Terence E. Horgan - Connectionism and the Philosophy of Psychology

Connectionism arose very rapidly in the 1980s as a rival to the standard computer-based approach to cognitive science. Connectionism quickly attracted a great deal of attention among philosophers, largely because it suggests the possibility of an alternative to the conception of mind on the model of the modern digital computer (the so-called computer metaphor)a conception that had become prominent in thinking about the mind, both popular and philosophical, with the advent of the field of artificial intelligence in the 1950s.

By reflecting on connectionism, and on the reasons it rose to prominence when it did, we have been led to a view of cognition and cognitive processing that is significantly different from familiar views of cognition, and also from the views of other philosophers who have reflected on connectionism. We believe that human (and other natural) cognition is too rich and flexible to be simulated by computer programs. Hence, the computer model of the mind must be abandoned. However, this very richness of cognition requires mental representations that are syntactically structured. That is, cognition requires a language of thought, but one with processes that are not programmable or computable. We suggest that cognitive processes are effected by interacting cognitive forces that are systematically related to content. As a result, there are many generalizations that are true of cognitive processes. But they are ceteris paribus generalizations from which the ceteris paribus clause is ineliminable. Finally, the organization and the interaction of cognitive forces are best understood in terms of the mathematical theory of dynamical systems.

In this chapter we provide a sketch of this view and give an overview of the course of the argument we will pursue in the rest of the book. We begin by sketching the circumstances in which we arrived at the view.

The picture of mind as computer dominated theory and methodology in artificial intelligence and cognitive science for a quarter of a century, and has deservedly been called the classical view in cognitive

In rejecting classicism as a conception of human cognition, we do not mean to deny the value of classical cognitive science as an ongoing research program. A great deal can be and has been learned about cognitive problems by writing programs aimed at solving them, and a great deal is revealed about theories (and their defects) by implementing them classically. It is quite likely that these things cannot be accomplished in other ways. As far as we know, no one has learned anything comparable about any cognitive or philosophical problem from connectionism. The effort to solve cognitive problems by classical methods may well remain forever an unequalled route to understanding the nature of particular cognitive problems.

In chapter 4 we sketch an alternative framework for cognition: Noncomputable Dynamical Cognition, in which dynamical systems replace algorithms at the middle, mathematical/design level. We begin the chapter by generalizing Marr's three-level framework for classical cognitive science, which yields (1) cognitive-state transitions (but not necessarily tractably computable cognitive-transition functions), (2) mathematical-state transitions (but not necessarily algorithms), and (3) implementation. We then set forth a succession of approaches to mentality that conform to this general three-level framework while deviating increasingly from classicism; Noncomputable Dynamical Cognition is the most radical of these nonclassical alternatives.

Chapters 58 are concerned primarily with the top (cognitive) level. Chapter 9 then ties this discussion to the middle (dynamical systems) level.

Classical cognitive science is a package deal, involving syntactically structured representations and rules referring to those representations. In chapter 5 we argue that cognitive systems must have syntactically structured representations that make a difference in cognitive processingwhat we call effective syntax. Thus, what is to be rejected from the classical package is rules that refer to those representations (PRL rules).

It is necessary to argue anew for syntactic structure because many connectionists, and many philosophers who have rejected classicism, have wanted to throw out syntax with classical cognitive science, and because many arguments for syntactic structure have a distinctly classical flavor.

Our main argument for syntactic structure, which we call the tracking argument, concerns getting around in the world. We discuss the capacity to represent sufficiently any immediate locale one might be in, and the cognitive demands of complex physical skills. To get around in the world, a cognizer must keep track of enduring individuals that have changing, repeatable properties and relations. Doing this requires that mental predicates be applied to mental subjects, and it requires the

or similar outcomes. Then they will cooperate with one another, strengthening the likelihood that the outcome each one pushes for will be realized. Some of the tendencies will end up being defeatedi.e., completely overridden by other, competing tendencies. Some will end up deflectedi.e., exerting an influence on the outcome of processing, although the outcome is a "compromise" rather than what it would have been had other competing factors not been present. 5 And some will end up being neither deflected nor defeated; for them,