THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

Do 3- to 4-year-olds understand everything there is to know regarding the DCCS? Do they try to sort by the
postswitch rules but fail? Considerable evidence suggests that they do not. One finding (Zelazo et al., 1996,
Exp. 2) suggests that 3- to 4-year-olds perseverate in the DCCS even after a single preswitch trial. In other
words, sorting a card even once by one dimension prevents the majority of 3- to 4-year-olds from switching
to the other dimension, so perseveration in this situation cannot be due to failure to inhibit an overlearned
response. The findings by Jacques et al . (1999) that 3- to 4-year-olds judge a puppet's perseveration on the
DCCS to be correct makes this point even more strongly. If 3- to 4-year-olds know what should be done in
the task and are not required to make the response themselves, why is it still as difficult for them to evaluate
another's performance? Taken together, these results show that 3- to 4-year-olds' have difficulty formulating
what should be done and not just difficulty doing it (cf. Frye et al., 1996; Zelazo et al., 1995).
It remains possible, however, that 3- to 4-year-olds have difficulty inhibiting attention to particular aspects of
the target cards (Kirkham et al ., in press). CCC theory agrees with Kirkham et al. that inhibition and refocusing
are required in the DCCS. That is, both accounts agree that, in the context of this task, 3- to 4-year-olds have
difficulty inhibiting attention to a previously useful aspect of the stimulus, and refocusing on another conflicting
aspect of the same stimulus. However, CCC theory attempts to explain how inhibition and refocusing occur,
why failures of inhibition and refocusing occur in some situations and not others, and why there are particular
age-related changes in inhibition and refocusing. According to CCC theory, inhibition and refocusing are made
possible by (a) reflection on rules and (b) formulation of a higher order rule for selecting the appropriate setting
condition. In the absence of reflection and the formulation of a more complex rule system, children cannot
properly be said to understand what to do on the DCCS. Although they know the relevant rules, these rules
remain unintegrated and children cannot appreciate the relation among them.
The findings from Study 2 show that children are indeed capable of inhibition and refocusing when pre- and
postswitch rules are not nested under different major branches of the hierarchical tree structure in Figure 3. This
finding was expected based on CCC theory, but it is unclear how it could be accounted for in terms of Kirkham
et al.'s (in press) approach. Further, unlike CCC theory, Kirkham et al. do not differentiate between persistent
attention to a dimension and persistent activation of specific rules. The results of Experiment 7, which showed
that children were more likely to perseverate on the preswitch sorting rules than the preswitch sorting
dimension, clearly favor CCC theory in this regard. Finally, Experiments 8 and 9 show that 3- to 4-year-olds
have difficulty disinhibiting the postswitch rules, a finding that is at odds with the suggestion that children fail
the DCCS because of too little inhibition.
It could be argued, however, that the combination of inhibition and working memory can account for the
findings presented in this Monograph. In fact, working memory plus inhibition accounts have been proposed by
a variety of researchers (e.g., Diamond, 2002; H ala et al., 2003; Roberts & Pennington, 1996) . A working
memory plus inhibition account would predict that children will only encounter difficulties in versions of the
DCCS that involve conflict because conflict pits a prepotent but incorrect response against a weaker but correct
response. The joint development of working memory and inhibition would then be responsible for children's
eventual success on versions of the DCCS that involve conflict. Thus, for example, on this account, the finding
that children performed well on unidimensional versions and 4-Rule versions of the DCCS may be attributed to
the lack of conflict in these versions.
Although clearly both working memory and inhibition play a role in the DCCS, a working memory plus
inhibition account by itself encounters some of the same problems that undermine the appeal of simple
inhibition or working memory accounts. That is, children encounter conflict at many different levels, and they
fail tasks that involve conflict at different ages. A working memory plus inhibition account lacks a clear metric
that can be used to order these different tasks in an a priori fashion. For example, the 4-Rule and 2+2-Rule
version used in Study 1 likely do involve conflict in the sense that children must inhibit a motor tendency to
put the test card into the same tray on trial n+1 that they put it into on trial n —a perseverative pattern exhibited