I read a great article today:
http://www.livescience.com/othernews/060124_political_decisions.htmlTo summarize, when a strong partisan is shown a clip of his party leader speaking, the logical part of his brain goes unused; instead, the emotional part lights up, followed by activity in the "reward" part of the brain (the part linked with addictions). Further, they see no contraction in what their chosen candidate says, but they see it in what the opposed candidate says. They also see contradictions made by Tom Hanks. People who are neutral to both parties tend to notice both contradictions.
I'm glad somebody did a study like this, actually. When I hear both American candidates or both main Canadian candidates talking, it bothers me about how dishonest they are, and how much they contradict themselves. I hate politics, period.