On combining recognizers for improved recognition of spelled names

This paper deals with the recognition of spelled names over the telephone. Two recognition approaches are recalled. One is based on a forward-backward algorithm in which the spelling lexicon is handled by the A* algorithm in the backward pass. The other is a 2-step approach, which relies on a discrete HMM-based retrieval procedure. Both approaches integrate a rejection test. Combinations of the two approaches are investigated in this paper. First, a sequential combination is presented. The 2-step approach is used only when the forward-backward approach does not yield an answer because of memory limitations. This sequential combination, evaluated on field data collected from a vocal directory service, takes the best of both approaches. Results are presented for the recognition of valid spelled names as well as for the rejection of incorrect data. Finally, a detailed analysis of the recognition results of the 2 approaches shows that a comparison of the 2 recognition results leads to an efficient reliability criterion.