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Developing a domain-general framework for cognition: What is the best approach?

Published online by Cambridge University Press:  12 April 2004

James L. McClelland*
Affiliation:
Department of Psychology and Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, PA15213http://www.cnbc.cmu.edu/~jlmhttp://www.cnbc.cmu.edu/~plaut
David C. Plaut*
Affiliation:
Department of Psychology and Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, PA15213http://www.cnbc.cmu.edu/~jlmhttp://www.cnbc.cmu.edu/~plaut
Stephen J. Gotts*
Affiliation:
Department of Psychology and Center for the Neural Basis of Cognition, Carnegie Mellon University, and Laboratory of Neuropsychology, NIMH/NIH, Bethesda, MD20892http://www.cnbc.cmu.edu/~gotts
Tiago V. Maia*
Affiliation:
Department of Psychology, Carnegie Mellon University, Pittsburgh, PA15213http://www.cnbc.cmu.edu/~tmaia

Abstract:

We share with Anderson & Lebiere (A&L) (and with Newell before them) the goal of developing a domain-general framework for modeling cognition, and we take seriously the issue of evaluation criteria. We advocate a more focused approach than the one reflected in Newell's criteria, based on analysis of failures as well as successes of models brought into close contact with experimental data. A&L attribute the shortcomings of our parallel-distributed processing framework to a failure to acknowledge a symbolic level of thought. Our framework does acknowledge a symbolic level, contrary to their claim. What we deny is that the symbolic level is the level at which the principles of cognitive processing should be formulated. Models cast at a symbolic level are sometimes useful as high-level approximations of the underlying mechanisms of thought. The adequacy of this approximation will continue to increase as symbolic modelers continue to incorporate principles of parallel distributed processing.

Type
Open Peer Commentary
Copyright
Copyright © Cambridge University Press 2003

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References

Notes

1. It is necessary to note that none of the models we have discussed fully embody all the principles of the PDP framework. For example, the interactive activation and TRACE models use localist, not distributed, representations, while the models of spelling-to-sound mapping (Seidenberg & McClelland 1989; Plaut et al. 1996) do not incorporate intrinsic variability. This fact can lead to confusion about whether there is indeed a theoretical commitment to a common set of principles.

In fact, we do have such a commitment. The fact that individual models do not conform to all of the principles is a matter of simplification. This leads to computational tractability and can foster understanding, and we adopt the practices only for these reasons. Everyone should be aware that models that are simplified embodiments of the theory do not demonstrate that models incorporating all of its complexity will be successful. In such cases further research is necessary, especially when the possibility of success is controversial. For example, Joanisse and Seidenberg (1999) used localist word units in their model of past-tense inflection, and Pinker and Ullman (2002a; 2002b) have argued that this is essential. In this context, we fully accept that further work is necessary to demonstrate that a model using distributed semantic representations can actually account for the data.

2. It should be noted here that none of these models assume that learning occurs through correction of overtly generated errors. Instead, it is assumed that exposure provides examples of appropriate usage in context. The learner uses the context as input to generate an internal representation corresponding to the expected phonological form. Learning is driven by the discrepancy between this internal representation and the actual perceived form provided by the example.

3. Marcus et al. (1995) claimed that German has a regular plural (the so-called +s plural) that conforms to the expectation of the symbolic approach, in spite of the fact that it is relatively infrequent. However, subsequent investigations indicate that the +s plural does not exhibit the properties one would expect if it were based on a symbolic rule (Bybee 1995; Hahn & Nakisa 2000).