Learning a Translation Model from Word Lattices

Translation models have been used to improve automatic speech recognition when speech input is paired with a written translation, primarily for the task of computer-aided translation. Existing approaches require large amounts of parallel text for training the translation models, but for many language pairs this data is not available. We propose a model for learning lexical translation parameters directly from the word lattices for which a transcription is sought. The model is expressed through composition of each lattice with a weighted finite-state transducer representing the translation model, where inference is performed by sampling paths through the composed finitestate transducer. We show consistent word error rate reductions in two datasets, using between just 20 minutes and 4 hours of speech input, additionally outperforming a translation model trained on the 1-best path.