Feedback as a Coindexing Mechanism in Connectionist Architectures

Abstract

Co-occurrence constraints play an important role in rule-based systems such as natural language processing. The constraints appear in many forms including agreement restrictions (e .g .. number agreement between subjects and predicates). selectional restrictions on complement types. and filler-gap movement dependencies. A general account of such constraints is given in a parallel execution model for rule-based systems - Active Production Networks (APNs). The APN model is similar to connectionist (or spreading activation) models. but explicitly provides a functional interpretation of rule-based phenomena such as variable binding. multiple instantiations (including recursion) . and contextual expectations. Co-occurrence constraints are represented by a theory of coindexing and trace capture. based on a feedback mechanism . Several examples of constraint processing are presented which . surprisingly. also include phenomena such as phonological nulls and contraction.