chess positions, de Groot (1978) found clear evidence of perception of chess
pieces in chunks, or complexes, as well as of encodings relating chunks to one
another to form a global encoding of the position. It appears necessary to as-
sume that global and integrating encodings account for the ability of chess
experts to recall accurately more than one briefly presented chess position at a
single trial (Frey & Adesman, 1976).
In analyses of superior memory performance in domains other than chess,
evidence of global integration of the presented information has also been found
(Egan & Schwartz, 1979; Reitman, 1976). Studies in other domains, however,
have also revealed differences from the findings regarding chess experts. In
domains with complex stimuli, such as medicine (Patel & Groen, 1991) and
computer programming (Adelson, 1984), it is clear that part of the integration
of the presented information involves identification of the relevant and critical
information, and any analysis of subsequent recall must distinguish between
relevant and irrelevant information. For different domains of expertise, the
processes of encoding presented information will be quite different, depending
on the demands of the particular type of expertise (Allard & Starkes, 1991).
Expert dancers display superior memory for presented dance sequences,
whereas skilled volleyball players can detect the location of the volleyball with
superior speed. Superior perceptual processing has also been demonstrated as
a function of chess expertise for tasks involving simple perceptual judgments
about critical aspects of presented chess positions (Charness, 1991).
General Comments on the Analysis of Expert Performance. Once the expert per-
formance can be elicited by a collection of tasks in the laboratory, the full range
of methods in cognitive science can be applied to assess the mediating cogni-
tive structures and processes. The mediating mechanism for an expert perfor-
mance should be stable and not much influenced by the additional experience
in the laboratory, as the laboratory experience will constitute only a minor
fraction of the experts’ total experience of tasks in their domains. In fact, an
absence of further improvement during extended laboratory testing should
provide a nice index for evaluating our ability to capture the mechanisms un-
derlying the real-life expertise.
On the basis of this argument, one immediately realizes some potential dan-
gers of studying aspects of ‘‘real’’ expert performance with tasks not encoun-
tered in the normal environments of the experts. If we provide an expert with
unfamiliar tasks, we need to consider the possibility that the expert may resort
to nonoptimal and unstable strategies that can be rapidly improved even dur-
ing just a couple of sessions. With respect to memory for briefly presented
chess positions, Ericsson and Oliver (Ericsson & Staszewski, 1989) found sub-
stantial improvement in the memory performance of a candidate chess master
during a few months of testing. They found no evidence of changes in the
mediating processes, however, only a marked speedup of the processes.
We have been unable to find much evidence concerning the effects of
extended testing of experts. Ericsson (1985) reported several instances of
marked improvements in the performance of memory experts when they were
observed on several test occasions. In several cases the tests were separated by
several years, and one cannot distinguish between the effects of testing and the
538 K. Anders Ericsson and Jacqui Smith