Mind, Body, World- Foundations of Cognitive Science, 2013a

particular production to act. This changes the contents of the memory, which in
turn can result in a different production being selected during the next cycle of the
architecture.
On the other hand, production system control is usually not completely stigmergic.
This is because the stigmergic relationship between working memory
and productions is loose enough to produce situations in which conflicts occur.
Examples of this type of situation include instances in which more than one production
finds its triggering pattern at the same time, or when one production finds
its triggering condition present at more than one location in memory at the same
time. Such situations must be dealt with by additional control mechanisms. For
instance, priorities might be assigned to productions so that in a case where two
or more productions were in conflict, only the production with the highest priority
would perform its action.
Production systems have provided an architecture—particularly if that architecture
is classical in nature—that has been so successful at simulating higher-order
cognition that some researchers believe that production systems provide the foundation
for a unified theory of cognition (Anderson, 1983; Anderson et al., 2004;
Newell, 1990). Production systems illustrate another feature that is also typical of
this approach to cognitive science: the so-called classical sandwich (Hurley, 2001).
Imagine a very simple agent that was truly incapable of representation and reasoning.
Its interactions with the world would necessarily be governed by a set of
reflexes that would convert sensed information directly into action. These reflexes
define a sense-act cycle (Pfeifer & Scheier, 1999).
In contrast, a more sophisticated agent could use internal representations to
decide upon an action, by reasoning about the consequences of possible actions
and choosing the action that was reasoned to be most beneficial (Popper, 1978,
p. 354): “While an uncritical animal may be eliminated altogether with its dogmatically
held hypotheses, we may formulate our hypotheses, and criticize them. Let
our conjectures, our theories die in our stead!” In this second scenario, thinking
stands as an intermediary between sensation and action. Such behaviour is not
governed by a sense-act cycle, but is instead the product of a sense-think-act cycle
(Pfeifer & Scheier, 1999).
Hurley (2001) has argued that the sense-think-act cycle is the stereotypical form
of a theory in classical cognitive science; she called this form the classical sandwich.
In a typical classical theory, perception can only indirectly inform action, by sending
information to be processed by the central representational processes, which in turn
decide which action is to be performed.
Production systems exemplify the classical sandwich. The first production systems
did not incorporate sensing or acting, in spite of a recognized need to do so.
“One problem with psychology’s attempt at cognitive theory has been our persistence
Elements of Classical Cognitive Science 91