Respond to every digit as it flashes past — except the number 3. Simple to grasp, ruthless at exposing the moment your attention wanders.
Digits from 1 to 9 will flash by. Press GO for every single one. But when you see a 3, do nothing at all. The whole test is that one act of restraint, repeated.
The SART is deceptively hard: the steady stream builds an automatic “respond” habit, and the target asks you to break it on demand. Failing to withhold — a commission error — is a clean index of vigilance and impulse control, both of which erode fast once you're past your peak hours.
Inside a programme, sustained attention is measured on immersive reaction hardware that captures response variability far more precisely than a browser can — the tell-tale signature of an attention lapse.