Influence of content and intensity of thought on behavioral and pupil changes during active mind-wandering, off-focus, and on-task states

Mind wandering (MW) is a pervasive phenomenon that occurs very frequently, regardless of the task. A content-based definition of MW holds that it occurs when the content of thought switches from an ongoing task and/or an external stimulus-driven event to self-generated or inner thoughts. A recent account suggests that the transition between these different states of attention occurs via an off-focus state. Following this suggestion, previous work relating MW to pupil size might have lumped attentional states that are critically different from each (i.e., off-focus and MW states). In the present study, both behavior and pupil size were measured during a sustained-attention-to-response task, to disentangle the content of thought (on task or MW) from an off-focus state of mind. The off-focus state was operationalized by probing the intensity with which participants were on task or mind-wandering. The results of two experiments showed that the behavioral and phasic pupillary responses were sensitive to changes related to the content of thought. The behavioral responses were furthermore related to the intensity of the thought. However, no clear relation between the different attentional states and tonic pupillary diameter was found, suggesting that it is an unreliable proxy for MW.