The term memory span refers to the maximum length of a sequence of items that can be reproduced from memory following a single presentation. Scientists have been interested in memory span since the publication of the first important study of memory, nineteenth-century German experimental psychologist Hermann Ebbinghaus's monograph in 1885. Using himself as his only subject, Ebbinghaus determined the number of presentations necessary for an error-free reproduction of a sequence of items; he found that this number decreased dramatically as the length of the sequence decreased until the sequence included only seven items, at which point only a single presentation was needed. Ebbinghaus showed no particular interest in this finding, but others did. Within two years, memory span was shown to increase systematically during childhood and to be appreciably shorter for the mentally impaired. Within a decade, memory span was firmly established in what was then an...