By Clare Wilson
A bizarre illusion where fake faeces is put on a rubber hand could become a way of treating obsessive compulsive disorder (OCD).
The process, designed to help those affected get more comfortable with encountering germs, could be less upsetting than existing forms of therapy where people have to see their real hands getting dirty, says Baland Jalal at the University of Cambridge.
The original illusion, which was discovered about 20 years ago, involves someone putting one of their hands out of sight, such as under a table, and seeing a fake hand in its place. If someone else strokes both the fake and real hand at the same time, most people start feeling that the fake hand is their own.
Psychologists often employ this technique to study how we feel ownership of our bodies, which helps generate our sense of self. But in what may be its most revolting application to date, it has been used to incite feelings of disgust with fake poo.
Jalal and his team used this version of the test on people with obsessive compulsive feelings about hygiene. People with OCD obsess over certain fears and carry out repetitive rituals to feel safe – such as washing their hands again and again.
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They are usually treated with exposure therapy, helping them encounter their fears without the repetitive actions, so they gradually learn that nothing bad happens. But some find this too distressing – a quarter won’t even start.
This is where the fake poo comes in. The substance was made from foods such as chocolate, peanut butter and flour, but smelled bad thanks to a spray of joke-shop faeces odour. “It smells pretty real,” says Jalal.
The team asked 29 people with OCD to go through the illusion set-up and then dabbed fake faeces on the rubber hand, while touching their real hand out-of-sight with a damp towel. Although they knew the poo wasn’t real, they reported feeling contaminated and disgusted. “The patients were terrified of this stuff,” says Jalal.
Even the half of the group who had undergone a weaker version of the experiment – where the rubber and real hands are stroked out of synchrony – still experienced the illusion initially, suggesting people with OCD are more susceptible to it, says Jalal.
His team plan to use the technique as a way of treating OCD, as they hope people will be more tolerant to exposure therapy that begins with using a fake hand.
Journal reference: Frontiers in Human Neuroscience, DOI: 10.3389/fnhum.2019.00414
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