Hypnosis can alter the way the brain processes information. In a new study, researchers successfully used hypnosis to rapidly induce and extinguish a form of synesthesia.
Synesthesia is a unique phenomenon in which a sense, such as sound, triggers another sense, such as sight or smell. For example, upon hearing a certain sound, a person might automatically perceive the sound as red.
“The current study confirms the research group’s previous results which showed that it is possible to use hypnotic suggestion to trigger visual hallucinations in a way that is otherwise not possible — say, through practiced use of mental imagery,” said Dr. Sakari Kallio from the University of Turku in Finland.
The findings, published in the journal Scientific Reports, could pave the way into previously unexplored domains of cognitive neuroscience and offer fresh inspiration to the budding science of consciousness studies.
For the study, participants were videotaped and then interviewed about their experiences and strategies while performing a stroop-like color-naming task (for example, the word RED printed in green letters). The interviews revealed that, among highly hypnotizable participants, the same suggestions could lead to strikingly different experiences.
The researchers induced an equivalent to synesthesia in which some symbols in a selection — circles, crosses, and squares — were each suggested to come with a specific given color.
“Of the four highly hypnotizable participants in the study, three showed a strong synesthesia-like association between symbol and color, as shown by their verbal reports and confirmed by eye tracking,” Kallo said.
“However, the nature of this association varied widely. Two participants reported that they visually experienced the symbols as having the suggested color: in one case with full self-awareness of doing so and in another case not.”
In a third case, the participant did not experience any color change and was not aware of the given suggestions, but nevertheless showed difficulty in naming the actual colors of the three target symbols.
A control group performed a similar task but had to rely on memory or strategy: for example, they might be told by the researchers to practice thinking of all the squares as being green. The control group was unable to reproduce the effect of the highly hypnotizable subjects.
“Perhaps most importantly, the results showed both definite similarities and clear differences to naturally occurring synesthesia. Nevertheless, and beyond the demonstrated ability to rapidly induce — and cancel — a form of synesthesia, one should avoid drawing general conclusions until further research is carried out,” said Kallio.
“A key methodological difference from earlier research is that hypnosis was induced and cancelled very quickly.”
“Earlier studies have typically used a five-to-ten-minute hypnotic induction period. In this study, hypnosis was induced by counting forward from one to three and cancelled by counting backward from three to one. All tasks were executed in a perfectly normal state of waking consciousness — not under hypnosis, which was induced only when the color suggestions were made,” said Kallio.
Source: University of Turku