THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

Negative Priming version are not. By contrast, the findings from the Negative Priming version are consistent
with the negative priming hypothesis, but the findings from the Partial Change are not. In order to capture the
full pattern of empirical findings, an alternative account is needed that includes both processes of activation and
processes of inhibition. This alternative is described in Chapter VI.
VI. THE DEVELOPMENT OF EXECUTIVE FUNCTION: COGNITIVE COMPLEXITYAND
CONTROL-REVISED
SUMMARY OF RESULTS ACROSS STUDIES
The current Monograph consisted of four studies (9 experiments) designed to explore the development of
children's executive function, as revealed by their performance on the DCCS. The DCCS is a widely used
measure of rule use, and, as such, it provides a relatively well-defined window on the development of
executive function during the preschool years. Executive function in general, and as assessed by the DCCS in
particular, has been implicated in children's behavior in a variety of domains and in a variety of subject groups,
including bilingual children, children with autism, and children with Down's syndrome.
By experimentally manipulating features of the DCCS paradigm, we tested hypotheses about the cognitive
mechanisms underlying executive function and its development. Results of this research have the potential to
shed light not only on children's development in a variety of domains, but also on dorsolateral prefrontal
cortical function especially during the preschool years. Performance on the DCCS almost certainly relies on
neural systems involving prefrontal cortex. In particular, dorsolateral regions of prefrontal cortex have been
implicated in a number of tasks quite similar to the DCCS (see Nagahama et al., 2001; Rogers, Andrews,
Grasby, Brooks, & Robbins, 2000, for research using functional magnetic resonance imaging [fMRI] and
positron-emission tomography [PET], respectively).
Study 1 examined whether 3- to 4-year-olds' errors on the DCCS can be attributed to capacity limitations on
memory. Three experiments showed that 3- to 4-year-olds performed well on four versions of the DCCS in
which children were required to use four nonoverlapping rules (i.e., children were not required to treat the
same test card differently depending on the relevant dimension). In Experiment 1, the two new versions were
unidimensional. In Experiment 2, children were given the 2+2-Rules (bidimensional, no overlap) version, in
which they were shown four target cards and asked to sort test cards first by two rules based on one dimension
(e.g., color) and then by two rules based on the other dimension (e.g., shape). Although children needed to
remember which cards to sort by color and which cards to sort by shape, there was no conflict among rules
because each test card was uniquely associated with a single rule. Children performed well on this version,
showing that bidimensionality per se does not cause children's difficulty on the DCCS.
In Experiment 3, children performed well on the 4-Rules (super-ordinate) 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. Not only did children need to keep four
superordinate distinctions in mind, but they also need to determine which rule applied to each test card (i.e.,
there were storage plus processing demands). 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 most memory capacity accounts of performance on the DCCS, and
they point to the importance of conflict among rules.
Study 2 was designed to explore further the role of conflict among rules by determining more precisely the
circumstances in which children can and cannot treat a single test card in two different ways. Three experiments
assessed the effects of rule dimensionality (bidimensional vs. unidimensional rules) and two types of stimulus
characteristic (1 vs. 2 test cards; integrated vs. separable stimuli). Here, unlike Study 1, bidimensional rule sets
always involved conflict among rules whereas unidimensional rule sets did not. Results revealed effects of rule
dimensionality but no effects of stimulus characteristics. Sorting by even a single pair of rules was difficult for
3- to 4-year-olds when the two rules spanned major branches of the hierarchical tree structure shown in Figure