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<Paper uid="C92-1032">
  <Title>LEFT-CORNER PARSING AND PSYCHOLOGICAL PLAUSIBILITY</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> One of our most robust observations about language -dating back at least to the seminal work of Miller and Chomsky \[MC63\] -- is that right- and left-branching constructions such as (la) and (lb) seem to cause no particular difficulty in processing, but that multiply center-embedded constructions such as (lc) are difficult to understand.</Paragraph>
    <Paragraph position="1"> a. \[\[\[John's\] brother's\] eat\] despises rats.</Paragraph>
    <Paragraph position="2"> b. This is \[the dog that chased \[the cat that bit \[the rat that ate tbe cheese\]\]\].</Paragraph>
    <Paragraph position="3"> c. #\[The rat that \[the cat that lille dog\] chased\] bit\] ate the cheese.</Paragraph>
    <Paragraph position="4"> The standard explanation for this distinction is a tight bound on space in the human sentence processing mechanism: center-embedded constructions require that the head noun phrase of each subject be stored until the processing of the embedded clause is complete and the corresponding verb is finally encountered) Alternative accounts have been proposed, most sharing the premise that the parser's capacity for recursion is limited by bounds on storage. (See, for exmnpie, \[Kim73\] and \[MI64\]; for opposing views and other pointers to the literature see \[DJK+82\].) The distinction between center-embedding and left/right-branching has important implications for those who wish to construct psychologically plausible models of parsing. Johnson-Laird \[JL83\] observes that neither the top-down nor the bottom-up methods of constructing a parse tree fit the facts of (1), arid proposes instead the lesS-well-known alternative of left-corner parsing. Abney mid Johnson \[AJgl\] discuss a somewhat more general version of Johnson-Laird's argument, introducing the abstract notion of a parsing sf~ntegy in order to characterize what is meant by bottom-up, top-down, and left-corner parsing.</Paragraph>
    <Paragraph position="5"> In this paper, we examine the argument as presented by Abney and Johnson and by Johnson-Laird, and point out a central problem with each variation.</Paragraph>
    <Paragraph position="6"> We then present the argument in a form that remedies those difficulties, and, in so doing, we identify a previously underrated aspect of the discussion that turns out to be of central importance. In particular, we show that the psychological plausibility argument hinges on the operation of composition and not left-corner prediction per se.</Paragraph>
  </Section>
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