The word that fights the ink
The word BLUE written in red ink: your reading reflex and your colour sense answer differently, and reading is faster.
Reading is so automatic it fires even when you try to ignore the word.
When the word and the ink disagree, the two answers collide; that collision costs time.
Choosing the ink anyway is attention control, and it strengthens with practice.
Then and now
Stroop's task is still administered today, in fMRI scanners and clinics; what evolved is WHY it matters: interference control is now a core executive function.
Stroop, J. R. (1935)
Where it began“Studies of interference in serial verbal reactions”
Journal of Experimental Psychology, 18, 643-662
Naming ink colours is dramatically slower when the ink spells a different colour word: the classic interference effect.
Diamond, A. (2013)
State of the art“Executive Functions”
Annual Review of Psychology, 64, 135-168
The modern framework places interference control among the three core executive functions that predict school and life outcomes.
What we do and do not claim
Stroop measures interference control in this task. Getting faster here means better focus here; we claim no more.