Cyclic variations in our vigilance

I had been unaware that our vigilance during a sustained attention task varies in a systematic way. Aue et al. have examined suggested rhythmic oscillations in the vigilance with which we maintain sustained attention by developing some continuous performance tasks:

...The current series of investigations sought to manipulate suggested periodicities of 1.5 and 5.2 min by altering task difficulty: tracking a white dot moving in a random pattern across an otherwise black computer display , administering caffeine, and testing on an ecologically valid task (simulated driving). Strong evidence of a 1.5 min periodicity was found across studies. Most participants did not demonstrate a 5.2 min periodicity. Moreover, the 1.5 min periodicity was resistant to task manipulations and appeared in similar levels across conditions in all experiments. These rhythms may be indicative of an endogenous system that modulates sustained attention in humans.