This week, NPR senior correspondent Juan Williams was fired, after saying on "The O'Reilly Factor" that he was fearful when seeing passengers dressed in Muslim garb aboard airplanes.
Williams may not be alone in feeling this way — but saying those things are a different matter. How do these stereotypes get into our minds? And what happens when a person crosses the line between thinking something and saying it?
Valerie Purdie-Vaughns studies what we say about the way we think. She runs the Intergroup Relations & Diversity Laboratory at Columbia University.