Web site where black and white faces flash along with positive and negative words and you have to click which?

Does anyone know what web site has the photos of people of different races and they are flashed and you have to quickly click on a positive or negative word each time? It's a timed test that demonstrates that people usually have a hard time picking the positive word when looking at a photo of someone from a different race unless they take more time to correct their initial instinct. My college psychology professor showed it to us once, but I don't remember it and can't find it. Some scientists believe there is a natural instinct in us to avoid the 'other' and this test measures the extra time it takes to correct your instinct to go to the negative word when seeing a face from another race. Other scientists had a different explanation for it, but I can't remember what it was.