Can Any Procedure Be Hypnosis? Exploring the Effect of Framing on Hypnotic Depth and Electrophysiological Correlates of Hypnosis in a Balanced Placebo Design

Expectancy theory of hypnosis posits that any procedure can serve as a hypnotic induction provided it is labeled as "hypnosis". The present study explored this hypothesis by contrasting the effects of two conventional and two unconventional (placebo) hypnotic inductions on hypnotic experiences and electrophysiological correlates. In a 2 × 2 balanced placebo design, all participants were exposed to four conditions: conventional induction labeled as "hypnosis", conventional induction labeled as "control", unconventional induction labeled as "hypnosis", and unconventional induction labeled as "control". EEG was recorded from 61 channels. We computed EEG features that were identified in previous studies as correlates of hypnosis or hypnotizability. Consistent with the predictions of expectancy theory, we found that labeling of the procedure was most influential in determining subjective hypnosis depth, and one of the unconventional (placebo) inductions, "white noise hypnosis", evoked comparable hypnosis depth to the conventional hypnotic inductions. However, contrary to its predictions, "embedded hypnosis", another unconventional induction, evoked smaller hypnosis depth reports than the other three inductions. Both relaxation and embedded induction procedures showed decreased gamma power in the midline occipital area. Most EEG features we explored were comparable between conventional and unconventional induction conditions, but labeling also seemed to have no effect on EEG changes, which is contrary to the prediction of the expectancy theory. Possible exceptions were a negative effect of conventional induction on functional connectivity between the O1-Pz channels in the theta band, and a decrease in anterior and posterior alpha power in trials labeled "hypnosis". However, these effects were inconclusive. Overall, our results provide only partial support for the expectancy theory of hypnosis. The most promising EEG correlate of hypnosis based on our results is decreased occipital gamma power. However, our findings should be considered exploratory. Confirmatory research is required to strengthen our confidence in these effects. TRIAL REGISTRATION: The research plan of this study was registered on the Open Science Framework (https://osf.io/kugdf) before any data collection. The data collection of the first 9 participants was not in accordance with the research plan due to a programming error. The data from these trials was not used in the confirmatory analysis. Consequently, we made changes to the sampling plan and the analysis plan. The altered version of the research plan had been registered at the Open Science Framework (https://osf.io/wvhda) before any new data was collected.