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. 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 one of the unconventional (sham) 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. Most EEG features we
explored did not differ between conventional and unconventional
induction conditions. A possible exception is frontal theta activity,
which appeared to increase more in conventional induction trials. The
change in frontal gamma power negatively correlated with hypnosis depth,
and occipital theta activity positively correlated with hypnotizability
in both conventional and unconventional inductions. 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.