Figure 1. The Müller-Lyer illusion (Müller-Lyer, 1889).
Even when the percipient knows that the two lines are of equal length the two lines are still
perceived as different. In other words, explicit knowledge (System 2) about physical reality
does not alter the visual percept (System 1). This classical example provides anecdotal evi-
dence for the existence of two cognitive systems, because people can believe in two contrary
responses simultaneously. A rich body of research demonstrates that the balance between
these two stipulated types of thinking can be shifted. Methods for shifting the balance to
System 1 processes involve concurrent working memory load (Gilbert, 1991) in order to in-
terfere with System 2 processes and the use of time pressure (Finucane et al., 2000) to impose
temporal processing constrains on System 2. Moreover, System 2 processing can be facili-
tated by explicitly instructing people to employ logical reasoning (Klauer et al., 2000). In ad-
dition, there are dispositional factors which are correlated with the functioning of System 2,
for instance, individual differences variables like the extensively studied “need for cognition”
(Shafir & LeBoeuf, 2002) and general cognitive ability (Stanovich & West, 1998, 2000). In ad-
dition, individual differences in executive functioning, working-memory capacity, and self-
control appear to play a pivotal role in this context. From a neuroscientific point of view, the
prefrontal cortices (PFC) are assumed to be responsible for executive control of different tasks
(Miller & Cohen, 2001). However, precise localization of function is difficult because the brain
is a complex and integrated system. Many researchers argue against a fully modular and de-
partmentalized anatomical view and for a continuous view on psychological constructs and
processes (but see Stuss, 1992). It has been noted that, “it is entirely possible that, although
the frontal lobes are often involved in many executive processes, other parts of the brain may
also be involved in executive control” (Baddeley, 1996, p. 6-7; see also Braver et al., 1997).
However, it seems as if certain brain regions are more involved in executive functioning than
others and the prefrontal cortices have been associated with executive control function (Della
Sala et al., 1998), supervisory system (Shallice, 2001; Alexander et al., 2007), and dysexecutive
syndrome (Baddeley & Wilson, 1988; Laine et al., 2009). Three regions seem to be particularly
involved in executive functioning, working memory, and self-control: 1) the dorsolateral pre-
frontal cortex (DL-PFC) 2) the ventromedial prefrontal cortex (vmPFC) and 3) the and the an-
terior cingulate cortex (ACC) (see Figure 2).