greatly from those of very young children, some po-
tential memories may not be accessed.
Developmental Changes in Information
Processing Capacity
Does the absolute capacity of the memory stores
change with development? The answer to this ques-
tion is unknown and, according to some experts, may
be unknowable. It is clear, however, that memory
span, a measure of working memory, improves reli-
ably 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 in-
formation 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 re-
sources. 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 pat-
tern 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 ap-
plying strategies. Hence, developmental differences
in speed of processing can influence children’s capa-
bilities 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. Sim-
ply 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. Fa-
miliarity with the to-be-remembered material affects
the memory process at every step of information pro-
cessing. Imagine how difficult it would be, for exam-
ple, for someone who speaks only English to
remember a string of digits presented in another lan-
guage.
Michelene Chi provided a classic demonstration
of the importance of prior knowledge. In this investi-
gation, children who were chess experts had better
memories for chess positions than did nonexpert
adults, even though the adults demonstrated the ex-
pected advantage in remembering digits. Here, prior
knowledge of chess eliminated age differences in
memory. Because children’s knowledge bases in-
crease as they get older simply through their experi-
ences 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 or-
ganization 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. Knowl-
edge about a particular content domain (such as dino-
saurs or soccer) creates semantic associations between
previously unconnected items, resulting in the forma-
tion 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 re-
ported. Items that are represented as part of an ex-
tensive 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 de-
velopment of memory strategies is another important
reason for age-related increases in children’s ability
to remember, especially in academic settings.The Acquisition of Memory Strategies
A child’s intentional memory shows dramatic im-
provement when he can effectively use memory strat-
egies. These deliberate tactics for remembering
develop over a lengthy period that spans the elemen-
tary and middle school years. Preschool children use
very simple tactics for remembering in some special
task settings; for example, a four-year-old can be ex-
pected to use a marker to denote an object’s hiding
place in preparation for subsequently finding it. Pre-
schoolers do not, however, use mental strategies and
indeed do not typically differentiate memory and
perception. By age seven, most children spontane-
ously use rehearsal to enhance short-term memory
performance. Retrieval strategies (such as going se-
quentially through the alphabet) begin to be sponta-
neously used around third grade. Children’s self-
directed use of organization, the ability to impose a
semantic structure on the to-be-remembered items to258 MEMORY