THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

The main new finding from Experiment 8 is that 3- to 4-year-olds exhibited considerable difficulty on the
Negative Priming version. Although the findings from the Total Change (no preswitch feedback) and Partial
Change (no preswitch feedback) versions lend support to CCC theory and the idea that children persist in
applying activated preswitch rules (rather than perseverating on a dimension per se), CCC theory cannot explain
why children perseverated on the Negative Priming version. Persistent activation would not interfere
with performance on the Negative Priming version.
Surprisingly, this experiment revealed a main effect of sex: girls performed better than boys across versions
(there was no interaction). An effect of sex on the DCCS has also been reported by Carlson and Moses
(2001; see also Bjorklund & Kipp, 1996), but was not found in any of the other experiments described in this
Monograph (although there was a Sex x Version interaction in Experiment 6 reflecting the fact that girls
performed better than boys on the more difficult versions). Therefore, it is possible that the effect is simply a
Type I error. Alternatively, however, it may reflect a genuine difference. The effect size associated with the
effect was f = .23, which is considered a medium effect size (Cohen, 1988).
A genuine sex difference favoring girls would not be entirely unexpected on this task insofar as it relies heavily
on language and is likely to be heavily dependent on dorsolateral prefrontal cortex. Considerable evidence
suggests that various aspects of language acquisition proceed more rapidly in girls (see Kimura, 1999, for a
review), and these differences may (at least eventually) be reflected in patterns of functional neuroanatomical
organization within prefrontal cortex (cf. Shaywitz, Shaywitz, Pugh, et al., 1995).
There is no direct evidence for more rapid development of dorsolateral prefrontal cortex in girls. However, there
is evidence for reciprocal suppression between dorsolateral prefrontal cortex and orbitofrontal cortex (Drevets
& Raichle, 1998), consistent with the view that dorsolateral prefrontal cortex stands in a hierarchical relation to
orbitofrontal cortex and regulates it (Zelazo & Muller, 2002b). Moreover, there is evidence from monkeys (e.g.,
Clark & Goldman-Rakic, 1989) and from toddlers (Overman, Bachevalier, Schuhmann, & Ryan, 1996) that
orbitofrontal cortex develops more rapidly in males than in females, and that this sex difference is under the
control of gonadal hormones (Clark & Goldman-Rakic; Goldman, Crawford, Stokes, Galkin, & Rosvold, 1974).
Together these findings prompt the speculation that whereas orbitofrontal cortex develops more rapidly in boys,
perhaps dorsolateral prefrontal cortex develops more rapidly in girls. Clearly, however, this is no more than an
intriguing possibility, and further work remains to be done simply to determine whether the sex difference in
DCCS performance, however small in size, is a reliable effect. Pending such work, the effect of sex observed in
Experiment 8 will not be discussed further.
EXPERIMENT 9
Experiment 8 revealed evidence of negative priming in the DCCS. In the Negative Priming version,
performance during the postswitch phase could not depend on persistent activation of the specific preswitch
rules because these rules could not be applied during the postswitch phase. Moreover, children's good
performance on the Total Change version provides evidence that children are unlikely perseverate on a
dimension per se. Taken together, these findings indicate that the rules that are irrelevant during the preswitch
phase are negatively primed. Indeed, the finding that the Negative Priming version was not significantly easier
than the standard version suggests that negative priming may make a major contribution to 3- to 4-year-olds'
difficulty on the DCCS. However, the Negative Priming version did not significantly differ from the Partial
Change versions, and it was only marginally different from the Total Change version, raising the possibility that
the finding from Experiment 8 is not reliable and/or that the role of negative priming is relatively minor.
Experiment 9 was designed to replicate the finding with respect to the negative priming version and to
explore further the circumstances in which negative priming is elicited in the DCCS. One possibility is that
negative priming is only seen when children are required to select the preswitch pair of rules against a
competing alternative (Perner & Lang, 2002; cf. Houghton & Tipper, 1994). On the other hand, it is also
possible that whenever children attend to the values from one dimension, everything else is negatively primed