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RENEE MONTAGNE, host:

Lady Macbeth famously tried to clean her conscience by rubbing invisible blood stains off her hands. Well, Shakespeare was on to something. Hand washing can ease psychological turmoil. NPR's Nell Greenfieldboyce reports that soaping up may help us feel better about choices we've made.

NELL GREENFIELDBOYCE: A few years ago, scientists discovered the Macbeth effect. Hand cleaning seemed to ease the guilt people felt after being asked to recall something unethical they'd done in the past. This fascinated Spike Lee. He's a psychology researcher at the University of Michigan, who wondered if hand washing could influence emotions beyond a sense of moral purity. After all, people have this idea of starting over with a clean slate.

Mr. SPIKE LEE (Researcher, University of Michigan): Maybe there's a broader phenomenon here. Anything from the past, any kind of negative emotional experiences, might be washed away.

GREENFIELDBOYCE: He and a colleague named Norbert Schwarz decided to see if they could wash away one kind of bad feeling: the lingering unease we feel after being forced to choose between two attractive options.

Lee says psychologists know that people usually try to soothe this inner conflict by later exaggerating the positive aspects of whatever it is they chose.

Mr. LEE: In other words, after they make the choice, they will like a chosen option more than before the choice.

GREENFIELDBOYCE: The researchers figured that people wouldn't need to do this kind of justification if hand washing could relieve their tension instead. To test this idea, the researchers first asked students to rate a list of music CDs. They then offered the students two of the CDs and told them to select one as take-home gift.

Afterwards, some students lathered up with soap. Others only looked at the soap or sniffed it.

As the researchers had suspected, those left with dirty hands later gave their chosen CD a higher score than they had on the initial ranking. But the hand washers didn't.

Mr. LEE: They feel no need at all to justify the choice.

GREENFIELDBOYCE: They hand washers ranked their chosen CD pretty much as they had before.

In the journal Science, the researchers report that they saw the same effect in a similar experiment that let people use antiseptic wipes.

Mr. NORBERT SCHWARZ (University of Michigan): Apparently you do not need water and soap.

GREENFIELDBOYCE: Norbert Schwarz says, on the one hand - so to speak -washing may help decision makers by rinsing away mental turmoil, but on the other hand...

Mr. SCHWARZ: We may not do you a favor when you wash your hands and you're not doing that cognitive work to make your decisions appear in the best possible light.

GREENFIELDBOYCE: Schwarz says it may be that if people don't justify their choices, they may end up feeling more remorse in the long run.

Nell Greenfieldboyce, NPR News.

MONTAGNE: And we've been hearing a lot about bad water this week water covered in oil, threatening the shores of Louisiana, Florida, Alabama and Mississippi, water washing away lives and music in Nashville.

So we thought we'd end the week on a more hopeful note this classic sung by Johnny Cash.

(Soundbite of song, "Bridge Over Troubled Water")

Mr. JOHNNY CASH (Singer): (Singing) When times get rough and friends just can't be found, like a bridge over troubled water I will lay me down. Like a bridge over troubled water, I will lay me down. When you're down and out...

MONTAGNE: This is NPR News.

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