Short-term memory is thought to process information by actively repeating, grouping, and summarizing it to aid its storage in long-term memory. Information is thought to last within short-term memory for only a short period of time before it is either passed into long-term memory or discarded. For information to be transferred into long-term memory, it must be rehearsed or repeated.
Generally, short-term memory can hold five to nine units of information for between twenty seconds to one minute in length. It holds information for as long as its actively thought about, or until new information basically forces it out. Unless we repeat the information and purposely try to retain it, most, or all of it, will be lost. A good example of this process can be seen when you look up a new phone number, and repeat it to yourself as you dial it. After dialing it, within a few seconds you will usually forget it. Yet if you do this repeatedly (repetition or rehearsal), like for a friend with a new phone number, it will eventually enter long-term memory.
These "units" of information can represent single pieces of information, such as an individual's name, or the units can be single pieces of information that represent a number of different pieces of information, as in the last name of a family representing all of the family's members. The process of using a single item to represent a number of items is called chunking, and researchers have found that short-term memory's information holding capacity can be greatly enhanced with this process.
It seems there are many factors that determine what information enters long-term memory, two of the strongest being repetition and intense emotion. If something is repeated often enough, such as multiplication tables, it will enter long-term memory. And it is hard to forget intensely emotional experiences such as being involved in a serious car accident or falling in love.
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