A "Bunsetsu" speech recognition system using a top-down processor controlled by bottom-up information

This paper is concerned with a system to recognize continuously uttered "bunsetsu", which is a syntactic unit in the Japanese language. This system has two main features. One is that its top-down processor is directly controlled by bottom-up information: in the first stage, the bottom-up processor recognizes relatively unambiguous parts of the input speech signal using only local acoustical information, and then the recognition result is used to control the top-down processor for restriction of the number of hypotheses. The other feature is an unsupervised learning algorithm for vowel templates. This algorithm generates new vowel templates automatically by cutting out appropriate portions from the input speech, thus acquiring new knowledge for phonemes such as devocalized and nasalized vowels. A recognition experiment shows that the "bunsetsu" recognition rate for 1022 "bunsetsu"s uttered by 1 male speaker at 3 mora/sec rate is 86 %, and 65 % at 4 mora/sec rate.