The computational problem introduced by ambiguity and the experimental problem of attempting to prove that a particular alleged feature of the human sentence parsing mechanism is psychologically ``real'' create an interest in psychologically motivated computational models of sentence processing that can address these issues. This thesis presents a computational model of sentence processing that attempts to be as psychologically plausible as possible, with the two-fold goal of better evaluating an existing psychological theory, and of developing a superior processing model. Firstly, we identify several important psychological claims about the human sentence parsing mechanism, namely that processing is influenced by limitations on working memory and by a number of structural preferences, such as Right Association, Minimal Attachment, Revision as Last Resort, and verb-frame preferences, and then see how some existing sentence processing systems deal with these issues. We find that although many of them provide reasonable accounts of some subset of the psycholinguistic data, none give a good account of how the remaining data could be integrated consistently.
We then propose a processing model that tries to give a reasonable account of how one might bring all these necessary constraints and preferences together in one system. The starting point for this proposal is the Sausage Machine model of Frazier and Fodor, which gives a good account of memory constraints and sentence complexity, and incorporates most of the structural preferences we seek to include. From there, we attempt to overcome the more serious deficiencies of the Sausage Machine model, namely its dependence on ad hoc aspects of its grammar, and its omission of verb-frame preferences. The resulting model incorporates a principled theory of grammar, namely Government-Binding theory, includes mechanisms to handle lexical disambiguation and semantic processing in parallel with syntactic processing, and uses estimated timing information to resolve conflicting preferences. The sentence processor provides new support for the original Sausage Machine model, and provides a mechanism for incorporating several accounts of the psychological data and for resolving conflicts among them.
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