This paper presents an automatic sentence segmentation method for an automatic speech summarization system. The segmentation method is based on combining word-and class-based statistical language models to predict sentence and non-sentence boundaries. We study both the performance of the sentence segmentation system itself and the effect of the segmentation on the summarization accuracy. The sentence segmentation is done by modelling the probability of a sentence boundary given a certain word history with language models trained on transcriptions and texts from several sources. The resulting segmented data is used as the input to an existing automatic summarization system to determine the effect it has on the summarization process. We conduct all our experiments with two types of evaluation data: broadcast news and lecture transcriptions. The automatic summarizations are created with different sentence segmentations and different summarization ratios (30% and 40%) and evaluated by comparing them to human-made summaries. We show that a proper sentence segmentation is essential to achieve good performance with an automatic summarization system.
Contemporary approaches to automatic speech summarisation comprise several components, among them a linguistic model (LiM) component, which is unrelated to the language model used during the recognition process. This LiM component assigns a probability to word sequences from the source text according to their likelihood of appearing in the summarised text. In this paper we investigate LiM topic and stylistic adaptation using combinations of LiMs each trained on different adaptation data. Experiments are performed on 9 talks from the TED corpus of Eurospeech conference presentations, as well as 5 news stories from CNN broadcast news data, for all of which human (TRS) and speech recogniser (ASR) transcriptions along with human summaries were used. In all ASR cases, summarisation accuracy (SumACCY) of automatically generated summaries was significantly improved by automatic LiM adaptation, with relative improvements of at least 2.5% in all experiments.
The performance of automatic speech summarisation has been improved in previous experiments by using linguistic model adaptation. We extend such adaptation to the use of class models, whose robustness further improves summarisation performance on a wider variety of objective evaluation metrics such as ROUGE-2 and ROUGE-SU4 used in the text summarisation literature. Summaries made from automatic speech recogniser transcriptions benefit from relative improvements ranging from 6.0% to 22.2% on all investigated metrics.
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