THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

Discussion
Experiment 3 explored further the possibility that memory constraints are responsible for 3-year-old children's
perseveration on the DCCS by comparing children's performance on the standard version to their performance
on a new 4-Rules (superordinate) version. The 4-Rules (superordinate) version likely posed even greater
memory demands than the previous 4-Rules versions because the rules were relatively abstract and the test
cards were heterogeneous. Despite this, children performed significantly better on the 4-Rules (superordinate)
version. This finding therefore provides further evidence against the suggestion that limitations on children's
memory capacity play an important role in 3- to 4-year-olds' poor performance on the DCCS.
GENERAL DISCUSSION
Study 1 involved three experiments that examined whether 3- to 4year-olds' errors on the DCCS can be
attributed to age-related limitations on memory capacity. Several theories (e.g., Case, 1985, 1992; Gathercole,
1998; Gordon & Olson, 1998; Morton & Munakata, 2002) suggest that age-related changes in short-term,
active, or working memory are major determinants of children's performance on a wide variety of measures,
including measures of executive function. In the DCCS, 3- to 4-year-olds may simply have difficulty keeping
the postswitch rules in mind. Experiment 1 tested this memory account by comparing children's performance on
the standard version of the DCCS to their performance on two new versions, the 4-Rules (unidimensional) and
2+2-Rules (unidimensional) versions, that were similar to the standard version in that they required children to
sort by four rules. If memory constraints are a major determinant of children's performance, then the two new
versions should be at least as difficult as the standard version and possibly more difficult because children are
told the four rules simultaneously. Results showed that performance was significantly worse in the standard
version; indeed, most children failed the standard version but not the other two versions.
Experiment 2 addressed the possibility that children did not really need to hold four rules in mind in order to
succeed on the 4-Rules (unidimensional) and 2+2-Rules (unidimensional) versions. If children simply
remembered the single relevant dimension, they could perhaps infer what went where in a given trial. In
Experiment 2, children were given the 2+2-Rules (bidimensional, no overlap) version, in which they were told
to sort first by two rules based on one dimension (e.g., color) and then by two rules based on the other
dimension (e.g., shape). In this version, children needed to remember which cards to sort by color and which
cards to sort by shape. Results revealed that 3- to 4-year-olds performed well on the 2 + 2- Rules
(bidimensional, no overlap) version.
Experiment 3 presented children with the 4-Rules (superordinate) version, which likely posed even greater
memory demands than the 4-Rules versions used in Experiments 1 and 2 because it involved superordinate rules
and a heterogeneous series of test cards. Nonetheless, children performed significantly better on the 4-Rules
(superordinate) version than on the standard version of the DCCS. Taken together, findings from the three
experiments provide strong evidence against a memory account of performance on the DCCS.
The findings also help isolate what may be a crucial determinant of difficulty. In each of the modified versions
of the DCCS, there was no conflict among rules and children did not have to sort the same test card in two
different ways. Because each test card was uniquely associated with a different rule, children arguably did not