Hypnosis subdues the visual brain

A new brain-scan investigation indicates that one type of hypnotic suggestion may literally change the way people see the world.

A group led by Amir Raz of Columbia University studied 16 adults, ages 20 to 35. The researchers used a test in which participants viewed words denoting colors, with the letters printed in colors either matching or differing from the words’ meanings. Participants indicated as quickly as possible each word’s ink color by pressing one of four computer keys. The researchers took advantage of long-standing observations that it takes longer to identify colors that clash with word meanings, such as red ink that spells the word blue.

Before the test, the volunteers had participated in sessions with a professional hypnotist who identified half of them as easily hypnotizable. In later sessions, a hypnotist performed trance-inducing techniques and then instructed the volunteers to view words on the screen as strings of meaningless symbols.

In later tests, the easily hypnotized individuals identified clashing colors faster than the other study participants did. Functional magnetic resonance imaging scans showed that the easily hypnotized group displayed unusually low blood flow, a sign of reduced cellular activity, in two critical brain areas, the scientists report in the July 12 Proceedings of the National Academy of Sciences. One area handles incoming visual information; the other monitors conflicting thoughts.

The investigators propose that the easily hypnotized people paid much less focused attention than usual to what they saw during the trials. One result was that they avoided reading the words so didn’t experience the clash with ink colors.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.