Human Memory

Long-Term Memory

Long-term memory is that more permanent store in which information can reside in a dormant state -- out of mind and unused -- until you fetch it back into consciousness (working memory).

Organization of Information in LTM

Given the vast amount of information that a person stores in long-term memory during a lifetime, there must be some highly efficient way to access this formation when it is needed, or else we would spend weeks or months just trying to recall the simplest things. A library organizes its books by assigning them a catalog number and placing them on the shelves by call number. A catalog allows you to look up the book by author, title, or subject and determine its call number, thus allowing you to efficiently locate the book on the shelf. In some way, the brain must do something like the same to allow you to retrieve memories efficiently.

We still have much to learn about the process by which the brain accesses its stored information, but a key element in that process is the ability of certain inputs, both sensory experiences and internally generated inputs (from thought or imagination), to activate memory traces through associative links. That is, the human memory system uses what computer folks term associative addressing. For example, the sound of a word produces a pattern of activity in the brain that in some way matches a stored pattern for that sound; activation of that stored pattern (the remembered word) in turn, through associative connections, activates other memory traces of information associated with the word. Thus the sound (or sight if you are reading) of the word "basket" brings immediate recognition and with it, access to all sorts of information about baskets -- how they look, what they are made of, what they are used for, and so on. Thus, given an appropriate input cue, the cue stimulates activity in the brain that results in the retrieval of all sorts of information you have stored relating to that cue.

This associative model implies that if you lack an appropriate cue, you will not be able to recall information even though it is stored in your brain. It also implies that information you may have thought you had forgotten may be retrieved if you can find the right retrieval cue.

The model also explains how we often can come up with information so quickly -- the retrieval cue immediately activates the memory trace associated with it, or a small set of traces that can be searched quickly for relevance to the question being answered. The model also shows how it is that we can quickly determine that we don't know something: if the information we seek is not retrieved by the retrieval cue, then it likely isn't there.


Mnemonics are memory aids. Several popular mnemonic techniques make use of the associative nature of human memory by visually associating the item to be remembered with something else that is easily remembered. This something else then provides the retrieval cue for the item. An example is the method of loci.

The Method of Loci

"Loci" is Greek for "locations." The ancient greek orators used the method of loci to make sure that they recalled each part of a speech in its proper order. The technique involves visualizing moving through some familiar place and placing each item to be recalled as a specific place. During the speech, the orator would imagine visiting each location in turn and retrieving the item.

The Pegword System

The pegword system allows you to associate items with numbers, so that, given the item, you can recall its number, or vice versa. It requires you to first memorize a set of rhymes which associate the numbers (one through 10) with easily visualized items -- e.g., "one is a bun, two is a shoe . . ." You then imagine each item to be remembered visually connected with the item you have associated with the number. For example, if your first item is "automobile," you might imagine a car made out of a huge bun. Later, when asked to remember which item was number one, one reminds you of bun, which leads you to picture the automobile-bun, and thus you recall "automobile." Or if given the word "automobile," you picture the auto-bun, and remember "one."

Long-Term Memory Classifications

Long-term memories belong to two broad categories: declarative and procedural. Declarative memories are further subdivided into semantic and episodic memories: