This paper has three aims: (1) to generalize a computational account of the discourse process called CENTERING, (2) to apply this account to discourse processing in Japanese so that it can be used in computational systems for machine translation or language understanding, and (3) to provide some insights on the effect of syntactic factors in Japanese on discourse interpretation. We argue that while discourse interpretation is an inferential process, syntactic cues constrain this process, and demonstrate this argument with respect to the interpretation of ZEROS, unexpressed arguments of the verb, in Japanese. The syntactic cues in Japanese discourse that we investigate are the morphological markers for grammatical TOPIC, the postposition wa, as well as those for grammatical functions such as SUBJECT, ga, OBJECT, o and OBJECT2, ni. In addition, we investigate the role of speaker's EMPATHY, which is the viewpoint from which an event is described. This is syntactically indicated through the use of verbal compounding, i.e. the auxiliary use of verbs such as kureta, kita. Our results are based on a survey of native speakers of their interpretation of short discourses, consisting of minimal pairs, varied by one of the above factors. We demonstrate that these syntactic cues do indeed affect the interpretation of ZEROS, but that having previously been the TOPIC and being realized as a ZERO also contributes to the salience of a discourse entity. We propose a discourse rule of ZERO TOPIC ASSIGNMENT, and show that CENTERING provides constraints on when a ZERO can be interpreted as the ZERO TOPIC

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Abstract. In this paper the Centering model of anaphora resolution and discourse coherence (Grosz, Joshi and Weinstein, 1983, 1995) is reformulated in terms of Optimality Theory (ot) (Prince and Smolensky 1993). One version of the reformulated model is proven to be descriptively equivalent to an earlier algorithmic statement of Centering due to Brennan, Friedman and Pollard (1987). However, the new model is stated declaratively, and makes clearer the status of the various constraints used in the theory. In the second part of the paper, the model is extended, demonstrating the advantages of the ot reformulation, and capturing formally ideas originally described by Grosz, Joshi and Weinstein. Three new applications of the extended ot Centering model are described: generation of linguistic forms from meanings, the evaluation and optimization of extended texts, and the interpretation of accented pronouns.

In this paper, I discuss machine translation of English text into a relatively "free" word order language, specifically Turkish. I present algorithms that use contextual information to determine what the topic and the focus of each sentence should be, in order to generate the contextually appropriate word orders in the target language. Introduction Languages such as Catalan, Czech, Finnish, German, Hindi, Hungarian, Japanese, Polish, Russian, Turkish, etc. have much freer word order than English. For example, all six permutations of a transitive sentence are grammatical in Turkish (although SOV is the most common). When we translate an English text into a "free" word order language, we are faced with a choice between many different word orders that are all syntactically grammatical but are not all felicitous or contextually appropriate. In this paper, I discuss machine translation (MT) of English text into Turkish and concentrate on how to generate the appropriate word order in the t...

this paper, I investigate the interaction between Centering Theory and word order in a "free" word order language, i.e. Turkish. In "free" word order languages, e.g. Czech, Finnish, German, Hindi, Hungarian, Japanese, Korean, Polish, Russian, Turkish, Urdu, the word order serves to structure the information being conveyed to the hearer by indicating what is the topic and the

In this work we explore the possibility of formalizing explanations based in the notion "deletion under recoverability": information should be omitted in expressions if that information can be recovered without being overtly expressed -- e.g., from information already encoded in the state of the discourse. This style of explanation is difficult to formalize for many reasons, among them that the contradictory factors involved are not resolved in a simple, consistent way. Optimality Theory permits the conflicts to be formally adjudicated, and allows the conflicts to be resolved in different ways in di#erent languages. We will present what to our knowledge is the first formal theory of the cross-linguistics typology of discourse anaphora systems.

In this paper we are concerned with the location of topics in text processing and the determination of the update unit in looking up topic continuations and topic shifts. Using key elements of the Centering Model of local discourse coherence and empirical evidence from Modern Greek and Japanese we argue that the appropriate update unit for topic tracking is the sentence in its traditional sense and not the finite clause, thus providing an account for the status of the subordinate clause in the calculation of topic transitions. We bring forth an argument from English, Modern Greek (MG) and Japanese for keeping topic and information structure distinct. We briefly discuss the significance of the current work to automated essay scoring and coreference-based summarization systems. 1 Introduction This paper is concerned with the issue of identifying the location of topics in text processing. Adopting the framework of the Centering Model, we discuss the importance of defining the appropriat...

Existing software systems for automated essay scoring can provide NLP researchers with opportunities to test certain theoretical hypotheses, including some derived from Centering Theory. In this study we employ ETS's e-rater essay scoring system to examine whether local discourse coherence, as defined by a measure of Rough-Shift transitions, might be a significant contributor to the evaluation of essays. Our positive results indicate that Rough-Shifts do indeed capture a source of incoherence, one that has not been closely examined in the Centering literature. These results not only justify Rough-Shifts as a valid transition type, but they also support the original formulation of Centering as a measure of discourse continuity even in pronominal-free text.

this paper, I will try to shed light on the mechanisms underlying the interpretation of pronominal subjects in Greek; as it turns out, my empirical findings greatly resemble the properties reported by Di Eugenio (forthcoming) and Turan (1995) for Italian and Turkish, respectively. Thus I will tentatively extend my conclusions to these languages as well. I will show below that in Greek, the function of the overt pronoun aftos is to signal that its antecedent should be, not the most "prominent" potential antecedent from the previous sentence, but something somewhat less prominent. That is, that we should "skip" the most obvious candidate and move down to the next one. The overt pronoun signals this merely by its presence, not by any featural or referential information that it provides. In general, we can associate with each type of pronoun a method for selecting its antecedents. I will argue that these "methods" are not predictable through Gricean implicatures alone, hence they must be grammaticized, and specific to particular lexical items. But what exactly is a "prominent" antecedent? I am not using prominent as a technical term! In the following sections, I show that an appropriate notion of prominence is provided within the framework of Centering Theory (Grosz et al. 1986, 1995); specifically, I will argue that the type of pronominal used determines where in the list of forward looking centers its antecedent will appear: A null subject should be construed with the "compatible" antecedent that is highest in the list (where compatibility is determined by factors like featural agreement and agentivity) , while the proximal demonstrative aftos `this one' is (almost) never used to refer to the highest element in the list; it is used instead for antecedents that are lower...

Centering is a model of the conversants’ center of attention in discourse that is concerned with the relationship of attentional state, inferential complexity and the form of referring expressions. Centering models discourse processing factors that explain the difference in the perceived coherence of discourses such as (1) and (2)