People change their minds about a choice after they make it. If you ask someone how he feels about Athens and Paris, he might rate them the same. But after you make him choose one as a vacation destination, he'll rate that city higher. This is thought to be a way to reduce the psychological tension that is created by rejecting one perfectly reasonable alternative and picking another one.

But recently critics have pointed out a flaw in this experimental design: the person might actually have already liked Paris more than Athens, but for some reason this preexisting preference didn't show up when he was asked to rate them.

Tali Sharot and Raymond J. Dolan of University College London and Cristina M. Velasquez of Lake Forest College set out to improve on the experimental design. They asked people to rate a list of vacation destinations, and then choose between pairs of places. Next, the participants were told they were taking part in a test of subliminal decision making: they would have to choose between the names of two vacation destinations shown on a screen, side by side, for two milliseconds. However, what actually flashed on the screen was nonsense strings (such as "%^!x *&()%), so the participants were making a completely blind choice. After the test was finished, they were told which place they'd chosen and were asked to rate the destinations again.

Indeed, people's evaluations of the destinations they chose improved; if they blindly chose Thailand, they rated it higher after the test than they did before. The study is published in Psychological Science, a journal of the Association for Psychological Science.

"It's a relief to know that psychologists are right about this basic principle," says Tali Sharot. But "The effect is much smaller than what we usually see when we do non-blind choice." This means that the critics were right to point out the flaw in the usual experimental design; people do have a preexisting preference, even if it's not strong enough to show up in ratings. Her team has also found this to be true using functional MRI studies, a kind of imaging that shows activity in the brain.

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