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<Paper uid="W04-0305">
  <Title>Lookahead in Deterministic Left-Corner Parsing</Title>
  <Section position="1" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
Abstract
</SectionTitle>
    <Paragraph position="0"> To support incremental interpretation, any model of human sentence processing must not only process the sentence incrementally, it must to some degree restrict the number of analyses which it produces for any sentence pre x. Deterministic parsing takes the extreme position that there can only be one analysis for any sentence pre x. Experiments with an incremental statistical parser show that performance is severely degraded when the search for the most probable parse is pruned to only the most probable analysis after each pre x. One method which has been extensively used to address the di culty of deterministic parsing is lookahead, where information about a bounded number of subsequent words is used to decide which analyses to pursue. We simulate the e ects of lookahead by summing probabilities over possible parses for the lookahead words and using this sum to choose which parse to pursue. We nd that a large improvement is achieved with one word lookahead, but that more lookahead results in relatively small additional improvements. This suggests that one word lookahead is su cient, but that other modi cations to our left-corner parsing model could make deterministic parsing more e ective.</Paragraph>
  </Section>
class="xml-element"></Paper>