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Not Total Recall

December 7, 2014

I was watching an episode of Midsomer Murders, a BBC detective series, recently.  The murder had been committed with a large pair of taylor’s shears.  DCI Barnaby’s wife had been in the taylor’s shop just before the incident.  She witnessed a scuffle that broke out in the shop.  After the murder, Barnaby asked her to recall her memory of the taylor’s shop.  She reported that the shears were hanging on a peg in the shop before the scuffle, but then they disappeared.  Barnaby was able to use this information to identify the murderer.

Memory doesn’t work like that.  This is the “watching a movie model” of memory recall, one that we now know is incorrect.  Recalling a memory is not like viewing a movie.  People who work in IT know how much storage even a short video clip takes.  We don’t have that sort of memory.  There’s no survival advantage for us or for other animals in devoting that much of our brains to storing movies.  We won’t be able to discover additional details of an event by reviewing our memory of it.

We really only remember fragments of an event.  These are significant fragments, probably the ones with the highest emotional content.  All of our memories are reconstructed.  They seem complete and logical, but this is an illusion.  Our mind fills in the gaps from our general knowledge, making the memory complete.  It does this in recalling a memory the same way as it does it when we are experiencing reality.  Details of an existing memory can be altered.  Entire memories can be implanted.  Regardless, they still seem real, complete, and logical to us.  Our mind makes it that way.

In fact, our mind is as economical as possible.  It uses the same facilities for dreaming, for recalling memories, and for experiencing reality.  Of course, we can generally tell which is which, but they all seem real.  Steven Pinker explains some of this in his book How the Mind Works.  I know that realizing that memory is always reconstructed is contrary to our normal beliefs.  It gets even stranger.  Apparently, when we recall a memory, the original memory is erased from our minds and a new memory is stored in its place.  Memories can therefore change each time they are recalled.  It’s not at all like watching a movie, even though it may seem like that.


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