Bilingual-LSA Based LM Adaptation for Spoken Language Translation

We propose a novel approach to crosslingual language model (LM) adaptation based on bilingual Latent Semantic Analysis (bLSA). A bLSA model is introduced which enables latent topic distributions to be efficiently transferred across languages by enforcing a one-to-one topic correspondence during training. Using the proposed bLSA framework crosslingual LM adaptation can be performed by, first, inferring the topic posterior distribution of the source text and then applying the inferred distribution to the target language N-gram LM via marginal adaptation. The proposed framework also enables rapid bootstrapping of LSA models for new languages based on a source LSA model from another language. On Chinese to English speech and text translation the proposed bLSA framework successfully reduced word perplexity of the English LM by over 27 % for a unigram LM and up to 13.6% for a 4-gram LM. Furthermore, the proposed approach consistently improved machine translation quality on both speech and text based adaptation.

LOCATING AND REDUCING TRANSLATIONDIFFICULTY

The challenge of translation varies from one sentence to another, or even between phrases of a sentence. We investigate whether variations in difficulty can be located automatically for Statistical Machine Translation (SMT). Furthermore, we hypothesize that customization of a SMT system based on difficulty information, improves the translation quality.We assume a binary categorization for phrases: easy vs. difficult. Our focus is on the Difficult to Translate Phrases (DTPs). Our experiments show that for a sentence, improving the translation of the DTP improves the translation of the surrounding non-difficult phrases too. To locate the most difficult phrase of each sentence, we use machine learning and construct a difficulty classifier. To improve the translation of DTPs, we introduce customization methods for three components of the SMT system: I. language model; II. translation model; III. decoding weights. With each method, we construct a new component that is dedicated for the translation of difficult phrases. Our experiments on Arabic-to-English translation show that DTP-specific system customization is mostly successful.Overall, we demonstrate that translation difficulty is an important source of information for machine translation and can be used to enhance its performance