with a chess position for 5 seconds with the sole task of the subjects being to
recall the locations of as many chess pieces as possible. We shall later review
more carefully to what extent this new task can be viewed as capturing the cog-
nitive processes underlying superior chess-playing performance.
With that memory task, Chase and Simon (1973) were able to corroborate de
Groot’s earlier finding that chess players with higher levels of expertise recalled
the correct locations of many more pieces for representative chess positions.
They also went a significant step farther and experimentally varied the charac-
teristics of the presented configurations of the chess pieces. For chessboards
with randomly placed pieces, the memory performances of the chess masters
were no better than those of novice chess players, showing that the superior
memory performance of the master depends on the presence of meaningful
relations between the chess pieces, the kinds of relations seen in actual chess
games.
Chase and Simon (1973) found that a player’s ability to reproduce from mem-
ory the previously presented chess position proceeded in bursts in which chess
pieces were rapidly placed, with pauses of a couple of seconds between bursts.
The pieces belonging to a burst were shown to reflect meaningfully related con-
figurations of pieces (i.e., chunks) that corresponded well to the complexes dis-
covered by de Groot (1978). The chess masters were found to differ from other
chess players primarily in the number of pieces belonging to a chunk, that is,
the size of the chunk. In support of the hypothesis that memory and perception
of chess positions rely on the same encoding processes, Chase and Simon (1973)
demonstrated that the recall process had a structure similar to that of the pro-
cess of reproducing perceptually available chess positions. Rather than discuss
the large number of additional empirical studies by Chase and Simon (1973),
we shall change the focus and consider their theoretical effort to specify the
detailed processes underlying superior memory performance and the relation
of these processes to general constraints on human information processing.
One of the most severe constraints on an account that is based on acquired
knowledge and skill involves explicating what has been acquired and showing
that the acquired characteristics are sufficient to account for the superior per-
formance without violating the limitations of the general capacities of human
information processing (Newell & Simon, 1972). The superior recall of 15–30
chess pieces by chess masters would at first glance seem to be inconsistent with
the limited capacity of short-term memory in humans, which allows storage of
around 7 chunks (Miller, 1956). Chase and Simon (1973) found that the number
of chunks recalled by chess players at all skill levels was well within the limit of
around 7G2. They attributed the difference in memory performance between
strong and weak players to the fact that the more expert chess players were
able to recognize more complex chunks, that is, chunks with a larger number of
chess pieces per chunk.
On the basis of computer simulations of the encoding and recall of middle-
game chess positions, Simon and Gilmartin (1973) were able to show that 1,000
chunks were sufficient to reproduce the memory performance of a chess expert.
They estimated that simulation of the performance of a chess master would re-
quire between 10,000 and 100,000 chunks. Assuming that the superior perfor-
526 K. Anders Ericsson and Jacqui Smith