Memory

Childhood Development of Working Memory

Studies of working memory suggest that it functions even in infancy. Infants can often detect a change from one visual display or sound to the next, reacting with signs of interest or surprise, because of their memory of a previously repeated display. Most tests of working memory, however, depend upon language to instruct the participant about a desired manual or verbal response, so most of these tests have been used with children at least 4 years of age. In simple span tests, a list of items is presented (e.g., from 2 to 8 spoken digits) and the participant tries to repeat the list verbatim. Span refers to the longest list repeated successfully. This kind of test shows steady increases in performance as the brain matures, beginning at age 4 years through about 10 years of age. Developmental increases occur even when age groups are equated on other factors, such as knowledge about the stimuli and the ability to filter out irrelevant information.

One explanation for this developmental improvement in span depends on the ability to rehearse the list verbally. Although this kind of [Page 1375]rehearsal tends to be relatively effortless among mature individuals, other working memory tests make this rehearsal impossible even for adults and may require instead that the maintenance of the list take place using a more attention-demanding form of refreshing the memory of list items. Among the latter type, in running span tests, the endpoint of the list is unpredictable and the required response is to repeat as many items as possible from the end of the list after it terminates. In complex span tests, some process is interposed between the items to be remembered; in counting span, for example, participants must count the number of objects of a certain type in each display and then repeat the sums. (e.g., given three successive displays of dots, the participant might count three dots, five dots, and two dots, and then recall three, five, two.) These kinds of procedures show continued development at least through middle adolescence, and sometimes until 18 years, and span correlates well with individual differences in the rate of maturation or basic aptitude measures such as intelligence quotient.

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