Hypnosis as a retrieval cue in posthypnotic amnesia.

The effectiveness of hypnosis as a retrieval cue was tested in a group of 80 highly hypnotizable subjects who demonstrated posthypnotic amnesia on an initial recall test. The 40 subjects who received a reinduction of hypnosis showed a significant improvement in memory on a retest; there was a significant loss of memory on a third test following termination of the second hypnosis and a more substantial recovery on a fourth test following administration of a prearranged reversibility cue. Another 40 subjects, who merely relaxed before the second test, showed a similar improvement in memory on the retest but no subsequent memory loss. The amount of trial-to-trial improvement in memory shown by the subjects was unaffected by explicit instructions to maintain amnesia until the reversibility cue had been given. Posthypnotic amnesia is not a case of state-dependent retention, nor does hypnosis provide retrieval cues that can lead to the emergence of previously unrecalled memories.