By now you’ve seen it, as have millions of Americans: last week’s cover of The New Yorker. The infamous illustration features false views of Barack Obama taken by his fiercest opponents. Speaking on the Charlie Rose show, the editor of The New Yorker, David Remnick, has pointed out that the magazine's liberal leanings are well-known. He wonders: can't people take a joke? The short answer is that we would, but our brains won’t let us.

The brain does not save information permanently, as do computer drives and printed pages. After our brains store a fact, the information does not rest. Instead, as a piece of information is recalled, it may be “written” down again as part of the process of strengthening it. Along the way, the fact is gradually separated from the context in which it was originally learned. The phenomenon, known as source amnesia, allows us to have semantic knowledge, a type of memory in which we recall a fact (i.e. “at a red light, stop”) without the bother of recalling exactly when we learned it.

Most of the time this trick is useful. If we had to remember where we learned that red meant stop, we wouldn’t drive very safely. But the same trick can lead people to forget whether a statement is even true. A false statement from a noncredible source that is at first not believed can gain credibility during the months it takes to reprocess memories from short-term to longer-term storage. As the source is forgotten, the message and its implications gain strength. So any intended satire in the magazine cover may eventually be forgotten, leaving people to recall vaguely that Barack Obama is somehow un-American.

Another brain trick compounds the false memory problem. Daniel Gilbert and his colleagues have shown that if people aren't given enough time to think, they tend to automatically accept a statement as being true. Visual information is processed particularly rapidly. And what's more immediate than a caricature?

Psychologists have suggested that legends propagate by striking an emotional chord. In the same way, ideas can spread by emotional selection, rather than by their factual merits, encouraging the persistence of falsehoods. Indeed, unscrupulous campaign strategists know that if their message is initially memorable, its impression will persist long after it is debunked. One emotionally-laden false belief about Senator John McCain dates back to the 2000 Presidential primary campaign. He did well until the South Carolina primary, at which time rumors surfaced about a mixed-race child that he had allegedly fathered. Apparently, this did not play well with Southern voters. Shortly thereafter, his candidacy faltered. As one study has shown, ideas have special staying power if they evoke a feeling of disgust.

Because of these tricks your brain plays on you, journalists can paradoxically make misinformation stick by repeating a falsehood even as they debunk it. In covering the controversy that was evoked over the New Yorker cover, virtually every major TV journalist repeated the stereotyped charges against the candidate—many citing polling data on how many Americans believe them—before noting that the beliefs were false. An especially bad variant is the common habit of replaying parts of an ad that they are about to show is false. In television, which above all else is a visual medium, image can easily trump verbal content.

If journalists are to avoid adding to the public’s misinformation, they need to find other strategies, such as offering an equally competing, true storyline. For instance, rather than repeating the false belief then denying that Obama is a Muslim, a less misleading approach would be to report on the candidate’s discovery of Christianity after a secular youth.

In other words, when journalists write their stories, they should spend less time worrying about presenting both sides of a story when one side is false - and more time considering the quirky ways that brains process the disagreement.