Intonational Boundaries, Speech Repairs, and Discourse Markers: Modeling Spoken Dialog

Intonational Boundaries, Speech Repairs and Discourse Markers: Modeling Spoken Dialog Peter A. Heeman and James F. Allen Department of Computer Science University 9f Rochester Rochester NY 14627, USA {heeman, j ames }~cs. rochester, edu Abstract To understand a speaker's turn of a con- versation, one needs to segment it into in- tonational phrases, clean up any speech re- pairs that might have occurred, and iden- tify discourse markers. In this paper, we argue that these problems must be resolved together, and that they must be resolved early in the processing stream. We put for- ward a statistical language model that re- solves these problems, does POS tagging, and can be used as the language model of a speech recognizer. We find that by ac- counting for the interactions between these tasks that the performance on each task improves, as does POS tagging and per- plexity. 1 Introduction Interactive spoken dialog provides many new chal- lenges for natural language understanding systems. One of the most critical challenges is simply de- termining the speaker's intended utterances: both segmenting the speaker's turn into utterances and determining the intended words in each utterance. Since there is no well-agreed to definition of what an utterance is, we instead focus on intonational phrases (Silverman et al., 1992), which end with an acoustically signaled boundary lone. Even assuming perfect word recognition, the problem of determin- ing the intended words is complicated due to the occurrence of speech repairs, which occur where the speaker goes back and changes (or repeats) some- thing she just said. The words that are replaced or repeated are no longer part of the intended ut- terance, and so need to be identified. The follow- ing example, from the Trains corpus (Heeman and Allen, 1995), gives an example of a speech repair with the words that the speaker intends to be re- placed marked by reparandum, the words that are the intended replacement marked as alteration, and the cue phrases and filled pauses that tend to occur in between marked as the editing term. Example 1 (d92a-5.2 utt34) we'll pick up ~ . uh the tanker of oranges reparandu "q'ml ~ • ~ • editing term alteration interruption point Much work has been done on both detect- ing boundary tones (e.g. (Wang and Hirschberg, 1992; Wightman and Ostendorf, 1994; Stolcke and Shriberg, 1996a; Kompe et al., 1994; Mast et al., 1996)) and on speech repair detection and correction (e.g. (Hindle, 1983; Bear, Dowding, and Shriberg, 1992; Nakatani and Hirschberg, 1994; Heeman and Allen, 1994; Stolcke and Shriberg, 1996b)). This work has focused on one of the issues in isolation of the other. However, these two issues are intertwined. Cues such as the presence of silence, final syllable lengthening, and presence of filled pauses tend to mark both events. Even the presence of word cor- respondences, a tradition cue for detecting and cor- recting speech repairs, sometimes marks boundary tones as well, as illustrated by the following example where the intonational phrase boundary is marked …

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