THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

Even Adults Have Difficulty With Task Switching and Surely They Can Use Higher Order Rules Kirkham et
al. (in press) cited evidence that adults have difficulty with the DCCS and related tasks (such as measures of
task switching; e.g., Allport & Wylie, 2000). They suggested that because adults are capable of using higher
order rules, difficulty using higher order rules cannot explain the costs associated with task switching, and
hence cannot explain children's performance either. However, although CCC theory proposes that adults are
capable of using high-order rules, it does not state that they always will. Indeed, just as inhibition
can be expected to be effortful and have a cost in increased latencies, so reflection and higher order rule use is
effortful and has a cost associated with it (Zelazo, Craik, & Booth, in press).
Children Only Have Difficulty on the DCCS When There Is Conflict Between Rules
Kirkham et al. (in press) claimed that children only have difficulty on the DCCS when they are required to shift
their attentional focus from one dimension to another that conflicts with the first, and they suggested that this
undermines the claim that children normally require a higher order rule to succeed. However, according to
CCC theory, it is only when children must switch between incompatible rule pairs nested under different major
branches in a hierarchical tree structure that a higher order rule is required.
Another example of this same general criticism has been offered by Towse and colleagues (2000) and Perner
and Lang (2002), who noted that target cards seem to be required to elicit 3- to 4-year-olds' errors on the
DCCS. However, on the CCC account, it is only when there is conflict, as when there are target cards, that a
higher order rule is going to be required in order to overcome the conflict. Otherwise no higher order rule is
required by children in order to change their behavior. Simply using one pair of lower order rules and then
another (i.e., in succession, without any need to reconcile them) will suffice.
FUTURE DIRECTIONS
The results of the research described in this Monograph answer several questions, but they also leave many
questions unanswered. For example, theoretical questions remain regarding relations between CCC-r and other
approaches to the development of executive function, such as Perner's redescription theory and accounts
emphasizing the development of both working memory and inhibitory control. There are also many empirical
questions. For example, future work should assess more directly some of the fundamental processes (e.g., the
use of self-directed speech) postulated by CCC-r theory, and it would be worthwhile to do so using a variety of
different measures of executive function, not just the DCCS. In this section, however, we describe in more
detail just two of the ways in which future research might usefully continue to examine the development of
executive function.
Development of Executive Function in Older Children
The research reported in this Monograph involved 3- to 4-year-old children, and inferences were made about
age-related changes occurring between the ages of 3 and 5 years. However, it will be important in future
studies to examine directly the development of performance on some of the new versions of the DCCS
introduced here, especially given the possibility that age-related changes on some of these versions may be
nonmonotonic. For example, it is possible that performance on the Total Change version actually declines as
children begin to construe the stimuli in terms of dimension. Similarly, although CCC-r theory predicts that
performance on the Negative Priming version will improve between the ages of 3 and 5 years, the fact that
Tipper et al. (19 89) failed to find evidence of negative priming in 7-year-olds raises the possibility negative
priming is a U-shaped function of age in early childhood.
Development should also be assessed beyond the preschool years. Indeed, several studies suggest that the
development of executive function follows a protracted course, and performance on executive function tasks
such as the WCST (Chelune & Baer, 1986), the Tower of Hanoi (Welsh, 1991), and a variety of working
memory measures (Luciana & Nelson, 1998) continues to improve at least until adolescence. For example,
Welsh, Pennington, and Groisser (199 1) used a battery of relatively global measures of executive function tasks
and found that children passed different tasks at a range of different ages. Interpretation of these results is