An auditory hallucination might sound scary. Science, and Science, say it’s easier to trick the brain into hearing non-existent noises than you might think.
New research from Yale suggests it’s possible to trigger a sound hallucination, or hearing things that don’t exist, even in people who don’t normally suffer from those conditions.
It’s even easier to cause a hallucination if a person already hears voices or sounds in their head that aren’t real.
“Hallucinations may arise from an imbalance between our expectations about the environment and the information we get from our senses,” says Al Powers, the lead author of the Yale study and an instructor in clinical psychiatry. He and his partner, Philip Corlett, wanted to see whether it was possible to find triggers that would cause hallucinations. They also were curious about whether those imaginary sounds were harmful or harmless.
“You may perceive what you expect, not what your senses are telling you,” Powers told EurekAlert.com.
Old methods, new technology, same results
This isn’t a new experiment, by the way: Corlett and Powers are building on a 125-year-old experiment.
The original experiment aimed explicitly to make people have a hallucination of sounds that weren’t there. Four groups of people participated in the test, including those with illnesses and those without, and people who did and did not report hearing voices. The test subjects saw a light and heard a sound simultaneously. During the light and sound test, an MRI scanned the test subjects’ brains.
It’s like the old experiment where dogs learned to think they were about to get food every time they heard a bell. Mental conditioning can do some powerful things.
When asked to signal hearing the very quiet tone, eventually many of the test subjects indicated they heard a noise when the light came on but the sound didn’t. Those people who were already hearing voices that weren’t there were much more likely to say they heard the very soft tone when it wasn’t being played than those who did not say they heard voices or other sounds.
Seeing evidence of the hallucination didn’t convince everyone
The new version of the experiment used computer modeling to divide the results of people who said they heard voices from those who didn’t. The researchers found that people who believed they heard voices or noises were more hesitant to believe no tone was played.
“In both clinical and non-clinical subjects, we see some of the same brain processes at work during conditioned hallucinations as those engaged when voice-hearers report hallucinations in the scanner,” Corlett said.
Included among the test group were some “psychics,” according to Mental Floss. The 15 self-identified psychics said they had a hallucination almost every day but weren’t bothered or worried by them. Instead, they believed the voices are communication from supernatural sources.
Powers and Corlett think that studying people who believed they heard noises, and their brain scans, might help better find those who suffer from auditory hallucinations and get them better treatment.