Discourse roles : a mechanism to establish coherence
Discourse comprehension involves more than just connecting and interpreting the individual words on the page. We need to establish not only the connections between the words, but also how the situation described in the text relates to our general knowledge. One of the main ways to achieve integration is by the process of anaphoric reference. Sometimes, the antecedent is explicit in the text, other times it is implicit. It is the ability to refer to implicitly introduced information that is explored in this thesis. How is implicitly introduced information represented so it can support subsequent reference? The proposal that implicitly introduced information is best conceptualised in the form of variables, termed Discourse Roles, is evaluated. It is proposed that Disclosure Roles contribute to the establishment of discourse coherence by functioning as antecedent sites for reference. The availability of antecedent role information was assessed with respect to Instrument Discourse Roles. By exploring the boundary conditions on the establishment of Instrument Roles, the conflicting empirical evidence for the encoding of implicit instruments is explained. It is necessary to establish the origin of Discourse Roles. Are they derived from the text, or background knowledge? The contribution of lexical and contextual information to the establishment of Instrument Discourse Roles was evaluated in a series of eye tracking experiments and Questionnaire tasks. "General Verbs" were used because their associated Instruments are context dependent: certain instruments will be used to perform actions in specific contexts. For instance, the instruments used to perform various acts of "cutting" will vary according to the context: "to cut cake" you would generally use a "knife", but "to cut hair" you would normally use "scissors". The questionnaire data demonstrated that "General Verbs" have a preference for a particular Instrument, regardless of context. The Default Instrument for "cut" is "knife". The relative contribution of lexical and contextual information was assessed by exploiting the conflict between lexically and contextually appropriate Default Instruments. i.e., if the verb "cut" is used in the context "cut hair" then the contextual and lexical default values conflict, "scissors" rather than "knife".