Remember those ads attacking Michael Ignatieff - "he didn't come back for you" - that the Conservatives released earlier this year? Ever since they appeared, I've been conducting a little experiment. The results are in. But first, some background: Everyone knows political ads are produced by spin doctors. Everyone knows spin doctors are, shall we say, more concerned with influencing the audience than being fair and factual. And everyone knows that spin doctors often sucker some people. Of course, by "some people" we mean "other people." Not us. People who fall for political spin tend to be stupid and ignorant. We are smart and informed. And being smart and informed protects us from hucksters. Or so lots of people think, unfortunately. Heaps of research shows that intelligence and knowledge are not, in themselves, effective defences against snake oil salesmen. Indeed, smart and informed people may actually be at greater risk of buying bunkum. My little experiment is a demonstration of this uncomfortable truth. (For the record, this is not a shot at Conservatives. All parties have run misleading attack ads and what I'm about to describe is a phenomenon that can be found among partisans of all stripes.) In one of the Conservative ads, a sombre voice mentions several allegedly unpatriotic statements Michael Ignatieff has made, concluding with: "He even called our peacekeeping reputation 'entirely bogus.'" On-screen, that claim appears in stark white letters on a black background, along with a source. "Maclean's, July 17, 2009," it says. It's easy to find that article. Even Googling "entirely bogus" and "Maclean's" will do it. What the article says is that, in 2005, Ignatieff gave a lecture in Dublin. At the time, he was the director of the Carr Center for Human Rights Policy at Harvard University. In the lecture, Ignatieff defended the United States as a force for good in the world and argued that protecting the world's most vulnerable people takes "men with guns." In response to a question about peacekeeping, Ignatieff said Canada is trading on its "entirely bogus reputation as peacekeepers," noting that "we used to be peacekeepers, we used to have the capabilities (but) we gave them away. ... If you are a human rights defender and you want to stop (a) massacre, you have to go to the Pentagon, because no one else is serious. ... It's disgusting in my own country, and I love my country, Canada, but they would rather bitch about their rich neighbour to the south than actually pay the note." So to sum up, Ignatieff respects the United States, denounces cuts to the Canadian military, and wants to see Canadian soldiers and other "men with guns" protect defenceless people. He also says he loves his country. Stephen Harper could have given that speech to a Conservative convention. And got a standing ovation. So here's the experiment: What happens when a Conservative ad rips the Liberal leader for making a comment which, read in context by a Conservative, would make Conservatives leap to their feet and cheer? Answer: nothing. I can't find any Conservative reaction. No backlash against the spin doctors who made the ad. No anger at the party for approving it. And certainly no Conservative saying they thought a little better of Michael Ignatieff. So what happened? In a phrase, "confirmation bias." All people tend to embrace without question information that squares with existing beliefs, but the strength of this bias varies according to the strength of the existing belief. Thus, if you are a fiercely committed Conservative and you see a shot at the Liberal leader, that's good enough. It doesn't occur to you to ask if it makes sense, much less to Google the source. And what sort of person is more likely to be a fiercely committed partisan? Not the stupid and ignorant. They're more likely to be apathetic. It's the smart and informed. Fine, you may think. Smart and informed partisans may not question information that supports their beliefs. But what happens when contrary information is put under their noses? Surely then they will revise their opinions accordingly. Well, we can test that now. After reading this column, will any fiercely committed Conservative partisans read the Maclean's article, protest their party's misleading ad, and change their opinion of Michael Ignatieff? No. They will rationalize: They will stitch together an explanation that allows them to see the Conservative ad as less misleading than it is and Ignatieff's comments as less simpatico than they are. Once they have that, their cognitive dissonance will melt like snow in the sun. Everyone can cobble together self-serving explanations but some are better at it than others. The superior rationalizers? Again, it's not the stupid and ignorant. It's the smart and informed. Of course there are plenty of smart and informed people who do not fall for spin, but it's not their intelligence and knowledge that protects them. Or rather it's not their intelligence and knowledge alone. People who see through flim-flam are self-critical. They know they can make mistakes, they know their thoughts are biased, they know they tend to rationalize rather than face awkward truths. And so they think about their thinking, which makes them more likely to catch and correct errors. Psychologists call thinking about thinking "metacognition." That, in combination with intelligence and knowledge, is the best and only defence against those who would manipulate us.