Accounts Focusing on Memory Functioning. The Chase-Simon hypothesis that
the superior memory of the expert reflects storage of more complex indepen-
dent chunks in short-term memory has been seriously questioned, and most of
the empirical evidence also suggests storage of interrelated information in long-
term memory, as mentioned earlier. Even without the constraints of indepen-
dence of chunks and storage in a limited-capacity short-term memory, human
information-processing theory suggests a number of limits and processing
constraints that must be taken into consideration in any acceptable account. But
let us first review some of the empirical characteristics of the superior memory
of experts.
Over a broad range of domains, experts have superior memory restricted to
information in their domains of expertise. Furthermore, de Groot (1978) and
Chase and Simon (1973) found that chess skill among a small number of sub-
jects was monotonically related to their memory performance, which would
suggest a high correlation between skill level and memory performance. Sub-
sequent studies with representative samples involving large numbers of sub-
jects found reliable correlations, but the strength of the association was lower
than would have been expected from the Chase-Simon theory (Charness, 1991;
Holding, 1985).
Although experts with decades of experience nearly always exhibit memory
performance superior to that of subjects lacking expertise, there is at least one
intriguing counterexample: Even though experts in mental calculation show far
better memory performance for numbers than do normal subjects, their perfor-
mance is far inferior to that of subjects who have practiced memorizing digits
over extended periods (Chase & Ericsson, 1982; Ericsson, 1985). Whereas the
mental-calculation experts rely predominantly on their vast mathematical
knowledge of numbers, the trained subjects draw on a variety of knowledge
essentially unrelated to mathematics. The most important difference between
mental calculators and memory experts is that mental calculators require years
and decades of practice to achieve memory performance comparable to what
can be achieved by normal subjects after 50–100 hours of practice in a memory
task. Hence, it is possible that the superior memory performance of experts has
only a weak association with their expert knowledge.
Similarly, superior memory for briefly presented chess positions can be
trained. Ericsson and Harris (1989) found that after 50 hours of practice, a sub-
ject without chess-playing experience was able to recall chess positions at a
level of accuracy approaching that of some chess masters. In similarity to the
digit-span experts, a close examination of the mediating processes revealed that
the subject’s performance was mediated by perceptually salient configurations
of chess pieces, without implications for playing chess. Hence, it appears that
by means of practice directed toward improving memory of performance, sub-
jects without expertise can, after a couple of months of daily practice, match or
surpass the superior memory performance of experts.
To account for the results concerning memory experts and long-term training
studies, Chase and Ericsson (1981, 1982; Ericsson, 1985, 1988; Ericsson & Stas-
zewski, 1989) proposed a skilled-memory theory to account for how memory
performance can be improved within the known limits of human information
processing. Chase and Ericsson proposed that experts can develop skilled
542 K. Anders Ericsson and Jacqui Smith