Stroop Effect test

American psychologist John Ridley Stroop published the study that made this effect famous in 1935. In his experiment, people saw a list where the ink color and the word did not match—for example, the word “yellow” printed in red.

They were asked to name the color of the ink, not the word. The idea is that the brain saves effort by reading familiar words almost automatically, so the task is hardest for people who read the language fluently: answers come more slowly, and people often mix up the written color name with the color they actually see.

The Stroop test drew a lot of attention in the United States during the Cold War, when Russian text was used: from color words printed in Cyrillic, it was relatively easy to tell whether someone actually understood the language.

This test looks very simple, but in fact only about 5% of people get through it without a single mistake.

Tasks modeled on Stroop’s experiment are still used in psychology to study cognitive flexibility—how fast you can switch from reading a word to naming a color. The difficulty comes from the clash between what you read and what you see.