There are so many studies like this it is hard to say which one specifically he may be referring to. There is a mountain of literature on the topic; as usual, Wikipedia is a good place to start: http://en.wikipedia.org/wiki/Cognitive_dissonance
It frustrates me a little when people conflate cognitive dissonance with effects caused by dissonance reduction, like in this article. Cognitive dissonance is simply the uncomfortable experience of believing two conflicting things. Dissonance reduction is the class of biases that we use to reduce that discomfort.
