Tuesday, 9 October 2012

Why NOT to give a witness your opinion on a case!

I have mentioned before how witnesses will often remember 'new' aspects to an experience they have already described in detail. It almost always happens when a plausible 'natural explanation' is suggested for the experience. And the 'new' aspect invariably serves to discount the natural explanation suggested as a possibility. In this week's New Scientist there is a feature on memory and I think it goes some way towards explaining this phenomenon.

It is well known that memory is unreliable and that it can change. Recent research has found specific causes for memory alteration. For instance, whenever we recall an event the chemical changes required to reproduce it actually change it forever! So your memories change whenever they are recalled, though usually only subtly! And it seems that memory may have evolved to allow us to predict future events rather than as an autobiography. When you imagine a future possible scenario, it actually changes existing memories! And people in close relationships, such as a couple or siblings, can 'adopt' some of the memories from the other person involved. So some of your treasured childhood memories may actually have really happened to your sibling! This puts into perspective reports of paranormal events from couples and family groups. Another interesting thing is that people tend to remember things that reinforce their own view of themselves, while forgetting things that contradict it. So if someone thinks they are psychic, they may remember the few times they successfully predicted the future, while forgetting all the others when their prediction failed.

How might this help explain the 'new' memory scenario I mentioned above? It seems likely that when the witness considers the 'natural explanation' being suggested, they try to fit it with what they remember. In doing so they may affect the original memory itself, just as they would if they were imagining a future possible scenario. But why should this memory alteration always happen to contradict the suggested explanation? That is probably because the witness has, possibly unconsciously, decided that they what they experienced really was paranormal. So any explanation that challenges that idea will cause the memory to alter in such a way that dismisses the possibility. Also, they will remember anything that serves to confirm their paranormal interpretation of the incident, while forgetting anything that might contradict it. As I commented recently (here), witnesses may actually see the solution to the mystery of their weird experienced at the time but either not realise or remember it.

It is likely that once a memory has been altered in this way, it will not go back to the way it was before. This means that it may not be a good idea to suggest likely natural explanations to witnesses! It is better not to discuss your theories with witnesses unless they insist on knowing. In some cases people accept suggested natural explanations happily, even expressing relief! But there are always those who react in the way I've described.

Of course, there is always the possibility that the 'new' details remembered by the witness are correct. However, this scenario happens so consistently, often multiple times with the same witness, that it is difficult to dismiss the idea of it being an example of memory altering. All of this reinforces the logic of using things like cognitive interviewing techniques which seek to minimise memory alteration. Memory should always be treated as the fragile and unreliable thing that it really is!


  1. Interesting! Do you have any links to the 'New Scientist' article, or the research it references? If recall affects memory at the chemical level (which seems to take for granted that the memory and its chemistry are one and the same) doesn't this negate the psychological explanation for the alteration of memories which you advance later in the article?

  2. Recent New Scientist articles are generally only available online to the magazine's subscribers. I have considerably simplified the process of changing memories by saying it is chemical. It is thought to be an epigenetic process. Such a mechanism does not preclude it being controlled by psychological processes. When you move your arm, your brain translates that thought into electrochemical signals that tell a muscle how to use chemicals to bring about the movement about.