Research Article: The Existence of a Hypnotic State Revealed by Eye Movements

Date Published: October 24, 2011

Publisher: Public Library of Science

Author(s): Sakari Kallio, Jukka Hyönä, Antti Revonsuo, Pilleriin Sikka, Lauri Nummenmaa, Jan Lauwereyns.

Abstract: Hypnosis has had a long and controversial history in psychology, psychiatry and neurology, but the basic nature of hypnotic phenomena still remains unclear. Different theoretical approaches disagree as to whether or not hypnosis may involve an altered mental state. So far, a hypnotic state has never been convincingly demonstrated, if the criteria for the state are that it involves some objectively measurable and replicable behavioural or physiological phenomena that cannot be faked or simulated by non-hypnotized control subjects. We present a detailed case study of a highly hypnotizable subject who reliably shows a range of changes in both automatic and volitional eye movements when given a hypnotic induction. These changes correspond well with the phenomenon referred to as the “trance stare” in the hypnosis literature. Our results show that this ‘trance stare’ is associated with large and objective changes in the optokinetic reflex, the pupillary reflex and programming a saccade to a single target. Control subjects could not imitate these changes voluntarily. For the majority of people, hypnotic induction brings about states resembling normal focused attention or mental imagery. Our data nevertheless highlight that in some cases hypnosis may involve a special state, which qualitatively differs from the normal state of consciousness.

Partial Text: Does a hypnotized person enter a special hypnotic state that is completely outside the range of normal mental states and cognition? This question has been under debate throughout the history of hypnosis research [1], [2], [3]. Major psychological models of hypnosis called the Non-State View theories explicitly reject the existence of a special hypnotic state [2], [3]. Instead, they assume that all hypnotic phenomena involve only cognitive and neural states similar to those occurring outside of hypnosis [3]. The opposing theoretical view called the State-View posits that a hypnotic state exists which differs qualitatively from the normal waking baseline state [2], [3]. So far, no hypnotic state fulfilling objective empirical criteria has ever been convincingly demonstrated. Consequently, a special altered hypnotic state is currently considered by some researchers to be merely a popular myth in psychology [4]. Nevertheless, it is generally agreed that the existence of a hypnotic state could be defined empirically by behavioural criteria reflecting changed information processing that cannot be imitated or simulated by nonhypnotized control subjects [2], [3].

In the Fixation task, TS-H showed a markedly reduced eye-blinking rate (Figure 3) in HC (0.012 ± 0.04 blinks/s) as compared to NC (1.18 ± 0.63 blinks/s). Although some control subjects could mimic rather well this external feature of the “trance stare”, at the group level the changes were far less marked (0.58±0.56 blinks/s in NC and 0.15±0.23 blinks/s in HSC).

We showed that a Hypnotically Induced Stare (HIS) is accompanied by large, objective and inimitable changes in the patterns of eye movements in the case TS-H. The amplitude, velocity and frequency of reflexive saccades were radically suppressed, and the fixation time was increased. Also the pupil size of TS-H diminished during the hypnosis condition.