Mind-wandering (sometimes referred to as task unrelated thought) is a topic in experimental psychology that refers to the experience that thoughts rarely remain on a single topic for a long period of time when people are not engaged in an attention-demanding task (classically referred to as the train of thought, see William James). In particular, mindwandering refers to a sub-topic in the study of attention and consciousness, relating to times when attention may lapse, or wander. Mind-wandering experiences are defined by their lack of relation to the task in hand and are more likely to occur during driving, reading and other activities where vigilance may be low. In these situations, people report having no memory of what happened in the surrounding environment whilst pre-occupied with their thoughts. Although mind-wandering was first discussed by John Antrobus and Jerome Singer in the late 1960's it has more recently become a growing research topic in cognitive psychology, cognitive science and cognitive neuroscience.
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. Another way in which mind-wandering has been studied is through the use of the sustained attention to response (SART) task originally developed by Ian Robertson and his colleagues at Trinity College, Dublin to explore deficits in executive control after lesions to the frontal lobe.
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 as the stream of consciousness. This aspect of mindwandering research is focused on understanding how the brain generates the spontaneous and relatively unconstrained thoughts that are experienced when the mind wanders. One candidate neural mechanism for generating this aspect of experience is a network of regions in the frontal and parietal cortex, which Washington University neuroscientist Marcus Raichle has dubbed the default network. This network of regions is highly active even when subjects are resting with their eyes closed suggesting a role in generating spontaneous internal thoughts.
The second aspect of mind-wandering of scientific interest is what it means for the mind 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.
In addition to neural models, computational models of consciousness based on Bernard Baars' Global Workspace theory 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.