Representation of Feature Systems in a Non-Connectionist Molecular Machine

REPRESENTATION OF FEATURE SYSTEMS IN A NON-CONNECTIONIST MOLECULAR MACHINE L~zI6 K6im~n Institute of Linguistics Hungarian Academy of Sciences Budapest I., P.O.Box 19. H-1250 HUNGARY ABSTRACT This paper is part of an enterprise whose aim is to represent linguistic knowledge in the form of a molecular machine (a dynamic network). That is, the molecules of the network not only store, but also send, receive, and process information. It is claimed that such a network can be conceived of as a model of the coalition structure of a connectionist network. The paper describes how the class of feature systems called unary feature hierarchies (whose importance is supported by phonological theory but will not be argued for in the paper) can be represented in the molecular machine. INTRODUCTION Of the various branches of modern linguistic theory, phonology, as usual, was the first one to come up with really restrictive theories of features and feature systems, largely supported by empirical evidence coming from the study of a legion of linguistic phenomena. Phonology will most probably remain main source of evidence as far as the functioning of feature-based cognitive processes is concerned. The present paper sets out to outline how a particular kind of feature system, close to several recent theories of phonological features, can be represented in connectionist networks. However, since some of the mechanisms involved, seriality and synchronization in particular, fall outside the scope of the existing connectionist networks, a non- connectionist model simulating would-be serial connectionist networks will be used instead. The automaton described in the paper is able to unify feature structures as programs to be run on the machine itself. UNARY FEATURE HIERARCHIES The feature systems under scrutiny can be termed unary feature hierarchies. The underlying concept is close to the 'feature geometry' approach to autosegmental phonology (Clements 1985) in that a feature specification consists of features appearing on tiers, and features on adjacent tiers can be linked by association ~ines. Tiers are ordered in a multi-dimensional space, and the set of features that may appear on a particular tier is predefined. Unarity, on the other hand, means that a feature either appears within a given 'span' (of time) or it does not (instead of having different values); the absence of a feature simply means lack of information or undersDecification. Features can only be linked to specified slots; on the other hand, tiers are adjacent to features rather than to tiers (hence the use of hierarchv instead of qeometry); that is, the following configuration may be ruled out if the H tier is adjacent to F but not to G: F/G tier .... F .... G .... l I H tier .... H .... H .... Figure I. This configuration may be ruled out. Unarity is opposed to traditional binary feature systems (with a marked '+' and an unmarked '-' value for each feature) and to ternary systems (with a marked '+', an unmarked '-', and an unspecified '0' value), while feature geometries (and hierarchies) replace the old-fashioned 'feature bundle' …

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