«LANGUAGE AND COGNITIVE PROCESSES, 2004, 19 (6), 665–675 Discourse coherence and pronoun resolution Florian Wolf and Edward Gibson Massachusetts ...»
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LANGUAGE AND COGNITIVE PROCESSES, 2004, 19 (6), 665–675
Discourse coherence and pronoun resolution
Florian Wolf and Edward Gibson
Massachusetts Institute of Technology, Cambridge, MA, USA
Ghent University, Belgium
This paper used self-paced reading to test processing preferences in
pronoun interpretation in English two clause sentences. The results
demonstrate that people’s preferences can be reversed by changing the coherence relation between the clauses. The results are not compatible with the existence of a single all-purpose strategy in pronoun resolution. Rather, the results support Kehler’s (2002) hypothesis that the processing patterns observed in pronoun processing are a byproduct of more general cognitive inference processes underlying the establishment of coherence, such that discourse coherence guides pronoun reference, and pronoun reference guides discourse coherence.
INTRODUCTIONAn important component of language comprehension in most natural language contexts involves connecting clauses and phrases together in order to establish a coherent discourse. One critical way in which coherence can be established between clauses is by the use of referring expressions, such as pronouns (Garnham, 2001; Halliday & Hassan, 1976;
Johnson-Laird, 1983; Kintsch & Van Dyke, 1978; Sanford & Garrod, 1989). Thus an important part of discourse comprehension involves discovering how antecedents for pronouns are resolved. One well-known account of discourse processing with implications on pronominal resolution is Centering Theory, which predicts that pronouns prefer to have Correspondence should be addressed to Florian Wolf, MIT NE20-448, 3 Cambridge Center, Cambridge, MA 02139, USA. Email: email@example.com Timothy Desmet is a Research Assistant of the Fund for Scientiﬁc Research – Flanders (Belgium) (F.W.O. Vlaanderen).
c 2004 Psychology Press Ltd http://www.tandf.co.uk/journals/pp/01690965.html DOI: 10.1080/01690960444000034 76 MFK-Mendip Page: 666 of 675 Date: 17/11/04 Time: 11:06am Job ID: LANGUAGE 007037 666 WOLF, GIBSON, DESMET antecedents in subject position (Brennan, Friedman, & Pollard, 1987;
Grosz, Joshi, & Weinstein, 1995; cf. also Wundt, 1911). In support of Centering Theory, Gordon, Grosz and Gilliom (1993) found that there is a preference to use pronouns to refer to entities in subject position, but not
for entities in object position. Consider the sentences in (1):1
(1) a. Fiona complimented Craig, and she congratulated James.
b. Fiona complimented Craig, and he congratulated James.
Intuitively, (1a) is easier to process than (1b). Centering explains this preference because the pronoun ‘she’ in (1a) refers back to the subject of the preceding clause, whereas the pronoun ‘he’ in (1b) refers back to the object of the preceding clause. A problem for Centering Theory is
provided by the contrast in (2):
(2) a. Fiona complimented Craig, and James congratulated her.
b. Fiona complimented Craig, and James congratulated him.
Contrary to Centering Theory’s subject preference prediction, Chambers and Smyth (1998) found in a self-paced reading experiment that sentences like (2b) were read faster than sentences like (2a). This pattern of results motivates the Parallel Preference account (Chambers & Smyth, 1998; see Lappin & Leass, 1994, for a combination of Centering Theory and Parallel Preference). Under the parallel preference account (Smyth, 1994), pronouns are argued to prefer antecedents in a parallel position when the pronoun- and the antecedent-containing sentence have the following properties: (a) both sentences have the same global constituent structure, (b) the thematic roles of the verbs in both sentences concur.
When these conditions are met, subject pronouns should prefer subject antecedents, and object pronouns should prefer object antecedents. This is the case in (1) and (2) above. In (1), people prefer the preceding clause’s subject as the referent for the subject pronoun, whereas in (2) people prefer the preceding clause’s object as the referent for the object pronoun.
Although a parallel preference account can explain the preferences in (1) and (2), it does not explain the preferences in (3), from Winograd (1972):
(3) a. The city council denied the demonstrators the permit because they advocated violence.
b. The city council denied the demonstrators the permit because they feared violence.
This paper follows the processing literature in focusing on the interpretation of unstressed pronouns. See Akmajian and Jackendoff (1970) among others for a discussion of the interpretation of stressed pronouns.
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DISCOURSE COHERENCE AND PRONOUN RESOLUTION
In sentence (3a) the pronoun ‘they’ refers to ‘the demonstrators’, whereas in sentence (3b) it refers to ‘the city council’. Neither sentence seems particularly difﬁcult to process. Notice, however, that both Centering Theory and Parallel Preference predict a preference for ‘they’ to refer to the subject, ‘the city council’ – Centering Theory because it predicts a preference for subject antecedents, and Parallel Preference because it predicts a preference for an antecedent in a parallel position. Examples like (3) motivate causal-inference-based accounts of pronoun processing (Hobbs, 1979; Hobbs, Stickel, Appelt & Martin, 1993; Kehler, 2002).
According to such accounts, ‘they’ refers to ‘the demonstrators’ in sentence (3a) because advocating violence is assumed to be a good reason for being denied a permit. In sentence (3b) ‘they’ refers to ‘the city council’ because fearing violence by demonstrators is a good reason for denying a permit to these demonstrators.
Experimental evidence relevant to causal-inference-based accounts of pronominal resolution is provided by Ehrlich (1980), who used an off-line questionnaire to investigate people’s preferred pronoun resolution.
Ehrlich found that pronoun resolution is only driven by causal inferences (cf. Caramazza, Grober, Garvey, & Yates, 1977; Stewart, Pickering & Sanford, 2000) when the clauses containing pronoun and antecedent respectively are in a causal relation. When there is no such causal relation, Ehrlich found that people prefer antecedents in topic or subject position (cf. Centering Theory, Grosz et al., 1995).
Although causal-based strategies can explain the effects in (3), they do not explain the patterns in (1) and (2), because there is no causal connection between the two clauses in each of these sentences.
Furthermore, resorting to a topic-based strategy like Centering Theory as suggested by Ehrlich makes the right prediction for (1), but not for (2), where the pronoun with an object antecedent is easier to process.
Based on Hobbs (1979), Kehler (2002) provides a hypothesis that aims to explain all of these patterns of pronoun resolution. Instead of arguing for pronoun-speciﬁc processing mechanisms, Kehler (2002), like Hobbs (1979), argues that pronoun resolution is a byproduct of establishing coherence. Kehler (2002) extends Hobbs’ (1979) key insight that the establishment of coherence guides pronoun resolution and vice versa, noting that discourse coherence and pronoun resolution mutually constrain each other: Pronoun resolution guides coherence, but coherence also guides pronoun resolution. Thus he hypothesises that how a pronoun is resolved may depend on the coherence relation between the clauses.
Two classes of coherence relations that are particularly relevant to the examples that have been discussed in the pronoun resolution literature are cause-effect and resemblance. A cause-effect relation holds between two clauses if a plausible causal relation can be inferred to hold between the 76 MFK-Mendip Page: 668 of 675 Date: 17/11/04 Time: 11:06am Job ID: LANGUAGE 007037
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events described by the two clauses. The event described by one clause is the cause for the event described by the other clause, as in (3a). Because the demonstrators advocated violence, the city council denied them a permit to demonstrate. Kehler (2002) argues that the pronoun is interpreted such that a plausible cause-effect relation between the two clauses can be established. Pairing ‘they’ with ‘the demonstrators’ provides a more plausible interpretation for (3a) than pairing ‘they’ with ‘the city council’. A similar analysis applies to the pronoun resolution of ‘they’ in (3b).
The resemblance discourse relation is relevant to explaining the pattern of preferences in (1) and (2). A resemblance relation holds between two clauses if the events described by the two clauses are in a similarity or in a
contrast relation, as in the following examples from Kehler (2002):
(4) a. Resemblance, Similarity Gephardt organized rallies for Gore, and Daschle distributed pamphlets for him.
b. Resemblance, Contrast Gephardt supported Gore, but Armey opposed him.
Kehler (2002) hypothesizes that the ﬁrst step in establishing a resemblance relation between clauses is to ﬁnd parallel corresponding entities and events. Then these entities and events are put into similarity or contrast relations. For example, in sentence (4a), ‘organised rallies’ is parallel and similar to ‘distributed pamphlets’ (both predicates describe actions of supporting a political candidate), and ‘Dick Gephardt’ is parallel and similar to ‘Tom Daschle’ (both are American politicians that are similar in that they support Al Gore). Then, Kehler (2002) argues, the pronoun ‘him’ is paired with its parallel preceding element, ‘Gore’. In sentence (4b), ‘supported’ is parallel and in contrast to ‘opposed’. ‘Gephardt’ is parallel and in contrast to ‘Armey’ (both are politicians that are in contrast in that one of them supports Gore and the other one opposes him). Then, as in sentence (4a), the pronoun ‘him’ is paired with its parallel preceding element, ‘Gore’. Thus, in both sentences (4a) and (4b), the pronoun is bound to its antecedent during the establishment of a resemblance coherence relation, when parallel entities are matched.
The resemblance relation is the most plausible coherence relation between each of the clauses in the sentences in (1) and (2). In particular, the use of the similar verbs ‘complimented’ and ‘congratulated’ in the absence of any other cues induces a resemblance-similarity relation between each pair of clauses. Kehler’s theory then predicts that a parallel preference strategy would be in effect under the resemblance relation, which has been observed experimentally in such sentences (Chambers & Smyth, 1998).
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A strong prediction of Kehler’s theory is that pronoun resolution preferences can be altered depending on the coherence relation between clauses. The experiment presented here tests this prediction directly.
Materials. Twenty sets of sentences were constructed, each with four conditions in a 2 Â 2 design: coherence relation (resemblance, causeeffect) Â parallel reference (parallel, nonparallel). An example item is
presented in (5):
(5) a. Resemblance, Parallel Reference Fiona complimented Craig and similarly James congratulated him after the match but nobody took any notice.
b. Resemblance, Nonparallel Reference Fiona complimented Craig and similarly James congratulated her after the match but nobody took any notice.
c. Cause-Effect, Parallel Reference Fiona defeated Craig and so James congratulated him after the match but nobody took any notice.
d. Cause-Effect, Nonparallel Reference Fiona defeated Craig and so James congratulated her after the match but nobody took any notice.
Each sentence consisted of three clauses. The second clause was the target clause which consisted of the same words across the coherence manipulation. We manipulated the coherence relation between resemblance and cause-effect by making two changes to the items: (1) by using different connectives between the clauses (‘and similarly’ vs. ‘and so’), (2) by using a different verb in the ﬁrst clause. For resemblance, the verbs in the two clauses were semantically similar according to the WordNet lexical database (Fellbaum, 2001), e.g., ‘compliment’ and ‘congratulate’ in (5).
For the cause-effect conditions, the verb of the ﬁrst clause in the causeeffect condition was chosen so that there was a plausible causal relation between the two clauses such that the object pronoun referred to the subject of the ﬁrst clause, e.g., ‘defeat’ and ‘congratulate’ in (5). The ﬁrst clause verb in the cause-effect conditions always differed from the ﬁrst clause verb in the resemblance conditions. The remainder of the sentences consisted of a prepositional phrase and a third clause. This portion of the 76 MFK-Mendip Page: 670 of 675 Date: 17/11/04 Time: 11:06am Job ID: LANGUAGE 007037
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items was the same across the four conditions. Overall, the only differences between the resemblance and cause-effect conditions were the verbs of the ﬁrst clause and the connectives relating the two clauses.
Notice that this experiment did not explore the relative contribution of different coherence cues to changing pronoun interpretation preferences.
This does not diminish the point of the current design, which is simply to show that changing the coherence relation by using one or more cues may alter pronoun interpretation preferences.
The target sentences were combined with 76 ﬁllers of various types in four lists balancing all factors in a Latin Squares design. Appendix A provides a complete list of the stimuli. The stimuli were pseudorandomised separately for each participant, so that at least one ﬁller item intervened between two targets.