Depth of the attentional blink is modulated by circadian phase; Nayantara Santhi, Todd. S. Horowitz & Jeremy. M. Wolfe; Brigham & Women's Hospital and Harvard Medical School How is attentional selection in time related to alertness? Alertness is governed by two factors: time awake, and the phase of the endogenous circadian pacemaker. These two factors are also known to affect reaction time and psychomotor vigilance, but not the rate of visual search. In this experiment, we studied circadian and time awake effects on attentional blink. We did not observe any effects on the duration of the blink. Time awake did not affect the depth of the blink, even after 36 h of sleep deprivation. However, blink depth varied with circadian phase. We conclude that the attentional dwell time may be constant over time, while attentional capacity is governed by the circadian pacemaker, independent of overall alertness.