Psychologists, and especially magicians, know that a lot escapes our attention, even things happening right under our noses. The most impressive example I have seen of this comes out of an experiment in which unwitting subjects are asked for directions by a stranger.  In the middle of giving the directions, an obstruction briefly allows the stranger to swap places with another stranger.  When the new stranger comes back into view the subject doesn’t notice that he is talking to someone completely different.

Its not just that we don’t notice.  Instead, our minds often prefer to explain away the unexpected rather than investigate. A new series of experiments show just how far this can go and they raise deep questions about how we make decisions.  In these experiments, subjects were shown photos of two strangers and asked to pick the more attractive photo.  Then they were handed the photo they chose and asked to explain why they picked it.  But by a sleight-of-hand, the subjects were actually handed the other photo, the one they deemed less attractive.

Not noticing the switcheroo, these subjects went on to point to the photo and give detailed reasons why they prefer the one that they in fact did not prefer.

Here is an article from the New Scientist about this and related experiments. (thanks to Toomas Hinnosaar for the pointer.)

Here is a video of the swapped stranger experiment.