Short-Term Memory • 127How did you do? This task isn’t easy, because it involves remembering a series of 12 individual
letters, which is larger than the usual letter span of 5 to 9.
Now try remembering the following sequence of letters in order:
C I A F B I N B C C B S
How did your performance on this list compare to the one above?Although the second list has the same letters as the fi rst group, it was easier to
remember if you realized that this sequence consists of the names of four familiar orga-
nizations. You can therefore create four chunks, each of which is meaningful, and there-
fore easy to remember.
K. Anders Ericsson and coworkers (1980) demonstrated an effect of chunking by
showing how a college student with average memory ability was able to achieve amaz-
ing feats of memory. Their participant, S.F., was asked to repeat strings of random
digits that were read to him. Although S.F. had a typical memory span of 7 digits, after
extensive training (230 one-hour sessions), he was able to repeat sequences of up to
79 digits without error. How did he do it? S.F. used chunking to recode the digits into
larger units that formed meaningful sequences. For example, 3492 became “3 minutes
and 49 point 2 seconds, near world-record mile time,” and 893 became “89 point 3,
very old man.” This example illustrates an interaction between STM and LTM, because
S.F., who was a runner, created some of his chunks based on his knowledge of running
times that were stored in LTM.
Another example of chunking that is based on an interaction between STM and
LTM is provided by an experiment by William Chase and Herbert Simon (1973a,
1973b) in which they showed chess players arrangements of chess pieces taken from
actual games, for 5 seconds. The chess players were then asked to reproduce the posi-
tions they had seen. Chase and Simon compared the performance of a chess master who
had played or studied chess for more than 10,000 hours to the performance of a begin-
ner who had less than 100 hours of experience. The results, shown in ● Figure 5.9a,
show that the chess master placed 16 pieces out of 24 correctly on his fi rst try, com-
pared to just 4 out of 24 for the beginner. Moreover, the master required only four trials
to reproduce all of the positions exactly, whereas even after seven trials the beginner
was still making errors.
Does this result mean that chess masters
have a more highly developed short-term
memory than the beginners? Chase and Simon
answered this question by testing the ability
of masters and beginners to remember ran-
dom arrangements of the chess pieces. Under
these conditions, the chess master performed
as poorly as the beginner (Figure 5.9b). Chase
and Simon concluded that the chess master’s
advantage was due not to a more highly
developed short-term memory, but to his
ability to group the chess pieces into mean-
ingful chunks. Because the chess master had
stored many of the patterns that occur in real
chess games in LTM, he saw the layout of
chess pieces not in terms of individual pieces
but in terms of 4 to 6 chunks, each made up
of a group of pieces that formed familiar,
meaningful patterns. When the pieces were
arranged randomly, the familiar patterns
were destroyed, and the chess master’s advan-
tage vanished (also see DeGroot, 1965; Gobet
et al., 2001).● FIGURE 5.9 Results of Chase and Simon’s (1973a, 1973b) chess memory
experiment. (a) The chess master is better at reproducing actual game
positions. (b) The master’s performance drops to the level of the beginner’s
when the pieces are arranged randomly. (Source: Based on W. G. Chase & H. A. Simon,
“Perception in Chess,” Cognitive Psychology, 4, 55–81, 1973.)
(a) Actual game positions (b) Random placement
Master Beginner128Correct placements^4016Master Beginner12816Correct placements^40No advantage for
master if can’t chunkMaster does better
because can chunk
based on game positionsCopyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.