An Information Structural Approach To Spoken Language Generation

An Information Structural Approach to Spoken Language Generation Scott Prevost The Media Laboratory Massachusetts Institute of Technology 20 Ames Street Cambridge, Massachusetts 02139-4307 USA prevost@media, mit. edu Abstract This paper presents an architecture for the generation of spoken monologues with con- textually appropriate intonation. A two- tiered information structure representation is used in the high-level content planning and sentence planning stages of generation to produce efficient, coherent speech that makes certain discourse relationships, such as explicit contrasts, appropriately salient. The system is able to produce appropriate intonational patterns that cannot be gen- erated by other systems which rely solely on word class and given/new distinctions. 1 Introduction While research on generating coherent written text has flourished within the computational linguistics and artificial intelligence communities, research on the generation of spoken language, and particularly intonation, has received somewhat less attention. In this paper, we argue that commonly employed models of text organization, such as schemata and rhetorical structure theory (RST), do not adequately address many of the issues involved in generating spoken language. Such approaches fail to consider contextually bound focal distinctions that are mani- fest through a variety of different linguistic and par- alinguistic devices, depending on the language. In order to account for such distinctions of fo- cus, we employ a two-tiered information structure representation as a framework for maintaining lo- cal coherence in the generation of natural language. The higher tier, which delineates the lheme, that which links the utterance to prior utterances, and the theme, that which forms the core contribution of the utterance to the discourse, is instrumental in de- termining the high-level organization of information within a discourse segment. Dividing semantic rep- resentations into their thematic and rhematic parts allows propositions to be presented in a way that maximizes the shared material between utterances. The lower tier in the information structure repre- sentation specifies the semantic material that is in "focus" within themes and themes. Material may be in focus for a variety of reasons, such as to empha- size its "new" status in the discourse, or to contrast it with other salient material. Such focal distinc- tions may affect the linguistic presentation of infor- mation. For example, the it-cleft in (1) may mark John as standing in contrast to some other recently mentioned person. Similarly, in (2), the pitch accent on red may mark the referenced car as standing in contrast to some other car inferable from the dis- course context 3 (1) It was John who spoke first. (2) Q: Which car did Mary drive? A: (MARY drove)th (the RED car.)rh L+H* LH(%) H* LL$ By appealing to the notion that the simple rise-fall tune (H* LL%) very often accompanies the rhematic material in an utterance and the rise-fall-rise tune of- ten accompanies the thematic material (Steedman, 1991 i Prevost and Steedman, 1994), we present a spoken language generation architecture for produc- ing short spoken monologues with contextually ap- propriate intonation. 2 Information Structure Information Structure refers to the organization of information within …

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