Language and thought

Mind-wandering (Smallwood and Schooler, 2006) refers to the experience that thoughts rarely stand still (our train of thought, see William James). When not engaged in a complex task our thoughts flit easily from topic to topic. These experiences are referred to as mind-wandering and are usually defined by their lack of relation to the task in hand. Mind-wandering is common during driving and reading, when vigilance may not be high. In these situations, it seems that we have no memory of what happened in the surrounding environment whilst we were pre-occupied with our thoughts (Smallwood et al., 2003). Recently, mind-wandering has become a growing research topic in cognitive psychology, cognitive science and cognitive neuroscience. In particular, mindwandering refers to a sub-topic in the study of attention and consciousness, relating to times when our attention may lapse, or wander. Today's research on mind-wandering is largely based on the pioneering work of John Antrobus and Jerome Singer in the late 1960's (e.g., Antrobus et al., 1970). Mind-wandering and other private experiences can be studied using thought sampling, or simply asking participants what they are thinking about at any given moment.

From a scientific perspective, two aspects of mind-wandering are of interest. The first is understanding how the brain produces what William James referred to in the Principles of Psychology as the stream of consciousness. This research is focused on understanding how the brain generates the spontaneous and relatively unconstrained thoughts that we experience when the mind-wanders. One candidate process for generating this aspect of experience is what Marcus Raichle referred to in 2001 as the default network, which depends on regions of the frontal and parietal cortex, which are highly active even when subjects are resting with their eyes closed (see Gusnard & Raichle, 2001 for a review).

The second aspect of mind-wandering that interests scientists is what it means for our minds to process information that is unrelated to the outside environment. One way to describe this state of attention is to say that when the mind wanders awareness is decoupled from the task environment. Studies have suggested that memory for concurrently presented information is impaired when the mind wanders (Smallwood et al., 2003).

In addition to neural models, computational models of consciousness based on the Global Workspace theory (Baars, 1988, 1997) suggest that mind-wandering, or "spontaneous thought," may involve competition between internally and externally generated activities attempting to gain access to a limited capacity central network (Dehaene & Changeux, 2005).