Scientists develop robot technique to study why people hear voices

The researchers from the Federal Institute of Technology Lausanne (EPFL) and the University of Geneva published a study on their research into auditory-verbal hallucinations in the medical journal Psychological Medicine. © Keystone / Laurent Gillieron

Researchers in Switzerland have developed a technique that uses a robot to trigger auditory hallucinations in healthy people. They want to investigate the causes of this common problem among people with psychiatric illnesses in order to develop possible treatments

Scientists have “no idea what happens in the brain when people have auditory hallucinations”, explains neuroscientist Pavo Orepic from the University of Geneva.

Together with a team of researchers from the Federal Institute of Technology Lausanne (EPFL) and the University of Geneva, he published a study on this subject in October in the medical journal Psychological Medicine.

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Studies indicate that 5-10% of all people sometimes hear voices – those of dead relatives, for example – without having any kind of illness. In other words, the phenomenon is not restricted to people with psychiatric disorders, as is generally assumed. But scientists say over 70% of people with schizophrenia hear voices, with the significant difference that the voices they hear are generally very negative.

Medicines taken by schizophrenics make it difficult to study the voices they hear, as the drugs have severe side-effects, complicating the interpretation of the results. Hence the importance of being able to study this phenomenon in healthy subjects.

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Some studies indicate that auditory hallucinations can occur when sensory impressions do not match the brain’s expectations – for example if you put a bakery product that you expect to be sweet in your mouth only to find that it is savoury. Other investigations found an alternative explanation – that hallucinations occur when the brain has been conditioned by previous impressions and interprets sensory perceptions incorrectly as a result.

Now Orepic has designed an experiment that triggers these two mechanisms simultaneously. The people taking part in the experiment are blindfolded, then asked to press a lever in front of them. As they do so, a robot that they cannot see prods them in the back.

As a result, the sensory impression they receive does not align with what their brain expects, as described in the first theory. Earlier studies have shown that over time, this process gives the test subjects the illusion that they are touching their own back. Once they have got used to this experience, the prod is delayed very slightly.

“Now the brain explains that delayed sensory feedback as someone else being present and touching them in the back,” Orepic says.

According to the second theory, incorrectly perceiving a presence in this way can lead to hallucinations. To determine whether the procedure encourages auditory hallucinations, the researchers then played the test subjects noises into which they had mixed either very soft voices – sometimes the subjects’ own, sometimes someone else’s – or no voice at all. They found that after the “delayed prod” procedure, the subjects were more likely to hear other people’s voices among the noises compared to control conditions even if no voice had been mixed in.

“Our study confirms that the mechanisms behind the hallucinations are actually in everyone’s brain,” Orepic says. “But for some reason, some people are more susceptible to them than others.”

He also believes that the boundary between harmless and pathological hallucinations is also permeable.

Through his work on the causes of hallucinations, the researcher hopes to contribute to destigmatising people who hear voices.

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