Summary: Hypnotic suggestion can trigger visual hallucinations similar to those experienced by people with synethesia, researchers report.
Source: University of Turku.
Hypnosis can alter the way certain individuals information process information in their brain. A new phenomenon was identified by researchers from the University of Skövde in Sweden and the University of Turku in Finland, who have successfully used hypnosis to induce a functional analogue of synesthesia. The discovery can open a window into the previously unexplored domains of cognitive neuroscience.
synesthesia is generally understood to be a rare phenomenon where, for example, seeing a certain letter or number is uniformly accompanied by an automatic association to or a visual perception of a colour.
“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,” says Docent Sakari Kallio from University of Turku.
Participants were videotaped and afterwards interviewed about their experiences and strategies while doing a STROOP-type colour-naming task. The interviews revealed that the same suggestions could, for highly hypnotizable subjects, 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 of always taking a specific given colour.
“Of the four highly hypnotizable participants in the study, three showed a strong synesthesia-like association between symbol and colour, as shown by their verbal reports and confirmed by eye tracking. However, the nature of this association varied widely. Two participants reported that they visually experienced the symbols as having the suggested colour: in one case with full self-awareness of doing so and in another case not,” Kallio says.
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 colours of the three target symbols. A control group mimicked the task by using their memory or strategies suggested by the research group: for example, to practice thinking of the squares all being green. The control group was unable to reproduce the effect.
“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.”
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 colour suggestions were made,” says Kallio.
These alterations allow the possibility to change colour perception by explicit verbal suggestion. Such highly hypnotizable subjects can open a window into hitherto unexplored domains of cognitive neuroscience and give fresh impetus to the budding science of consciousness studies.
Source: University of Turku
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to the researchers.
Original Research: Full open access research for “Synaesthesia-type associations and perceptual changes induced by hypnotic suggestion” by Sakari Kallio, Mika Koivisto & Johanna K. Kaakinen in Scientific Reports. Published online December 11 2017 doi:10.1038/s41598-017-16174-y
Synaesthesia-type associations and perceptual changes induced by hypnotic suggestion
Are synaesthetic experiences congenital and so hard-wired, or can a functional analogue be created? We induced an equivalent of form-colour synaesthesia using hypnotic suggestions in which symbols in an array (circles, crosses, squares) were suggested always to have a certain colour. In a Stroop type-naming task, three of the four highly hypnotizable participants showed a strong synaesthesia-type association between symbol and colour. This was verified both by their subjective reports and objective eye-movement behaviour. Two resembled a projector- and one an associator-type synaesthete. Participant interviews revealed that subjective experiences differed somewhat from typical (congenital) synaesthesia. Control participants who mimicked the task using cognitive strategies showed a very different response pattern. Overall, the results show that the targeted, preconsciously triggered associations and perceptual changes seen in association with congenital synaesthesia can rapidly be induced by hypnosis. They suggest that each participant’s subjective experience of the task should be carefully evaluated, especially when studying hypnotic hallucinations. Studying such experiences can increase understanding of perception, automaticity, and awareness and open unique opportunities in cognitive neuroscience and consciousness research.
“Synaesthesia-type associations and perceptual changes induced by hypnotic suggestion” by Sakari Kallio, Mika Koivisto & Johanna K. Kaakinen in Scientific Reports. Published online December 11 2017 doi:10.1038/s41598-017-16174-y