The writer recalls a demonstration of hypnosis conducted under the medical supervision of a reputable psychiatrist, where the subject recalled her 5th birthday including naming every single person attending the party, the colour of the dresses the little girls wore and the presents they brought to the party. This amazing detail was confirmed in part by the recollections of other adults. The subject at the time was in her mid thirties and claimed to have a bad' memory for names.
However, it should be added that great care should be taken when evaluating the significance of such anecdotal evidence. Some psychologists suggest that there is mounting evidence correlating an increase in the production of memories under hypnosis with a decrease in their accuracy. Hypnosis seems to make the subject less critical, and keener to please the hypnotist.
Hypnosis has been described as a social interaction in which the subject acts on suggestions for experiences involving alterations in perception, memory and the voluntary control of action (Kihlstrom, 1999). This involves some division in consciousness that excludes phenomenal awareness of these alterations.
In post hypnotic amnesia many highly hypnotizable subjects come out of hypnosis unable to remember the events and experiences that transpired while they were hypnotized. Subjects who have been instructed to study and memorise a list of names whilst under hypnosis have been unable to recall these names afterwards. However if the amnesia suggestion is removed by use of a prearranged reversibility cue then the subject is able to remember the same list of words that previously could not be recalled. This reversibility of amnesia contrasts with organic amnesia associated with hippocampal damage, which is not reversible. Posthypnotic amnesia appears to reflect a deficit in retrieval rather than encoding. This retrieval deficit also appears limited to explicit memory as demonstrated by the subject's ability to remember the list of names after the amnesia reversibility cue has been actioned.
Post hypnotic suggestion can be considered as a form of implicit memory since subjects act on a suggestion made during hypnosis but they have no memory of the suggestion itself. However, according to Kihlstrom (1999) post hypnotic suggestion provides an involuntary quasi-automatic cue that does not always win out when placed in competition with a waking instruction.
Subjects who are cued to perform a particular task and then given a waking instruction not to perform the task show symptoms of mental conflict and it becomes possible for either the post hypnotic suggestion or the waking instruction to win out. Although subjects are consciously unaware of why they behave as they do, or even that they are behaving as they are, post hypnotic suggestion doesn't appear to have the coercive power some have claimed. Despite the appearance of automaticity, processing post hypnotic suggestions consume a lot of cognitive resources and the tasks cued under hypnosis are not automatized by extensive practice.