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What Is Memory Span?
Memory span is defined as the amount of material which can be remembered perfectly, 75% of the time, immediately after a single presentation. Measurement is usually accomplished by presenting a series of unfamiliar composition, although the separate elements are familiar; for example, a number series like the following:
7 1 4 9 2 8 5
If the individual succeeds on the first span presented, he is given another scrambled list with one more digit, and so on until he fails. If he fails the first, he is given lists of decreasing length until he succeeds. If careful measurement is desired, a variety of lists will be tried to be sure that he can normally succeed at one level and will fail at the next longer list.
Memory span is a common measure of short-term memory. It is also a component of cognitive ability tests such as the WAIS. Backward memory span is a more challenging variation which involves recalling items in reverse order.
Memory span tends to increase with age. Children four to six years old can hold about four digits in immediate memory; college students average about eight. This span can be improved by training.
The effect of overloading on memory span is interesting. If one can just handle eight digits and is presented with nine, he will successfully recall, not eight, but five or six. The attempt to “stretch” and encompass a series beyond the effective span results in breakdown of the whole process. Two factors are involved here: (1) the retroactive interference of later items in the series, blocking recall of the early items; and (2) the interference with discrimination when an excessively difficult task is presented.
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