Memory

Does the absolute capacity of the memory stores change with development? The answer to this question is unknown and, according to some experts, may be unknowable. It is clear, however, that memory span, a measure of working memory, improves reliably with age. Memory span is defined as the number of single words or digits individuals can report in order immediately after hearing them. It increases from about two items at age two to five items at age seven to seven items in adulthood. The amount of information that individuals can hold in memory at any one time determines at least in part what they can learn.

It appears that age-related improvements in the memory span are attributable to two factors: changes in the resources that are available in the information processing system and differences in the efficiency with which older children and adults apply these resources. One of the most important developmental changes in the information processing system is in the speed of processing. Robert Kail asked individuals from ages six to twenty-one to perform a variety of cognitive tasks ranging from mental addition to memory search. He found a remarkably similar pattern of age-related increases in reaction time in the performance of all of the tasks. It should be noted that speed of processing is important in executing many cognitive functions, from moving information from the sensory register to working memory to applying strategies. Hence, developmental differences in speed of processing can influence children's capabilities to perform a variety of academic and everyday tasks.

Processing capacity increases if more resources are available; it can also be enhanced if the resources necessary to perform the task can be decreased. Simply providing extra time for study or problem solving improves children's performance in some but not all tasks. Perhaps the most important determinant of task demands is the learner's relevant knowledge. Familiarity with the to-be-remembered material affects the memory process at every step of information processing. Imagine how difficult it would be, for example, for someone who speaks only English to remember a string of digits presented in another language.

Michelene Chi provided a classic demonstration of the importance of prior knowledge. In this investigation, children who were chess experts had better memories for chess positions than did nonexpert adults, even though the adults demonstrated the expected advantage in remembering digits. Here, prior knowledge of chess eliminated age differences in memory. Because children's knowledge bases increase as they get older simply through their experiences in the world, age differences in memory may be explained to a great extent by differences in task-relevant knowledge.

Changes in the knowledge base also affect the organization of information in long-term memory and hence partially determine whether or not material can be reported. As depicted in the semantic network model of memory, items are represented as nodes and the nodes for associated items are linked. Knowledge about a particular content domain (such as dinosaurs or soccer) creates semantic associations between previously unconnected items, resulting in the formation of connections between nodes. When one item is recalled, the activation spreads to associated items as well, increasing the likelihood that they will also be reported. Items that are represented as part of an extensive network of information within a content area are also less likely to be lost over time. Moreover, age differences in children's long-term event recall are minimized when younger and older children have high levels of prior knowledge about the to-be-remembered components of the experience.

Knowledge also enhances memory by making it easy to apply strategies for encoding and retrieving information. As discussed in the next section, the development of memory strategies is another important reason for age-related increases in children's ability to remember, especially in academic settings.