The present study was designed to explore whether sustained attention tasks can be adequately described by a mindlessness perspective or a limited resource perspective. One hundred and seventy six participants (88 women and 88 men) were assigned at random to one of two signal salience conditions: high and low. Performance and self-reported states, Energetic Arousal, Tense Arousal, Task-Related-Thoughts, and Task-Unrelated-Thoughts, were collected. Overall performance efficiency and the rate of the vigilance decrement were influenced by the salience level of the signal being observed. Post-task self-reports of Task-Unrelated-Thoughts were significantly related to overall performance efficiency, but not with the vigilance decrement. Post-task self-reports of Energetic Arousal were significantly related to both overall performance and the vigilance decrement. The results support a resource theory perspective in regards to the vigilance decrement and are in contradiction to the mindlessness theory in regards to the vigilance decrement.