Stimuli and timing for the transient display version of the sustained attention task. Sequence of events is shown for one non-target trial (long line stimulus) and one target trial (short line stimulus). The transient mask appeared before and after every line (both targets and non-targets) as depicted. In the stable display version, the mask was presented continuously throughout the entire 1850 ms inter-event interval (e.g., in place of the sole fixation square shown in the figure). Stimuli are shown in white for illustrative clarity, but were presented in light grey during the tasks; the fixation square was presented in red in Experiment 1 and yellow in Experiment 2. In Experiment 2, the inter-event interval varied randomly across trials (M = 1850, range = 1350–2350 ms). The fixation square was continuously visible at the center of the screen during all tasks.