Short Term Memory contains information that we are actively using.
If you want to call your friend and you don't know his or her number, you might:
- Look it up in a telephone directory.
- Find and write down the number. What if you don't have pen or paper handy?
- You might try repeating the number in your head, "saying" the number silently to yourself, maybe even out loud.
- Pick up the phone and dial the number (seven digits in many countries).
- However, if the number is busy, and you cannot make a connection, what will happen to this "memorized" phone number.
- ...The chances are great
that you will have to look up the number when you try again five minutes later,
because you've already forgotten the sequence! If you don't have a re-dial
button on your phone or if someone used the phone since your previous call,
you'll have to look it up again!
This is because your friend's phone number was only stored in your short-term memory, which lasts less than a minute without repetition or rehearsal! (Matlin, 1998, p. 115)(Benjamin, Hopkins, & Nation, 1994.p. 253) (Loftus, 1900.p.393)
A person's short term memory capacity, also called the memory span, is approximately 7 pieces ("plus or minus two"), or units of information (Miller, 1956, as cited in Matlin, 1998, p. 119). This could be numbers, letters, words, etc.
But wait a minute -- how could a unit be a letter OR a word, and the size-limit be 7? What about one seven-letter word? The man who calculated the human memory span, George Miller, described these units as chunks. Chunking is a method of organizing information so that it makes sense to us. Try our chunking demonstration to see how chunking might be helpful.
Another way of describing the use of short-term memory is called working memory.
