- Measurement of hypnosis and hypnotisability
One of the key developments in 20th century hypnosis research was the development of hypnotic susceptibility scales for the reliable measurement of hypnotic susceptibility. These allow researchers to understand more about how & why hypnosis works, and some clinicians use them to judge how best to help clients. A person's susceptibility to hypnosis is usually gauged as 'high', 'medium', or 'low'. Approximately 80% of the populations are medium, 10% are high and 10% are low. Being able to reliably measure hypnotic susceptibility has allowed researchers to study hypnosis and its correlates in the laboratory.
- How hypnotic susceptibility scales work?
Hypnotic susceptibility scales normally begin with a quick discussion to allay any fears or misconceptions participants may have, then proceed to a hypnotic induction which encourages participants to enter a hypnotized 'state'. The scales then consist of a number of test suggestions which participants can either pass or fail. Suggestions are either for motor (movement) or cognitive (thought) effects, and either aim to produce or inhibit an effect. There is a full list of scales on the hypnotic susceptibility scales page.
Susceptibility scales typically contain a number of test suggestions which the participant will either pass or fail. The suggestions chosen are designed to test a range of hypnotic domains. Test suggestions are either 'motor' or 'cognitive' and also either 'positive' or 'negative' in nature. A positive motor suggestion would be trying to produce a motor effect, e.g. a suggestion that the participant's arm will raise all by itself. A negative motor suggetion would be aimed at inhibiting a willed motor action, e.g. a suggestion that the participant will not be able to open their eyes (traditionally called eyelid catalepsy). Cognitive suggestions are aimed at producing or inhibiting perceptions or sensations. An example of a positive cognitive suggestion would be a visual hallucination of someone's best friend. A negative cognitive suggestion might be where it is suggested that a participant cannot hear (hypnotic deafness).
- Involuntariness is crucial
The 'classic suggestion effect' (Weitzenhoffer, 1980) posits that for a suggestion to be genuinely experienced it must be experienced involuntarily. That is: it should feel like it is happening by itself. For example, one item might give a suggestion that your arm is getting lighter and is beginning to float up into the air. If your arm feels like it is floating effortlessly and actually moves up in the air you are said to have passed the item. The subjective involuntariness with which a suggestion is experienced is measured by a number of scales.