A central feature of our waking mental experience is that our attention naturally toggles back and forth between "external" and "internal" stimuli. In the midst of an externally demanding task, attention can involuntarily shift internally with no clear reason how or why thoughts momentarily shifted inward. In the case of external attention, we are typically exploring and encoding aspects of our external world, whereas internal attention often involves searching for and retrieving potentially relevant information from our memory networks. Cognitive science has traditionally focused on understanding forms of internal and external attention separately, leaving a mystery about what sparks the seemingly automatic shifts between the two. Specifically, what shifts attentional focus from being outward-directed to being inward-directed? We present a candidate mechanism: Familiarity-detection.

Although mind-wandering research is rapidly progressing, stark disagreements are emerging about what the term "mind-wandering" means. Four prominent views define mind-wandering as 1) task-unrelated thought, 2) stimulus-independent thought, 3) unintentional thought, or 4) dynamically unguided thought. Although theorists claim to capture the ordinary understanding of mind-wandering, no systematic studies have assessed these claims. Two large factorial studies present participants (*N*=545) with vignettes that describe someone’s thoughts and ask whether her mind was wandering, while systematically manipulating features relevant to the four major accounts of mind-wandering. Dynamics explains between four and forty times more variance in participants’ mind-wandering judgments than other features. Our third study (*N*=153) tests and supports a unique prediction of the dynamic framework—obsessive rumination contrasts with mind-wandering. Our final study (*N*=277) used vignettes that resemble mind-wandering experiments. Dynamics had significant and large effects, while task-unrelatedness was non-significant. These results strongly suggest that the central feature of mind-wandering is its dynamics.

The recent surge of scientific research into mind-wandering has occurred amidst a definitional haze. ‘Mind-wandering’ has been used to refer to a wide range of mental phenomena, from attentional lapses to purposeful, task-unrelated planning; from free-flowing thought and creative idea generationto highly constrained, perseverative rumination. Should we continue to group these disparate phenomena under the umbrella of ‘mind-wandering’ despite the lack of scientific consensus on what mindwandering is and what it is not? Or should we treat ‘mind-wandering’ as a scientific concept in need of a rigorous theoretical definition that distinguishes it from other types of thought?

This chapter provides an introduction to the philosophy of mind-wandering. It begins with a philosophical critique of the standard psychological definitions of mind-wandering as task-unrelated thought or stimulus-independent thought. Although these definitions have helped bring mind-wandering research onto center stage in psychology and cognitive neuroscience, they have substantial limitations. They do not account for the dynamics of mind-wandering, task-unrelated thought that does not qualify as mind-wandering, or the ways in which mind-wandering can be task-related. The chapter reviews philosophical accounts that improve upon the current psychological definitions, in particular an account of mind-wandering as "unguided thinking." It critically assesses the view that mind-wandering can be defined as thought lacking meta-awareness and cognitive agency, as well as the view that mind-wandering is disunified thinking. The definition of mind-wandering as unguided thinking not only is conceptually and phenomenologically precise, but also can be operationalized in a principled way for empirical research.

An often-overlooked characteristic of the human mind is its propensity to wander. Despite growing interest in the science of mind-wandering, most studies operationalize mind-wandering by its task-unrelated contents, which may be orthogonal to the processes constraining how thoughts are evoked and unfold over time. In this chapter, we emphasize the importance of incorporating such processes into current definitions of mind-wandering, and proposing that mind-wandering and other forms of spontaneous thought (such as dreaming and creativity) are mental states that arise and transition relatively freely due to an absence of constraints on cognition. We review existing psychological, philosophical, and neuroscientific research on spontaneous thought through the lens of this framework, and call for additional research into the dynamic properties of the mind and brain.

Most research on mind-wandering has characterized it as a mental state with contents that are task unrelated or stimulus independent. However, the dynamics of mind-wandering––how mental states change over time––have remained largely neglected. Here, we introduce a dynamic framework for understanding mind-wandering and its relationship to the recruitment of large-scale brain networks. We propose that mind-wandering is best understood as a member of a family of spontaneous-thought phenomena that also includes creative thought and dreaming. This dynamic framework can shed new light on mental disorders that are marked by alterations in spontaneous thought, including depression, anxiety and attention deficit hyperactivity disorder.

Anticorrelation between the default network (DN) and dorsal attention network (DAN) is thought to be anintrinsic aspect of functional brain organization reflecting competing functions. However, the effect size offunctional connectivity (FC) between the DN and DAN has yet to be established. Furthermore, the stability ofanticorrelations across distinct DN subsystems, different contexts, and time, remains unexplored. In study 1 wesummarize effect sizes of DN-DAN FC from 20 studies, and in study 2 we probe the variability of DN-DANinteractions across six different cognitive states in a new data set. We show that: (i) the DN and DAN have anindependent rather than anticorrelated relationship when global signal regression is not used (median effectsize across studies: r=−.06; 95% CI:−.15 to .08); (ii) the DAN exhibits weak negative FC with the DN Coresubsystem but is uncorrelated with the dorsomedial prefrontal and medial temporal lobe subsystems; (iii) DN-DAN interactions vary significantly across different cognitive states; (iv) DN-DAN FCfluctuates across timebetween periods of anticorrelation and periods of positive correlation; and (v) changes across time in thestrength of DN-DAN coupling are coordinated with interactions involving the frontoparietal control network(FPCN). Overall, the observed weak effect sizes related to DN-DAN anticorrelation suggest the need to re-conceptualize the nature of interactions between these networks. Furthermore, ourfindings demonstrate thatDN-DAN interactions are not stable, but rather, exhibit substantial variability across time and context, and arecoordinated with broader network dynamics involving the FPCN.

Freely moving thought is characterized as thoughts that shift from one topic to another without any prompts or overarching directions. As this phenomenon is often linked to creative thinking and positive mood, detecting when freely moving thought occurs can ultimately help improve our creative thought processes and mood. Despite its benefits, no studies to date have attempted to detect freely moving thought using electroencephalography (EEG) signals and machine learning approaches. This is the first study to our knowledge to examine the feasibility of using event-related potential (ERP) and spectral features of EEG signals in machine learning to detect freely moving thought. To address this aim, our classification models for detecting freely moving thought relied on previously collected EEG signals while performing a simple attention task. The statistical and entropy features of the P3 ERP and alpha spectral measures were entered as inputs to the support vector machine (SVM) for detecting freely moving thoughts. EEG features were first examined with both inter-subject and intra-subject strategies. The best combination of EEG features achieving higher classification performance in both strategies were then selected to combine with behavioral features to further enhance classification performance. Our best performing model has an MCC and AUC of 0.3105 and 0.6665 for inter-subject models and 0.2815 and 0.6407 for intra-subject models respectively. The above chance level performance in both strategies using EEG and behavioral features shows great promise for machine learning approaches to detect freely moving thought and highlights their potential for real-time prediction of freely moving thought.

The science of mind-wandering has rapidly expanded over the past 20 years. During this boom, mind-wandering researchers have relied on self-report methods, where participants rate whether their minds were wandering. This is not an historical quirk. Rather, we argue that self-report is indispensable for researchers who study passive phenomena like mind-wandering. As a case study, we consider purportedly "objective" methods that measure mind-wandering with eye tracking and machine learning. These measures are validated in terms of how well they predict self-reports, which means that purportedly objective measures of mind wandering retain a subjective core. Mind-wandering science cannot break from the cycle of self-report. Skeptics about self-report might conclude that mind-wandering science has methodological foundations of sand. We take a rather more optimistic view. We present empirical and philosophical reasons to be confident in self-reports about mind-wandering. Empirically, these self-reports are remarkably consistent in their contents and behavioural and neural correlates. Philosophically, self-reports are consistent with our best theories about the function of mind-wandering. We argue that this triangulation gives us reason to trust both theory and method.

Humans spend much of their lives engaging with their internal train of thoughts. Traditionally, research focused on whether these thoughts are related to tasks or not, and have identified reliable but distinct behavioural and neural correlates of task-unrelated and task-related thought. A recent theoretical framework highlighted a different aspect of thinking – how it dynamically moves between topics. However, the neural correlates of such thought dynamics are unknown. The current study aimed to determine the electrophysiological signatures of these dynamics by recording EEG while participants performed an attention task, and periodically answered thought sampling questions about whether their thoughts were 1) task-unrelated, 2) freely moving, 3) deliberately constrained, and 4) automatically constrained. We examined three EEG measures across different time windows as a function of each thought type: stimulus-evoked P3 event-related potentials, and non-stimulus evoked alpha power and variability. Parietal P3 was larger for task-related relative to task-unrelated thoughts, whereas frontal P3 was increased for deliberately constrained compared to unconstrained thoughts. Frontal electrodes showed enhanced alpha power for freely moving thoughts relative to non-freely moving thoughts. Alpha power variability was increased for task-unrelated, freely moving, and unconstrained thoughts. Our findings indicate distinct electrophysiological patterns associated with task-unrelated and dynamic thoughts, suggesting these neural measures capture the heterogeneity of our ongoing thoughts.

Mind wandering is frequently defined as task-unrelated or perceptually decoupled thought. However, these definitions may not capture the dynamic features of a wandering mind, such as its tendency to 'move freely'. Here we test the relationship between three theoretically dissociable dimensions of thought: freedom of movement in thought, task-relatedness, and perceptual decoupling (i.e., lack of awareness of surroundings). Using everyday life experience sampling, thought probes were randomly delivered to participants’ phones for ten days. Results revealed weak intra-individual correlations between freedom of movement in thought and task-unrelatedness, as well as perceptual decoupling. Within our dataset, over 40% of thoughts would have been misclassified under the assumption that off-task thought is inherently freely moving. Overall, freedom of movement appears to be an independent dimension of thought that is not captured by the two most common measures of mind wandering. Future work focusing on the dynamics of thought may be crucial for improving our understanding of the wandering mind.

How do you measure something so elusive as a dream or mind-wandering? I follow Windt and defend an old fashioned answer. Scientists can––indeed, they must––measure dreams with introspective self-reports, which have been in use since the inception of dream research. Yet this raises a question: what is self-report so central in research on dreams and mind-wandering? I con- sider and reject an obvious answer: dream reports are methodolgically necessary because dreams are conscious experiences. I provide an alternative, action-theoretic, explanation for the special role of dream reports. Because the onset of dreaming is not under voluntary control, subjects cannot perform voluntary experimental tasks that initiate dreaming. In lieu of experimental tasks, dream researchers rely on self-report. Dream reporting is part of a broader methodological movement that I call 'task-free psychology', whose practitioners use self-report to study passive processes like dreaming and mind-wandering. Although task-free psychology holds promise, I argue that it faces a unique problem of causal inference: without tasks, it's unclear how psychologists can perform the interventions necessary to determine the effects of dreaming or mind- wandering. Drawing on action theory and interventionist theories of causation, we can better understand the motivations and limits of task-free psychology, as well as ways that the field can progress.