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<Paper uid="P84-1104">
  <Title>Conceptual Analysis of Garden-Path Sentences</Title>
  <Section position="2" start_page="0" end_page="487" type="intro">
    <SectionTitle>
1. INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> The phenomenon we wish to model is the understanding of garden path sentences (GPs) by native speakers of English.</Paragraph>
    <Paragraph position="1"> 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.</Paragraph>
    <Paragraph position="2"> (1) The horse raced past the barn fell.</Paragraph>
    <Paragraph position="3"> Thinking first that *r~cedS is the main verb, most readers become confused when they see the word, &amp;quot;fell'. Our parser, responding like the average reader, initially makes this mistake, but later determines that *fell&amp;quot; is intended to be the main verb, and * raced* is a p.~sive participle modifying &amp;quot;horse'.</Paragraph>
    <Paragraph position="4"> 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.</Paragraph>
    <Paragraph position="5">  (~) Three percent of the courses filled with freshmen were cancelled.</Paragraph>
    <Paragraph position="6"> (8) The chicken cooked with broccoli is delicious.</Paragraph>
    <Paragraph position="7">  The syntactic structure of (2) is similar to that of sentence (1). However, most readers do not initially mistake 'filled&amp;quot; to be the  main verb. LAZY goes a step further than previous parsers by modeling the average readers ability to deterministieally recognize sentences (2) and (3).</Paragraph>
    <Paragraph position="8"> If &amp;quot;filled&amp;quot; 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 &amp;quot;to fill&amp;quot; would be violated. LAZY prefers not to violate selectional restrictions. Therefore, when processing (2), LAZY will delay deciding the relationship among *filled&amp;quot; and &amp;quot;three percent of the courses&amp;quot; until the word &amp;quot;were* is seen and it is clear that &amp;quot;filled&amp;quot; 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.</Paragraph>
    <Paragraph position="9"> 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 &amp;quot;the horse&amp;quot; is the subject of the main verb &amp;quot;raced&amp;quot; as soon as the word &amp;quot;raced&amp;quot; is seen because the selectional restrictions associated with =raced = are satisfied.</Paragraph>
    <Paragraph position="10"> One implication of LAZY's parsing strategy, is that people could understand some true GPs if they were more careful and waited longer to select among alternative parses. Experimental evidence \[Matthews 791 suggests that people can recognize garden path sentences as grammatical if properly prepared. Mathhews found that subjects recognized sentences such as (21 as being grammatical, and after doing so, when later presented with a sentence like (1) will also judge it to be grammatical. {In a more informal experiment, we have found that, colleagues who re~d papers on GPs, understand new GPs easily by tile end of a paper.) LAZY exhibits this behavior by being more careful after encountering SDGPs or when reanalyzing garden path sentences.</Paragraph>
    <Paragraph position="11">  1I. SYNTAX IN A CONCEPTUAL ANALYZER The goal of conceptual analysis is to map natural language text into memory structures that represent the meaning of the text. It is claimed that this mapping can be accomplished without a prior syntactic analysis, relying instead on a variety of knowledge sources including expectations from both word definitions and inferential memory (see \[Ricsbeck 76\], \[Schank 80\], \[Gershman 82\], \[Birnbaum 81\], {Pazzani 83\] and \[Dyer 83\]). Given this model of processing, in sentence (4), (~) Af~rg kickcd John.</Paragraph>
    <Paragraph position="12"> llow is it possible to tell who kicked whom? There is a very simple answer: Syntax. Sentence (4) is a simple active sentence whose verb is &amp;quot;to kick'. &amp;quot;Mary&amp;quot; is the subject of the sentence and * Bill&amp;quot; is the direct object. There may be a more complicated answer, if, for example, John and Mary are married, Mary is illtempered, John is passive, and Mary has just found out that John has been unfaithful. In this case, it is possible to expect that Mary might hit John, and confirm this prediction by noticing that the words in (4) refer to Mary, John, and hitting. In fact, if this prediction was formulated and the sentence were &amp;quot;John kicked Mary&amp;quot; we might take it to mean &amp;quot;Mary kicked John' and usually notice that the speaker had made a raistake. Although we feel that this type of processing is an important part of understanding, it cannot account for all language comprehension. Certainly, (4) can be understood in contexts which do not predict that Mary might hit John. requiring syntactic knowledge to determine who kicked whom. fla. Precedes and Follows Syntactic information is represented in a conceptual analyzer, in a number of ways, the simplest of which is the notion of one word preceding or following another. Such information is encoded as a positional predicate in the test of a type of production which Riesbeck calls a request. The test also contains a semantic predicate (i.e., the selectional restrictions). A set of requests make up the definition of a word. For example, the definition of &amp;quot;kick&amp;quot; has three requests: REQI: Test: true Action: Add the meaning structure for &amp;quot;kick&amp;quot; to an ordered list of concepts typically called the C-list.</Paragraph>
    <Paragraph position="13"> REQg: Test: Is there a concept preceding the concept for &amp;quot;kick&amp;quot; which is animate? Action: ...</Paragraph>
    <Paragraph position="14"> REQ3: Test: Is there a concept following the concept for &amp;quot;kick&amp;quot; which is a physical object? Action: ...</Paragraph>
    <Paragraph position="15"> The action of a request typically builds or connects concepts. Although people who build conceptual analyzers have reasons for not building a representation of the syntax of a sentence, there is no reason that they can not. LAZY builds syntactic representations. --&amp;quot; lib. Requests in LAZY LAZY, unlike other conceptual analyzers, separates the syntactic (or positional) information from the selectioual restrictions by dividing the test part of request into a number of facets. There are three reasons for doing this. First, it allows for a distinction between different kinds of knowledge. Secondly, it is possible to selectively ignore some facets. Finally, it permits a request to access the information encoded in other requests.</Paragraph>
    <Paragraph position="16"> In many conceptual analyzers, some syntactic information is hidden in the control structure. At certain times during the parse, not all of the request are considered. For example, in (5) it is necessary to delay considering a request.</Paragraph>
    <Paragraph position="17"> (5) Who is Mar~l reernitingf To avoid understanding the first three words of sentence {5) as a complete sentence, &amp;quot;Who is Mary?', some request from &amp;quot;is&amp;quot; must be delayed until the word &amp;quot;recruiting&amp;quot; is processed. In LAZY, the time that a request can be considered is explicitly represented as a facet of the request. Additionally, separate tests exist for the selectional restriction, the expected part of speech, and the expected sententiM position.</Paragraph>
    <Paragraph position="18"> In LAZY, REQ2 of &amp;quot;kick&amp;quot; would be:  In REQ2a, Subject is a function which examines the state of the C-list and returns the proper constituent as a function of the clause type. In an active declarative sentence, the subject precedes the verb, in a passive sentence it may follow the word &amp;quot;by', etc. \[The usage of &amp;quot;subject&amp;quot; is incorrect in the usual sense of the word.) The Time facet of REQ2a states that the request should be considered only after the type of the clause is know. The predicates which are included in a request to control the time of consideration are: End-Of-Noun-Group?, Clause-Type-Known?, Head.Of, Immediate-Noun-Group?, and End-Of-Sentence?. These operate by examining the C-list in a manner similar to the positional predicates. The other facets of REQ2a state that the subject of &amp;quot;kick&amp;quot; must be animate, and should be a noun or s pronoun.</Paragraph>
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