Assigning reference through discourse-operations
3.3 General discussion
3.3.5 Agrammatic data
The results of the experiment discussed in this chapter showed individuals with Broca’s aphasia performed at chance level in the condition, repeated where the pronoun is in object position and they performed above chance in sentences where the pronoun is in subject position. It appears as if the agrammatic patients obey the parallelism constraint in one experimental condition and in the other condition they fail to do so. I argue that they generally fail to implement the parallelism constraint in both conditions. As a result of this failure they are often left with an ambiguous context and they resort to topic preference as the default mechanism for assigning reference in such contexts.7
As we have seen in the previous chapters, the Primitives of Binding model assumes a hierarchy of levels and consequently of the operations that occur at these levels through which reference can be assigned to a pronominal element (in healthy adults). What seems to be the case is that if reference can be assigned through a syntactic operation, this option will block all other operations through which reference can possibly be assigned. The system works in such a way that there is a competition between modules and its core, narrow syntax, always wins because it is the most automatic and economical route of resolving reference. The
7 The controls also perform less well on the object condition but they are still
rules that apply at this level are absolute and structures are either grammatical or ungrammatical. The discourse level, on the other hand, can be influenced by pragmatics so the competition between these two levels is different and the outcome is less clear than when a syntactic route is an option. The more one gets removed from the core, the easier it is to use the alternative routes, the less strict the rules are, hence, the more options there are. At the level of discourse there are no absolute rules but preferences, often couched in terms of a competition between different constraints.
As we saw in the previous chapter, the agrammatic performance on pronouns in ECM sentences reveals a competition between the grammatical levels, syntax and discourse, in which one of the two will provide the information on the assignment of the appropriate referent for the pronoun. In the case of the experimental sentences tested and discussed in this chapter, the competition is not between different levels but between two discourse mechanisms. One mechanism is the parallelism constraint, which requires an amount of resources that exceeds their capacity. The other is the topic preference, which seems to operate as a basic rule of pronoun resolution in ambiguous situations.
The relationship and the competition between the grammatical levels discussed in the previous chapter and the constraints discussed here is dynamic and what makes one win over another is not yet clear. However, chance performance is an indicator of such a competition. In section 3.3.3, I addressed the issue of why the agrammatic patients often fail to apply parallelism. In order for them to correctly apply this constraint, they need to have the syntactic and lexical-semantic information for both conjuncts available on time in order to map it onto discourse. They also have to retain in their working memory the relations between the entities; the file cards in each event. This exceeds their processing capacity and the default topic preference comes into play and provides the antecedent for the pronoun. In the subject pronoun condition (25), there is no difference between the antecedent assigned through parallelism and through topic preference. In both cases it is the topic, which is the correct antecedent for the pronoun and that is why most Broca’s patients score above chance in this condition. However, in the object pronoun condition (26) applying topic preference yields an incorrect response.
Finally, I predict that in order to provide additional evidence for the failure of agrammatic patients to correctly apply the parallelism constraint, it would be interesting to test sentences (23) and (24) discussed in section 3.3.3. In these sentences the first conjunct is identical
to that of the experimental sentences in (25) and (26), and it is an active sentence. The second conjunct is a passive sentence where the thematic roles are reversed; the subject carries a patient role and the second DP carries an agent role. The agrammatic patients are predicted to perform at chance level on sentences such as (23) as a result of the competition between the parallelism constraint and the topic preference; they are predicted to perform above chance in (24) because the agent is also the topic of the first utterance.
3.4 Conclusion
The aim of this chapter was to examine the comprehension of pronouns in environments where Rule-I does not apply. I tested two types of conjoined constructions with the pronoun in the subject or object position of the second conjunct. The only way to establish reference in such sentences is through the discourse operation of coreference. The agrammatic patients performed at chance level on these sentences, which indicates that the errors they make when interpreting pronouns are not limited to instances where Rule-I is at work.
The error pattern Broca’s patients exhibited, was related to a competition between two different constraints that apply at the level of discourse. The competition discussed here differs from the one discussed in the previous chapter in that it is a competition between rules within the same module and not between different modules. In the present chapter I argued that in the experimental sentences parallelism of thematic roles and topic preference compete in both healthy adults and in agrammatic aphasic patients. In the non-brain-damaged adults parallelism of thematic roles seems to be the preferred way of assigning reference to the pronoun and topic preference occasionally comes into play when pragmatic cues create an ambiguity which imposes more load on the processing. In the agrammatic patients, the slower-than-normal syntactic processing argued for in the previous chapter creates an ambiguous situation where the patients resort to a default rule of topic preference that comes into play when they are in doubt and need to interpret the pronoun without all the thematic information available to rely on the constraint of parallelism of thematic roles.