Centering: A Framework for Modeling the Local Coherence of Discourse

5 Factors governing centering

1. How do the “Susan gave Betsy a pet hamster” variants show there is a single \(C_b\)?
   After “Susan gave Betsy a pet hamster. She reminded her that such hamsters were quite shy.”, continuations get worse from “She asked Betsy whether she liked the gift” to “She told Susan that she really liked the gift” (unacceptable to many). If Susan and Betsy were equal candidates all would be equally good; Susan must be the \(C_b\).
   • Grosz et al., 1995, Centering (Computational Linguistics), §5
2. What ranking of the forward-looking centers does the paper argue for?
   By grammatical role: subject > object(s) > other. Other factors (word order, fronting, subordination, lexical semantics) were left to further research.
   • Grosz et al., 1995, Centering (Computational Linguistics), §5
3. How did psycholinguistic research bear on centering’s claims?
   It supported a single \(C_b\) and a determining role of grammatical role in identifying it, but not of thematic role or surface position; grammatical role and surface position both affect the \(C_f\) ordering. Kameyama first argued for grammatical rather than thematic role.
   • Grosz et al., 1995, Centering (Computational Linguistics), §5
4. What does the tugboat/teddy bear example show about the \(C_b\) and grammatical role?
   The \(C_b\) can be realized in other roles (here, a pronominalized direct object, the tugboat); a discourse where pragmatics forces “the silly thing” to mean the bear instead of the higher-ranked boat is less coherent.
   • Grosz et al., 1995, Centering (Computational Linguistics), §5