Man who learned psychics tricks and proved them wrong?

In my psychology class we watched youtube videos on this older man who proved psychics were basically full of ****. He wrote a book and has gone on talk shows. I think he proved a guy wrong on David Letterman but i could be wrong. He also did stuidies on horoscopes and has done a bunch of tests with that. I cannot figure out what his name is. If any one knows it would be greatly appreciated!!! :D