Vigilance Decrement and Mind-Wandering: Two Sides of the Same Coin?

Background: Decrements in performance and the propensity for increased mind-wandering (i.e., task-unrelated thoughts) across time-on-task are two pervasive phenomena observed when people perform vigilance tasks. Whether vigilance decrement and mind-wandering (MW) are independent phenomena is still an open question. In the present study, we addressed such a contention by introducing two critical manipulations: increasing task demands and applying anodal high-definition transcranial direct current stimulation (HD-tDCS) over the left dorsolateral prefrontal cortex. Method Seventy-eight participants were randomly assigned to one of the four groups resulting from the factorial combination of task demand (low, high) and stimulation (anodal, sham). Participants completed the sustained attention to response task (SART), which included thought probes about intentional and unintentional MW. Moreover, we investigated the crucial role of alpha oscillations in a novel approach. By evaluating prepost resting EEG, we explored whether participant variability in the alpha power baseline predicted performance in MW and vigilance decrement related to tDCS or task demands, respectively, and whether such variability was a stable characteristic of participants. Results Our results showed that task demands exclusively affected vigilance decrement, while anodal tDCS exclusively affected the rate of MW. Critically, alpha-band activity at rest predicted tDCS-related gains in unintentional MW but not vigilance decrement and remained stable after participants completed the task. Conclusions These results suggest that vigilance decrement and MW are two independent phenomena. Additionally, the results provide the first evidence of how individual differences in alpha power at baseline may be of crucial importance in predicting the effects of tDCS on MW propensity.