Synaesthesia induced by hypnosis

Wired Science has an interesting preview of an upcoming study that used hypnosis to induce colour-number synaesthesia in highly hypnotisable participants.

Synaesthesia is where the senses merge, and in colour-number synaesthesia, the affected people experience colours associated with specific numbers.

This new study used hypnosis to induce exactly this experience in people who didn’t have it before:

The researchers, led by Roi Kadosh of University College, London and Luis Fuentes of Spain’s University of Murcia, put three women and one man under hypnosis, then instructed them to perceive digits in color: one as red, two as yellow, three as green, and so on.

Upon waking, the subjects found it difficult to find numbers printed in black ink against correspondingly colored backgrounds. The numbers seemed to blend in — a telltale sign of synesthesia. When the hypnosis was removed, the ability vanished.

How the synesthesia formed so suddenly isn’t clear, but the researchers said that new neural connections are probably not responsible. “Such new anatomical connections could not arise, become functional, and suddenly degenerate in the short time scale provided by the current experiment,” they wrote.

Instead they suggest that hypnosis broke down neurological barriers between sensory regions. Marks agreed, but cautioned against extrapolating the findings too broadly: Many different varieties of synesthesia exist, from seeing emotions to tasting sounds, and may have different neurological and psychological origins.

Hypnosis has been studied before for it’s ability to induce anomalous colour experiences.

In a study published in 2000, the researchers used hypnosis to induce the experience of colour when the participants were viewing a black and white image, as well as the reverse.

What was most fascinating about this particular study was that it was run in a PET scanner and the researchers discovered that the colour-based focused hypnotic suggestions actually altered the function the colour perception areas in the visual cortex, which is known to be involved in the perception of colour.

In other words, it is likely that hypnosis was not simply leading the people to make false claims, but was actually affecting what they perceived.

Link to ‘Hypnosis Lets Regular People See Numbers as Colors’.
Link to PubMed entry for colour study (with full-text link).