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<Paper uid="W04-0301">
  <Title>Competence and Performance Grammar in Incremental Processing</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Incremental processing can be achieved with a combination of grammar formalism and derivation/parsing strategy. In this paper we explore some of the computational consequences of deriving the incremental character of the human language processor from the competence grammar. In the following paragraphs, we assume that incremental processing proceeds through a sequence of processing steps. Each step consists of a con guration of partial syntactic structures (possibly connected into only one structure) and a con guration of semantic structures (again, possibly connected into one single expression).</Paragraph>
    <Paragraph position="1"> These semantic structures result from the application of the semantic interpreter to the syntactic structures in the same processing step.</Paragraph>
    <Paragraph position="2"> Depending on the semantic rules, some syntactic structures may not be interpretable|that is, some processing steps do not involve an updating of the semantic representation. In the view we present here, competence grammar is responsible for the de nition of both the set of well-formed sentences of the language and the set of possible partial structures that are yielded by the derivation process. According to this view, the performance component is responsible for other aspects of language processing, including ambiguity handling and error handling. The latter issues are not addressed in this paper.</Paragraph>
    <Paragraph position="3"> In the psycholinguistic and computational literature, many models for incremental processing have been discussed. These models can be characterized in terms of the location of the border between competence and performance. In particular, we discuss the relative responsibility of the competence and performance components on three key areas of syntactic processing: a) the space of well-formed partial syntactic structures; b) the space of the possible con gurations of partial syntactic structures at each processing step; c) the sub-space of partial structures that can actually be interpreted.</Paragraph>
    <Paragraph position="4"> The de nition of well-formedness is almost universally assigned to the competence component, whether in a direct implementation of the grammar formalism (cf. the Type Transparency hypothesis (Berwick and Weinberg, 1984)) or a compiled version of the competence grammar (e.g. LR parsing (Shieber and Johnson, 1993)).</Paragraph>
    <Paragraph position="5"> The space of the possible con gurations of partial structures refers to those partial syntactic structures that are built and stored during parsing or derivation. Di erent algorithms result in di erent possibilities for the con gurations of partial structures that the parser builds. For example, a bottom{up algorithm will never build a partial structure with non{terminal leaf nodes. The standard approach is to assign this responsibility to the parsing algorithm, whether the grammar is based on standard context-free formalisms (Roark, 2001), on generative syntactic theories based on a context-free backbone (Crocker, 1992), or on categorial approaches, like e.g. Combinatory Categorial Grammar (CCG { (Steedman, 2000)). A di erent method is to assign this responsibility to the competence component. In this case the space of possible con gurations of partial structures is constrained by the grammatical derivation process itself, and the parsing algorithm needs to be aligned with these requirements. This approach is exempli ed by the works of Kempson et al. (2000) and Phillips (2003), who argue that many problems in theoretical syntax, like the de nition of constituency, can be solved by extending this responsability to the competence grammar.</Paragraph>
    <Paragraph position="6"> This issue of constituency is also relevant in the third key area, which is the de nition of the space of interpretable structures. The assignment of responsibility with respect to current approaches usually depends on the implementation of the incremental technique. Approaches based on a coupling of syntactic and semantic rules in the competence grammar (Steedman, 2000; Kempson et al., 2000) adhere to the</Paragraph>
    <Section position="1" start_page="0" end_page="0" type="sub_section">
      <SectionTitle>
so-called Strict Competence Hypothesis (Steed-
</SectionTitle>
      <Paragraph position="0"> man, 2000), which constrains the interpreter to deal only with grammatical constituents, so the responsibility for deciding the interpretable partial structures is assigned to competence1. In contrast, approaches that are based on competence grammars that do not include semantic rules, like CFG, implement semantic interpreters that mimic such semantic rules (Stabler, 1991), and so they assign the responsibility for deciding the interpretable partial structures to performance.</Paragraph>
      <Paragraph position="1"> In this paper we explore the empirical consequences of building a realistic grammar when the formalism constrains all these three areas, as is the case with Kempson et al. (2000) and Phillips (2003). The work relies upon the Dynamic Version of Lexicalized Tree Adjoining Grammar (DV{TAG), introduced in (Lombardo and Sturt, 2002b), a formalism that encodes a dynamic grammar (cf. (Milward, 1994)) in LTAG terms (Joshi and Schabes, 1997). The consequence of encoding a dynamic grammar is that the con gurations of partial structures discussed above are limited to fully connected structures, that is no disconnected structures are allowed in a con guration. In particular, the paper focuses on the problem of building a realistic DV{TAG grammar through a conversion from an LTAG, in order to maintain the 1Notice that these approaches may, however, di er in the time-course with which semantic rules are applied in the interpreter, and this issue depends directly on the space of con gurations of partial structures discussed above linguistic signi cance of elementary trees while extending them to allow the full connectivity.</Paragraph>
    </Section>
  </Section>
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