The stage theory of memory was developed about forty years ago as an attempt at explaining how memories are stored in the brain. It says that there are several systems memory uses to store information that all have different storage mechanisms. Short term or working memory and long term memory are the main systems used. Some people also think think that there's another kind of memory that comes before the other two, which is referred to as a sensory register, which only holds information for a second or two.

It is thought that long term memory has an incredibly large capacity. For example, the average college student knows the meanings of 80,000 words, facts about hundreds or thousands of events in their life and the lives of others, random facts, skills, and snippets of memories. On the other hand working memory is limited to seven items, plus or minus two, and this has been shown in a number of studies with different approaches to the topic.

Working memory is often referred to as a "loading dock" for long term memory since everything that enters long term memory has to pass through working memory and this is the basis of the stage theory of memory. Although most things never make it into long term memory, if they spend enough time in working memory they will be placed into long term storage from the "loading dock".

Things in working memory are lost very quickly. As we go through life we note all sorts of details in the world around us only to forget them a few minutes later if even that. One theory that explains this idea is decay: over time the memory "erodes" and becomes less distinct, only leaving the major details to enter long term memory. The other main theory is displacement: as new things enter working memory other things are pushed out and not all of them make the cut for long term memory. For now it is thought that both are partially right and no matter which one is right it's fairly clear that nothing stays for more than a few minutes in "short term" memory so that our memories do not become clogged with useless details such as the color of the car behind you on the road.

Pushing something into long term memory can be difficult. The most common approach is called rehearsal: repeating something so it stays in working memory longer and is more likely to be pushed into long term memory. This theory has been tested using free recall and it seems very likely that this is the best approach to storing something long term. We even subconsciously repeat important moments to ourselves that we want to remember so they'll be pushed into long term memory.

You can use a number of methods to enhance your short term memory and make yourself more likely to remember something in the long run. Remember the magic number seven? Try to take all the things you want to remember and group them together into smaller groupings, but not more than seven or so. This approach is called chunking. This is why acronyms and mnemonics work so well.

Henry Gleitman, et. al. Psychology. New York City: W.W. Norton & Company, 1999

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