Can any procedure be hypnosis? Exploring the effect of framing on
hypnotic depth and electrophysiological correlates of hypnosis in a
balanced placebo design.
Abstract
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.