What is hypnosis? Spanos and Chaves point out that, for most laypeople and many research workers and health care providers, it involves a trance, or at least an altered state of consciousness. It is brought on by some repetitive verbal rituals, known as an induction procedure. The person hypnotised becomes a passive automaton, and comes under the control of the hypnotist.

The vogue began with the German physician Anton Mesmer in the late 18th century. It became entwined with a range of other occult beliefs, and took on a new lease of life. And now here we are towards the end of the 20th century, with the American Psychological Association sheltering a fully-fledged Division of Psychological Hypnosis (are there other kinds?).

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The subjects who showed up best in tests of hypnotic susceptibility were those who had been asked to pretend to be hypnotised. And hypnotic performance could be noticeably improved by some training. In other words, what had been thought of as a genetically endowed susceptibility was in fact a skill that could be learned.

In a similar experiment, Spanos and his associates found that subjects all dutifully coughed when they heard the word ‘psychology’ in the experimental situation. But Spanos had arranged for a confederate to pose as a lost student asking for the psychology department. None of the subjects responded to the cue word.