Project Awarded: $20,160
Philosophers have long been fascinated by the stream of consciousness––thoughts, images, and bits of inner speech that dance hither and thither across the inner stage. Yet for centuries, such “mind-wandering” was deemed essentially private and thus resistant to empirical investigation. We seek to develop an understanding of mind-wandering that is philosophically precise, objectively measurable, and grounded in our knowledge of the brain.
Recent research into streams of thought has focused on a broad, overarching category called task-unrelated thought (TUT), which consists in whatever you think about when you are not focusing on the current task (Smallwood & Schooler, 2006, 2015). Building on our work in philosophy (Irving, 2016a; Irving & Thompson, in press) and theoretical neuroscience (Christoff, Irving, Fox, Spreng, & Andrews-Hanna, 2016), we have recently challenged this view. We have proposed a dynamic framework in which there are several dissociable types of streams of thought broadly and TUT specifically: a wandering subtype that freely moves between topics, as well as two subtypes whose movement is constrained. One constrained subtype is directed towards a specific goal, whereas the other is “stuck” on something emotionally or perceptually salient. We further propose that these subtypes make importantly different contributions to our mental lives, and to agency and wellbeing more broadly. For example, we propose that that the freely wandering subtype of thought specifically makes critical contributions to creativity (Christoff et al., 2016; Sripada, 2016; in press).
The current project will use novel thought sampling probes, pupillometry, and electroencephalogram (EEG) to dissociate and objectively measure the key subtypes of streams of thought. Thought sampling is a widely-used technique in mind-wandering research, in which participants are asked to rate their preceding thoughts after random interruptions (Smallwood & Schooler, 2006). Our thought sampling questions distinguish the subtypes of thinking in terms of their dynamic features: that is, whether thoughts freely wander or whether they are constrained.
Using these thought sampling questions, we investigate the neural mechanisms that produce distinct subtypes within the stream of thought and build objective markers for these subtypes. Our first experiment will use pupillometry to examine the role of the locus coeruleus norepinephrine (LC-NE) system in producing distinct subtypes of thinking (Franklin, Broadway, Mrazek, Smallwood, & Schooler, 2013; Mittner et al., 2014). We hypothesize that freely wandering thought should be conceptualized as a form of mental exploration. Since the LC-NE system has been implicated in mental exploration (Aston-Jones & Cohen, 2005; Gilzenrat, Nieuwenhuis, Jepma, & Cohen, 2010; Yu & Dayan, 2005), our experiment will therefore test whether the LC-NE system regulates mind wandering (Aston-Jones & Cohen, 2005; Gilzenrat, Nieuwenhuis, Jepma, & Cohen, 2010; Yu & Dayan, 2005). Our second experiment will use EEG to test whether mind-wandering is associated with frontal alpha signatures of creative thinking (Lustenberger, Boyle, Foulser, Mellin, & Fröhlich, 2015), rather than frontal theta signatures of cognitive control (Cavanagh & Frank, 2014). Using the temporally sensitive and multidimensional nature of EEG, we will also attempt to build machine-learning classifiers that could specifically distinguish freely wandering thought from other subtypes. Such a classifier would represent an objective and nonintrusive method for measuring the wandering mind, which could complement or replace subjective thought sampling methods.
Our project integrates philosophical analysis, subjective report, and objective brain measurements. We believe that such an interdisciplinary approach is necessary to quantify what has remained elusive for centuries: the mechanisms that structure the dynamic stream of thought.