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Abstract
Subjects susceptible to hypnosis, who could also be classified as vestibular “normals”, were selected for the investigation. After a preliminary hypnotic training, they were subjected to rotatory and caloric stimulation using test conditions as close as possible to those used in oto-neurological examinations. The nystagmus induced was recorded behind closed eyelids.
Nystagmic responses to vestibular stimuli of similar intensity were measured in five successive tests: (1) control without hypnosis, (2) hypnosis alone, (3) hypnosis and suggestion of decreased rotatory sensation, (4) hypnosis and suggestion of increased rotatory sensation and (5) control without hypnosis.
The results showed that in most of the subjects the intensity of the induced nystagmus was lowest under test 3 and highest under test 4. Thus it was usually possible to change the intensity in a desired direction by means of hypnosis and verbal suggestion.
In the rotatory tests it was possible to influence both the eye-speed and the duration of the nystagmus. In the caloric tests only the eye speed changed. These differences might be explained by the differences in principle in stimulating both labyrinths during rotation but only one when performing the caloric test.
Special attention is directed to slow pendular eye-movements which can be induced by hypnosis alone. Vestibular stimuli tend to interrupt this kind of eye-movements, an effect which is interpreted as an “arousal response”.
Habituation or response decline was to some extent present in the rotatory tests but the experimental arrangements made it possible to show that hypnosis and verbal suggestion was the main reason for the changes in nystagmus intensity observed.
The clinical and theoretical implications of the findings are discussed.
