Synaesthesia-type associations and perceptual changes induced by hypnotic suggestion

Abstract

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.

Neurophenomenology of induced and natural synaesthesia

“…This marks a difference with respect to natural synaesthesia, suggesting that hypnotically induced synaesthesia-like experiences do indeed have some perceptual presence—since they would seem to be confusable and continuous with other perceptions. Indeed, Kallio et al conclude that while hypnotic suggestion can create a condition that displays some functional similarities to synaesthesia, it also displays clear differences [39]. We note that the findings of Cohen Kadosh et al [8] are also interpretable in this way—failure to detect a (black) digit when presented on a background congruent with the (induced) colour is compatible with the idea of the induced concurrent perceptually ‘replacing’ the inducer.…”

“…[37]sound-phosphenebrain injuryphenomenologyKelly [38]sound-colourassociative learning—Kallio et al . [39]symbol-colourpost-hypnotic suggestionphenomenology, behaviourKusnir & Thut [40]letter-colourincidental learning (visual search)behaviourMeier & Rothen [30]letter-colourassociative learningbehaviour, psychophysiologyNair & Brang [9]sound-phosphenesensory deprivationphenomenology, behaviourNiccolai et al [41]grapheme-colourtraining battery (several tasks)behaviourNunn et al . [42]word-colourassociative learningbehaviourOvalle Fresa & Rothen [43]grapheme-colourincidental learning (generation of associations)behaviourRo et al .…”

“…A more recent study attempted to induce form-colour synaesthesia using hypnotic suggestion [39]. Four highly suggestible participants were given the hypnotic induction that symbols within an array (circles, crosses or squares) would always display a certain colour, even though they were presented in differing colours.…”

“…Kallio et al . put it this way: ‘Their subjective experience appeared very similar to a projector-type synaesthete, with the key difference that they reported the object as having the suggested colour’ [39, p. 7]. This marks a difference with respect to natural synaesthesia, suggesting that hypnotically induced synaesthesia-like experiences do indeed have some perceptual presence—since they would seem to be confusable and continuous with other perceptions.…”

The Effects of Hypnosis and Hypnotic Suggestions on the Mismatch Negativity in Highly Hypnotizable Subjects

“…In the visual modality, some findings obtained with highly hypnotizable subjects also suggest that by using hypnotic suggestions, it is possible to influence preconscious or highly automatized information processing such as color perception Koivisto, Kirjanen, Revonsuo, & Kallio, 2013), but possibly only with some of the most hypnotizable individuals (Kallio, Koivisto, & Kaakinen, 2017). Although the auditory and visual information processing systems are differently structured and located in the human brain, there may also be similarities in the effects of hypnotic suggestions between them.…”