Reaping the Benefits of Interactive Syntax and Semantics

REAPING THE BENEFITS OF INTERACTIVE SYNTAX AND SEMANTICS* Kavi Mahesh Georgia Institute of Technology College of Computing Atlanta, GA 30332-0280 USA Internet: mahesh@cc.gatech.edu Abstract Semantic feedback is an important source of informa- tion that a parser could use to deal with local ambigu- ities in syntax. However, it is difficult to devise a sys- tematic communication mechanism for interactive syn- tax and semantics. In this article, I propose a variant of left-corner parsing to define the points at which syntax and semantics should interact, an account of grammat- ical relations and thematic roles to define the content of the communication, and a conflict resolution strategy based on independent preferences from syntax and se- mantics. The resulting interactive model has been im- plemented in a program called COMPERE and shown to account for a wide variety of psycholinguistic data on structural and lexical ambiguities. INTRODUCTION The focus of investigation in language processing research has moved away from the issue of seman- tic feedback to syntactic processing primarily due to the difficulty of getting the communication be- tween syntax and semantics to work in a clean and systematic way. However, it is unquestionable that semantics does in fact provide useful information which when fed back to syntax could help elimi- nate many an alternative syntactic structure. In this article, I address three issues in the commu- nication mechanism between syntax and semantics and provide a complete and promising solution to the problem of interactive syntactic and semantic processing. Since natural languages are replete with ambi- guities at all levels, it appears intuitively that a processor with incremental interaction between the levels of syntax and semantics which makes the best and immediate use of both syntactic and semantic information to eliminate many alternatives would win over either a syntax-first or a semantics-first mechanism. In order to devise such an interactive mechanism, one has to address three important is- sues in the communication: (a) When to communi- cate: at what points should syntax and semantics interact, (b) What to communicate: what and how *The author would like to thank his advisor Dr. Kurt Eiselt and his colleague Justin Peterson for their support and valuable comments on this work. much information should they exchange, and (c) How to agree: how to resolve any conflicting pref- erences between syntax and semantics. In this article, I propose (a) a particular variant of left-corner parsing that I call Head-Signaled Left Corner Parsing (HSLC) to define the points where syntax and semantics should interact, (b) an ac- count of grammatical relations based on thematic roles as a medium for communication, and (c) a simple strategy based on syntactic and semantic preferences for resolving conflicts in the communi- cation. These solutions were motivated from an analysis of a large body of psycholinguistic data and account for a greater variety of experimen- tal observations on how humans deal with struc- tural and lexical ambiguities than previous models (Eiselt et al, 1993). While it also appears that the proposed interaction with semantics …

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