Karen Ward


July 1992

Document Type


Degree Name



Dept. of Computer Science and Engineering


Oregon Graduate Institute of Science & Technology


This thesis develops a computational representation for air traffic control dialogue. Such a model might be used in developing a spoken language understanding system to represent and reason about utterances. Currently, speaker-independent, continuous speech systems rely primarily on constraints such as sharply limited vocabularies, simple grammars, and word-pair probabilities to limit the possibilities considered in mapping sounds to phonemes, words, and ultimately, meaning. When speech understanding systems are applied to unconstrained speech in real-world settings, though, the range and complexity of potential utterances increases dramatically. To overcome this complexity, additional knowledge sources are needed. Of particular interest are "higher-level" knowledge sources, which describe information above the phonemic level. One class of higher-level knowledge that is beginning to prove useful in speech understanding is dialogue modeling. By predicting the form and content of the next utterance from the content of prior utterances, dialogue models allow the recognizer to consider only a subset of the application's full grammar and vocabulary. Dialogue context is also used after the fact to correct the output of the speech recognizer, to select among several possible interpretations of the utterance, to handle ellipses and anaphora, and to disambiguate meaning. This thesis will focus on the use of two dialogue models, speech acts and the collaborative view of conversation, to explain and predict the intended meaning of an utterance. The domain selected for this analysis is air traffic control, which exhibits several characteristics that make it interesting for both dialogue modeling and speech recognition studies. For this analysis, radio exchanges between air traffic controllers and pilots were taped and transcribed. A complete dialogue, consisting of all exchanges between the controller and the pilot of a commercial flight approaching the airport to land, was explicated at the speech act level in terms of the beliefs and intentions of the conversants.





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