Richard P. Cooper

Soar and the case for unified theories of cognition

Despite the potential importance to cognitive psychology of unified theories no attempt has been made to assess concretely the methodological problems that such theorising produces. This paper addresses this issue of unified theorising, and in particular the arguments for unified theories put forward by Newell (1990). Close examination of these arguments reveals that Newells approach does not adequately counter the difficulties which beset the grand theories of the 1930s, nor the problems of irrelevant specification which arise in modern computational psychological work. These difficulties do not prevent the development of unified theories, but they do pose serious problems, problems which it is argued can only be met by rigorous empirical testing together with extreme methodological sensitivity. The methodological concerns lead us to examine Soar, perhaps the most well-developed unified theory, from methodological, computational, and empirical perspectives. Our conclusions are that, whilst Soar represents an impressive body of research, its methodological foundations are insecure, it is ill specified as a computational/psychological theory, and under empirical testing it does not stand up to close scrutiny as a unified theory. The Soar research programme as it currently stands thus fails to meet the necessary methodological demands imposed by unified theorising.

Interruptibility as a constraint on hybrid systems

It is widely mooted that a plausible computational cognitive model should involve both symbolic and connectionist components. However, sound principles for combining these components within a hybrid system are currently lacking; the design of such systems is oftenad hoc. In an attempt to ameliorate this we provide a framework of types of hybrid systems and constraints therein, within which to explore the issues. In particular, we suggest the use of “system independent” constraints, whose source lies in general considerations about cognitive systems, rather than in particular technological or task-based considerations. We illustrate this through a detailed examination of an interruptibility constraint: handling interruptions is a fundamental facet of cognition in a dynamic world. Aspects of interruptions are delineated, as are their precise expression in symbolic and connectionist systems. We illustrate the interaction of the various constraints from interruptibility in the different types of hybrid systems. The picture that emerges of the relationship between the connectionist and the symbolic within a hybrid system provides for sufficient flexibility and complexity to suggest interesting general implications for cognition, thus vindicating the utility of the framework.

Integrating rules and connectionism for robust commonsense reasoning by Ron Sun, John Wiley & Sons, New York, 1994, pp 273, £49.50, ISBN 0-471-59324-9.

The first is Turings insistence that the computer has a hardware system that would be as simple as possible. Turings philosophy being that the main functionality of the ACE computer would be achieved by programming rather than complex electronic circuitry. The trend in computer architectures since the publication of this report has been towards more and more complex hardware. However, the inevitable result of this has been the computer becoming increasingly baroque and inefficient. This has resulted in a new generation of very powerful Reduced Instruction Set Computers which, while not exactly matching Turings Spartan hardware design, are conceptually much nearer to it than the vast majority of the computer architectures that have been designed over the last three decades.