Types of Human Memory

Memory is the retention of information over time. Although the word memory may conjure up an image of a singular, “all-or-none” process, it is clear that there are actually many kinds of memory, each of which may be somewhat independent of the others. One way to describe memory is by reference to the form it takes, that is, the different ways memory may be assessed: recall, recognition, and paired associates.

The most popularly studied kind of memory is recall. Recollection of a telephone number you have just heard, a list of items you are to purchase at the store, or a list of dates you learned in history class are all examples of recall.

A second type of memory is recognition, which is generally easier than recall, for example a history teacher gives four dates and learners are to choose the one that goes with the specific historical event.

People often underestimate just how powerful their recognition memory is. Roger Shepard showed hundreds of photographs of faces to adults and later presented them with a recognition problem: they were to identify which face in a pair they had previously seen in his collection. With literally hundreds of such test pairs, recognition accuracy was between 90 and 100 percent for most subjects.

Another kind of memory is called paired associates. It is a person's ability to memorize a list of paired items, such as pictures and names, common objects and nonsense syllables, or words and corresponding visual scenes.

Memory as the Flow of Information

One prominent view conceives of memory as the flow of information through the mind. In a number of statements about this view, three broad stages of information processing can be distinguished. First, there is the sensory register, a very short-term sensory memory of the event. At the second level is a short-term, or working memory.

Roughly speaking, the sensory register concerns memories that last no more than about a second. If a line of print were flashed at you very rapidly, say, for one-tenth of a second, all the letters you can visualize for a brief moment after that presentation constitute the sensory register. This visualization disappears after a second.

When you are trying to recall a telephone number that was heard a few seconds earlier, the name of a person who has just been introduced, or the substance of the remarks just made by a teacher in class, you are calling on short-term memory, or working memory. This lasts from a few seconds to a minute; the exact amount of time may vary somewhat. You need this kind of memory to retain ideas and thoughts as you work on problems. In writing a letter, for example, you must be able to keep the last sentence in mind as you compose the next. To solve an arithmetic problem like (3 X 3) + (4 X 2) in your head, you need to keep the intermediate results in mind (i.e., 3 X 3 = 9) to be able to solve the entire problem.

The distinction between short-term memory and working memory is an ongoing debate. The terms are often used interchangeably. Many scholars, however, claim that some kind of manipulation of remembered information is needed in order to make the task a working memory task. According to Cowan, short-term memory refers to the passive storage of information when rehearsal is prevented with storage capacity around four items. When rehearsal is allowed and controlled attention is involved, it is a working memory task and the capacity is closer to seven items. Repeating digits in the same order they were presented would thus be a short-term memory task, while repeating them backwards would be a working memory task.

Recent data has shown that working memory capacity can be affected by training.

Long-term memory lasts from a minute or so to weeks or even years. From long-term memory you can recall general information about the world that you learned on previous occasions, memory for specific past experiences, specific rules previously learned, and the like.