Although eye movements during reading have been studied extensively, their variation due to attentional fluctuations such as spontaneous distractions is not well understood. Here we used a naturalistic reading task combined with an attentional sampling method to examine the effects of mind wandering-and the subsequent metacognitive awareness of its occurrence-on eye movements and pupillary dynamics. Our goal was to better understand the attentional and metacognitive processes involved in the initiation and termination of mind wandering episodes. Our results show that changes in eye behavior are consistent with underlying independent cognitive mechanisms working in tandem to sustain the attentional resources required for focused reading. In addition to changes in blink frequency, blink duration, and the number of saccades, variations in eye movements during unaware distractions point to a loss of the perceptual asymmetry that is usually observed in attentive, left-to-right reading. Also, before self-detected distractions, we observed a specific increase in pupillary diameter, indicating the likely presence of an anticipatory autonomic process that could contribute to becoming aware of the current attentional state. These findings stress the need for further research tackling the temporal structure of attentional dynamics during tasks that have a significant real-world impact.

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