Hypnosis and Memory

In TV shows or movies, there are scenes in which people are given a suggestion that they would not remember a certain thing (such as a person's name or an incident, either during the session itself (hypnotic amnesia) or at the end of hypnosis (posthypnotic amnesia). A reversal cue could also be given, a phrase such as "You will now remember everything"; once the person hears this, their state of amnesia ends.

According to research, around 25% of hypnotised college students could be led to experience amnesia. Although researchers agree that hypnotic and posthypnotic amnesia occur, they do still debate the causes. Some feel that it's a result of voluntary attempts in avoidance of thought on certain information, while others believe it to be caused by an altered state of conscientiousness which weakens normal memory systems.

Memory Enhancement

In contrast to producing the effect of forgetting, can hypnosis enhance memory?

Law enforcement agencies sometimes use hypnosis in aid of eyewitnesses to a crime. In a famous case in California which occurred in 1977, a bus carrying 26 children and its driver disappeared without a trace. The victims, buried underground in an abandoned trailer truck by three kidnappers, were later found alive. After the rescue, an expert hypnotised the bus driver and asked him to recall the ordeal. The driver formed a vivid image of the kidnappers' white van and could "read" all but one digit of the vans licence plate. The information helped track down the kidnappers.

Despite occasional success stories such as this, controlled experiments find that hypnosis is unable to improve memory. In some experiments, participants watch videotapes of simulated bank robberies or other crimes. Next, while hypnotised or not, they are questioned by police investigators or criminal lawyers. Hypnotised individuals tend to remember better than non-hypnotised individuals in some studies, but not all. There have been experiments where hypnotised participants had performed much poorly than non-hypnotised people; they had recalled more information, but much of it was inaccurate.

Another concern regarding this is that some memories recalled under hypnosis maybe pseudomemories—false memories created during hypnosis by statements or leading suggestions made by the examiner. In some experiments, hypnotised and non-hypnotised participants are intentionally exposed to false information about an event (e.g.: about a bank robbery). Later, once the hypnotised subjects are brought out of their hypnosis, they are questioned. Highly suggestible individuals that have been hypnotised are the ones most likely to report the false information as being a true memory and often tend to be confident of the accuracy of their memories.

Although some psychologists are exploring ways to minimise hypnosis-induced memory errors, at present, many courts have banned or limited testimonies obtained under the influence of hypnosis. The increased suggestibility of hypnotised individuals makes them particularly susceptible to memory distortion caused by leading questions, and they may come to believe things that never occurred in the first place. Similarly, if a therapist uses hypnosis to help patients recall long-forgotten memories of sexual abuse, what shall we conclude? Are the memories real, or are they pseudomemories created during therapy sessions?

Disassociation

What is hypnosis ad how does it produce its effects?

Several researchers propose theories that view hypnosis as an altered state involving a disassociation of consciousness. Ernest Hilgard proposed that hypnosis creates a division of awareness in which the person simultaneously experiences two streams of consciousness that are cut off from each another. One stream responds to hypnotic suggestions, while the other—the part of consciousness which monitors behaviour—remains in the background, but is aware of everything that goes on. Hilgard reefers to this second part of consciousness as the Hidden Observer.

Suppose a hypnotised subject is given a suggestion that she wouldn't feel pain. Her arm is lowered into a tub of ice-cold water for 45 seconds and every few minutes, she reports the amount of pain. In contrast to unhypnotised subjects, who find this experience moderately painful, she would probably report feeling less pain. But suppose the procedure is done differently. Before lowering the subject's arm, the hypnotist says, "Perhaps there is another part of you that is more aware than your hypnotised part. If so, would that part of you report the amount of pain."

In this case, the subject's other stream of consciousness, the Hidden Observer, would report a higher level of pain.

For Hilgard, this disassociation explained the reason behind the involuntary automatic behaviour that occurs under hypnosis. Given the suggestion "Your arm will start to feel lighter and will begin to rise," the subject intentionally raises his or her arm, but only the Hidden Observer is aware of this. The mainstream of consciousness that responds to the command is blocked from this awareness and perceives that the arm is rising all by itself.