extended problem-solving efforts by digit-span experts to identify strategies
and encoding methods to increase their digit-span performance, as well as
similar efforts by other subjects, whose performance never improved or did not
improve beyond a certain level. When that evidence is considered together
with studies of other memory experts (Ericsson, 1985, 1988) past and present, it
appears that all memory experts rely on the same limited set of mechanisms
(Chase & Ericsson, 1982). Given that most memory experts have not been
instructed but have themselves discovered the structures necessary for their
memory skills over extended periods, the importance of problem solving for
their ultimate performance can hardly be overestimated. Similarly, studies of
the development of a number of perceptual motor skills suggest the importance
of discovered methods and strategies for performing tasks such as juggling
(Norman, 1976). There appears to exist a wealth of phenomena such that suc-
cessful performance in the future cannot be predicted on the basis of current
performance. Similarly, there is no reason to believe that such problem solving
is limited to the early stages in the development of expert performance.
Accounts Focusing on the Ability to Plan and Reason. Analyses in several different
domains of expertise have revealed that experts engage in a number of complex
mental activities involving reasoning that relies on mental models and internal
representations. The most frequently studied activity has been the planning of
chess moves. Charness (1981) found that the depth to which a possible move
sequence for a chess position was explored was closely related to the level of
chess skill, at least for chess players at or below the level of chess experts. Mental
planning and evaluation of possible move sequences place greater demands on
memory as the depth increases, and such a cognitive activity will be particu-
larly tractable using acquired skilled memory to represent chess positions.
As noted earlier, de Groot (1978) found no reliable differences in regard to
depthofsearchamongadvancedchessplayerswithdifferinglevelsofchess
ability. Holding (1985) suggested that the differences were too small to be
detected, because of the small number of subjects. Charness (1989), however,
presented a case study suggesting that the depth of search may increase with
chess skill only up to some level of chess skill and then level off. One should
also keep in mind that the task of searching for a move for a middle-game chess
position is not designed to measure the capacity to make deep searches and
hence may well reflect pragmatic criteria for sufficient depth of exploration to
evaluate a prospective move.
In support of the findings of remarkable capacities to explore chess positions
mentally, it is well known that chess players at the master level can play while
blindfolded with only a minor reduction in chess capability without any prior
specialized practice (Holding, 1985). In the absence of a strict time constraint,
thereappearstobenoclearlimittothedepthtowhichachessmastercanex-
plore a position. Ericsson and Oliver (Ericsson & Staszewski, 1989) found that a
candidate chess master was able to access all the information about a mentally
generated chess position rapidly and accurately, and they showed that the
memory representation of the chess position was consistent with the character-
istics of skilled-memory theory (Chase & Ericsson, 1982; Ericsson & Staszewski,
1989).
544 K. Anders Ericsson and Jacqui Smith