THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

children may represent and remember the first two rules but then be unable to hold the second pair of rules in
mind due to limited available processing space.
In the standard version of the DCCS, children are told the postswitch rules on every trial, so prima facie it
seems unlikely that an inability to remember the rules can account for 3- to 4-year-olds' failure to use them.
Similarly, children correctly answer questions about the postswitch rules (Zelazo et al., 1996), suggesting that
they have not forgotten these rules. Finally, some manipulations that might be expected to increase memory
demands (e.g., removing target cards; Towse et al., 2000) actually appear to improve performance.
On the other hand, it could be argued that capacity constraints and/or proactive interference (Keppel &
Underwood, 1962) prevent children from keeping the postswitch rules in mind long enough to control
responding. Also, Morton and Munakata (2002) were able to model performance on the DCCS in terms of
competition between active and latent memory.
The results of Study 1 showed that 3- to 4-year-olds performed well on versions of the DCCS in which children
were required to use four rules but not required to respond in two different ways to the same test card. These
findings clearly suggest that errors on the DCCS cannot be attributed in any straightforward way to limitations
on memory. However, the findings from Study 1 leave open the possibility that 3- to 4-year-olds' memory for
the rules is limited in a way that permits them to succeed in some situations (i.e., those without conflict) but not
others (those with conflict), as suggested by Morton and Munakata (2002), and they leave open the possibility
that memory plays a critical role in performance on the DCCS and in other measures of executive function.
Indeed, according to CCC theory, children formulate explicit rules in self-directed speech, maintain them in
working memory, and then use them to guide their behavior. What the findings from Study 1 suggest is simply
that 3- to 4-year-olds' difficulty on the DCCS depends more on the conflict among rules than on the requirement
that rules be remembered. It seems unlikely that age-related increases in memory capacity alone can explain
age-related increases in performance on the DCCS.
Inhibition Accounts
Several accounts suggest that children perform poorly on measures of executive function because of poor
inhibitory control (e.g., Carlson & Moses, 2001; Carlson et al., 1998; Dempster, 1993, 1995; Diamond &
Gilbert, 1989; Harnishfeger & Bjorklund, 1993; Luria, 1961; Perner et al., 1999; White, 1965). Perseveration
seems to implicate inhibition by definition behavior is exhibited that should have been inhibited. In the DCCS,
for example, children are not supposed to sort by the preswitch rules during the postswitch phase, and when
they do this, they may reasonably be described as failing to inhibit sorting by the preswitch rules. But this is
simply a description of their behavior, not an explanation of why they fail to inhibit sorting by the preswitch
rules.
An inhibitory control account of the DCCS gains leverage, however, when it implies that 3- to 4-year-olds
understand everything they need to understand in order to perform correctly. On this type of account, 3- to 4-
year-olds know perfectly well what to do during the postswitch phase of the DCCS, and even try to do it, but
cannot inhibit a prepotent tendency acquired during the preswitch phase. Even when conceptualized in this way,
inhibition accounts are problematic for a number of reasons (Zelazo & Muller, 2002b). One limitation of these
accounts is their inability to support predictions regarding the specific situations that will pose problems for
children at different ages. For example, they generally fail to explain in a noncircular way why children at a
particular age perseverate in particular situations but not others (e.g., why 3- to 4-year-olds perseverate in the
standard DCCS but not the standard A-not-B task). A second limitation of inhibition accounts is that the
construct of inhibition fails to address how one decides what is to be inhibited, and when (Rapport, Chung,
Shore, & Isaacs, 2001). A third limitation is that inhibition accounts do not explain how children acquire new
levels of conceptual understanding: "Inhibitory-based accounts ... cannot explain knowledge level transitions
per se" (Perret et al., 2003, p. 287).