Stay focused. After a random quiet period (2–10 seconds), a millisecond counter will start inside the red box. Press Space or click the box as soon as you see it counting. Your reaction time appears for one second, then the next round begins. 40 valid responses total. Pressing too early counts as a false start.
The PVT is widely used to study alertness and fatigue. Random foreperiods and lapse counts (very slow responses) make it sensitive to sleep debt and time-on-task — useful for tracking how sharp you feel, not for diagnosing disorders.
ISI varies randomly each trial (2–10 s).
Lapses are responses slower than 500 ms. False starts are key presses or clicks before the counter starts.