Mind

Here's Why Some People Experience Auditory Hallucinations

Yale Researchers teamed up with psychics to study why people hear voices and found that hallucinations arise when the brain puts too much emphasis on its own expectations.

A team of Yale researchers tapped local Connecticut psychics for a novel study into why some people hear voices — with results suggesting future avenues for research into treating hallucinations among schizophrenics.

In the process, they also managed to develop a technique for inducing hallucinations, even in mentally healthy people.

Researchers Phillip Corlett and Albert Powers wanted to locate subjects who hear voices but experience no other psychotic symptoms. To do so, they turned to local community of psychics near Yale University through an organization representing regional clairvoyants and sought out people who report hearing voices — including those who believe they’re hearing spirit guides, dead relatives, guardian angels, or other ethereal beings. 

For example, one of their subjects, a middle-aged woman who works as a police dispatcher, said she occasionally hears a voice that gives her innocuous, helpful advice, such as which direction to turn in traffic.

In fact, studies indicate that at least 4 percent of the general population report hearing voices at some point in their lives, even those who show no other symptoms of mental illness. That’s significantly more than the 1 percent of the global population thought to suffer from schizophrenia, which doesn’t always involve auditory hallucinations.

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At the heart of Powers and Corlett’s study was a question: What is the brain actually doing, both in schizophrenics and in otherwise healthy people, when it perceives sounds that aren't there?

One possibility considered over the years is that the brain might somehow lose its ability to cancel out “inner speech” — giving a new, persuasive realness to the voice-like thoughts most people perceive when they think in words.

But another theory suggests that, in fact, hallucinations actually stem from an overdeveloped reliance on expectations — something like the feeling that your cell phone just alerted you to an incoming text, when in fact it didn’t, at the moment you’re waiting for an important message.

Corlett and Powers devised a study involving four groups of patients. The first had schizophrenia or schizo-affective disorder and heard voices. The second also had psychotic symptoms, but didn’t hear voices. The third group came from Corlett and Powers’s psychic outreach: They heard voices, but didn’t show any other psychotic symptoms. And the fourth had no psychotic symptoms at all and didn’t hear any voices.

All subjects then went through the same experiment: They were shown a checkerboard visual stimulus that was occasionally accompanied by a tone.

Corlett and Powers were able to make all four groups occasionally believe that they had heard the tone when in fact they had only seen the checkerboard — in other words, all four groups could be made to hallucinate.

But they found, however, that this was much easier to do in the two groups of people who report hearing voices — both those who have schizophrenia and those who don’t.

“People started to believe that they heard tones that we didn’t present them with when they saw the checkerboard, and particularly the people who heard voices in their head,” said Corlett. “People who experience hallucinations in their everyday lives were five times more likely to show the effect than people who didn’t hallucinate.”

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In other words, the study, which was published in the journal Science, presented evidence that auditory hallucinations arise when the brain puts an out-of-proportion emphasis on what it expects will happen.

“Hallucinations appear to arise from an over-weighting of our expectations,” said Powers.

If so, that suggests future treatment might arise from studying the brain’s cholinergic system, which is thought to be involved in wakefulness and alertness, Powers said.

“The most striking thing to me about this study was how easy it was to engender hallucinations in people in the lab,” said Corlett. “I think it speaks to the fragility of something we consider quite robust: our perception.”

WATCH: Why Do We Hallucinate?