National Geographic News
A MRI brain scan.

An MRI scan of a human head (file picture).

Image by Harry Sieplinga, HMS/Getty Images

Christine Dell'Amore

National Geographic News

Published December 7, 2011

People can hallucinate colors just with the power of suggestion, a new study says.

In a recent experiment, scientists asked a group of prescreened people to look at a set of gray patterns and try to visualize color. Eleven members of the group had been identified as highly susceptible to hypnosis while seven of the subjects were not susceptible.

(See "Coffee May Cause Hallucinations.")

Hypnosis is a trance-like state characterized by heightened focus, concentration, and inner absorption, according to the Mayo Clinic. About 10 percent of people worldwide are highly susceptible to hypnosis while 10 percent are not influenced at all.

The remaining 80 percent—the majority of the population—are moderately susceptible, said study co-author William McGeown, a neuroscientist at the U.K.'s Hull University.

The new study found that all the subjects who were easily hypnotized reported seeing a range of colors even while not under hypnosis, McGeown said.

The scientists didn't just take their word for it—MRI scans showed that the parts of the subjects' brains linked to color perception lit up when they saw the imaginary hues.

"We can see changes in these color-sensitive regions of their brains, which they have no way of faking," said McGeown, who published the study with colleagues in the December issue of the journal Consciousness and Cognition.

Brain Scans Back Up Results

The new study also found that being under hypnosis enhanced color hallucination in susceptible subjects. But those who were not susceptible to hypnosis could not hallucinate color with or without hypnosis.

Stephen Kosslyn, a psychologist at Stanford University, said the results reinforce his team's earlier research.

In 2000, Kosslyn and colleagues published one of the first studies on hallucinating color. Their experiment asked highly susceptible people under hypnosis to imagine gray squares as being in color.

That study, which used PET scans of the subjects' brains, also found that the subjects activated parts of their brains associated with color perception.

The new study confirms a similar finding with MRI scans, which are more often favored in today's experiments because they provide better spatial resolution, co-author McGeown said.

Mere Suggestions May Help Phobias, Pain

Ultimately, the hallucination research may help medical professionals who use hypnosis to treat a range of conditions, from phobias to pain, McGeown noted.

That's because, despite its medical use, many people are fearful of the procedure. (See "Friday the 13th Superstitions Rooted in Bible and More.")

The new research shows that suggestion can be almost as powerful a tool, which means there may be a less intimidating alternative for people fearful of hypnosis, he said.

"Psychological therapies which consist of making suggestions to a patient—even in the absence of hypnosis—may help with their problem substantially."

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