The stroop effect is a cool little thing my professor showed us in abnormal psychology here at the College of Wooster. What the stroop effect does is show how words can get in the way of perceptions. It was first reported in 1935 in the Journal of Experimental Psychology by John Ridley Stroop.
What we did in class differs slightly from Stroop's original experiment. In class, the professor showed us four squiggles, each a different color, blue, green, red and brown. The colors themselves don't matter too much, any four will do. He had us say the name of the color of the squiggle he pointed to with his pen aloud. He also did this with the following slides. The next page he showed us was similar, it contains groups of 3-6 jumbled letters, broken up as if they were words, in the four different colors. A third slide was then shown, using actual words colored in one of the four colors (each word was a different color). The fourth slide was the kicker, it was the word versions of the four colors, all in a different color than the word they spelt. Red would be in blue, blue in brown, etc. When the class tried to read these aloud, we all failed. No one in the class could read the color of the word without confusing it up with the word that was colored. This is believed to be due to the Automatic word recognition hypothesis.
Liveforever suggests this link, http://faculty.washington.edu/chudler/wo rds.html, instead of the previous one here, as that one no longer worked