Imaginative Guidance: A Mind Forever Wandering
IN CHAPTER 3 WE DISCUSSED THE MANY FORMS OF
prospection that are deliberate and controlled. We now turn to the kinds of prospection that are spontaneous and discursive.
Think about what goes consciously through your mind during idle moments. Thoughts of various kinds spontaneously pop into your head. You think about your recent experiences. You gaze into the future. Many of your thoughts are accompanied by images and quasi-perceptual content. The train of thoughts is discursive: It meanders from topic to topic. There are some associative connections and thematic links between successive thoughts, but there are also substantial discontinuities, leaps, and odd transitions.
This is mind-wandering, and it is deeply puzzling to theorists (Callard, Smallwood, Golchert, & Margulies, 2013; Smallwood & Schooler, 2006, 2015). The biggest puzzle is why we do so much of it. One study, which used experience sampling methods with 2,250 adults, found mind-wandering occurred in a remarkable 46.9% of the time points sampled (Killingsworth & Gilbert, 2010).
Neural evidence tells a complementary story. Mind-wandering has been tied to the default mode network, a set of brain regions that are involved in episodic memory and imagination (Buckner, Andrews-Hanna, & Schacter, 2008). This network was identified from observations of brain activation during prolonged functional imaging tasks. These tasks often provide for intermittent rest intervals, and it was noticed that during these rests, a network of midline and medial temporal lobe structures reliably turn on (Raichle & Snyder, 2007). These regions were dubbed the default network because their ongoing operation appears to be the brain's default state of activity (Raichle et al., 2001). It was subsequently shown that this network subserves mind-wandering activity (Andrews-Hanna, Reidler, Huang, & Buckner, 2010; Christoff, Gordon, Smallwood, Smith, & Schooler, 2009; Mason et al., 2007). The overall picture, then, is that when nothing else is going on, people don't simply "power down" and let their minds go idle. Rather, they engage a network of brain regions specialized for a distinctive activity: churning out discursive trains of episodes from the past and prospections into the future. The question is: Why?
An increasingly common explanation for mind-wandering says it serves the purpose of planning. Thus Jonathan Smallwood and Jessica Andrews-Hanna write:
From an evolutionary perspective, prospection allows us to simulate plausible outcomes to alternative future events, including the emotional states of ourselves and other people in response to ... events (Gilbert and Wilson, 2007). In this way self-generated thought [i.e., mind-wandering] is an adaptive process that helps us select the optimal course of action, prepare for upcoming events, and achieve our upcoming goals (Schacter et al., 2007; Suddendorf and Corballis, 2007; Suddendorf et al., 2009; Szpunar, 2010). (Smallwood & Andrews- Hanna, 2013, pp. 3-4; see original for references)
While we think Smallwood and Andrews-Hanna are right, there is a need for additional specificity in the proposal. How specifically can engaging in discursive trains of thought help to prepare us for the future? In addressing this question, there is a useful distinction to be made between planning and learning, which can be illustrated with an example.
Suppose you have a map of New York City and need to get from LaGuardia Airport to lower Manhattan. You can look at the map and plan the best route. One route takes the Long Island Expressway through Queens and crosses the Brooklyn Bridge. Another crosses Harlem and then heads down the Henry Hudson Parkway. A third route takes a bus to 145th street and then the A train south. You can evaluate these options and figure out which is best. Planning, then, takes a circumscribed body of knowledge and uses it to answer a specific action-directed question.
Learning, at least the kind of learning being emphasized here, is different; it is the process by which this body of domain knowledge is generated in the first place. Learning isn't usually done for answering a specific action-directed question. It is ultimately useful because later one can interrogate the "map" that is learned and address an open-ended array of specific action-directed questions whenever they happen to come up. But the rationale for learning can't be identified with its utility for answering any one of these specific questions; the utility of learning is far more indirect and diffuse.
We agree that people sometimes engage in prospective thought to plan for their futures and thereby achieve their goals. But notice that prospection for the purposes of deliberate planning, such as planning routes from LaGuardia to lower Manhattan, is not very much like mind-wandering. When engaged in planning, the mind doesn't discursively move from one topic to the next, following associative links (or digressively jump without any obvious links at all). In addition, planning is usually effortful. It requires sustained attention and working memory (Fincham, Carter, van Veen, Stenger, & Anderson, 2002; Newman, Carpenter, Varma, & Just, 2003), and it leaves a person cognitively fatigued (Vohs et al., 2008). Mind-wandering, in contrast, is not effortful. Trains of thought during mind-wandering occur spontaneously, without conscious supervision or control, and without placing substantial demands on attention and working memory (McVay & Kane, 2010). There thus appear to be substantial differences between mind-wandering and structured planning in terms of discursivity, phenomenology, cognitive processes, and neural substrates. This suggests that mind-wandering is unlikely to prepare us for the future by itself being a form of planning.
In this chapter, we advance the view that mind-wandering is not (directly) for planning but rather plays a pivotal role in learning;
it contributes to building a highly general "map" of the world that can later be queried for whatever specific purposes a person happens to have. More specifically, our view sees mind-wandering as involving in a highly interesting and widely underappreciated process for facilitating certain kinds of learning: the process of repeated presentation of learning examples. We will argue that in the right sort of learning contexts, presenting discursive ongoing streams of learning examples can facilitate identification of the deeper hidden patterns. We call this the "deep learning" account of mind-wandering.
We begin this chapter with an extended discussion of the complementary learning systems (CLS) model, one of the most influential views of memory to have emerged in the last several decades. In the second section, "The Extended CLS Model," we propose various refinements and extensions to the CLS model and locate mindwandering as a critical driver of deep learning within this extended model. With the third section, "Trains of Thought," we delve further into the distinctive discursive quality of mind-wandering. The fourth section provides evidence that mind-wandering enhances deep learning, and the fifth section draws links between mind-wandering and dreaming. We suggest that daydreaming and night dreaming form part of a continuum of mind-wandering states that differ importantly.