Integrating Prosody into an Account of Discourse Structure

In this thesis a study of discourse segmenting is carried out, which investigates both segment boundaries and segment content. The results are related to discourse theory. We study the questions of how the prosody and the text structure influence subjects' annotations of discourse boundaries and discourse prominence. The hypothesis was that the annotations would be influenced by the discourse type. Two studies were carried out. 1) a study of boundary annotation, 2) a study of prominence annotation. All studies were made on four different discourse types, scripted and spontaneous monologue and scripted and spontaneous dialogue. In addition the annotations were carried out under two different conditions 1) based on transcripts alone and 2) based on transcripts together with access to the speech signal. The results indicate that the boundary annotations were less dependent on the speech signal than the prominence annotations. It seems that subjects have segmented on the basis of the text structure, while prominence to a great extent was annotated on the basis of the prosody. In the case of boundary markings the boundary context in terms of parts of speech differs across speaking styles, which is not the case for the prominences. A separate study of segment intentions was also made, and it was found that the interpretation of a specific intention, questions, seems to be arrived at primarily on the basis of the text structure. However, in some cases also the prosody affects the annotations. The picture that emerges indicates a distribution of labour between text structure and prosody, governed by the principle of economy. In cases where the boundaries were less well definied, as in e.g. spontaneous monologue, the pattern of the prominences was clearer. In cases where the boundaries were more clearly indicated, as in read aloud text, the prominences were less clearly communicated. The findings were interpreted within Grosz and Sidner's (1986) discourse theory. It is suggested that differences in the segmenting strategy originating from the interaction of text structure and prosody can be expressed as differences in the contributions from the different components of discourse suggested in the framework of Grosz and Sidner (1986).