StudiesofParticularAspectsofExpertPerformance. Up to this point we have
discussed studies of expert performance using tasks selected to capture the
essence of that performance. It was pointed out that in many cases particular
cognitive activities associated with expertise could be identified that could be
more effectively examined in tasks designed to focus on those particular cogni-
tive activities. For example, in their study of experts in physics, Chi et al. (1981)
focused on the initial encoding of physics problems to account for these
experts’ immediate availability of plans for complete solutions to those prob-
lems. They asked experts and novices to sort a large number of physics prob-
lems into categories of similar problems. Consistent with the hypothesis that
experts’ encodings would incorporate information about solution methods, the
experts’ categories of problems reflected the physical principles underlying the
solutions, whereas the novices’ categories were based on the situations and
objects mentioned in the problem text. In this case, the knowledge uncovered
stands in close correspondence to the knowledge evoked during the solution of
the physics problems. Several other investigators have used similar sorting
methods to assess the immediate encodings of mathematical problems (Berger
& Wilde, 1987, 1981), as well as encodings of pictures of situations in team
sports (Allard & Starkes, 1991). It is, of course, possible to examine the knowl-
edge of experts more generally. In their study of representation of expert
knowledge, Olson and Biolsi (1991) discuss a wide range of methods. Attempts
to measure knowledge about chess directly with psychometric tests have been
quite successful, and scores on these tests show a clear correlation with rated
chess performance (Charness, 1991).
During a study of the selection of the best move for an unfamiliar chess po-
sition, de Groot (1978) also found that the critical differences in cognitive pro-
cesses relating to chess expertise occurred within the initial perception of the
chess position. After a brief exposure to an unfamiliar chess position, the chess
masters could give very informative verbal reports about the perceived char-
acteristics of the presented chess position, along with virtually perfect recall of
the locations of all chess pieces. In subsequent research, superior memory per-
formance and superior perceptual performance of experts have been studied in
specially designed tasks.
As reported earlier, Chase and Simon (1973) accounted for the superior
memory performance of chess masters in terms of their storage of chess posi-
tions in short-term memory using complex independent chunks of chess pieces.
The assumptions of storage in short-term memory and of independence of
chunks have been seriously questioned by more recent investigators. Carefully
designed studies of superior memory performance for chess positions, as
reviewed by Charness (chapter 2, 1991), showed that chess experts store infor-
mation about chess positions in long-term memory, not solely in short-term
memory as Chase and Simon (1973) originally proposed.
Subsequent researchers have questioned Chase and Simon’s (1973) assump-
tion that chunks of chess pieces were distinct and that a given chess piece could
therefore belong to only a single chunk. Chi (1978) showed that occasionally a
chess piece can belong to more than one chunk, a finding that suggests rela-
tions between the chunks from a given chess position. On the basis of retro-
spective verbal reports of grand masters and masters after brief exposures to
Prospects and Limits of the Empirical Study of Expertise 537