THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

Developmental research indicates that inflexibility occurs in different contexts at different ages. One of the most
widely studied examples of infant perseveration is the A-not-B error. As originally described by Piaget (1954),
the A-not-B error occurs when infants (typically between of 8 and 10 months of age) successfully retrieve an
object at one location (location A), and are then allowed to search for it when it is conspicuously hidden at
another location (location B). Remarkably, infants at this age often search at the first location despite having
last seen the object at location B. The basic finding has proved to be robust (for a recent meta-analysis, see
Marcovitch & Zelazo, 1999). Whereas Piaget attributed the error to an immature understanding of the object
concept, a popular contemporary interpretation of the error is that infants have difficulty using a representation
of an object's location to override a prepotent response (e.g., Diamond, 1991)—that is, they exhibit a failure of
executive function, or more precisely, a failure of response control.
Studies with older infants and with preschoolers indicate that the development of representational flexibility and
response control follows a protracted course. For example, DeLoache (e.g., 1987) observed changes between
2.5 and 3 years of age in children's ability to use a three-dimensional model of a room to guide search for an
object hidden in the room itself. In particular, DeLoache (1999; Sharon & DeLoache, 2003; see also O'Sullivan,
Mitchell, & Daehler, 2001) observed that 2.5-year-olds often committed perseverative errors, searching for the
object at the location where it had been found on a previous trial. Three-year-olds, in contrast, searched
successfully. DeLoache (1995) suggested that the age-related changes observed in this task reflect an increase in
representational flexibility: 2.5-year-olds persist in thinking of the model as a three-dimensional object (e.g., a
toy room) rather than thinking of it in terms of the thing it represents (viz., the room).
There is also a large body of research indicating that 3- to 4-year-olds have difficulty switching between
incompatible perspectives on a single object—they perseverate in representing objects in a particular way even
when it is no longer appropriate to do so. In tasks assessing understanding of appearance and reality, for
example, children are shown a misleading object such as a sponge painted to look like a rock and asked about
its appearance ("What does it look like?") and its true nature or function ("What is it really?"). Three-year-olds
are much more likely than 5-yearolds to give the same answer to both questions (Flavell , Green, & Flavell ,
1986).
Further evidence of representational inflexibility in 3- to 4-year-olds has been obtained in research on numerous
topics, including understanding false beliefs (see Wellman, Cross, & Watson, 2001, for a meta-analysis),
reasoning about physical causality (e.g., das Gupta & Bryant, 1989; Frye, Zelazo, Brooks, & Samuels, 1996),
moral reasoning (e.g., Zelazo, Helwig, & Lau, 1996), reasoning about delayed representations (e.g., Povinelli,
Landau, & Perilloux, 1996; Zelazo, Sommerville, & Nichols, 1999), predicting outcomes based on past
experience (Kessen & Kessen, 1961), inferring word meanings (Deck, 2000), and generating multiple labels for
a single object (e.g., Doherty & Perner, 1998; Markman, 1989; but see Deal( & Maratsos, 1998), among other
topics. In each case, younger preschoolers seem to have difficulty switching between conflicting
representations; they tend to perseverate on a salient representation, and there are age-related increases in
flexibility between about 3 and 5 years of age. How best to interpret these increases in flexibility is currently a
matter of debate, but there is a growing consensus that these increases may be usefully studied under the rubric
of executive function (e.g., Carlson & Moses, 2001; Deak, 2000; Frye, 1999; Halford, Wilson, & Phillips, 1998;
Kirkham, Cruess, & Diamond, in press; Munakata & Yerys, 2001; Perner, Stummer, & Lang, 1999; Zelazo,
1999; Zelazo & Frye, 1997; Zelazo & Muller, 2002b) .
The Dimensional Change Card Sort
One widely used measure of executive function in early childhood is the Dimensional Change Card Sort
(DCCS; see Figure 2; Frye, Zelazo, & Palfai, 1995; Zelazo, Frye, & Rapus, 1996). In this task, children are
shown two target cards (e.g., a blue rabbit and a red boat) that vary along two dimensions (e.g., color and
shape), and they are asked to sort a series of bivalent test cards (e.g., red rabbits and blue boats), first according
to one dimension (e.g., color, for which they are told, "If it's blue it goes here; if it's red it goes there.") and then
according to the other (e.g., shape, for which they are told, "If it's a rabbit it goes here; if it's a boat it goes
there."). Regardless of which dimension is presented first, 3- to 4-year-olds typically perseverate by sorting