts for a substantial proportion of an individual’s
time. As psychologists, we must confront this phenomenon di-
rectly, recognizing the importance of mind wandering as a psy-
chological phenomenon.
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A neglected aspect of the study of social cognition has been the way in which people select information for further processing from the vast amount available in social environments. A major contemporary model of attention holds that there are two separate types of processes that operate concurrently: a flexible but resource-limited control process that regulates the contents of conscious awareness, and a relatively inflexible automatic process that can attract attention to stimuli without conscious intent. Passive automatic processes, can either facilitate or inhibit active attentional processing, necessitating either less or more attentional effort, depending on the characteristics of the information that is currently present. On a dichotic listening task in which subjects attended to or ignored self-relevant stimuli, it was found that self-relevant information required less attentional resources when presented to the attended channel, but more when presented to the rejected channel, relative to neutral words. This differential capacity allocation occurred despite subjects' lack of awareness of the contents of the rejected channel. The results supported the existence and interaction of the two processes of attention in social information processing.
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A theory of ironic processes of mental control is proposed to account for the intentional and counterintentional effects that result from efforts at self-control of mental states. The theory holds that an attempt to control the mind introduces 2 processes: (a) an operating process that promotes the intended change by searching for mental contents consistent with the intended state and (b) a monitoring process that tests whether the operating process is needed by searching for mental contents inconsistent with the intended state. The operating process requires greater cognitive capacity and normally has more pronounced cognitive effects than the monitoring process, and the 2 working together thus promote whatever degree of mental control is enjoyed. Under conditions that reduce capacity, however, the monitoring process may supersede the operating process and thus enhance the person's sensitivity to mental contents that are the ironic opposite of those that are intended.