In the January / February 2006 Skeptical Inquirer, Martin Gardner writes about the still-simmering debate over recovered or repressed memories about childhood sexual abuse:
Of all such techniques the most worthless is hypnotism. Mesmerized patients are in a curious, little-understood state of extreme suggestibility and compliance. They will quickly pick up subtle cues about what a hypnotist wants them to say, and then say it. The notion that under hypnosis one’s unconscious takes over to dredge up honest and accurate memories of a distant past event is one of the most persistent myths of psychology.
There simply is no known way, short of confirming evidence, to distinguish true from false memories aroused by hypnotism or any other technique. After many sessions with a sincere but misguided therapist, false memories can become so vivid and so entrenched in a patient’s mind that they will last a lifetime.
The key to the claim about recovering “repressed” memories is confirmation. How do you tell the difference between a genuine memory that has been repressed and a false one that has essentially been created by an incompetent or dishonest hypnotist? There is nothing inherent in the memories themselves which can provide this information. You can’t rely on how strongly a person believes in a memory — in fact, there is evidence that stronger confidence is associated with greater error in memories.
The only thing we can do is find independent evidence that confirms what has been reported — but if we have that independent evidence, of what value are the memories? At best they might be used as a reason for looking in particular places for evidence, but hopefully a good investigator will have already thought to look there and doesn’t need the “recovered” memories in the first place.
All in all, then, it would appear that hypnotism for the purpose of “recovering” a “repressed” memory has no real value at all. It’s not reliable and doesn’t produce decent information. Why do people use it so much, then?