More about memory

A friend recently told me about visiting a family friend’s house as a small child. When they arrived, a huge St. Bernard bounded up to her, put its paws on her shoulders, and pushed her to the ground. She remembers it as though it were yesterday. Her mother and the family friend remember it too–except they say the dog was an Afghan. My friend, however, is adamant: it was a St. Bernard.

Okay, so forgetting whether a dog was an Afghan or a St. Bernard isn’t a big deal. But all of us can cite similar experiences. We remember things that never happened, forget things we shouldn’t, and yet, for some reason, can still sing jingles to TV commercials from when Pearson was prime minister.

Still, the fact our memories are sometimes unreliable isn’t nearly as remarkable as the fact that we have memories at all: that somehow, we can call up sights, sounds and feelings from months, years, or decades ago. It’s almost like time travel!

There are three main types of memory: short-term, middle-term, and long-lasting. Short-term memory lasts just a few seconds, long enough for us to dial a number we looked up in the phone book, for example

Middle-term memory lasts a few hours. It reminds us whether we’ve had lunch yet or that we’re supposed to take the kids to the dentist this afternoon. But it fades; by Thursday, you will have forgotten most of Monday.

Sometimes, middle-term memory becomes long-lasting memory, which remind us of what we’ve done in the past, of goals we’ve set for ourselves, of joys and disappointments. Our long-lasting memories are, in a sense, ourselves: they’re inextricably intertwined with our identities.

Whenever any new information enters the brain–say, somebody’s name–it does so in the form of electric impulses, passed from neuron to neuron (the nerve cells that are the brain’s basic building blocks). These impulses die away in milliseconds, but their passage reinforces a particular pattern of connections among a particular set of neurons, making it possible for the brain to recreate the name. The more often that pattern is reinforced, from hearing the name again or thinking about it, the more likely it will become a long-lasting memory. Whereas short-term and middle-term memory involve only chemical changes in the neurons, long-lasting memory is “hard-wired”–the synapses that link the neurons involved grow thicker and stronger.

Most of us constantly edit, ignore and overlook information, rather than committing it all to memory. A few people remember everything, and they find the enormous flood of memories associated with every person, event and object makes it difficult for them to interact normally with people or hold down a job. The best known example, a Russian named Shershevsky, ended up as a Vaudeville act.

The editing and sorting process, however, leaves us open to false memories. Several studies have shown just how easy it easy to create these. For example, volunteers who listen to a list of related words, such as “bed,” “dream,” “blanket,” “doze” and “pillow,” when later asked to recall the words they heard, will often include another related word, “sleep,” which wasn’t on the list.

Then there’s “hindsight bias.” Suppose you see a picture of a politician and you think, “He has shifty eyes.” If that politician is later convicted of misusing public funds (not that THAT would ever happen), you’re likely to be convinced that the first time you laid eyes on him, you thought, “What a crook.” Since later events proved your initial negative reaction to be justified, you become convinced you were much more perceptive than you really were.

Entire events can also be created out of nothing. In another study, college students were prompted on two consecutive days to imagine having spilled a bowl of punch at a wedding as a child. The next day, several of those students were convinced they really had spilled a bowl of punch at a wedding. Typically, they inserted the false memory into a larger, more accurate memory of a particular wedding…just as my friend inserted a St. Bernard into a scene that really involved an Afghan.

We may eventually be able to distinguish between false memories and real ones: recent research with PET scans shows that real memories activate regions of the brain related to sensory input, whereas false memories do not.

Someday, we may be able to settle the St. Bernard/Afghan question–or your personal equivalent–once and for all.

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