Topic preference

Theories of discourse representation and formal approaches to discourse coherence have assumed that assignment of reference to a pronominal element in ambiguous contexts with more candidates for an antecedent follows a rule-guided ranking of the candidate DP antecedents. Both Ariel’s (1990) Theory of Accessibility and Centering Theory (Grosz, Joshi & Weinstein, 1995) hypothesise that when two DPs appear in an utterance (n) and a pronominal element appears in utterance (n+1), the DP that is the topic of the utterance (n) is more likely to be interpreted as the referent of the pronominal element than any other DP.6 This

preference for the topic is demonstrated in (27) below:

6 _{The reason the notion topic is used instead of subject is because I am discussing}

rules that apply at the level of discourse representation. Subject is a syntactic notion that is not applicable at discourse level.

(27) a. A long time ago Mary quarrelled with Sue.

b. She thought that was the end of their friendship.

c. Peter thought she would never get over it.

In (27a) both Mary and Sue are possible candidates for the reference of the pronoun she in (27b) and in (27c). However, most speakers have a strong preference for the topic in utterance (27a) as the antecedent for the pronoun in (27b) and (27c). Although this preference for the topic can be overridden by pragmatic cues (e.g.: Mary gave Sue a present. She was

grateful), it is taken to be a basic principle in reference resolution, one

that might serve as a default option when no other cue is available. This principle will become an important factor in explaining the aberrant aphasic performance in relation to the parallelism constraint.

Evidence for the validity of the topic preference comes from corpus studies which show that in both spoken and written language a pronoun which is preceded by two gender/number matching DPs is more likely to refer to the DP that is the topic of an utterance. Pander Maat & Sanders (submitted) analysed 100 passages from newspaper articles in Dutch. They focused on instances where the pronoun could refer to more than one possible antecedent in the previous utterance. From the 100 tokens they checked, in 70 cases the pronoun had two candidate antecedents in the preceding clause. In 76% of the cases the referent for the pronoun was the topic of the preceding utterance. An additional piece of evidence for the validity of topic preference comes from speakers’ judgements of discourse coherence and is given in Grosz et al. (1995). These authors show that even in cases where speakers show little or no preference for the topic, such preference can be uncovered through judgements of utterances that follow the relevant pronoun. This is demonstrated in (28).

(28) a. Suzan gave Betsy a pet hamster.

b. She reminded her that such hamsters were quite shy.

Grosz et al. (1995) report that many people at this point did not show a clear preference for the topic (DP Suzan). However when a third utterance was added, it drastically affected people’s judgments and revealed that a hidden preference for the topic antecedent was present from the moment the pronoun was encountered. This is demonstrated in (29).

(29) a. Suzan gave Betsy a pet hamster.

b. She reminded her that such hamsters were quite shy. c. She asked Betsy whether she liked the gift.

d. She told Suzan that she really liked the gift.

The authors report that people’s judgments changed into disfavouring and sometimes rejecting sentence (29d). If at the point of the second utterance there was no preference towards Suzan as the antecedent, we should have expected no difference between (29c) and (29d). The fact that such preference is attested can be taken as evidence that Suzan was ranked higher than Betsy as a possible antecedent. Additional evidence is provided by experimental studies (Hudson, Tanenhaus & Dell, 1986; Hudson-D’Zmura & Tanenhaus, 1997; Gordon & Scearce, 1995) which show that ambiguous pronouns refer to the subject of the previous utterance even in situations where there are competing cues, such as pragmatic plausibility and causal bias associated with verbs (see also Chambers & Smyth, 1998).

This is a very important finding, which I assume was also at work in the healthy adults when they were tested experimentally, on the sentences described in this chapter. However, I will first reconsider the results on parallelism reported by Solan (1983). He claimed that the adults he tested relied equally on the parallelism of grammatical and thematic roles. I would like to suggest that they relied either on the parallelism of thematic roles or the topic preference, rather than what Solan claimed. In the sentences he tested, a mismatch between grammatical roles and a match between thematic roles gave a correct response. The pronoun (see examples (23) and (24)) in the second conjunct was always in the subject position and so the match of thematic roles had to involve a mismatch of grammatical roles. It is also the case that the match in grammatical roles allowed the subject pronoun to refer to the subject of the first conjunct. It could be the case that instead of using parallelism of grammatical roles as a condition on pronoun resolution, the subjects were relying on topic preference. There is no way of distinguishing between the two options on the basis of Solan’s results. In the experiment discussed in this chapter, besides pronouns in the subject position of the second conjunct, I also tested pronouns in the object position of the second conjunct. The latter is the crucial condition that points towards a competition between topic preference and parallelism of thematic roles. The healthy adults in my experiment made significantly more errors in the object pronoun condition than in the subject pronoun condition. Their performance was nonetheless above

chance on this condition. This means that they allowed the pronoun in this condition to refer to the subject, which was also the topic of the preceding utterance. This choice represents a violation of the parallelism constraint, allowing the topic preference to occasionally take over. In the subject pronoun condition, on the other hand, they hardly ever allowed the pronoun to refer to the object of the preceding utterance because both parallelism and topic preference point to the same referent – topic of the first conjunct.

The same competition is at work in agrammatic patients and crucially it is more expressed than in the healthy adults. The agrammatic patients perform at chance with pronouns in the object position. The slower-than- normal syntactic structure building in agrammatism results in other cues, such as topic preference, becoming available sooner than in healthy adults and competing with syntax even more prominently in providing the information for pronoun resolution. To my knowledge, there have been no other comprehension studies examining topic preference in agrammatic Broca’s aphasia.