Conceptual Analysis of Garden-Path Sentences

Conceptual Analysis of Garden-Path Sentences Michael J. Pazzani The MITRE Corporation Bedford, MA 01730 ABSTRACT By integrating syntactic and semantic processing, our parser (LAZY) is able to deterministically parse sentences which syntactically appear to be garden path sentences although native speakers do not need conscious reanalysis to understand them. LAZY comprises an extension to conceptual analysis which yields an explicit representation of syntactic information and a flexible interaction between semantic and syntactic knowledge. 1. INTRODUCTION The phenomenon we wish to model is the understanding of garden path sentences (GPs) by native speakers of English. Parsers designed by Marcus [81] and Shieber [83] duplicate a reader's first reaction to a GP such as (1) by rejecting it as ungrammatical, even though the sentence is, in some sense, grammatical. (1) The horse raced past the barn fell. Thinking first that *r~cedS is the main verb, most readers become confused when they see the word, "fell'. Our parser, responding like the average reader, initially makes this mistake, but later determines that *fell" is intended to be the main verb, and • raced* is a p.~sive participle modifying "horse'. We are particularly interested in a class of sentences which Shieber's and Marcus' parsers will consider to be GPs and reject as ungrammatical although many people do not. For example, most people can easily understand (2) and (3) without conscious reanalysis. (~) Three percent of the courses filled with freshmen were cancelled. (8) The chicken cooked with broccoli is delicious. The syntactic structure of (2) is similar to that of sentence (1). However, most readers do not initially mistake 'filled" to be the Current Address: The Aerospace Corporation P.O. Box 92957 Los Angeles, CA 90009 main verb. LAZY goes a step further than previous parsers by modeling the average readers ability to deterministieally recognize sentences (2) and (3). If "filled" were the main verb, then its subject would be the noun phrase =three percent of the courses* and the selectional restrictions [KATZ 63] associated with "to fill" would be violated. LAZY prefers not to violate selectional restrictions. Therefore, when processing (2), LAZY will delay deciding the relationship among *filled" and "three percent of the courses" until the word "were* is seen and it is clear that "filled" is a passive participle. We call sentences like (2) semantically disambiguatable garden path sentences (SDGPs). Crain and Croker [79] have reported experimental evidence which demonstrates that not all potential garden path sentences are actual garden paths. LAZY uses a language recognition scheme capable of waiting long enough to select the correct parse of both (1) and {2) without guessing and backing up [MARCUS 76]. However, when conceptual links are strong enough, LAZY is careless and will assume one syntactic (and therefore semantic) representation before waiting long enough to consider alternatives. We claim that we can model the performance of native English speakers understanding SDGPs and misunderstanding GPs by using this type of strategy. For example, when processing (1), LAZY assumes that "the horse" is the subject of the …

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