Initial Experiments with Estonian Speech Recognition

Proceedings of the 16th Nordic Conference of Computational Linguistics NODALIDA-2007. Editors: Joakim Nivre, Heiki-Jaan Kaalep, Kadri Muischnek and Mare Koit. University of Tartu, Tartu, 2007. ISBN 978-9985-4-0513-0 (online) ISBN 978-9985-4-0514-7 (CD-ROM) pp. 249-252

Morphologically motivated word classes for very large vocabulary speech recognition of Finnish and Estonian

We study class-based n-gram and neural network language models for very large vocabulary speech recognition of two morphologically rich languages: Finnish and Estonian. Due to morphological processes such as derivation, inflection and compounding, the models need to be trained with vocabulary sizes of several millions of word types. Class-based language modelling is in this case a powerful approach to alleviate the data sparsity and reduce the computational load. For a very large vocabulary, bigram statistics may not be an optimal way to derive the classes. We thus study utilizing the output of a morphological analyzer to achieve efficient word classes. We show that efficient classes can be learned by refining the morphological classes to smaller equivalence classes using merging, splitting and exchange procedures with suitable constraints. This type of classification can improve the results, particularly when language model training data is not very large. We also extend the previous analyses by rescoring the hypotheses obtained from a very large vocabulary recognizer using class-based neural network language models. We show that despite the fixed vocabulary, carefully constructed classes for word-based language models can in some cases result in lower error rates than subword-based unlimited vocabulary language models.We study class-based n-gram and neural network language models for very large vocabulary speech recognition of two morphologically rich languages: Finnish and Estonian. Due to morphological processes such as derivation, inflection and compounding, the models need to be trained with vocabulary sizes of several millions of word types. Class-based language modelling is in this case a powerful approach to alleviate the data sparsity and reduce the computational load. For a very large vocabulary, bigram statistics may not be an optimal way to derive the classes. We thus study utilizing the output of a morphological analyzer to achieve efficient word classes. We show that efficient classes can be learned by refining the morphological classes to smaller equivalence classes using merging, splitting and exchange procedures with suitable constraints. This type of classification can improve the results, particularly when language model training data is not very large. We also extend the previous analyses by rescoring the hypotheses obtained from a very large vocabulary recognizer using class-based neural network language models. We show that despite the fixed vocabulary, carefully constructed classes for word-based language models can in some cases result in lower error rates than subword-based unlimited vocabulary language models.Peer reviewe

Automatic Speech Recognition for Northern Sámi with comparison to other Uralic Languages

Speech technology applications for major languages are becoming widely available, but for many other languages there is no commercial interest in developing speech technology. As the lack of technology and applications will threaten the existence of these languages, it is important to study how to create speech recognizers with minimal effort and low resources. As a test case, we have developed a Large Vocabulary Continuous Speech Recognizer for Northern Sámi, an Finno-Ugric language that has little resources for speech technology available. Using only limited audio data, 2.5 hours, and the Northern Sámi Wikipedia for the language model we achieved 7.6% Letter Error Rate (LER). With a language model based on a higher quality language corpus we achieved 4.2% LER. To put this in perspective we also trained systems in other, better-resourced, Finno-Ugric languages (Finnish and Estonian) with the same amount of data and compared those to state-of-the-art systems in those languages.Peer reviewe

Conference Program

Proceedings of the 16th Nordic Conference of Computational Linguistics NODALIDA-2007. Editors: Joakim Nivre, Heiki-Jaan Kaalep, Kadri Muischnek and Mare Koit. University of Tartu, Tartu, 2007. ISBN 978-9985-4-0513-0 (online) ISBN 978-9985-4-0514-7 (CD-ROM) pp. xiii-xviii

The Comparative Evaluation of Dependency Parsers in Parsing Estonian

Loomuliku keele töötluse (LKT) tehnoloogia on pidevalt arenemas, viimastel kümnenditel on selles valdkonnas toimunud väga suured edasiminekud. Üks LKT põhiülesanne on sõltuvussüntaksi analüüs, mis on sageli aluseks ka paljudele teistele ülesannetele, näiteks masintõlkele, nimeolemite tuvastamisele jne. Sõltuvussüntaksi analüüsi eesmärgiks on leida lause süntaktiline struktuur ja tuvastada sõnadevahelised grammatilised seosed. Enamik sõltuvussüntaksi analüüsi uuringuid on keskendunud inglise keele analüüsimisele. Antud ma-gistritöö eesmärgiks on hinnata ja võrrelda erinevate süntaksianalüsaatorite tulemuslikkust eesti keele analüüsimisel. Võrdlusesse valitud sõltuvussüntaksi analüsaatorid on: MaltParser, spaCy, Stanford’i neuroanalüsaator (nndep), SyntaxNet ja UDPipe. Hindamiseks kasutati peamiselt märgendatud seoste täpsust (Labelled Attachment Score), märgendamata seoste täpsust (Unlabelled Attachment Score) ning märgenduse täpsust (Label Accuracy). Magistritöö käigus treeniti spaCy, Stanfordi neuroparseri ning UDParseri mudelid eesti keele süntaksi analüüsimiseks, MaltParseri ja SyntaksNet’i jaoks kasutati eksperimentides olemasolevaid eeltreenitud mudeleid.Natural Language Processing (NLP) technology has been constantly developing and has seen a vast improvement in the last couple of decades. One key task in NLP is dependency parsing that oftentimes is a prerequisite for many other tasks such as machine translation, Named Entity Recognition (NER) and so on. The idea of dependency parsing is to perform a syntactic analysis of a sentence and extract the grammatical relations among the words in that sentence. Most research on dependency parsing has been focusing on English text parsing. In this thesis, an effort has been made to evaluate and compare the performance of some of the state-of-the-art dependency parsers in parsing Estonian. The dependency parsers chosen for evaluation are: MaltParser, spaCy, Stanford neural network dependency parser (nndep), SyntaxNet and UDPipe. The comparison is done using mainly Labelled Attachment Score (LAS), Unlabelled Attachment Score (UAS) and Label Accuracy (LA). New models for Estonian were trained for the spaCy, Stanford nndep and UDPipe parsers while pretrained models for the MaltParser and SyntaxNet were used in the experiments