PASCAL - Pattern Analysis, Statistical Modelling and Computational Learning

Morphologically motivated language models in speech recognition
Teemu Hirsimäki, Mathias Creutz, Vesa Siivola and Mikko Kurimo
In: AKRR 2005, 8-10 Jun 2005, Espoo, Finland.

Abstract

Language modelling in large vocabulary speech recognition has traditionally been based on words. A lexicon of the most common words of the language in question is created and the recogniser is limited to consider only the words in the lexicon. In Finnish, however, it is more difficult to create an extensive lexicon, since the compounding of words, numerous inflections and suffixes increase the number of commonly used word forms considerably. The problem is that reasonably sized lexica lack many common words, and for very large lexica, it is hard to estimate a reliable language model. We have previously reported a new approach for improving the recognition of inflecting or compounding languages in large vocabulary continuous speech recognition tasks. Significant reductions in error rates have been obtained by replacing a traditional word lexicon with a lexicon based on morpheme-like word fragments learnt directly from data. In this paper, we evaluate these so called statistical morphs further, and compare them to grammatical morphs and very large word lexica using n-gram language models of different orders. When compared to the best word model, the morph models seem to be clearly more effective with respect to entropy, and give 30\% relative error-rate reductions in a Finnish recognition task. Furthermore, the statistical morphs seem to be slightly better than the rule-based grammatical morphs.

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EPrint Type:Conference or Workshop Item (Paper)
Project Keyword:Project Keyword UNSPECIFIED
Subjects:User Modelling for Computer Human Interaction
Natural Language Processing
Speech
ID Code:1037
Deposited By:Mikko Kurimo
Deposited On:07 August 2005