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 MW occurs when the content of thought switches from an on-going task and/or 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., an off-focus and a MW state). In the current study, both behavior and pupil size were measured during a Sustained Attention to Response Task (SART) 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 MW. Results of two experiments showed that the behavioral and phasic pupillary responses were sensitive to changes related to the content of thought. Behavioral responses were furthermore related to the intensity of the thought. However, no clear relation between the different attentional states and the tonic pupillary diameter was found suggesting it is an unreliable proxy for MW.