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An individual's memory span is a measurement of the number of items from a list that he can repeat immediately after seeing or hearing the list. Usually, the subject being tested is asked to recount the items in the correct order, but in some trials he is asked to recall the items in reverse order. In normal tests of one's memory span, the individual being tested is asked to repeat the contents of several similar lists and the results of each trial is averaged. Memory span is one of the most common metrics used to measure one's short-term memory.
There are many different variables used in memory span tests that examine various parts of one's memory. In some, for instance, the test subject knows how many items are in the list to be memorized while in others the list stops at an unspecified time. Generally speaking, the subject needs to repeat the list in forward order or in reverse order, but in some cases he is asked to group the items into categories or to recount them in any order. Words, numbers, and letters, or a mix thereof may be used in such tests. Altering the variables of the tests provides researchers with information on how different facets of one's short-term memory work.
Different memory span tests present the items on the list to be memorized in different ways. Sometimes the items are read very quickly to the test subject while in other cases they are read slowly. In some cases there is some predictable rhythm to the presentation while in other cases the rhythm is arbitrary. Some tests also present the list visually rather than verbally. Intentional distractions in the form of visual oddities or background noise are sometimes worked into the test space to examine how the subject's short-term memory differs in the presence of distraction.
Many qualities of the test subject himself also effect the outcome of memory span tests. Memory span, for instance, changes based on a person's age and tends to increase to a certain extent over time. Various psychological and neurological disorders can also effect one's memory span, usually in a negative way. Even chronic physical conditions have been demonstrated to cause a noticeable decrease in an individual's short-term memory. Researchers speculate that other characteristics, including sex, physical fitness, and education may also have some connection to short-term memory.