Sixth European Conference on Speech Communication and Technology
(EUROSPEECH'99)

Budapest, Hungary
September 5-9, 1999

Task Dependent Loss Functions in Speech Recognition: A* Search over Recognition Lattices

Vaibhava Goel, William Byrne

Center for Language and Speech Processing, Johns Hopkins University, Baltimore, MD, USA

A recognition strategy that can be matched to specific system performance criteria such as word error rate or F-measure has recently been found to yield improvements over the usual maximum aposteriori probability strategy [1] [2] [3]. In this matched-to-the-task strategy a hypothesis is chosen to minimize the expected loss or the Bayes Risk under a loss function defined by a performance measure of interest. Due to the prohibitive of exact implementation of this strategy, only an approximate implementation as an N-best list rescoring scheme been used [1] [2]. Our goal is to improve the performance of such risk-based decoders by developing search strategies that can consider more hypotheses and incorporate more acoustic evidence. In this paper we present search algorithms to implement the risk-based recognition strategy over word lattices that contain acoustic and language model scores. These algorithms are extensions of the N-best list rescoring approximation and are formulated as A* algorithms. Results are reported on the Switch-board conversational telephone speech corpus. We find that lattice based rescoring yields modest but significant improvements in word error rate relative to N-best list rescoring at comparable computational cost.


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Bibliographic reference.  Goel, Vaibhava / Byrne, William (1999): "Task dependent loss functions in speech recognition: a* search over recognition lattices", In EUROSPEECH'99, 1243-1246.