Most people are capable of storing a maximum of about seven separate units of information in short-term memory—e.g., the seven random letters F, L, I, X, T, Z, R. Thus, one may consult a directory for a 10-digit telephone number but forget some of the digits before one has finished dialing. However, if the units of information are grouped or “chunked” into meaningful patterns, it is possible to recall many more of them, as shown by the series of 24 letters F, R, A, N, C, E, G, E, R, M, A, N, Y, P, O, L, A, N, D, S, P, A, I, N. According to the American psychologist George A. Miller, such chunking of information is essential for short-term memory and plays an important role in learning.
Short-term memory is restricted in both capacity and duration: a limited amount of information will remain active for a few seconds at best unless renewed attention to the information successfully reactivates it in working memory. Before such “renewal” occurs, most information arrives in working memory through sensory inputs, the two most prevalent being aural and visual. Baddeley posited that working memory is supported by two systems: the phonological loop, which processes aural information, and the visuospatial sketch pad, which processes visual and spatial information. When information is acquired aurally, the brain encodes the information according to the way it sounds. A person who hears a spoken telephone number and retains the information long enough to complete dialing is employing the phonological loop, a function of working memory involving, in effect, an inner voice and inner ear each person utilizes to rehearse and recall information. Children who are slow to learn this type of encoding are also generally delayed in learning to read.
Visual and spatial encoding are an integral part of daily problem solving. A person solves a jigsaw puzzle by constructing an image of a missing piece and then seeking the piece that matches the constructed image. It would not make sense for this construct to be held in long-term memory, but its function as a short-term memory is essential to reaching a solution. Such short-term encoding of visual-spatial information is important in any number of tasks, such as packing suitcases in the trunk of a car or searching for a missing shoe in the bottom of a closet. Long-term memory
Memories that endure outside of immediate consciousness are known as long-term memories. They may be about something that happened many years ago, such as who attended one’s fifth birthday party, or they may concern relatively recent experiences, such as the courses that were served at a luncheon earlier in the day.
Accumulated evidence suggests that a long-term memory is a collection of information augmented by retrieval attributes that allow a person to distinguish one particular memory from all of the other memories stored in the brain. The items stored in long-term memory represent facts as well as impressions of people, objects, and actions. They can be classified as either “declarative” or “nondeclarative,” depending on whether their content is such that it can be expressed by a declarative sentence. Thus, declarative memories, like declarative sentences, contain information about facts and events. Nondeclarative memory, also known as procedural memory, is the repository of information about basic skills, motor (muscular) movement, verbal qualities, visual images, and emotions. A crosscutting distinction is made between memories that are tied to a particular place and time, known as “episodic” memories, and those that lack such an association, known as “semantic” memories. The latter category includes definitions and many kinds of factual knowledge, such as knowledge of the name of the current pope, which one might not recall having learned at any particular time or place. Patterns of acquisition in long-term memory
There are roughly three phases in the life of a long-term memory. It must be acquired or learned; it must be stored or retained over time; and, if it is to be of any value, it must be successfully retrieved. These three phases are known as acquisition, storage, and retrieval. Relatively little is known about the factors influencing the storage of memory over time, but a good deal is understood about the mechanisms by which memories are acquired and successfully retrieved. Intervals
Memory researchers have identified specific techniques for improving one’s ability to remember information over a long period of time. One of the most powerful means involves scheduling regular practice sessions over a relatively long period. Consider, for example, two groups of people learning vocabulary words in a foreign language. One group studies for five hours on one day, and the other group studies for one hour per day for five days in a row. Athough both groups practice for a total of five hours, they will differ in their ability to recall what they have learned. If the two groups are tested on the day after the first group studied for five hours, the first group will perform better than the second; if, on the other hand, the test occurs one week after the two groups completed their study, the second group will perform better and remember more of the words in the future. Such cases suggest that, while there may be some short-term benefit to “cramming” for a test, the most effective means of committing facts to long-term memory depends upon routine and repetitive study. Rehearsal
Although the ability to commit information to memory is greatly enhanced through repetition or rehearsal, not all rehearsal techniques are effective in facilitating later recall. Simply saying something to oneself over and over again, a technique called “rote rehearsal,” helps to retain the information in short-term memory but does little to build a long-term memory of the event.
Another form of rehearsal involves motor coordination, whereby movements or series of movements are “memorized” for greater efficiency or skill of execution in the future. A skilled touch typist who frequently inputs a short string of letters might thereby encode the movements involved in typing the full string, rather than relying on the separate movements he has already encoded for each letter. In this sense rehearsal occurs through repeated attention to each of several movements in a series. This form of rehearsal enables the performance of countless activities, such as riding a bicycle, dancing a particular step, or executing a competitive dive. Mnemonic systems
More-effective types of rehearsal consist of reflection—thinking about the material one is trying to learn and discovering ways in which it is related to something one already knows. One traditional technique for committing a list of items to memory involves imagining that one is traveling a familiar route in one’s town while stopping to place an image of each item at specific landmarks on the route. This technique, called the method of loci, was used by Greek orators such as Cicero and Simonides as a means of organizing and remembering points in their speeches.
The method of loci is based on the principle that encoding new information—such as items from the list to be memorized—to previously stored data—landmarks along a familiar route in one’s town—can be an effective means of improving memory function. When encoding techniques are formally applied, they are called mnemonic systems or devices. (The popular rhyme that begins “Thirty days hath September” is an example.) Verbal learning can be enhanced by an appropriate mnemonic system. Thus, paired associates (e.g., DOG-CHAIR) will be learned more rapidly if they are included in a simple sentence (e.g., The dog jumped over the chair). Imagery that can associate different words to be learned (even in a bizarre fashion) has been found beneficial. Indeed, some investigators hold that pure rote learning (in which no use is made of established memories except to directly perceive the stimuli) is rare or nonexistent. They suggest that all learning elaborates on memories already available.