Part of the Thomas D. Stoker Cognitive Test Battery
What to do: Letters appear one at a time. Press the Space bar only when you see the letter X. Do nothing for any other letter.
Stay focused. The test runs for 150 letters and takes around 4 minutes. It is designed to be sustained — your attention will be tested across the whole sequence, not just the first few letters.
Speed matters too. Press as quickly as you can when you see X. Slow responses are recorded alongside missed ones.
About 30% of letters will be X.