(Department of Psychology, University of Missouri, United States)

Working memory can be viewed as the information that is held in an active or accessible state temporarily, for the purpose of completing a task. In attempting to understand why working memory capacity changes with development during childhood, many theorists have focused on the increasing contributions of knowledge and strategies (analogous to computer software). Although such changes undoubtedly do occur, I have focused instead on the potential contributions of changes with maturation in basic parameters of information processing (analogous to computer hardware). On the basis of past research, I assume that humans have the ability to retain large amounts of sensory information at any one time, though each sensation is retained only briefly unless the information is attended; and the ability to draw only a small amount of information from sensory memory into the focus of attention at any one time. My presentation focuses on three basic parameters that appear to change with development: (1) the rate of retrieval of an item from working memory when it is needed; (2) the capacity of working memory, expressed as the number of independent chunks that can be retained simultaneously; and (3) the rate of forgetting of information from sensory memory. The evidence comes from span procedures, measurements of the timing of spoken recall, and experiments in which spoken lists were ignored at the time of their presentation but occasionally were attended shortly afterward.

Emphasis also will be placed on a general method that can be used to make comparisons across different age groups. A perennial problem with such comparisons is that overall differences in levels of performance make it difficult to interpret Age x Condition interactions. The work to be presented shows that it is sometimes possible to identify basic parameters of information processing that do not depend on the difficulty of the stimulus materials. These “difficulty-insensitive measures” in list recall studies yield similar estimates of performance at each age, and thus similar portraits of developmental change, regardless of the length of the list examined.

The evidence points to the existence of maturational changes in several parameters of information processing in working memory: retrieval rate, capacity, and sensory memory loss. It also points to the possibility of different profiles of abilities that can lead to equivalent performance levels. Perhaps most importantly, it shows that one can identify difficulty-insensitive measures that circumvent the usual difficulties that one faces in making cross-age cognitive comparisons.

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