Multiple Interpreters in a Principle-Based Model of Sentence Processing

Multiple Interpreters in a Principle-Based Model of Sentence Processing Matthew W. Crocker e-mail: mwc@aipna.ed.ac.uk Department of Artificial Intelligence Human Communication Research Centre University of Edinburgh and University of Edinburgh 80 South Bridge 2 Buccleuch Place Edinburgh, Scotland, EH1 1HN Edinburgh, Scotland, EH8 9LW Abstract This paper describes a computational model of human sentence processing based on the principles and pa- rameters paradigm of current linguistic theory. The syntactic processing model posits four modules, re- covering phrase structure, long-distance dependencies, coreference, and thematic structure. These four mod- ules are implemented as recta-interpreters over their relevant components of the grammar, permitting vari- ation in the deductive strategies employed by each module. These four interpreters are also 'coroutined' via the freeze directive of constraint logic program- ruing to achieve incremental interpretation across the modules. 1 Introduction A central aim of computational psycholinguistics is the development of models of human sentence processing which account not only for empirical performance phe- nomena, but which also provide some insight into the nature of between parser and grammar relationship. In concurrent research, we are developing a model of sentence processing which has its roots in the princi- ples and parameters paradigm of syntactic theory [1], [2], which holds that a number of representations are involved in determining a well-formed analysis of an utterance. This, in conjunction with Fodor's Modu- larity Hypothesis [6], has led us to postulate a model which consists of four informationally encapsulated modules for recovering (1) phrase structure, (2) chains (3) coreference, and (4) thematic structure. In this paper we will briefly review a model of sen- tence processing which has been previously proposed in [5] and [3]. We will illustrate how this model can be naturally implemented within the logic program- ming paradigm. In particular, we sketch a subset of GB theory which defines principles in tern~ of their representational units, or schemas. We then discuss how the individual processors may be implemented as specialised, informationally encapsulated interpreters, and discuss how the 'freeze' directive of constraint logic programming can be used to effectively coroutine the interpreters, to achieve incremental interpretation and concurrency. 2 The Processing Model In the proposed model, we assume that the sentence processor strives to optimise local comprehension and integration of incoming material, into the current con- text. That is, decisions about the current syntactic analysis are made incrementally (for each input item) on the basis of principles which are intended max- imise the overall interpretation. We have dubbed this the Principle of Incremental Comprehension (PIC), stated roughly as follows: (1) Principle of Incremental Comprehension: The sentence processor operates in such a way as to maximise comprehension of the sentence at each stage of processing. The PIC demands that the language comprehen- sion system (LCS), and any sub-system contained within it (such as the syntactic and semantic pro- cessors), apply maximally to any input, thereby con- structing a maximal, partial interpretation for a given partial input signal. This entails that each module within the LCS apply concurrently. The performance model …

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