How Quickly We Forget: The Transience of Memory
This is the first in a new series on the 7 deadly sins of memory. First up, how the passage of time affects our memories.
My memory continues to surprise me, and not usually in a good way. I recently reread a book which I first read, and greatly enjoyed, about 13 years ago. It is fiction by one of my favourite authors - the writing is vivid, the story exciting and the set-piece action breathtaking.
Despite all this I had almost no memory of reading the book the first time. Almost everything about the book seems to have seeped away in the intervening years. I couldn't remember the plot, most of the characters or any of the scenes. The only thing I vaguely remembered was the main character's name, but I couldn't be sure I hadn't invented that memory, after all I couldn't recall anything else about the book.
This is an example of what Harvard psychologist Daniel L. Schacter calls the first deadly sin of memory: transience (Schacter, 1999). Transience can be seen in both short- and long-term memory. Short-term memory, for psychologists, means the things that are in your mind right now, and only those things. On the other hand long-term memory is anything you store to be retrieved at a later time. Studies have shown that both types of memory can be extremely fragile over their respective timescales.
Short-term memory: fast forgetting
A classic experiment on fast forgetting was carried out by Peterson and Peterson (1959). They asked participants to memorise a three-letter sequence, then count backwards in sets of threes. Participants were then asked to try and recall the three-letter sequence after different lengths of time counting backwards.
Participants did surprisingly poorly on this test. After only six seconds of counting backwards in threes, on average half of the original three letters had disappeared from memory. By the time participants had been counting backwards for 12 seconds, less than 15% of the original memory remained. Finally after 18 seconds it was all but gone.
This experiment clearly shows how quickly information leaks out of short-term memory. So perhaps the book I was reading just went straight in and straight out again? No doubt a lot of it did, but surely some of it must have stuck. Otherwise I wouldn't have been able to follow the story and would have ended up reading the first page again and again.
Long-term memory: slow forgetting
No, some aspects of the book must have become lodged in my long-term memory, so what types of processes affect how much we retain from long-term memory? In fact relatively little is known about how we forget over substantial periods of time. Thirteen years is a long time for an experimenter to wait just to find out if I can remember the details of that book.
Nevertheless, studies do suggest that forgetting probably follows a power function. That means we lose a lot of information soon after it goes in, then, over time, the rate of forgetting slows down.
Storage, retrieval and rehearsal
Of course not all memories are created equal, and so the reasons why we fail to recall information are many and varied. Indeed, some psychologists have argued that we never really forget anything. Perhaps, they say, the memory is still in our minds but we can no longer access it.
Cues are clearly important to retrieving memories. The smell of varnish might remind us of the day we spent canoeing in the rain, lost in solitary thought. Conversely some experiences can hinder the retrieval of certain memories. The memory of a parent's anger at our childish misdemeanour might completely block out the memory of what we actually did.
Memory is certainly more likely to fade if we don't use it. The retrieval and rehearsal of memories has been shown to enhance their storage. Interestingly there's no actual evidence in humans that memories which remain unrehearsed or unretrieved actually do dissipate over time. Perhaps all our memories really are still in there.
Gone, and forgotten
But even if my memory of reading that book the first time is still in there, it's doing a very good job of hiding. Especially since rereading the book should be a massive cue to its recall. Maybe we do completely forget or maybe I have just forgotten that I didn't actually read the book in the first place. Either way, perhaps I'll be able to enjoy the same book all over again in another 13 years!
- » How Quickly We Forget: The Transience of Memory
- Absent-Mindedness: A Blessing in Disguise?
- On the Tip-of-the-Tongue: Blocked Memories
- How Memories are Distorted or Invented: Misattribution
- When Suggestibility is a Liability: Wrongful Convictions
- How the Consistency Bias Warps Our Personal and Political Memories
- The Persistence of Memory
[Image credit: Peter Bowers]
References
Peterson, L. R., & Peterson, M. J. (1959). Short-term retention of individual verbal items. Journal of Experimental Psychology, 58, 193-198.
Schacter, D. L. (1999). The seven sins of memory. Insights from psychology and cognitive neuroscience. American Psychologist, 54, 182-203.
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An excerpt from "Forgetfulness" by Billy Collins:
The name of the author is the first to go
followed obediently by the title, the plot,
the heartbreaking conclusion, the entire novel
which suddenly becomes one you have never read,
never even heard of,
as if, one by one, the memories you used to harbor
decided to retire to the southern hemisphere of the brain,
to a little fishing village where there are no phones.
I encourage readers to seek out the poem in its entirety. A humorous musing on the transience of memory.
Great article. Thanks!
The beginning of it reminded me of a little story about Leo Tolstoy mentioned by Nabokov in his Lectures on Russian literature:
Tolstoy in his later years once took a random book from his bookshelf and started reading it. The book turned out to be amazing! He couldn't stop reading it for a while. He then took a look at the tiltle and was greatly surprised as he read "Anna Karenina".
I'd mention that memory choses itself what to remember, and what to retain over time, and that cannot be controlled consciously.
For example, memories that were used are usually better retained.
Also, in mentioned experiment, three-letter sequence might be well memorized through some associations (don't know how that method is called, though, but it should be somewhat known).
P.S. "excuse my bad english"...
What book?
I have done myself the experiment by Peterson and Peterson (and other ones...) and I can say it is quite difficult. The explanation they gave is that the information about the three letters is erased from our working memory (short term memory) by the counting task, so it cannot consolide in long term memory and disappears. It is not only time that makes our memories go away, it is also interference.
Forgetting something like a book you read 13 years ago is not that hard to explain. Your memories are stored in brain tissue. If you access it frequently (say you discuss this book many times over the years) that brain tissue will be maintained, the fibers strengthened. If it goes untouched for over a decade, the tissue loses its elasticity like an old rubber band and the memory is all but gone. Your brain won't waste efforts maintaining every single thing you ever learned, and the things you never reach for even once are the first memories you lose.
Thank you for the article. I would like to see memories broken down even further. I believe I lost non-declarative memories due to PTSD. I didn't loose factual memories (distorted or not), but lost what is often termed as the auto pilot of the mind. In other words I was fully aware that I should never leave my purse in a restaurant, but I did it time and time again. I even had to and was able to make the decision not to carry it anymore. So I knew I shouldn’t, didn’t want to, feared the consequences and yet it was years before any action resulted. I have found very little “good” information on this type of memory loss and would love to see more articles. Oh yeah, couldn’t carry a purse but could type 70 wpm.