| Summary: | Mind wandering (MW) is a heterogeneous and private phenomenon, which is nonetheless omnipresent in people’s lives. Research on this phenomenon has grown considerably during the past decade, thanks also to the development of neuroimaging techniques which have given us a window into the brain’s activity while we are lost in our thoughts. However, there are still two important issues for researchers in this field. The first, is the need to evoke in an experimental setting what is, by definition, a spontaneous phenomenon. This can be solved by developing an experimental task that creates certain conditions in which MW is more or less likely to arise. The second issue is the reliance on individuals’ self-reports, which are inherently subjective, to understand the emergence, and content, of MW. This issue is harder to tackle, but one possibility is to develop a physiological, objective marker of MW. Recently, two candidates have emerged as potential markers of MW: one is the default mode network (DMN), a set of brain areas that show coordinated activity when people drift off to their inner thoughts; the second candidate is baseline pupil size, which has showed sensitivity to changes in external and internal attention, such as during episodes of MW. This thesis describes the development of a novel paradigm for the study of mind wandering, and its use to understand the potential that the DMN and baseline pupil size have as markers of this phenomenon. In three empirical studies, this paradigm successfully modulates individuals’ performance, MW, and on-task focus. Further, evidence from these studies indicates that DMN activity and baseline pupil size don’t provide sufficient precision to be used in isolation as markers of MW: in particular, it is suggested that their predictive power strongly depends on taking into account the content of the MW experience, and the context in which it occurs.
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