Expectancy theory of hypnosis posits that any procedure can serve as a hypnotic induction provided it is labelled as “hypnosis”. The present study explored this hypothesis by contrasting the effects of two conventional and two unconventional (sham) hypnotic inductions on hypnotic experiences and electrophysiological correlates. In a 2x2 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 128 channels. Consistent with the predictions of expectancy theory, we found that one of the unconventional (sham) inductions, “white noise hypnosis”, evoked comparable hypnosis depth to the conventional hypnotic inductions. Moreover, EEG correlates of conventional versus unconventional inductions did not substantially differ. Furthermore, we found that labeling a procedure as “hypnosis” resulted in greater hypnosis depth and greater baseline-to-hypnosis reductions in midline frontal alpha activity compared to procedures labeled “control”. However, contrary to the predictions of the expectancy theory, “embedded hypnosis”, another unconventional induction, evoked smaller hypnosis depth reports than the other three inductions. The change in midline frontal gamma power negatively correlated with hypnosis depth in both conventional and unconventional inductions. Conversely, correlations of frontal gamma power, occipital theta power, and frontoparietal connectivity in the alpha2 band with hypnotizability differed between conventional and unconventional induction trials. Overall, our results provide partial support for the expectancy theory of hypnosis. However, our findings should be considered exploratory. Confirmatory research is required to strengthen our confidence in these effects.
