How understanding the mind-wandering state can inform our appreciation of conscious experience
Mahiko Konishi & Jonathan Smallwood
Department of Psychology, The University of York, Heslington, United Kingdom.
Address for correspondence:
Mahiko Konishi, Department of Psychology, University of York, Heslington, York, YO10 5DD, UK.
The mind-wandering state illustrates two fundamental aspects of consciousness: its generative nature, which is reflected by the stimulus-independent content of thought that occurs when our minds wander; and metacognition, the unique capacity of the mind to reflect and understand itself. Self-generated thought, which allows us to consider people and events that are not present in the immediate environment, and metacognition, allowing us to introspect and report our inner experiences, are both essential to the scientific study of mind-wandering. Nevertheless, they also inevitably lead to specific issues that mirror more general problems in the field of consciousness research. The generative nature of consciousness makes it difficult to have direct control on the phenomenon, and the act of introspecting on inner experience has the potential to influence the state itself. We illustrate how the field of mind-wandering research can overcome these problems. Its generative nature can be understood by triangulating the objective measures (such as neural function) with subjective measures of experience and it can be manipulated indirectly by varying the demands of the external environment. Furthermore, we describe candidate covert markers for the mind-wandering state, which allow the phenomenon to be observed without direct interference, minimizing the concern that instructions to introspect necessarily change conscious experience.
Conscious experience is one of the most self-evident aspects of the human condition and yet its operation remains a mystery. There are at least two aspects of consciousness that are central to its status as a topic of scientific enquiry and that are also at the core of what makes it an empirically difficult line of investigation: its generative, stimulus-independent nature and its unique capacity to reflect and understand itself, also known as metacognition. The stimulus-independency of consciousness refers to the fact that its continuous stream of content is always active and can often be unrelated to the immediate environment . Metacognition is the capacity of consciousness to introspect its own processing, allowing people to report their inner experiences . Both stimulus independence of conscious experience and its meta-cognitive access are exemplified in the experiences that arise during the mind-wandering state.
Mind-wandering refers to the experience that attention is not always tied to an external task being performed or to stimuli in the present environment, and that instead mental content can be experienced that is generated by the individual . The mind-wandering state makes up at least 25-50% of our waking lives and shows similar features across many different cultures (such as a focus on the future) . Mind-wandering has broad implications for the human condition: for example it has been linked to disruption of comprehension of material during reading and understanding of lectures in an educational context , issues in performance of executive control tasks , or being associated with unpleasant mood . It has also been suggested to play a role in planning and creative insight .
Contemporary accounts suggests that at least two different component processes are engaged during the mind-wandering state: a decoupling process, which allows inner experience to be independent from events in the external environment; and a representational process, which provides mental content that is not directly attributable to the events in the here and now . As the representations upon which we are focused during mind-wandering are different from those related to the stimuli in the moment, these experiences are by definition stimulus independent. Moreover, the gold standard method to assess the mind-wandering state is experience sampling, which in turn depends on our capacity to introspect on our own experiences. Our capacity for meta-cognition is therefore a key element to the mind-wandering state since it is how participants share their experiences with the experimenter. The experience of mind-wandering seems to have a parallel in night dreaming. Both are forms of self-generated thought that require decoupling from the external environment; both depend on mental content that is self-generated based on prior experience.. The two phenomena also seem to rely on overlapping brain areas and networks, so that it has been suggested that dreaming is “an intensified version of mind-wandering” . Indeed, the term daydreaming might hold more scientific truth than previously assumed. Meta-cognition and stimulus independent representations are both important in other aspects of research into conscious experience and these are summarized in Figure 1, illustrating the paradigms of resting-state fMRI, continuous flash suppression (CFS), and binocular rivalry.
Challenges of Exploring the Wandering Mind - 1 - Stimulus Independence
Although stimulus independence is a hallmark of consciousness, it is also at the center of key methodological challenges in studying this aspect of the human condition. Since what we are aware of, is not always the same as the stimulus environment in which an experience occurs, the degree of mapping between the input into the system and the emergence of conscious experience can vary significantly across different situations. This is exemplified by the thoughts that occur during mind-wandering, in which external stimuli are only minimally integrated into the content of our thoughts. This independence between the stimulus environment and experience means that controlling or manipulating perception-action contingencies alone cannot isolate the neurocognitive basis of consciousness. This dissociation between input and experience is obvious in the case of the thoughts that arise during the mind-wandering state. It is an explicit assumption of researchers that the mental content that arises during the mind-wandering state is intrinsically driven and that this limits the capacity of the experimenter to directly manipulate the state . Researchers can exploit the stimulus-independent nature of the thoughts that occur during the mind wandering state experience to understand this feature of conscious experience. In a similar fashion, a number of paradigms have been developed in other fields, especially in visual awareness research, which aim to zone in on a neural correlate of consciousness (NCC) by exploiting its stimulus-independent nature. In Box 1 we briefly describe some of these paradigms, but see Axelrod et al. , and Kim & Blake for more extensive reviews of this area of investigation.
BOX 1 –The Stimulus-Independent Nature of Consciousness in Different Experimental Paradigms
To study consciousness, paradigms are needed that capture its stimulus-independent nature. In the last decade, different paradigms have been developed that explore changes in psychological or neurocognitive processing that are minimally caused by external events.
Mind-wandering studies explore how conscious attention can be devoted to representations that are independent of stimuli in the environment. Typical paradigms involve asking participants to perform tasks of varying levels of external demands and to use combinations of different types of experience sampling to assess the conditions under which conscious experience has ceased to focus on events in the environment and instead has become directed to mental content that has been self-generated by the participant. By understanding the psychological and neural features of the representations that are not directly caused by environmental stimulation, studies of the mind-wandering state can reveal the neural processes that are associated with stimulus independent conscious states.
Resting-state. Advances in cognitive neuroscience have allowed investigation of neurocognitive processes that take place during wakeful rest. Studies of resting-state assess neurocognitive function when participants have no explicit task to do. Collecting measures of neural function under conditions with no salient environmental input allows the assessment of how the brain organizes itself.
Masking paradigms provide a simple environment in which to study access to stimulus independent aspects of conscious experience. In a typical study, a target stimulus is briefly flashed for a few milliseconds, and is preceded and/or followed by another stimulus, known as a mask. By varying the presentation time of the target, mask, or the inter-stimulus interval between the two, it is possible to create conditions in which the participant’s ability to report the identity of the stimulus is at chance level. As the physical, objective features (presentation time, size, contrast, etc.) of the stimulus presented are unchanged between unseen and seen trials, it is hypothesized that the differences between the two reflect the neurocognitive basis of conscious experience of perceptual information .
Perceptualrivalry paradigms allow processes involved in shifts in conscious access to be determined. One such paradigm is binocular rivalry in which participants are presented with one image to each eye. Instead of perceiving two superimposed images, subjects usually perceive the images to alternate every few seconds. As with masking paradigms, the physical properties of the two images remain unchanged so neurocognitive changes that are correlated with changes in perception may reflect processes that are important for shifts in the content of consciousness.
Continuous Flash Suppression (CFS; ) is a particular paradigm combining aspects of binocular rivalry and masking paradigms, in which images flashed into one eye reliably suppress visual awareness of an image presented to the other eye. CFS has gained incredible traction in consciousness research because it seems to allow participants to be exposed to stimuli that do not reach consciousness for much longer durations than with classical masking or binocular rivalry paradigms, thus improving the exploration of unconscious processes.
Challenges of Studying the Wandering Mind - 2 - Introspection
The stimulus independent aspects of consciousness can be explored by exploiting the second aspect of the experience: the capacity for introspective access to the contents of awareness. The use of self-report to understand the nature of conscious experience has a long history in psychology. It is widely accepted that Wilhelm Wundt was one of the first scientist to adopt the introspective method, which he used to explore the relationship between task stimuli and an individual’s subsequent experience, although he was careful to point out that the method should only be used under carefully controlled conditions . This method was expanded and applied to experimental psychology by, among others, Alfred Binet in France, and Oswald Külpe and Karl Marbe in Germany, and Edward Titchener, who pioneered the use of introspection to understand other mental processes such as memory, thinking or attention . Indeed, Wundt original idea of a psychology experiment and the application of introspection to it, was very different from some of his students’ such as Külpe and Titchener, and in fact he was one of their harshest critics. The application of introspection in experimental psychology was then heavily criticized by the Behaviourist movement led by John Watson, which rejected it as a truly scientific methodology in favour of the study of behaviour. It was not until the 1950s with the rise of the Cognitive Revolution that introspection became a tenable scientific approach again with the development of a variety of methodologies, such as experience sampling (ES) and the think-aloud protocol , in which participants are asked to verbalize their every thought as they perform a particular task. The resulting verbal protocols are then analyzed to provide insight into how cognitive processes are organized to perform a particular task.
In mind-wandering research introspection is especially important, as the experience is often entirely unrelated to events in the here and now or any particular task being performed. This independence of a participant’s experience from any perception-action contingencies means that experience sampling is the only way to directly discern instances of spontaneous self-generated thought. The systematic investigation of the mind-wandering state using the technique of experience sampling began in the 1960’s with the pioneering work of Jerome Singer, John Antrobus and Eric Klinger and is still the gold standard in this field of research . Experience sampling refers to the systematic collection of self-reports of a participant’s ongoing experience . Online probe-caught ES requires participants to answer random or quasi-random questions regarding their experience either in the lab or in daily life . Retrospective ES involves the gathering of self-reports at the end of a task, either via questionnaires or open-ended questions. Descriptive Experience Sampling (DES; ) is a particular type of ES in which participants record their inner experiences throughout the day and then subsequently report them to the researcher in a expositional interview.
Although metacognition provides access to the stimulus independent features of conscious experience, it is not without limitations: for example, online ES is problematic because it disrupts the natural evolution of experience. By periodically interrupting participants during the course of a task, the natural dynamics of performance and of the phenomenon measured (in this case, mind-wandering). Moreover, repeatedly probing participants about their experience is likely to alert them of the key dependent variable measured by the experiment and once more, to alter its natural occurrence . Some other fundamental issues of introspective evidence are its inherent subjectivity, confabulations, the interference between cognitive processes, and the privacy of mental content: unlike objective measures, such as response times, the veracity of subjective experiences cannot be (yet) verified with additional measures. As the participant is the only one to have direct access to his/her own mental content. It is also well known that in many cases people have little introspection access to a variety of cognitive processes; for example, participants can be unaware of the real reasons that influence a decision and at the same time confabulate that another reason is the cause . Introspecting and reporting one’s own mental content also involves performing two tasks at the same time. The act of introspection, therefore, might influence the mental content that is being experienced. This could either alter the likelihood that a particular form of experience will arise, or could change the qualities that the experience will have. Finally, there are cases in which participants might be unwilling to share certain private experiences, so that their reports could be systematically biased. Participant might purposely omit to report cultural/social taboo subjects, such as an embarrassing memory or a violent or erotic fantasy, and report a more “neutral” narrative.
Studies of mind-wandering, therefore, highlight one of the fundamental paradoxes in studying conscious experience: without the capacity for metacognitive access to our experiences, studies of conscious experience would be almost impossible; however, our access to our own experience means that the method of inquiry as part of an experiment may fundamentally alter the conscious experience itself. These issues between self-reports and the mind-wandering state can be seen as arising from more general problems of a science of consciousness that relies simply on the introspective method.
Refining Methods of Measuring Mind-Wandering
In the last decade, important strides in understanding conscious experience have been made through the refinement of the method through which self-reports are collected. In the domain of mind-wandering one way that this has occurred is through the investigation of different types of mind-wandering. Work on the functional outcomes of the mind-wandering state has highlighted that it has both costs and benefits . For example, studies have shown that the mind-wandering state has costs and benefits: it affords creative and planning processes when external demands are low but can disrupt task performance when external task demands are elevated . This is known as the context-regulation hypothesis; . Other work has highlighted that the nature of the experience that emerges during mind-wandering has implications for measures of well-being, with negative or past related experiences being linked to higher unhappiness . This is known as the content-regulation hypothesis.
One reason why this complex pattern of costs and benefits may arise is because there are several, different types of experience that emerge in the mind-wandering state, each associated with unique functional outcomes, and initial ES methods were too crude to accurately differentiate between these distinctive states. For example, one fMRI investigation has directly tested the possibility that mind-wandering depends on the interaction of two orthogonal dimensions, task-relatedness and stimulus-dependency, and has distinctive neural correlates when compared to external distractions or internal, task-related thoughts . Other recent work has focused on patterns of co-variation between different aspects of the mind-wandering state using the technique of Multidimensional Experience Sampling (MDES) : this refers to the investigation of mental content through questionnaires and/or thought probes acquiring a large amount of data with questions investigating different aspects of experience, and then using dimension reduction techniques such as principal component analysis to reveal the dimensions that underlie these data. This methodology has shown to reliably reproduce certain dimensions of the content of mind wandering experience, for example patterns of temporal (future-past) thought . Using techniques that focus on co-variation between experiential features of the mind-wandering state has made it possible to identify structural patterns in experience sampling reports. These are consistent across different samples of individuals and correspond in broad terms to patterns of thought (shown in Figure 2, sub-panel A). Importantly the different categories of thought explain unique variation associated functional outcomes: measures of emotional state, physiological arousal and ongoing task performance have all been shown to vary with differences in the content of experience that arises during the mind-wandering state .
One way that the utility of experience sampling could be improved is through an assessment of the accuracy of the reports. In this regard important strides have been through the development of the meta-d’ measure , which objectively measures metacognitive sensitivity using signal detection theory (SDT). SDT was originally developed to measure stimulus discrimination accuracy independently of response bias : in standard stimulus discrimination experiments, participants are involved in forced-choice tasks (known as the “type 1 task”), classifying a range of stimuli. On top of this, participants can be asked to classify their confidence level on the response they just made (type 2, or metacognitive task). SDT can be applied to both tasks to get a measure of participants’ sensitivity in the stimulus discrimination (type I d-prime) or metacognitive task (type 2 d-prime): Maniscalco & Lau extended this method by “characterizing the observed type 2 sensitivity as the value of d’ that a metacognitively optimal observer would have required to produce the empirically observed type 2 data”. In this sense, meta-d’ is a measure of type 2 sensitivity expressed at the level of type 1 d’, or in other words, a measure of the signal that is available to the subject to perform the type 2, metacognitive, task and is not influenced by either response bias or type 1 sensitivity.
The development of meta-d’ has revolutionised the understanding of metacognition because through a process of triangulation with objective neurocognitive markers, it has revealed the complex and heterogeneous nature of the metacognitive state. Fleming and colleagues found evidence for a neural substrate of metacognitive ability for perceptual decision-making in a region of rostro-lateral prefrontal cortex. Building on these findings, it has been identified that metacognition for different aspects of experience depend on different neural substrates (see Figure 2, subpanel B, showing different neural substrates for meta-cognition of perception, and memory) . Intriguingly, the integrity of key aspects of the default mode network (DMN, the medial pre-frontal cortex, precuneus and the inferior parietal lobule) determines an individual’s metacognitive accuracy for information from memory , an observation that is important for understanding the role of the DMN in the mind-wandering state (see Box 3: Open Questions).
Triangulation as a method for understanding conscious experience
Although it is possible to refine measures of ES, the inherent limitations of this approach mean that it will be necessary to develop measures that provide a proximal measure of conscious experience without requiring participants to actively report on the contents of their experience. Ultimately, it is only with this development that it is possible to address whether the act of introspection as part of the experimental procedure produces the effects that are measured by the paradigm. One way that this could be achieved is to explore the neural basis of the experiences that subjective reports are used to assess, the so-called neural correlate of consciousness. By pairing subjective reports with neurocognitive measures, it may be possible to develop techniques that infer inner mental states without relying on introspection.
The combination of objective and subjective information is referred to as the process of triangulation . Borrowing this term from the field of land surveying, triangulation refers to the pairing of subjective reports with behavioural and physiological measures, in order to minimize the weaknesses, and maximize the strengths of each type of measure. In mind-wandering research, triangulation can be achieved in different ways. For example it is known that mind-wandering is more common in easy or practiced tasks and behavioural performance is usually spared in these cases. This well documented situational modulation of the mind-wandering state allows researchers to explore objective neurocognitive measures in non-demanding conditions, or at rest, as a proximal measure of the mind-wandering state. In principle, these gross situational variations can be compared to online measures of ES to explore similarities in objective measures (such as the BOLD signal).
A second way to use triangulation in mind-wandering research is to exploit the capacity for these experiences to disrupt performance on a wide range of demanding tasks ; even when performance is not completely disrupted, there is evidence that mind-wandering episodes alter behavioural performance in other ways, such as increasing response variability . Under demanding conditions, if a participant reports an episode of mind-wandering and her performance in that period was also impaired, this would provide supporting evidence that attention was decoupled from events in the here and now.
Reports can be further corroborated by the use of different physiological or neurocognitive measures. Using fMRI, it is now well known that mind-wandering is linked to activity of the default mode network (DMN), a large scale network anchored by hubs on the anterior and posterior medial surface of the cortex . Similarly, differences between periods of on task versus mind-wandering periods have been found using EEG , pupillometry and eye movements or blinks . Following our example, if a participant’s report of a mind-wandering episode in an MRI scanner was accompanied by poor task performance, heightened baseline pupil dilation and concurrent activation of the default mode network, this triangulation of physiology, behaviour, experience and neural processing would provide converging evidence that attention was decoupled from the events in the here and now. Figure 3 illustrates four examples on how different methods of ES, such as online probes vs. retrospective questionnaires, can be paired with different neurocognitive measures, such as Electroencephalography (EEG) and Pupillometry.
The process of triangulation is important in other paradigms that explore conscious awareness, as for example with the combination of the binocular rivalry paradigm with pupillometry and optokinetic nystagmus (OKN) measures in a study by Frässle and colleagues . Using this technique, they showed that the OKN and pupil diameter were reliably tracking rival alternating percepts, as measured by participants’ reports. Furthermore, they showed that the act of reporting modulated both the speed of rival percepts alternation and the activation of frontal brain areas, which could be dissociated by pure rivalry alternations and seemed to reflect only the act of introspection and reporting. Their conclusions focus on three key points: 1) they could track a subjective experience (the alternation of rival percepts) using only objective measures (OKN and pupillometry), 2) the act of reporting changed the experience itself, by accelerating the alternation of percepts, and 3) much of the frontal brain activation present in fMRI binocular rivalry studies could be explained simply by self-monitoring and the act of reporting, and not the phenomenon itself.
The discussion on the advantages and disadvantages of using participants’ reports in consciousness research has received a lot of attention in the last few decades , and while the development of an objective marker of conscious experience is necessary to advance the field, subjective reports remain the gold standard for accessing participants’ inner experiences. Moving towards a covert marker of the mind-wandering state requires that research focus on how accurately people can introspect on the contents of their experience. It is possible that incorporating techniques of hypnosis could help in maximizing participants’ differences between their external vs. internal awareness, and shed light on the role of meta-awareness in self-generated thought, as was shown in a recent study . Nevertheless, another recent study suggests that participants have reasonable metacognitive access to their experience; the combination of this method with behavioral measures linked to the mind-wandering state can help to define an objective marker of conscious experience in the near future, in a way similar to Frässle and colleagues’ study.
The Mind-Wandering State as a Paradigm for Assessing Conscious Experience
It is clear that canonical features of conscious experience (stimulus independency and metacognitive access) that are the core of its value as a topic of investigation are also central to the empirical challenges that it poses as an experimental phenomenon. It is equally apparent that the mind-wandering state embodies both features of conscious experience in a manner that can be readily accessed in the real world as well as under controlled laboratory conditions. This combination of the applicability of the mind-wandering state to consciousness research with the empirical tractability of its investigation means that it provides a powerful paradigm to understand the conscious state (Box 2).
BOX 2 – Capturing the wandering mind
The mind-wandering state is a common example of a conscious state that involves both stimulus-independence and metacognition that is common in daily life. There are at least three ways that mind-wandering can provide a useful paradigm to understand key aspects of conscious experience.
Comparison of situational modulation and transient occurrence. The thoughts and feelings that emerge in the mind wandering state are transient changes motivated by intrinsic processes and this spontaneous feature of the experience makes it hard to understand. Studies, however, have shown that participants moderate the occurrence of unrelated thoughts as the complexity of an external task increases (context-regulation hypothesis). The situational modulation of the mind-wandering state allows the researcher to exert indirect control over the occurrence of the mind-wandering state and so develop more causal accounts of the experience.
Combining online and retrospective experience sampling. Online and retrospective measures of ES both provide ways to access subjective aspects of experience; however they both have different weaknesses. Online ES is disruptive of the natural dynamics of a task, whereas Retrospective ES is limited in temporal specificity since it relies on a person’s memory. Complementary experimental findings from different ES techniques, however, cannot be the result of limitations in either approach and so provide a less biased method of exploring the mind-wandering state.
Combination of objective and subjective markers Subjective measures of experience remain the gold standard measure of the mind-wandering state, however, in isolation these cannot be verified. Studies have shown that the mind-wandering state has objective behavioural and neural correlates . Common neural markers associated with both experiential measures of mind-wandering and its associated behavioural consequences, allow researchers to identify verifiable accounts of this aspect of conscious experience.
We have developed a paradigm that takes advantage of how the mind-wandering state can be assessed in the laboratory . In a recent version of this paradigm (illustrated in Figure 4) participants alternate between task blocks that require constant external attention (1-back) and blocks that only require rare, highlighted moments of external attention in order to be performed successfully (0-back). This manipulation allows the occurrence of mind-wandering to be manipulated indirectly. Performance failure on the 1-back condition reflects periods when explicit maintenance of the task fails allowing for objective indicators that attention is decoupled form the tasks. The task can be combined with different measures of neurocognitive functioning (such as functional magnetic resonance imaging, pupillometry) allowing objective information to be gained on the status of ongoing cognitive processing. Finally, in this paradigm experience can be measured using both online and retrospective ES. In combination with objective indicators this would allow the identification of covert markers of the mind-wandering state that could not be determined by the act of introspection.
BOX 3 – Open Questions
Although recent work has identified important aspects of how the mind-wandering state can inform our understanding of conscious experience, there are several important questions that remain unanswered:
What is the link between metacognition and mind-wandering? A number of studies have shown that metacognitive awareness is implicated in the regulation of mind wandering and also in the capacity to report it effectively. It is also possible that the capacity to engage in self-generated thought in the first place is a metacognitive process. Experiencing thoughts about the future, for example, depends upon being aware of representations generated from stored knowledge and studies have shown that a similar network is implicated in this process as is involved in the effective meta cognition of information from memory . This evidence suggests that the process of conscious attention to thoughts and feelings during the mind-wandering state may be inherently metacognitive in nature.
Neural substrates of stimulus independent aspects of consciousness. Is there a general neural substrate of stimulus-independency regardless of the content? The neural substrates for metacognition seem to be domain specific . Studies of brain organisation at rest suggest that most neural systems exhibit structured activity in the absence of an external task. These two lines of evidence suggest that stimulus independency may be a mode of cortical function rather than a property of a specific neural system.
The functions of stimulus independent cognition. Initial work exploring mind-wandering focused on its negative role in on-going tasks such as reading . More recent work has demonstrated that there are beneficial aspects of the experience such as creativity and planning. Understanding the functional benefits that emerge from the mind-wandering state will be important in identifying the value that the stimulus independent aspect of conscious experience brings to the organism.
The experiences that emerge in the mind-wandering state illustrate that the contents of conscious experience can be dissociated from the environment within which it is embedded (stimulus independence) as well as underlining that we have introspective access to this aspect of experience (metacognition). Since it can be studied easily in the laboratory and in daily life, the mind-wandering state provides a paradigm in which consciousness can be understood in an ecologically valid manner. Advances in experience sampling techniques have confirmed the heterogeneity of the mind-wandering state in terms of its functional outcomes while advances in neuroimaging have revealed the underlying mechanisms that support these aspects of experience. Importantly, the technique of triangulating between experiential and neurocognitive measures holds the promise of identifying covert markers that describe the contents of consciousness without relying solely on the introspective process. Building on these advances, the continuing development of our understanding of the mind-wandering state will illuminate how we escape the constraints of our immediate environment and, since this state makes an important contribution both to normal and abnormal functioning, it will help understand the functional role that conscious experience plays in our lives.
1. Smallwood J, Schooler JW: The science of mind wandering: empirically navigating the stream of consciousness.Annual review of psychology 2015, 66:487-518.
2. Singer JL: Daydreaming: An introduction to the experimental study of inner experience. 1966.
3. Singer JL: Experimental studies of ongoing conscious experience.Experimental and theoretical studies of consciousness 1993, 174:100-122.
4. Pope K: The stream of consciousness: Scientific investigations into the flow of human experience. Springer Science & Business Media; 2013.
5. Smallwood J: Distinguishing how from why the mind wanders: a process–occurrence framework for self-generated mental activity.Psychological Bulletin 2013, 139:519.
6. ANTROBUS JS, Singer JL, GREENBERG S: Studies in the stream of consciousness: experimental enhancement and suppression of spontaneous cognitive processes.Perceptual and Motor Skills 1966, 23:399-417.
7. Giambra LM: The influence of aging on spontaneous shifts of attention from external stimuli to the contents of consciousness.Experimental Gerontology 1993, 28:485-492.
8. Wegner DM: Why the mind wanders.Scientific approaches to consciousness 1997:295-315.
9. Flavell JH: Metacognition and cognitive monitoring: A new area of cognitive–developmental inquiry.American psychologist 1979, 34:906.
10. Metcalfe JE, Shimamura AP: Metacognition: Knowing about knowing. The MIT Press; 1994.
11. Nelson TO: Consciousness and metacognition.American psychologist 1996, 51:102.
12. Koriat A: Metacognition and consciousness. Institute of Information Processing and Decision Making, University of Haifa; 2006.
13. Smith JD: The study of animal metacognition.Trends in cognitive sciences 2009, 13:389-396.
14. Kane MJ, Brown LH, McVay JC, Silvia PJ, Myin-Germeys I, Kwapil TR: For whom the mind wanders, and when an experience-sampling study of working memory and executive control in daily life.Psychological science 2007, 18:614-621.
15. Killingsworth MA, Gilbert DT: A wandering mind is an unhappy mind.Science 2010, 330:932-932.
16. Singer JL, McCraven VG: Some Characteristics of Adult Daydreaming.The Journal of Psychology 1961, 51:151-164.
17. Giambra LM, Stone BS: Australian-American differences in daydreaming, attentional processes, and curiosity: First findings based on retrospective reports.Imagination, Cognition and Personality 1982, 2:23-35.
18. Giambra LM: Daydreaming: A Black–White comparison for 17–34-year-olds.Journal of Personality and Social Psychology 1982, 42:1146.
19. Song X, Wang X, Krueger F: Mind wandering in Chinese daily lives–an experience sampling study.PLoS One 2012, 7:e44423.
20. Dixon P, Bortolussi M: Construction, integration, and mind wandering in reading.Canadian Journal of Experimental Psychology/Revue canadienne de psychologie expérimentale 2013, 67:1.
21. Smallwood J: Mind‐wandering while reading: Attentional decoupling, mindless reading and the cascade model of inattention.Language and Linguistics Compass 2011, 5:63-77.
22. Smallwood J, Fishman DJ, Schooler JW: Counting the cost of an absent mind: Mind wandering as an underrecognized influence on educational performance.Psychonomic Bulletin & Review 2007, 14:230-236.
23. Szpunar KK, Khan NY, Schacter DL: Interpolated memory tests reduce mind wandering and improve learning of online lectures.Proceedings of the National Academy of Sciences 2013, 110:6313-6317.
24. Mrazek MD, Smallwood J, Franklin MS, Chin JM, Baird B, Schooler JW: The role of mind-wandering in measurements of general aptitude.Journal of Experimental Psychology: General 2012, 141:788.
25. Smallwood J, Fitzgerald A, Miles LK, Phillips LH: Shifting moods, wandering minds: negative moods lead the mind to wander.Emotion 2009, 9:271.
26. Smallwood J, O'Connor RC: Imprisoned by the past: unhappy moods lead to a retrospective bias to mind wandering.Cognition & emotion 2011, 25:1481-1490.
27. Poerio GL, Totterdell P, Miles E: Mind-wandering and negative mood: Does one thing really lead to another?Consciousness and cognition 2013, 22:1412-1421.
28. Baird B, Smallwood J, Schooler JW: Back to the future: autobiographical planning and the functionality of mind-wandering.Consciousness and cognition 2011, 20:1604-1611.
29. Smallwood J, Schooler JW, Turk DJ, Cunningham SJ, Burns P, Macrae CN: Self-reflection and the temporal focus of the wandering mind.Consciousness and Cognition 2011, 20:1120-1126.
30. Ruby FJ, Smallwood J, Sackur J, Singer T: Is self-generated thought a means of social problem solving?Frontiers in psychology 2013, 4.
31. Baird B, Smallwood J, Mrazek MD, Kam JW, Franklin MS, Schooler JW: Inspired by distraction mind wandering facilitates creative incubation.Psychological Science 2012:0956797612446024.
32. Kam JW, Handy TC: The neurocognitive consequences of the wandering mind: a mechanistic account of sensory-motor decoupling.Frontiers in psychology 2013, 4.
33. Fox KC, Nijeboer S, Solomonova E, Domhoff GW, Christoff K: Dreaming as mind wandering: evidence from functional neuroimaging and first-person content reports.Frontiers in human neuroscience 2013, 7.
34. Chalmers DJ: 2 What Is a Neural Correlate of Consciousness?Neural correlates of consciousness: Empirical and conceptual questions 2000:17.
35. Axelrod V, Bar M, Rees G: Exploring the unconscious using faces.Trends in cognitive sciences 2015, 19:35-45.
36. Kim C-Y, Blake R: Psychophysical magic: rendering the visible ‘invisible’.Trends in cognitive sciences 2005, 9:381-388.
37. Dehaene S: Conscious and nonconscious processes: distinct forms of evidence accumulation.Better than conscious 2008:22-49.
38. Kouider S, Dehaene S: Levels of processing during non-conscious perception: a critical review of visual masking.Philosophical Transactions of the Royal Society of London B: Biological Sciences 2007, 362:857-875.
40. Danziger K: The history of introspection reconsidered.Journal of the History of the Behavioral Sciences 1980, 16:241-262.
41. Schultz D, Schultz S: A modern history of psychology.A modern history of psychology 2000.
42. Costall A: ‘Introspectionism’and the mythical origins of scientific psychology.Consciousness and Cognition 2006, 15:634-654.
43. Van Someren MW, Barnard YF, Sandberg JA: The think aloud method: A practical guide to modelling cognitive processes. Academic Press London; 1994.
44. Kahneman D, Krueger AB, Schkade DA, Schwarz N, Stone AA: A survey method for characterizing daily life experience: The day reconstruction method.Science 2004, 306:1776-1780.
45. Hurlburt RT, Akhter SA: The descriptive experience sampling method.Phenomenology and the Cognitive Sciences 2006, 5:271-301.
46. Seli P, Carriere JS, Levene M, Smilek D: How few and far between? Examining the effects of probe rate on self-reported mind wandering.Frontiers in psychology 2013, 4.
47. Nisbett RE, Wilson TD: Telling more than we can know: verbal reports on mental processes.Psychological review 1977, 84:231.
48. Johansson P, Hall L, Sikström S, Olsson A: Failure to detect mismatches between intention and outcome in a simple decision task.Science 2005, 310:116-119.
49. Stawarczyk D, Majerus S, Maj M, Van der Linden M, D'Argembeau A: Mind-wandering: phenomenology and function as assessed with a novel experience sampling method.Acta psychologica 2011, 136:370-381.
50. McVay JC, Kane MJ: Drifting from slow to “d'oh!”: Working memory capacity and mind wandering predict extreme reaction times and executive control errors.Journal of Experimental Psychology: Learning, Memory, and Cognition 2012, 38:525.
51. Smallwood J, Andrews-Hanna J: Not all minds that wander are lost: the importance of a balanced perspective on the mind-wandering state.Frontiers in psychology 2013, 4.
52. Stawarczyk D, Majerus S, Maquet P, D'Argembeau A: Neural correlates of ongoing conscious experience: both task-unrelatedness and stimulus-independence are related to default network activity.PloS one 2011, 6:e16997.
53. Ruby FJ, Smallwood J, Engen H, Singer T: How self-generated thought shapes mood—the relation between mind-wandering and mood depends on the socio-temporal content of thoughts.PLoS One 2013, 8:e77554.
54. Gorgolewski KJ, Lurie D, Urchs S, Kipping JA, Craddock RC, Milham MP, Margulies DS, Smallwood J: A correspondence between individual differences in the brain's intrinsic functional architecture and the content and form of self-generated thoughts. 2014.
55. Maniscalco B, Lau H: A signal detection theoretic approach for estimating metacognitive sensitivity from confidence ratings.Consciousness and cognition 2012, 21:422-430.
57. Fleming SM, Dolan RJ: The neural basis of metacognitive ability.Philosophical Transactions of the Royal Society of London B: Biological Sciences 2012, 367:1338-1349.
58. Fleming SM, Huijgen J, Dolan RJ: Prefrontal contributions to metacognition in perceptual decision making.The Journal of Neuroscience 2012, 32:6117-6125.
59. Fleming SM, Weil RS, Nagy Z, Dolan RJ, Rees G: Relating introspective accuracy to individual differences in brain structure.Science 2010, 329:1541-1543.
60. Baird B, Smallwood J, Gorgolewski KJ, Margulies DS: Medial and lateral networks in anterior prefrontal cortex support metacognitive ability for memory and perception.The Journal of Neuroscience 2013, 33:16657-16665.
61. Baird B, Mrazek MD, Phillips DT, Schooler JW: Domain-specific enhancement of metacognitive ability following meditation training.Journal of Experimental Psychology: General 2014, 143:1972.
62. McCurdy LY, Maniscalco B, Metcalfe J, Liu KY, de Lange FP, Lau H: Anatomical coupling between distinct metacognitive systems for memory and visual perception.The Journal of Neuroscience 2013, 33:1897-1906.
63. Schooler J, Schreiber CA: Experience, meta-consciousness, and the paradox of introspection.Journal of consciousness studies 2004, 11:17-39.
64. Teasdale JD, Dritschel BH, Taylor MJ, Proctor L, Lloyd CA, Nimmo-Smith I, Baddeley AD: Stimulus-independent thought depends on central executive resources.Memory & cognition 1995, 23:551-559.
65. Mason MF, Norton MI, Van Horn JD, Wegner DM, Grafton ST, Macrae CN: Wandering minds: the default network and stimulus-independent thought.Science 2007, 315:393-395.
66. Franklin MS, Smallwood J, Schooler JW: Catching the mind in flight: using behavioral indices to detect mindless reading in real time.Psychonomic Bulletin & Review 2011, 18:992-997.
67. Schooler JW: Zoning Out while Reading: Evidence for Dissociations between Experience and Metaconsciousness Jonathan W. Schooler, Erik D. Reichle, and David V. Halpern.Thinking and seeing: Visual metacognition in adults and children 2004:203.
68. Feng S, D’Mello S, Graesser AC: Mind wandering while reading easy and difficult texts.Psychonomic bulletin & review 2013, 20:586-592.
69. Seli P, Cheyne JA, Smilek D: Wandering minds and wavering rhythms: linking mind wandering and behavioral variability.Journal of Experimental Psychology: Human Perception and Performance 2013, 39:1.
70. Bixler R, D'Mello S: Detecting boredom and engagement during writing with keystroke analysis, task appraisals, and stable traits. In Proceedings of the 2013 international conference on Intelligent user interfaces. ACM; 2013: 225-234.
71. McKiernan KA, D'Angelo BR, Kaufman JN, Binder JR: Interrupting the “stream of consciousness”: an fMRI investigation.Neuroimage 2006, 29:1185-1191.
72. Andrews-Hanna JR, Reidler JS, Huang C, Buckner RL: Evidence for the default network's role in spontaneous cognition.Journal of neurophysiology 2010, 104:322-335.
73. Allen M, Smallwood J, Christensen J, Gramm D, Rasmussen B, Jensen CG, Roepstorff A, Lutz A: The balanced mind: the variability of task-unrelated thoughts predicts error monitoring.Frontiers in human neuroscience 2013, 7.
74. Konishi M, McLaren DG, Engen H, Smallwood J: Shaped by the Past: The Default Mode Network Supports Cognition that Is Independent of Immediate Perceptual Input.PloS one 2015, 10:e0132209.
75. Cunningham S, Scerbo MW, Freeman FG: The electrocortical correlates of daydreaming during vigilance tasks.Journal of Mental Imagery 2000.
76. Barron E, Riby LM, Greer J, Smallwood J: Absorbed in thought the effect of mind wandering on the processing of relevant and irrelevant events.Psychological science 2011.
77. Smallwood J, Beach E, Schooler JW, Handy TC: Going AWOL in the brain: Mind wandering reduces cortical analysis of external events.Journal of cognitive neuroscience 2008, 20:458-469.
78. Baird B, Smallwood J, Lutz A, Schooler JW: The decoupled mind: mind-wandering disrupts cortical phase-locking to perceptual events.Journal of cognitive neuroscience 2014.
79. Smallwood J, Brown KS, Tipper C, Giesbrecht B, Franklin MS, Mrazek MD, Carlson JM, Schooler JW: Pupillometric evidence for the decoupling of attention from perceptual input during offline thought.PloS one 2011, 6:e18298.
80. Franklin MS, Broadway JM, Mrazek MD, Smallwood J, Schooler JW: Window to the wandering mind: Pupillometry of spontaneous thought while reading.The Quarterly Journal of Experimental Psychology 2013, 66:2289-2294.
81. Smallwood J, Brown KS, Baird B, Mrazek MD, Franklin MS, Schooler JW: Insulation for daydreams: a role for tonic norepinephrine in the facilitation of internally guided thought.PloS one 2012, 7:e33706-e33706.
82. Bixler R, D’Mello S: Toward Fully Automated Person-Independent Detection of Mind Wandering. In User Modeling, Adaptation, and Personalization. Springer; 2014: 37-48
84. Smilek D, Carriere JS, Cheyne JA: Out of mind, out of sight eye blinking as indicator and embodiment of mind wandering.Psychological Science 2010, 21:786-789.
85. Frässle S, Sommer J, Jansen A, Naber M, Einhäuser W: Binocular rivalry: frontal activity relates to introspection and action but not to perception.The Journal of Neuroscience 2014, 34:1738-1747.
86. Tsuchiya N, Wilke M, Frässle S, Lamme VA: No-Report Paradigms: Extracting the True Neural Correlates of Consciousness.Trends in Cognitive Sciences 2015, 19:757-770.
87. Demertzi A, Vanhaudenhuyse A, Noirhomme Q, Faymonville M-E, Laureys S: Hypnosis modulates behavioural measures and subjective ratings about external and internal awareness.Journal of Physiology-Paris 2015.
88. Seli P, Jonker TR, Cheyne JA, Cortes K, Smilek D: Can research participants comment authoritatively on the validity of their self-reports of mind wandering and task engagement? 2015.
89. Schooler JW, Smallwood J, Christoff K, Handy TC, Reichle ED, Sayette MA: Meta-awareness, perceptual decoupling and the wandering mind.Trends in cognitive sciences 2011, 15:319-326.
90. Schooler JW: Re-representing consciousness: Dissociations between experience and meta-consciousness.Trends in cognitive sciences 2002, 6:339-344.
91. Fox KC, Christoff K: Metacognitive facilitation of spontaneous thought processes: when metacognition helps the wandering mind find its way. In The cognitive neuroscience of metacognition. Springer; 2014: 293-319
92. Smith SM, Fox PT, Miller KL, Glahn DC, Fox PM, Mackay CE, Filippini N, Watkins KE, Toro R, Laird AR: Correspondence of the brain's functional architecture during activation and rest.Proceedings of the National Academy of Sciences 2009, 106:13040-13045.
94. Kam JW, Dao E, Farley J, Fitzpatrick K, Smallwood J, Schooler JW, Handy TC: Slow fluctuations in attentional control of sensory cortex.Journal of cognitive neuroscience 2011, 23:460-470.
Figure 1 – The Stimulus-Independent Nature of Consciousness
A) Regions of the default mode network (DMN) activate during mind wandering. Data taken from . B) The same network shows co-ordinated activity during wakeful rest, in the absence of any particular task. Data taken from . C) In continuous flash suppression (CFS) paradigm participants are consciously unaware of a stimulus presented to one eye as it becomes masked by another stimulus presented to the other eye. D) In binocular and perceptual rivalry paradigms (subpanels a) and b), respectively), what is consciously perceived changes even though the stimulus itself remains unchanged. The effects of the two paradigms correlate in individuals (subpanels c) and d)). Figure taken from .
Figure 2 – Refining measures of introspection
A) Applying statistical methods such as principal component analysis to multidimensional experience sampling (MDES) data, shows that self-generated thought has a stable internal structure. Data taken from two different samples of healthy adults (n=87 & n= 64 respectively) see for details of the method. B) Metacognition for perception and memory depend on different neural substrates and are not correlated across individuals. Figure adapted from . C) By combining MDES and neurocognitive measures, it is possible to investigate the neural substrates of different types of self-generated thought, such as future- and past-related thought. Figure adapted from .
Figure 3 – Experience Sampling (ES) and Neurocognitive Measures
A) The amplitude of a positive event-related potential, the P3, as measured through EEG, is reduced during periods of off-task thought compared to on-task, as measured through online ES. Figure adapted from . B) Online ES can also be paired with pupillometry, showing larger pupil dilation in period of off-task thought compared to on-task. Figure adapted from . C) Retrospective ES shows reduced evoked responses to target stimuli during off-task thought. Figure adapted from . D) Pairing of retrospective ES and pupillometry, showing a relation between mind-wandering, reaction times and pupil dilation. Figure taken from .
Figure 4 – Mind-Wandering Paradigm, Behavioral and fMRI Results
A) Participants alternate between a 0-back task, which allows and induces mind-wandering, and a 1-back task, which requires constant on-task focus. B) Participants performing the easier, 0-back task, have higher accuracy, lower RTs, and are less on task, as measured through online thought-probes. C) Key areas of the default mode network are active during periods of 0-back task. Figure taken from .