Short-term memory has a limited capacity: it can store about seven pieces of information, plus or minus two pieces. These pieces of information can be small, such as individual numbers or letters, or larger, such as familiar strings of numbers, words, or sentences. A method called chunking can help to increase the capacity of short-term memory. Chunking combines small bits of information into bigger, familiar pieces.
Example: A person confronted with this sequence of twelve letters would probably have difficulty remembering it ten seconds later, because short-term memory cannot handle twelve pieces of information: HO TB UT TE RE DP OP CO RN IN AB OW L However, these letters can be easily remembered if they’re grouped into six familiar words, because short-term memory can hold six pieces of information: HOT BUTTERED POPCORN IN A BOWL
Psychologists today consider short-term memory to be a working memory. Rather than being just a temporary information storage system, working memory is an active system. Information can be kept in working memory while people process or examine it. Working memory allows people to temporarily store and manipulate visual images, store information while trying to make decisions, and remember a phone number long enough to write it down.
Information can be transferred from short-term memory to long-term memory and from long-term memory back to short-term memory. Long-term memory has an almost infinite capacity, and information in long-term memory usually stays there for the duration of a person’s life. However, this doesn’t mean that people will always be able to remember what’s in their long-term memory—they may not be able to retrieve information that’s there.
Imagine what would happen if a psychology textbook weren’t organized by section, by chapter, or in any other way. Imagine if the textbook didn’t have a table of contents or an index. If the textbook just contained lots of information in a random order, students would have difficulty finding a particular concept, such as “encoding of memory.” They’d know the information was in there somewhere, but they’d have trouble retrieving it.
Long-term memory stores much more information than a textbook, and people would never be able to retrieve the information from it if it weren’t organized in some way.