Irrational Animals: a neuroscience take on the news

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Trying to start afresh this year? Have a bath. No, really

Martha Gill's "Irrational Animals" column.

Bathtub acrobat David O'Mer during a performance
"Bathtub acrobat" David O'Mer during a performance. Photograph: Getty Images

When actors do that scene in which Lady Macbeth washes imaginary blood from her hands (“Out, damned spot! Out, I say!” etc), most play it slightly mad. I’d prefer them to play it deadpan, partly because it would be funny, and partly because recent research suggests that Lady Macbeth was actually performing a fairly sound bit of self-therapy.

A slew of studies by Spike W S Lee and Norbert Schwarz of the University of Michigan looked into the power of washing as a psychological act and found something significant. Cleansing helps us get over our dark deeds: the metaphor holds.

In one study, participants had to remember a time where they had acted immorally. Those who cleaned their hands afterwards were able to get rid of the guilt. Being asked to imagine being “clean” rather than “dirty” also gave them a feeling of moral superiority; they made stricter judgements about others and felt better about themselves. With the right sanitiser, what is done evidently can be undone.

We instinctively seek this psychological comfort, too. In one experiment, subjects were asked to tell a lie by either email or voicemail. Afterwards, when given the choice, those who had lied over the phone wanted mouthwash, while those who had lied in writing were more likely to take the hand sanitiser.

Evidence suggests that we also apply the cleaning principle to others’ doings. One study found that copying out a story about someone else’s immoral behaviour increased people’s desire for cleaning products – and these were products that cleanse the outside world, such as detergent and disinfectant.

The metaphor is surprisingly strong. The researchers point out that we use the same facial expressions of disgust when we come across moral wrongdoing and contaminants – from open wounds to rotten food. The two also consistently overlap in language use.

Why might this be? Any conceptual associations will be grounded in brain structure. The brain usually builds certain functions on top of existing ones to save space – physical disgust towards bad food is likely to be an earlier adaptation (avoiding unhealthy objects and environments) and disgust towards evil doings a later one, which happens to piggyback on the same neural pathways.

Abstract reasoning (about concepts such as morality) is also often linked to direct sensory experience (seeing maggots emerging from a loaf of bread, for example), which is why images in dreams can often tell you something about your mental state.

Clean break

Washing also seems to get rid of doubts and worries outside the moral sphere. Recently cleaned people who had just made a decision (in one case, between two types of jam) needed to spend less time justifying their choice to feel all right about it. Gamblers who had just had a run of bad luck were back making risky bets again after a quick wash. It seems the trick works, whatever feeling you are trying to dispose of. 

So, if you’re looking to start the new year afresh – have a bath. It’ll make you feel better and God knows it may make those around you feel better, too.