Problems of modeling phone deletion in conversational speech for speech recognition

Recently we proposed a novel method to explicitly model the phone deletion phenomenon in speech, and introduced the context-dependent fragmented word model (CD-FWM). An evaluation on the WSJ1 Hub2 5K task shows that even in read speech, CD-FWM could reduce word error rate (WER) by a relative 10.3%. Since it is generally expected that the phone deletion phenomenon is more pronounced in conversational and spontaneous speech than in read speech, we extend our investigation of modeling phone deletion in conversation using CD-FWM on the SVitchboard 500-word task in this paper. To our surprise, much smaller recognition gain is obtained. Through a series of analyses, we present some plausible explanations for why phone deletion modeling is more successful in read speech than in conversational speech, and suggest future directions in improving CD-FWM for recognizing conversational speech.