THE DEVELOPMENT OF EXECUTIVE FUNCTION IN EARLY ...

difficult, however, because global measures of executive function depend on many different underlying
processes (i.e., there are no process-pure measures) and because some sort of framework is required for making
systematic comparisons across tasks that differ in difficulty in addition to which aspects of executive function
they assess. Certainly it is problematic to compare performance on an easy measure of planning and a difficult
measure of rule use and then conclude that planning develops before rule use. CCC-r theory provides a
framework for making such comparisons that can be extended to account for age-related changes beyond the
preschool years (e.g., through the emergence of higher levels of consciousness and the ability to formulate
increasingly higher order rules; Zelazo et al., in press).
In any case, however, in order to capture executive function at different ages in more detail, complex
executive function tasks need to be broken down into more molecular processes and these processes need to
be studied experimentally, as was done with the DCCS in the current Monograph.
Development of "Hot" Executive Function
A second direction for future research is to explore the relatively "hot" affective aspects of executive
function associated with orbitofrontal cortex in addition to the more purely cognitive, "cool" aspects
associated with dorsolateral prefrontal cortex (Zelazo & Muller, 2002b). Whereas cool executive function is
more likely to be elicited by relatively abstract, decontextualized problems, hot executive function is
required for problems that involve the regulation of affect and motivation (i.e., regulation of basic limbic
system functions).
This characterization of hot executive function in contradistinction to cool executive function is consistent with
several recent proposals regarding the function of orbitofrontal cortex (e.g., Damasio, 1994; Rolls, 1999). For
example, based on single-cell recordings of neurons in orbitofrontal cortex together with neuroimaging data
and evidence that damage to orbitofrontal cortex impairs performance on simple tests of object reversal and
extinction, Rolls (e.g., 1999) suggested that orbitofrontal cortex is required for the flexible representation of the
reinforcement value of stimuli. A rather different theory has been proposed by Damasio (e.g., 1994).
According to this theory, the somatic marker theory, orbitofrontal cortex is required for processing learned
associations between affective reactions and specific scenarios, and this processing plays a crucial but often
overlooked role in decision making. Despite their differences, however, both approaches capture the fact that
the control of thought and action depends on different cortical systems, depending on whether or not it occurs
in motivationally significant contexts.
Traditionally, research on executive function in human beings has focused almost exclusively on cool
executive function, using measures such as the Wisconsin Card Sorting Test. Recently, however, there has
been growing interest in hot executive function as well, and in particular in what might be called affective
decision making, or decision making about events that have emotionally significant consequences (i.e.,
meaningful rewards and/or losses). The hot aspect of executive function appears to be involved, for example, in
theory of mind (Zelazo & Muller, 2002b), delay of gratification (Mischel, Shoda, & Rodriguez, 1989), and
affective decision making (Damasio, 1994). It is currently unclear whether the development of hot executive
function can be conceptualized in terms of a hierarchical model like CCC-r theory, and it remains to be seen
whether and how the development of hot and cool aspects of executive function are related (for a discussion,
see Zelazo & Muller, 2002b). An experimental approach to hot executive function using tasks such as delay of
gratification or the children's gambling task (Kerr & Zelazo, in press) might usefully address this gap in the
literature.
CONCLUSION
Considerable research has shown that most 3- to 4-year-olds perseverate during the postswitch phase of the
DCCS, whereas most 4-year-olds switch flexibly. The DCCS provides a window on the development of
executive function, and this Monograph described four studies that used variants of the DCCS to experimentally
test hypotheses derived from different theoretical perspectives on executive function. Among the most
important findings are the following: (a) Three-year-old children can use four rules to sort cards, showing that