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

ased on informed judgment, and how much is convenience? (Oreskes, Shrader-
Frechette, & Belitz, 1994, p. 644)
Because of similar concerns, mathematical psychologists have argued that computer
simulations are impossible to validate in the same way as mathematical models of
behaviour (Estes, 1975; Luce, 1989, 1999). Evolutionary biologist John Maynard
Smith called simulation research “fact free science” (Mackenzie, 2002).
Computer simulation researchers are generally puzzled by such criticisms,
because their simulations of cognitive phenomena must conform to a variety of
challenging constraints (Newell, 1980, 1990; Pylyshyn, 1984). For instance, Newell’s
(1980, 1990) production system models aim to meet a number of constraints that
range from behavioural (flexible responses to environment, goal-oriented, operate
in real time) to biological (realizable as a neural system, develop via embryological
growth processes, arise through evolution).
In validating a computer simulation, classical cognitive science becomes an
intrinsically comparative discipline. Model validation requires that theoretical
analyses and empirical observations are used to evaluate both the relationship
between a simulation and the subject being simulated. In adopting the physical
symbol system hypothesis, classical cognitive scientists are further committed
to the assumption that this relation is complex, because it can be established
(as argued in Chapter 2) at many different levels (Dawson, 1998; Marr, 1982;
Pylyshyn, 1984). Pylyshyn has argued that model validation can take advantage of
this and proceed by imposing severe empirical constraints. These empirical constraints
involve establishing that a model provides an appropriate account of its
subject at the computational, algorithmic, and architectural levels of analysis. Let
us examine this position in more detail.
First, consider a relationship between model and subject that is not listed
above—a relationship at the implementational level of analysis. Classical cognitive
science’s use of computer simulation methodology is a tacit assumption that the
physical structure of its models does not need to match the physical structure of the
subject being modelled.
The basis for this assumption is the multiple realization argument that we have
already encountered. Cognitive scientists describe basic information processes in
terms of their functional nature and ignore their underlying physicality. This is
because the same function can be realized in radically different physical media. For
instance, AND-gates can be created using hydraulic channels, electronic components,
or neural circuits (Hillis, 1998). If hardware or technology were relevant—if
the multiple realization argument was false—then computer simulations of cognition
would be absurd. Classical cognitive science ignores the physical when models
are validated. Let us now turn to the relationships between models and subjects
that classical cognitive science cannot and does not ignore.
94 Chapter 3