The Stroop effect relates to asking people to say what colour the font is when words are written in different colours.
For example, you might have the words RED in blue font, BLUE in green font, and GREEN in red font. Then you ask people to say what colour the font is. The information conveyed by the word RED interferes with the brain identifying and saying, "Green" and so on. You can use it to see if someone speaks a language because if the words have no meaning because you don't speak the language, there will be no interference.
Anyway, just a random fact, now recorded in a place where I can find it again by searching my LJ and another piece of paper has been put in the recycling box.