A flanker task: answer the direction of the middle arrow out of five. The gap between your mean reaction time on opposite-flanker trials and matching ones is your attentional interference.
Adult flanker effects are usually reported around 40–60 ms. Smaller means you stayed on the centre arrow instead of being pulled by its neighbours.
Below 80% accuracy the interference figure is flagged as untrustworthy — mashing either button quickly drives it toward zero.
Both measure interference, but the stimulus differs. Stroop needs you to read colour words, which ties it to a language; the flanker task only shows arrow directions, so it is the same task anywhere.
Interference is a difference between two condition means, so a handful of trials makes it noisy. Twenty per condition steadies it.
That trial counts as an error and is left out of the interference figure. Accuracy is shown separately in the result.